Ethylene Oxide Sterilization Preserves Bioactivity and Attenuates Burst Release of Encapsulated Glial Cell Line Derived Neurotrophic Factor from Tissue Engineered Nerve Guides For Long Gap Peripheral Nerve Repair

Abstract

Synthetic nerve guides are widely utilized to reconstruct peripheral nerve defects that are less than three centimeters. However, there are no clinically available nerve guides that are approved to promote repair over long gaps (>3 cm). Many currently available guides are unable to sustain large defect regeneration either because of limitations in fabrication or short degradation times in vivo. Furthermore, current clinically available nerve guides do not contain neurotrophic factor delivery systems to promote nerve tissue regeneration over long gaps. The purpose of this paper is to describe the manufacturing parameters and sterilization procedures of a 5.2 cm poly(caprolactone) nerve conduit with embedded polymeric microspheres that encapsulate glial cell line-derived neurotrophic factor (GDNF) for implantation into a preclinical rhesus macaque 5 cm median nerve defect model. Nerve conduits were sterilized with room temperature ethylene oxide (RT EtO) and assessed for morphology as well as maintenance of porosity. Release kinetics and bioactivity of GDNF were also assessed in RT EtO sterilized guides. Scanning electron microscopy indicated that RT EtO treatment did not affect morphology and porosity percentage of nerve guides. Furthermore, RT EtO had no effect on GDNF bioactivity based on Schwannoma cell migration studies. RT EtO guides exhibited significantly slowed GDNF release compared to GDNF release from nonsterile guides indicating that EtO treatment may enhance the long-term delivery kinetics of GDNF from polymeric microspheres within the nerve guide.

Long-gap peripheral nerve repair through sustained release of a neurotrophic factor in nonhuman primates

“…On the basis of our previous success in the small animal studies, we pursued our evaluation of the PCL/GDNF guide in the large animal model described here. In addition, we examined the bioactivity of GDNF released from the guide after ethylene oxide (EtO) sterilization, determining that the GDNF remained active and about 14 ng was released from the PCL/GDNF nerve guide over 50 days (56).…”

“…The polycaprolactone nerve conduit fabrication was based on our previously conducted nerve repair study using a small animal model (see Supplementary Materials and Methods) (14,15). Conduits were autoclaved using room temperature ethylene oxide sterilization, as previously described (56).…”

Peripheral Nerve Regeneration: Current Status and New Strategies Using Polymeric Materials

“…The presence of a grooved structure helped reducing the excessive mechanical properties of the material, approximating it to the ones of the healthy nerve. Another study evaluated the effect of encapsulated neurotrophic factor derived from glial cell (GDNF) embedded in a nerve conduit made with PCL . The bioactivity of GDNF was confirmed and also the sterilization technique proved to be suitable for this material, as it did not alter its structure or porosity percentage.…”

Effects of Terminal Sterilization on PEG‐Based Bioresorbable Polymers Used in Biomedical Applications

“…Chemical‐based (vaporized hydrogen peroxide (VHP) and ethylene oxide (EO)) and radiation‐based sterilization methods (gamma and electron‐beam (E‐beam)) are the most commonly used sterilization tools for a wide variety of polymers and polymeric scaffolds. For example, the effects of EO, gamma, and E‐beam sterilizations have been investigated for electrospun PLA fiber membranes, silk fibroin sponges, PCL nerve conduits, cyclodextrin‐hexamethyldiisocynate crosslinked polymers and most recently on a proprietary hydrogel (Cyborgel) . VHP is a low‐temperature alternative to EO and has mostly been used for sterilizing polyurethane scaffolds, polyethylene (LDPE) tubing, polyvinylchloride (PVC) tubing, and PVC films …”