Influence of structures on the mechanical and absorption properties of a textile pile debridement material and its biological evaluation

Abstract

Debridement describes the removal of necrotic tissue, cell debris and bacteria from a wound site. It aids the wound healing process and is considered as the cornerstone in proper wound management. The present work introduces a feasible approach to fabricate textile pile debridement materials with controllable structures. Six pile materials with variable pile densities and numbers of ground yarns were prepared based on the sliver knitting technology followed by back-coating, heat setting and shearing. Their surface morphology and chemistry were inspected by using SEM and FTIR. The mass per unit area and stitch density were measured to describe the basic geometric structures of the pile materials. The mechanical, liquid absorption and biological properties for the textile pile materials were assessed and compared with a commercial cotton gauze which is commonly used in clinical practice. The influence of structures on the mechanical, liquid absorption properties of the textile pile materials was also analyzed. Results show that pile density is the primary structure factor that affects the properties of the textile pile materials. Furthermore, all the six pile materials prepared in this study exhibited superior performance in both mechanical behaviors and liquid absorption capacity compared to the commercial gauze control. In addition, the results of biological evaluation indicate a satisfactory biocompatibility of the pile debridement material. Therefore the textile pile material offers a potential for wound debridement application.

---

1. Introduction

Devitalized tissue in chronic wounds presents as a mixture of senescent cells, slough, debris, exudate as well as exogenous components.¹ The necrosis around the wound not only acts as a physical barrier to assess the extent and size of the wound, but also facilitates bacterial growth and increases the risk of infection.² The necrotic layer as well as the bacterial burden are the key factors that prevent or impair cellular migration, granulation and re-epithelization which are necessary for the normal cascade of the wound healing process.^3,4 In order to start the process of regular wound healing, the first step must be to undertake effective debridement which is an established procedure in wound management and is considered as an essential part of proper wound care.^5,6 Debridement is defined as the removal of foreign materials, necrotic and contaminated tissue from the wound and its surrounding area until underlying healthy tissue is exposed.⁷ It recruits neutrophils and macrophages so that the normal stages of healing can be progressed through more effectively.^8,9

Among various debridement strategies, the application of gauze as a debridement material has a long history ever since the World War I.¹⁰ It can be used as either a swab material or wet-to-dry dressing. The most commonly used gauzes are woven or nonwoven fabrics made of cotton, rayon or polyester. Though the “moist wound healing” theory introduced by Dr Winter has been widely accepted, wet-to-dry and gauze dressings continue to be used for mechanical debridement in some countries.^11–13 The gauze is usually moistened with saline before applied to the wound. As the impregnated gauze dries out, it sticks to the dead tissue on surface of the wound bed, which will be removed together with the dried gauze.¹² However, wet-to-dry technique is a means of nonselective debridement and there is a high risk that the healthy tissue will be removed unintentionally.^10,12,14 This may cause reinjury resulting in pain for the patient and impede the wound healing.¹⁵ Studies found that the repeated change of dressing causes a local cooling which lead to vasoconstriction, hypoxia and impairment of leukocyte mobility and phagocytic efficiency.^15,16 In addition, the whole cost of wet-to-dry debridement including the cost of labor and other indirect costs caused by infection control and longer care period is far more expensive than the cost of gauze itself.¹⁷ Take all these into account, wet-to-dry dressing is not an optimal wound debridement modality.

Recently, a monofilament fiber pad has been introduced as a new method for mechanical debridement.¹⁸ The mode of action of this pad is totally different from wet-to-dry dressing.¹⁹ After moistened with water or saline, the monofilament fiber pad is wiped gently across the wound to remove the necrotic tissue together with the exudate in the wound bed.²⁰ Clinical evidences revealed that the pad allows for effective and non-traumatic debridement with well tolerance on the wounds featured with hyperkeratosis, haematomas and soft slough.²¹

However, the requirements on debridement varies from patients to patients depending on the age, gender and health situation of the patients as well as wound characteristics.^22,23 The idiosyncratic nature of each wound, such as the wound type, duration, position, size and depth, along with wound bed condition, correlate with the healing process and are important aspects to consider in wound debridement.^24,25 For example, soft slough on the yellow wound are relatively easy to be removed compared with the black wound covered by a layer of thick hard eschar which requires intensive mechanical action.²⁶ In addition, the level of wound exudate can be classified as light, moderate and copious.²⁷ Accordingly, the required liquid absorption capacity of the debridement material differs from each other.^28,29 Thus, customized debridement materials with specific properties are needed to meet the requirements from different patients. On the other hand, structures of the debridement material have an internal decisive implication on its properties. In order to expand the applied range of the debridement material and meet the requirements from different patients, it is necessary to investigate the relationship between structures and properties of the debridement material, such as mechanical properties and liquid absorption capacity.

The aim of this study was first to introduce a feasible approach to fabricate a textile pile material with controllable structures. Afterwards, the basic geometric structures, mechanical properties and liquid absorption of this pile debridement material and a commercial gauze control were studied. The influence of structures on these properties of the textile pile material was also explored and summarized. In addition, biological evaluations of the pile debridement material were assessed in comparison with the commercial cotton gauze to investigate their penitential clinical application.

2. Materials and methods

2.1. Materials

Polyester staple fiber and polyester multifilament draw textured yarn (DTY) (Jiangsu Chemical Fiber Co., Ltd, China) were chosen as the pile fiber and ground yarn to fabricate the pile fabric. A back-coating of polyacrylate latex with a viscosity of 5.97 mPa s and 40% solids content was applied to the reverse side of the knitted fabric to lock the pile fibers in place and stabilize the dimensions of the fabric. In addition, a gauze from Winner Industries Co., Ltd was included as a control. It is an 8 ply cotton gauze woven in a plain weave and supplied in 10 × 10 cm². The basic information about the raw materials is presented in Table 1.

Table 1 Basic information about the raw materials

	Specification	Tensile strength (cN dtex^−1)	Elongation (%)	Modulus (cN dtex^−1)
a D = denier (mass in g of 9000 m length), F = number of filaments.
Polyester staple fiber	3 D^a × 32 mm	3.11 ± 0.23	48.05 ± 9.34	21.67 ± 2.75
Polyester DTY	150 D^a/36F^a	3.20 ± 0.13	28.29 ± 0.70	364.69 ± 31.94

---

2.2. Preparation of the textile pile materials

The preparation process of the textile pile materials includes fiber carding, sliver knitting and finishing.³⁰ As shown in Fig. 1, the loose polyester staple fibers were firstly sent through a carding machine that combed the fibers, aligning them parallel to each another. The straight fibers were then reassembled into a continuous uniform sliver.

Fig. 1 Preparation process of the textile pile materials.

Then, the slivers were fed into a circular knitting machine (SK18, Mayer Industries Inc., Germany) together with the polyester yarns. The needles on the machine picked up fibers from each sliver and locked them into the knitted backing formed by ground yarns. The free ends of pile fibers extended from only one side of the fabric to provide a deep pile face.

After knitting, the prototype pile fabrics went through a series of technical finishing processes including back-coating, heat setting and shearing. The back side of textile pile fabric were coated with a biocompatible polyacrylate latex and cured in an oven. Afterwards, the fabric pile face was subjected to a shearing machine and the pile fibers were cut to the desired height of 10 mm.

Six prototype samples of textile pile materials with different structures were designed and fabricated. The number of yarns to each needle, and the target values for pile density, stitch density and total mass per unit area are listed in Table 2.

Table 2 Structural design parameters of six prototype samples

Sample No.	Number of yarns in each stitch	Target pile mass per unit area (g m^−2)	Target stitch density^a (course × wale) (cm^−2)	Target total mass per unit area (g m^−2)
a “Target stitch density” refers to the target stitch density of the final textile pile materials.
H3	3	High (530)	9.0 × 6.0	675
M3	3	Middle (400)	9.0 × 6.0	545
L3	3	Low (380)	9.0 × 6.0	525
H2	2	High (530)	9.0 × 6.0	640
M2	2	Middle (400)	9.0 × 6.0	510
L2	2	Low (380)	9.0 × 6.0	490

---

2.3. Surface characterizations

Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were employed to investigate the surface characteristics of the textile pile materials. The surface morphology of the samples was inspected using a TM-3000 SEM (Hitachi, Japan). The surface chemistry of the back side of the samples before and after coating was compared on a Nicolet 6700 FTIR (Thermo Fisher Scientific, USA).

2.4. Basic geometric structure

2.4.1. Mass per unit area. Five samples measuring 10 cm × 10 cm were conditioned in the standard atmosphere for 24 h before testing.³¹ The fabric weight was measured on an analytical balance and average value of the mass per unit area was calculated according to eqn (1).³²where M₀ is the mass per unit area in g m⁻², M is the weight of the specimen (g) measuring an area of A, which is 0.01 m² in this study.

2.4.2. Stitch density. Stitch density, i.e. the total number of rows of stitches in a unit length of a fabric (course count) multiplied by the number of needle loops in a unit width of the fabric (wale count) were measured with a Model Y511B fabric density meter at zero pressure in both directions with the fabric.³³ They were calculated using eqn (2) and (3).where P_A and P_B are course count (cm⁻¹) and wale count (cm⁻¹) respectively, N_A and N_B are the number of loops in the length L_A and the width L_B directions.

2.5. Mechanical properties

2.5.1. Tensile properties. The tensile properties were tested using the parallel strip method with a YG(B)-026H textiles universal strength tester.³⁴ Fabric specimens with a length of 50 mm and width of 20 mm were clamped between two jaws separated by a gauge length of 30 mm and stretched at a rate of 100 mm min⁻¹.

2.5.2. Compression properties. The compression properties were evaluated using a compression tester (LLY-06D, Laizhou Electron instrument Co., Ltd, China).³⁵ The experimental conditions involved using a presser foot with a 10 mm diameter, a compression distance of 50% of the sample's initial thickness and a displacement rate of 10 mm min⁻¹.

2.5.3. Stiffness properties. The bending length was measured on a LLY-01 electronic cantilever fabric stiffness tester (Laizhou Electron instrument Co., Ltd, China) and the flexural rigidity was calculated as follows:³⁶

G = m × c³ × 10⁻³ (4)

where G is the flexural rigidity in mN cm, m is the mass per unit area in g m⁻², and c is the bending length in cm.

2.6. Liquid absorption capacity

The liquid absorption capacity (LAC) was evaluated employing the method described in ISO 9073-6 with slight modification.³⁷ Dry specimens (10 mm × 10 mm) were weighed on an analytical balance with a precision of 0.1 mg (BS124S, Sartorius AG). After kept in distilled water for 10 s, they were removed and hung vertically to drain for 10 s, then weighed again. LAC was calculated using following equation:where LAC is expressed as %, m₀ and m are the mass of dry and wet samples respectively in g.

2.7. Biological evaluations

2.7.1. In vitro cytotoxicity test. The prototype pile sample H2 and cotton gauze were tested for in vitro cytotoxicity by Cell Counting Kit-8 (CCK-8) colorimetric assay.³⁸ Fluid extracts of the test samples were prepared from 0.2 g of these two materials separately in 2 ml DMEM at 37 °C for 24 hours. Porcine iliac artery endothelial cells (PIECs) (Keygen Biotechnology Company) were cultured in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum and 1% penicillin–streptomycin at 37 °C in a 5% CO₂ incubator. After 3 passages PIECs were seeded into 96-well plates at a density of 5 × 10³ per well and cultured for 4 hours. The culture medium was replaced by the liquid extract and cultured for 1, 3, 5 and 7 days. Then 10 μl CCK-8 solution was added to each well and incubated for 4 hours before measuring the optical density (OD) at 450 nm with a microplate reader (Multiskan FC, Thermo).

2.7.2. Irritation test.
(a) Irritation test on intact skin. The skin irritation test was performed according to ISO10993-10: 2010 in two New Zealand white rabbits weighing 3.0–3.5 kg obtained from Shanghai Jiagan Biological Technology Co., Ltd. The certificate of conformity is SCXK (Shanghai) 2010-0028. The investigation was in accordance with and approved by the Institutional Animal Ethics Committee of Donghua University. The backs of the animals were clipped free of hair and divided into two groups: H2 pile fabric group and gauze group. Test samples (2.5 cm × 2.5 cm) were moistened with saline to ensure an effective contact with the skin. For single exposure test, samples were kept on the skin for 24 h, while for repeated exposure test, the materials were applied for 4 h per day for consecutive three days. Assessments were made 24 h, 48 h, and 72 h after the removal of test materials in terms of the severity of erythema and/or edema. The primary irritation index (PII) and accumulative irritation index (CII) were calculated as the arithmetical mean values from the two animals.³⁹
(b) Irritation test on breached skin. Four test sites were abraded using a sterile blade to breach the epidermal layer of the stratum corneum. The H2 pile sample and gauze were applied in the same way as described above for the irritation test on intact skin.

2.7.3. Skin sensitization test. Six guinea pigs weighing 300–350 g were purchased from Shanghai Jiagan Biological Technology Co., Ltd (License no. SCXK-2010-0028) and divided into two groups: three in the H2 pile fabric group and the other three in the gauze group. The investigation was in accordance with and approved by the Institutional Animal Ethics Committee of Donghua University. The fur on the back of the guinea pigs were clipped prior to the standard skin sensitization test procedure.³⁹ Samples of H2 textile pile material and gauze were soaked in saline and applied on the right side of the exposed skin. In induction phase, these materials were kept on skin for 6 h a day and three consecutive days a week for three weeks. After two weeks' rest, the same materials were applied on the left side of the dorsal skin for 6 h to complete the challenge. All sites were observed for erythema and/or edema and graded for sensitization at 24 h and 48 h following the challenge exposure.

2.8. Statistical analysis

The results were analyzed statistically using Origin 8.5 software (Origin Lab Inc, USA). Statistical differences were determined by a one-way analysis of variance (ANOVA) and the means were considered significantly different at p ≤ 0.05 (*), p ≤ 0.01 (**) and p ≤ 0.001 (***).

3. Results and discussion

3.1. Preparation of the textile pile materials

A series of six pile fabrics with different structural parameters were designed and manufactured from polyester staple fiber and polyester draw textured yarn using sliver knitting technology followed by back-coating, heat setting and shearing.

The SEM photos and structural diagrams of the textile pile material are presented in Fig. 2. From the pile side view (Fig. 2a), it is clear to see that a number of single fibers are compacted with each other in an almost vertical status. While the back side of the textile pile material shown an evident jersey stitch construction (Fig. 2b). The structural diagrams (Fig. 2c and d) illustrate how the pile fibers (purple) and the ground yarns (yellow) were constructed in the sliver pile fabric. The ground yarns interloped with each other in a single jersey stitch and formed continuous loops in weft direction. While pile fibers were physically locked at the middle of their length by the knitted loops.⁴⁰ In fact, loops of the fabric are much more compact (Fig. 2b) than are indicated in the schematic diagrams. Therefore, there are not only vertical pressure on the pile fibers caused by the upper ground yarns, but also squeeze and friction in different directions between pile and pile, pile and yarns. All these interactions contribute to a comprehensive bond force preventing the losing of pile fibers.

Fig. 2 SEM photos and structural diagrams of the textile pile material: (a) and (c) pile side view; (b) and (d) back side view.

The procedure of back-coating changed the back side morphology of the pile fabric, resulted in the adhesive filling of the gaps between adjacent fibers (Fig. 3b). The results from FTIR (Fig. 3c) confirm the chemical changes on the back side of the sample. The absorbance at the frequency of 2957 cm⁻¹ and 2874 cm⁻¹ are characteristic stretching peaks of the C–H bonds (CH₃, CH₂); the stretching around 1732 cm⁻¹ can be assigned to the carbonyl group C=O; the absorbance at 1452 cm⁻¹ corresponds to the distortion vibration of –COO–; while the stretching bands at 1166 cm⁻¹, 962 cm⁻¹ and 843 cm⁻¹ are the absorption peaks of C–O–C, C–C and C=O in the acrylic group respectively.⁴¹ The back-coating procedure provides not only an improved dimensional stability, but also a chemical bond between the pile fibers and ground yarns, which offers a secondary guarantee to prevent fiber loosing from the material during application.

Fig. 3 SEM and FTIR (c) results of the textile pile materials before (a) and after (b) back-coating.

3.2. Basic geometric structure

Mass per unit area and stitch density are the most important two parameters of a knitted fabric. Usually they are set before and calculated later to determine the quality of the knitted fabric.⁴²

3.2.1. Mass per unit area. By adjusting the speed of feed rollers, the amount of sliver folded around each needle can be controlled, thus the number of fibers incorporated in each stitch can be changed. Moreover the number of yarns knitted into each stitch can also be monitored at manufacturing. So samples with different pile weights and ground yarn numbers were obtained. The actual and target mass per unit area of six samples are given in Fig. 4, from which we can see that the experimental values for mass per unit area of each sample are close to the target values set before preparation.

Fig. 4 Mass per unit area of different samples.

3.2.2. Stitch density. The target stitch density for all the six samples are set as 9.0 × 6.0 cm⁻² (Table 2). While the measured course and wale counts are presented in Table 3 as well as the average values calculated among six samples. For both weft and warp directions, no statistical differences at the 0.05 confidence level were observed between the six samples. So the calculated stitch density for all the six samples was consider as the average value 9.13 × 6.17 cm⁻², which is consistent with the designed value. It is also interested to notice that the average wale count after back-coating decreased 16.96% compared with that of samples before back-coating, whereas the average course count rose 2.01% after back-coating, from 8.95 cm⁻¹ to 9.13 cm⁻¹. This is most likely the result of the back-coating procedure, when an external force was applied in the weft direction, leading to crosswise stretching and a decrease in the number of wales per cm. Meanwhile, due to the anisotropy of textiles, the extending in weft direction brought about the constriction in warp direction, in other words, the course count increased slightly.

Table 3 Stitch density before and after back-coating

Samples	Course count (cm^−1)		Wale count (cm^−1)
	Before back-coating	After back-coating	Before back-coating	After back-coating
H3	9.1 ± 0.2	9.4 ± 0.6	7.4 ± 0.2	6.2 ± 0.3
M3	8.8 ± 0.3	9.1 ± 0.2	7.4 ± 0.4	6.1 ± 0.2
L3	9.0 ± 0.4	9.1 ± 0.2	7.7 ± 0.5	6.4 ± 0.2
H2	8.9 ± 0.2	8.9 ± 0.2	7.1 ± 0.2	6.2 ± 0.3
M2	8.7 ± 0.3	9.0 ± 0.4	7.3 ± 0.3	6.0 ± 0.4
L2	9.2 ± 0.5	9.3 ± 0.5	7.6 ± 0.2	6.1 ± 0.2
Average value	8.95 ± 0.19	9.13 ± 0.19	7.43 ± 0.21	6.17 ± 0.14

---

The measured results of mass per unit area and stitch density are in good agreement with the target values set before manufacture. Therefore sliver knitting is a feasible technology for fabricating textile pile materials with a range of designed mass per unit area and controllable stitch densities.

3.3. Mechanical properties

Tensile, compression and stiffness tests were carried out to investigate the mechanical properties of the special pile debridement materials. The influence of fabric structures on these properties of the pile materials were also explored.

3.3.1. Tensile properties. The pile debridement materials should be able to sustain a certain force and deformation during application. To acquire an insight into these important factors, tensile test was performed in both weft and warp directions. The maximum tensile force and elongation of samples were extracted from the tensile curves and corresponding data are summarized in Table 4. In weft direction, the maximum tensile force and elongation of six pile materials were obviously higher than that of the gauze, which suggests a better tensile performance for pile materials than gauze. Thus all the pile materials were strong and ductile enough to be used as debridement materials. Comparing the forces among six pile materials, samples with three ground yarns (H3, M3, L3) had a similar maximum tensile force around 160 N, while samples with two ground yarns (H2, M2, L2) showed a relatively lower tensile force (about 120 N). This indicates the tensile behavior is much more relied on the number of ground yarns, while the change in pile density has no obvious effect on the resulting tensile force. Same trends can be found in warp direction.

Table 4 Maximum tensile force and elongation of pile materials and gauze

Samples	Maximum tensile force (N)		Elongation (mm)
	Weft direction	Warp direction	Weft direction	Warp direction
H3	161.09 ± 5.72	267.72 ± 4.04	62.10 ± 3.53	33.47 ± 1.19
M3	159.57 ± 2.70	275.85 ± 9.54	65.14 ± 2.95	39.42 ± 2.51
L3	162.85 ± 1.94	268.69 ± 15.32	47.68 ± 1.49	32.16 ± 2.40
H2	113.82 ± 2.40	200.90 ± 3.70	52.92 ± 1.68	32.47 ± 1.58
M2	120.00 ± 5.50	204.89 ± 11.80	43.86 ± 1.19	29.08 ± 1.97
L2	113.15 ± 3.01	196.38 ± 2.65	47.37 ± 3.16	27.85 ± 0.86
Gauze	27.29 ± 5.72	62.83 ± 1.92	3.24 ± 0.13	2.69 ± 0.11

---

In comparison of the results in weft and warp directions, it is clear that all the samples exhibited a higher tensile force but a lower elongation in warp direction than that in weft direction. This means the pile materials have a relatively better capacity to sustain force in warp direction and a better ductility in weft direction. It is also interesting to notice the difference at the end of these curves. The tensile curves in warp direction had a liner end (Fig. 5a) which implies a dramatically decline in force value, while the end part in weft direction experienced several vibrations before final break of the pile material (Fig. 5b). All these phenomena can be attributed to the heterogeneity of the knitted structure.

Fig. 5 Typical tensile curves of different samples: (a) weft direction; (b) warp direction.

3.3.2. Compression properties. The unique action mode of this mechanical debridement material needs repeated wipe on the wound.^18,19,21 In order to effectively loosen the necrotic tissue, it should include not only relative movement on the wound surface, but also an appropriate compression action perpendicular to the surface. On the other hand, excessive compression may lead to an uncomfortable or even painful response for the patients.⁴³ Thus the compression properties of this pile material is worthy of attention. Compression test was performed on both pile materials and gauze control to compare the applied compressive load required to halve the thickness of these samples.

The results of 50% applied compressive load are shown in Fig. 6. It is evident that all the six pile samples had lower load values (less than 40 cN) than that of gauze (above 120 cN). In other words, to get the same percentage of deformation, the pile materials needed a lower load than gauze. It was also reported that when a finger moves across the surface of a textile, the applied normal force varies depending on the weight, gender, and age of the person. Generally, the value falls in the range 1.5 ± 0.7 N,⁴⁴ which is significantly higher than the experimentally measured applied compression loads for all the six samples. This indicates that the prototype textile pile materials are not likely to elicit an uncomfortable or painful response from the patients during debridement.

Fig. 6 Results of compression test on different samples. (Significant differences were marked by *** for p ≤ 0.001 compared with gauze control.)

From the results of six pile materials, the 50% applied compressive load of samples with high, middle and low pile density (samples H3, H2, samples M3, M2 and samples L3, L2) were about 33 cN, 23 cN and 11 cN respectively. This indicates that pile density was the main structural factor which influenced the compressive properties of these pile materials rather than the number of ground yarns.

3.3.3. Stiffness properties. Wounds come with different shapes, depths and locations.⁴⁵ Venous ulcers are often superficial whereas arterial ulcers are deeper and have a “pinched out” appearance.⁴⁶ In order to provide effective debridement on various kinds of wounds, the pile materials should be flexible enough to be folded into different shapes. Flexural rigidity calculated from bending length was used to assess the flexibility of the pile materials.

Comparing the flexural rigidity in both weft and warp directions (Fig. 7), it is noticeable that gauze sample had an obviously higher value than all six pile samples. This means all the six pile samples displayed a superior performance in flexibility compared to the gauze control. While among the six pile materials, samples H3, H2 had the highest flexural rigidity, samples L3, L2 had the lowest values, and samples M3, M2 had values in between. Similar to the compression test reported earlier, pile density was the main factor that influenced the flexural rigidity of the pile materials rather than the number of ground yarns.

Fig. 7 Flexural rigidity of different samples. (Significant differences were marked by ** for p ≤ 0.01 and *** for p ≤ 0.001 compared with gauze control.)

3.4. Liquid absorption capacity

The accumulation of wound fluid could lead to skin maceration, bacterial proliferation and the risk of other infections.^29,47 Therefore good liquid absorption capacity is required for the pile debridement materials. Results in Fig. 8 show that the lowest liquid absorption capacity among the six pile samples (L3, 881.37%) was higher than that of gauze (720.65%). So the application of pile materials could help to overcome the challenge of collection and leakage of excess exudates on exuding wounds. It is also evident to notice that the liquid absorption capacity for pile materials shown an ascending trend with the increase in pile density. This suggests a relatively higher pile density is preferred in consideration of liquid absorption. While compare samples with different numbers of ground yarns, samples with 2 ground yarns (H2, M2, L2) had higher values compared to samples H3, M3, L3. In other words, the number of the ground yarns contributed more to increase the mass of samples rather than absorb liquid.

Fig. 8 Liquid absorption capacity of different samples. (Significant differences were marked by *** for p ≤ 0.001 compared with gauze control.)

3.5. Biological evaluations

According to ISO 10993-1: 2009, the selection of biological evaluation tests on medical devices should be based on the nature and the duration of body contact.⁴⁸ For textile pile debridement material, it will have a contact with wounds for few minutes during application. Therefore, cytotoxicity, irritation and sensitization tests were performed to evaluate the biocompatibility of the pile materials.

Based on the results of mechanical tests, all the six samples exhibited better performance in tensile, compression and stiffness properties compared with the gauze control. This indicates that the textile pile materials meet the mechanical requirements for use as a debridement material. While in terms of liquid absorption capacity, sample H2 gave the highest liquid absorption value among all the six pile materials. In other words, sample H2 has the optimal structure among the six pile materials prepared in this study. Therefore, H2 pile material was selected as the test material for biological evaluations of the textile pile fabrics and cotton gauze was included as reference.

3.5.1. In vitro cytotoxicity test. Cytotoxicity is the most common method used to evaluate the biocompatibility of medical devices.^49,50 In this study, the cell viability of textile pile material H2 and cotton gauze were assessed by CCK-8 assay. Tissue culture plates (TCPs) were included as the blank control. As shown in Fig. 9, the average OD values for the pile material H2 and cotton gauze shown an uptrend with increasing culture time. Moreover, the OD values for both samples were relatively higher than that of the TCPs at the same time interval. This indicates a good cytocompatibility for both H2 pile material and cotton gauze.

Fig. 9 Cytotoxicity results of textile pile fabric H2 and cotton gauze. (Significant differences were marked by *, ** and *** for p ≤ 0.05, p ≤ 0.01 and p ≤ 0.001 respectively compared with blank control TCPs.)

3.5.2. Irritation test. The findings of the irritation tests provide an important measure of the suitability of the pile debridement materials. Table 5 lists the results of the single and repeated exposure tests on intact and breached skin. For H2 pile fabric, the primary irritation index (PII) and cumulative irritation index (CII) on intact skin for the signal and repeated exposure test were 0.042 and 0.083 respectively. Whereas the results of breached skin test were marginally higher at 0.125 and 0.167 separately. However all these values are less than 0.4, including those for the cotton gauze control. According to ISO10993-10: 2010, the skin irritation of H2 pile fabric and the cotton gauze can be classified as negligible.

Table 5 Irritation test scores

Group	Intact skin		Breached skin
	Single exposure test (PII)	Repeated exposure test (CII)	Single exposure test (PII)	Repeated exposure test (CII)
H2 pile fabric sample	0.042	0.083	0.125	0.167
Gauze control	0.042	0.125	0.167	0.209

---

3.5.3. Skin sensitization test. The results reported in Table 6 indicate that none of the animals in either the test or the control group showed any dermal reactions associated with an immune response throughout the entire test period. No evidence of erythema or edema formation was observed in the shaved and exposed area on the skin of the guinea pigs. Additionally, the rate of sensitization in the H2 pile fabric test group was the same as for the gauze control group, confirming that the H2 pile sample has no adverse effect on skin cells and is considered nonallergenic.

Table 6 Skin sensitization test results

Group	n	24 h				48 h				Sensitization rate (%)	Response category
		0	1	2	3	0	1	2	3
H2 pile fabric sample	3	3				3				0	Negligible
Gauze control	3	3				3				0	Negligible

---

4. Conclusion

In the current study, sliver knitting technology was introduced as a method to prepare the textile pile debridement material. Six textile pile materials with different structures were knitted from polyester staple fiber and polyester draw textured yarn on a circular knitting machine and finished by back-coating, heat setting and shearing. By controlling the knitting parameters, it was possible to generate samples with controllable mass per unit area and stitch density.

Mechanical (tensile, compression and stiffness) and liquid absorption tests were performed to investigate the relationship between structures and these properties of textile pile materials. In general, the influence of pile density was more prominent than that of ground yarn number in terms of compression, stiffness and liquid absorption properties. Conversely, the number of ground yarns was the dominating structure factor that determine tensile properties rather than the pile density. Furthermore, it is remarkable to point out that all the six pile materials prepared in this study exhibited superior performance in both mechanical behaviors and liquid absorption capacity compared to the commercial cotton gauze. In addition, the results of in vitro cell culture tests and in vivo animal studies indicate that the textile pile materials were not responsible for any cytotoxic effects, dermal irritation, or skin sensitization. It looks that these textile prototype pile fabrics have a potential application for wound debridement. Further work will be conducted to analyze other properties such as fiber shedding and protein absorption capacity of the textile pile materials.

Acknowledgements

This work was supported by the Chinese Universities Scientific Fund (CUSF-DH-D-2014008) and the 111 project “Biomedical Textile Materials Science and Technology” (B07024). In addition, the State Scholarship Fund from the China Scholarship Council is gratefully acknowledged.

References

1. G. Kammerlander, A. Andriessen, P. Asmussen, U. Brunner and T. Eberlein, J. Wound Care, 2005, 14, 349–352.
2. M. O'Brien, Br. J. Community Nurs., 2002, 10, 10–18.
3. T. K. Hunt, Ann. Emerg. Med., 1988, 17, 1265–1273.
4. D. L. Steed, Surg. Clin., 2003, 83, 547–555.
5. R. D. Wolcott, J. P. Kennedy and S. E. Dowd, J. Wound Care, 2009, 18, 54–56.
6. A. F. Falabella, Dermatol. Ther., 2006, 19, 317–325.
7. M. Granick, J. Boykin, R. Gamelli, G. Schultz and M. Tenenhaus, Wound Repair Regen., 2006, 14, S1–S10.
8. C. E. Attinger and E. J. Bulan, Foot Ankle Clin., 2001, 6, 627–660.
9. S. Vuorisalo, M. Venermo and M. Lepantalo, J. Cardiovasc. Surg., 2009, 50, 275–291.
10. C. A. Fleck, Journal of the American College of Clinical Wound Specialists, 2009, 1, 109–113.
11. S. K. McCallon, C. A. Knight, J. P. Valiulus, M. W. Cunningham, J. M. McCulloch and L. P. Farinas, Ostomy Wound Management, 2000, 46, 28–34.
12. L. G. Ovington, Home Healthc. Nurse, 2001, 19, 477–484.
13. M. H. Armstrong and P. Price, Wounds, 2004, 16, 56–62.
14. B. A. Dale and D. H. Wright, Home Healthc. Nurse, 2011, 29, 429–440.
15. J. Whitney, L. Phillips, R. Aslam, A. Barbul, F. Gottrup, L. Gould, M. C. Robson, G. Rodeheaver, D. Thomas and N. Stotts, Wound Repair Regen., 2006, 14, 663–679.
16. M. Slater, Br. J. Nurs., 2008, 17, S4–S15.
17. S. Kordestani, M. Shahrezaee, M. N. Tahmasebi, H. Hajimahmodi, D. Haji Ghasemali and M. S. Abyaneh, J. Wound Care, 2008, 17, 323–327.
18. M. Benbow, J. Community Nurs., 2011, 25, 17–18.
19. J. C. Whitaker, J. Lymphoedema, 2012, 7, 46–50.
20. L. Atkin, Br. J. Nurs., 2014, 23, S10–S15.
21. D. Gray, P. Cooper, F. Russell and S. Stringfellow, Wounds UK, 2011, 7, 42–46.
22. M. Y. Sieggreen and J. Maklebust, Adv. Wound Care, 1997, 10, 32–37.
23. D. L. Steed, Am. J. Surg., 2004, 187, 71S–74S.
24. G. S. Schultz, R. G. Sibbald, V. Falanga, E. A. Ayello, C. Dowsett, K. Harding, M. Romanelli, M. C. Stacey, L. Teot and W. Vanscheidt, Wound Repair Regen., 2003, 11, S1–S28.
25. B. M. Madhok, K. Vowden and P. Vowden, Int. Wound J., 2013, 10, 247–251.
26. S. Bahr, N. Mustafi, P. Hattig, A. Piatkowski, G. Mosti, K. Reimann, M. Abel, V. Dini, J. Restelli, Z. Babadagi-Hardt, F. Abbritti, T. Eberlein, T. Wild, K. Bandl and M. Schmitz, J. Wound Care, 2011, 20, 242–248.
27. S. Thomas, J. Wound Care, 1997, 6, 327–330.
28. K. Vowden and P. Vowden, Br. J. Community Nurs., 2003, 8, 4–13.
29. C. Dowsett, J. Wound Care, 2008, 17, 249–252.
30. L. Wang, Y. Fu, F. Wang, W. Wang, B. Shen and X. Hu, Chinese Pat., CN 203724324, 2014.
31. ISO 139, Textiles – Standard atmospheres for conditioning and testing, 2005.
32. FZ/T 72002, Sliver knitting fake fur.
33. D. J. Spencer, Knitting Technology: A Comprehensive Handbook and Practical Guide, CRC Press, 2001, pp. 16–18.
34. ISO 13934–1, Textiles - Tensile properties of fabrics - Part 1: Determination of maximum force and elongation at maximum force using the strip method, 2013.
35. P. Larose, Text. Res. J., 1953, 23, 730–735.
36. ISO 9073–7, Textiles - Test methods for nonwovens - Part 7: Determination of bending length, 1995.
37. ISO 9073–6, Textiles – Test methods for nonwovens – Part 6: Absorption, 2000.
38. L. Chen, J. Hu, J. Ran, X. Shen and H. Tong, RSC Adv., 2015, 5, 56410–56422.
39. ISO 10993–10, Biological evaluation of medical devices - Part 10: Tests for irritation and skin sensitization, 2010.
40. S. C. Ray, Fundamentals and advances in knitting technology, Woodhead Publishing India Pvt. Ltd, 2012, pp. 62–63.
41. O. Yilmaz, Prog. Org. Coat., 2014, 77, 110–117.
42. S. C. Ray, Fundamentals and advances in knitting technology, Woodhead Publishing India Pvt. Ltd., 2012, pp. 37–38.
43. B. Jorgensen, G. J. Friis and F. Gottrup, Wound Repair Regen., 2006, 14, 233–239.
44. S. Derler, U. Schrade and L.-C. Gerhardt, Wear, 2007, 263, 1112–1116.
45. D. G. Armstrong, L. A. Lavery and L. B. Harkless, Diabetes Care, 1998, 21, 855–859.
46. S. Rajendran, Advanced textiles for wound care, Woodhead Publishing Limited, 2009, pp. 100–105.
47. J. S. Boateng, K. H. Matthews, H. N. E. Stevens and G. M. Eccleston, J. Pharm. Sci., 2008, 97, 2892–2923.
48. ISO 10993–1, Biological evaluation of medical devices – Part 1: Evaluation and testing within a risk management process, 2009.
49. ISO 10993–5, Biological evaluation of medical devices - Part 5: Tests for in vitro cytotoxicity, 2009.
50. V. Metzler, H. Bienert, T. Lehmann, K. Mottaghy and K. Spitzer, ASAIO J., 1999, 45, 264–271.

---