A design for seat cushion and back-supporter using finite element analysis for preventing decubitus ulcer

Abstract

Decubitus ulcer is a disease that causes the necrosis of skin tissue through the disorder of blood circulation on a certain part of the body where bones protrude. This study is aimed at obtaining an optimal design of a set composed of a rubber air-cell seat cushion and back-supporter, showing even distribution of the interface pressure and minimizing its peak value on the buttocks through optimization using the simulation. The finite element (FE) human model was a human body model developed by the MADYMO (mathematical dynamic model; TASS, Netherlands) and consisted of 44 FE models such as skeletal structures, flesh, muscles, and internal organs. For the optimization of a seat cushion and a back-supporter, a basic model for seat cushion and back-supporter were designed using 50th percentile European male model. To design an optimal seat cushion and back-supporter system, the optimization was performed considering the design factors such as the air-cell height of buttocks and thighs, air-cell height of back-supporter, and angle of back-supporter. The results of the sensitivity analysis confirmed the two design factors (height of buttock air-cell and height of thigh air-cell). The optimization result was 55 mm for the buttock air-cell's height, 60 mm for the thigh air-cell's height, 90 mm for the back-supporter air-cell's height, and 100 ° for the back-supporter's angle. Based on this study, there is preliminary evidence to show that the design of seat cushion and back-supporter is necessary to reflect biomechanical characteristics, such as body shape (difference of body shape between thigh and buttocks). A main advantage of air-cell type for seat cushion and back-supporter is the good effect of interface pressure distribution.

Finite Element Methods for Modeling the Pressure Distribution in Human Body–Seat Interactions: A Systematic Review

“…Other papers [2,19,28] have used scans from a seated position. A 50th percentile male model is the most used model in different papers [1,2,[15][16][17][18]21,23,[26][27][28][29][30][31][32][33][34][35][36][37][38][39] as it is considered to be the average human being. A few papers [19,34,38] have used a 95th percentile male model, and one paper [39] used an 80th percentile male model.…”

“…Papers studied for this review have been divided into two categories. The first category includes papers that used a full-body geometry model [1,2,16,17,[28][29][30][33][34][35]40], and the second category includes the ones that used a specific section of the body [15,19,21,[23][24][25]27,31,32,[36][37][38][39][41][42][43][44]. Within those groups, there are models that include mechanical properties [15,19,21,[23][24][25]27,32,[36][37][38][39][42][43][44], and they are also divided into anatomical [15,21,[23][24][25]38,…”

“…This is because the authors in the studies have only investigated a certain behavior such as the pressure distribution of the model interacting with a seat or other padded furniture. in different papers [1,2,[15][16][17][18]21,23,[26][27][28][29][30][31][32][33][34][35][36][37][38][39] as it is considered to be the average human being. A few papers [19,34,38] have used a 95th percentile male model, and one paper [39] used an 80th percentile male model.…”

“…Nonetheless, other papers decided to lump the skin with the soft tissue material and model it as a soft tissue [2,17,20,21,25,27,31,35,38,40,43], which is discussed in the next section. Papers that assigned a material for the skin [1,16,30,32,47] used a linear isotropic elastic material with an elasticity of 0.15 MPa.…”

“…Many finite element models have been developed to simulate the soft human tissues, and various approaches have been observed from the papers read for this review paper. Several authors have used a single model to describe the behavior of all the components [1,2,[17][18][19]21,[23][24][25][26][27][28][29]32,37,39,40,42,44]; however, other papers have used mathematical models for tendinous structures, and muscular tissue and a changed one for fat [15,16,30,31,[33][34][35][36]38,41,43]. However, there are a few models that have been used by many papers because of the accuracy of the results that they portray.…”