High-Strength Fiber-Reinforced Composite Hydrogel Scaffolds as Biosynthetic Tendon Graft Material

The development of suitable synthetic scaffolds for use as human tendon grafts to repair tendon ruptures remains a significant engineering challenge. Previous synthetic tendon grafts have demonstrated suboptimal tissue ingrowth and synovitis due to wear particles from fiber-to-fiber abrasion. In this study, we present a novel fiber-reinforced hydrogel (FRH) that mimics the hierarchical structure of the native human tendon for synthetic tendon graft material. Ultrahigh molecular weight polyethylene (UHMWPE) fibers were impregnated with either biosynthetic polyvinyl alcohol/gelatin hydrogel (FRH-PG) or with polyvinyl alcohol/gelatin + strontium-hardystonite (Sr-Ca2ZnSi2O7, Sr-HT) composite hydrogel (FRH-PGS). The scaffolds were fabricated and assessed to evaluate their suitability for tendon graft applications. The microstructure of both FRH-PG and FRH-PGS showed successful impregnation of the hydrogel component, and the tendon scaffolds exhibited equilibrium water content of ∼70 wt %, similar to the values reported for native human tendon, compared to ∼50 wt % water content retained in unmodified UHMWPE fibers. The tensile strength of FRH-PG and FRH-PGS (77.0–81.8 MPa) matched the range of human Achilles' tendon tensile strengths reported in the literature. In vitro culture of rat tendon stem cells showed cell and tissue infiltration into both FRH-PG and FRH-PGS after 2 weeks, and the presence of Sr-HT ceramic particles influenced the expression of tenogenic markers. On the other hand, FRH-PG supported the proliferation of murine C2C12 myoblasts, whereas FRH-PGS seemingly did not support it under static culture conditions. In vivo implantation of FRH-PG and FRH-PGS scaffolds into full-thickness rat patellar tendon defects showed good collagenous tissue ingrowth into these scaffolds after 6 weeks. This study demonstrates the potential viability for our FRH-PG and FRH-PGS scaffolds to be used for off-the-shelf biosynthetic tendon graft material.