Plasminogen-Loaded Fibrin Scaffold as Drug Delivery System for Wound Healing Applications

Plasminogen is a protein involved in intravascular and extravascular fibrinolysis, as well as in wound healing, cell migration, tissue formation and angiogenesis. In recent years its role in healing of tympanic perforations has been demonstrated in plasminogen deficient mice. The aim of this work was to fabricate a fibrin-based drug delivery system able to provide a local and sustained release of plasminogen at the wound site. Initially, the biological activity of plasminogen was evaluated by in vitro experiments on cell cultures. A metabolic assay (MTT) was carried out on L929 mouse fibroblast to determine the concentration that does not affect cell viability, which turned out to be 64 nM. The effect of plasminogen on cell migration was evaluated through a scratch test on human keratinocytes: cells treated with 64 nM plasminogen showed faster scratch closure than in complete medium. Fibrin scaffold loaded with plasminogen was fabricated by a spray process. SEM analysis showed the typical nano-fibrillar structure of a fibrin scaffold. Tensile tests highlighted significantly higher value of the ultimate stress and strain of fibrin scaffold with respect to fibrin clot. The in-vitro release kinetic showed an initial plasminogen burst, after that the release slowed, reaching a plateau at 7 days. Plasminogen-loaded fibrin scaffold applied in full-thickness diabetic mouse lesions showed a significantly higher closure rate at 14 days than scaffold used as a reference material. Histological analysis demonstrated an improved reepithelization and collagen deposition in granulation tissue in mouse treated with plasminogen-loaded fibrin scaffold in comparison to unloaded fibrin scaffold. The obtained results demonstrated the suitability of the fibrin scaffold loaded with plasminogen as drug delivery system and suggest its use in wound healing applications, such as for the treatment of chronic diabeticulcers.