Tissue reactions to synthesized biodegradable polymers in hamster skin

Poly-L-Lactic acids (PLA) are biodegradable polymers commercially available as screws and plates for internal fixation of mandibular fractures. Polyhydroalkanoates (PHA) are carbon and energy reserve material synthesized by bacteria and viewed as natural products with potential uses in biomedical fields either as scaffolding materials or barriers in tissue engineering. Objectives: To examine and compare the tissue response of PLA and PHA within the subcutaneous environment. Methods: Twenty adult male Syrian golden hamsters ( Mesocricetus auratus )of both sexes, average age 1 month and weighing 100 gm, were used. 2 mm discs of PLA and PHA were implanted in the dermis of the animal back, and the wounds allowed to heal by primary intention. The total sample size for each polymer was 20. The entire experimental period was 20 weeks. An animal was sacrificed at a weekly interval, and the skin containing the polymers was excised and submitted for histopathological evaluation blind. Results: At the early implantation phase (week 1), a mixed acute and chronic inflammatory cell reaction was present in the subcutaneous connective tissues at the implant site for both types of polymers. Between weeks 2 and 5 a fibroblastic reaction was seen around an intact PHA whereas dense scar-like tissues had encased PLA which demonstrated progressive fragmentation and degradation. By week 6, there was no evidence of PLA in the subcutaneous tissues whilst PHA remained intact. In addition, 2 animals showed osteoid formation adjacent to the intact PHA. Late implantation phase (week 20) was marked by fibrosis, encapsulation and evidence of foreign body giant cell granuloma proximal to PHA. Conclusions: Differences in polymer composition underlie the different tissue reactions and dissolution characteristics of these materials. (This study was supported by the IRPA Vote 06-02-03-0169)