A model for pressure enhancement in the diabetic nerve: simulations of diabetic rat peripheral nerve and nerve collagens

We hypothesize that the extracellular matrix of both the endoneurium and epineurium remodel in response to the modified chemical and mechanical environment induced by diabetic peripheral neuropathy. Here, we describe quantitative comparisons of mechanical properties based on uniaxial testing, endoneurial fluid pressure (EFP) measurement, image analysis, and content (collagens I, III and IV) analysis of healthy and diabetic sciatic nerve collagens from Sprague-Dawley and BioBreeding rats. Nonlinear response of fibrous structures generally results from three phenomena: alignment of fibers, sequential failure of fibers in the array, or nonlinear response of the fibers themselves. Our preliminary approach employs a thin-walled pressure vessel assumption to model mechanical response of ex vivo tissue relaxation and uniaxial stretching at the millimeter scale. We also present results of a preliminary study of collagen fibers´ mechanics, using a sinusoidal bundle-theory assumption, wherein equal load sharing among fibers is assumed. Measured moduli of epineuria are in general agreement with model results for the pressure vessel model, for literature values of modulus and measured EFP. The bundle theory demonstrably captures both the toe and yield regions in the tissue. Results suggest that a multiscale approach is needed to model tissue-property changes during remodeling.