Injectable PNIPAM/Hyaluronic acid hydrogels containing multipurpose modified particles for cartilage tissue engineering: Synthesis, characterization, drug release and cell culture study.

Novel injectable thermosensitive PNIPAM/hyaluronic acid hydrogels containing various amounts of chitosan-g-acrylic acid coated PLGA (ACH-PLGA) micro/nanoparticles were synthesized and designed to facilitate the regeneration of cartilage tissue. The ACH-PLGA particles were used in the hydrogels to play a triple role: first, the allyl groups on the chitosan-g-acrylic acid shell act as crosslinkers for PNIPAM and improved the mechanical properties of the hydrogel to mimic the natural cartilage tissue. Second, PLGA core acts as a carrier for the controlled release of chondrogenic small molecule melatonin. Third, they could reduce the syneresis of the thermosensitive hydrogel during gelation. The optimum hydrogel with the minimum syneresis and the maximum compression modulus was chosen for further evaluations. This hydrogel showed a great integration with the natural cartilage during the adhesion test, and also, presented an interconnected porous structure in scanning electron microscopy images. Eventually, to evaluate the cytotoxicity, mesenchymal stem cells were encapsulated inside the hydrogel. MTT and Live/Dead assay showed that the hydrogel improved the cells growth and proliferation as compared to the tissue culture polystyrene. Histological study of glycosaminoglycan (GAG) showed that melatonin treatment has the ability to increase the GAG synthesis. Overall, due to the improved mechanical properties, low syneresis, the ability of sustained drug release and also high bioactivity, this injectable hydrogel is a promising material system for cartilage tissue engineering.