Analytical design and fabrication of thermal latch valve driven flexible microscaffold for applications in tissue engineering

This paper presents a flexible microscaffold driven by a thermal latch valve, which helps meet the necessity of engineered tissues with different structures for engineered organ assembly. Unlike the conventional approach, which normally utilizes a fixed scaffold, our flexible microscaffold offers many temporary scaffolds as needed. It consists of a 3×3 microactuator array with a diameter of 500 μm and a pitch of 650 μm. The type of PDMS membrane actuator is designed so as to prevent the leakage of culture media, and have high actuator displacement. The integration of a thermal latch valve with our microscaffold is proposed, as phase-change property of paraffin is beneficial for maintaining the actuator shape over the tissue cultivation period, without energy consumption. The liquid phase of paraffin acts as a valve that allows the adjustment of the actuator shape, while the solid phase acts as a latch that keeps the actuator shape stable over time. The phase-change of paraffin is induced by the joule heat generated by a microheater, made of nickel. The temperature coefficient of resistance and the heating-cooling response of three microheater designs are examined. Experiment results of all designs show that it normally takes 2 minutes to reach over the paraffin´s melting point, and 3-4 minutes to cool the heaters down. The high pressure of about 19 kPa is needed in order to obtain an actuator displacement of about 180 μm, which suggests the possibility of using the thermal latch valve to control the scaffold structure.