High-force, precise, and bidirectional uniaxial stretcher for real-time imaging of normally closed h-PDMS crack-valves for femto-liter fluid delivery

• Published in: Microfluidics and nanofluidics Vol. 26; no. 4
• Main Authors: Ginga, Nicholas J., Chiu, Joyce Han-Ching, Lee, Ji-Hoon, Thouless, M. D., Takayama, Shuichi
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.04.2022; Springer Nature B.V
• Subjects: Actuation; Analytical Chemistry; Biomedical Engineering and Bioengineering; Computer control; Control stability; Control valves; Cracks; Engineering; Engineering Fluid Dynamics; Fabrication; Flow rates; Flow velocity; Fluid dynamics; Fluid flow; Fluoroscopic imaging; Imaging techniques; Microchannels; Microscopes; Nanotechnology and Microengineering; Optical microscopes; Real time; Research Paper; Stepping motors; Stretching; Substrates; Thickness; Valves; Width
• ISSN: 1613-4982; 1613-4990
• DOI: 10.1007/s10404-022-02533-3

To meet the expanding demands of current cross-disciplinary research, this article presents a uniaxial tensile tester that is capable of high forces (500 N), large displacements (100 mm), bidirectional and symmetric stretching, and high spatial precision (< ± 0.5 µm) while being compatible with optical microscopes for real-time bright-field and fluorescent imaging. The design and characterization of this computer-controlled, stepper–motor-based tensile tester (i.e., stretcher) is presented. Its performance is demonstrated using it to stretch and form cracks in an h-PDMS nanoscale film on top of a more compliant PDMS substrate. The width of the cracks can be nano or micro scale and the width is controlled by the strain applied by the stretcher. These cracks are then used as crack-valves to provide femto-liter fluid delivery between traditional microchannels. The fabrication of these crack-valves is a new process that utilizes dilute solutions of h-PDMS that are spin coated, which allows h-PDMS films with nanoscale thickness to be achieved. The capabilities of the tensile tester are explored by controlling the stretching and relaxation of the PDMS device with crack-valves and, thereby, opening and closing the variable width crack-valves and thus controlling fluid flow. The flow rate through these crack-valves was controlled with a high degree of precision between 0 and 2600 fL s −1 . Computer control of the tensile tester allowed for cyclic actuation, and the stability of the crack-valves was demonstrated for over 100 cycles of open/close operations in two scenarios; one between a flow rate of 280 fL s −1 and fully stopped flow and the second between 2600 fL s −1 and fully stopped flow.