Collagen bioinks redefined: Optimizing ionic strength and growth factor delivery for cartilage tissue engineering

This study investigates the impact of ionic strength on the gelation kinetics of collagen biomaterial inks and evaluates the efficiency of TGFβ-1 sequestration within these hydrogels, alongside their compatibility with bioprinting live chondrocyte and adipose-derived stem cell lines for cartilage tissue engineering. By adjusting sodium chloride and phosphate-buffered saline (PBS) concentrations, we demonstrate that reduced ionic strengths accelerate gelation, facilitating high-fidelity bioprinting while supporting high cell viability and post-printing proliferation of chondrocytes. Furthermore, at a 1% collagen concentration, the hydrogel effectively immobilized TGFβ-1, with less than 0.5% released over two weeks, indicating potent sequestration capabilities. Using adipose-derived mesenchymal stem cells, histomorphological and transcriptomic analyses reveal that the presence of TGFβ-1 significantly enhances chondrogenesis. These findings underscore the critical role of ionic strength in optimizing collagen ink properties for advanced bioprinting applications and highlight the potential of collagen hydrogels as effective carriers for sustained growth factor delivery, paving the way for successful cartilage tissue engineering strategies. Compare 3D bioprinted SVF cells in collagen vs collagen+TGFb bioinks in terms of chondrogenesis. We also compare these two bioprinting approaches to the gold standard of 3D spheroids (micromasses). All conditions are compared to SVF cells grown in standard 2D (monolayer) cultures.