"Cutaneous chronic wounds are characterized by the absence of healing after six weeks. The classic treatment is the debridement of the wound bed followed by a compression method. When the treatment is not efficient enough, the application of wound dressings is required. To date, no dressings are appropriated to treat the different kinds of wounds. Nowadays, research orientation is towards medicated wound dressings incorporating therapeutic molecules within biomaterials in order to favor skin repair. In this study, dense collagen/PLGA composite hydrogels have been developed to deliver dexamethasone or spironolactone in a controlled manner to modulate inflammation and favor wound healing. To evaluate composite hydrogels as a novel medicated wound dressing, their physical properties, drug loading and release kinetic were analyzed. Then, the in vivo performance of composites was evaluated in a pig model of impaired wound healing.
Dense fibrillar collagen hydrogels concentrated at 40 mg/mL were incubated in PLGA solutions containing dexamethasone or spironolactone for 24 hours. Different chain lengths from 7 to 60 kDa were tested. Then, the mixtures were incubated in PBS to trigger in situ PLGA nanoprecipitation within the collagen network. The ultrastructure and the mechanical properties of composite hydrogels were analyzed. Last, the drug release kinetic from composites was studied over one month and their cytotoxicity evaluated on fibroblasts and keratinocytes using a live/dead assay. Composite hydrogels loaded with spironolactone were then applied onto full thickness wounds of a pig model. Their effect on wound closure and re-epithelialization was evaluated.
The nanoprecipitation enabled the immobilization of a large amount of PLGA regardless of the chain length (50 % of the total mass). The presence of PLGA negatively impacted the swelling properties but all hydrogels exhibited a high degree of hydration (over 80%). Unlike PLGA 28 and 60 kDa, PLGA 7 kDa did not altered the hydrogel deformability and doubled the hydrogel stiffness. The ultrastructure analysis revealed the presence of polydispersed nano/microparticles at the surface of collagen fibrils. Compared to pure collagen hydrogels, the drug loading in all composite hydrogels was 5 times higher. The release kinetic of spironolactone and dexamethasone from collagen/ PLGA 7kDa hydrogels was quasi constant over the first two weeks and complete after a month. Unlike pure collagen hydrogels, no burst release was observed. Increasing the chain length negatively impacted the drug delivery as only 20% of the initial dose was released at day 28 for PLGA 60 kDa. Cell viability experiments showed the absence of cytotoxic effect of composite hydrogels on fibroblasts and keratinocytes regardless of the PLGA type used. The in vivo experiment in pig revealed a high performance of collagen/PLGA composite hydrogels on wound healing. Spironolactone loaded composite hydrogels improved wound closure by 50% and permitted a complete re-epithelialization after 6 days.
Taken together, these results show that dense collagen/PLGA composite hydrogels are promising medicated wound dressings for the treatment of chronic wounds as they deliver constant doses of drugs favoring skin repair, possess good physical properties and promote wound healing in vivo."