Chitosan-Based Materials for Peripheral Nerve Repair-New Pre-Clinical Data on Degradation Behavior at the Nerve Repair Site and Critical Opinion on Their Translational Impact

Before clinical approval of chitosan nerve conduits (CNCs) less than 10 years ago, substantial material degradation was not reported from pre-clinical research. The current study investigated the biodegradation of two different CNC variants in the median nerve model. In adult rats, 10 mm long CNCs were secured covering end-to-end repair sites. After 2, 6, 12, and 18 months, the implantation sites were inspected, and samples harvested. Histology was performed in order to analyze local immune response or foreign body tissue reaction around the devices or within nerve samples. Further, the number of myelinated nerve fibers and the condition of the chitosan material was evaluated. Data confirmed that different CNC variants did not induce tissue reaction or negatively impact the condition of the regenerated nerve. At late time points, some specific variants were demonstrated to have resulted in encapsulated material debris in the vicinity of the original implantation side. The reported degradation behavior resembles recent clinical reports and indicates that implantation sites for CNCs need to be chosen carefully. Nerve regeneration itself is undisturbed, but narrow implantation sites should be avoided for eliminating the risk of foreign body sensation with immunologically inert material degradation.