JCJC SIMI 8 - JCJC - SIMI 8 - Chimie du solide, colloïdes, physicochimie

Thin Films of Stimuli-Responsive Hydrogels for Microfluidics – GELTHINFILM

Responsive Hydrogel Thin Films as Microvalves for Microfluidics

Development of thin films of stimuli-responsive polymers (to temperature, light or electric field). Applications as microvalves to control hydrodynamic flows in microfluidics.

Development of autonomous, individual and high-density fluidic microvalves

Context. The existing microvalves (Quake’s valves) using pneumatic way, require expensive and bulky external equipments.It is necessary to develop simple and autonomous microvalves. <br />General Objective. The objective is to develop autonomous microvalves made with stimuli-responsive polymer hydrogels which are embedded in the microchannels. They can respond to stimuli such as temperature, light or electric field. It provides the ability to control the fluid flows in the microchannel or a lab-on-a-chip. <br />Resolved Problems. The fabrication of hydrogel-based microvalves is controlled by externalizing the synthesis of gels prior to the microfabrication. The strategy is very simple and versatile using thiol-ene click chemistry to fabricate hydrogel films with various responsiveness. This chemistry allows the fabrication of localized (or patterned) hydrogels for the development of individual and high-density hydrogels.<br />Perspectives. The project can have a real significant effect on the development of lab-on-a-chips.<br />

We develop the synthesis of responsive hydrogels thin films through thiol-ene click chemistry. This straightforward approach allows the synthesis of hydrogel films with various kinds of responsiveness. For temperature, polymers with LCST (Lower Critical Solution Temperature) properties are used. For light, the shift of the LCST is obtained by grafting an azobenzene group on LCST polymer. For the electriv field, a polyelectrolyte is used. The strategy also allows the synthesis of hydrogel films on a wide range of thickness from nanometer to micrometers which is suitable for microfluidic applications.
Once the hydrogel films synthesize and well characterized, they are embedded in fluidic microchannels to be exploited as mechanical microvalves. The localization of surface-attached hydrogels by patterning allows the development of individual and high-density microvalves.

• Synthesis of responsive polymers. The strategy of the synthesis was successful and allows the development of various responsive polymers, thermo-responsive polymers, in particular polymers with LCST properties with different transition temperature and polymers with UCST properties for biology applications.
• Synthesis of hydrogel films through thiol-ene reaction by thermal activation or UV irradiation. We showed that hydrogel films can be obtained by thermal activation and also by photo-irradiation (which was not planned at the origin). The UV-irradiation allowed the patterning of surface-attached hydrogels.
• Thermo-responsive mcrovalves. We showed the possibility to fabricate thermo-responsive microvalves. We develop lab-on-a-chips with high density microvalves. We are now working on biology applications of the microvalves.
• Fabrication of new gel films with various architectures. We exploited the strategy of the synthesis of single-network films to develop novel films with various and well-controlled architectures such as multilayers, interpenetrating networks and hybrid hydrogels.

Microfluidic applications. Numerous applications exploiting the technology of microvalves based on responsive hydrogel films are envisaged in biology domain (digital PCR, unique cells, microbiology…).
Future prospect. We aim to develop new materials, in particular coatings with reinforced mechanical properties and also multilayers for optics (Bragg mirror).

A patent was filed. A start-up called Microfactory was created by the partners from Gulliver laboratory Patrick Tabeling and Fabrice Monti to develop the microvalves (among their activities).
An article is submitted. Other articles are in preparation.

Polymer hydrogels with stimuli-responsive properties are interesting materials for several applications due to their large volume change by absorption or expulsion of water. The hydrogels can respond to various stimuli such as pH, salt concentration, temperature, light, electric or magnetic field. The reversibility of the volume transition is an additional advantage for the applications of these gels as responsive materials. However, the swelling/collapse phase transition of macroscopic hydrogels is a diffusion-limited process. The decrease of the feature size in thin films is an appropriate way to create structures with fast response times. Hydrogel thin films can be then rendered multifunctional and multiresponsive without compromising their mechanical stability, which is secured by a 3D cross-linked network structure. The hydrogel thin films we are interested to study are chemical polymer networks that are covalently linked to the surface. Their size can range from nanometers to hundred of microns. The advantages of gel thin films can be explored for the fabrication of miniaturized devices with fast response times. A stimuli-responsive gel material embedded inside a microfluidic channel can operate as a valve (functional gate) which opens or closes the microchannel for a water flow. “Smart” hydrogel valves eliminate the need of bulky external control and thus allow the creation of handy and autonomous “lab-on-a-chip” systems for analytics. The project fits precisely within that framework and focuses on three areas: 1) Development of the surface-attached hydrogel thin films. Among the possible external stimuli, we choose to focus on gels responding to temperature, light or electric field. The synthesis follows a straightforward approach which allows easily the variation of the chemical functions of the polymers and then of the responsive properties of the hydrogels. The principle is based on thiol-ene chemistry. The formation of surface-attached gel films will be achieved by adding bifunctional thiol molecules as cross-linkers to the ene-reactive polymers on thiol-modified surfaces. The objective is to obtain hydrogel films with a wide range of thicknesses and with the desired responsiveness nature. 2) Structure of the surface-attached hydrogel thin films. The structural investigation of these thin films tackles a fundamental aspect of confined and constrained systems. We will attempt to answer the following questions. What is the effect of the confinement on the swelling of the gel films? How does the attachment on surface affect the free surface of the gels? Three stages will be exploited: the linear swelling ratio of the hydrogel films in the direction normal to the substrate (using ellipsometry), the interfacial width (using neutron reflectivity) and the wrinkling aspects (using AFM) of the free surface of the hydrogels. 3) Microfluidic applications of the hydrogel thin films as microvalves. We will show the possibility to design surface-attached hydrogel thin films in microfluidic devices for the actuation of mechanical microvalves. It means that the surfaces functionalized by the hydrogel layers will be embedded in miniaturized systems and their function as microvalves will be tested. The use of light and electric field as stimuli parameters is innovative, providing microvalves easily activated with fast responses. The nature of the responsiveness is also compatible with patterning processes. This route is very promising for the development of more and more high-performance “lab-on-a-chip”. The strong point of the project is the complete investigation of thin films of stimuli-responsive hydrogels, starting from a controlled synthesis and a detailed characterization of the structure to a concrete application in microfluidics. This multidisciplinary project provides the possibility to assemble chemistry of polymers, fundamental aspects of physics on confined systems and pioneering concepts of microfluidics engineering.

Project coordination


The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.



Help of the ANR 170,040 euros
Beginning and duration of the scientific project: January 2012 - 48 Months

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