Design, Fabrication, and Characterisation of Hierarchical Biomimetic Nerve Scaffolds

Abstract

Peripheral nerve injury represents a persistent clinical burden, and severe transections still depend on autograft as the gold standard treatment despite their risk of donor-site morbidity. First-generation FDA-approved synthetic conduits remain hollow tubes that struggle to drive regeneration across critical gaps compared to autograft. Recent preclinical research shows a recurrence of filling implantable lumens with hydrogels because they provide compliant matrices to scaffold regenerating nerve tissue. This work builds on that approach while challenging the single homogeneous matrices that dominate the literature. When a human allograft is freeze-dried and imaged at micron resolution, what remains is an interconnected network whose walls define porous and heterogeneous microchannels extending in one elongated direction. If the benchmark graft is itself microstructurally graded network, then directional freeze-casting combined with additive manufacturing can supply a route to template distinct morphological regions, within one synthetic scaffold.

This work pursues this through a dual-material rational design. Poly(glycerol sebacate) acrylate (PGSA, E > 6 MPa) was DLP-printed into outer shells to approximate the whole-nerve scale, and co-cast gelatin methacryloyl (GelMA, 5% and 12.5% w/v) contributed at the endo-perineurial scale. A radial boundary was established from a highly compliant core (E≈ 200 Pa) to a stiffer boundary (E≈ 3.5 kPa), and constructs were subjected to directional freezing conditions at−20,−80 and−196∘ °C to
create elongated microstructures.

Freezing temperature and polymer concentration interacted significantly for both transverse pore density (p < 0.0001) and axial directionality (p = 0.006), demonstrating that cooling behaviour cannot not be generalised across biopolymer densities alone. During templating, 5% GelMA formed wide, macro-porous channels with longer absolute axial lengths (143.7–182.4 µm, mean AR≈ 1.8-2.2), whereas 12.5% GelMA formed tightly packed, microporous channels whose narrow transverse widths (5.3 µm at−80∘C) possessed high aspect ratios (mean AR = 14.78), but reduced longitudinal directionality. However, the 12.5% gels templated in extreme cryogenic conditions produced extreme aspect ratios (mean AR = 103.57) and unfragmented polymer walls. These heterogeneous pore architectures were shown to be preserved across shared interfaces within the same processing conditions. Initial in vitro cell attachment after 7 days demonstrated the preliminary cytocompatibility of the material system’s processing methods. By demonstrating this, this work can present a scalable method towards the manufacturing of hierarchical, anatomically graded nerve scaffolds.