Affiliations: [a] Center of Biomedical Engineering (CBME), Frankfurt/Main, Germany | [b] Institute for Materials Science, University of Applied Sciences, Frankfurt/Main, Germany | [c] Department of Diagnostic and Interventional Radiology, Hospital of the Johann Wolfgang Goethe University, Frankfurt/Main, Germany | [d] University of Science & Technology, Teheran, Iran
Correspondence:
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Address for correspondence: G. Silber, Institute for Materials Science, University of Applied Sciences, Nibelungenplatz 1, D-60318 Frankfurt am Main, Germany. Tel.: +49 69 1533 3035, +49 69 1533 3081; Fax: +49 69 1533 3030; E-mail: silber@fb2.fh-frankfurt.de.
Abstract: The most common complication associated with immobilization is pressure sores caused by sustained localized tissue strain and stress. Computational simulations have provided insight into tissue stress-strain distribution, subject to loading conditions. In the simulation process, adequate soft tissue material parameters are indispensable. An in vivo procedure to characterise material parameters of human gluteal skin/fat and muscle tissue has been developed. It employs a magnetic resonance imaging (MRI) device together with an MRI compatible loading device. Using the derived data as constraints in an iterative optimization process the inverse finite element (FE) method was applied. FE-models were built and the material constants describing skin/fat and muscle tissue were parameterized and optimized. Separate parameter sets for human gluteal skin/fat and muscle were established. The long-term shear modulus for human gluteal skin/fat was G∞,S/F=1182Pa and for muscle G∞,M=1025Pa. The Ogden form for slightly compressible materials was chosen to define passive human gluteal soft tissue material behaviour. To verify the approach, the human skin/fat-muscle tissue compound was simulated using the derived material parameter sets and the simulation result was compared to empirical values. A correlation factor of R2=0.997 was achieved.
Keywords: Human tissue, separation of fat and muscle, material parameters, bed sore
