1. Introduction
Skin wounds with various characteristics are a global issue and a major threat to the public health and economy [
1,
2,
3]. Those that fail to heal within an anticipated time and do not proceed through a highly organized reparative process, which results in anatomic and functional integrity, are considered chronic [
2,
4]. Pressure, venous and diabetic foot ulcers are the three main categories of chronic wounds [
5,
6,
7]. To solve these problems, the primary step in chronic wound treatment is to achieve effective debridement or wound bed preparation. Wound debridement is the medical removal of devitalized, damaged, infected or contaminated tissue from the wound bed to improve the healing potential for the remaining healthy tissue [
8,
9]. It is the main tool for maintaining a healthy wound bed in most chronic wounds and a recognized component of good wound care as it reduces the bioburden of the wound and improves the life quality of patients [
10,
11]. The TIME concept (Tissue, Inflammation (or Infection), Moisture, Edge) proposed by European Wound Management Association (EWMA) in 2003 has been widely accepted as a practical guide for the debridement of chronic wounds [
12,
13].
Inflammation, a natural physiological reaction in the circumstance of wounds, is a normal stage in the wound healing process. However, intensive or inappropriate inflammation always results in infection, which complicates the wound, impedes wound healing, and increases patient discomfort and/or anxiety [
14,
15]. To control the inflammation or infection, a totally removal of the necrotic tissues is requisite in the procedure of debridement. Meanwhile, new pollutant or foreign body should not be introduced into the wound bed. Among various debridement methods, medical cotton and absorbent gauze are the most commonly seen biomedical textile materials, which can be used as either a swab or patch to clean wounds [
16,
17]. They are preferred due to the low cost and easy operating [
18,
19]. However, fiber shedding phenomenon was reported when a gauze was attached or detached during the wet-to-dry debridement [
20,
21]. The shed fibers remained in the wound bed not only contaminate the microenvironment but also increase the susceptibility of infection [
20]. Thus, fiber shedding property is an indispensable aspect of any materials designed for wound debridement application.
A monofilament fiber pad has been recently introduced as a new solution to offer quick, effective and non-traumatic wound debridement for patients suffering from chronic wound [
22,
23]. It was reported in our previous study that this material exhibited sufficient mechanical properties, superior liquid absorption and satisfactory biocompatibility [
24,
25]. However, since this material is a kind of knitted pile fabric consists of abundant single fibers in the face side which has a direct contact with the wound site. A close look into the fiber shedding property of this debridement material is of great necessity.
Several testing methods are available to evaluate the fiber shedding propensity of textile fabrics. The modified Gelbo Flex method is a normative method used to assess the lint and particles generated from medical textile products in dry state, such as surgical drapes, gowns and protective clothing [
26,
27]. The fabric sample is subjected to a combined twisting and compression action in a test chamber. Number of particles released from the testing fabric is counted and classified using a particle counter within the size range from 0.3 to 25 μm. Another test method for evaluation of the wet linting in nonwoven dressings is introduced in the EN 1644-2 [
28]. The test sample is firstly shook in water at the frequency of 300–350 Hz for 10 min. Then, fibers shed from the dressing are collected using a gridded filter. Number of shed fibers is counted and taken as the result. Other testing methods, such as abrading and tape methods, are also reported to estimate the fiber shedding propensity of the apparel or garment textiles [
29,
30,
31]. Though the detailed operation modes of these testing methods are diverse from each other, they all aim to simulate the type of motions that may cause lint or particles during application. However, results of all these tests are only presented as the amount (number and/or mass) of the loosing fibers. Thus, profound analysis on fiber shedding mechanisms is hardly to be achieved through these methods.
Therefore, the aim of this study was first to propose an in vitro testing method, which can be employed to evaluate the fiber shedding property of the textile pile debridement material. Furthermore, influence of structural design (pile density, number of ground yarns and back-coating time) on the fiber shedding property of the debridement material was explored. In addition, the typical load–displacement curve and failure modes of the single fiber pull-out test were investigated to better understand the fiber shedding mechanisms of this textile pile debridement material.
3. Materials and Methods
3.1. Materials
Polyester staple fiber and multifilament yarn (Jiangsu Chemical Fiber Co., Ltd., Suqian, China) were selected as the raw materials to fabricate the textile pile fabric.
Table 5 lists some general information of these raw materials. A biocompatible polyacrylate latex was also coated onto the backside of the pile material during the procedure of post treatment.
3.2. Design and Fabrication of the Textile Pile Debridement Material
Eight prototype samples of the textile pile materials were designed in this study. The structural parameters for each sample, including pile density, ground yarn plies and back-coating time, are listed in
Table 6, together with the pile height and stitch density. All the samples were knitted with the same single jersey stitch structure, as shown in
Figure 11. From the backside view (
Figure 11a), the pile fibers (blue) were physically anchored by the ground fabric (red), while, seen from the face side (
Figure 11b), typical knitting loops formed by the ground yarns were clearly observed and two ends of the pile tufts vertically extended out of the ground fabric to form the U shape pile face.
All the samples were firstly knitted on a special circular machine (SK18, Mayer Industries Inc., Tailfingen, Germany) under ambient conditions of 20 °C and 60% RH. Then, the pile face went through a cutting machine and the pile fibers were trimmed to the height of 10 mm, as designed in
Table 6. After cutting, the backside of the samples were coated with biocompatible polyacrylate latex and dried in an oven.
3.3. Microstructure
Scanning electron microscopy (SEM) was employed to investigate the surface characteristics of the textile pile materials. The micrographs of the backside of samples before and after back-coating were obtained using a TM-3000 SEM (Hitachi, Tokyo, Japan) with an accelerating voltage of 15 kV.
3.4. Surface Chemistry Analysis
Fourier transform infrared spectrometer (FTIR) analysis was performed on a Nicolet 6700 FTIR (Thermo Fisher Scientific, Waltham, MA, USA) to study the surface chemistry of the backside of samples before and after back-coating in the range from 4000 to 500 cm−1. The spectra were analyzed using proprietary software (Omnic V 7.3, Thermo Fisher Scientific, Waltham, MA, USA, 2006).
3.5. Fabric and Pile Weight per Unit Area
Five specimens measuring 10 cm × 10 cm were conducted under standard condition for 24 h before weighting on an analytical balance [
54]. Then the pile fibers were carefully detached from the ground yarns, collected and weighted. Special attention was paid to avoid fiber losing during this procedure. Both fabric and pile weight per unit area were calculated as Equations (2) and (3) [
55], respectively.
where
Wf and
Wp are the fabric and pile weight per unit area in g/m
2,
W1 and
W2 are the weight of the total fabric and collected pile fibers (g) in a testing area of
A, which is 0.01 m
2 in this study.
3.6. Characterizations of the Ground Fabric
3.6.1. Morphology Observation
Samples with a size of 10 cm × 10 cm were conducted under standard condition for one day [
54]. Then, the pile fibers in the central of the samples were carefully extracted out of the loops formed by ground yarns to give an exposed area of ground fabric measuring 2 cm × 2 cm. Afterwards, the exposed area was taken for morphology observation under a PXS8-T stereoscopic microscope (Olympus, Takachiho, Japan).
3.6.2. Surface Yarn Coverage
The photomicrographs of the ground fabric were analyzed by Image J software (Version 1.49q, National Institutes of Health, Bethesda, MD, USA, 2015) to obtain the surface yarn coverage. The original light microphotograph (
Figure 12a) was firstly transferred into binary image, as shown in
Figure 12b. Then, the percent coverage of the ground yarn was calculated by dividing the pixelated value of the black area by that of the total area.
3.6.3. Distribution of the Stitch Size
Image Pro Plus software was used to measure the stitch size of the ground fabric. As shown in
Figure 13, only the intact stitches that hold pile fibers were marked and measured (red parts). A total of 100 stitches were collected on each sample and the distribution of the stitch size was investigated.
3.7. Single Fiber Pull-Out Test
Single fiber pull-out test is a well-recognized test for fiber composite [
56]. In this study, an XQ-2 single fiber tensile tester (Shanghai Lipu Applied Science and Technology Research Institute, Shanghai, China) was employed to evaluate the single fiber pull-out behavior of the textile pile debridement materials at the stretching speed of 20 mm/min. The schematic diagram and photograph of the experimental system are illustrated in
Figure 14. Testing specimen with a length of 4 cm and a width of 2 cm was folded at its length direction with pile fibers outward. The two ends of the specimen were snipped free of fibers, warped with scotch tape and held in the lower jaw. A clip was employed to clamp a single pile fiber stood upright from the ground fabric of the pile material. The other side of the clip was fixed with yarn, which was gripped by the upper jaw. A total of 100 pile fibers were extracted from each pile debridement material on 10 specimens.
3.8. Statistical Analysis
The results were analyzed statistically using Origin 8.5 software (Origin Lab Inc., Northampton, MA, 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 (***).
4. Conclusions
In this research, single fiber pull-out test was proposed as an in vitro method to evaluate the fiber shedding property of the textile pile debridement materials. The influence of structures on the single fiber pull-out force was studied. By increasing pile density and number of ground yarns, a slight ascending trend in single fiber pull-out force was achieved. Moreover, back-coating treatment prominently enhanced the pull-out force of single fiber in pile materials. That is to say, back-coating is an effective means to improve the fiber shedding property of textile pile debridement materials. These results imply that textile pile debridement materials with back-coating have a relatively low probability for fiber shedding during wound debridement application. Thus, in order to avoid any unexpected infection caused by the shed fibers, back-coating treatment is highly recommended for the preparation of textile pile materials. To better understand the mechanisms of the fiber shedding phenomenon in textile pile debridement materials, a close look into the single fiber pull-out behavior and modes of failure were performed. Typical load–displacement curve of samples without back-coating were characterized with consecutive fluctuating, which indicates a totally extracted pile fiber. In contrast, three modes of failure were observed on samples with back-coating, namely fiber slippage, coating point rupture and fiber breakage. All findings in this study not only provide a feasible in vitro approach for fiber shedding evaluation, but also offer a guideline for designing and manufacturing of the textile pile materials that meet the basic clinical requirements for wound debridement application.