Abstract: BACKGROUND: Minimally invasive treatment of cartilage injury is highly demanding for microcarriers, which need to have high cytocompatibility, strong cell adhesion, better mechanical properties with low immunogenicity. Simultaneously, the clinical use conditions are more demanding compared to the laboratory, and liquid microcarriers are significantly better than solid microcarriers when they are used minimally invasively or for injection.
OBJECTIVE: To prepare a brand-new polymer organic microcarrier for repairing cartilage.
METHODS: Gelatin microspheres at a concentration of 6% were prepared by chemical emulsification of gelatin mixed and stirred with liquid paraffin (w/O), fixed by lyophilization followed by absolute ethanol treatment, then fixed using ultraviolet cross-linking. The microsphere morphology was observed by electron microscopy. The gelatin-alginate composite gel was prepared by dispensing the gel with sodium alginate at a concentration of 7% and incubating with gelatin microspheres for 2 hours. Cell-containing gelatin-alginate composite microspheres were prepared by dropping adipose mesenchymal stem cell suspension into gelatin-alginate composite gel and incubating for 24 hours, and fully crosslinking by dropping into 5% CaCl2 solution. The cytotoxicity of the extracts from cell-free gelatin-alginate composite microspheres was examined by CCK-8 assay. The cytocompatibility of cell-containing gelatin-alginate composite microspheres was observed by using live & dead staining. Approximately 1 mL of gelatin-alginate composite gel was aspirated into a 10 mL needle tube for injection, and the gel not injected versus injected 1 and 3 times was observed by light microscopy.
RESULTS AND CONCLUSION: (1) As observed by scanning electron microscope, the pores of gelatin microspheres were relatively uniform and the surface was hierarchical, and most of the particles were distributed between 180 and 500 μm in size. (2) As indicated by the live & dead staining, the cells in gelatin-alginate composite microspheres containing cells grew well and carried a large number and even distribution of cells at 24 hours of culture, and the cell viability was above 90% after 1, 3, and 7 days of culture. (3) CCK-8 assays showed no significant cytotoxicity of extracts from cell-free gelatin-alginate composite microspheres. (4) The morphology of the gelatin microspheres in the gelatin-alginate composite gel was unchanged after 1 and 3 injections compared with that when it was not injected, indicating good mechanical properties of the gelatin-alginate composite gel. (5) The results indicated that the combined use of cell-containing gelatin-alginate composite microspheres and cell-containing gelatin-alginate composite gels could make the gels play the role of tissue glue, which is beneficial for materials to adhere closely to the target area.

Key words: gelatin, alginate, composite microspheres, composite gel, polymer organic materials, chemical emulsification, cell compatibility, photo crosslinking, cartilage