Biomimetic Thermal-sensitive Multi-transform Actuator

Tae Hyeob Kim,Jung Gi Choi,Seon Jeong Kim,Sung Min Kim,Ju Young Byun,Yongwoo Jang,Geoffrey. M. Spinks

doi:10.1038/s41598-019-44394-x

Abstract

Controllable and miniaturised mechanical actuation is one of the main challenges facing various emerging technologies, such as soft robotics, drug delivery systems, and microfluidics. Here we introduce a simple method for constructing actuating devices with programmable complex motions. Thermally responsive hydrogels based on poly(N-isopropylacrylamide) (PNIPAM) and its functionalized derivatives (f-PNIPAM) were used to control the lower critical solution temperature (LCST) or the temperature at which the gel volume changes. Techniques for ultra-violet crosslinking the monomer solutions were developed to generate gel sheets with controllable crosslink density gradients that allowed bending actuation to specified curvatures by heating through the LCST. Simple molding processes were then used to construct multi-transform devices with complex shape changes, including a bioinspired artificial flower that shows blossoming and reverse blossoming with a change in temperature.

Highlights

The development of stimuli-responsive actuating materials is a promising solution to the need for controllable miniature mechanical motors in new technologies such as soft robotics[1,2,3,4], drug delivery[5], microfluidics[6] and artificial muscles[7,8]
The f-PNIPAM copolymers used in the present study were based on monomer mixtures of NIPAM, acrylamide (AM) and 2,2′-hydroxyethyl methacrylate (HEMA)
A flower-shaped device illustrates the multi-transforming actuators that could be fabricated with f-PNIPAM materials (Fig. 1a)

Summary

Introduction

The development of stimuli-responsive actuating materials is a promising solution to the need for controllable miniature mechanical motors in new technologies such as soft robotics[1,2,3,4], drug delivery[5], microfluidics[6] and artificial muscles[7,8]. Patterning of the actuating elements within the device structure can produce complex shape transformations through a series of discrete manipulations[17,20] To date, these demonstrated multi-transforming gel actuated structures need complicated fabrication methods such as electrospinning with controlled fiber orientation[23,25] and stripe polymerization using photo-masking techniques[19,20,23,24]. We demonstrate control of the gel actuation by incorporating variants of PNIPAM to give a range of LCSTs within the same device. Bending actuators are generated using an UV-photopolymerization method to control the crosslink density of the gel through the film thickness and simple molding methods are used to control the location of two different gel actuators within a single device Using these methods we are able to generate multiple shapes through thermal control. Controlling the monomer ratios and by using a simple UV-curing method gave hydrogels with two distinct temperature phase-transition points (48.0 °C and 60.8 °C)

Methods

Results

Conclusion