Injectable chitosan-platelet-rich plasma implants to promote tissue regeneration: in vitro properties, in vivo residence, degradation, cell recruitment and vascularization.

The purpose of this study was to develop freeze-dried chitosan formulations that can be solubilized in platelet-rich plasma (PRP) to form injectable implants for tissue repair. A systematic approach to adjust formulation parameters, including chitosan number average molar mass (Mn ), chitosan concentration and lyoprotectant concentration, was undertaken to identify compositions that would rapidly (< 1 min) and completely solubilize in PRP, would have paste-like handling properties upon solubilization and coagulate rapidly (< 5 min) to form solid chitosan-PRP hybrid implants that are stable and homogenous. Freeze-dried cakes containing calcium chloride, as well as distinct chitosan Mn , chitosan concentration and lyoprotectant concentration, were prepared. PRP was used to solubilize the freeze-dried cakes and assess in vitro and in vivo performance, the latter as dorsal subcutaneous injections into New Zealand White rabbits. Freeze-dried polymer formulations containing low and medium chitosan Mn and concentrations were rapidly and completely solubilized in PRP. The paste-like chitosan-PRP mixtures coagulated quickly to form solid chitosan-PRP hybrids, which retracted much less than PRP-only controls. Homogeneous dispersion of chitosan within the hybrid clots was strongly dependent on chitosan Mn , and occurred only with medium Mn chitosan. Chitosan-PRP hybrid clots were resident subcutaneously in vivo until at least 2 weeks while PRP controls were quickly degraded in one day. Compared to PRP alone, chitosan-PRP hybrids had much greater capacity to induce local cell recruitment accompanied by angiogenesis, suggesting a strong potential for their use in regenerative medicine.