Investigating auxetic insole material and its effect on plantar pressure in patients living with type 2 diabetes mellitus

Abstract

Background: Foot orthotic treatment is one of the primary means used in the treatment and prevention of ulceration as orthoses reduce peak plantar pressures by providing a larger contact surface area over which forces can be better re-distributed thus preventing skin breakdown. The most common materials that have been used for decades in insole fabrication are EVA (ethyl vinyl acetate) and PE (polyethylene). In recent years auxetic materials have attracted a lot of attention due to their enhanced mechanical properties. Auxetic materials have been described as a class of materials with a negative Poisson’s ratio that is they become fatter when stretched and narrower when compressed.This factor contributes to enhanced properties such as increased shear stiffness, increased plane strain fracture toughness and also an increased indentation resistance. Conventional insole materials such as EVA and polyethylene behave contrary to Auxetic material since they possess a positive Poisson’s ratio. Thus, this material was used in this study in order to determine whether it is more effective in reducing plantar pressure in diabetic foot when compared to conventional insole material. Aim: The aim of the study was to determine whether the innovative Auxetic foam material, when applied as an insole material is effective in reducing plantar pressure in the diabetic foot. Research Design and Method: The study employed a Quasi-experimental design where participants acted as their own control. In this study participants were invited to perform four main trials with the control, EVA,60PPI and 90PPI insole materials. Foot pressure mapping was done using the in-shoe system to obtain the mean peak plantar pressure and mean pressure-time integral for the 1st metatarsophalangeal joint region, 2nd - 4th metatarsophalangeal joint region and 5th metatarsophalangeal joint region bilaterally. Results: The results indicate that that the highest peak plantar pressures were recorded with the EVA insole in all foot masks when compared to the control, 60PPI and 90PPI insole. Also the 90PPI auxetic material was found to be effective in reducing the mean peak plantar pressure whilst the 60PPI insole was found to be ineffective in pressure reduction. From the results of this study weight when seen collectively did not have an effect on peak plantar pressure but when it was categorized in three different weight groups and examined individually, in the lowest weight category, a significant result was observed especially in the right 2-4th MPJ region.