Innovative Spiral Nerve Conduits: Addressing Nutrient Transport and Cellular Activity for Critical-Sized Nerve Defects

Abstract

Large-gap nerve defects require nerve guide conduits (NGCs) for complete regeneration and muscle innervation. Many NGCs have been developed using various scaffold designs and tissue engineering strategies to promote axon regeneration. Still, most are tubular with inadequate pore sizes and lack surface cues for nutrient transport, cell attachment, and tissue infiltration. This study developed a porous spiral NGC to address these issues using a 3D-printed thermoplastic polyurethane (TPU) fiber lattice. The lattice was functionalized with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) electrospun aligned (aPHBV) and randomly (rPHBV) oriented nanofibers to enhance cellular activity. TPU lattices were made with 25%, 35%, and 50% infill densities to create scaffolds with varied mechanical compliance. The fabricated TPU/PHBV spiral conduits had significantly higher surface areas (25% TPU/PHBV: 698.97 mm², 35% TPU/PHBV: 500.06 mm², 50% TPU/PHBV: 327.61 mm²) compared to commercially available nerve conduits like Neurolac™ (205.26 mm²). Aligned PHBV nanofibers showed excellent Schwann cell (RSC96) adhesion, proliferation, and neurogenic gene expression for all infill densities. Spiral TPU/PHBV conduits with 25% and 35% infill densities exhibited Young's modulus values comparable to Neurotube® and ultimate tensile strength like acellular cadaveric human nerves. A 10 mm sciatic nerve defect in Wistar rats treated with TPU/aPHBV NGCs demonstrated muscle innervation and axon healing comparable to autografts over 4 months, as evaluated by gait analysis, functional recovery, and histology. The TPU/PHBV NGC developed in this study shows promise as a treatment for large-gap nerve defects.

Note:
Funding declaration: The authors wish to acknowledge Nano Mission, Department of Science & Technology (DST) (SR/NM/TP-83/2016 (G)), and Prof. T. R. Rajagopalan R & D Cell of SASTRA Deemed University for financial and infrastructural support. We also wish to acknowledge ATGC grant, Department of Biotechnology (DBT) (BT/ATGC/127/SP41147/2021), Adhoc funding, Indian Council of Medical Research (ICMR) (17x3/ Adhoc/23/2022-ITR) and DST SERB CRG (Exponential Technologies) grant (CRG/2021/007847) for financial support. Dr. Kumbar acknowledges the funding support provided by the National Institutes of Health 8 (#R01NS134604, #R01EB034202, #R01AR078908, and #R01EB030060) and the U.S. Army Medical Research Acquisition Activity (USAMRAA) through the CDMRP Peer Reviewed Medical Research Program (Award No. W81XWH2010321, PR230581 and HT94252410137).

Conflict of Interests: There is no conflict of interest in publishing this research article.

Ethical Approval: All animals were maintained and cared for according to methods approved by the Institutional Animal Ethics Committee of SASTRA Deemed University (659/SASTRA/IAEC/RPP) and the Indian government animal welfare guidelines.

Keywords: Nerve guide conduits, Spiral micro-nanostructures, large-gap nerve defect, Poly(3-hydroxybutyrate-co-3-hydroxy valerate) (PHBV), thermoplastic polyurethane (TPU)