gms | German Medical Science

Objectives: Current therapeutic options for tendon injuries have limited clinical outcomes owing to the poor and slow self-repair capacity of tendon tissue. Thermosensitive hydrogels have been studied as alternative cell carriers in cell-based regenerative therapies due to several great advantages to hard scaffolds, such as easier handling, good biocompatibility and cell distribution, molding to the injury site dimensions and long-distance delivery through percutaneous injections. This work aimed to investigate a synthetic/natural hybrid thermosensitive butane diisocyanate (BDI)-collagen (BC) hydrogel combined with TSPCs for potential application in tendon tissue engineering.

Methods: First, we optimized BDI hydrogel with the addition of 20% (v/v) collagen I (COL I) to obtain the thermosensitive hybrid BC hydrogel, which was then seeded with TSPCs derived from human Achilles tendons (three healthy young donors) which were previously well characterized by our group. COL I gel served as positive control. We evaluated the hydrogels, BC vs COL I, in terms of how they affect TSPC behaviour using quantitative gel contraction assay, cell morphology, survival, proliferation, real-time PCR gene expression and matrix organization analyses. The vascular permeability of BC and COL I hydrogel was also assessed with human umbilical vein endothelial cells (HUVECs) cultivation and investigation of tube formation after 7 days.

Results and conclusion: Our findings revealed that the BC hydrogel showed to harden above 25 °C. BC hydrogel supported TSPCs survival with satisfying compatibility and did not induce apoptosis. TSPCs distributed evenly in BC hydrogel and expanded with high viability during prolonged culture time from day 0 to 7. Analyses of gel contraction showed that both BC hydrogel and COL I gel were contracted by the TSPCs; however, the latter significantly more. Phalloidin-based visualization of F-actin demonstrated that the TSPC cell shape in BC hydrogel was comparable to that of cells cultured in COL I gel. The gene expression profile of TSPCs, studied by quantitative RT-PCR of 24 different tenogenic genes, in the BC hydrogel was comparable with that in COL I gel. Moreover, the BC hydrogel supported capillary-like structure formation by HUVECs, suggesting the hydrogel is permeable for blood vessels and nutrition supply at the site of implantation. Taken together, these results show that the thermosensitive BC hydrogel is very biocompatible for TSPCs, and holds great potential as an injectable cell delivery carrier of TSPCs for tendon tissue engineering. In vivo examination of the TSPCs-BC hydrogel combination in pre-clinical tendon injury model is on the way.