Mechanical behaviors of tension and relaxation of tongue and soft palate: Experimental and analytical modeling

Biophysical models of slowly and rapidly adapting mechanosensitive tactile afferents in human tongue

Upon contact, the spike firing patterns of touch afferents encode object attributes such as force, vibration, and spatial geometry. Computational models in cutaneous skin have sought to emulate firing patterns of slowly and rapidly adapting afferents. Herein, for the tongue, we develop biophysical versions of such models, and which rely upon functions and parameters with physiological relevance, as opposed to stimulus features, and are extendable to a broad range of object interactions. The models are evaluated with mechanical inputs relevant to the oral processing of food, in particular, across stress ranges spanning material compliances and periodic vibrations emulating surface sliding. The results indicate the models recapitulate spike firing patterns of human afferents innervating the tongue. Moreover, predicted patterns of spike firing, e.g., the mean and peak firing frequency, first spike latency, and number of spikes, compare favorably with neural recordings across force magnitudes, as do the number of spikes per cycle across a range of periodic amplitudes and frequencies. For extension into a population of afferents in oral mucosa, these single-unit models are a starting point for the further efforts to capture the encoding of higher-level perceptible attributes, e.g., compliance, geometry, surface roughness, and movement velocity.

Region- and layer-specific investigations of the human menisci using SHG imaging and biaxial testing

In this paper, we examine the region- and layer-specific collagen fiber morphology via second harmonic generation (SHG) in combination with planar biaxial tension testing to suggest a structure-based constitutive model for the human meniscal tissue. Five lateral and four medial menisci were utilized, with samples excised across the thickness from the anterior, mid-body, and posterior regions of each meniscus. An optical clearing protocol enhanced the scan depth. SHG imaging revealed that the top samples consisted of randomly oriented fibers with a mean fiber orientation of 43.3 ^o . The bottom samples were dominated by circumferentially organized fibers, with a mean orientation of 9.5 ^o . Biaxial testing revealed a clear anisotropic response, with the circumferential direction being stiffer than the radial direction. The bottom samples from the anterior region of the medial menisci exhibited higher circumferential elastic modulus with a mean value of 21 MPa. The data from the two testing protocols were combined to characterize the tissue with an anisotropic hyperelastic material model based on the generalized structure tensor approach. The model showed good agreement in representing the material anisotropy with a mean r ² = 0.92.