4D Printing with Bio-based Polymers for Adaptive Wearable Devices

Compared to conventional manufacturing processes, 3D printing has proved its capability of building various structures with high accuracy and material economy. 4D printing adds the fourth dimension, time, to 3D printing technology. Changing through time is a key property of products built by 4D printing. This research focused on bio-based responsive materials, as a means of initiating change and transforming 3D printing to 4D printing. A number of studies have been done to develop the performance of responsive materials or to explore geometric structures for these materials in order to configure products that can benefit from this transformation. Precedents in medical field show great potential for combining bio-based materials with 4D printing in manufacturing highly customised products that adapt to the shape, movement and physiological requirements of a human body. This research project was initiated by the development of printable and responsive bio-based polymers through the National Science Challenge (NSC) Portfolio 5 Spearhead Project “Additive manufacturing and 3D or 4D printing of bio-composites”. The research is inspired by the adaptability and biocompatibility of the medical precedents and explores the possibility of engaging 4D printing in building wearable devices; exemplified by an adaptive wrist splint for progressive rehabilitation. This included researching wound healing processes and related rehabilitation methods to determine the required functionality of the splint and exploring relevant biological structures as inspiration for the design geometry. Working alongside materials scientists, the design was developed along two paths. Firstly, using the new experimental polymers and testing their responsiveness to configure a printable shape- shifting layer of the splint that adapts to changes in the wrist during the healing process. Secondly, integrating these experiments into 3D models for an adaptive splint, comprised of three layers, that responds to the requirements of progressive rehabilitation. The research challenges the properties of the new materials and the associated printing processes, and more research will need to be done to improve both printability and responsive performance. However, the design of the splint provides a case study for potential applications in the broader field of wearable devices that incorporate multiple layers of responsive materials and different geometries that can adapt to the needs of a human body.