Characterization of slow-gelling alginate hydrogels for intervertebral disc tissue-engineering applications

• Controlled gelation time allows for alginate to form uniform geometric structures.
• Slow-gelling alginate mechanical properties can be maintained over 28 days at 37°C.
• Homogenous gelation enhances alginate hydrogel diffusivity & mechanical stability.
• Slow-gels have enhanced cell viability with no leachable cytotoxicity over control.
• Mechanical properties of slow gelling alginate are similar to native IVD tissue.

Reversal of intervertebral disc degeneration can have a potentially monumental effect on spinal health. As such, the goal of this research is to create an injectable, cellularized alginate-based nucleus pulposus that will restore disc function; with the primary goal of creating an alginate gel with tailorable rates of gelation to improve functionality over standard CaCl2 crosslinking techniques. Gelation characteristics of 1% sodium alginate were analyzed over various molar concentrations of a 1:2 ratio of CaCO3:glucono-δ-lactone (GDL), with 10% CaCl2 as the control crosslinker. Alginate construct characterization for all concentrations was performed via ultimate and cyclic compressive testing over a 28 day degradation period in PBS. Dehydration, swell testing, and albumin release kinetics were determined, and cytotoxicity and cell homogeneity tests showed promise for cellularization strategies. Overall, the 30 and 60 mM GDL alginate concentrations presented the most viable option for use in further studies, with a gelation time between 10 and 30 min, low hysteresis over control, low percent change in thickness and weight under both PBS degradation and swelling conditions, and stable mechanical properties over 28 days in vitro.