Substrate stiffness regulates type II diabetic fibroblast phenotype and metabolic activity.

In people living with diabetes, impaired wound healing is a major concern as the formation of ulcerated wounds can drastically reduce both the effectiveness of the healing process and the quality of life of the patient. The healing of dermal wounds in particular involves a patient's fibroblasts building up a strong extracellular matrix of mostly collagen I and collagen III fibers, which the cells of diabetic patients struggle to do. Extracellular matrix stiffness, and growth substrate stiffness in general, have already been shown to have a significant effect on the growth and development of already existent cells, and in diabetic dermal fibroblasts, morphological and physiological characteristics associated with the healing process appear to be altered from their healthy state. In this study we utilized a PDMS surface with a stiffness comparable to a wound environment (16 kPa) and a softer surface (0.2 kPa) to study the effects on diabetic and normal fibroblasts. We found diabetic fibroblast morphology became more fibroblast like when placed on the softer surfaces. This was demonstrated by a 15.6% decrease in the aspect ratio and a 16.4% increase in the circularity. The presence of the stress fibers was decreased by 19.4% in diabetic fibroblasts when placed on a softer surface. The proliferation rate of the diabetic fibroblasts was unaffected by the change in stiffness, but the metabolic activity greatly decreased (76%) on the softer surface. The results suggest that the softer surface may have a therapeutic effect on diabetic fibroblast metabolic activity. Further studies could focus on investigating this relationship and utilize it in tunable biomaterials to facilitate and accelerate the healing process for diabetic wounds.

In Vitro and In Vivo Assessment of the Infection Resistance and Biocompatibility of Small-Molecule-Modified Polyurethane Biomaterials.

Bacterial intracellular nucleotide second messenger signaling is involved in biofilm formation and regulates biofilm development. Interference with the bacterial nucleotide second messenger signaling provides a novel approach to control biofilm formation and limit microbial infection in medical devices. In this study, we tethered small-molecule derivatives of 4-arylazo-3,5-diamino-1H-pyrazole on polyurethane biomaterial surfaces and measured the biofilm resistance and initial biocompatibility of modified biomaterials in in vitro and in vivo settings. Results showed that small-molecule-modified surfaces significantly reduced the Staphylococcal epidermidis biofilm formation compared to unmodified surfaces and decreased the nucleotide levels of c-di-AMP in biofilm cells, suggesting that the tethered small molecules interfere with intracellular nucleotide signaling and inhibit biofilm formation. The hemocompatibility assay showed that the modified polyurethane films did not induce platelet activation or red blood cell hemolysis but significantly reduced plasma coagulation and platelet adhesion. The cytocompatibility assay with fibroblast cells showed that small-molecule-modified surfaces were noncytotoxic and cells appeared to be proliferating and growing on modified surfaces. In a 7-day subcutaneous infection rat model, the polymer samples were implanted in Wistar rats and inoculated with bacteria or PBS. Results show that modified polyurethane significantly reduced bacteria by ∼2.5 log units over unmodified films, and the modified polymers did not lead to additional irritation/toxicity to the animal tissues. Taken together, the results demonstrated that small molecules tethered on polymer surfaces remain active, and the modified polymers are biocompatible and resistant to microbial infection in vitro and in vivo.