Engineered human skin is commonly fabricated using collagen scaffolds that often have poor mechanical properties. To improve the strength of collagen-based scaffolds, poly(caprolactone) (PCL) was blended with collagen and formed into submicron fibers using electrospinning. At concentrations < 10% PCL (M _PCL /[M _Collagen + M _PCL ] × 100), the PCL component was evenly distributed within the collagen matrix. Increasing the PCL component to 30% caused separation of the collagen and PCL phases forming local domains of PCL within the collagen matrix. Tensile testing indicated that 10–100% PCL concentrations significantly improved the strength and stiffness of the acellular scaffolds. Engineered skin (ES) made with blended collagen–PCL at a concentration of up to 10% PCL did not significantly alter the stratification of the cells, cell proliferation, or epidermal differentiation compared to the 100% collagen group. Ultimate tensile strength of ES fabricated with the collagen–PCL blends was not significantly greater than that of ES made with 100% collagen scaffolds (0% PCL). The 30% PCL group had the least amount of mechanical strength likely caused by poor epidermal formation and reduced cell viability. These results indicate that minimal additions of PCL can be blended with collagen to produce scaffolds suitable for tissue engineering of human skin. However, the increase in scaffold strength with higher PCL concentrations did not result in significantly stronger ES, indicating that high cell viability and proper development of the epidermis are important factors for developing ES with high strength.

Objective: The objective of this work was to causatively link biofilm properties of bacterial infection to specific pathogenic mechanisms in wound healing. Background: Staphylococcus aureus is one of the four most prevalent bacterial species identified in chronic wounds. Causatively linking wound pathology to biofilm properties of bacterial infection is challenging. Thus, isogenic mutant stains of S. aureus with varying degree of biofilm formation ability was studied in an established preclinical porcine model of wound biofilm infection. Methods: Isogenic mutant strains of S. aureus with varying degree (ΔrexB > USA300 > ΔsarA) of biofilm-forming ability were used to infect full-thickness porcine cutaneous wounds. Results: Compared with that of ΔsarA infection, wound biofilm burden was significantly higher in response to ΔrexB or USA300 infection. Biofilm infection caused degradation of cutaneous collagen, specifically collagen 1 (Col1), with ΔrexB being most pathogenic in that regard. Biofilm infection of the wound repressed wound-edge miR-143 causing upregulation of its downstream target gene matrix metalloproteinase-2. Pathogenic rise of collagenolytic matrix metalloproteinase-2 in biofilm-infected wound-edge tissue sharply decreased collagen 1/collagen 3 ratio compromising the biomechanical properties of the repaired skin. Tensile strength of the biofilm infected skin was compromised supporting the notion that healed wounds with a history of biofilm infection are likely to recur. Conclusion: This study provides maiden evidence that chronic S. aureus biofilm infection in wounds results in impaired granulation tissue collagen leading to compromised wound tissue biomechanics. Clinically, such compromise in tissue repair is likely to increase wound recidivism.

Inflammation, following injury, induces cellular plasticity as an inherent component of physiological tissue repair. The dominant fate of wound macrophages is unclear and debated. Here we show that two-thirds of all granulation tissue fibroblasts, otherwise known to be of mesenchymal origin, are derived from myeloid cells which are likely to be wound macrophages. Conversion of myeloid to fibroblast-like cells is impaired in diabetic wounds. In cross-talk between keratinocytes and myeloid cells, miR-21 packaged in extracellular vesicles (EV) is required for cell conversion. EV from wound fluid of healing chronic wound patients is rich in miR-21 and causes cell conversion more effectively compared to that by fluid from non-healing patients. Impaired conversion in diabetic wound tissue is rescued by targeted nanoparticle-based delivery of miR-21 to macrophages. This work introduces a paradigm wherein myeloid cells are recognized as a major source of fibroblast-like cells in the granulation tissue.