Thermoresponsive injectable hydrogel for three-dimensional cell culture: chondroitin sulfate bioconjugated with poly(N-isopropylacrylamide) synthesized by RAFT polymerization
A major challenge in in vitrocell delivery is to provide an optimum environment that mimics natural conditions to maintain correct cellular functions. To address this challenge, we present a biohybrid injectable hydrogel based on chondroitin sulfate (ChS) and poly(N-isopropylacrylamide) (PNIPAAm). PNIPAAm was synthesized at various molecular weights between 5 to 20 kDa by RAFT polymerization in the presence of S-1-dodecyl-S′-(α, α′-dimethyl-α′′-acetic acid) trithiocarbonate as a chain transfer agent. The molecular weight range suitable for renal clearance was an important factor in the experimental design. The phase transition behavior and the gelation time of the hydrogel were measured to evaluate its possibility for further clinical application. Furthermore, hydrogel degradation was also a concern for clinical application. Samples were incubated in PBS with 100 U/ml of hyaluronidase at 37 °C to determine their degradation behaviors and the results revealed that the hydrogel was biodegradable in physiological conditions. To evaluate the biocompatibility for potential use of the hydrogel as a cell delivery vehicle, in vitro two-dimensional (2-D) and three-dimensional (3-D) cell cultures were performed. Cells demonstrated excellent viability when cultured with the hydrogel. In addition, the arrangement of multiple cell layers in the hydrogel was achieved. These results indicate the thermoresponsive injectable hydrogel may be expected to have wide potential applications as a vehicle for the delivery of therapeutic cells.