M. M. Ibrahim1, E. R. Lorden2, K. J. Miller1, L. Bashirov1, E. Hammett2, C. Quiles1, A. Rastegarpour1, A. Selim3, K. W. Leong2, H. Levinson1,3 1Duke University Medical Center,Department Of Surgery, Division Of Plastic Surgery,Durham, NC, USA 2Duke University Medical Center,Department Of Biomedical Engineering,Durham, NC, USA 3Duke University Medical Center,Department Of Pathology,Durham, NC, USA
Introduction:
Over 2.4 million Americans and tens of millions of patients worldwide suffer from hypertrophic scar (HSc) contraction following thermal injuries. HSc contraction is a debilitating condition that results in disfigurement and decreased range of motion in affected joints. The current standard of care involves skin grafting with or without the placement of a collagen based, biodegradable, bioengineered skin equivalent (BSE). Commercial BSEs assist in tissue regeneration, but do not focus on mitigating the debilitating effects of HSc and they are marginally effective. To overcome this significant unmet medical need, we have created and tested an elastomeric, polyurethane (PU) based BSE that will last throughout the remodeling phase of repair. In unwounded skin, collagen is arranged randomly, myofibroblasts are absent, and dermal stiffness is low. Conversely, in scar contractures, collagen is arranged in linear arrays, myofibroblast density is high, and dermal stiffness increases. The electrospinning process allowed us to create scaffolds with randomly-oriented fibers that will promote random cellular orientation, decrease myofibroblast formation, and mitigate HSc contraction.
Methods:
Electrospun PU scaffolds were fabricated, covalently coated with bovine type-1 collagen, characterized for their tensile mechanical properties, and tested in vivo. Scaffolds were surgically inserted beneath skin grafts in a validated immune competent murine burn and HSc model we have previously developed. Wounds were excised at day 30 post-surgery. Collagen was assessed with Masson. Macrophages were detected with F4/80 immune. Vascularity was assessed with CD31 immune. Myofibroblasts were assessed with alpha-smooth muscle actin (ASMA) immune. Elastic moduli were analyzed using a microstrain analyzer. All were compared to Integra™.
Results:
In vivo, at D30, collagen coated PU scaffolds integrated into the host tissue and restricted wound contraction to 70±4% of the original wound size. Meanwhile, control mice treated with skin graft alone contracted to 45±2%, while wounds treated with Integra™ beneath skin graft contracted down to 28±1.5% of the original size. Histological analysis demonstrated that PU scaffolds promote fibroblast invasion, angiogenesis, and macrophage recruitment compared to skin graft alone and Integra™. ASMA stains showed decreased numbers of myofibroblasts in PU scaffolds compared to control skin grafts and Integra™. Elastic modulus of excised PU treated wounds was significantly lower than skin-grafted control scars.
Conclusion:
These data suggest that collagen-coated elastomeric electrospun PU scaffolds provide mechanical support to prevent wound bed contraction during healing, and decrease myofibroblast activation associated with HSc . Our long-term goal is to develop a rationally designed, translational medical therapy to mitigate HSc,