Determining the effect of hydration upon the properties of ligaments using pseudo Gaussian stress stimuli.

The level of tissue hydration is known to effect viscoelastic material properties. However, prior studies have not fully investigated the effect of hydration on dynamic behavior nor compared the results of transient and dynamic behavior. The material properties of medial collateral rat knee ligaments were studied in relation to hydration, using (sequentially) 0.

Rat cutaneous RA afferents activated by two-dimensional skin stretch.

Skin develops biaxial stresses and strains when stretched. Rapidly adapting cutaneous mechanoreceptor neurons are known to be stretch sensitive, yet in the past, they have been studied using stretch stimuli applied along only a single direction. In this study, cutaneous rapidly adapting mechanoreceptors were studied in preparations of isolated skin in which the skin was stretched dynamically using biaxial stretch stimuli and in which loads and displacements were measured along two directions.

Stretch sensitivity of cutaneous RA mechanoreceptors in rat hairy skin.

Twenty-five rapidly adapting mechanoreceptor afferents were recorded in an in vitro preparation of rat skin and nerve. Single units were recorded while the skin was subjected to dynamic uniaxial stretch using a pseudo-Gaussian noise (PGN) input waveform. Force was the controlled variable in stretch stimuli.

Using electrical noise to enhance the ability of humans to detect subthreshold mechanical cutaneous stimuli.

Stochastic resonance (SR) is a phenomenon wherein the response of a nonlinear system to a weak input signal is optimized by the presence of a particular, nonzero level of noise. Our objective was to demonstrate cross-modality SR in human sensory perception. Specifically, we were interested in testing the hypothesis that the ability of an individual to detect a subthreshold mechanical cutaneous stimulus can be significantly enhanced by introducing a particular level of electrical noise.

Stretch responses of cutaneous RA afferent neurons in mouse hairy skin.

Rapidly adapting (RA), stretch-sensitive neurons were recorded in vitro, using an isolated preparation of skin and nerve from mouse hindlimb. The skin was stretched uniaxially using a pseudo-Gaussian noise stimulus. Loads and displacements were recorded as were spike responses of single RA afferent neurons.

Three-dimensional load analysis of indentation stimulators.

The properties of three types of indentation stimulators: filament indenters, a spring gauge indenter, and an electromechanical stimulator, were evaluated by actuating each device against a 3-direction load cell. The on-axis loads produced by filament indenters were independent of the degree of buckling. The off-axis loads produced by a filament increased with the degree of buckling of the filament, and had magnitudes that were up to 25% of the on-axis load.

Stretch sensitivity of cutaneous afferent neurons.

Experiments were done to characterize responses to stretch and to determine what stretch-related mechanical variables are most closely associated with stretch. Cutaneous afferent neurons were recorded using an in vitro preparation of rat hairy skin. SA2 afferents and mechanically sensitive C afferents were studied using static stretch stimuli in which the skin was stretched along different directions.

Using uniaxial pseudorandom stress stimuli to develop soft tissue constitutive equations.

A nonlinear systems identification method was used to develop constitutive equations for soft tissue specimens under uniaxial tension. The constitutive equations are developed from a single test by applying a pseudorandom Gaussian (PGN) stress input to the specimen, measuring the resulting strain, and calculating the Volterra-Wiener kernels. First and second order kernels were developed for two tissues with widely different properties, rat medial collateral knee ligaments, and rat skin.