Shear-Thinning Composite Hydrogel Incorporating Polycaprolactone (PCL) Short Nanofibers for Cell Therapy Applications

Nanofibers-reinforced hydrogels offer improved mechanical properties as compared to classic hydrogels and can potentially better support cell viability and cell therapy outcomes. Here, we optimized polycaprolactone (PCL) short nanofibers production and combined them with a soft hydrogel based on kappa-carrageenan and gelatin type B (kCGb) to perform umbilical cord pericyte (UCP) delivery and promote re-endothelialization of injured blood vessels. Electrospinning of PCL identified 12.5% w/v concentration, 0.5 mL/h flow rate, 21 kV voltage, and 6.8 m/s drum collector speed as optimal parameters for aligned beadless nanofibers. Coaxial PCL/gelatin type A (Ga) fibers were successfully produced with diameters of 180-190 nm (core) and 225-245 nm (shell). The Ga acts as a temporary shell, which was removed during postfabrication processing by washing the nanofibers with deionized water (DIW) at 37°C for 30 min. Mechanical cryostat cutting generated short nanofibers (~75 μm ± 28 μm) with higher yields from coaxial mats (2 × 10⁶ fibers/mL ± 1.6 × 10⁵ fibers/mL) compared to single PCL mats (5 × 10⁴ fibers/mL ± 1.3 × 10⁴ fibers/mL). kCGb hydrogel showed a significant improvement in mechanical properties when reinforced with short PCL nanofibers. The recovery percentage, measured using rheology, increased from 12.1% ± 0.3% to 90.9% ± 0.4% when a small amount (0.05 wt%) of short PCL nanofibers was added. The injection force using clinically relevant needles of 0.5kC2Gb0.05PCL was about ~37 N, and there was no significant reduction in UCPs viability after injection up to 1 week of culture. Injection delivery of kCGbPCL mixed with UCPs (1 × 10⁶ cells/mL) in an ex vivo model of porcine artery injury led to a marked improvement in endothelial coverage from 47.2% ± 19.1% in the injured artery to 76.5% ± 13.2% after cell therapy, with a restoration index of about 89.8% after 1 week of culture. These results represent a further step toward developing physically cross-linked and mechanically stable injectable scaffolds for different applications, such as drug delivery, 3D printing, in vitro modeling, and tissue engineering.