Design and Analysis of Auxetic Structures in Bedsore Patient Mattresses for Uniform Weight Distribution

Abstract

Currently, polymeric foams are widely utilized in the creation of passive support surfaces such as mattresses, cushions, and seating. However, these materials encounter challenges in prolonged use, including diminished performance, permanent deformation, reduction in thickness, and nonuniform pressure distribution. These issues can lead to pressure concentration in sensitive bodily areas, particularly the gluteal region, thereby increasing the risk of pressure ulcers. Advances in additive manufacturing technology, alongside the capability to design engineered structures with controllable mechanical properties, have directed researchers' attention toward employing this method as an alternative to traditional foams. Among these, auxetic structures have garnered interest for applications related to skin wound healing due to their unique mechanical characteristics. In this study, re-entrant auxetic structure samples were numerically designed using the finite element method and subsequently fabricated via the fused deposition modeling (FDM) additive manufacturing process, utilizing thermoplastic polyurethane (TPU). The mechanical performance of these structures was assessed through compression testing, in accordance with ISO 3386-1, and fatigue testing. These analyses investigated the impact of parameters such as unit cell dimensions and cell angle on the compressive stress and resilience of the structure. The results indicated that the designed auxetic structure, when utilizing TPU with A95 hardness, could achieve a compressive stress between 7 and 8 kPa at 40% compression. Furthermore, fatigue tests demonstrated that the structure's resilience is dependent on the amount of strain, whereas the loading duration did not significantly affect its rebound behavior. These findings underscore the high potential of auxetic structures in designing support surfaces with customizable mechanical performance, tailored to the biomechanical needs of the body.