Photo-Cross-Linkable, Injectable, and Highly Adhesive GelMA-Glycol Chitosan Hydrogels for Cartilage Repair

Microindentation-based mechanical characterization of cartilage–hydrogel constructs was performed using a CellScale high-precision, piezoelectric actuator-controlled microcompression system. Constructs were tested submerged in a temperature-controlled PBS bath at 37 °C. A spherical indenter (0.5 mm zirconium oxide bead) mounted on a cantilevered microbeam was positioned above the sample center and driven at a constant jogging speed (reported as 4 µm/s). The system continuously quantified indentation force and indentation depth by optically tracking microbeam deflection while controlling z-displacement via the piezo actuator. Samples were subjected to cyclic compression (three cycles) with force amplitude corresponding to ~10% of sample height, using 30 s loading and 30 s recovery phases per cycle (no rest between phases). Force–indentation data were then fit to a Hertz spherical contact model to calculate elastic modulus of the hydrogel construct under hydrated, physiologic-temperature conditions.