Bioadhesive polymeric films based on usnic acid for burn wound treatment: Antibacterial and cytotoxicity studies

Usnic acid (UA) is a lichenic secondary metabolite useful for the treatment of burn wounds thanks to its antimicrobial activity, particularly toward strains responsible for their infections. However, the poor solubility is the main factor limiting the activity and thus its use in health care products. Adhesive polymeric films were designed to improve UA use by enhancing its bioavailability in the wounded tissues. Three different NaCMC hydrogel films, NaCMC 2% alone (F1), mixed to PVP K90 0.1% (F2) or to Carbopol 971 P 0.1% (F3), were prepared by casting method. Ex vivo experiments performed on pig skin samples showed their suitable adhesion capacity. in vitro release test, performed using the extraction cell, showed that film F2 provides the highest UA concentrations. Differential scanning calorimetry and X-ray analyses performed on the three films highlighted that UA is present in a more soluble form in F2. The in vitro antibacterial activity studies demonstrated that F2 is the most effective film against UA sensitive bacteria S. Epidermidis, E. Faecalis, B. Cereus and S. Pyogenes. In vitro cytotoxicity assays on human keratinocytes and fibroblasts showed that cells viability is not compromised.