Correlative light and electron microscopic cytochemical demonstration of biodegradation of polyester implants

Abstract

There are situations in which an implant material is required only temporarily, e.g., when it is needed as a scaffold to support a nondegradable material until the latter can be incorporated by the body; or when it is required for the uniform release of a therapeutic agent over a long period of time. Biodegradable organic polyesters such as poly(glycolic acid), poly(lactic acid) or their copolymers are of particular interest for such purposes because they undergo hydrolysis (Fig. 1) to form glycolic or lactic acids which are metabolites normal to the body. Recent studies were performed on the use of polyglactin 910 mesh (VicrylR, a lactic-glycolic acid polymer) as a conduit (sleeve) to guide the reconnection of regenerating fibers of the proximal stump of rat sciatic nerve, across an llmm gap, with fibers in the distal stump of the interrupted nerve. For experimental set-up and procedure see reference 3.Gross examination of the repaired sciatic nerves at 1 month showed complete reconnection of the stumps but the VicrylRmesh was not apparent.When cryostat or paraffin sections were made of repaired nerve there was some disruption of structure due to movement of the polyester filaments through the tissue during the sectioning process. This could be avoided by embedding the specimens in epoxy resin and making semi-thin sections with a glass knife. Staining of the sections with either toluidine blue or the PATS reaction (a light and electron microscopy variation of the Keriodic acidSchiff PAS, reaction depositing silver, 5) revealed numerous VicrylRfilaments in different degradation stages (Figs. 2-4). The toluidine blue stained filaments were reminiscent of earlier results on methylene blue-stained muscle sections that contained cross-sections of polyglactin 910 braided sutures.