Advancements of eco-friendly natural antimicrobial agents and their transformative role in sustainable textiles

Abstract

In the face of mounting environmental concerns, the textile industry is undergoing a pivotal transformation, with sustainability at the forefront of innovation. This review focuses on the exploration of natural compounds, renowned for their antimicrobial properties, as viable alternatives to conventional chemical agents that pose significant environmental challenges. It delves into a diverse array of natural sources, including plant extracts, essential oils, and microbial-derived compounds, which have been identified for their potent antimicrobial efficacy. These natural agents not only demonstrate a broad spectrum of activity against pathogenic microorganisms but also represent a stride towards eco-friendly textile processing by offering a sustainable substitute for synthetic antimicrobials. The integration of these green antimicrobial agents into textiles is scrutinized, with a particular emphasis on their impact on enhancing fabric functionalities. This includes improvements in durability, wash resistance, and the sustained antimicrobial effectiveness of treated fabrics, without sacrificing environmental integrity. Moreover, the study underscores the potential health benefits of these natural agents, such as a decrease in allergic reactions and skin irritations commonly associated with traditional antimicrobial treatments. The review culminates by highlighting the significant role these eco-conscious solutions play in revolutionizing antimicrobial textiles, promoting industry-wide sustainable practices, and catering to the escalating consumer demand for environmentally responsible products.

Highlights

• Provides eco-friendly and sustainable alternatives in textile processing, offering a greener choice over synthetic options.
• Enhances fabric functionality while preserving environmental integrity, addressing sustainability concerns throughout production.
• Improves fabric durability, wash resistance, and long-lasting efficacy, thereby contributing to superior product performance.
• Reduces allergic reactions and skin irritations, underscoring the health benefits of eco-friendly antimicrobial treatments.
• Promotes sustainable practices, shaping the future of antimicrobial textiles and catering to the growing demand for environmentally conscious consumer choices in the industry.

1 INTRODUCTION

The landscape of textile dyeing has been profoundly transformed with the advent of synthetic dyes over the last century, resulting in the diminished use of natural dyes.^1-3 Despite their widespread adoption, synthetic dyes have come under scrutiny due to their environmental and health repercussions. These include the toxicity and pollution associated with wastewater from dyeing processes, which have led several countries to enact stringent environmental regulations.⁴ The deleterious effects of synthetic dyes, characterized by harmful and allergic reactions, have ignited a renewed interest in the utilization of natural dyes. This resurgence is fueled by growing awareness of the environmental and health hazards posed by synthetic counterparts^{5, 6} Natural dyes are now celebrated for their superior biodegradability, environmental compatibility, minimal toxicity, and reduced allergenic potential,^{7, 8} making them a cornerstone for developing textile products that are both safe and environmentally friendly.^9-13

The exploration of natural dyes is not only driven by their eco-friendly attributes but also by their potential to imbue textiles with antimicrobial properties. This dual functionality offers a promising avenue for conserving water, energy, chemicals, and time, thereby economizing the dyeing and finishing processes^14-16 The quest for novel sources of natural dyes is paralleled by research endeavors aimed at mitigating health risks associated with microbial proliferation on textiles.¹⁷ The integration of dyeing and finishing processes, when employing natural dyes with antimicrobial properties, is shown to enhance the efficacy and reliability of antimicrobial finishes.^18-20

Furthermore, natural dyes are being increasingly sought after for their multifunctional benefits, including insect repellency, deodorization, flame retardancy, ultraviolet protection, fluorescence, antimicrobial activity, and biocompatibility. These attributes are contributing to the global popularity of natural dyes in the creation of highly functional and esthetically pleasing textiles, especially in medical applications, where the diversity of active compounds such as tannins, flavonoids, curcuminoids, and alkaloids plays a pivotal role.^{21, 22} The sustainability and eco-friendliness of natural dyes are compelling reasons for their growing acceptance, as they offer enhanced biodegradability and environmental friendliness.^23-25

Traditionally, the application of natural dyes involves the use of mordants, typically metallic salts, to facilitate the dye-fiber affinity. While this method produces unique and subtle hues, along with inherent functional qualities, it raises concerns over the environmental and health impacts of metallic mordants.²⁶ The quest for sustainable dyeing practices has led to research into natural mordants as 100% earth-friendly alternatives, aiming to mitigate the adverse effects associated with conventional metallic mordants.²⁷

2 RECENT APPLICATION OF NATURAL DYES AS ANTIMICROBIAL AGENTS ON TEXTILES

The advent of natural dyes in the realm of antimicrobial textile finishes represents a significant stride towards enhancing the health-protective qualities of textiles. This encompasses a broad spectrum of applications, including but not limited to, medical textiles, hygiene-oriented textiles, and personal protective equipment (PPE). In this context, natural dyes, derived from diverse biological sources such as plants, microbes, and fungi, in conjunction with various mordants, have been rigorously studied for their potential to imbue textiles with antimicrobial properties (see Figure 1). This segment aims to elucidate the efficacy of plant-based natural dyes in conferring antimicrobial activities to different fabric types, examining both the scenarios of mordant usage and its absence.

FIGURE 1

Personal protective clothing with a newly developed, cost-effective technology that can reduce the presence of enveloped viruses such as SARS-CoV-2 and phi-6, as well as methicillin-resistant bacteria like Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MRSE). Reproduced under the terms of CC-BY-NC-ND 4.0²⁸ Copyright 2021, American Chemical Society.

In the pursuit of health-protective textiles, researchers have embarked on the exploration of plant-based dyes, renowned for their antimicrobial virtues. These natural dyes, when applied to textiles, either through conventional dyeing techniques or in combination with mordants, have shown promising results in inhibiting the growth of pathogenic microbes. The significance of this research lies not only in its contribution to public health by enhancing the antimicrobial properties of textiles but also in its alignment with sustainable practices by employing eco-friendly materials. The continued investigation into the antimicrobial potential of natural dyes on textiles underscores the growing demand for safer, more sustainable alternatives to synthetic chemicals in the textile industry.

2.1 Viburnum Opulus L. (Caprifoliaceae)

Viburnum opulus L., commonly known in the Middle-Anatolia region of Turkey, particularly in the city of Kayseri, as gilaburu, and referred to as the European cranberry bush in English, is a distinguished member of the Caprifoliaceae family.²⁹ This plant is notable for its berries, which are rich in polyphenolic components. These components encompass a diverse range including hydroxybenzoic acids, tannins, anthocyanins, chlorogenic acid, catechin, epicatechin cyanidin-3 glucoside, cyaniding-3-rutinoside, and quercetin.³⁰ The biochemical richness of Viburnum opulus berries has spurred various studies focused on their antioxidant and antibacterial activities, particularly in the context of textile applications.

Recent investigations into the application of Viburnum opulus extracts on textiles have yielded promising outcomes in terms of antimicrobial activity. For instance, research conducted by F. Yilmaz et al. explored the use of cranberry fruits and branches for dyeing cotton fabrics, assessing the antimicrobial efficacy of the dyed materials. Their findings revealed that cotton fabrics dyed with cranberry fruit juice, without the use of any mordants, exhibited significant antibacterial properties. However, it was noted that there was no discernible bacterial reduction in samples treated with extracts derived from the cranberry fruit branches.²⁹ Notably, the dyeing process involving cranberry fruit juice at 70°C demonstrated particularly effective antibacterial action against S. aureus. This heightened antibacterial effect is believed to be attributable to the high concentration of metal ions, such as copper and zinc, present in the cranberry juice, in addition to its phenolic compounds, which are known for their antimicrobial properties.¹

Another study ventured into dyeing wool fabrics with extracts from cranberry fruits and onion skins (Allium cepa), assessing the antimicrobial activity of the dyed fabrics against two bacterial strains (E. coli and E. aeroginosa) and a yeast strain (C. albicans), without employing any mordants. The findings highlighted that fabrics dyed with onion skins and Viburnum opulus fruit juice exhibited significant antimicrobial effects. While Viburnum opulus juice dyed fabrics showed superior activity against bacterial strains, onion skin extracts were more effective against the yeast strain. Specifically, Viburnum opulus extracts demonstrated the highest activity against E. coli, whereas onion skins were most effective against C. albicans.³¹ These studies underscore the potential of Viburnum opulus L. as a natural dye with promising antimicrobial properties for textile applications, highlighting an eco-friendly approach to enhancing the functional attributes of fabrics.

2.2 Berberine (Rhizoma coptidis)

R. coptidis, a distinguished herb in traditional Chinese medicine, has been documented since the second century in the Shen Nong Ben Cao Jing (Divine Husbandman's Classic of Materia Medica). Known commonly as coptis or coptis root in English, this herb is particularly noted for its content of berberine and other protoberberine alkaloids.³⁰ Berberine stands out as the only cationic dye among natural plant dyes, predominantly found in the roots of R. coptidis and the stems of Phellodendron.¹

The antibacterial potential of berberine on textile materials has been a subject of interest in various research studies. In 2005, Guizhen Ke and colleagues embarked on a study to explore the antimicrobial properties of wool fabric dyed with R. coptidis extracts, employing different mordants in the process. The wool fabric, post-dyeing with R. coptidis extracts, demonstrated notable antibacterial properties, exhibiting a higher inhibition rate against E. coli compared to C. albicans. The findings indicated that the R. coptidis extract-treated wool fabric maintained robust antibacterial characteristics.¹

Further research involved dyeing wool fibers with berberine extracted from Berberis vulgaris wood, with the root extract of Rumex Hymenosepolus being utilized as a bio-mordant to assess antimicrobial efficacy. This study observed significant antibacterial activity in the berberine-dyed wool, suggesting that the extract of Berberis vulgaris could serve as an effective natural dye for woolen fabrics, ensuring both good fastness and remarkable antibacterial properties.³¹

Continuing this line of inquiry, the same researcher conducted a subsequent study 2 years later, aiming to evaluate the antibacterial activity, color strength, and other properties of wool fibers dyed with berberine. This investigation employed alum, copper sulfate, and potassium dichromate as mordants. The colored wool exhibited extensive antimicrobial activity against both gram-positive and gram-negative bacteria, indicating that the berberine colorant, especially in mordanted and dyed samples, provided superior antibacterial efficacy. The conclusion reaffirmed the potential of Berberis vulgaris extract as a viable natural dye for woolen fabrics, characterized by excellent fastness and antibacterial properties.³²

2.3 Turmeric (Curcuma longa L.)

Turmeric, derived from Curcuma longa L., is distinguished by its active component, curcumin, which has been extensively utilized as a natural dye in both fabric and food industries due to its vibrant color and bactericidal properties.^{33, 34} The application of turmeric for antibacterial finishes on textiles reveals its capacity to combat bacteria such as E. coli and S. aureus. Han and Yang documented that turmeric's antimicrobial effectiveness on treated fabrics diminishes with increased washing cycles, yet it retains considerable bacteriostatic activity after initial laundering. Notably, curcumin-treated wool exhibits semi-durable antibacterial capabilities, demonstrating greater resilience to home laundry than to light exposure.³⁵

Further exploration into turmeric's potential involved dyeing silk fabric with turmeric extract, facilitated by mordants like copper sulfate, ferrous sulfate, and potassium aluminum sulfate. The study illuminated that textiles mordanted and dyed with turmeric extract exhibited enhanced antibacterial properties. Remarkably, using 3% copper sulfate (on the fabric's weight) conferred complete antibacterial effectiveness. It was observed that all treated textiles displayed superior antibacterial efficacy against E. coli over S. aureus, indicating the feasibility of employing turmeric extract dyeing as an efficient method for imparting color and antibacterial benefits to silk materials.³⁶

Mirjalili et al. (2013) investigated the antibacterial attributes of polyamide fabrics dyed with turmeric, employing ferric sulfate, cupric sulfate, and potassium aluminum sulfate as mordants. The bacteriostatic activity assessed against S. aureus (Gram-positive) and E. coli (Gram-negative) demonstrated that turmeric-dyed polyamide showcased outstanding antibacterial activity, with mordanted samples outperforming those without mordant.³⁷

In a novel approach, an antibacterial acid dye, derived from a chemically modified structure of curcumin, was utilized for the simultaneous dyeing and antibacterial finishing of silk fabrics. The modification involved integrating heterocyclic rings such as sulphadiazine and sulfathiazole into curcumin's sulphonamide structure. The synthesized sulphonamide dyes containing curcumin effectively inhibited both Gram-positive and Gram-negative bacteria, maintaining antibacterial properties even after multiple washes.³⁸

Exploring curcumin's application further, its efficacy on cotton fabric in batch or continuous processes was examined, focusing on antimicrobial and color properties. Curcumin-treated cotton textiles displayed significant antibacterial action against both E. coli and S. aureus, with a pronounced inhibitory effect on S. aureus.³⁹ Additionally, the direct application of curcumin powder dye to polyester fabric in a supercritical CO₂ (scCO₂) medium, without mordants or pre-treatment, revealed the dyed textiles' favorable antibacterial, antioxidant, and UV-protective qualities alongside washability and rubbing resistance.⁴⁰

Dyeing various fabrics (cotton, wool, polyester, polyamide) with an aqueous extract of curcumin without mordants demonstrated exceptional antimicrobial properties across natural and synthetic substrates. This indicates curcumin's potential as a sustainable natural dye alternative for sensitive applications, like infant clothing, given its strong antibacterial activity.⁴¹ Research incorporating some dyes such as turmeric, cinnamon, and saffron in dyeing cotton fabric with turmeric and copper sulfate (CuSO₄) showcased 100% antibacterial effectiveness against both S. aureus and E. coli, highlighting turmeric's superior antibacterial activity compared to cinnamon and saffron when used without mordants.⁴²

2.4 Pomegranate peels and walnut green husks

In the quest for sustainable and non-toxic alternatives to synthetic dyes in the textile industry, pomegranate peels and walnut green husks have emerged as promising sources of natural dyes and antimicrobial agents.⁴³ The shift towards natural dyes is driven by growing environmental and health concerns related to the use of conventional textile dyes. Extensive research has been conducted to explore the efficacy of dyes derived from pomegranate peels and walnut green husks in imparting both color and antimicrobial properties to fabrics.

One study focused on the application of these natural dyes on wool fabrics treated with inorganic salts such as Ag, Ag/Cu, and Cu. The dyeing process endowed the wool yarns with excellent antibacterial activity, achieving nearly 100% effectiveness against S. aureus and E. coli. Notably, wool yarns treated with silver nanoparticles (Ag NPs) exhibited the highest antibacterial activity among the inorganic salts tested. The inclusion of citric acid as a crosslinking agent was crucial for achieving such promising antibacterial properties. Remarkably, the antibacterial efficacy of samples treated with Ag NPs and dyed with pomegranate and walnut extracts remained exceptionally high (above 91%) even after 10 washing cycles.⁴⁴

Another investigation compared the antimicrobial activity of cotton, wool, silk, and nylon fabrics dyed with natural dyes, including pomegranate peel, curcumin, cutch, red onion peel, and a blend of red onion peel/curcumin, with and without the use of mordants. The findings revealed significant antimicrobial activity against a variety of microorganisms such as S. aureus, K. pneumoniae, and C. albicans. Among the tested dyes, textiles dyed with curcumin extract exhibited the most potent antibacterial action against both gram-positive and gram-negative bacteria, as well as fungi.⁴⁵

A study focusing on Tencel fabric (lyocell) utilized pomegranate peel extract as a natural dye to assess the antibacterial properties of the dyed samples. Various mordants, including tin chloride, alum, potassium dichromate, copper sulfate, and ferrous sulfate, were employed in an exhaust dyeing process to apply color to the lyocell materials. The fabric dyed with pomegranate peel demonstrated satisfactory antibacterial activity against S. aureus. In contrast, undyed lyocell textiles exhibited minimal antibacterial capabilities. Interestingly, lyocell textiles dyed with stannous chloride as a mordant showed superior antibacterial activity compared to those dyed with other mordants.⁴⁶

Pomegranate extracts, derived from the rinds of Punica granatum, have been recognized for their potent antimicrobial properties and have seen increasing utilization in the dyeing of textiles. Research spearheaded by Rajendran et al. in 2011 explored the application of these natural dyes on cotton fabrics, focusing on evaluating the dyed textiles' antimicrobial efficacy, dyeability, and color fastness.⁴⁷ The study revealed that fabrics dyed with pomegranate extracts exhibited significant antimicrobial activity, which was not present in untreated control fabrics. This antimicrobial action was confirmed through both qualitative and quantitative assessments, including clear zones of bacterial inhibition and a reduction in bacterial counts. Moreover, the durability of these antimicrobial properties was tested through multiple wash cycles, with results indicating that the dyed fabrics retained their antibacterial activity for up to 10 washes.

Expanding on the application of pomegranate extracts, another study investigated their use in dyeing wool fabrics, employing various metal salt mordants to enhance and stabilize the imparted antimicrobial characteristics.⁴⁸ The research aimed to optimize the natural dyeing process to ensure the longevity of the antimicrobial properties in the dyed wool. The findings demonstrated that wool samples dyed with pomegranate extracts and treated with different mordants (tin chloride, alum, and ferrous sulfate) showed a remarkable level of antibacterial activity, particularly against S. aureus and C. albicans. The sequence of effectiveness of the mordanted materials against the microbes tested was SnCl₂ > alum > FeSO₄, highlighting the role of the mordant in amplifying the antimicrobial action. Furthermore, pre-treating wool with a mordant before dyeing was found to enhance the persistence of the antimicrobial properties through repeated washing cycles, emphasizing the potential of pomegranate extracts in creating textiles with durable antimicrobial features.

2.5 Gallnut extract

Gallnut extract has shown considerable promise as a natural antibacterial agent for textile applications.⁴⁹ The use of gallnut extract for treating wool and cotton fabrics through a pad-dry-cure method was explored in a study by Koh and Hong (2014). The treatment resulted in textiles that were darker and had a yellowish tint, attributed to the natural brown colorants, such as ellagic acid, present in the gallnut extract. These colorants have a longstanding history in Asian fabric dyeing practices. The treated textiles exhibited antibacterial activity; notably, wool textiles treated with gallnut extract were effective against S. aureus but not against K. pneumoniae.⁵⁰

Further research by Shahid et al. focused on dyeing woolen yarns with gallnut extract, assessing the fastness and antimicrobial properties against pathogens such as E. coli, S. aureus, and C. albicans. Mordanting with metallic salt mordants like stannous chloride (SnCl₂.2H₂O) and potash alum [K₂Al₂(SO₄)₄.24H₂O] was performed, showing an inhibitory effect on microbial growth by more than 90%. The antimicrobial activity of gallnut extract proved to be semi-durable against all tested microorganisms.⁵¹

The antifungal activity of silk textiles dyed with madder (Rubia tinctorium L.) and gallnut (Quercus infectoria Olivier) was also evaluated, demonstrating a significant inhibition rate of about 99.98% against C. albicans after five laundering cycles. This indicated the potent antifungal efficacy of textiles dyed with gallnut and madder.⁵² An analysis of cotton, silk, and wool fabrics dyed with natural extracts from peony, pomegranate, clove, Coptis chinensis, and gallnut revealed exceptional antibacterial action against S. aureus and K. pneumoniae, with reduction rates ranging from 96.8% to 99.9%. Notably, peony extract showed no antibacterial properties.⁵³

Jung et al. found that silk textiles dyed with extracts from gallnuts, areca nuts, and pomegranate peels exhibited a 99.9% antibacterial activity against S. aureus and K. pneumoniae. This solution, when applied to other fabrics such as cotton, silk, and wool, maintained the same level of antibacterial efficacy, underscoring the potential of naturally colored textiles as functional materials with excellent antibacterial and deodorizing qualities.⁵⁴

In another experiment, cotton fabrics were treated with gallnut extract using infrared dyeing equipment and a pad-dry-cure technique, aiming to create multipurpose garments without adverse side effects. This treatment resulted in textiles that exhibited both antibacterial and antioxidant properties.⁴⁹ A further study involved dyeing six organic cotton interlock knitting fabrics with gallnut (Quercus infectoria), four of which were post-mordanted with FeSO₄.7H₂O. Antimicrobial tests conducted on gram-positive bacteria revealed an efficacy of over 91%. These findings highlight the feasibility of producing sustainable, eco-friendly, non-toxic, and antibacterial textiles, which are especially important for use in hospital settings, newborns, and children's clothing.⁵⁵

2.6 Catechu and its dyed substrate

In the realm of natural dyeing processes, catechu stands out for its potential in imparting not only rich natural colors but also antibacterial properties to textiles. A meticulous study has delved into evaluating the antimicrobial efficacy of wool samples dyed with catechu against a spectrum of microorganisms, including E. coli, S. aureus, C. albicans, and C. tropicalis. The dyeing process incorporated mordants such as ferrous sulfate and stannous chloride, which are known for their ability to fix dyes onto the fabric, enhancing both the color fastness and the antimicrobial activity of the dyed materials.

The findings from this investigation were promising, showing that the catechu-dyed samples exhibited significant antibacterial activity against the tested bacteria. This suggests that catechu, as a natural dye, possesses inherent antimicrobial properties that can be effectively transferred to textile substrates. The significance of these results lies in the demonstration that natural colorants extracted from catechu can be used not only to achieve esthetically pleasing, sober natural colors but also to produce fabrics with quality antibacterial properties.

Moreover, the dyed fabrics displayed negligible cytotoxicity, underscoring the safety of using catechu in textile applications. This aspect is particularly important in the context of developing bioactive textile materials and clothing, where the balance between efficacy and safety is paramount. The antimicrobial characteristics of catechu-dyed textiles position this natural dye as a promising agent for the creation of functional and health-conscious textile products. The integration of catechu into the dyeing process, therefore, holds significant potential for the textile industry, aiming to meet the growing demand for sustainable and biologically active fabrics.⁵⁶

2.7 Red prickly pear plant (Opuntia humifusa)

In an illuminating study conducted by Ali et al. (2012), the antimicrobial properties of wool fabric dyed with the red prickly pear plant extract were thoroughly investigated.⁷ Employing a variety of test organisms, including E. coli, B. subtilis, P. aeruginosa, and S. aureus, the research demonstrated significant antimicrobial activity, evidenced by sizeable inhibition zones around the dyed fabric samples. Notably, an increase in the concentration of the prickly pear dye resulted in a corresponding enlargement of the inhibition zones for all microorganisms tested, indicating a dose-dependent efficacy of the dye. This study effectively showcased the red prickly pear's potent antimicrobial capabilities, highlighting its potential as a natural dye that offers not only esthetic value but also functional benefits in terms of inhibiting microbial growth on wool fabrics.

2.8 Leaves of henna (Lawsonia inermis)

The antibacterial properties and dyeing potential of henna leaf extract on woolen yarn were explored in another research initiative. This study aimed to assess the effectiveness of henna extract against common pathogens such as E. coli, S. aureus, and C. albicans. Remarkably, while untreated woolen yarn samples exhibited no antibacterial activity, the dyed substrates showed substantial inhibition against all tested microorganisms.⁵⁷ The study found that the highest concentration of henna dye used (20% on the weight of fabric, owf) led to the most significant reduction in microbial growth, with an impressive efficacy of 91% against E. coli, 94% against S. aureus, and 93% against C. albicans. These findings suggest that henna leaf extract not only imparts a rich color to woolen yarns but also imbues them with strong antibacterial properties. Conclusively, dyeing woolen yarn with henna leaf extract emerges as a promising, straightforward, and environmentally friendly approach for achieving both coloration and antimicrobial functionality, offering a sustainable alternative to the expensive, synthetic, and potentially toxic antimicrobial agents currently prevalent in the market.

2.9 Indian rhubarb (Rheum emodi L.)

A notable study explored the use of Rheum emodi L. dye for its application in dyeing wool yarns, assessing its antimicrobial efficacy against common pathogenic bacteria, E. coli and S. aureus. The investigation revealed that wool yarns dyed with this natural dye exhibited significant antimicrobial activities, achieving more than 90% reduction in bacterial and fungal populations. A key finding of the research was that wool yarn mordanted with 10% Alum achieved the highest percentage of microbial growth inhibition, ranging between 70% and 83%.⁵⁸ This study highlights the potent antibacterial capabilities of Indian rhubarb dye, suggesting its valuable application in the production of antimicrobial textiles.

2.10 Arjun tree (Terminalia arjuna)

In the realm of natural dyes, Terminalia arjuna, derived from the Arjun tree, has been a subject of interest among researchers for its antimicrobial properties when applied to woolen yarn. A study focusing on this natural dye evaluated its effectiveness against a spectrum of bacteria including S. aureus, Pseudomonas aeruginosa, E. coli, and Bacillus subtilis. The findings indicated that both the Terminalia arjuna solution and the dyed woolen yarn exhibited more than 85% inhibition of microbial growth.²⁰ Notably, while the antimicrobial activity was observed to diminish in mordanted samples, these samples demonstrated superior retention of antimicrobial properties through successive washing cycles compared to un-mordanted samples. The hierarchy of antibacterial activity persistence post multiple washes was identified as Alum > SnCl₂ > FeSO₄ > MgSO₄ > un-mordanted woolen yarn, correlating to the differential dye depletion rates and the enhanced interactions facilitated by the mordanting process.

2.11 Hawthorn fruits (Crataegus monogyna)

The application of natural dyes derived from Hawthorn fruits on Polyamide (nylon 6) cloth was investigated for its antimicrobial potential, specifically against E. coli and S. aureus bacteria. This study found that the application of Hawthorn fruit dyes significantly bolstered the antibacterial activity of the polyamide fabric samples. The enhanced antimicrobial effects were attributed to the high content of phenolic compounds present in the dye extracts from hawthorn fruits. Moreover, the dyed textiles not only exhibited excellent color fastness but also demonstrated remarkable antibacterial and antioxidant properties. These beneficial characteristics are closely linked to the chemical composition of the natural dyes extracted from Hawthorn fruits.^{59, 60} This research underscores the potential of utilizing Hawthorn fruit-based dyes in the development of textiles with inherent antimicrobial and antioxidant functionalities.

2.12 Liquorice root (Glycyrrhiza glabra L.)

The exploration into the antibacterial and color-fastness properties of woolen textiles dyed with Glycyrrhiza glabra L. roots showcased noteworthy outcomes. Utilizing a diverse set of mordants, including copper (II) sulfate, tin chloride, iron (II) sulfate, zinc chloride, and potassium aluminum sulfate, each at a concentration of 3%, significantly impacted the antibacterial effectiveness against both S. aureus and E. coli. The study found that woolen fabric samples treated with these mordants and dyed with Glycyrrhiza glabra roots exhibited good antibacterial results. Specifically, fabric samples dyed with mordant displayed an outstanding 99.99% antibacterial effectiveness. Meanwhile, samples dyed without the use of mordants achieved a minimum antibacterial effect of 70%, highlighting the significant role of mordants play in enhancing the antimicrobial properties of dyed textiles.⁶¹

2.13 Eucalyptus bark (Eucalyptus globulus)

Research into the antimicrobial properties of natural dyes extracted from Eucalyptus globulus bark against clinical pathogens, including S. aureus, E. coli, P. fluorescence, and B. cereus, revealed promising results. Utilizing an aqueous dyeing technique for cotton fabrics, it was discovered that the addition of alum and FeSO₄ mordants notably improved the antibacterial effectiveness of the eucalyptus dye. The study reported that while S. aureus and E. coli exhibited resistance to the eucalyptus dye alone, the inclusion of specific mordants enhanced the dye's susceptibility to exert antibacterial action against P. fluorescence and B. cereus. This suggests that eucalyptus bark-derived natural dye, especially when combined with certain mordants, has potential as an effective antimicrobial agent against a range of bacterial pathogens.⁶²

2.14 Other plant-based dyes

In the quest for sustainable and eco-friendly textile solutions, researchers have delved into the realm of plant-based dyes, exploring their potential for imparting color fastness and antimicrobial properties to fabrics. A noteworthy investigation involved dyeing wool fabric with natural dyes derived from Terminalia chebula (Myrobalan), Alkanna tinctoria (Flower-based dye), and Tagetes erecta (Marigold). To enhance the dye uptake and durability, woolen yarn samples were pre-treated with three eco-friendly metal salts: alum, iron, and tin. The study revealed that dyes from T. chebula and A. tinctoria exhibited significant resistance against gram-positive bacteria such as B. subtilis and S. aureus, with T. chebula standing out for its superior color properties and antibacterial efficacy. In contrast, T. erecta extract was found to promote bacterial growth. Among the dyed woolen yarns, the greatest antimicrobial activity was observed against B. subtilis, followed by S. aureus, E. coli, and P. aeruginosa, highlighting the effectiveness of these plant-based dyes in enhancing the antimicrobial properties of textiles.⁶³

Further exploration into the antimicrobial capabilities of plant-based dyes involved pre-treating wool and silk fibers with neem oil before dyeing them with chlorophyll, saffron red, and yellow natural dyes. The study assessed the antimicrobial activity of the dyed fibers against various bacteria and fungi. Notably, wool fibers treated with neem oil and dyed with chlorophyll exhibited a significant suppression of microbial growth. It was observed that wool and silk fibers processed with neem oil demonstrated enhanced antibacterial properties compared to untreated fibers, suggesting the synergistic effects of neem oil treatment and natural dyes in imparting antimicrobial qualities to the textiles.⁶⁴

Ranjitsingh et al. contributed to this field by extracting natural dyes from the dried seed endosperm of Syzygium cumini L. Jambolan fruit and evaluating their antibacterial properties on dyed cloth. The alkaline extract of the Jambolan dye showed effectiveness against E. coli and P. fluorescens. Additionally, water extraction from the dry seed endosperm of the Jambolan fruit inhibited several bacterial species, including S. lutea, E. coli, P. aeruginosa, P. fluorescens, and S. aureus. The study demonstrated the potential of Jambolan dye's antibacterial properties in the development of antimicrobial cloth, opening new avenues for the application of plant-based dyes in creating health-conscious textile products.⁶⁵

The dyeing and antibacterial properties of Mimusops elengi leaves extract were evaluated on blended wool/acrylic and silk fabrics.⁶⁶ Aqueous extract alone, when applied to blended wool/acrylic fabric, demonstrated an impressive 99.88% reduction against Staphylococcus aureus, and 48.33% for silk fabric, albeit less effective against Escherichia coli. Zinc and copper salt mordants exhibited the ability to enhance antibacterial properties to almost 100% against Staphylococcus aureus and Escherichia coli in both blended wool/acrylic and silk fabrics.

3 METHODS OF APPLICATION FOR NATURAL ANTIMICROBIAL FINISHES

The application of natural antimicrobial finishes to textiles encompasses a wide array of chemical and physical methods, contingent upon the fiber type, its form, content, surface texture, and the specific antimicrobial agent utilized.^{67, 68} These finishes can be applied through various innovative approaches to enhance antimicrobial activity effectively. Techniques such as microencapsulation, cross-linking, plasma technology, surface modification, enzyme treatment, chemical modification, nanotechnology, ultrasound, and UV technologies are at the forefront of research for imparting durable antimicrobial properties to textile products.⁶⁹ Each method offers unique advantages in terms of effectiveness, durability, and suitability for different types of fibers and textiles, paving the way for advanced antimicrobial textile finishes.

3.1 Microencapsulation technology

Microencapsulation technology, initially used in the 1950s for carbonless duplicate paper, has since evolved into a commercially widespread innovation across various industries including food processing, cosmetics, pharmaceuticals, and agrochemicals. This technology is particularly prominent in the textile industry, facilitating advancements in technical, medical, and cosmetic textiles by imparting various functional features.^{70, 71} Microencapsulation involves encasing tiny droplets or particles of liquid or solid materials within a continuous polymeric layer, producing microcapsules typically ranging from 10 to 40 μm in diameter.⁷² This technique has been used to integrate antimicrobial agents and insect repellents into textiles, enhancing the functionality and handling of antimicrobial finishes in textiles through controlled release and facilitating various chemical processes.⁷¹ For example, Simões et al. (2020) successfully demonstrated the microencapsulation of eugenol in cellulose derivatives and its application on cotton fabrics using padding methods (see Figure 2).^{73, 74}

FIGURE 2

Schematic representation of eugenol microencapsulation using cellulose derivatives and its application in functionalized textiles. Reproduced under the terms of CC-BY-NC-ND 4.0.⁷⁵ Copyright 2020, Springer.

Microencapsulation technology also finds significant applications in the medical field. It has been used to address conditions like atopic dermatitis with underwear infused with microencapsulated herbal medicines such as Cortex Moutan in a chitosan sodium alginate matrix using the PentaHerbs formula, demonstrating antibacterial properties and aiding in disease recovery.⁷⁶ Clinical trials have highlighted the effectiveness of Aloe vera extract gel microcapsules with gum acacia on medical clothing in treating atopic dermatitis, showing exceptional antimicrobial activity against S. aureus and E. coli.⁷⁷

The scope of this technology extends to the encapsulation of various natural oils and extracts, which have been applied to textiles to confer antibacterial properties. Ozonated red pepper seed oil, grapefruit seed extract oil, and patchouli oil have been microencapsulated and applied to different fabric types, demonstrating significant antibacterial and antifungal activities.⁷⁸ Moreover, complex mixtures of essential oils like lavender, rosemary, and sage have been encapsulated and applied to shoe fabrics, showing effectiveness against both fungi and bacteria.^{79, 80} Chen and his colleagues experimented with another fruit, strawberry chitosan composite microcapsules, via a single coagulation and grafting method. The whole process of microcapsule preparation of strawberry and treated multifunctional fabric is shown in Figure 3.

FIGURE 3

(A) Schematic diagram of the preparation of microcapsules containing strawberry extract and their application to multifunctional fabric; (B) Antibacterial development in treated versus control fabrics, including (a) images showing the growth of two bacteria (S. aureus and E. coli), (b) a representation of bacterial growth on the treated and control fabrics, and (c) average numbers of bacteria on the control fabric, sample 1, and sample 2, where Samples 1 and 2 have been treated with strawberry/chitosan composite microcapsules. Reproduced with permission.⁸³ Copyright 2022, Elsevier.

Recent research continues to explore the potential of microencapsulated plant extracts. Guava leaf extract, Aerva lanata leaf extract, and piper betel leaf extract have been microencapsulated and applied to cotton and bamboo fabrics, showing promising antibacterial properties against a range of pathogenic bacteria typically found in wound infections.⁸¹ Similarly, microencapsulation has been used to enhance the antibacterial efficacy of pomegranate rind extract and berberine on textile substrates.⁸²

Continued innovation in microencapsulation techniques has led to the development of multifunctional textiles, such as those treated with microencapsulated neem, tulsi, and turmeric using yeast, which show enhanced inhibition zones against E. coli, S. aureus, and P. aeruginosa.⁸⁴ Other examples include the microencapsulation of limonene and vanillin, and clove oil, each demonstrating sustained antibacterial activity suitable for medical textile applications.⁸⁵ Furthermore, marine species like Halophila stipulacea, Colbomenia sinuosa, and Ulva fasciata have been encapsulated and applied to cotton fabrics, effectively inhibiting bacterial growth even after multiple wash cycles.⁸⁶

This extensive application of microencapsulation technology in textiles not only enhances their functional properties but also contributes significantly to the fields of medical textiles and active wear, demonstrating the technology's versatility and its pivotal role in advancing textile functionalities.

3.2 Cross-linking method

Cross-linking represents a pivotal technique for embedding antibacterial finishes within fibers. This method involves the use of a cross-linker to form intermolecular covalent bonds between the polymer chains of the fiber and the antibacterial molecule. Various cross-linkers, such as citric acid, glyoxal, genipin, glutaraldehyde, 1,1,3,3-tetramethoxypropane, tris(hydroxymethyl) phosphine, dextran sulfate, oxidized cyclodextrins, ethylene glycol diglyceryl ether, and diisocyanate, have been successfully employed for this purpose.^87-89

Aubert-Viard et al. (2019) utilized this methodology to modify nonwoven polyethylene terephthalate textiles using a chitosan (CHT) cross-linked with genipin. The treated textiles underwent a multilayer deposition of methyl-beta-cyclodextrin polymer (anionic) and CHT (cationic), significantly enhancing the antibacterial properties of the textile surface, as confirmed through scanning electron microscopy.⁹⁰ Figure 4 depicts the systematic process of layer-by-layer dip-coating for building up the multilayer assembly.

FIGURE 4

Systematic process of layer-by-layer dip-coating is used to build up the multilayer assembly. Reproduced with permission.⁹⁰ Copyright 2019, Elsevier.

Further research demonstrates the versatility of cross-linking methods. Aloe Vera was cross-linked onto silk using 1,2,3,4-butane tetracarboxylic acid, resulting in textiles with impressive antibacterial activity against S. aureus and K. pneumoniae.⁹¹ Similarly, Aloe vera extract and chitosan were applied to cotton textiles using citric acid as the cross-linking agent, achieving excellent resistance against the growth of S. aureus, and to a lesser extent, E. coli.^{92, 93}

Other natural extracts such as neem, prickly chaff, glycyrrhiza, and coffee, along with chitosan, were developed on cotton fabric using glyoxal and citric acid as cross-linkers, displaying notable antimicrobial efficacy.^{72, 94} Chitosan-neem seed composites cross-linked with citric acid and glutaraldehyde and applied to cotton fabrics showed enhanced bacterial resistance compared to untreated cotton.⁹⁵ Chitosan crosslinked with genipin has been applied to modify nonwoven textile dressings, demonstrating antibacterial effects against S. aureus through thermal treatment.⁹⁶ Chitosan derivatives have shown promise as long-lasting antimicrobial textile finishing agents when applied to cotton fabrics using citric acid as the crosslinking agent, achieving antibacterial effectiveness above 96% against E. coli and above 99% against S. aureus.^{97, 98}

In previous research, cotton textiles treated with chitosan butane tetracarboxylic acid (BTCA) and Arcofix NEC, both known as crosslinking agents, showed that the antibacterial activity of fabrics treated with BTCA was stronger than those treated with Arcofix NEC.⁹⁹ Additionally, a chitosan-cyanuric chloride hybrid used to crosslink cotton fabrics exhibited promising antibacterial activity against both gram-negative and gram-positive bacteria¹⁹ Using a pad-dry-cure procedure, berberine combined with citric acid was applied to cotton fabric as a crosslinking agent, resulting in high antibacterial actions against both gram-positive and gram-negative bacteria in the dyed samples.¹⁷ Bamboo pulp fabric treated with chitosan crosslinking displayed excellent antibacterial properties against E. coli and S. aureus, maintaining effectiveness even after 50 washes.¹⁰⁰ Cotton and blend fabrics were also treated with herbal Tulsi leaf extract and glutaraldehyde as a crosslinking agent. Compared to control samples, the treated fabrics suppressed the growth of S. aureus and E. coli by more than 92%.¹⁰¹ Additionally, Commiphora myrrha was grafted onto cellulose dressings through chitosan and a carbohydrate polymer, then crosslinked with polyacrylic acid, showing significantly improved antimicrobial behavior against M. luteus, S. aureus, P. aeruginosa, and E. coli.⁹⁶

Exploring further, propolis combined with cotton fabric and treated with glyoxal significantly hindered both gram-positive and gram-negative bacteria.¹⁰² The cross-linking of lysozyme from chicken egg white using tris(hydroxymethyl) phosphine on wool fiber dramatically enhanced the antibacterial capability against E. coli, maintaining bacteriostatic properties even after multiple washes.¹⁰³ Alginate, a natural biopolymer, is integrated into cotton or wool fabrics through ionic crosslinking, where an alginate-copper coating significantly enhances antibacterial properties against both gram-positive and gram-negative bacteria.¹⁰⁴ Additionally, B-cyclodextrin is grafted onto cotton fabric using butane tetracarboxylic acid as a crosslinking agent, demonstrating effective antibacterial action against gram-positive and gram-negative bacteria, as well as fungi.¹⁰⁵ Sophorolipids, surface-active glycolipids produced by yeasts, are employed as crosslinking agents on fabrics with butane tetracarboxylic acid, aiming for prolonged antibacterial protection. These treatments notably excel in combating gram-positive bacteria, showing superior results compared to their efficacy against gram-negative bacteria.¹⁰⁶ Gelatin, derived from the natural polymer collagen, is applied to cotton fabrics and cross-linked with dimethyloldihydroxyethelyene urea. The processed fabrics exhibit excellent antibacterial activity, particularly effective against pathogens such as S. aureus and E. coli.¹⁰⁷ Hydrogel, created from crosslinking quaternized and native cellulose, demonstrates remarkable antibacterial effectiveness against Saccharomyces cerevisiae, highlighting its potential in medical and hygienic applications.¹⁰⁸

Moreover, microgels cross-linked with 1,2,3,4-butane-tetracarboxylic acid and applied to cotton fabrics show significant bacterial anti-adhesion properties, with a 96.5% effectiveness against S. aureus and E. coli.¹⁰⁹ This broad spectrum of innovative cross-linking applications underscores the versatility and efficacy of these methods in enhancing the antibacterial properties of textile materials.

3.3 Plasma technology

Plasma technology has revolutionized the textile industry by offering a sustainable alternative to traditional wet processing techniques. Known for its environmentally friendly approach, plasma technology consumes minimal energy and eliminates the need for chemicals, making it an attractive option for textile processing.¹¹⁰ Since the 1980s, extensive research has been conducted in laboratories worldwide on low-temperature plasma treatments for various fibrous materials. These studies have consistently reported promising improvements in the functional properties of textiles treated with plasma.¹¹¹ Plasma treatments involve the use of electrons, ions, free radicals, metastable species, and photons, which are generated by applying electrical energy in a plasma reactor. This advanced technology has been applied to textiles to introduce beneficial properties such as enhanced adhesion, wettability, dyeability, water repellence, flame retardancy, and exceptional antibacterial characteristics.^{112, 113}

Recent applications of plasma technology have explored the incorporation of natural compounds for enhanced functionality. For instance, nonwoven textiles treated with plasma and impregnated with herbal medicine from Atractylodes macrocephala rhizome extract have shown significant inhibition against bacteria such as S. aureus and E. coli.¹¹⁴ Additionally, cotton/bamboo textiles treated with plasma and infused with herbal extracts from Achillea millefolium L. and Reynoutria japonica Houtt exhibited effective antimicrobial properties against E. coli, S. aureus, and C. albicans.¹¹⁵ Plasma technology has also been employed to enhance the efficacy of natural antibacterial agents. Thymol, extracted from plants and applied to cotton fabrics modified with low-temperature plasma, demonstrated a robust antibacterial impact.¹¹⁶ Similarly, a blend of viscose/spandex coated with Aloe vera and ZnO and treated with low-pressure plasma showed pronounced antimicrobial activity against both gram-positive S. aureus and gram-negative E. coli.¹¹⁷

Building on the advancements provided by plasma technology, the application of natural dyes to enhance the antibacterial properties of textiles has shown significant progress. Natural dyes like berberine were successfully mordanted on cotton, wool, and nylon fabrics using plasma techniques, displaying excellent antibacterial action against both gram-positive and gram-negative bacteria.^118-120 Continuing this trend, research conducted 2 years later utilized banana peel extracts as natural dyes on plasma-treated cellulosic fabrics. The dyed fabrics demonstrated effective antibacterial activity against E. coli and K. pneumoniae.¹²¹ Three years following this development, Peran et al. employed oxygen plasma pretreatment on wool fabrics before dyeing with pomegranate peel extract, which exhibited good antibacterial activity against K. pneumoniae and S. aureus.¹²² Moreover, the use of logwood dye, Haematoxylum campechianum L., on plasma-treated polyester fabrics showed satisfactory antibacterial properties against gram-positive Staphylococcus epidermidis.¹²³ These findings underscore the effectiveness of plasma as a pretreatment process in enhancing the functional properties of textiles, significantly reducing the need for water and time in the finishing process, as illustrated in Figure 5.

FIGURE 5

In comparison, the plasma technique is more sustainable in terms of water and time usage than A) the conventional wet processing technique (pad–dry–cure method) and B) plasma application for antimicrobial finishing of textiles. Reproduced under the terms of CC-BY-NC-ND 4.0.¹²⁴ Copyright 2022, Elsevier.

Expanding the scope of plasma treatments, chitosan was applied to cotton fabrics using nitrogen plasma and chlorine, resulting in notable antibacterial effects against S. aureus and K. pneumoniae.¹²⁵ In a similar vein, Wang et al. (2016) prepared and applied a carboxymethyl chitosan composite finish on plasma-treated cotton, further validating the efficacy of plasma treatments in textile finishing.¹²⁶ Additionally, oxygen plasma treatment was used to bind chitosan to viscose fabrics, which proved extremely effective in suppressing 100% of the Gram-positive Candida fungi.¹²⁷ Further applications of plasma technology include the treatment of PET fabrics with N, O-carboxymethyl chitosan using oxygen plasma, achieving a 38.8% bacterial reduction against S. aureus, although it showed no decrease in E. coli.¹²⁶ Moreover, neem oil vapor applied to cotton cellulose fabric via air plasma imparted significant antimicrobial properties against both E. coli and S. aureus.¹²⁸

Finally, glycerin derived from vegetable oils or animal fats was used as a pretreatment agent on polyester fabrics through atmospheric discharge plasma. This treatment led to a bacterial reduction of over 60% for K. pneumoniae and over 90% for S. aureus, although the antibacterial impact was not maintained after 20 washing cycles.¹²⁹ This range of studies highlights the versatility and efficiency of plasma treatments in developing sustainable and effective textile finishes.

3.4 Surface modification

The pathway to commercializing antimicrobial fabrics hinges critically on the ability to produce cost-effective and durable materials. This is often achieved by converting the textile's inert surface into a reactive one prior to applying an antibacterial finish. While a modification refers to a limited alteration in a material's properties, surface modification encompasses any physical or chemical transformation performed on the material's surface. These modifications can be realized through physicochemical, chemical, and biological methods.¹³⁰ In the textile industry, surface modification techniques are employed to enhance properties such as softness, absorbency, dyeability, and wettability. Recent advancements in textile chemistry have enabled these modified textiles to offer antibacterial properties, reduced skin irritation, and improved odor resistance, establishing surface modification as a paramount technique for contemporary textile treatments.¹³¹

Innovative developments include the creation of an L-Cysteine modified silk fiber aimed at treating atopic dermatitis. This condition was detailed earlier in this review. The modified fibers demonstrated significant antimicrobial activity against S. aureus, achieving a 100% microbial reduction after several days of incubation.¹³² The sol–gel method has been utilized to bind capsaicin to wool surfaces effectively. Although washing diminished its antibacterial effectiveness, capsaicin remained bonded to the fabric post-wash, indicating durable surface modifications against E. coli.¹³³ Surface modification has also been applied to coir fibers using cashew nutshell liquid, enhancing their antimicrobial properties. These coated fibers inhibited up to 95% of fungal growth from species such as Aspergillus niger and Rhizopus stolonifera.¹³⁴ Cotton fabrics have been similarly modified using betaine molecules through a conventional pad-dry-cure technique, which has been shown to suppress the growth of E. coli and S. aureus effectively, maintaining antibacterial efficacy even after 20 laundering cycles.¹³⁵

Additional methods of modifying cotton fabric surfaces for antibacterial purposes include the use of AgNPs–alginate coatings, which exhibited significant inhibitory effects against pathogens like P. aeruginosa, E. coli, and S. aureus.¹³⁶ Furthermore, green walnut shell extracts have been applied as natural dyes on cotton using mordants through surface modification, completely reducing the presence of S. aureus and E. coli, while also showing more than 85% antifungal effectiveness against C. albicans.¹³⁷ Surface modification has also been extended to naturally dyed jute, enhancing its antimicrobial properties. The modified jute demonstrated antibacterial activity, with the inhibitory zone effective against pathogens such as Salmonella bacillus and S. aureus.¹³⁸ This illustrates the broad applicability and effectiveness of surface modification techniques in advancing the functionality of textile products.

Chitosan surface modification on cotton fabric has been shown to substantially boost antibacterial properties against E. coli and S. aureus.¹³⁹ Using the pad-dry-cure method, both chitosan and aloe vera were applied to cotton woven fabrics, resulting in enhanced bacterial resistance, particularly against the gram-positive S. aureus.⁹³ Furthermore, a combination of chitosan and natural biosurfactants such as lignosulfonates has been explored for surface modification on cellulose fibers. Testing showed that fibers with a multilayer coating, featuring chitosan as the outermost layer, exhibited superior antibacterial efficacy against E. coli.¹⁴⁰

Carboxymethyl chitosan was effectively grafted onto cotton fibers using quaternary ammonium salts, achieving a bacteriostatic reduction rate over 99.9% against both E. coli and S. aureus. Cytotoxicity tests confirmed the human safety of the modified fabric.¹⁴¹ Additionally, a hybrid of chitosan and poly(propylene) imine dendrimer was grafted onto wool fabrics, providing effective antibacterial capabilities against both gram-positive and gram-negative microorganisms.¹⁴²

Chitosan was also surface-modified using acrylic acid on polypropylene nonwoven fabric, resulting in enhanced antibacterial action against Pseudomonas aeruginosa.¹⁴³ In another study, surface modification of polyester fabric involved treatment with dodecyl amine along with chitosan and its derivatives. This treatment resulted in significant elimination of E. coli, with reduction rates ranging from 75% to 93% within just 1 h.¹⁴⁴ The application of anhydrides for grafting chitosan onto wool fabric surfaces was also investigated. The modified wool samples exhibited antibacterial properties against both E. coli and S. aureus, with a notably higher reduction in microbial presence against E. coli.¹⁴⁵ These advancements underscore the potential of surface modification techniques in enhancing the antimicrobial properties of various textile materials, contributing to safer and more effective textile products.

3.5 Enzymes

Enzymatic treatments in textiles have gained significant traction as environmentally friendly and non-toxic alternatives to traditional chemical processes, especially in the face of pressing demands to reduce pollution in textile manufacturing.¹⁴⁶ Enzymes, which are complex polypeptides also known as biological catalysts, have been effectively employed in textile processes for their cost-efficiency and minimal environmental impact.¹⁴⁷ This research explores the potential of enzymes for antibacterial modification of textiles, highlighting their unique advantages and significant opportunities in the production of high-value textiles.¹⁴⁶ Enzymes function by binding substrate molecules at their active sites, forming an enzyme-substrate complex, which subsequently transforms the substrate into a product while regenerating the enzyme (refer to Figure 6).

FIGURE 6

Formation and activity of the enzyme-substrate complex: Binding, conversion, and regeneration steps.¹⁴⁸

The immobilization of pectinolytic enzymes on cotton fabric has shown considerable antimicrobial activity against S. aureus and Staphylococcus epidermidis, but only partial activity against Pseudomonas aeruginosa, suggesting its promising potential for use in antimicrobial textile and apparel production as an alternative to synthetic treatments.¹⁴⁹ Further enhancements in antibacterial properties were observed with cotton fabrics treated with neem extract and plasma, followed by enzyme treatment. These textiles exhibited a 100% reduction in S. aureus and a 98% reduction in E. coli¹⁵⁰ by chitosanolysis via pectinase enzyme, compositions containing chitosan impregnated on cotton textiles. The cotton textiles that resulted had antibacterial solid activity for Gram-positive and Gram-negative fungi activity and lasted for up to 10 washings.¹⁵¹

Chitosanolysis using a pectinase enzyme to treat cotton fabrics impregnated with chitosan resulted in textiles with strong antibacterial activity against both Gram-positive bacteria and Gram-negative fungi, maintaining effectiveness for up to 10 wash cycles.^{102, 151} In addition to enzymes, the development of silver nanoparticles (AgNPs) via biological synthesis methods has attracted attention for their broad-spectrum antibacterial properties and low toxicity to humans. The mycosynthesis of AgNPs using Aspergillus caespitosus as an enzymatic source was performed on various textile finishes. AgNPs produced in this manner displayed antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as C. albicans, showcasing the role of the nitrate reductase enzyme in the eco-friendly synthesis of metal nanoparticles.^{147, 149, 150}

To enhance the antibacterial properties of linen surfaces, a laccase enzyme sourced from the ascomycete Myceliophthora thermophila was used to facilitate the coupling of catechin and chitosan. The chitosan-treated samples demonstrated antibacterial activity primarily against E. coli, while the addition of catechin inhibited this effect in the bacteria. In contrast, S. aureus was susceptible to both chitosan and catechins, showing the complex interactions between these substances.¹⁵² A combined approach using sonochemical and laccase-catalyzed techniques produced hybrid antimicrobial coatings with ZnO nanoparticles and gallic acid on cotton fabrics. Remarkably, the antibacterial effectiveness of these materials exceeded 100% retention after 20 washing cycles at 75°C and maintained more than 60% effectiveness after 60 washing cycles, highlighting their durability.¹⁵³ On cotton fabric dyed with vat dye, enzymes such as laccase, cellulase, and their combination were employed, resulting in fabrics with enduring anti-fungal and antibacterial properties. Even after 50 household washing cycles, the fabrics maintained significant inhibitory effects on S. aureus, E. coli, and C. albicans, reducing their presence by 64.90%, 69.39%, and 61.99% respectively.¹⁵⁴ Further, laccase enzyme preparations from the Cerrena unicolor fungus were integrated into linen fabrics, producing materials with excellent antimicrobial activities against C. albicans, and significant antibacterial activities against both Gram-positive and Gram-negative microorganisms.¹⁴⁶

Protease enzymatic hydrolysis was applied to enhance the dyeing and antibacterial properties of natural dyes on wool fibers with mordanting. This treatment was effective against both types of bacteria, whereas the only dyed fabric was limited to combating gram-positive S. aureus.^{69, 155} Fabrics treated with proteases and lipases along with mordants demonstrated a potential 100% reduction in E. coli, showcasing an enhanced approach to hydrolyze wool and polyester surfaces.¹⁵⁶ Fabric treated with protease and subsequently processed with butane tetra-carboxylic acid, citric acid, and nano TiO₂ exhibited improved antimicrobial durability. The treatment significantly reduced bacteria, with E. coli and S. aureus populations reduced by more than 92.69% and 87.30%, respectively.¹⁴⁵ The cotton fabric pre-treated with Acacia catechu dye and subsequently treated with three different enzymes—acid cellulase, neutral cellulase, and xylanase—showed a significant improvement in antibacterial activity against both gram-positive and gram-negative bacteria, with the xylanase enzyme showing the strongest effect.¹⁵⁷

Wool fabrics that had lysozyme immobilized with glutaraldehyde displayed enhanced bacteriostatic properties against S. aureus.¹⁵⁸ Similarly, nanocellulose combined with allicin and lysozyme enzymes demonstrated antimicrobial action against C. albicans, S. aureus, and E. coli.¹⁵⁹ Cotton fabrics were also innovatively modified with chitosan microspheres containing immobilized lysozyme, achieving effective bacterial elimination against S. aureus, Enterococcus faecalis, and Pseudomonas aeruginosa.¹⁴⁴ Finally, the application of transglutaminase to integrate ε-poly-L-lysine into wool revealed that this treatment provided the wool with enhanced antibacterial capabilities, demonstrating significant antibacterial rates of 96.98% against E. coli and 97.93% against Micrococcus luteus.^{142, 143}

3.6 Chemical modification

Chemical modification plays a crucial role in the functionalization of fabrics by improving or introducing new physicochemical characteristics.¹⁶⁰ For instance, sugarcane bagasse lignin extract was chemically modified to enhance its antibacterial efficacy against both gram-positive Staphylococcus epidermidis and gram-negative bacteria such as Pseudomonas aeruginosa and E. coli.¹⁶¹ Similarly, Areca nut extract-based natural dyes were chemically modified on silk fabrics, demonstrating outstanding antibacterial properties against S. aureus and K. pneumoniae.¹⁶² Additionally, deacetylated acemannan extracted from Aloe vera was utilized as an antibacterial finish on conventional cotton goods through chemical modification techniques, achieving significant microbial reduction rates of 70.2% and 72.4% against S. aureus and E. coli, respectively.¹⁶³

There is substantial evidence indicating that chitosan can be chemically modified for a wide range of biomedical applications. For instance, chitosan was used to modify cotton textiles by incorporating silver nanoparticles into the fibers, enhancing the antibacterial activity against E. coli.¹⁶⁴ In another study, a chitosan hydrogel was synthesized and applied to cotton fabric to impart antibacterial properties, which showed efficacy against E. coli, Listeria monocytogenes, and S. aureus, albeit with a slight reduction in air permeability.¹⁶⁵ Furthermore, the antifungal properties of chitosan-coated gauze and carboxymethyl chitosan-coated gauze were investigated, revealing that C. albicans is resistant to carboxymethyl chitosan, which displayed antifungal properties.¹⁶⁶ Chemical modification of chitosan with bamboo rayon also demonstrated antibacterial effects against both gram-positive and gram-negative microorganisms, maintaining efficacy even after 30 wash cycles.¹⁶⁷ A novel antibacterial molecule, (4-(2,5-Dioxo-pyrrolidin-1-yloxycarbonyl)-benzyl)-triphenyl-phosphonium bromide, was synthesized for the chemical modification of chitosan, resulting in a series of new polymeric antimicrobial compounds—N-quaternary phosphonium chitosan derivatives with enhanced antibacterial properties against S. aureus and E. coli.¹⁶⁸ Chemically modified cotton, wool, silk, polyamide, and polyester textiles, as well as blended fabrics, were developed with silica–Ag composites, exhibiting antibacterial effects against S. aureus, E. coli, and the fungus Aspergillus niger.¹⁶⁹ Figure 7 illustrates the schematic diagram for the preparation of polyvinyl alcohol (PVA)-modified and silver nanoparticles (Ag NPs)-loaded polypropylene (PP) composite non-woven fabrics. The process involves immersing the fabric in a solution of PVA and glucose, which serves as the modifier and reducing agent, respectively. After immersion, the fabric is dried to fix the modifier and reducing agent, forming an encapsulation layer. Subsequently, the fabric undergoes repeated immersions in a silver ammonia solution to facilitate the in-situ deposition of Ag NPs. The concentration of the modifier, the molar ratio, the concentration of the solution, and the reaction temperature are critical factors that influence the deposition of Ag NPs.¹⁷⁰

FIGURE 7

Schematic diagram showing the preparation of Ag/PVA/PP non-woven fabrics and their antibacterial action against bacteria. Reproduced under the terms of CC-BY-NC-ND 4.0.¹⁷⁰ Copyright 2022, Nature.

Sustainable and eco-friendly monochlorotriazinyl β-cyclodextrin was applied to viscose fabric via chemical modification, subsequently treated with active ingredients like green tea extract and Aloe vera gel. The treated fabric displayed antibacterial effects against E. coli and S. aureus, albeit with some decline in efficacy.¹⁷¹

3.7 Nanotechnology

Nanotechnology refers to the science of manipulating materials at dimensions typically smaller than 100 nm.¹⁷² This technology has made significant impacts across various sectors including material science, electronics, mechanics, medicine, plastics, energy, optics, and aerospace, with the use of nanoparticles and nano-based technologies experiencing rapid growth.^{14, 173} In the field of textiles, nanotechnology is increasingly recognized as a revolutionary approach for enhancing antibacterial properties, making it one of the most promising technologies for new commercial applications.^{174, 175} Nanoparticles, due to their unique physicochemical properties and bioactivities, which can be substantially different from their ionic and bulk counterparts, are being extensively utilized in textile research as antimicrobial agents.¹⁷⁶

Significant research has been conducted in this area, demonstrating the effective use of nanotechnology in textiles. For instance, Wu et al. (2021) successfully used electrospinning technology to infuse nanofiber yarn with high-efficiency antibacterial agents, resulting in textiles that not only exhibit high antibacterial activity but also maintain this efficacy over an extended period, as illustrated in Figure 8.

FIGURE 8

Schematic diagram of graphene oxide-silver nanocomposites embedded in nanofiber core-spun yarns, produced by the electrospinning technique for antibacterial textiles. Reproduced with permission.¹⁷⁷ Copyright 2020, Elsevier.

Additionally, neem extract nanoparticles have been used to treat cotton textiles, showing excellent antimicrobial properties against S. aureus and E. coli, and maintaining effectiveness for up to 25 washes.¹⁷⁸ In another innovative application, nanocapsules containing Aloe vera extract were applied to cotton fabrics, enhancing their wound healing and antimicrobial properties against S. aureus, E. coli, and C. albicans.¹⁷⁹ Furthermore, nanoparticles made from sodium alginate and chitosan were loaded with Ocimum sanctum leaf extracts and used as a finishing treatment for cotton fabrics. This treatment demonstrated strong antibacterial effects, with the highest inhibitory area observed against a range of organisms, with P. aeruginosa showing the most significant inhibition, followed by S. aureus, E. coli, and B. subtilis showing the least.¹⁸⁰ Additionally, a nanoemulsion combining Hibiscus flower, Curry leaves, and a droplet of coconut oil was developed for the delivery of essential oils. The antimicrobial activity of the treated fabric was particularly effective against S. aureus and K. pneumoniae.^{181, 182} Moreover, lignin and polyvinyl alcohol nanocomposite fibers incorporating silver demonstrated remarkable antibacterial activity against E. coli, highlighting the potential of nanocomposites in the development of antimicrobial textiles.^{183, 184}

Sericin, a biological protein extracted from silk, was effectively utilized in conjunction with TiO₂ nanoparticles to enhance the antibacterial properties of cotton fabrics. The finishing process applied to the cotton significantly improved its efficacy against S. aureus compared to E. coli.¹⁸⁵ Additionally, in the context of treating burn patients, who are particularly susceptible to infection and wound sepsis, innovative antimicrobial wound dressings were developed.¹⁴¹ These dressings incorporated human serum albumin and silk fibroin nanocapsules immobilized onto cotton and polyethylene terephthalate blends containing eugenol, which showed a notable ability to inhibit the growth of S. aureus and E. coli by 81% and 33%, respectively.¹⁴⁰

Further advancements in nanotechnology have been demonstrated through the use of chitosan combined with herbal extracts from Senna auriculata and Achyranthes aspera at the nanoscale. This combination significantly enhanced the antibacterial properties of fabrics, showing greater inhibition of both E. coli and S. aureus.¹⁸⁶ Moreover, wool fibers treated with chitosan-propolis nanoparticles have exhibited particularly strong antibacterial action against Gram-positive bacteria, surpassing that against Gram-negative bacteria.¹⁸⁷ In textile applications, the exhaustion method was used to infuse 100% cotton, viscose, and polyester fabrics with chitosan nanoparticles. It was found that cotton fabric, in particular, showed superior antibacterial activity against both Gram-positive and Gram-negative bacteria compared to viscose and polyester.^{188, 189} Additionally, cotton fabrics treated with carboxymethyl chitosan and silver nanoparticles demonstrated an exceptional antibacterial effect, effectively reducing bacterial presence by 99% for both S. aureus and E. coli.¹⁹⁰ The antibacterial capabilities of textiles were further enhanced by coating cotton or polyester fabrics with chitosan and ZnO nanoparticles, which proved to be significantly effective against both types of bacteria.^{191, 192} Similarly, chitosan silver nanoparticles have been used to augment the antibacterial properties of polyester fabrics, with treated samples showing efficacy primarily against S. aureus.¹⁹³ A green synthesis approach was also explored, where antimicrobial nanofiber mats featuring silver nanoparticles encapsulated in chitosan were developed following a reduction in glucose. These mats displayed high bactericidal efficacy against E. coli.¹⁹⁴ These studies underscore the profound impact that nanotechnology continues to have on textile research, particularly in enhancing the antimicrobial properties of various fabrics, demonstrating its vital role in advancing textile functionalities.

3.8 Ultrasound and UV technology

Ultraviolet (UV) treatment leverages the power of UV light to modify the molecular structures on the surface of fibers, efficiently triggering photochemical reactions. This method serves as a suitable alternative to traditional thermal stabilization processes, providing a swift and low-temperature option that reduces processing times significantly. UV technology is not only safe but also cost-effective, making it an ideal choice for commercial applications.

Ultrasound technology is increasingly recognized for its significant advantages in the textile industry, particularly within the framework of clean textile processing technology. It offers numerous benefits over conventional chemical treatments.^{195, 196} Researchers are drawn to ultrasound technology for various reasons. In 2019, Ramirez and his colleagues successfully used ultrasound to coat fabrics with water-based polypyrrole dispersions, achieving uniform coatings on the fiber surfaces and demonstrating excellent antibacterial activity (Figure 9).

FIGURE 9

Schematic diagram of the development of polypyrrole-treated fabrics using the ultrasound technique. Reproduced under the terms of CC-BY-NC-ND 4.0.¹⁹⁷ Copyright 2019, Elsevier.

Prior to this, Rehman and his team utilized ultrasonic techniques to effectively extract dyes from pomegranate peel for application on lyocell fabrics. The dyed fabrics displayed adequate antibacterial capabilities against S. aureus, while undyed samples showed minimal activity.⁴⁶ Moreover, optimal conditions for the ultrasonic-assisted extraction of natural dyes from pomegranate rind were established using a response surface methodology, enhancing the antibacterial effectiveness of the textiles.¹³⁹

The application of ultrasound has also facilitated the development of purple sweet potato powder extract treated with silver nanoparticles on silk, cotton, and leather, using an environmentally friendly dyeing process. The antibacterial activity of the treated materials was notably effective against P. acnes, B. linens, B. cereus, and S. epidermidis.¹⁹⁸ Similarly, aqueous extracts from natural dyes such as Berberis vulgaris and red onion skin were used on wool and cotton samples, with the ultrasonic method proving effective in enhancing the antibacterial properties of the dyed wool. The cotton dyeing's antibacterial efficacy was further improved by combining two dyestuffs with ultrasonic treatment.¹⁹⁹ Coconut coir (Cocos nucifera) and walnut bark containing juglone have been identified as novel sources of natural dyes for wool dyeing using ultrasonic radiation.¹³⁸ These materials possess excellent antifungal and antibacterial properties.¹³⁵ Furthermore, peppermint oil was applied to cotton fabric using ultrasonic irradiation and subsequently stabilized with UV curing, a process that enhances the durability of textiles and prolongs the release of antibacterial, aromatic, and insect-repellent properties.²⁰⁰ These advancements highlight the growing integration of ultrasound and UV technologies in textile processing, underscoring their potential to revolutionize material treatments while adhering to environmental and safety standards.

Tragacanth nanocapsules encapsulating Chamomile extract were efficiently manufactured using an ultrasound-aided process and subsequently attached to cotton fabric via UV curing. This treatment endowed the cotton fabric with notable antibacterial and antifungal activities, evidenced by the low survival percentages of S. aureus (9%), E. coli (11%), and C. albicans (6%). Such properties make this fabric suitable for diverse applications including medical, hospital, sports, and domestic textiles.¹³⁴ In another instance, Scutellaria baicalensis, known for its primary active compound baicalin, was integrated into linen fabric using a combination of impregnation and ultrasonic processing. The processed fabric demonstrated impressive antimicrobial properties, with an antibacterial rate exceeding 73%. Notably, the fabric showed a greater inhibitory impact on S. aureus compared to E. coli.¹³³ The ultrasound technique was also employed to dye merino wool fibers using extracts from C. camphora waste leaves. The dyed material exhibited good antibacterial activity against a range of bacteria including S. aureus, Pseudomonas aeruginosa, E. coli, and Bacillus subtilis.¹³² Additionally, gelatin fibers containing silver nanoparticles were introduced using UV technology, which significantly enhanced their antibacterial activity against both Gram-negative and Gram-positive bacteria.²⁰¹ The UV grafting of chitosan onto wool and cotton has also been suggested as a viable eco-friendly method, effectively providing good antibacterial properties against both E. coli and S. aureus.^202-204 Furthermore, UV-cured chitosan applied to silk and cotton fabrics showed potent antibacterial activity specifically against E. coli.²⁰⁵ These diverse applications of ultrasound and UV technologies in textile treatments demonstrate their potential in enhancing the functional properties of fabrics. All these techniques are meticulously summarized in Table 1, providing a comprehensive overview of their effectiveness and utility across different types of textiles and treatments.

TABLE 1. Method of application for natural antimicrobial finish.

Methods	Natural agents	Fabric/fiber type	Antimicrobial activity		References
			Antibacterial activity	Antifungal activity
Micro-encapsulation	Cortex Moutan/Aloe vera	Textile Materials	Both Gram (ve+) and Gram (ve−)		12, 82
	Red pepper seed oil	Nonwoven	Both	Yes	16
	Grapefruit seed extract oil	Cellulose	Both		15
	Patchouli oil	Cotton	Both		14
	Lavender, rosemary, and sage essential oil	Nonwoven	Both		17, 206
	Guava leaf extract	Cotton	Both	Yes	20
	Aerva lanata leaves	Cotton	Both		19
	Piper betel leaves	Cotton and Bamboo	Both		18
	Pomegranate rind extract	Textile Materials	Only Gram (ve−)		22
	Berberine	Cotton	Only Gram (ve+)		21
	Neem, tulsi and turmeric	Cotton and Silk	Both		207
	Limonene and vanillin	Cotton	Both		208
	Clove oil	Textile Materials	Only Gram (ve+)		209
	Halophila stipulacea and Colbomenia sinuosa and Ulva fasciata	Cotton	Both		1
Crosslinking	Alovera/ Alovera gel	Silk/Cotton	Both		26, 98
	Alovera	Cotton	Only Gram (ve+)		27
	Neem, prickly chaff extract, glycyrrhiza extract, coffee extract and chitosan	Cotton	Both		7
	Chitosan–Neem seed composites	Cotton	Both		29
	Chitosan	Nonwoven	Only gram (ve+)		30
	Berberine	Cotton	Both		33
	Chitosan	Bamboo pulp fabric	Both		35
	Tulsi leaf	Cotton and Blend	Both		36
	Commiphora myrrha	Cellulose	Both		37
	Propolis	Cotton	Both		38
	Lysozyme	Wool	Only Gram (ve−)		39
	Alginate	Cotton/Wool	Both		40
	Sophorolipids	Cotton	Both		42
	Gelatin	Cotton	Both		59
	Hydrogel	Cellulose	Both	Yes	45
	Microgels	Cotton	Both		46
Plasma	Atractylodes macrocephala rhizome	Nonwoven	Both		210
	Achillea millefolium L. and Reynoutria japonica Houtt	Cotton/bamboo	Both	Yes	49
	Thymol	Cotton	Only Gram (ve+)		55
	Alovera	Viscose blend	Both		63
	Berberine	Cotton, Wool, Nylon	Both		56, 64, 65
	Banana peel	Cellulose	Only Gram (ve−)		47
	Pomegranate peel	Wool	Both		48
	Logwood	Polyester	Only Gram (ve+)		57
	Chitosan	Cotton	Both		58
	Chitosan	Viscose	Only Gram (ve+)	Yes	59
	Neem oil	Cotton	Both		62
	Glycerin	Polyester	Both		67
Surface modification	L-Cysteine	Silk	Gram (ve+)		70
	Capsaicin	Wool	Gram (ve−)		211
	Cashew nut shell	Coir	Both	Yes	72
	Betaine	Cotton	Both		71
	Green walnut shell	Cotton	Both	Yes	76
	Chitosan/ Alovera	Cotton	Gram (ve+)		212
	Chitosan/lignosulfonates	Cellulose	Gram (ve−)		77
	Chitosan	Nonwoven	Gram (ve−)		213
Enzyme	Pectinase/Chitosan	Cotton	Both	Yes	82, 84
	Enzyme preceded neem	Cotton	Both		214
	Aspergillus caespitosus	Textile Materials	Both	Yes	147, 149, 150
	Catechin/chitosan	Linen	Both		85
	Laccase enzyme	Cotton/Linen	Both	Yes	86, 146
	Protease enzyme	Wool	Both		4, 88
	Protease and lipase enzyme	Wool/Polyester	Gram (ve−)		87
	Acid cellulase, neutral cellulase, and xylanase	Cotton	Both		157
	Lysozyme	Wool	Gram (ve+)		89
	Allicin/lysozyme	Textile Materials	Both	Yes	91
	Chitosan/ lysozyme	Cotton	Both		144
	Transglutaminase	Wool	Both		142, 143
Chemical modification	Sugarcane baggase lignin	Textile materials	Both		93
	Areca nut	Silk	Both		94
	Aloe vera	Cotton	Both		95
	Chitosan	Cotton	Gram (ve−)		90
	Chitosan derivatives	Cotton	Both	Yes	100, 215
	Silica	Cotton, wool, silk, polyamide, and polyester	Both	Yes	101
	β-cyclodextrin/green tea and Aloe vera gel	Viscose	Both		96
Nanotechnology	Neem	Cotton	Both		108
	Aloe vera	Cotton	Both	Yes	109
	Ocimum sanctum leaves	Cotton	Both		110
	Hibiscus flower, Curry leaves and coconut oil	Textile materials	Both		111, 216
	Lignin	Composite	Both		112, 113
	Sericin	Cotton	Both		114
	Human serum albumin/silk fibroin	Cotton and PET	Both		140
	Chitosan/Senna auriculata and Achyranthes aspera	Textile Materials	Both		115
	Chitosan/Propolis	Composite	Both		116
UV and ultrasound	Pomegranate peel	Lyocell	Gram (ve+)		126
	Purple sweet potato powder	Silk, cotton	Both		217
	Berberis vulgaris and red onion skin	Wool	Both		128
	Coconut coir and walnut bark	Wool and cotton	Both	Yes	135, 136
	Peppermint oil	Cotton	Both		129
	Tragacanth/Chamomile	Cotton	Both	Yes	134
	Scutellaria baicalensis	Linen	Both	Yes	133
	C. camphora waste leaf	Wool	Both		132
	Collagen	Gelatin	Both		130
	Chitosan	Wool and Cotton	Both		131, 132, 218

4 EXTRACTION AND APPLICATION PROCESS OF SOME IMPORTANT NATURAL ANTIMICROBIAL AGENTS

In the realm of textile production, antimicrobial agents are categorized into two types based on their origin: synthetic and natural. Synthetic agents, including metals and their salts, quaternary ammonium compounds, triclosan, poly hexamethylene biguanide (PHMB), regenerable n-calamine, and peroxy acid, have been widely utilized due to their effective antibacterial properties. These agents are already incorporated in various commercially available textiles. However, they often pose environmental risks such as significant biocidal action against non-target microorganisms and potential water contamination.²¹⁹ In contrast, the use of natural antimicrobial agents, particularly plant extracts, is gaining traction due to their eco-friendliness and lower risks of adverse environmental impacts. This section details the extraction and application processes of natural antimicrobials, focusing on the primary active components responsible for their antibacterial activity.

4.1 Neem

Neem has been revered since ancient times in India, where it has been used extensively in traditional medicine to address a plethora of health issues. Its application spans approximately 700 herbal formulations across various traditional health systems such as Ayurveda, Siddha, Unani, and Amchi.²²⁰ Internationally, in countries like China, the United States, France, Germany, and Italy, neem has garnered significant interest not only as an herbal insecticide but also in various therapeutic formulations. While the active compounds of neem are present throughout the tree, they are predominantly extracted from its seeds, bark, leaves, and roots.²²¹

4.1.1 Neem extraction

Neem's natural repellent properties and its ability to inhibit the growth of both Gram-positive and Gram-negative bacteria have made it a popular choice in herbal pesticide formulations. However, its incorporation as an antibacterial agent in textiles has not been extensively researched until recently. A few patents have been filed concerning the use of neem oil and its microencapsulation in textiles, indicating a growing interest in its potential applications.²²² Recent systematic studies have focused on the integration of neem seed and bark extracts into cotton²²³ and cotton/polyester blend textiles,²²⁴ showing promising results. Additionally, neem bark extract has been effectively utilized as a natural dye for wool under optimal conditions, further demonstrating its versatility and efficacy in textile applications.²²⁵

4.1.2 Application of neem extract

In an investigation, glyoxal/glycol served as the cross-linking agent to facilitate the application of neem extract on textiles. The antibacterial activity was assessed against Bacillus subtilis, a gram-positive bacterium, and Proteus vulgaris, a gram-negative bacterium, according to the standard AATCC 147-1997. The primary antifeedant compounds identified in neem—azadirachtin, salanin, and meliantriol—were key to its efficacy. Initial results indicated that all unwashed mixed fabric samples retained significant antibacterial activity, achieving a 95% reduction in Bacillus subtilis and an 80% reduction in Proteus vulgaris.²²⁶ However, the effectiveness of these fabrics declined dramatically after just a single wash, and notably, fabrics that were not treated with a cross-linking agent displayed no antibacterial activity when wet.

Further studies expanded on these findings. Cotton fabrics were treated with extracts from Terminalia chebula and Azadirachta indica. Analysis revealed that the combination-treated fabrics exhibited bacterial reduction percentages ranging from 57% to 64% against gram-negative bacteria and from 60% to 68% against gram-positive bacteria.²²⁷ In another study from 2010, false rosary tree extracts (Azadirachta indica) were utilized to develop natural antibacterial finishing techniques. This research employed the pad-dry-cure impregnation-drying-thermophilic method for applying microcapsules filled with plant extracts to silk and cotton fabrics. The antibacterial properties were evaluated using disc diffusion and parallel steak methods according to AATCC 143-1993, demonstrating effective antibacterial properties against S. aureus, E. coli, and Pseudomonas.²²³

Another 2010 study explored the use of neem tree extracts in conjunction with chemicals such as cadmium chloride, zinc sulfate, boric acid, and urea formaldehyde to protect cotton fibers from damage caused by fungi (Aspergillus sp., Fusarium sp., and Trichoderma sp.) and bacteria (Pseudomonas sp.).²²⁸ More recently, Jain et al. (2022) conducted a study where Azadirachta indica extract was applied along with silver nanoparticles (AgNPs). This combination was highly effective against Bacillus licheniformis with a 93.3% inhibition rate, while showing moderate effects against Klebsiella pneumoniae (20%) and Escherichia coli (10%), as demonstrated in Figure 10.²²⁹

FIGURE 10

Application of neem extract with AgNPs to cotton fabric for antimicrobial applications. Reproduced under the terms of CC-BY-NC-ND 4.0.²²⁹ Copyright 2022, MDPI.

4.2 Chitosan

Chitosan and its derivatives have been extensively studied for their applications in textiles, attracting significant attention due to their promising properties.^230-232 Chitosan, a deacetylated derivative of chitin, is derived from the shells of shrimp and other sea crustaceans. It is composed of 1–4 glycosidic linkages that connect glucosamine and N-acetylglucosamine units. Known for its nontoxic, biodegradable, biocompatible, and antimicrobial qualities, chitosan is increasingly utilized in various textile applications. The antibacterial activity of chitosan is influenced by several factors including the type of chitosan used, its degree of deacetylation, molecular weight, the species of bacteria, and other physical and chemical parameters such as pH, ionic strength, and the presence of non-aqueous solvents.⁷² These variables critically affect how chitosan interacts with microbial cells and determines its effectiveness as an antimicrobial agent.

Chitosan's mechanism of antibacterial action, although not fully elucidated, is primarily attributed to the electrostatic interactions between the positively charged amine groups (NH₃+) at the C2 position of glucosamine monomers (at pH levels below its pKa of 6.3) and the negatively charged residues on the cell surfaces of bacteria and fungi. These interactions lead to disruptions in cell surface integrity, increasing cell permeability. This permeability change allows essential cellular components such as electrolytes, UV-absorbing materials, proteins, amino acids, glucose, and lactate dehydrogenase to leak out. The disruption of these vital cellular processes ultimately leads to the death of the microorganisms. This hypothesis underscores the importance of electrostatic contact in the antibacterial activity of chitosan.¹⁴

Moreover, while many glucopyranose residues in chitin appear as 2-acetamido-2-deoxy-β-D-glucopyranose, chitosan primarily consists of 2-amino-2-deoxy-β-D-glucopyranose units due to the deacetylation of chitin. The extent of this deacetylation, known as the degree of deacetylation (DD), profoundly affects the solubility and solution behavior of chitosan. Chitin, in its native form, does not dissolve in dilute acetic acid; however, when deacetylated beyond a certain threshold (typically around 60%), chitosan becomes soluble in acidic solutions.¹⁴ This solubility is crucial for its application in textile processing where it can be effectively used to impart antimicrobial properties to fabrics.

4.2.1 Chitosan extraction

Chitosan was extracted from shrimp shells using a detailed procedure designed to optimize yield and quality. Initially, the shrimp shells were thoroughly rinsed to remove any adhering contaminants, dried under vacuum conditions, and finely ground using a mortar and pestle. This fine powder was then subjected to an alkaline treatment, immersing it in 1 M NaOH for 24 h, which helped in removing proteins and other organic materials. After rinsing and drying the treated shells, they underwent a demineralization process using 1 M HCl to eliminate mineral content. Subsequently, the material was deproteinized with 1 M NaOH and bleached using potassium permanganate (KMnO₄) and oxalic acid to produce pure chitin powder.²³³

The chitin obtained was then subjected to deacetylation through treatment with 50% NaOH, a process repeated multiple times to achieve a higher degree of deacetylation, thus converting the chitin into chitosan. This method ensures high-quality chitosan suitable for textile applications, focusing on achieving the desired physical and chemical properties.²³³

4.2.2 Application of chitosan

Chitosan and its derivatives have gained considerable attention as antimicrobial agents in the textile industry.²³⁴ One common method involves using cross-linking agents like glutaric dialdehyde and polycarboxylic acids, which chemically bond chitosan to cotton fibers, enhancing durability and efficacy.^235-237 Chitosan is typically applied to cotton fabric by impregnating the material with a chitosan and citric acid solution, followed by a curing process at elevated temperatures. This process, known as the dry-cure technique, effectively secures the chitosan citrate onto the fabric, providing lasting antibacterial properties.²³⁷

Additionally, chitosan has been used as a binder and thickener in the pigment printing of polyester and polyester/cotton blends. Experiments show that within an hour of application, printed fabrics exhibit up to a 96% reduction in Staphylococcus aureus colonies, underscoring chitosan's potent antibacterial activity.²³⁸ Commercially available chitosan fibers further extend these benefits, offering enhanced dye uptake, antistatic properties, and deodorant activities, making chitosan a versatile and valuable additive in textile finishing (see Figure 11).²³⁹

FIGURE 11

Application of chitosan in textile form. Reproduced under the terms of CC-BY-NC-ND 4.0.²⁴⁰ Copyright 2022, SAGE.

4.3 Silk sericin

Silk sericin serves as a natural adhesive that coats fibroin fibers, facilitating the layering of filaments during cocoon formation. It is a biologically derived macromolecular protein produced by the silkworm Bombyx mori and constitutes approximately 25%–30% of the silk protein. Typically, sericin is removed during the production of raw silk and prior to the textile dyeing and finishing processes. Sericin is notable for its multifunctional properties, including antibacterial, anti-UV, antioxidant, and moisturizing effects. Recovering sericin not only mitigates water pollution caused by degumming liquors and waste cocoons but also offers significant commercial potential, finding applications in cosmetics like lotions and shampoos, as well as in various biomaterials for the textile industry.²⁴¹

4.3.1 Extraction of silk sericin

The process of extracting silk sericin is relatively straightforward and has been optimized through various enhancements. According to Khalifa et al., the sericin extraction involves initially chopping 50 g of silk cocoons into small pieces. These pieces are then combined with deionized water and autoclaved at 120°C for 30 min. Following autoclaving, the mixture of sericin and fibroin is filtered through Whatman filter paper to separate the silk fibroin. The sericin solution is subsequently centrifuged to precipitate the sericin, which is then dried in an oven at 100°C to yield sericin powder. This method is notable for its absence of chemical additives, making it environmentally friendly.²⁴²

4.3.2 Application of silk sericin

Sericin has been explored for its potential to enhance the properties of synthetic fibers, such as polyester. For instance, when polyester fiber was modified using sericin, its hygroscopic property improved fivefold compared to untreated polyester. However, the antibacterial properties of the treated polyester fiber showed a reduction in effectiveness ranging from 38 to 51% only. Further research by Rajendran et al. involved using a pad–dry–cure process to extract sericin from B. mori cocoons and apply it to cotton fabrics. Fourier-transform infrared spectroscopy (FTIR) was utilized to characterize the treated fabric, revealing distinct amide peaks associated with sericin. The antibacterial activity of the sericin-coated cotton was significant, with reductions of 89.5% and 81% against S. aureus and E. coli, respectively, suggesting that sericin could be an effective component in the development of antimicrobial textiles. The modification of polyester with sericin not only enhanced its moisture absorption capacity but also demonstrated the potential for improving comfort and functional attributes in textiles.²⁴³

4.4 Aloe vera (Aloe barbadensis)

Aloe vera, belonging to the Liliaceae family and also known as the ‘Lily of the Desert,’ has been a cornerstone in skin care for nearly 2000 years. This plant is highly valued not only in folk medicine but also in modern cosmetic applications. It is enriched with approximately 75 nutrients and 200 active compounds, including 20 minerals, 18 amino acids, and 12 vitamins, which are integral to its broad use in skin care products. Since the 1970s, Aloe vera gel has been a common ingredient in cosmetics across the United States, and its presence is now ubiquitous in skincare products globally. The therapeutic properties of Aloe vera stem not only from its nutrient content but also from its polysaccharides, which include glucomannan of varying molecular weights, acetylated glucomannan, galactogalacturan, glucoga-lactomannan of various compositions, and acetylated mannan, or acemannan.²⁴⁴ Acemannan is known for its immunomodulatory, antibacterial, antifungal, and anticancer properties, comprising randomly acetylated linear D-mannopyranosyl units.

4.4.1 Extraction of aloe vera

The process of extracting aloe vera is meticulous to preserve its bioactive compounds. To begin with, Aloe vera leaves are sliced thinly and placed on a glass plate. These slices are then lyophilized in vacuo for 2 days to ensure thorough drying, after which they are milled into a fine powder. This powder serves as the starting material for extraction. For the extraction, 50 milliliters of 80% ethanol (v/v) are added to 1 gram of the lyophilized Aloe vera powder. The mixture is sonicated for 30 min to enhance the extraction of active ingredients. Following sonication, the mixture is filtered, and the residue is washed twice with 10 mL of ethanol to ensure maximal recovery of the compounds. The filtrate is then transferred to a pre-weighed flask and subjected to rotational evaporation at 30°C under reduced pressure to remove the ethanol, leaving behind the dry extract. The final mass of the extract is determined by the weight difference between the pre-weighed empty flask and the flask containing the dried extract, thus quantifying the yield of the solid Aloe vera extract.⁹³

4.4.2 Application of aloe vera

Aloe vera, known for its versatile applications in biomedicine and textiles, has been extensively researched for its potential in wound healing, tissue engineering, medical textiles, health care textiles, curative garments, cosmetotextiles, UV protective textiles, and wearable electronics (see Figure 12). This wide-ranging utility is due to its antibacterial and antifungal properties, making it suitable for inclusion in medical textiles like wound dressings and bioactive textiles. Jothi²⁴⁵ focused on an innovative approach by isolating a specific enzyme, lipase, from Aloe vera for a bio-scouring process aimed at treating single jersey knitted fabrics. When applied in varying concentrations (1%, 2%, and 3%) and temperatures (40, 60, and 70°C), the enzyme treatment enhanced the dye uptake, color fastness, and overall quality of 100% cotton fabrics. This bio-scouring method not only improved the textile properties but also significantly reduced the environmental impact by lowering effluent volumes, chemical oxygen demand (COD), total dissolved solids (TDS), and pH levels, achieving substantial energy savings (50% thermal and 40% electrical). Furthermore, bio-scouring wastewater showed a 40%–50% reduction in COD and 60% in TDS compared to conventional scouring.²⁴⁶

FIGURE 12

Application of aloe vera-finished textiles in wound healing and UV-resistant textiles. Reproduced under the terms of CC-BY-NC-ND 4.0.²⁴⁸ Copyright 2020, Springer Nature.

The protective properties of Aloe vera against UV radiation have also been highlighted in recent studies. UV-protected Aloe-anthraquinone-treated cotton fabric demonstrated an ultraviolet protection factor (UPF) of 57, significantly higher than untreated fabric (UPF 14), providing efficient protection against harmful UV radiation.²⁴⁷

In addition to medical and protective applications, Aloe vera is utilized in the dyeing sector due to its natural salt, acid, enzymes, and other dye facilitating components. Amanuel and Teferi explored the substitution of conventional salt with Aloe vera gel in a reactive dyeing process, observing varied depth and quality of color based on the concentration of Aloe gel used. Fabrics treated with 100% Aloe gel exhibited rich color depths, whereas lower concentrations resulted in duller shades. Specifically, fabric dyed with 80% and 60% Aloe vera concentrations achieved medium and dull depths of shade, respectively.²⁴⁹ Aloe vera gel also serves as an effective thickener in both reactive and pigment printing processes, offering a cost-effective and environmentally friendly alternative to synthetic thickeners. Its high performance at concentrations of 30%–40% Aloe gel, alongside a 2% binder, ensured excellent wash and color fastness, comparable to synthetic thickeners.²⁴⁷

4.5 Clove oil (Syzygium aromaticum)

Clove oil, derived from Syzygium aromaticum, has been explored extensively for its antimicrobial properties. Sarkar et al. investigated the application of clove oil as a bioactive agent in textile processing, particularly as a size preservative and a finishing agent for cotton textiles to impart antibacterial properties. Their studies demonstrated that when clove oil was used at a 0.5% concentration, it effectively inhibited the growth of Staphylococcus aureus and Klebsiella pneumoniae by 17 mm. Enhancing the concentration to 1% in combination with a dimethylol dihydroxyethylene urea-based in-built catalyst (KVSI) significantly improved the antimicrobial activity, inhibiting S. aureus by 47 mm.²⁵⁰ which proves its effectiveness as an antimicrobial agent. This increase not only confirmed the potent antimicrobial efficacy of clove oil but also underscored the enhanced wash fastness of the treated fabric.

4.6 Azuki beans (Vigna angularis)

The antibacterial properties of Azuki beans (Vigna angularis), particularly the colored varieties (green, black, and red), have been studied for their efficacy against various pathogens, including Staphylococcus aureus, Aeromonas hydrophila, and Vibrio parahaemolyticus. In contrast, white Azuki bean extracts showed no inhibitory effect against these pathogens. Hori et al. highlighted that extracts from colored Azuki beans, which are rich in polyphenols such as proanthocyanidins, resulted in significantly lower counts of S. aureus after 24 hours compared to both controls and extracts from white beans.²⁵¹ These findings suggest that the high polyphenol content in colored Azuki beans contributes to their antibacterial properties, presenting a potential for application in antibacterial textile treatments.²⁵¹

4.7 Other natural agents

Research into natural antibacterial agents continues to expand, incorporating a variety of substances. Onions (Allium cepa), a member of the Liliaceae family, are commonly used in culinary contexts but also have applications in antibacterial textile treatments. Chen and Chang explored the antibacterial properties of cotton fabrics treated with onion pulp extracts. They found that grafted fabrics displayed zones of inhibition against S. aureus ranging from 1.1–0.8 cm with 10 min of onion skin extraction grafting, and 0.7–0.5 cm with 30 minutes of extraction time.²⁵² Turmeric, known for its vibrant yellow color derived from the rhizomes of the plant, not only serves as a natural dye for wool, silk, and mordanted cotton but also exhibits antibacterial properties. ²⁵³ Additionally, recent studies have explored the use of Hiba oil (cypress oil) as an antibacterial agent for textiles, expanding the scope of natural substances in textile applications.²⁵⁴

5 CONCLUSIONS

In conclusion, recent developments in eco-friendly natural antimicrobial agents for textiles represent a significant advancement toward sustainable and responsible manufacturing practices. The textile industry, historically known for its substantial environmental footprint, is undergoing a transformative shift with the emergence of innovative solutions designed to address microbial contamination without sacrificing ecological integrity.

The integration of natural antimicrobial agents, sourced from renewable materials, not only enhances the durability and functionality of textiles but also significantly reduces the environmental impact traditionally associated with synthetic chemical treatments. This shift is in line with global efforts to decrease the carbon footprint and foster eco-conscious consumer behavior. The significance of these advancements extends beyond the textile industry, contributing to the broader framework of circular economies and waste reduction. By adopting bio-based antimicrobial solutions, the textile sector promotes a healthier balance between product performance and environmental stewardship. This transition is timely, as consumers increasingly demand sustainable products, and the market for eco-friendly antimicrobial agents is expanding to meet this need.

As we progress towards a future where sustainability is paramount, the ongoing research and application of these natural agents mark a critical moment in the evolution of textile innovation—a moment that not only ensures public health but also supports a sustainable coexistence between industry and the environment. This journey towards environmentally friendly textile solutions marks a promising path towards a more accountable and sustainable future, exemplifying a commitment to both enhancing consumer products and preserving our natural world.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

Open Research

DATA AVAILABILITY STATEMENT

Data can be available under request.