ColMA‐based bioprinted 3D scaffold allowed to study tenogenic events in human tendon stem cells

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.