Development of bio-inspired cellulosic smart composites for morphing

• Main Author: Mulakkal, Manu
• Other Authors: Seddon, Annela ; Ting, Valeska
• Published: University of Bristol 2018
• Subjects: 629.1
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761184

Materials capable of self-actuation and architectures facilitating re-configuration are highly valued and profoundly sought-after for numerous applications in the fields of robotics, deployable and morphing structures. Here, a bio-inspired approach to realising a programmable materials system capable of morphing was explored and implemented with a specific focus on the sustainability of the material components. The deployment of manually folded paper architectures using a fluid medium as the morphing stimulus presents a simple and inexpensive methodology capable of self-actuation. The materials-based as well as the stimuli parameters of this system were found to be programmable to control the actuation response of folded paper architectures. These results confirmed the suitability of cellulose as a cost effective and sustainable smart material capable of further functionalisation, and thus justified its consideration in developing programmable morphing systems. Following nature’s inspiration, a strain-gradient mediated methodology for self-folding paper architectures was realised by locally patterning ‘fold-lines’ with a compatible hydrogel system. The architectures were designed to actuate along the principles of paper folding techniques such as origami and kirigami thus providing proven and elegant programmability and actuation attributes. As such, a novel methodology for self-folding and subsequent stimuli responsive deployment of cellulosic architectures was established. The developments in 3D printing (3DP) technology allow the controlled placement of building materials in 3D space and this feature was harnessed to complement the strain-gradient mediated actuation of the cellulosic substrates. Therefore, a bespoke bio-inspired cellulose-hydrogel (carboxymethyl cellulose - CMC) composite for 3D printing was developed which can morph in the time domain (4D) according to the design rules developed from the previous chapters to mimic the actuation of responsive cellulosic structures observed in nature. Consequently, these responsive materials permit 4D printing - a process which pertains the transformation of 3D printed forms with respect to time. In this material system, the cellulose-hydrogel composite constitutes the programmable substrate and the CMC hydrogel acts as the localised component responsible for actuation. The strategy of drying and crosslinking following 3D printing results in a high fibre volume fraction cellulosic composites. The versatility of the materials and fabrication strategies demonstrated here enables the development of complex morphing architectures from computer aided design files with the tuneable material and structural features permitting programmability of the actuation responses. As such, this project demonstrates the realisation of sustainable cellulosic architectures capable of morphing via 4D Printing.