Microfluidic actuators based on temperature-responsive hydrogels

Abstract

The concept of using stimuli-responsive hydrogels to actuate fluids in microfluidic devices is particularly attractive, but limitations, in terms of spatial resolution, speed, reliability and integration, have hindered its development during the past two decades. By patterning and grafting poly(N-isopropylacrylamide) PNIPAM hydrogel films on plane substrates with a 2 μm horizontal resolution and closing the system afterward, we have succeeded in unblocking bottlenecks that thermo-sensitive hydrogel technology has been challenged with until now. In this paper, we demonstrate, for the first time with this technology, devices with up to 7800 actuated micro-cages that sequester and release solutes, along with valves actuated individually with closing and opening switching times of 0.6 ± 0.1 and 0.25 ± 0.15 s, respectively. Two applications of this technology are illustrated in the domain of single cell handling and the nuclear acid amplification test (NAAT) for the Human Synaptojanin 1 gene, which is suspected to be involved in several neurodegenerative diseases such as Parkinson's disease. The performance of the temperature-responsive hydrogels we demonstrate here suggests that in association with their moderate costs, hydrogels may represent an alternative to the actuation or handling techniques currently used in microfluidics, that are, pressure actuated polydimethylsiloxane (PDMS) valves and droplets.

Transformer Hydrogels: A Review

“…At temperatures lower than the critical temperature, the polymer chains reverse to an extended coil chain causing the hydrogel to swell and become transparent . This temperature‐dependent reversible swelling of pNIPAM, its derivatives and composites have been utilized to fabricate a variety of smart sensors and actuators …”

“…Hence, there is a significant opportunity for the integration of soft and stimuli‐responsive hydrogels into microfluidics devices . Transformer hydrogels offer the promise of easy fabrication and integration to the current microfluidic devices, providing precise control of the fluids through shape change based on various external stimuli including thermal, pH, light, electrical, magnetic, and chemical reactions …”

“…Essential hydrogel components include actuators, valves, and trapping devices that respond to a variety of stimuli. For example, D'Eramo et al were able to pattern pNIPAM hydrogel pillars with a 2 µm sized horizontal resolution as a microfluidic actuator . They were able to actuate as many as 7800 microcages in 0.6 s by raising the system temperature of the hydrogel above its LCST ( Figure a).…”

“…a) Microfabricated thermoresponsive hydrogel microcages as valves traps in microfluidic applications. Adapted under the terms of the Creative Commons Attribution 4.0 International license . Copyright 2018, The Authors.…”

Vacuum‐driven fluid manipulation by a piezoelectric diaphragm micropump for microfluidic droplet generation with a rapid system response time

“…Some research groups have developed compact, low‐cost, and simple fluid pumping systems for microfluidic droplet generation and there have been a few implementations of such devices. These include piezoelectric (PZT) actuator‐based pumps , responsive hydrogel‐based pumps , degassed poly(dimethylsiloxane) (PDMS)‐powered pumps , and finger squeeze‐driven pumps .…”