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Abstract

The contact layer of traditional medical dressing is easy to adhere to the new wound granulation tissue, which brings the deficiency of secondary wound injury. This work assumed that low-cost and soft mesh spunlace nonwoven was used as medical dressing contact layer. After micro-nano SiO₂ modification, polydimethylsiloxane (PDMS)/n-heptane were uniformly sprayed on the surface of materials. PDMS modification was studied by using the three-factor three-level orthogonal experiment. The results showed that when the PDMS concentration was 1%, the heat treatment temperature and time were 120°C and 12 h respectively, material possessed the optimal hydrophobicity and its water contact angle (CA) was 151.0 ± 1.1°. Meanwhile, the hydrophobicity, microstructure, thermogravimetry, composition, tensile mechanics, adhesion resistance and durability of materials with/without treatment were compared. It was proved that PDMS was indeed grafted onto the material and could effectively improve the hydrophobicity in coordination with micro-nano SiO₂ without affecting the mesh structure of material. The machine direction (MD) and cross-machine direction (CD) strength of material decreased but the elongation increased slightly. The MD and CD peeling energy was 129.7 ± 33.9 J/m² and 98.1 ± 38.3 J/m², respectively. Moreover, the water CA of material modified by micro-nano SiO₂/PDMS was still 139.4 ± 1.4° after 10 friction stroke tests, indicating that the modified material possessed the great durability. Overall, this study can provide the research basis for the development of anti-adhesion medical dressing contact layer.

Keywords

Mesh spunlace nonwoven polydimethylsiloxane hydrophobicity water contact angle peeling energy

Introduction

Traditional cotton gauze had the characteristics of great absorption of wound tissue exudate, skin-friendly and low price.¹ However, the material possessed a large pore structure, which was easy to reverse infiltration after absorbing tissue exudate and adhere to new tissue after removal. Although soaking petroleum jelly could prevent the dressing from being adhered to the wound, there were problems such as low permeability, non-absorption of tissue seepage and being vulnerable to trauma when taken out.^2,3 Although researchers had used grafting hydrogel and other methods for dressings to reduce adhesion and achieve a certain anti-adhesion effect, the cost would rise significantly and there were hidden dangers of losing functions for long-term storage.^4–7 The tendency of the medical dressing contact layer to adhere to the wound has attracted considerable attention.

The hydroentangled fiber aggregation (spunlace nonwoven) was formed by the high-speed waterjet needle impinging on the fiber web, and possessed great softness, comfort, skin affinity, water absorption and low cost.^8,9 In particular, the cellulose fiber spunlace nonwoven was very suitable for medical dressing substrate. However, when it was in direct contact with the wound, it still tended to adhere to new tissue.

As of now, studies showed that the rough surface morphology had anti-adhesion properties against non-specific proteins for cell growth and itself, and low surface free energy substrates could inhibit cell adhesion and diffusion.^10,11 The rough surface of nano-silica (SiO₂) could be precisely constructed on the cellulose fiber by means of soaking and baking to form hydrophobic fabrics.¹² The hydrolyzed nano SiO₂ was adsorbed on the surface of cellulose fiber by hydrogen bonding, but the washing fastness of SiO₂ nanoparticles on the surface of material was relatively low.¹³ Zorko¹⁴ and Vasiljević¹⁵ used sol-gel and in situ growth method to immobilize micro-nano SiO₂ particles on the surface of material. The nano SiO₂ particles spontaneously polymerized to form the polysiloxane layer, slightly improving the fastness of particle fixation. However, the bonding fastness of multi-level micro-nano SiO₂ structure on the material surface was unstable, and the superhydrophobic effect could not be achieved, which limited the anti-adhesion ability of material.¹⁶

Polydimethylsiloxane (PDMS) was a type of safe and low surface energy silicone material, which had no irritation to human skin and mucous membrane.¹⁷ Material surface coated PDMS could reduce the surface energy, which inhibited cell adhesion and diffusion.¹⁸ Many scholars had found that PDMS could be evenly dispersed n-heptane or tetrahydrofuran solvents, and then grafted with nano SiO₂ hydrolyzed polysiloxane silanol groups to generate stable slicon-oxygen bonds.^19–21 Meanwhile, PDMS could be crosslinked with cellulose material by means of heating condition, and the finished material had great chemical stability and mechanical toughness.^22,23 In the functional finishing of materials, spraying was a simple and low-cost operation method, which was suitable for spraying the surface of various materials and making the material possess special function.²⁴ Nevertheless, there has been no valuable research on the preparation of great hydrophobic dressing contact layer by using micro-nano SiO₂ particles and low-surface substances to synergistically modify the spunlace nonwovens.

In this paper, 22-mesh viscose mesh spunlace nonwoven was used as the substrate of medical dressing contact layer, and SiO₂ sol-gel and in situ growth method were used to modify the material to construct multi-level micro-nano SiO₂ structure. Meanwhile, PDMS/n-heptane solution was evenly sprayed on the material surface. Orthogonal optimization experiments were carried out to obtain the optimal process condition. In addition, the hydrophobicity, microstructure, thermogravimetry, composition, tensile mechanical properties, adhesion resistance and durability of materials with/without modification were investigated. This can help to understand how to construct firm and stable structure on spunlace nonwoven to achieve hydrophobicity, and provide reference for the development of anti-adhesion spunlace nonwoven-based medical dressings.

Materials and methods

Materials

The 22-mesh viscose mesh spunlace nonwoven was kindly supplied by Hangzhou Hanford Technology Co., LTD. Tetraethyl orthosilicate (TEOS), anhydrous ethanol and ammonia were purchased from Sinopharm Chemical Reagent Co., LTD (Shanghai, China). Isopropyl alcohol, dimethyl silicone oil PMX-200 (viscosity 30000 mPa·s, 25°C), n-heptane were bought from Shanghai Aladdin Biochemical Technology Co., LTD (Shanghai, China).

Micro-nano SiO₂/PDMS modification

Anhydrous ethanol as the solvent was put in a beaker, and 0.4 mol/L TEOS, 0.3 mol/L ammonia, and 4 mol/L water were added. The solution A was fabricated by stirring at 1000 r/min for 2 min and then at 360 r/min for 60 min in a 40°C water bath. On the other hand, the solution B was prepared by adding 0.4 mol/L TEOS and 0.5 mol/L ammonia water with isopropyl alcohol as solvent (Figure 1(a)). The condensation reaction process of TEOS was shown in Figure 1(b). When the solution A was used, it needed to be oscillated in ultrasound for 5 min to make the nano SiO₂ particles evenly dispersed. The sample was cut to a size of 4 × 4 cm² and then was impregnated with the solution A for 10 s. Next, the excess solution was removed by a small rolling mill, and the residual ratio was controlled between 160% and 180%. After soaking and rolling, it was placed in the oven at 100°C for 15 min. Finally, it was taken out and placed at room temperature for 24 h.¹⁵ The previously treated samples were put into solution B and heated in a water bath at 50°C for 20 min and then taken out. The surface moisture of samples was dried with tissue paper and then samples were put into the oven at 100°C for 15 min. After being taken out, samples were placed at room temperature for 24 h.^14,25 Finally, the samples modified by micro-nano SiO₂ were obtained and recorded.

Figure 1.

Material handling process: (a) Preparation of solutions, (b) Condensation reaction process of TEOS, (c) Material modification, (d) Spraying device and (e) Friction testing equipment.

When PDMS was used to modify the material, it needed to be evenly dispersed into n-heptane solution through magnetic stirrers. Meanwhile, the spraying distance, time and pressure were 15 cm, 20 s and 25 psi, respectively. The micro-nano SiO₂/PDMS modified sample process was shown in Figure 1(c). During the modified process of PDMS, these factors (PDMS concentration, heat treatment temperature and time) had great effect on the experimental results. To obtain the best hydrophobic modification effect, the three-factor three-level orthogonal test project had been designed to determine the optimal parameters. Factor level table and orthogonal experimental scheme table were shown in Table 1 and Table 2, respectively. Then the solution was sprayed onto the sample surface through the spraying device, as shown in Figure 1(d). Next, samples were placed in a fume hood for 12 h to volatilize n-heptane solvent, and the modified samples were weighed and recorded the next day. Finally, samples were put into the oven to obtain stable micro-nano SiO₂/PDMS modified samples.

Table 1.

Factor level scheme.

Factor level	(A) PDMS concentration (wt%)	(B) Heat treatment temperature (°C)	(C) Heat treatment time (h)
1	0.5	90	4
2	1.0	120	8
3	1.5	150	12

Table 2.

Orthogonal experiment scheme.

Experiment	(A) PDMS concentration (wt%)	(B) Heat treatment temperature (°C)	(C) Heat treatment time (h)
1	1	1	1
2	1	2	2
3	1	3	3
4	2	1	2
5	2	2	3
6	2	3	1
7	3	1	3
8	3	2	1
9	3	3	2

Water CA measurements

The water CA measurements were performed according to ASTM D7334-08 (2013).²⁶ The water CAs of samples were acquired by the automatic CA measuring instrument (dataphysics OCA50Micro, Germany). During the test, the liquid output and velocity were 4 uL per time and 5 uL∙s⁻¹, respectively. The test area should avoid the mesh and selected the place where the fiber assemblies were evenly distributed as far as possible. When the water droplets were stable, the water CAs of samples at three different positions were measured. Each position was tested twice, and the average value of the three valid test results was obtained.

Scanning electron microscopy (SEM) studies

The SEM images were obtained by using the cold field emission electron microscope (Hitachi SU8010, Japan). Samples needed to be coated with a thin gold layer to minimize the surface charge. Meanwhile, the sample morphology was observed under an acceleration voltage of 10.0 kV.

Thermogravimetry (TG) analysis

The sample TG weight was measured by the thermogravimetric analyzer (Seikosha TG6300, Japan) and the mass of tested sample was about 5 mg. All analyses were performed in a dynamic nitrogen atmosphere (100 mL∙min⁻¹), between 30°C and 700°C. The scanning rate was set at 10°C∙min⁻¹.

Fourier Transform Infrared (FTIR) spectroscopy

The composition analysis was carried out using the FTIR spectrometer (Shimadzu IRPrestige-21, Japan). The data collection was performed with a resolution of 4 cm⁻¹, and its range is 4000-550 cm⁻¹ with a total of 32 scans. According to the peak of FTIR spectra and the difference of bond vibration of samples, the composition was analyzed.

Covalent connection verification experiment

Samples were sprayed with PDMS according to the optimized process parameters. Three samples were divided into one group, and three groups of samples were fabricated. After spraying, all samples were placed in fume hood for 12 h. Notably, the second group was baked at 120°C for 12 h, and put into n-heptane solution after cooling. In addition, the third group was directly put into n-heptane solution. The n-heptane solution with sample was treated with a magnetic mixer at 300 r/min for 30 min and then placed in a fume hood for 12 h. Finally, three groups of samples were tested and analyzed by FTIR spectroscopy.

Tensile measurement

The tensile properties were measured by Instron 3365 universal material tester. The tensile interval, the pre-added tension and the tensile speed were set as 2 cm, 5 CN and 100 mm/min, respectively. Prior to testing, the sample should be balanced in laboratory conditions (the temperature was 20°C and the relative humidity was 65%) for 24 h.

Adhesion resistance test in vitro

Based on the Andrews and Kamyab in vitro gelatin model, the adhesive situation of wound seepage on the material was simulated and the anti-adhesive property was characterized by the peeling energy of gelatin-material.^27–29 Firstly, the sample of 3 × 15 cm² was immersed in deionized water for 5 min and tiled on the clean surface. A PTFE mold was placed on the surface (Figure 2(a)). Secondly, the gelatin was dissolved in deionized water at 70°C with a mass score of 40% and then poured into the mold window. The gelatin/sample module was placed in an environment of 25 ± 1°C and 65 ± 2% humidity for 24 h. Next, the material testing machine (Instron 3365, USA) was used to complete the stripping of gelatin from samples. When the gelatin was stripped from the sample, the gelatin and sample were at 180° and the stretching speed was 100 mm/min (Figure 2(b)). Eventually, Origin 2018 software was used to calculate the integration of the area surrounded by the curve and the X-axis (displacement). Each group of experiments was measured 3 times.

Figure 2.

(a) PTFE mold for adhesion resistance test and (b) Stripping test diagram.

Abrasion resistance measurement

The abrasion resistance measurements were implemented in reference to ISO 105-X16:2016.³⁰ The standard stick-lined cotton fabric was fixed at one end of the friction color fastness tester (Fang Yuan Instrument Y571 B, China). The sample was coated on the friction head and pressed with a pressure of 56 kpa in contact with the standard stick-lined cotton fabric, as shown in Figure 1(e). Then the sample was moved for 10 cm forth and 10 cm back as one friction stroke. After 10 friction strokes, the water CA of sample was measured, and the changes of sample hydrophobicity were compared and analyzed.

Statistical analysis

Three measurements were performed per sample, and the results were averaged. Data were expressed as the mean with standard deviation (SD). A 5% significance level was used for all analyses. The error bars in the figures were the standard deviation of data.

Results and discussion

Effect of PDMS spraying on materials

Table 3

Table 3.

Orthogonal experiment results.

Experiment	(A) PDMS concentration (wt%)	(B) Heat treatment temperature (°C)	(C) Heat treatment time (h)	Water CA (°)
1	1 (0.5)	1 (90)	1 (4)	146.5±2.7
2	1 (0.5)	2 (120)	2 (8)	146.1±1.3
3	1 (0.5)	3 (150)	3 (12)	146.8±1.1
4	2 (1.0)	1 (90)	2 (8)	148.4±3.9
5	2(1.0)	2(120)	3(12)	151.0±1.1
6	2 (1.0)	3 (150)	1 (4)	150.7±2.0
7	3 (1.5)	1 (90)	3 (12)	146.2±1.2
8	3 (1.5)	2 (120)	1 (4)	146.5±1.4
9	3 (1.5)	3 (150)	2 (8)	148.6±2.3
K1	146.5	147.0	147.9
K2	150.0	147.9	147.7
K3	147.1	148.7	148.0
R	R_A = 3.5	R_B = 1.7	R_C = 0.3

The bold values are the best experimental group analyzed in the subsection “Effect of PDMS spraying on materials”.

is an analysis table of orthogonal experimental results. The results show that K1, K2 and K3 are the average water CAs of the corresponding factor level, representing the effect of the corresponding factor level on the material hydrophobicity. The range R is the difference between maximum and minimum values of K1, K2 and K3, and indicates the effect of each factor on the material hydrophobicity. Meanwhile, the sequence of range is R_A>R_B>R_C, that is, the PDMS concentration has the greatest effect on the material hydrophobicity, followed by the heat treatment temperature and time. In theory, when the factor A is level 2, the factor B is level 3 and the factor C is level 3 (A2B3C3), the treated material has the best hydrophobicity. Although the heating treatment temperature of 150°C has the greatest effect on the hydrophobicity of material, the sample treated at this temperature is prone to yellow. Therefore, the heat treatment temperature is suitable for 120°C. Meanwhile, the optimal PDMS treatment process is that the PDMS concentration is 1%, the heat treatment temperature and time is 120°C and 12 h respectively, and the modified material has the water CA of 151.0 ± 1.1°.

Surface morphology

Figure 3 shows the appearance of four types of mesh viscose spunlace samples (S1, S2, S3, S4), and they correspond to original sample, samples modified by micro-nano SiO₂, PDMS or micro-nano SiO₂/PDMS under the optimized process conditions. Notably, the viscose fibers in the material are entangled together and the whole material has the apparent mesh structure. The longitudinal surface of viscose fiber has obvious grooves (Figure 3 S1). Meanwhile, these modification methods have almost no effect on the macroscopic pore size of samples.

Figure 3.

Apparent morphologies of four types of samples (S1-S4).

After the in situ growth of nano SiO₂, the fiber surface is filled with multi-scale micro-nano particles, which results in obviously rough fiber surface (Figure 3 S2). This may be due to the fact that nano SiO₂ particles are combined in the fiber surface for in situ growth. In particular, the unoccupied hydroxyl group on the fiber surface and the adsorbed water molecules are both acted as reactants to promote the formation, nucleation and growth of new nano SiO₂ particles. However, due to the different degree of polymerization, multi-level micro-nano rough structures are finally formed on the fiber surface.

After PDMS modification, the entanglement and cohesion among fibers are still obvious, and no bond is caused by being sprayed. It is noticeable that PDMS has been arranged on the surface of viscose fiber. The fiber surface is generally smooth, and the fiber grooves are filled with PDMS. Although the local area has been filled, the groove outline of viscose fiber is still visible (Figure 3 S3). The main reason is that PDMS can be effectively crosslinked with cellulose material.¹⁹ Meanwhile, the specific surface area of the groove on the surface of viscose fiber is large, which leads to strong physical adsorption of PDMS.

Figure 3 S4 displays the morphologies of samples modified by micro-nano SiO₂/PDMS. Notably, there is no adhesion or blockage of interfibrous pores due to modification, and the entangled fibers in the sample have still obvious entanglement and rough surface structures. Although the surface grooves of viscose fiber still exist, they are not obvious and are only visible at high magnification. Because there are a lot of gaps among the micro-nano SiO₂ particles on the surface of viscose fiber. When the material is sprayed with PDMS, PDMS can easily fill these gaps, especially the surface grooves of viscose fiber. In addition, PDMS can be easily crosslinked with viscose fiber and micro-nano SiO₂ particles after being heated.

Material TG analysis

Figure 4(a)

Figure 4.

(a) TG curves of samples and (b) Sample weight of each process.

presents the TG curve of four types of samples. In general, the trend of residual mass ratio change of all samples is consistent. With the increase of temperature, the sample mass residual ratios gradually decrease. From 100°C to 260°C, the sample TG curve tends to be stable, and the residual mass ratio has little change, which further indicates that the optimal process temperature of 120°C has no damage to the material. When the temperature was about 260°C, the sample residual mass ratio begins to decline rapidly until 350°C, which is mainly due to the carbonization decomposition of cellulose materials. The quality begins to slowly decrease after 350°C, and it is attributed to the further decomposition of cellulose and the beginning of PDMS pyrolysis.³¹ At the end, the residual mass ratio of S1, S2, S3 and S4 is 11.23%, 12.01%, 11.79% and 12.56%, respectively. The final order of sample residual mass ratios is S4>S2>S3>S1. Figure 4(b) exhibits the mass distribution of the four types of samples after various processes. It should be pointed out that the mass distribution of samples is S4>S2>S3>S1, which is consistent with the residual mass distribution of samples after decomposition. Meanwhile, the sample mass increases by 8.39 mg after micro-nano SiO₂ modification, but increases by 2.11 mg after PDMS modification. The difference in weight of four types of samples is significant (p < .5). Moreover, a huge amount of micro-nano SiO₂ particles on the surface of sample is not decomposed at high temperature, and the quality of nano SiO₂ modified on S2 is much higher than that of PDMS modified on S3. Therefore, the residual mass ratio of S4 is the largest, followed by S2 and S3 (S2 is larger than S3), and S1 is the least.

Material chemical structure

Figure 5

Figure 5.

FTIR spectra of four types of samples (S1-S4).

indicates the infrared spectra of four types of samples. According to the previous band assignments on the cellulose structure,³² the characteristic peaks at 1020 cm⁻¹, 2880 cm⁻¹ and 2980 cm⁻¹, which correspond to the vibration of C-O, -CH₂ and -OH bonds of cellulose fibers, respectively. Except for S1, the FTIR spectra of S2, S3 and S4 have characteristic peak at 800 cm⁻¹, which corresponds to the vibration of Si-O bonds.¹⁴ It is worthwhile mentioning that the vibration of Si-O bonds of S4 is the largest, and S2 is close to S3. This is mainly due to the fact that S2 and S4 undergo in situ growth of nano SiO₂, and a lot of micro-nano SiO₂ particles are bound to the fiber surface. In addition, the PDMS in the S3 and S4 also exist Si-O bond. After modification, Si-O bonds are introduced. Thus, the vibration order of Si-O bonds at the peak of 800 cm⁻¹ is S4>S2>S3>S1. On the other hand, at the band of 1260 cm⁻¹ in the FTIR spectra, the characteristic peaks of Si-C bond appear in the S3 and S4, while S1 and S2 both were not obvious. Because PDMS with a large amount of Si-C bonds is combined on the surface of fibers of S3 and S4.

Covalent grafting of cellulose with PDMS

Figure 6(a) exhibits the FTIR spectra of samples treated by PDMS spraying. It is noticeable that the infrared transmittance of sample without being heat-treated and washed is low. After being washed, the overall bands of sample rise in the range of 500-1800 cm⁻¹, and the infrared transmittance increases. Previous studies³³ show that the two peaks at 800 cm⁻¹and 1260 cm⁻¹ correspond to the vibration of Si-O and Si-C bonds, respectively. They present lower vibration compared with being washed sample according to the local magnified bands in Figure 6(b). It obviously indicates that part of the spray solution has been washed away. When the samples are washed, the bond vibration of samples without being heat-treated decreases more obviously than that of the treated samples. This indicates that the bonding strength of sprayed PDMS with cellulose is weak without heat treatment. No covalent bonding is formed between PDMS and cellulose, but a simple physical adhesion. After being heat-treated, PDMS not only relies on its own viscosity, but chemically reacts with cellulose to form covalent connection, which further enhances the bonding fastness. The covalent grafting mechanism of cellulose and PDMS can be seen in Figure 6(c).

Figure 6.

(a) FTIR spectra of PDMS spray modified samples, (b) Local magnified FTIR spectra and (c) Schematic diagram of covalent grafting of cellulose and PDMS.

Material tensile analysis

Figure 7(a) and (b)

Figure 7.

Sample tensile properties: (a) Breaking strength and (b) Elongation.

respectively show the breaking strength and elongation of four types of samples. Compared with S1, the MD breaking strength and elongation of S2 have slightly increased, but the CD is not obvious. Because the surface of S2 has the micro/nano SiO₂ rough structure, which improves the friction between fibers during stretching. However, the MD orientation of fibers in spunlace nonwovens is higher than that of CD. Therefore, it has a great effect on the MD tension of materials, while the CD tension has a smaller effect.³⁴ In addition, the MD and CD breaking strength of S3 and S4 decreases slightly, while the elongation at break increases slightly. Because S3 and S4 have certain damage to the viscose spunlace samples after a long time of heat treatment, resulting in the reduction of breaking strength. Meanwhile, the surfaces of S3 and S4 are sprayed by PDMS, and an elastic film is formed on the surface, which improves the elongation at break of materials. On the other hand, S4 has larger breaking strength and smaller elongation at break compared with S3, S4. Because the micro-nano SiO₂ particles on the surface of S4 can improve the friction between fibers, but its existence also hinders the drafting of PDMS molecular chain.³⁵

Adhesion resistance analysis

Figure 8(a)

Figure 8.

(a) Sample Photos after being peeled and (b) Peeling energy of samples.

shows the sample photos after being stripped with gelatin. Compared to S1, gelatin ingress in S2, S3 was reduced, while gelatin ingress in S4 was almost non-existent. Figure 8(b) illustrates the MD and CD peeling energy of four types of samples and gelatin. According to previous research experience, when the peeling energy is less than 300-400 J/m², material meets the anti-adhesion requirements.²⁷ It is obvious that although the peeling energy of S2 and S3 can be slightly reduced compared with original S1, they do not meet the anti-adhesion requirements. Compared with S1, the peeling energy of S4 exhibits a significant downward trend. The MD and CD peeling energy are 129.7 ± 33.9 J/m² and 98.1 ± 38.3 J/m² respectively, which meet the requirements of anti-adhesion of dressing. It is due to the fact that gelatin is made up of polypeptide chains that form hydrogen bonds with cellulose and silicon dioxide. The presence of silicon dioxide on the surface of S2 reduces the hydrogen bonding points between gelatin and viscose. PDMS on S3 reduces the surface energy of material to a certain extent, and decreases the hydrogen bonding points between the base material and gelatin. However, the two methods still could not prevent the gelatin from growing into the material mesh and fiber clearance, thus the peeling energy of S2 and S3 are both slightly reduced, and the gelatin still grew into the samples after being stripped. Meanwhile, the collaboration of nano-silica and PDMS minimizes the surface energy of S4, resulting in the failure of gelatin to grow into the material. Therefore, the peeling energy of S4 and gelatin is the lowest. This conclusion is consistent with the morphology of samples and gelatin after being stripped (Figure 8(a)). In addition, Figure 8(b) also shows that the MD peeling energy of sample has a larger error than the transverse one. This may be due to the fact that the viscose fibers in spunlace nonwovens are mainly MD arrangement, and the uncertainty of gelatin growing into the groove of viscose fibers makes the MD peeling ability of materials more uncertain than that of CD.³⁴

Material durability analysis

Figure 9 describes the wettability diagram of four types of samples with/without friction. S1_F, S2_F, S3_F and S4_F correspond to S1, S2, S3 and S4 samples after friction respectively. It is obvious that S1, S1_F, S2 and S2_F have excellent wettability. On the contrary, S3, S3_F, S4 and S4_F possess low wettability. In addition, the wettability of samples has little change by friction. Meanwhile, the water CAs of S1 and S1_F are 29.8 ± 2.1° and 28.7 ± 2.6° respectively. It is mainly due to the great water absorption and excellent wettability of viscose fiber. Meanwhile, the water CA of S2 and S2_F are 25.9 ± 2.0° and 23.8 ± 2.1°, respectively, which are both slightly smaller than those of S1 and S1_F. The difference in water CAs of samples is significant (p < .5). According to the solid rough surface water CA equation (1).³⁶

\cos θ_{r} = r \frac{γ_{S V} - γ_{S L}}{γ_{L V}} = r \cos θ

(1)where θ_r is the water CA of rough surface, θ is the real water CA, cos θ is the material wettability, and γ is the surface tension. Meanwhile, S, L and V are the solid, liquid and gas respectively, and r is the ratio of the actual rough surface area to the apparent surface area (r ≥ 1). Viscose fiber has excellent wettability, thus its θ is far less than 90°. According to equation (1), it can be concluded that θ_r is less than θ, and an increase in surface rough of material will increase the wettability of material. Therefore, the micro-nano SiO₂ modification makes the viscose spunlace nonwoven easily infiltrated and slightly reduces the water CA of material.

Figure 9.

Sample wettability and water CAs with/without friction.

On the other hand, the water CA of S3 is 136.4 ± 2.9°, and the water CA of S3_F is 130.8 ± 3.2°. Obviously, the sample water CA decreases slightly after friction treatment. According to previous studies, the natural property of solid surface γ_SL is less than the natural energy of liquid surface γ_LV.³⁷ Therefore, the modified term kW_SL of adhesive work is introduced to obtain the relation equation (2) between the natural energy of solid surface and that of liquid surface.

γ_{S L} = γ_{L V} - k W_{S L}

(2)where W is the adhesion work and k is the constant. According to the Dupré adhesion work equation (3), it is substituted into equation (2) and equation (4) is obtained.³⁸

W_{S L} = γ_{L V} + γ_{S V} - γ_{S L}

(3)

W_{S L} (1 - k) = γ_{S V}

(4)

Equation (5) can be obtained by combining the young-Dupre equation (3). In combination with the W_SL of equation (4), equation (6) can be received.

W_{S L} = γ_{L V} (1 + \cos θ)

(5)

γ_{L V} (1 + \cos θ) (1 - k) = γ_{S V}

(6)

Therefore, the cos θ can be expressed by equation (7):

\cos θ = γ_{S V} {(1 - k)}^{- 1} {(γ_{L V})}^{- 1} - 1

(7)

According to equation (7), when γ_SV tends to 0, cos θ tends to −1. That is, an increase in the surface free energy of material will increase the water CA and the hydrophobicity of material. Therefore, the surface free energy decreases after PDMS modification and the hydrophobicity significantly improves. The water CA decreases correspondingly when the PDMS modified by friction is slightly damaged. Thus, the water CA of S3_F is smaller than that of S3.

After micro-nano SiO₂/PDMS modification, the water CA of S4 is 151.0 ± 1.1°. Obviously, it indicates that micro-nano SiO₂ and PDMS synergistically improve the material hydrophobicity, making the material have super-hydrophobicity. At the same time, the water CA of sample is still up to 139.4 ± 1.4° after friction treatment. Although the water CA of material decreases about 11.6°, it still has great hydrophobicity compared with S3. The main reason is that PDMS has great flexibility, and can be firmly cross-linked and grafted with viscose and SiO₂, and micro-nano SiO₂/PDMS synergistically improves the material durability.²⁰

Conclusions

In summary, the hydrophobic modification method of the contact layer of anti-adhesion dressing had been proposed. The mesh viscose spunlace nonwoven was used as the dressing contact layer, and the material was modified by sol-gel and in situ growth of nano SiO₂. At the same time, PDMS was sprayed to modify material, and the optimal treatment conditions (PDMS concentration was 1%, heat treatment temperature was 120°C and treatment time was 12 h) were obtained by orthogonal experiment. Material possessed the optimal hydrophobicity and its water CA was 151.0 ± 1.1°. In addition, PDMS was demonstrated to be covalently grafted onto viscose fiber of material. The MD and CD strength of material decreased but the elongation increased slightly. The MD peeling energy was 129.7 ± 33.9 J/m², and the CD peeling energy was 98.1 ± 38.3 J/m², which fully met the requirements of anti-adhesion of dressings. After 10 cycles of friction movement, the water CA of material was still up to 139.4 ± 1.4°. Moreover, micro-nano SiO₂/PDMS modification could be used to effectively construct hydrophobic and durable properties of material without affecting the mesh structure of spunlace nonwoven. This paper could provide reference for the development of anti-adhesion spunlace nonwoven-based dressing contact layer.

Footnotes

Acknowledgments

The author(s) wish to express their sincere gratitude to Zhejiang Hezhong Technology Nonwoven Co., Ltd and Hangzhou Hanford Technology Co., Ltd for their support in providing the means for conducting experiments.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study is supported by the National Natural Science Foundation of China Youth Found [grant number 51903156], the Zhejiang Provincial science and technology Department research and development project [grant number 2022C01SA691301], the Student Scientific Research Project of Shaoxing University [grant number Y20220702], the National Innovation and Entrepreneurship Training Program of College Students [grant number 202210349056S and 202310349040] and the Science and Technology Guiding Project of China National Textile Industry Council [grant number 2022027].

ORCID iD

Yinjiang Zhang

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Hydrophobic modification of mesh spunlace nonwoven for medical dressing contact layer

Abstract

Keywords

Introduction

Materials and methods

Materials

Micro-nano SiO2/PDMS modification

Water CA measurements

Scanning electron microscopy (SEM) studies

Thermogravimetry (TG) analysis

Fourier Transform Infrared (FTIR) spectroscopy

Covalent connection verification experiment

Tensile measurement

Adhesion resistance test in vitro

Abrasion resistance measurement

Statistical analysis

Results and discussion

Effect of PDMS spraying on materials

Surface morphology

Material TG analysis

Material chemical structure

Covalent grafting of cellulose with PDMS

Material tensile analysis

Adhesion resistance analysis

Material durability analysis

Conclusions

Footnotes

Acknowledgments

Declaration of conflicting interests

Funding

ORCID iD

References

Micro-nano SiO₂/PDMS modification