Study on Histocompatibility and Biodegradability of Polylactic Acid Gel in Rats

Objective: To investigatethe effects on histocompatibility and biodegradability of bioabsorbablepolylacticacid (PLA) gelin rats. Methods: Longitudinal incision of 30 mm was made along the spine, and subcutaneous tissues were separated bluntly to make four subcutaneous pouches, and PLA gel of different molecular weight (5, 10 and 20 kD) was implanted into the pouches. 4, 7, 11 and 14 weeks after implantation, the samples and surrounding tissues were collected to perform HE staining; meanwhile, the samples were weighted and compared after drying. Results: There were few inflammatory cells accumulations in tissues treated with different molecular weight PLA gel. The degradation rate of 5 kD-PLA gel was faster than other groups. With increase of the molecular weight of PLA gel, the degradation rate was gradually decreased. Conclusion: Our findings indicated that PLA gel had good biocompatibility and a definite degrading effect, which could be further used in surgery. Introduction The adhesion between tissues and organs is a big trouble in surgical field. The incidence of adhesions was more than 90% after laparotomy, although early peritoneal adhesions were beneficial for wound healing, the peritoneal adhesions could cause serious complications, such as intestinal obstruction, abdominal pain, female infertility and pelvic pain, which increased the difficulty of surgery [1-3] .Therefore, prevention of adhesions is a major problem in surgical field. Polylactic acid (PLA) gel is the polymer product which is made of PLA, it has good biocompatibility and biodegradability [4, 5] . PLA gel could form films rapidly when wet, then be attached to wound to prevent tissue adhesion without suture, eventually degraded in vivo; which could be used to prevent postoperative adhesions [6] . At present, studies focused on improvement of effects of PLA gel [7, 8] , and the histocompatibility and biodegradability of PLA gel were rarely reported [4, 5] . In our study, we will investigate the histocompatibility and biodegradability of PLA gel in Sprague Dawley (SD) rats. Materials and methods PLA gel Preparation Under sterile conditions, the polylactic acid hydrogel were tiled on one glass disk with 90 mm diameter, then were sprayed sterile water to form gel film. After natural drying, the film was made into diameter of 8.5 mm, thickness of 0.3 mm with puncher. Then 2 ml PLA gelwith 95% purity were placed in tube, and numbered 1, 2, 3 and 4. In which the molecular weight of the No. 1, 2, 3 were 5 kD, 10 kD, and 20 kD, and No. 4 was polylactic acid film reference substance. Animal Surgery Thirty two female SD rats (300±25 g) were provided by the Centers for Disease Control, Sichuan Province. Animals were anesthetized by intraperitoneal injection of 40 mg/kg sodium pentobarbital, then the limbs were fixed under the posture of back up; after skin preparation, longitudinal incision International Conference on Material Science and Application (ICMSA 2015) © 2015. The authors Published by Atlantis Press 597 of 30 mm was made along the spine, and subcutaneous tissues were separated bluntly to make four subcutaneous pouches. Four PLA gel samples were implanted into subcutaneous pouch, respectively, and the distance between each sample was more than 20 mm. At last, the skin was sutured, and antibiotics were injected to prevent infection. All animals were conventional breed under SPF conditions. Histocompatibility and Degradability Observation 4, 7, 11 and 14 weeks after implantation, all animals were killed and samples were harvested. Some samples were fixed in 4% paraformaldehyde and paraffin-embedded, then the sections were performed HE staining and the histocompatibility was observed under microscope. The other samples were dried at 70°C for 2 h, then weighed using a 1/10000 precision balance. Statistical Analysis All data were expressed as mean  standard deviation (x  s) and analyzed with Student T test (SPSS17.0, USA). A P<0.05 was considered as statistically significant. Results Histocompatibility of PLA gel Fig. 1 HE staining showed 4, 7, 11 and 14 weeks after PLA gel implantation. A, E, I, M: No.1 sample, 5 kD PLA gel; B, F, J, N: No. 2 sample, 10 kD PLA gel; C, G, K, O: No.3 sample, 20 kD PLA gel; D, H, L, P: PLA gel film reference substance. Bar: 100 μm. Four weeks after implantation, lots of fibroblasts were observed in PLA gel, there were few inflammatory cells. Seven weeks after surgery, there was a dense fiber wrapped around materials in all the four groups. In No.1 PLA gel, the adipocytes aggregated in fiber capsule; other groups showed a large number of fibroblasts which split wrapped the materials. At the 11 th week, the fibrous capsule cavity wall was formed, and the adipocyte aggregation appeared in the fibrous capsule in NO.4 PLA gel. At the 14 th week, the fibrous capsule wall showed relaxation, and the un-degraded residue materials showed graininess which were wrapped by fibroblasts (Figure 1).