Determining frictional properties of pants and cushion cover materials using human soft tissue and a rigid sled and how they affect seated shear forces.

Shear forces on the buttocks while seated are directly linked to friction, yet the frictional properties at the seat interface are unknown. Shear forces are one of the factors related to increase risk of pressure injury formation. The goals of this study included determining coefficients of friction between three cushion covers and two clothing fabrics using a mechanical system as well as human participants and to evaluate the impact of the cushion covers on shear loading on the buttocks while seated. A chair with separate seat pan tilt and back recline movements was built and instrumented with reflective markers and a load cell. A motion capture system and load cell were used to determine the angles of seat pan tilt at which the sled and participants started sliding, as well as shear forces at three recline angles for three cushion covers (vinyl, one-layer nylon, and two-layer nylon). Results showed the vinyl and two-layer nylon cushion covers respectively had the largest and smallest coefficients of friction for both pants materials. The coefficients of friction calculated with the human participants and rigid sled were within 10% of each other, demonstrating similar results. Further, increasing back recline increased shear load on the buttocks, while the two-layer nylon cover reduced shear forces seen on the buttocks. This work furthers the understanding of shear loading on the buttocks, will aid in the protocols for reducing pressure injuries, and suggests that coefficients of friction found using rigid bodies may be applied to deformable bodies.

Mapping kinematic functional abilities of the hand to three dimensional shapes for inclusive design.

Loss of hand function can have adverse effects on an individual's ability to maintain independence. The ability to perform daily activities, such as food preparation and medication delivery, is dependent on the hand's ability to grasp and manipulate objects. Therefore, the goal of this research was to demonstrate that three dimensional (3D) modeling of hand function can be used to improve the accessibility of handheld objects for individuals with reduced functionality through informed design. Individual models of hand functionality were created for 43 participants and group models were developed for groups of individuals without (Healthy) and with reduced functionality due to arthritis (RFA) of the hand. Cylindrical models representative of auto-injectors of varying diameters were analyzed in 3D space relative to hand function. The individual model mappings showed the cylinder diameter with the highest mapped functional values varied depending on the type of functional weighting chosen: kinematic redundancy of fingertip pad positional placement, fingertip pad orientation, or finger force directionality. The group mappings showed that for a cylinder to be grasped in a power grasp by at least 75% of the Healthy or RFA groups, a diameter of 40mm was required. This research utilizes a new hand model to objectively compare design parameters across three different kinematic factors of hand function and across groups with different functional abilities. The ability to conduct these comparisons enables the creation of designs that are universal to all - including accommodation of individuals with limits in their functional abilities.

Comparison between healthy and reduced hand function using ranges of motion and a weighted fingertip space model.

Detection and quantification of changes in hand function are important for patients with loss of function and clinicians who are treating them. A recently developed model, the weighted fingertip space (WFS) quantifies the hand function of individuals in three-dimensional space and applies kinematic weighting parameters to identify regions of reachable space with high and low hand function. The goal of this research was to use the WFS model to compare and contrast the functional abilities of healthy individuals with the abilities of individuals with reduced functionality due to arthritis (RFA). Twenty two individuals with no reported issues with hand function and 21 individuals with arthritis affecting the hand were included in the research. Functional models were calculated from the ranges of motion and hand dimension data for each individual. Each model showed the volume of reachable space for each fingertip of each hand, the number of ways to reach a point in space, the range of fingertip orientations possible at each point, and the range of possible force application directions (FADs) at each point. In addition, two group models were developed that showed how many individuals in both the healthy and RFA groups were able to reach the same points in space. The results showed differences between the two groups for the range of motion (ROM) measurements, the individual model calculations, and the group models. The ROM measurements showed significant differences for the joints of the thumb, extension of the nonthumb metacarpophalangeal (MCP) joints, and flexion of the distal interphalangeal (DIP) joints. Comparing the models, the two groups qualitatively showed similar patterns of functional measures in space, but with the RFA group able to reach a smaller volume of space. Quantitatively, the RFA group showed trends of smaller values for all of the calculated functional weighting parameters and significantly smaller reachable volume for all of the fingers. The group models showed that all healthy individuals were able to reach an overlapping space, while 18 of 21 RFA individuals were able to reach similar spaces. Combined, the results showed that the WFS model presents the abilities of the hand in ways that can be quantitatively and qualitatively compared. Thus, the potential of this hand model is that it could be used to assess and document the changes that occur in hand function due to rehabilitation or surgery, or as a guide to determine areas most accessible by various populations.