Aims
This study aimed to develop hydrogel-based surrogate constructs capable of reproducing the mechanical response of biological cervical spinal cord tissue across physiological and trauma-simulating transverse compression rates.
Methods
Poly(acrylamide)–alginate (PAAm–alginate) double-network hydrogels were synthesised to match geometry of the average human cervical spinal cord. A fully factorial design of 27 formulations was evaluated, incorporating three alginate concentrations (4.7%, 7.8%, 10.3% w/v) crosslinked in 0.1 M baths of three ionic crosslinking agents (CaCl₂, FeCl₃, AlCl₃) for three immersion durations (1, 2, 3 hours). Specimens were tested under quasi-static and dynamic transverse compression using comparable setups to those previously applied in human and porcine spinal cord experiments. Stress-strain responses were characterized using ARCGen and compared using statistical parametric mapping, which aligns and analyses full-curve data to identify statistically significant differences (α=0.05).
Results
All formulations exhibited J-shaped nonlinear stress–strain behaviour consistent with biological spinal cord tissue, and all demonstrated strain-rate-dependent stiffening with increasing loading velocity. Stiffness and peak stress generally increased with ion valency, alginate concentration, and immersion duration, consistent with higher crosslink density. Calcium formulations produced the closest match to native spinal cord stress-strain corridors across the physiological strain range. Specifically, the closest matching alginate concentrations were 4.7% for quasi-static rates, 10.3% for dynamic rates, and 7.8% for general, all-purpose agreement. Aluminium and iron hydrogels yielded stiffer, less compliant networks.
Conclusion
Ionically crosslinked PAAm-alginate hydrogels provide a tunable, reproducible, and physiologically relevant material system for developing artificial spinal cords. These materials replicate the nonlinear viscoelastic mechanics of native spinal tissue and can be further adapted for use in surgical training, device testing, or regenerative scaffolds. Ensuring mechanical fidelity will be critical for future integration with biocompatible drug-delivery and cell-supporting systems.