Microcavitary hydrogel-mediating phase transfer cell culture for cartilage tissue engineering.

Hydrogels have been widely used as cell-laden vehicles for therapeutic transplantation in regenerative medicine. Although the advantages of biocompatibility and injectability for in situ grafting have made hydrogel a superior candidate in tissue engineering, there remain challenges in long-term efficacy of tissue development using hydrogel, especially when more sophisticated applications are demanded. The major bottleneck lies in environmental constraints for neo-tissue generation in the gel bulk such as proliferation of encapsulated cells (colonies) per se and also accommodation of their endogenously produced extracellular matrices. In this study, we endeavor to develop an innovative tissue engineering system to overcome these drawbacks through a novel microcavitary hydrogel (MCG)-based scaffolding technology and a novel phase transfer cell culture (PTCC) strategy to enable phenotypically bona fide neo-tissue formation in an injectable artificial graft. For this purpose, microspherical cavities are created in cell-encapsulating hydrogel bulk via a retarded dissolution of coencapsulated gelatin microspheres. Based on proliferation and affinity selection, the encapsulated cell colonies adjacent to the gel-cavity interface will spontaneously outgrow the hydrogel phase and sprout into cavities, enabling neo-tissue islets to fill up the voids and further expand throughout the whole system for full tissue regeneration. The design of MCG-PTCC strategy was elicited from an observation of a spontaneous dynamic outgrowth of chondrocytes from the edge of a cell-laden hydrogel construct over prolonged cultivation--a phenomenon named edge flourish. This MCG-PTCC strategy potentially introduce a new application to hydrogels in the field of regenerative medicine through elevation of its role as a cell vehicle to a three-dimensional transplantable growth-guiding platform for further development of newly generated tissues that better fulfill the demanding criteria of scaffolds in therapeutic tissue regeneration.