Novel Biodegradable Polymeric Microparticles Facilitate Scarless Wound Healing by Promoting Re-epithelialization and Inhibiting Fibrosis

Despite decades of research, the goal of achieving scarless wound healing remains elusive. One of the approaches, treatment with polymeric microcarriers, was shown to promote tissue regeneration in various in vitro models of wound healing. The in vivo effects of such an approach are attributed to transferred cells with polymeric microparticles functioning merely as inert scaffolds. We aimed to establish a bioactive biopolymer carrier that would promote would healing and inhibit scar formation in the murine model of deep skin wounds. Here we characterize two candidate types of microparticles based on fibroin/gelatin or spidroin and show that both types increase re-epithelialization rate and inhibit scar formation during skin wound healing. Interestingly, the effects of these microparticles on inflammatory gene expression and cytokine production by macrophages, fibroblasts, and keratinocytes are distinct. Both types of microparticles, as well as their soluble derivatives, fibroin and spidroin, significantly reduced the expression of profibrotic factors Fgf2 and Ctgf in mouse embryonic fibroblasts. However, only fibroin/gelatin microparticles induced transient inflammatory gene expression and cytokine production leading to an influx of inflammatory Ly6C+ myeloid cells to the injection site. The ability of microparticle carriers of equal proregenerative potential to induce inflammatory response may allow their subsequent adaptation to treatment of wounds with different bioburden and fibrotic content

Fibroblasts upregulate expression of adhesion molecules and promote lymphocyte retention in 3D fibroin/gelatin scaffolds

Bioengineered scaffolds are crucial components in artificial tissue construction. In general, these scaffolds provide inert three-dimensional (3D) surfaces supporting cell growth. However, some scaffolds can affect the phenotype of cultured cells, especially, adherent stromal cells, such as fibroblasts. Here we report on unique properties of 3D fibroin/gelatin materials, which may rapidly induce expression of adhesion molecules, such as ICAM-1 and VCAM-1, in cultured primary murine embryonic fibroblasts (MEFs). In contrast, two-dimensional (2D) fibroin/gelatin films did not show significant effects on gene expression profiles in fibroblasts as compared to 3D culture conditions. Interestingly, TNF expression was induced in MEFs cultured in 3D fibroin/gelatin scaffolds, while genetic or pharmacological TNF ablation resulted in diminished ICAM-1 and VCAM-1 expression by these cells. Using selective MAPK inhibitors, we uncovered critical contribution of JNK to 3D-induced upregulation of these adhesion molecules. Moreover, we observed ICAM-1/VCAM-1-dependent adhesion of lymphocytes to fibroblasts cultured in 3D fibroin/gelatin scaffolds, but not on 2D fibroin/gelatin films, suggesting functional reprogramming in stromal cells, when exposed to 3D environment. Finally, we observed significant infiltration of lymphocytes into 3D fibroin/gelatin, but not into collagen scaffolds in vivo upon subcapsular kidney implantation in mice. Together our data highlight the important features of fibroin/gelatin scaffolds, when they are produced as 3D sponges rather than 2D films, which should be considered when using these materials for tissue engineering