Towards truly bio-integrative mobility assistance

The use and development of exoskeletal devices are rapidly increasing. These devices are used in order to assist in every-day activities, aid in rehabilitation, or increase abilities. Although success rates are high in achieving these goals in small targeted groups (Young and Ferris, 2016), many problems still exist in addressing the range of conditions and needs in the wider population. One of the main problems originates from the interface between the hard device and the soft tissue of the human body. It is estimated by Cherry et al. (2016) that up to 50% of the power supplied to move the exoskeleton is absorbed by compression of the soft tissue. This could be the cause of the common deep sheer tissue injury which could ultimately lead to ulcerations (Highsmith et al., 2011). It is no surprise that these problems limit the use of these assistive devices and therefore their success rates.
My PhD will focus on this body-device interface which is not yet well understood, with the ultimate aim of eradicating the problems associated with it. If this research proves successful, countless number of people could benefit, from assisting the elderly in everyday activities, to spinal cord patients undergoing rehabilitation, to increasing independence in amputees and reducing the number of follow up appointments required. In addition, an emphasis will be put on cost reduction in an attempt to allow accessibility to patients in third world countries.
Study of the body-device interface will focus on two key applications: 1. lower limb prosthetic sockets for amputees; and 2. soft wearable lower limb assist devices for the elderly. Discomfort leads to the reluctance of using these assistive devices, causing patients to become highly dependent on others, unable to move around freely. Additional problems such as fluctuations in residual stump volume and oedema will require the patient to attend multiple follow-up appointments in order to alter the fit of the prosthetic socket or wearable device (Sanders and Fatone, 2015). My research will focus on the development of intelligent lower limb interfaces between human tissue and machine materials that would adapt to the patients' ever fluctuating conditions and that would alleviate the deep sheer tissue injury. This can be achieved, for example, by supporting the residual limb only when and where required. Alternatively, totally soft prosthetic sockets and assist devices may be created, eliminating the hard-device-to-soft-tissue interface altogether.
In order to achieve this, sheer within the deep tissue and volume fluctuations need to be quantified and mapped throughout the gait cycle. A study would need to be conducted as to which method would provide the most accurate representation. Methods considered will include in-clinic measurements such as ultrasound (potentially 3D and spectrography) and Diffusion Tensor Imaging (DTI) and wearable measurements such as pressure and audio-frequency. Once these elements have been determined, Finite Element (FE) modelling could be used to help visualise the tissue stresses and strains occurring, providing a good starting point for designing an adaptive liner, new socket or bio-interface device, including material, sensor and actuation selection. Once a prototype has been created, it would need to be tested on subjects. This could be done with the use of a Motek Caren system (Buis, University of Strathclyde), allowing accurate analysis of gait, paying particular attention to gait symmetry. The potential longer term comfort benefits would need to be determined with a longer trial period, but initial evaluation will be conducted using formal qualitative evaluations with guidance from experts in experimental psychology (Kent, UoB) and user studies (Turton, UWE). Finally, the aesthetics of the new device would need to be addressed, as this will ultimately determine the patients' likelihood of utilising it and thus benefitting from it.