Over 3 million people in the United States rely on wheelchairs, spending about 12 hours in a wheelchair every day to carry out tasks of daily living [1], [2]. A common and expensive side effect of wheelchair use is the formation of pressure injuries, which are a result of sustained normal and shear pressures on the body, such as those experienced in the buttocks and thighs while seated [3]–[6]. The prevalence of pressure injuries in wheelchair users in care facilities is as high as 47%, and treatment costs up to $120,000 per incident [7], [8]. Because pressure injuries are destructive, both in terms of quality of life and financially, there is a clear need for strategies to prevent them.

Despite advances in technology used to prevent pressure injuries and models that assess risk, both the new technology and models have limitations. Even with the implementation of new wheelchairs, wheelchair cushions, and other pressure injury prevention tools, pressure injury prevalence only declined by one third over the past decade [9]. From the modeling perspective, the most advanced buttock and thigh models still use limited data from humans, excluding critical data from wheelchair users, the population most at risk for developing pressure injuries [10].

As such, the goals of this dissertation were to 1) determine the material properties of wheelchair users’ buttocks and thighs and compare them to those of able-bodied people, 2) to design an articulating chair that can reduce the seated normal pressure on the buttocks, and 3) to evaluate the ability of several seat pan covers to reduce shear pressure on the buttocks while seated.

The first task was to create a protocol to determine the material properties of the buttocks and thighs in a position representative of the seated position and accessible to wheelchair users. Force and deflection data of the buttocks and thighs of able-bodied people were obtained in seated, quadruped, and prone positions. It was found that the buttocks and thighs were similar in the seated and quadruped positions. As the quadruped position was accessible, it was used to test wheelchair users;​ and data collected from the buttocks to the middle regions of the thighs were softer in wheelchair users than able-bodied people, while the distal thighs of wheelchair users were stiffer.

An accessible articulating chair was created with independently rotating parts, including seat pan, back, pelvic support, and thoracic support. The chair was used to collect seated interface pressure data during induced back recline, seat pan tilt, and changes to back articulation in ablebodied individuals and wheelchair users. Recline increased pressure on the buttocks, while seat pan tilt decreased pressure on the buttocks, and changes in back articulation changed pressure patterns on the back.

Three seat pan covers were evaluated for their coefficients of friction when paired with materials used to make pants and their abilities to reduce shear pressure on the buttocks of seated individuals. A sled was used to determine the coefficients of friction of pants materials on vinyl, one-layer nylon, and two-layer nylon seat pan covers. Coefficients of friction were compared to values found using human participants, and finally it was shown that the two-layer nylon seat pan cover reduced shear on seated individuals in the articulating chair while undergoing back recline.

The material property data from the buttocks and thighs and the interface pressure data collected represent advances in both pressure injury risk assessment and prevention. The material property data from wheelchair users were the first of their kind and can be used in finite element models. Data collected from the articulating chair and seat pan covers yielded interface and boundary conditions for models of the seated buttocks and thighs as well as strategies to reduce the normal and shear pressures on the buttocks and thighs, reducing the risk of pressure injuries.