SKIN BIOMECHANICS AND MECHANORECEPTOR RESPONSE

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The primary goal of this project continues to be the investigation of the relationship between the biomechanics of the primate fingertip and responses of cutaneous mechanoreceptors during tactile sensing. In the past five years, the application of computational methods to the mechanistic analysis of idealized models of the primate fingertip has contributed to a deeper understanding of the mechanics of contact between the skin and objects of differing shapes, the transmission of the mechanical signals through the skin, and their transduction into neural impulses by cutaneous mechanoreceptors. The specific aims of this proposal are (l) to gradually refine the models so that they closely approximate the geometrical and material properties of the primate fingerpad, (2) to expand the variety of stimuli that are pressed or stroked on the models to include more shapes, soft objects and microtextures, and (3) to perform a series of biomechanical experiments under in vivo conditions using a variety of techniques including the use of videomicroscopy, Magnetic Resonance Imaging (MRI) and computer- controlled mechanical stimulators. The sequence of models will be verified at each stage by comparing their predictions with appropriate data from biomechanical and neurophysiological experiments. Starting points for these investigations are the three dimensional homogeneous models that have already been developed using empirical measurements of the external geometry of monkey and human fingertips using a videomicroscopy system. The necessary software for linear and nonlinear finite element analyses of homogeneous and nonhomogeneous models, as well as the usage of the various computer platforms (including the MIT supercomputer) for the large number of computations have been tested and verified. The major stages of model refinement consist of incorporation of realistic internal geometry based on MRI for nonhomogeneous models, viscoelastic behavior of the fingerpad based on experiments using videomicroscopy, together with geometry and mechanical behavior of papillary ridges based on fine biomechanical experiments with a high precision stimulator. The experiments are designed to help the model development, and together with the previously obtained biomechanical and neurophysiological data, will serve to rigorously verify the models of the fingerpads and transduction mechanisms. Long term benefits of such a quantitative understanding of the origins and mechanisms of tactile information would include the development of good tests for the evaluation of tactile sensibility to aid in rehabilitation of hand-impaired individuals and the design of tactile communication aids for visually impaired and deaf individuals.