Oxygen-generating microparticles in chondrocytes-laden hydrogels by facile and versatile click chemistry strategy

Currently, oxygen supply for in vitro cell culture is one of the major challenges in tissue engineering, especially in three-dimensional (3D) structures, such as polymeric hydrogels, because oxygen is an essential element for cells survival. In this context, oxygen levels must be maintained in articular cartilage to promote the differentiation, viability, and proliferation of chondrocytes due to the low level of oxygen presence in this region. Although some technologies employ oxygen-generating materials to add sufficient oxygen levels, the limitations and challenges of current technologies include the lack of controlled, sustained, and prolonged release of the oxygen. Moreover, the fabrication methods may leave some impurities or residues resulting in toxicity to the cells. "Click" chemistry is a facile, versatile, and compatible chemical strategy to engineer hydrogels for tissue engineering applications. Herein, we disclose the engineering of oxygen-generating microparticles in chondrocytes-laden hydrogels through a versatile catalyst-free tetrazine and norbornene inverse electron demand Diels‒Alder (iEDDA) click reaction. The hydrogels combine chondroitin sulfate (CS) and poly(ethylene glycol) (PEG) crosslinked in situ, displaying tunable rheological and mechanical properties, for sustained and prolonged oxygen-release. Gene expression analysis of the chondrocytes by real-time reverse transcription polymerase chain reaction (RT-PCR) demonstrated promising cell response within the engineered hydrogel.