Application of homogenization theory to the study of trabecular bone mechanics

It is generally accepted that the strength and stiffness of trabecular bone is strongly affected by trabecular microstructure. It has also been hypothesized that stress induced adaptation of trabecular bone is affected by trabecular tissue level stress and/or strain. At this time, however, there is no generally accepted (or easily accomplished) technique for predicting the effect of microstructure on trabecular bone apparent stiffness and strength or estimating tissue level stress or strain. In this paper, a recently developed mechanics theory specifically designed to analyze microstructured materials, called the homogenization theory, is presented and applied to analyze trabecular bone mechanics. Using the homogenization theory it is possible to perform microstructural and continuum analyses separately and then combine them in a systematic manner. Stiffness predictions from two different microstructural models of trabecular bone show reasonable agreement with experimental results, depending on metaphyseal region, (R2>0.5 for proximal humerus specimens, R2 <0.5 for distal femur and proximal tibia specimens). Estimates of both microstructural strain energy density (SED) and apparent SED show that there are large differences (up to 30 times) between apparent SED (as calculated by standard continuum finite element analyses) and the maximum microstructural or tissue SED. Furthermore, a strut and spherical void microstructure gave very different estimates of maximum tissue SED for the same bone volume fraction (BV/TV). The estimates from the spherical void microstructure are between 2 and 20 times greater than the strut microstructure at 10-20% BV/TV.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29647/1/0000736.pd

Influence of Visual Feedback on Passive Tactile Perception of Speed and Spacing of Rotating Gratings

Abstract. We studied the influence of visual feedback on the tactual perception of both speed and spatial period of a rotating texture. Participants were placed in a situation of perceptual conflict concerning the rotation speed of a cylindrical texture. Participants touched a cylindrical texture of gratings rotating around its axis at a constant speed, while they watched a cylinder without gratings rotating at a different speed on a computer screen. Participants were asked to estimate the speed of the gratings texture under the finger and the spacing (or spatial period) of the gratings. We observed that the tactual estimations of both speed and spacing co-varied with the speed of the visual stimulus, although the cylinder perceived tactually rotated at a constant speed. The first effect (speed effect) could correspond to the resolution of the perceptual conflict in favor of vision. The second effect (spacing effect) is apparently surprising, since no varying information about spacing was provided by vision. However, the physical relation between spacing and speed is well established according to every day experience. Thus, the parameter extraneou

Design and Performance of a Tactile Shape Display Using RC Servomotors (Short Paper)

Tactile displays are used to convey small-scale force and shape information to the fingertip. We describe a 6x6 tactile shape display design that is low in cost and easily constructed. It uses commercially available RC servomotors to actuate an array of mechanical pins. The pins deflect a maximum of 2mm. with a resolution of 0.1mm. The pin center spacing is 2mm and the pin diameter is 1mm. For the maximum deflection of 2mm, the display can represent frequencies up to 7.5 Hz; smaller deflections lead to achievable frequencies up to 25 Hz because the servos are slew-rate limited. This design is wel suited to tactile display research, as it offers reasonable performance in a robust and inexpensive package

Interaction of visual and haptic information in simulated environments: texture perception

This paper describes experiments relating to the perception of the roughness of simulated surfaces via the haptic and visual senses. Subjects used a magnitude estimation technique to judge the roughness of “virtual gratings” presented via a PHANToM haptic interface device, and a standard visual display unit. It was shown that under haptic perception, subjects tended to perceive roughness as decreasing with increased grating period, though this relationship was not always statistically significant. Under visual exploration, the exact relationship between spatial period and perceived roughness was less well defined, though linear regressions provided a reliable approximation to individual subjects’ estimates

Perceiving Surface Roughness via a Rigid Probe: Effects of Exploration Speed and Mode of Touch

Two experiments investigated the psychophysical consequences for roughness perception of altering the speed of motion with which textured surfaces are explored using a rigid probe. Two speed ranges were used: a 10-fold change (Experiment 1) and a 4-fold change (Experiment 2). Relative motion was altered both by moving the probe actively over a stationary surface (active mode) and by moving the surfaces under the stationary probe (passive mode). Substantial effects of speed were obtained. The results are examined both in terms of the complex effects of speed on the attributes of the psychophysical roughness functions and in terms of the systematic change in the magnitude of the speed effect contingent on the size of the speed range. We also consider how best to minimize any potentially harmful effects of speed on haptic exploration of simulated textures using haptic interfaces. Two operator training procedures are proposed to achieve effective haptic exploration strategies

Can the Efficiency of a Haptic Display be Increased by Short-Time Practice in Exploration?

The main aim was to investigate if short-term practice in exploration with a PHANToM can improve performance. A second aim was to find out if some exploration modes are more successful than other modes. Ten participants practiced exploration of nine blocks of 24 virtual objects distributed over three days. The result was that the performance for a majority improved during this practice, but that there were large individual differences. It was suggested that one of the modes has some advantage. A main conclusion is that there is a high risk that studies of displays with users without practice underestimate their usefulness