Environmentally responsive polymeric "intelligent" materials: the ideal components of non-mechanical valves that control flow in microfluidic systems

Abstract

-Miniaturization and commercialization of integrated microfluidic systems has had great success with the development of a wide variety of techniques in microfabrication, since they allowed their construction at a low cost and by following simple step-series procedures. However, one of the major challenges in the design of microfluidic systems is to achieve control of flow and delivery of different chemical reagents. This feature is especially important when using microfluidic systems in the development of cell culture systems, the construction of labs on a chip and the fabrication and design of chemical microreactors. Spatiotemporal control of the microenvironment in microfluidic devices has been only partially achieved by incorporating actuator parts (mechanical and non-mechanical) within these devices; nevertheless, recently there has been enormous progress due to advances in the materials sciences, and the development of novel polymeric "intelligent" materials. These materials have proved to be excellent candidates in the construction of non-mechanical actuators in the form of environmentally responsive valves. These valves can more efficiently control flows because these "intelligent" materials are capable of undergoing conformational changes and phase transitions in response to different local or external environmental stimuli; allowing them to turn the valves from "on" to "off". In addition, these valves have very simple designs, and are easy and cheap to incorporate into microfluidic systems. Therefore, although there are many reviews that focus on the development and design of non-mechanical actuators, the following review proceeds to describe the exciting characteristics, potential uses and synthesis methods of the building blocks of the most recent and innovative non-mechanical valves, environmentally responsive polymeric "intelligent" materials. In addition, the last section of this review will focus on the synthesis of composite materials that are capable of responding to more than one type of stimulus, since these materials are believed to be the future components that will boost the development of microfluidic systems with spatiotemporal controlled microenvironments.

Structural characteristics and bonding environment of Ag nanoparticles synthesized by gamma irradiation within thermo‐responsive poly(N‐isopropylacrylamide) hydrogel

“…Therefore, probably the presence of AgNPs limits the segmental mobility of the polymer chains and prevents the crystallization process in the amount that is proportional to the growing content of Ag. Moreover, it was obtained that PNiPAAm crosslinked polymer network stabilizes the metallic nanoparticles mainly by defect network structures (e.g., dangling chain ends) , thus inducing crystalline disorder of polymer .…”

Bifunctional nano-Ag3PO4 with capabilities of enhancing ceftazidime for sterilization and removing residues

“…The cell permeability was analyzed by propidium iodide (PI) stain. 30,31 As shown in Fig. 7, when 100 mg L À1 CAZ combined with 10 mg L À1 Ag 3 PO 4 , cell permeability increases 62.6% than 100 mg L À1 CAZ.…”

Bioinspired synthesis of optically and thermally responsive nanoporous membranes

“…[1][2][3] Environmentally responsive porous membranes (ERPMs) have a wide array of applications, including use in sensors, bioseparation, drug delivery systems and valves that serve to interconnect microfluidic systems and control interflow. [3][4][5][6][7][8][9][10][11][12] For decades, the efforts to develop ERPMs have been approached mainly through the coupling of environmentally responsive polymers to polymeric porous membranes. This technique allows for rapid 'on/ off' switching and flow control because it synergizes the chemical stability and mechanical strength of the polymer membrane with the fast response times of the free-ended polymer chains chemically bonded to them.…”

“…The synthesis involves prior grafting of poly(N-isopropyl acrylamide) (PNIPAM) chains to the walls of the polycarbonate membrane, followed by an in situ reduction of a metallic salt, HAuCl 4 . The synthesis pathway proposed is based on our previous work, 11,22,23 which describes the capability of PNIPAM to be coupled to metallic particles, control their sizes and shapes, and form opto-thermally responsive nanocomposite materials. 22,23 We present a bioinspired state-of-the-art technique and device that utilizes simplified mechanisms to outperform the 'on/off' switching of its natural counterpart.…”