Injectable citrate-based polyurethane-urea as a tug-of-war-inspired bioactive self-expansive and planar-fixing screw augmented bone-tendon healing

Inspired by tug-of-war, a game-changing bone-tendon fixation paradigm was developed. Specifically, injectable citrate-based bioactive self-expansive and planar-fixing screw (iCSP-Scr) consisting of reactive isocyanate (NCO) terminalized citrate-based polyurethane, proanthocyanidin modified hydroxyapatite (HAp) and water (with/without porogen) was developed and administrated in the bone-tendon gap. Instead of the "point to point" tendon fixation by traditional interface screws, along with the moisture-induced crosslinking and expansion of iCSP-Scr within the confined space of the irregularly shaped bone-tendon gap, the tendon graft was evenly squeezed into the bone tunnel in a "surface to surface" manner to realize strong and stable bone-tendon fixation via physical expansion, mechanical interlocking and chemical bonding (between -NCO and the -NH