| Author: | Leung, Sin Hang Matthew |
| Title: | Finite element analysis of dynamic plantar pressure distribution to enhance the design of diabetic insole |
| Advisors: | Yick, Kit-lun (SFT) Ng, Sun-pui (SPEED) |
| Degree: | M.Phil. |
| Year: | 2023 |
| Subject: | Orthopedic shoes Foot -- Diseases -- Treatment Diabetes -- Complications -- Prevention Hong Kong Polytechnic University -- Dissertations |
| Department: | School of Fashion and Textiles |
| Pages: | xvi, 132 pages : color illustrations |
| Language: | English |
| Abstract: | Diabetes mellitus (DM) is one of the most concerning diseases worldwide because the ailment has such a large economic burden on health systems. In 2021, more than 422 million people globally suffered from diabetes and the number is increasing every year. Due to the loss of the protective sensation that is associated with neuropathy, diabetic patients have difficulties in responding to pressure, wounds and/or injuries, especially on their feet. Wounds could quickly become infected with a long recovery duration, thus leading to foot ulceration and even foot amputation which greatly deteriorate their quality of life. Diabetic insoles are frequently used to provide optimal fit and reduce the magnitude of plantar pressure. It is anticipated that the three-dimensional (3D) design of diabetic footwear and insoles and the type of footwear material have a major impact on fit and wear comfort, which lead to increased compliance with treatment to prevent neuropathic diabetic foot ulcers. Diabetic insoles can also protect the plantar of the foot thus reducing the risk of such ulcers because they have the most contact with the plantar of the foot and can evenly distribute the pressure throughout the entire plantar. Diabetic insoles are generally made of soft materials, such as polypropylene (PP), ethylene vinyl acetate (EVA), polyethylene (PE), microcellular rubber (MCR), etc. As the pressure offloaded between the insole and plantar of the foot as well as the geometry of the foot during walking differ greatly from those of standing, a more in-depth understanding of the effects of changes in the geometry of the foot and insole material properties on diabetic insoles is therefore important to provide better protection for the diabetic foot. This study began with a discussion on the pressure distribution under different insole conditions during walking. The properties of 3 different traditional insole materials: EVA foam - Lunalastik®, a PE material - PeLite®, and a PU material - Poron®, were outlined. Also, the mean peak pressure of the plantar with the insole and barefoot condition were systematically evaluated. The result showed that the PU material had the best performance which could readily absorb energy and reduce the plantar pressure. The findings of this study provided very useful guidelines to enhance the anatomical design of diabetic insoles to optimize the pressure distribution throughout the plantar of the foot. After that, the geometry of the foot during an entire walking cycle was captured by using a four-dimensional (4D) foot scanning system. Different parts of the foot measured at 3 different walking speeds (slow, normal, and fast) and 5 different stances during walking (first heel contact, first metatarsal head contact, first toe contact, heel take off and metatarsal head take off) were systematically evaluated. The results showed that the foot measurements had no statistical difference with regard to walking speed, while 12 of the 13 foot measurements had a statistical difference with regard to the stances during walking. The deformation ratio could be used to provide a better understanding of the foot deformation which advanced the design and development of diabetic insoles. In addition, considering the very high contact pressure in the rearfoot and forefoot regions, insoles with a braced frame structure that used traditional insole materials were proposed to further reduce the shear stress and contact pressure at the interface between the plantar-insole surface to reduce the risk of foot injury. Finite element models (FEMs) were developed to evaluate the structural changes of the developed braced frame structure upon exertion of compressive forces. Also, the effect of different braced frame structures on the shear stress, contact area as well as the maximum contact force on the plantar were analysed through a finite element analysis (FEA). The validated FEMs showed that the proposed braced frame structure provided a reduction in the shear stress (~21%) and maximum contact force (~55%) in comparison to traditional diabetic insoles. To evaluate the planter pressure during heel strike posture, an auxetic heel pad was examined and a wear trial with the heel pad was subsequently conducted. This was a novel pressure relieving heel pad based on a circular auxetic re-entrant honeycomb structure which was constructed by using 3D printing technology to minimize the pressure on the heel, thus reducing the occurrence of foot ulcers. FEMs were developed to evaluate the structural changes of the developed circular auxetic structure upon exertion of compressive forces. Moreover, the effects of the internal angle of the re-entrant structure on the peak contact force and the mean pressure acting on the heel as well as the contact area between the heel and the pads were investigated through an FEA. Based on the result from the validated FEMs, the proposed heel pad facilitated a distinct reduction in the peak contact force (~ 10%) and the mean pressure (~14%) in comparison to the structure of a conventional diabetic insole (made of PU foam). The wear trial result confirmed that the proposed heel pad offered a better pressure relief performance than the traditional heel pad, hence reducing the risk of heel ulcers. The characterized result of the designed circular auxetic structure not only provided new insights into diabetic foot protection, but also the design and advancement of other impact resistance products. The outputs of this project therefore added a new dimension to diabetic insole design and diabetic foot treatment. More importantly, it could be used to protect the feet and reduce the risk of foot ulcers, and thus preserve the mobility of diabetic patients. |
| Rights: | All rights reserved |
| Access: | open access |
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