Triblock copolymers of PLLA-PEG-PLLA for nerve guidance channel scaffolds via 3D printin

The peripheral nervous system (PNS) is a complicated and extensive network of nerves that are the means by which the brain and spinal cord control the rest of the body. The PNS is fragile and can be easily damaged by injuries or trauma. Surgical treatment is the only remedy available currently, with the gold standard for defects greater than 8 mm being autologous nerve grafts. In addition, nerve grafts have been particularly ineffective at repairing critical-size nerve defects (> 3 cm). Scaffold-based strategies where a tubular nerve guidance channel (NGC) is used to bridge the nerve defect have been promoted as a potential alternative that could avoid the additional surgeries and associated donor site morbidity involved in the harvest of nerve grafts. Current research efforts mainly focused on creating more complex NGCs that can support regeneration of critical-size defects.;My research aims to use additive manufacturing technologies to create tunable NGCs with new biomaterials. The use of biodegadable block copolymers with both hydrophilic and relative hydrophobic functions can provide a flexible, partially-hydrated, biocompatible and bioresorbable NGC shell. In this study, ABA type triblock copolymers of polyethylene glycol (PEG; B block) combined with poly(L-lactic acid) (PLLA; A blocks) were synthesized with varied molecular weights of PEG and different degrees of polymerization of PLLA and were characterized with gel permeation chromatography (GPC), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and rheometry to determine molecular weight, polymer structure, and thermal and physical properties. In addition, equilibrium water content was evaluated and correlated to polymer structure. Characterization results showed that the copolymers with longer PLLA chains exhibited higher hardness but lower flexibility. The increasing addition of PLLA decreased the melting point, while increasing the PEG molecular weight increased the melting point. Water absorption increased with longer PEG blocks, however this also decreased copolymer integrity. Such degradable thermoplastic elastomers that are amenable to extrusion printing of flexible polymer tubes and exhibit tunable water content hold great promise for further development and application as cellular NGCs for the repair of peripheral nerve defects.