19 research outputs found
Developing a framework for an adaptive transtibial prosthetic socket using FEA-based tissue injury risk estimation and generalised predictive control
No full textTo perform daily activities, people with amputation depend on the socket for stability and proprioceptive feedback for control over their prosthetic. Sockets are bespokely fitted, rarely definitive, and require iterative, expensive replacement to accommodate residual limb changes. The socket is the primary load-bearing interface and user comfort is greatly linked to the quality of the socket fit. Poorly fitting sockets cause pain, limb tissue injuries, limited device usage, and potential rejection. Contact stresses at the socket-limb interface and strain of underlying soft tissues greatly determine user comfort and the risk of residuum tissue injury. Adjustable socket technologies exist, but are passive or semi-passive, entrusting responsibility of determining safe interface pressure levels solely on the user’s perception. This research entails a set of theoretical studies developing a framework for an automatically adjustable prosthetic socket system enabling estimation of residuum tissue injury risk for safe interface pressure modulation, within a control system structure. Candidate methods for functional interface actuation were identified, and their design specifications and theoretical models developed and described. A comparative Concept- Design Failure Mode and Effects Analysis was performed, considering the limitations of the different actuation options for the adaptive socket system. This revealed that the probability of detection of some potential design weaknesses largely determines overall failure risk criticality among the actuation options. Also, mitigation measures to address high scoring risks should consider users with compromised sensory perception of discomfort or injury. A study was performed using finite element modelling, to determine the effect of local socket stiffness changes on tissue strain and interface pressure, and between select anatomical regions. Minimal changes in compressive strain (< 2%) indicated negligible cross-effects between regions, and appropriate application of an uncoupled controller configuration for the multiple interface actuators. Application of representative prosthetic loading instances allowed estimation of interface pressure-tissue strain relationships at the actuator locations. These were used as training data to create surrogate models for each location for tissue injury risk assessment within the socket system control framework. Generalised Predictive Control (GPC) was simulated for active interface actuation within estimated safe and functional limits. Optimisation of a cost function to minimise tissue injury risk by adaptive interface pressure control showed adequate dynamic performance. Feasibility of the GPC formulation to satisfy operational requirements, and its influence on actuation performance of the different actuators for prosthetic device usage in several scenarios was demonstrated. This research provides a systematic development platform for designing an adjustable prosthetic socket integrating dynamic monitoring and minimisation of sub-dermal residuum tissue injury risk with active adaptation of the interface pressure. <br/
Adhesives for medical application - Peel strength testing and evaluation of biophysical skin response
No full textBackground: medical adhesives are commonly used for securing wound dressings and medical devices used for diagnostic or therapeutic purposes. Mechanical irritation of skin due to adhesive stripping and repeated application can lead to discomfort and device removal. This study aims to examine the peel strength and skin response to different medical adhesives in a cohort of healthy volunteers.Method: twelve healthy participants were recruited for peel strength testing of three candidate adhesive tapes, and evaluation of the skin response after adhesive removal. A modified ASTM D903 peel strength testing was performed at 180° peeling angle and a rate of 300 mm/min on the forehead, upper back and forearm skin. A longitudinal study was conducted on the forearm and back, with the adhesive samples left in-situ for up to 60 h for analysis of repeat application. The effects of two skin preparation approaches (water and alcohol cleaning) prior to adhesive application were also assessed. Skin biophysical properties were assessed at baseline and at various timepoints following adhesive removal using transepidermal water loss (TEWL), erythema and hydration.Results: peel strength reduced uniformly with repeat application over prolonged periods for all the adhesive samples tested. Skin preparation with water and alcohol cleansing prior to adhesive application increased peel strength at both the back (1.1% and 2.9%), and forearm (21.3% and 20%) sites. There was statistically significant increase from baseline to post-tape application for TEWL, skin redness and hydration (p < 0.001). However, there were no statistically significant differences between adhesive types (TEWL: p = 0.38, SR: p = 0.53, HY: p = 0.46). TEWL increased the most post-adhesion across all test sites and adhesive samples with repeat application (p < 0.05). Two-way ANOVA tests revealed no statistically significant interactions between the effects of application duration and adhesive on skin redness or TEWL for both the back and forearm sites (p > 0.05), though a significant interaction was indicted for hydration at the back site (p = 0.01).Conclusion: this study revealed that site and duration of adhesive application effected peel strength. The corresponding changes in skin properties identified that skin barrier function was disrupted with long-term application of adhesives. The back site was identified to be most reliable for adhesion testing and skin response assessment for future work.</p
Developing a control framework for self-adjusting prosthetic sockets incorporating tissue injury risk estimation and generalized predictive control
No full textTo perform activities of daily living (ADL), people with lower limb amputation depend on the prosthetic socket for stability and proprioceptive feedback. Poorly fitting sockets can cause discomfort, pain, limb tissue injuries, limited device usage, and potential rejection. Semi-passively controlled adjustable socket technologies exist, but these depend upon the user’s perception to determine safe interfacial pressure levels. This paper presents a framework for automatic control of an adjustable transtibial prosthetic socket that enables active adaptation of residuum-socket interfacial loading through localized actuators, based on soft tissue injury risk estimation. Using finite element analysis, local interfacial pressure vs. compressive tissue strain relationships were estimated for three discrete anatomical actuator locations, for tissue injury risk assessment within a control structure. Generalized Predictive Control of multiple actuators was implemented to maintain interfacial pressure within estimated safe and functional limits. Controller simulation predicted satisfactory dynamic performance in several scenarios. Actuation rates of 0.06–1.51 kPa/s with 0.67% maximum overshoot, and 0.75–1.58 kPa/s were estimated for continuous walking, and for a demonstrative loading sequence of ADL, respectively. The developed platform could be useful for extending recent efforts in adjustable lower limb prosthetic socket design, particularly for individuals with residuum sensory impairment.</p
Dataset for publication "Developing a control framework for self-adjusting prosthetic sockets incorporating tissue injury risk estimation and generalized predictive control"
No full textDataset to support paper "Developing a control framework for self-adjusting prosthetic sockets incorporating tissue injury risk estimation and generalized predictive control" in Biomedical Engineering Letters. This dataset contains an Excel spreadsheet containing the raw data behind the results figures in this publication.</span
Dataset supporting the thesis entitled "Developing a Framework for an Adaptive Transtibial Prosthetic Socket using FEA-based Tissue Injury Risk Estimation and Generalised Predictive Control"
No full textRaw data behind simulations and figures for the thesis entitled "Developing a Framework for an Adaptive Transtibial Prosthetic Socket using FEA-based Tissue Injury Risk Estimation and Generalised Predictive Control", University of Southampton, 2020</span
Predictive control for an active prosthetic socket informed by FEA-based tissue damage risk estimation
No full textThis paper presents an architecture for generalized predictive control for an active prosthetic socket system, based on a cost function performance index measure for minimization of residual limb tissue injury. Finite element analysis of a transtibial residuum model donned with a total surface bearing socket was used to provide controller training data and biomechanical rationale for deep tissue injury risk assessment, by estimating the internal deformation state of the soft tissues and the residuum-socket interface loading under a range of prosthetic loading instances. The results demonstrate the concept of this approach for interface actuation modelled as translational spring and damper systems
Dataset for publication "Evidence-Generated sockets for transtibial prosthetic limbs compared with conventional computer-aided designs: a multiple-methods study from the patient’s perspective"
No full textThis dataset supports the publication "Evidence-Generated sockets for transtibial prosthetic limbs compared with conventional computer-aided designs: a multiple-methods study from the patient’s perspective"
This dataset contains: An .xlsx file containing the raw data behind the figures in the linked journal paper.
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A Randomised cross-over study to evaluate the physiological effects of internal air pressure changes in advanced support surface design
No full textHigh specification mattresses periodically redistribute pressure using alternating air cells, offloading tissues. This study aimed to evaluate the effects of alternating air pressure gradients on sacral tissue physiology. This randomised cross-over study recruited 15 healthy participants to test the three mattress settings (fast cycle, normal cycle, and slow cycle). Participants were asked to adopt supine, lateral, and high sitting (head of bed at 40°) postures, whilst transcutaneous tissue gas tensions and interface pressures at the sacrum were continuously monitored. Comparison between mattress settings and postures showed no statistical difference (p > 0.05) between peak pressure index values at the sacrum for each air inflation cycle speed setting. By contrast, a significantly higher sacral (p < 0.05) contact area was observed for high sitting. During high sitting, ischemic responses during both fast and normal air inflation cycle speed settings were recorded. During the slow air inflation cycle speed, most participants (60%-100%) showed high levels of perfusion. The present study identified a main effect of posture on interface pressure and perfusion over the sacrum. The alternating mattress speed influenced local tissue perfusion, with the greatest changes in tissue oxygenation occurring in a high-speed setting
Dataset for publication "Insights into the spectrum of transtibial prosthetic socket design from expert clinicians and their digital records"
No full textThis dataset contains: A simple .csv file containing the raw data behind the figures in the linked journal paper.
The keys for the Excel sheets are as follows:
- Figure 2:
Raw data behind histograms showing relative size distributions of local and gross rectifications for prosthetic limbs designed nominally to patellar tendon bearing (PTB) and total surface bearing (TSB) philosophies.
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Design and Evaluation of a Propulsion System for Small, Compact, Low-Speed Maneuvering Underwater Vehicles
No full textUnderwater vehicles used to perform precision inspection and non-destructive evaluation in tightly constrained or delicate underwater environments must be small, have low-speed maneuverability and a smooth streamlined outer shape with no appendages. In this thesis, the design and analysis of a new propulsion system for such underwater vehicles is presented. It consists primarily of a syringe and a plunger driven by a linear actuator and uses different inflow and outflow nozzles to provide continuous propulsive force. A prototype of the proposed propulsion mechanism is built and tested. The practical utility and potential efficacy of the system is demonstrated and assessed via direct thrust measurement experiments and by use of an initial proof-of-concept test vehicle. Experiments are performed to enable the evaluation and modelling of the thrust output of the mechanism as well as the speed capability of a vehicle employing the propulsion system
