Injectable cell/microsphere aggregates for cartilage regeneration

Abstract

Injectable delivery systems have been attractive in tissue engineering, as they can deliver cells into the body in a minimally invasive manner. The hypothesis underlying in the thesis is that microspheres modified with cell adhesion ligands could be useful to form shear-reversible cell aggregates as an injectable. Alginate is a natural polymer that is broadly used in many biomedical applications, due to its good biocompatibility, low toxicity, and mild gelation conditions to form a cross-linked structure. Alginate microspheres were prepared by the water-in-oil emulsion method and solidified with a use of calcium chloride (mean diameter = 14.7 μm), followed by modification with RGD peptides using carbodiimide chemistry. RGD-alginate microspheres formed a solid-like, aggregated structure when mixed with either ATDC5 cells or primary chondrocytes without additional cross-linking agents, in which microspheres and cells were uniformly dispersed and closely packed. The aggregation behavior was shear-reversible, which was confirmed by a rotational rheometer. However, non-modified alginate microspheres formed a phase separated structure, due to the lack of specific interactions between microspheres and cells. RGD-alginate microspheres/chondrocytes aggregates were injected into the dorsal region of mice, and the efficacy of the aggregate in cartilage regeneration was tested in vivo. These cell/microsphere aggregates may find useful applications in tissue engineering as an injectable system.