Mr. Henry Tran Profile

Henry Tran

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Proceedings Article | 20 April 2022 Poster + Paper

Combined hydrogel and elastomer coatings for cooling supercoiled nylon actuators

Sukhneet Dhillon, Ali Redha Muljiani, Henry Tran, Soheil Kianzad, John D. Madden

Proceedings Volume 12042, 1204219 (2022) https://doi.org/10.1117/12.2638057

KEYWORDS: Actuators, Fiber coatings, Artificial muscles, Ultraviolet radiation, Polymerization, 3D modeling

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Silver-coated nylon actuators - a form of artificial muscle - are potential candidates in biomedical applications, , as they yield a large strain (5-20%+), high force (>20 MN/m² ), are compact and low-cost. But the on skin or internal application of these thermal actuators is limited by the heat released and the high activation temperatures (typically >80°C), which could cause tissue damage. We present a hybrid coating that reduces the temperature at the interface of the nylon actuator and surrounding tissue/skin, while maintaining the inner nylon actuator activation temperature. By taking advantage of the high heat capacity of water-swollen polyacrylamide (PAAm) hydrogel and the low thermal conductivity of silicone elastomer, we develop a hybrid coating for nylon actuators that provides effective heat dissipation and encapsulation without impacting strain. Hydrogel is used to absorb and dissipate heat. Using it alone dissipates heat quickly, and in turn, excess power is needed to achieve full strain. Therefore, silicone is used as a thin, inner insulating layer to retain the heat, so full strain can be achieved without excess power. We examined the strain and temperature of uncoated nylon fibres (control), single-layered silicone-coated nylon fibres, single-layered hydrogel nylon fibres and hybrid-coated (inner layer of silicone, outer layer of hydrogel) nylon fibres. At a constant current of 0.55 A, the mean strains of hybrid coated nylon fibres (6.0 %), and silicone coated nylon fibres (5.5%) were comparable to uncoated nylon fibres (5.3%). The mean strain for the hydrogel-coated nylon fibres was considerably lower (1.4%). The hybrid coating effectively maintains the fibre temperature (80-87°C) while cooling the outer surface (hydrogel) of the hybrid-coated nylon fibre (30-35°C). This provides a possible solution for use of these actuators in temperature sensitive applications.

Proceedings Article | 22 March 2021 Presentation + Paper

Supercoiled polymer-actuated pinch valve

Konstantin Borissov, Henry Tran, John D. Madden

Proceedings Volume 11587, 115870N (2021) https://doi.org/10.1117/12.2584495

KEYWORDS: Polymers, Actuators, Systems modeling, Silver, Polymeric actuators, Latex, Control systems, Artificial muscles

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Supercoiled polymer (SCP) actuators have shown promising applicability as artificial muscles due to their low-cost, high strains (10%+), work density that is more than 100 x that of muscle, and non-hysteretic behavior. Here, we present a lightweight, low-cost, SCP-actuated valve that operates by pinching rubber tubing closed. The valve comprises a 3D printable frame and incorporates a pulley system, which functions to reduce the total linear dimensions of the device. The actuator mechanism is compatible with different tubing diameters and materials and, by nature of its design, is isolated from direct contact with the working fluid. Using 1/4”/6.3 mm inside diameter latex tubing, a flow rate of up to 88 L/h and a holding pressure of over 29.4 kPa are demonstrated. The valve is normally open and takes 10 seconds to close by running a current through the coiled, silver-coated nylon actuator. An empirical model of the system is developed and open-loop control incorporated, which effectively reduced valve activation time by 30%. Further developments are suggested to achieve a faster response and pumping action.

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