Biogenic silver nano sol–loaded spunlace fabric for wound dressing;mechanical and functional characterization

Abstract

The biogenic silver nano sol (AgNS) is most suitable for biomedical applications due to its inherent properties. In the present investigation polyester (P), viscose (V) and polyester/viscose blend (50:50) (PV) spunlaced fabrics were coated with AgNS prepared using organic honey, manuka honey. The dip-coated fabric samples were found suitable for wound dressing purposes when evaluated layered wise for their mechanical properties. The layer-wise dispersion behavior of the V sample was found better than the P/V and P samples. In the case of the air permeability sample, P/V performed better compared to V and P samples. Water sorption ability of P/V and V are found suitable for wound dressing. The ultraviolet protection factor value of treated fabric found excellent when coated with only honey. Further, the AgNS loaded fabric exhibited good resistance against microbial organisms as revealed by the bromophenol blue stain.

Introduction

The wound dressing is one of the critical products of medical textiles. The wound management system includes wound dressings, bandages, pressure garments, and tissue engineering, etc. The main function of wound dressings is to heal the wound depending upon the severity of the wound, preventing infections, and providing appropriate conditions for faster wound healing. ¹ A wound is defined as a break in the epithelial integrity of the tissues. ² Wounds can be classified according to their thickness, the involvement of skin or other tissues, the time elapsed from the point of trauma (breaking of skin continuity), A wound is caused by physical trauma where the skin is torn, cut, or punctured (an open wound), or where a blunt force trauma causes a contusion (a closed wound), ³ the wound morphology (Figure 1), and the method of wound closure.^4,5

Figure 1.

Human skin structure.

The skin has three layers (Human Anatomy By Matthew Hoffman, WebMD):

The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone.

The dermis, beneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands.

The deeper subcutaneous tissue (hypodermis) is made of fat and connective tissue.

The epidermis prevents loss of water and body fluids, resists mechanical and chemical injury, and protects against bacteria, viruses, and parasite infections. The wound dressing used for healing should have certain properties like antimicrobial, antiodor, antifungal, anti-inflammatory, and antibiotic. Hence, fabric use for wounds needs to treat with some finish.^6-8 The Honey is well known for the millennia as a tropical treatment as medicine for a wide range of wounds, has recently been known for its revival in modern wound care management. ⁹ Topical honey has been recognized around the world for its skin healing properties and numeral technical researchers show the activity of honey as antimicrobial, antiodor, antifungal, anti-inflammatory, antibiotic, and also shows good debridement action in their various studies.^10,11 Recently, several pieces of literature available on the use of silver nanoparticles as potential nano-filler for the production of hygienic textiles.^12–15 Murugesan et al., 2020, reported that the different heteroatoms incorporated into multi-walled carbon nanotubes antibiofilm associated wound healing ability. ¹⁶

In our earlier work, Ag nano colloidal sol was prepared using honey and characterized in terms of its antibacterial properties. ¹⁷ In the present work, an attempt has been made to apply in-house synthesized nanosilver colloidal sol to spunlace nonwoven fabric by dip-dry-cure techniques. Effect of nanosilver colloidal sol on various properties of wound dressing spunlace nonwoven multilayered fabric, like UV transmittance and antimicrobial were also examined by standard methods.

Materials and experimental methods

Materials

Fabric

In this study, three spunlace nonwoven fabrics namely, 100% polyester (P), 100% viscose (V), and polyester/viscose blend (50:50) (PV) having GSM value 58, 55, and 53, respectively, were procured from GINNI Filaments Pvt. Ltd

Chemicals

Silver nitrate (AgNO₃) of analytical grade purity was procured from the LOBA Chemicals, Organic honey (Forest honey), and Manuka honey (MH) were purchased from the local market and used without further purification.

Methodology

Preparation of AgNS coated spunlace nonwoven fabrics

The AgNS were prepared as per the method reported in the literature by Hireni Mankodi et al., 2017. ¹⁷ Before the treatment, fabrics were cleaned with five gpl soap (Lissapol L) at 70⁰C for 30 min, rinsed with distilled water twice at room temperature (35°C) for 10 min, and equilibrated in a conditioned room (20°C, 60% RH). The fabrics were treated with AgNS colloid by a dip and dry method using 65% wet pick up. The silver nitrate concentrations in the liquor were kept at 0.5% v/v. A sol was prepared by mixing the silver nitrate and organic honey also mixing silver nitrate and MH one by one at 10 min intervals in separate vessels, maintaining a 250 r/min stirring rate for 20 min at room temperature. The specimens were immersed in a fresh colloidal bath for 10 min. The samples were dried at room temperature (35°C) for the prevention of thermo-migration of particles for 30 min. Finally, the prepared samples were analyzed for their mechanical and other functional properties.

Characterization of AgNS loaded fabrics

Before the test, the samples were kept in a standard atmosphere having a relative humidity of 65 ± 2% RH and 27 ± 2°C temperature. Five tests were conducted for each sample. An average of five readings was reported.

Determination of mechanical properties

Evaluation of base (untreated) nonwoven spunlace fabric included testing of its Physical Properties (GSM, Thickness), Mechanical Properties (Tensile), Comfort Associated Properties (Air permeability), Dispersion behavior of fabric (Water sorption ability) were measured for selecting the favorable fabric for using as a base fabric for preparing wound dressing patch. All the testing was done in standard laboratory set-up in the department itself and the fabric was conditioned at standard atmospheric conditions, i.e. 27 ± 2°C temperature and 65 ± 2% RH for 24 h before conducting test.

Tensile strength (ASTM D-4354)

The fabric samples of 2 cm × 8 cm were tested on Lloyd tensile tester LRX model at 100 mm/min traversing speed for the determination of breaking load, breaking elongation, stress, and strain.

Air permeability (ASTM D- 6476)

Air permeability of the fabric is the volume of the air measured in cubic centimeters which passes through one square centimeter of fabric in one second at the pressure of 10 mm of water level, which is expressed cm³/cm²/s. It was measured using METEFEM Air Permeability Tester. The digital air permeability tester accurately and swiftly determines the resistance of the fabric to the passage of air (air flow) under constant pre-set pressure while firmly clamped in the test rig. The measurements were performed at constant pressure drop of 50 Pa. (20 cm² test area). The specimen was loaded to the test area of the instrument easily by means of clamping lever. On pressing down the clamping lever, a powerful, muffled vacuum pump draws air through an interchangeable test head (rotameter) with a circular opening. The pre-selected air pressure was allowed to maintain, and after few seconds the air permeability of sample was digitally displayed in the measuring unit. The sample was released by lifting the clamping lever and shutting off vacuum pump.

Water sorption ability of fabrics (ASTM D737-04)

The dispersion behavior of the samples is conducted using the water permeability test method. The test method of measurement of water sorption ability is explained below.

The water sorption ability of spunlace nonwoven fabric specimens as follows:

Dry weight of the specimen is measured

The specimen is placed in water or solution for a specific period of time.

The wet weight of the sample is determined by first blotting the sample with filter paper to remove adsorbed water on the surface and then weighing it immediately on the electronic balance. The percentage water sorption of sample in the media is then calculated using the formula,

$${\mathrm{E}}_{\mathrm{sw}}=\left[\frac{\left(We-Wo\right) }{Wo}\right]\mathrm{\ast }100$$

Where:

E_sw is the percentage of water sorption of samples at equilibrium; $We$ denotes the weight of the specimen at equilibrium water sorption; and $Wo$ is the initial weight of specimen

Specimen of 5 cm × 5 cm was cut of each fabric and were put in the circular dish, and the specific duration was keeping the specimen was 2 min, after 2 min the excess liquid was removed using blotting paper keeping for 1 min. During the entire experiment, the specimen was weighed before putting in circular dish containing liquid and after blotting the specimen for 1 min. Reading of weighed samples was taken and the water sorption ability of three spunlace nonwoven fabric listed above were calculated using the above formula.

Evaluation of functional property

Ultraviolet protection factor (UPF)

Ultraviolet Transmittance Analyzer UV-2000F (SDL ATLAS, USA) was used to measure ultraviolet transmittance of treated and untreated fabrics. The UV-2000F satisfies all the requirements of the following standards viz., AS/NZ 4399:19961, EN 13758-1:2001, AATCC TM 183-2000, and GB/T18830. The UPF of a textile material is determined from the total spectral transmittance and the higher the value of UPF better is the UV protection.

Antimicrobial activity of fabric by BPB-stain test

Antimicrobial efficiency of textiles was measured by the bromophenol blue (BPB) method.

Testing of white or light-colored goods: BPB solution of 0.025% was prepared in distilled water; few drops of saturated Na₂CO₃ solution per 100 cc BPB solutions were added. 10 cc of the solution was taken in a beaker and the test specimen was soaked in the solution for 20 min. Finally, the sample was rinsed in distilled water. The sample was observed for the blue stain and compare against the Bramophenol Blue color test scale.

Results and discussion

The AgNS were prepared using a green technique at room temperature as reported by Hireni Mankodi et al., 2017. ¹⁷ The prepared AgNS were characterized in terms of size, shape, and elemental analysis using particle size analyzer, SEM micrographs, and AATCC 147 test method, respectively. In this work, the AgNS colloids were applied to spunlace nonwoven fabrics for the development of wound dressing textile material.

Effect of AgNS on mechanical properties

Changes in mechanical properties of AgNS coated fabric were evaluated in terms of strength, comfort associated properties, and dispersion behavior of fabric.

Evaluation of layer-wise strength of the fabric

Mechanical properties of textile material are basically a phenomenon describing the change in the shape of the material, which is a result of the material resistance on the application of external forces. The behavior of fabric used for wound dressing depends on the type of material, finish applied, and low-stress properties of the fabric. The strength of spunlace fabric used especially for wound dressing purposes is never inclined toward a higher strength value. It is always preferred that such material should possess sufficient strength to serve the purpose of design that means it should have enough strength to sustain stresses imposed at the point of usage and should not cause any undue rupture. The average tensile strength of human skin is 1.8 N/mm².

The tensile strength of the spunlace fabrics has been tested in a lengthwise direction and the results are given in Table 1. The fabric has been tested taking a maximum of three layers to simulate the number of layers taken for wound dressing. As mention earlier, the wound dressing strength should be higher than the value of human skin otherwise the stress near the area of the wound the dressing is likely to be ruptured. Hence, the number of layers of fabric has been tested (Up to three layers).

Table 1.

Tensile strength of spun lace fabrics.

Layer-wise strength	Polyester (PES)	Viscose (V)	Polyester/Viscose (PV)
I layer (N/mm2)	102.53	75.40	41.74
II layer (N/mm2)	101.71	83.72	43.70
III layer (N/mm2)	96.10	64.99	45.67

It has been observed that polyester showing the highest strength compared to polyester: viscose blend and viscose. The polyester: viscose having a lesser strength as compared to viscose but substantial for wound dressing. Material wise viscose and PV are more friendly to human skin, hence PV and V have been taken for wound dressing. As the number of the layer increases the little drop in strength value due to the slippage between layers may take place but that is not affecting the overall performance of wound dressing as these layers are going to be sandwiched between the top layer and the bottom layer of a wound dressing.

Effect on comfort associated properties

The comfort of the patients is the most important when the patient has been kept under observation should not feel uncomfortable due to medical devices. In wound dressing, one of the main aspects is to keep dressing breathable, comfortable, and protected against pathogenic microorganisms. The material used should have good permeability and moisture management to get good performance of the product. Air permeability of different spunlace fabrics has been given in Figure 2

Figure 2.

Air permeability of different spunlace fabrics.

Air permeability can be described as the volume of air passing through a specimen of a given area in a given time. It has been observed that as the number of the layer increases the permeability of fabric increases but out of three samples, PV (50:50) fabric shows more permeability as compared to (Polyester) and viscose. Hence, despite having a low strength value P/V (50:50) blend has been selected for further studies. As air permeability of the fabric has a prime consideration for wound dressing. Further, the combination of fabric has been taken like PES/V/PES and PV/V/PV, these combinations are not giving any significant change compared to individual material with three layers.

Dispersion behavior of fabric

The dispersion behavior of the fluid coming out from the wound depends on the type of wound dressing. The dispersion behavior of spunlace fabric can be determined by using a water sorption test. The sample has been tested using the standard method used by South India Textile Research Association. The sample has been dipped into the honey solution and extra solution has been removed and the difference in weight has been calculated. Table 2 shows the water sorption value layer-wise. The result shows the highest sorption value viscose and PV, respectively. Results in Table 2 and Figure 3 show the water sorption ability of spunlace fabric layer-wise.

Table 2.

Water sorption ability Esw (%).

Fabric	I layer	II layer	III layer
Polyester (PES)	244.83	260.39	286.58
Viscose (V)	482.62	514.45	684.87
PV (50:50)	416.64	524.37	398.93
PES/V/PES	-	-	443.67
PV/V/PV	-	-	322.40

Figure 3.

Water sorption ability of different spunlace fabrics.

Hence, PV and viscose are suitable for wound dressing. As the number of the layer increases the viscose shows the increasing trend due to its inherent nature (Cellulosic fiber), similar to polyester but higher in value. In PV fabric, the trend with increasing layer is variable that may be due to change in % of polyester and viscose material present in the sample. Further, the combination has been tried PES/V/PES and PV/V/PV, the value of these combinations found nearer to PES and V fabric.

Hence, taking the combination of viscose or PV with a top layer of PES can be used as a wound dressing where PES act as a less absorbing cover hence the liquid will disperse well in the wound dressing but will not bleed on the top surface.

Functional characterization of AgNS coated spunlace fabric

Effect on UV protection factor

The silver colloidal solution which has been characterized through the above analysis and the sample S = 04 equals to H = 04 concentration has been selected for dipping method with a concentration of 0.5 g of Ag in 100 mL doubled distilled water. The dipping method was selected for coating onto spunlace nonwoven fabrics by dipping 20 cm × 20 cm into a beaker containing the standardized solution with 0.5 Ag content in the stock solution. Nonwoven PV (Polyester: Viscose) blend fabrics were dipped for 30 min and was dried in ambient conditions.

Five samples were prepared for testing two comfort properties related to wound dressing and its UV protection activity has been carried out of as shown in Table 3. The application of a colloidal solution of the optimized standardized solution has been done by the dipping method. The UPF factor has been analyzed to get an idea about how the coated material gives protection against UV exposure.

Table 3.

UV Protection Factor (UPF) of samples.

Fabric samples	Critical wavelength (nm)	UV protection factor rating (UPF)
Untreated	384	11 (Poor)
Organic honey-coated (OH)	383	>50 (Excellent)
Silver and organic honey-coated (Ag-OH)	387	13 (Average)
Manuka honey-coated (MH)	381–382	>50 (Excellent)
Silver and manuka honey-coated (Ag-MH)	387	16 (Good)

The spunlace wound dressing with a natural finish like honey should exhibit good mechanical flexibility and excellent comfort of nonwoven material to the wound site. The most significant factor is to complete the covering on the wound site and to protect against the infection and Ultraviolet light with wavelengths between 200 - 280 nm light also facilitates wound healing. The wound site should be breathable but should have protection against UVA and UVB rays. Table 3 and Table 4 show the UPF values of untreated and treated samples. The Labsphere UV-2000F transmittance analysis was used to find the UPF value of five different samples.

Table 4.

UV/UPF transmittance properties of treated and untreated samples.

Fabric samples	Coated fabric samples	UV/UPF transmittance analysis
Untreated
Organic honey-coated (OH)
Silver and organic honey-coated (Ag-OH)
Manuka honey-coated (MH)
Silver and manuka honey-coated (Ag-MH)

The five different scan locations of fabric were taken and UPF factor rating was measured at critical wavelength. The results show that a similar wavelength in a range of 381–387 nm has the transmittance sample. It has been observed the untreated sample gives a poor UPF value (UPF of untreated fabric = 11). All treated samples give a higher UPF value compare to untreated fabric samples. The mean percentage of both the fabric samples treated with organic honey and MH gives excellent results with UPF value >50. The combination of honey with Ag has reduced the UPF value and gives the average value. This may be due to Ag affects the porosity and absorbs the UV rays which reduce the UPF value of colloidal sol treated fabric samples. It may be due to combine effect of chemical nature of silver and the nano size of plasmonic metal that enhance the UPF perfomance of the fabric.

It has been observed that the untreated sample and MH coated samples and with silver nano colloidal solution gives less coefficient of variation. This may be due to proper absorption and uniformity in terms of coating. Hence, MH gives the best protection against UV and is found more suitable for wound dressing.

Antimicrobial efficiency of samples

The AgNS efficiency of treatment on fabrics is given in Table 5. The results shows that the samples treated with only natural honey exhibited good antimicrobial properties compared to untreated samples as per the BPB stain test. It has been observed that the samples coated with organic honey and MH exhibited good antimicrobial properties as per the BPB scale. The efficiency of the treatment can be further enhanced by the coating with AgNS as an antimicrobial agent in both cases.

Table 5.

Rating of microorganisms growth on treated and untreated fabrics.

Sample	Optical density	Absorbency%	Rating in terms of resistance
Untreated	0.036	-	-(No Protection)
Organic honey-coated (OH)	0.013	67.66	-+ (Fair)
Silver and organic honey-coated (Ag-OH)	0.036	5.40	+++ (Excellent)
Manuka honey-coated (MH)	0.024	37.84	++ (Very Good)
Silver and manuka honey-coated (Ag-MH)	0.035	8.12	+++ (Excellent)

It may be due to the known fact that the AgNS act as a natural antimicrobial agent. The silver metallic ions and metallic compounds display a certain degree of sterilizing effect. It is considered that part of the oxygen in the air or water is turned into active oxygen through catalysis with the metallic ion, thereby dissolving the organic substance to create a sterilizing effect. ¹⁸ Nanosilver particles have an extremely large relative surface area, thus increasing their contact with bacteria and vastly improving their bactericidal effectiveness. Nanosilver is very reactive with proteins. When contacting bacteria, it adversely affects cellular metabolism and inhibits cell growth. It also suppresses respiration, the basal metabolism of the electron transfer system, and the transport of the substrate into the microbial cell membrane. ¹⁹

Development of wound dressing

Based on the above study, the wound dressing has been prepared taking three different layers as shown in Figure 4.

Skin contact layer

Absorbent layer

Active carbon cover

Top cover

Figure 4.

Assembly of spunlace wound dressing.

Skin contact layer

The skin contact layer has been made out of 100% polyester sterilized spunlace fabric. This layer is non-adherent to wound tissue and helps for transmission of wound exudates. This layer will simply transfer the liquid from one layer to another layer and keep the wound dressing surface dry.

Absorbing layer

The absorbing layer can be made from three layer PV, viscose, and PV blend viscose spunlace fabric. This is the main area where the bacteria which are coming will be killed, provide the cushioning effect to the wound, and give proper moisture management to enhance the healing of the wound. PV fabric has been taken as an absorbing layer to improve the wound dressing function by reducing the infection and enhancing the antimicrobial activity of the wound dressing. For secondary wounds, PV and V sandwich blends (PV + V + PV) can be used for better long-term dressing. It also keeps the moist wound and reduces irritation by avoiding the drying of the wound.

Activated carbon layer

Secondary wound tends to generate more amount of exudate and also give an unpleasant odor. To avoid this, the activated carbon is sprinkled over spunlace fabric which has a good capacity of absorbing odor. The strips of spunlace wipes can also be tried to avoid the odor. In this wound dressing, the activated carbon layer is included between the absorbing layer and top cover. Further, the analysis of this layer is needed.

Top cover

The top layer of wound dressing acts as a protecting and holding cover to the dressing. It keeps the wound away from injuries. In the present study, 100% polyester spunlace fabric has been taken as a top cover. This assembly can be used along with adhesive tape to apply the dressing to the wound.

Conclusions

The silver nano sol was prepared and applied on polyester, viscose, and polyester/viscose blend (50:50) spunlace fabrics through a simple and commercially low cost-effective green chemistry route by using easily available natural honey as a reducing agent. A three-layered spunlace wound dressing is developed using a natural finish like honey.

The viscose and PV fabric are both suitable as a wound dressing but PV will transfer the moisture from one to another layer and keep the wound site dry. Even the PV fabric is more breathable than viscose hence the expected odor generation is also less.

The combination of viscose or PV with a top layer of PES can be used as a wound dressing where PES act as a less absorbing cover hence the liquid will disperse well in the wound dressing but will not bleed on the top surface. The combination of honey solution with Ag reduced the UPF value and gives the average value. This may be due to Ag affects the porosity and absorbs the UV rays which reduce the UPF value of colloidal sol treated fabric samples.

The untreated sample and MH-coated samples and with silver nano colloidal solution gives less coefficient of variation. This may be due to proper absorption and uniformity in terms of coating. MH gives the best protection against UV and is found more suitable for wound dressing.

The treatment also improves the antimicrobial effect of fabric measured by the BPB stain test compared to untreated fabric. It suggests that the AgNS treated aprons may be used routinely to minimize transpersonal contamination in the environment.