To explore the feasibility on the preparation of novel negative pressure materials for constructing new matrix of full-thickness skin defect wounds in rats.

The experimental research method was applied. The microstructure of polyurethane foam dressing which was commonly used in negative pressure treatment was observed under scanning electron microscope, and its pore diameter was detected (n=5). Polycaprolactone (PCL) and polybutylene succinate (PBS) were used respectively as raw materials for the preparation of PCL and PBS negative pressure materials by melt spinning technology, with the measured pore diameter of polyurethane foam dressing as the spinning spacing at the spinning rates of 15, 25, and 35 mm/s, respectively. The microstructures of the prepared negative pressure materials were observed under scanning electron microscope, and their fiber diameters were measured. The tensile strength and tensile modulus of the prepared negative pressure materials and polyurethane foam dressing were measured by tensile testing machine and composite testing machine, respectively (n=5), to screen the spinning rate for subsequent preparation of negative pressure materials. Human skin fibroblasts (Fbs) in logarithmic growth phase were co-cultured with PCL negative pressure material and PBS negative pressure material prepared at the selected spinning rate, respectively. After 1, 4, and 7 day (s) of co-culture, the cell activity and adhesion in the materials was detected by living/dead cells detection kit, and the cell proliferation level in the materials was detected by cell counting kit 8 method (n=5). A full-thickness skin defect wound was prepared on the back of 18 5-6 weeks old Sprague-Dawley rats (gender unlimited). Immediately after injury, the injured rats were divided into PCL+polyurethane group, PBS+polyurethane group, and polyurethane alone group according to the random number table (with 6 rats in each group). The wounds were covered with materials containing corresponding component and performed with continuous negative pressure suction at the negative pressure of -16.7 kPa. The wound tissue along with materials directly contacted to the wound (hereinafter referred to as wound specimens) were collected from 3 rats in each group after 7 and 14 days of negative pressure treatment (NPT), respectively. The growth of granulation tissue and the attachment of material to wound surface were observed after hematoxylin-eosin staining, the collagen fiber deposition was observed after Masson staining, and CD34 and interleukin-6 (IL-6) positive cells were detected and counted by immunohistochemical staining. Data were statistically analyzed with one-way analysis of variance, analysis of variance for factorial design, least significant difference-t test, Kruskal-Wallis H test, Mann-Whitney U test, and Bonferroni correction.

The microstructure of polyurethane foam dressing was loose and porous, with the pore diameter of (815±182) μm. The spinning spacing for the subsequent negative pressure material was set as 800 μm. The microstructures of PBS negative pressure material and PCL negative pressure material were regular, with vertically interconnected layers and continuous fibers in even thickness, but the fibers of PBS negative pressure material were straighter than those of PCL negative pressure material. There was no obvious difference in the microstructure of negative pressure materials prepared from the same raw material at different spinning rates. The fiber diameters of PCL negative pressure materials prepared at three spinning rates were similar (P>0.05). The fiber diameters of PBS negative pressure materials prepared at spinning rates of 25 mm/s and 35 mm/s were significantly smaller than the fiber diameter of PBS negative pressure material prepared at the spinning rate of 15 mm/s (with t values of 4.99 and 6.40, respectively, P<0.01). Both the tensile strength and tensile modulus of PCL negative pressure materials prepared at three spinning rates were similar (P>0.05). The tensile strength of PBS negative pressure materials prepared at spinning rates of 15 mm/s and 25 mm/s was significantly lower than that of PBS negative pressure materials prepared at the spinning rate of 35 mm/s (with t values of 9.20 and 8.92, respectively, P<0.01), and the tensile modulus was significantly lower than that of PBS negative pressure materials prepared at the spinning rate of 35 mm/s (with t values of 2.58 and 2.47, respectively, P<0.05). Subsequently, PCL negative pressure material was prepared at the spinning rate of 35 mm/s, and PBS negative pressure material was prepared at the spinning rate of 15 mm/s. After 1, 4, and 7 day (s) of co-culture, the number of human skin Fbs that adhered to PCL negative pressure material and PBS negative pressure material increased with time, and there was no significant difference between the two materials. After 1 and 7 day (s) of co-culture, the proliferation levels of human skin Fbs between the two negative pressure materials were similar (P>0.05). After being co-cultured for 4 days, the proliferation level of human skin Fbs in PBS negative pressure material was significantly higher than that in PCL negative pressure material (t=6.37, P<0.01). After 7 days of NPT, the materials were clearly identifiable and a small amount of collagen fibers were also observed in the wound specimens of rats in the three groups; a small amount of granulation tissue was observed in the wound specimens of rats in polyurethane alone group. After 14 days of NPT, a large number of granulation tissue and collagen fibers were observed in the wound specimens of rats in the three groups; the materials and wound tissue in the wound specimens of rats in PCL+polyurethane group could not be clearly distinguished. After 7 and 14 days of NPT, the collagen fibers in the wound specimens of rats in polyurethane alone group were denser than those in the other two groups. After 7 days of NPT, the number of CD34 positive cells in the wound specimens of rats in PBS+polyurethane group was 14.8±3.6 per 400 times visual field, which was significantly less than 27.8±9.1 in polyurethane alone group (t=3.06, P<0.05); the number of IL-6 positive cells was 60 (49, 72), which was significantly more than 44 (38, 50) in polyurethane alone group (Z=2.41, P<0.05). After 14 days of NPT, the number of IL-6 positive cells in the wound specimens of rats in PBS+polyurethane group was 19 (12, 28) per 400 times visual field, which was significantly more than 3 (1, 10) in PCL+polyurethane group and 9 (2, 13) in polyurethane alone group (with Z values of 2.61 and 2.40, respectively, P<0.05).

The prepared PCL negative pressure material and PBS negative pressure material have good biocompatibility, and can successfully construct the new matrix of full-thickness skin defect wounds in rats. PCL negative pressure material is better than PBS negative pressure material in general.

Negative-pressure wound therapy; Wound healing; Tissue engineering; Skin; Fibroblasts; Melt spinning technology