Mesenchymal stromal/stem cell-interpenetrating network biomatrices for modulating inflammatory host response in cutaneous healing and phagocyte-mediated impact on Staphylococcus aureus bioburden

Biomaterials that incorporate therapeutically beneficial cells are increasingly being utilized in the fields of tissue engineering and regenerative medicine to enhance spatial localization and fill critical defects that results from trauma or disease. Designing supportive constructs that can maintain cell viability and function when implanted in vivo is a critical challenge that is being investigated by current biomaterials research investigators. Moreover, developing biomaterials that minimized adverse host foreign body response are critical for maintaining the fidelity of the biomaterial-cell constructs and for favorable promotion of wound healing. In this investigation we developed thiol-ene photopolymerized interpenetrating networks (IPNs) consisting of ECM-based gelatin and synthetic poly(ethylene) glycol diacrylate (PEGda) that had previously been applied as effective wound dressing to partial thickness and full thickness wounds in pigs and rats. This hydrogel platform was utilized to encapsulate MSCs, which were characterized for viability and retention of their immunomodulatory and multidifferentiation properties in the presence of biomatrix-adherent monocyte/macrophages. MSCs remained viable and suppressed inflammation (ie. decreased TNF-alpha expression) while promoting a pro-healing phenotype in biomatrix-adherent monocyte/macrophages designated as TNF-alphalow, IL-6high, IL-10 high, IL-12low by day 4. Encapsulated MSCs also retained their multidifferentiation capacity (differentiation into adipocytes, chondrocytes, and osteoblasts) albeit to varying degrees that was dependent on the material type (gelatin/poly(ethylene) glycol or collagen) or whether cultured in the presence of biomatrix-adherent monocyte/macrophages. Sprague-Dawley rat MSCs were rapidly encapsulated in gelatin/poly(ethylene) glycol IPNs via a thiol-ene Michael-type addition reaction and were directly applied as provisional dressings to full-thickness wounds. The three-way interaction of the MSCs, gelatin/poly(ethylene glycol) biomatrices, and host immune cells and adjacent resident cells in the wound microenvironment favorably modulated wound progression and host response. This was primarily indicated by attenuate immune cell infiltration, lack of foreign body giant cell (FBGC) formation, accelerated wound closure and re-epithelialization as well as enhanced neovascularization and granulation tissue formation by 7 days. Likewise, elevated infiltration of CD68+ macrophages at 4 days for both gelatin/PEG hydrogels and MSC-gelatin/PEG biomatrices was associated with accelerated wound closure and re-epithelialization at post-operative day 7.