Biomaterial composition and stiffness as decisive properties of 3D bioprinted constructs for type II collagen stimulation.

Gelatin methacrylate (GelMA) and hyaluronic acid methacrylate (HAMA) are frequently used biomaterials for 3D bioprinting, with individual well-established material characteristics. To identify an ideal combination of GelMA and HAMA for chondrogenesis, a novel, primary human chondrocyte COL2A1-Gaussia luciferase reporter system (HuCol2gLuc) was developed. With this non-destructive, high-throughput temporal assay, Gaussia luciferase is secreted from the cells and used as a proxy for measuring type II collagen production. GelMA:HAMA ratios were screened using the reporter system before proceeding to 3D bioprinting. This method is efficient, saving on time and materials, resulting in a streamlined process of biomaterial optimization. The screen revealed that the addition of HAMA to GelMA improved chondrogenesis over GelMA (15%) alone. Storage moduli were measured using dynamic mechanical analysis of the same GelMA:HAMA ratios and established an initial threshold for chondrogenesis of ∼30kPa. To determine if biomaterial storage moduli impact cell mobility, human primary chondrocytes transduced with green fluorescent protein (GFP) were 3D bioprinted in either 1:1 or 2:1 ratios with storage moduli of 32kPa and 57.9kPa, respectively. We found that reduced cell mobility, in the stiffer biomaterial, had higher type II collagen expression, than the softer material with more cell mobility. Finally, after 3D bioprinting with HuCol2gLuc cells we successfully identified an optimal combination (2:1) of GelMA:HAMA and photo-crosslinking time (38s) for chondrogenesis. STATEMENT OF SIGNIFICANCE: One challenge of 3D bioprinting is identifying ideal biomaterials that stimulate articular cartilage development. To identify an optimal combination of gelatin methacrylate and hyaluronic acid methacrylate for chondrogenesis we developed a primary human chondrocyte type II collagen Gaussia luciferase reporter cell (HuCol2gLuc). This non-destructive, high-throughput assay uses a secreted Gaussia luciferase as a proxy for temporal type II collagen production. This reporter system streamlines the biomaterial optimization process before 3D bioprinting. We also used it to determine the level of stiffness required for chondrogenesis. And for the first time, we quantified chondrocyte mobility in a 3D bioprinted construct. Together these results indicate that a biomaterial with a higher storage modulus and less cell mobility, improves chondrogenesis.