Multi-attribute parametric optimisation of shape memory polymer properties for adaptive orthopaedic plasters

Abstract

Fall-related injuries and road accidents often demand orthopaedic emergency care and management in hospitals. Early and effective fracture treatment immobilisation techniques are essential for stabilising the musculoskeletal system of the patient. During past decades, shape memory polymers (SMPs) have rapidly been developed and they have exhibited their potential to replace traditional plaster of Paris or wood casting orthopaedic treatment practices. In this context, SMPs must match all the operational conditions of traditional materials while keeping SMP's superior qualities such as adjustability and ease of removal for observation and reapplication. In order to achieve their significantly delicate shape memory effect and shape fixity properties, SMP needs an accurately engineered material characterisation process. Therefore, this research comprises and extensive evaluation of shape memory polymer composites’ (SMPCs’) thermo-mechanical properties under ASTM/ISO standards for extended use in the orthopaedic medical field.The robust Taguchi (L18) optimisation approach combined with a multi-responses grey relational study was employed to achieve optimum SMPC fabrication parameters for orthopaedic applications while prioritising the required thermo-mechanical and shape memory properties. It was determined that the number of fabric layers is the most decisive parameter (P-value 0.013, relative contribution > 37.86%) for achieving SMPs’ delicate and crucial properties for biomedical applications. In this study, it was found that one layer of glass fibre (SMP weight fraction > 89%) provided the optimum thermo-mechanical and shape memory properties. Moreover, optimised control variables assured the self-life of the SMP casting material by retaining a programmed shape for 30 days (shape fixity ratio >98%), which is an exclusive property for an orthopaedic device. This study provides first-hand pre-engineered experimental program optimisation techniques to meet the rapid growth of SMPC orthopaedic non-invasive smart plasters and adaptive devices.