Plantar soft tissue stiffening in diabetes leads to a risk of developing ulcers. There are relatively few studies providing methods for quantifying the mechanical properties of skin and fat in the plantar tissue of diabetic patients. Previous studies used linear or non-linear single layer deformable models or linear multi-layer models. This study aimed to investigate the mechanical properties of plantar soft tissue using multi-layer, non-linear models to estimate more accurate mechanical properties in the plantar tissues of diabetic patients. Ten healthy young (HY) subjects, ten healthy old (HO) subjects, and ten old diabetic patients (DB) volunteered for the study. Indentation tests were performed at two sites in the heel. The subjects underwent computed tomography (CT) to measure the respective thicknesses of the skin and fat at the indentation sites. Subject-specific finite element models were created to estimate the parameters of the first-order Ogden forms of the skin and fat. The initial shear modulus for the fat layer ${\mu }_F$ in DB, HO, and HY were 4.68 MPa (±0.87), 2.71 MPa (±1.25), and 2.27 MPa (±0.87), respectively. The initial shear modulus for the skin layer (${\mu }_S$) in DB, HO, and HY were 5.86 MPa (±2.51), 7.05 MPa (±1.94), and 14.58 MPa (±1.98), respectively. The DB had stiffer fat tissue than the normal subjects in the same age group but had the same soft skin. These aspects can cause different mechanical stress conditions in a diabetic foot than in a normal foot under the same mechanical loading, making the diabetic foot vulnerable to the initiation of mechanical breakdowns such as ulcers.

糖尿病患者的足底软组织僵硬会导致患溃疡的风险。很少有研究提供量化糖尿病患者足底组织中皮肤和脂肪机械特性的方法。先前的研究使用线性或非线性单层可变形模型或线性多层模型。这项研究旨在使用多层非线性模型研究足底软组织的机械性能，以评估糖尿病患者足底组织中更准确的机械性能。10名健康的年轻（HY）受试者，10名健康的老年（HO）受试者和10名老年糖尿病患者（DB）自愿参加了这项研究。在脚后跟的两个位置进行压痕测试。受试者进行计算机断层扫描（CT），以测量压痕部位皮肤和脂肪的各自厚度。创建特定于对象的有限元模型以估计皮肤和脂肪的一阶Ogden形式的参数。脂肪层的初始剪切模量${\mu }_F$DB中的HO，HO和HY分别为4.68 MPa（±0.87），2.71 MPa（±1.25）和2.27 MPa（±0.87）。蒙皮层的初始剪切模量（${\mu }_{\mathrm{小号}}$在DB中，HO和HY分别为5.86 MPa（±2.51），7.05 MPa（±1.94）和14.58 MPa（±1.98）。与同一年龄组的正常受试者相比，DB的脂肪组织较硬，但皮肤柔软。在相同的机械负荷下，这些方面会导致糖尿病足与正常足产生不同的机械应力状况，从而使糖尿病足容易受到诸如溃疡之类的机械故障的影响。