Utilizing core-shell fibrous collagen-alginate hydrogel cell delivery system for bone tissue engineering.

Three-dimensional matrices that encapsulate and deliver stem cells with defect-tuned formulations are promising for bone tissue engineering. In this study, we designed a novel stem cell delivery system composed of collagen and alginate as the core and shell, respectively. Mesenchymal stem cells (MSCs) were loaded into the collagen solution and then deposited directly into a fibrous structure while simultaneously sheathing with alginate using a newly designed core-shell nozzle. Alginate encapsulation was achieved by the crosslinking within an adjusted calcium-containing solution that effectively preserved the continuous fibrous structure of the inner cell-collagen part. The constructed hydrogel carriers showed a continuous fiber with a diameter of ~700-1000 μm for the core and 200-500 μm for the shell area, which was largely dependent on the alginate concentration (2%-5%) as well as the injection rate (20-80 mL/h). The water uptake capacity of the core-shell carriers was as high as 98%, which could act as a pore channel to supply nutrients and oxygen to the cells. Degradation of the scaffolds showed a weight loss of ~22% at 7 days and ~43% at 14 days, suggesting a possible role as a degradable tissue-engineered construct. The MSCs encapsulated within the collagen core showed excellent viability, exhibiting significant cellular proliferation up to 21 days with levels comparable to those observed in the pure collagen gel matrix used as a control. A live/dead cell assay also confirmed similar percentages of live cells within the core-shell carrier compared to those in the pure collagen gel, suggesting the carrier was cell compatible and was effective for maintaining a cell population. Cells allowed to differentiate under osteogenic conditions expressed high levels of bone-related genes, including osteocalcin, bone sialoprotein, and osteopontin. Further, when the core-shell fibrous carriers were implanted in a rat calvarium defect, the bone healing was significantly improved when the MSCs were encapsulated, and even more so after an osteogenic induction of MSCs before implantation. Based on these results, the newly designed core-shell collagen-alginate fibrous carrier is considered promising to enable the encapsulation of tissue cells and their delivery into damaged target tissues, including bone with defect-tunability for bone tissue engineering.