Study of a (trimethylenecarbonate-co- -caprolactone) polymer—Part 2: in vitro cytocompatibility analysis and in vivo ED1 cell response of a new nerve guide

Future surgical strategies to restore neurological function in peripheral nerve loss may involve replacement of nerve tissue with cultured Schwann cells using biodegradable guiding implants. Random copolymers of trimethylene carbonate and caprolactone (P( CL-TMC), 50 : 50) have been synthesized by ring opening polymerization using rare earth alkoxides as initiator. Their potential use as nerve guide repairs has been assessed through indirect and direct in vitro biocompatibility tests and in vivo soft tissue response to ED1 subclass macrophages. In vitro, we exposed monolayers of human skin fibroblasts and an established continuous cell line (Hela) to liquid extracts (either pure or diluted in the culture medium) of CL-TMC copolymer including positive (phenol) and negative controls. Then, colorimetric assays (Neutral red and MTT) were performed. The extracts of CL-TMC induced no significant cytotoxic effect. We also exposed in vitro Schwann cells to pieces of P( CL-TMC) and P(LA-GA) copolymers. We evaluated cell attachment at 1 and 3 h by measuring the activity of the lysosomal enzyme (N-acetyl-β-hexosaminidase) and cell proliferation at 1, 3, 6 and 9 days by measuring the cell metabolic activity (MTT assay). Values for attachment slightly decreased between 1 and 3 h but were significantly higher than on agars (negative control). Cells plated on CL-TMC showed a rate of proliferation comparable with that of normalized controls and higher than on PGA-PLA at day 9. Finally, we evaluated in vivo the soft tissue response after implantation of cylindrical tubes of P( CL-TMC) and P(LA-GA) copolymers with an immunohistochemistry staining procedure for the newly recruited ED1 macrophages. An image analysis system automatically measured the optical density of labelled positive ED1 cells at 9, 21 and 60 days after implantation. CL-TMC copolymer showed a mild soft tissue reaction with no adverse chronic inflammatory reaction. These data allowed us to consider this conduit as a potential effective substitute in nerve repair.