Extracellular matrix repair and organization of chronic infected diabetic wounds treated with methacrylated chitosan-based hydrogels

Diabetic foot ulcers (DFUs) are a multifactorial medical problem that require multifaceted approaches for effective healing. Most research on DFU healing has concentrated on promoting wound closure, with less emphasis on the quality of repaired tissue. This is problematic, however, since quality of the repaired tissues can have potential to improve wound healing outcomes and limit re-ulceration. If more functionally active dermis replaces the lost tissue, this can effectively maximize strength, organization, and overall structure of the plantar surface. Additionally, DFUs commonly show multi-strain infection, which further exacerbates the non-healing status of these wounds. Treatment of chronic wounds can be benefitted by application of oxygen and localized infection treatment, both can be achieved via our methacrylated chitosan-based (MACF) hydrogel. A non-healing diabetic infected wound model was used to explore extracellular matrix (ECM) organization, tensile strength, and metabolomic profiles at a 21-day endpoint as a marker for maturation and improved functionality of repaired tissues over normal scar formation. Effective remediation of infection was achieved with 14 days of polyhexamethylene biguanide (PHMB) application with improved wound repair compared to continuous treatment. Prolonged (21 day) application of PHMB showed resulting necrosis, although standard application times for patients with infected wounds can reach up to 28 continuous days. Biaxial mechanical analysis showed improved isotropic strength of infected tissues treated with MACF with PHMB stopped on D14, supported by collagen fiber orientation in second harmonics generation (SHG) imaging. Oxygenating MACF treatments also improved collagen deposition through the enhancement of the hydroxyproline fibrillary collagen synthesis pathway. These structural and mechanical results demonstrate a promising potential treatment for infected diabetic foot ulcers which shows improved dermal functionality. STATEMENT OF SIGNIFICANCE: Diabetic foot ulcers are a multifaceted problem in the medical field exacerbated by infection, with potential for gangrene, lower limb amputation, sepsis, or death. Current treatment regimens include oxygen therapy, physical debridement, and strong antibacterials. However, there is a lack of multi-faceted approaches, which we have designed in our oxygenating chitosan-based hydrogels capable of delivering antibiotics. Treatments currently focus on closure of wounds; however, functionality of regenerated tissues are limited due to fibrotic scar formation. Therefore, we have chosen to focus not only on closure, but also quality of regenerated tissues through mechanical testing and analysis of extracellular matrix composition and organization, with a goal of improving functionality of regenerated tissues.