Polylactic acid/cellulose nanocrystals/polyethylene glycol-based shape memory composite for a 4D printed thermoresponsive gripper system

Abstract

This work introduces a novel thermo-responsive 4D printable gripper system via polylactic acid (PLA), cellulose nanocrystals (CNC), and polyethylene glycol (PEG)-based shape memory composite. PEG, serving as a biocompatible plasticizer, and CNC, acting as a biodegradable reinforcing agent, were incorporated into PLA, a 3D printable shape memory thermoplastic matrix. Keeping CNC content the same, two series of shape memory composites (SMCs) were prepared with increasing weight percent (wt%) of PEG (1.25, 2.5, 5, 10, and 15 wt%) using PEG 40 and PEG 4000 via heat-press method. Thermal, mechanical, and shape memory properties of the as-prepared composites were analyzed with respect to neat PLA, the control. The glass transition temperature (T g ) and the activation temperature of the SMCs gradually decreased with increasing PEG content. Compared with the PEG 40 series, the PEG 4000 series exhibited a greater reduction in T g , decreasing from 49 ℃ to 40.5 ℃, accompanied by a reduction in the activation temperature from 49 ℃ to 40 ℃. Overall, an optimum balance between the mechanical and shape memory performance was achieved by the PLA/CNC/PEG(4000)-10 wt% composite. Furthermore, the composite was successfully 3D printed into a gripper w ith an activation temperature of 40.5 °C. To the best of our knowledge, this is the first reported 4D printed gripper to demonstrate excellent shape fixity and shape recovery ratios of ∼93% and ∼94%, respectively, at an activation temperature close to physiological conditions. Cyclic shape memory tests performed for the same composite evidenced ∼98% retention of the original shape recovery ratio even after the fifteenth cycle. This work paves the way for the future development of biodegradable, thermo-responsive, 4D printable shape memory devices for biomedical applications.