Hydrogel-matrix encapsulated Nitinol actuation with self-cooling mechanism

Abstract

Shape-memory Nitinol holds burgeoning promise as smart actuators due to its effective resilience, high energy density, and scalability for a myriad of mesoscale machines and robotic applications. However, the higher actuation temperature and prolonged cooling time for a cyclic response make Nitinol precarious and less appealing for commercial use. On the contrary, hydrogels belong to the three dimensional (3D) polymer family where the bulk of the matrix encapsulates water (z80-90 wt%) constituting a compelling heat-trapping medium. In this paper, we demonstrate a novel self-cooling mechanism comprising a Hydrogel-matrix Encapsulated Nitinol Actuator (HENA) where the heat emitted due to the high temperature (200-400 C) of Nitinol is trapped in the hydrogel-matrix, maintaining a surface temperature of 20-22 C. For quantitative analysis, we performed control tests with the stateof-the-art Silicone Elastomer Nitinol Actuator (SENA) which maintained a three times or higher temperature profile (65-90 C) than its HENA counterpart. HENA is able to entrap 85% heat for actuation of 200 cycles while SENA dissipates the same amount in the first cycle. For impending biomedical applications, HENA with a single Nitinol wire shows a bending displacement up to 45% of its length for trans-oral navigation purposes. A HENA soft robotic gripper with two Nitinol wires can carry delicate, low-melting-point food items (e.g. cheese, chocolate, tofu etc.) with different morphologies that weigh up to 450% of its own weight.

Thermo-Responsive Hydrogel-Based Soft Valves with Annular Actuation Calibration and Circumferential Gripping

“…Detailed steps involved are overlaid in Figure 2. The adapted one-pot method [8,19,59] was used to prepare stock solutions comprised of AAm, MBAA, PI, SA, and DI water. The resultant stock solution kept in the ultrasonic cleaner (Sonica 5200, Sonica) with continuous stirring for 4 h followed by a 24 h rest period for crosslinking.…”

“…The FE simulations of the heat transfer in the PAHV during the actuation process were carried out using the heat transfer module of COMSOL Multiphysics 5.3 using a time-dependent equation, following the data from our previous work [8]:…”

“…However, 3D bioprinting and regenerative medicine-driven organ transplantation are still far from their true potential. In this spirit, here we demonstrate a N-Isopropylacrylamide hydrogels-based valve (NPHV) that provides a new outlook based on temperature changes, and compares valve performance with previously established PAAm-Alginate hydrogels [8]. During tissue ablation and focused ultrasound treatment, the localized elevated tissue temperature can expedite the valve action and deploy it in the targeted position.…”

“…In this aspect, stimuli-responsive hydrogels can play a pivotal role [2]. Hydrogel-based, stimuliresponsive polymers in recent years have become an integral part of biocompatible, soft biomedical actuators and sensors [3][4][5][6][7][8]. Unlike conventional actuators, stimuliresponsive hydrogels can control volume change without the necessity of any external power source [9][10][11][12][13].…”

XPS study on surface modification of NiTi alloy by acidic solution immersion and subsequent heating in air

“…Nearly equiatomic nickel–titanium (NiTi) alloys with shape memory and superelasticity are used in industrial material involving robotics, aerospace, thermal sensor, and medical devices 1–4 . The surface condition of NiTi alloy is important in the manufacturing process and is also related to the alloy's functionality.…”