Design and fabrication of a 3D printed auxetic - electrospun scaffold for tendon structure modelling

Tendon tissue engineering requires scaffolds with an appropriate structure that can be cultured under cyclic strain in order to replicate both mechanical cues and biological commitments. This study presents a hybrid scaffold combining 3D-printed auxetic polycaprolactone (PCL) with electrospun gelatin-(3-Glycidyloxypropyl)trimethoxysilane (GPTMS) functionalized with collagen microfibers suitable for the purpose of tenogenic commitment and in vitro modelling. The auxetic core was fabricated via pneumatic melt extrusion at 1000 mbar and printing speed of 200 mm/min, achieving a re-entrant angle of 60.92 ± 2.1° and strut thickness of 350 ± 30 μm with high geometric fidelity. Mechanical characterization revealed that PCL scaffolds exhibited an elastic modulus of 51.97 ± 6.19 MPa and ultimate tensile strain of 6.75 ± 0.59%. Integration of electrospun gelatin-GPTMS without collagen increased the elastic modulus to 66.54 ± 7.16 MPa while reducing ultimate tensile strain to 4.14 ± 1.27%. Incorporation of 1 mg/mL and 2 mg/mL μCollaFibR™ significantly enhanced ultimate tensile strain to 21.70 ± 0.20% and 19.94 ± 0.20%, while decreasing elastic modulus to 47.65 ± 1.33 MPa and 39.83 ± 1.85 MPa. Field Emission-Scanning Electron Microscopy confirmed hierarchical architecture with collagen microfibers (1-5 μm diameter) interspersed throughout the electrospun gelatin matrix. Human tendon stem/progenitor cells seeded at 1 × 10⁵ cells/cm² maintained viability exceeding 85% at day 3 across all formulations, exhibiting elongated morphology and alignment along nanofiber axes. The developed multimaterial platform successfully integrates auxetic mechanics with extracellular matrix-mimetic topographies, offering a biomimetic scaffold structure for subsequent in vitro modelling of tenogenic events.