Biofabrication of tri-layered nerve guide conduits for peripheral nerve regeneration: Synergizing melt-electrowriting of polymeric fibers and extrusion-based 3D bioprinting

Nerve guide conduits (NGCs) are promising alternatives to autografts for the treatment of peripheral nerve injuries. These conduits are designed to replace the nerve tissue that has been damaged or removed from the injured nerve region. An ideal nerve conduit should effectively bridge the nerve gap and induce nerve cell growth and regeneration. Current FDA-approved NGCs predominantly address gaps smaller than 2 cm and are fabricated from rigid synthetic polymers. Nevertheless, cells prefer softer substrates that more closely mimic the extracellular matrix (ECM). While hydrogels emerge as an ideal ECM-mimicking material, their application is limited by challenges in suturing, maintaining structural integrity, and susceptibility to rapid biodegradation. In this study, we propose a tri-layered NGC biofabricated by combining melt-electrowriting (MEW) and extrusion-based bioprinting, thereby facilitating three functionalities—the outer layer of MEW-polycaprolactone (PCL) fiber monophasic structure for mechanical integrity, the middle layer of MEW-PCL aligned fibers providing topographical cues for axonal directionality, and the inner bioprinted gelatin methacryloyl layer for encapsulating cells in an ECM-mimicking matrix (~7 kPa stiffness matching nerve tissues). In addition to having tunable mechanical properties (by changing the outer layer design), these biocompatible materials are cost-effective, easily biofabricated, highly tunable for drug-loading, and can support the growth, proliferation, and differentiation of human neural stem cells to peripheral neurons, making the proposed tri-layered NGCs promising candidates for treating long nerve gap injuries.