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Top1. Introduction
Diabetes is a growing health problem around the world. WHO (World Health Organization) estimates that by 2030, more than 334 million people will suffer from diabetes (see Bernabeu et al., 2013; Davia et al., 2011, www.who.int/diabetes), while in 2009, diabetes affected 220 million people. Diabetes is a lifelong condition that seriously affects a person’s quality of life. In recent years, the progress of medical treatments for curing diabetes has fortunately resulted in a considerable lengthening of life expectancy for many sick people. One of the most common complications is foot ulceration which, if left untreated, can lead to infection and ultimately to full or partial amputation (Janisse and Coleman, 2008). There are a number of footware-related factors that are considered to increase the likelihood of an individual developing an ulcer. These include elevated temperature/humidity within a shoe, increased in-shoe plantar pressure (pressure under the foot) (see Lavery et al., 2003, Amstrong, 1998) and increased shear movement between the foot and the shoe. Each of these factors will be dictated by different aspects of the design such as insole geometry (Bus et al., 2004; Anggoro et al., 2017a; Anggoro et al., 2018a), outsole profile/stiffness (van Schie et al., 2000; Brown et al., 2004), and shoe lasting (Cavanagh et al., 2002; Ameersing and Yan, 2009; Sambhav et al., 2011; Marco Mandolini et al., 2015).
The activities of standing, walking, and running are daily routines for most human beings, making insoles an important factor in general foot health and associated health issues. This fact has transformed the need for insoles from merely being an accessory into something functional. Most insole manufacturers are primarily concerned with cost-effectiveness, which leads to mass production. Unfortunately, such insoles might not always fit an individual’s needs, as not everyone has the same gait or foot shape (Chung et al., 2011).
Researchers (Miguel et al., 2011; Luigi and Claudia, 2012) have described that the main problems for people with diabetes are due to the complications that such a sickness generates. One of the most relevant complications is called “diabetic foot”. People with diabetes are at a higher risk for foot ulcers, a common side effect of the disease. It is estimated that 15% of diabetic patients are affected by this complication, but this number will probably grow due to lifestyle modifcations in many parts of the world, especially in emerging countries. The main cause of foot ulceration in an adult diabetic is thought to be the presence of abnormally high plantar pressures; neuropathy secondary to plantar fasciitis. These pressures may be present as a result of compromised foot function such as tendon disorders in the heel area of a foot and the diabetic condition, Charcot Anthropathy. The figures regarding swollen bones are shown in Figure 1 (see Anggoro et al., 2017b, Anggoro et al., 2018a, Anggoro et al., 2018b, and Bawono et al., 2017).