In situ biomechanical properties of normal and diabetic nerves: an efficient quasi-linear viscoelastic approach

Biomechanical properties of nerves were investigated using the quasi-linear viscoelastic model. An improved parameter estimation technique based on fast convolution was developed and tested in sciatic nerves of normal and diabetic rats. In situ dynamic compression response of sciatic nerves was obtained by a modified custom-designed compression system. Six normal and five diabetic neuropathic Wistar rats were used. The model derived from the high strain rate (0.1 s(-1)) data could predict the responses of lower strain rates (0.05 and 0.01 s(-1)) satisfactorily. The computation time was cut down 49.0% by using the newly developed technique without increasing the root-mean-square error. The percentage of stress relaxation of the diabetic and normal rats, calculated directly from the experimental data, was not significantly different (51.03+/-1.96% vs. 55.97+/-5.89%, respectively; p=0.247). After model fitting, compared with the QLV parameters of normal nerves, the smaller parameter C for diabetic nerves (0.27+/-0.06 vs. 0.20+/-0.02, p < 0.05) indicated that diabetic nerves had a smaller amplitude of viscous response (stress relaxation). The larger parameter tau(2) of diabetic nerves (199+/-153 s vs. 519+/-337 s, p<0.05) implied that diabetic nerves needed a longer relaxation period to reach equilibrium.