Advanced Materials Based Soft Robots Toward Biomedical Applications

Abstract

Small soft robots, which are composed of stimuli-responsive materials including polymers, gels, fluids, as well as carbon, are attracting an increasing number of researchers in the last few years. Carbon-based materials are preferred due to their low cost, mechanical strength, excellent physical/chemical properties, and high photothermal conductivity. Several actuation mechanisms have been proposed to drive the carbon-based soft actuator, including electric, thermal, and optical fields. Among all these methods, optical driving exhibits high adjustability because the material can be selectively triggered by light spot remotely without electromagnetic disturbance. However, there are still some challenges for carbon-based soft actuator in robotic application, i.e. the uniform directional deformation regulated by the homogeneous light-sensitive materials constrains the motion flexibility of the robot to a single behavior; the integration of high bending amplitude and speed into a single actuator is still hard to achieve. Besides, to realize the robotic applications in biomedical engineering, direction controllable high-speed robot with potential multi-tasking abilities (i.e. cargo delivery) are also required. Furthermore, soft tactile sensing system with integrated force value sensing and addressing ability are also required for the robotic and biomedical applications. The main research issues and results are summarized as follows:

To improve the motion flexibility of light-driven soft robot, nature creatures (e.g. inchworm and snake) inspire. Inspired by the inchworm, which owns few joints while distinctive and high-efficiency locomotion, a small soft inchworm-inspired robot based on near-infrared (NIR) light-sensitive material graphene oxide (GO)–polydopamine (PDA)/ reduced GO (rGO) is proposed. By design, the robot is fabricated with GO-PDA body and rGO robot legs with different lengths, leading to the slanted posture of robot. By applying NIR light on the robot body, bending would generate with front leg and back moving forward alternatively, exhibiting good controllability. Inspired by the snake, which could generate controllable deformations accordingly and coordinate these DOF achieving multifarious locomotion behaviors, an instant self-folding triple-layer graphene-based paper is developed with programmed dual gradient to allow the soft robot to achieve bidirectional deformation as snake. Such soft material is capable of bidirectional deformation while NIR light is projected at different regions. It allows the robot to move continuously by periodically changing body shape on-demand with two locomotion modes like a snake, i.e., concertina locomotion and serpentine locomotion modes, corresponding to external NIR light stimulation, exhibiting high flexibility.

To improve the actuating efficiency of light-driven soft actuator, a dual active layer strengthened bilayer composite film made of GO-PDA-gold nanoparticles (Au NPs)/polydimethylsiloxane (PDMS) is developed. In this film, the conventional passive layer is replaced by another AuNPs-enhanced thermal responsive layer. Benefiting from the dual active bilayer mechanism, the thin film’s actuating efficiency is dramatically improved compared with that of conventional methods. Specifically, the bending amplitude is enhanced up to 173%, and the actuating speed is improved to 3.5-fold. The soft actuator can act as an artificial arm with high actuating strength and can be used as a wireless gripper for cargo transportation showing multifunctionality.

To implement the biomedical applications, a recyclable graphene-based soft robot is developed with target cargo delivery ability, which can work at liquid/air interface. Due to the integration of gold nanorods (Au NRs), the motion speed is highly improved by plasmonic effect. Actuated by NIR light, the soft robot could travel in desired direction due to the Marangoni effect. With on-demand manipulation, the robot can implement multi-robot assembling. Because of the high actuating strength assisted by plasmonic effect, it can act as wireless manipulator for cargo transportation and own high obstacle crossing ability. Assisted by the Ca-alginate layer, the robot could release the carried cargo by stimulus when arriving at the target location realizing target cargo delivery.

To realize robotic tactile sensing, a neural network-assisted tactile sensor is proposed which can implement the pressure value and force location sensing without the tactile array embedded. Compared with traditional tactile sensor, it does not need the electrode array for force location sensing, which is suitable for the large area tactile sensing. The working mechanism of this sensor is based on the unparalleled plate capacitor. Due to the difference of dielectric layer’s thickness, the capacitance varies at different points distributed which is determined by both the pressure amount and x and y coordinate. Besides, BP neural network is used for assisting the force sensing and detecting. The small error of predict data trained by neural network shows its great potential for the large area force sensing applications.

These works verify the great potentials of soft materials including the robotic actuation, locomotion, sensing as well as cargo delivery capability in biomedical applications. Thereby, this research opens new prospects for the development of soft robots and robotic sensing applications, which is expected to give a long-term impact on the biomedical areas, such as for medical treatment, rescue operation, targeted therapy, and haptic perception research.

Date of Award	28 Aug 2020
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yajing SHEN (Supervisor)