Abstract
The advent of bioprinting has enabled the creation of precise three-dimensional (3D) cell cultures suitable for biomimetic in vitro models. In this study, we developed a novel protocol for 3D printing methacrylated collagen (ColMa, or PhotoCol®) combined with tendon stem/progenitor cells (hTSPCs) derived from human tendon explants. Although pure ColMa has not previously been proposed as a printable hydrogel, this paper outlines a robust and highly reproducible pipeline for bioprinting this material. Indeed, we successfully fabricated a 3D bioengineered scaffold and cultured it for 21 days under perfusion conditions with medium supplemented with growth/differentiation factor-5 (GDF-5). This bioprinting pipeline and the culture conditions created an exceptionally favorable 3D environment, enabling the cells to proliferate, exhibit tenogenic behaviors, and produce a new collagen type I matrix, thereby remodeling the surrounding environment. Indeed, over the 21-day culture period under perfusion condition, tenomodulin expression showed a significant upregulation on day 7, with a 2.3-fold increase, compared to days 14 and 21. Collagen type I gene expression was upregulated nearly 10-fold by day 14. This trend was further confirmed by western blot analysis, which revealed a statistically significant difference in tenomodulin expression between day 21 and both day 7 and day 14. For type I collagen, significant differences were observed between day 0 and day 21, as well as between day 0 and day 14, with a p-value of 0.01. These results indicate a progressive over-expression of type I collagen, reflecting cell differentiation towards a proper tenogenic phenotype. Cytokines, such as IL-8 and IL-6, levels peaked at 8566 and 7636 pg/mL, respectively, on day 7, before decreasing to 54 and 46 pg/mL by day 21. Overall, the data suggest that the novel ColMa bioprinting protocol effectively provided a conducive environment for the growth and proper differentiation of hTSPCs, showcasing its potential for studying cell behavior and tenogenic differentiation.