Oscillating magnetic field-actuated microvalves for micro- and nanofluidics

Abstract

The feasibility of using tunable magnetic nanoparticles embedded in cylindrical hydrogel materials as a flow regulator via thermo-mechanical gating is studied within microfluidic channels. Ferromagnetic nanoparticles (Fe3O4) encapsulated within a thermo-sensitive polymer network (-poly(N-isopropylacrylamide) (PNIPAM)) was polymerized inside 300 µm diameter micro-capillary tubes. An oscillating magnetic field range 20–125 Oe, (100–1000 kHz) was used to induce heat and control the valving action. Valving action was effectively regulated by modulating the magnetically responsive PNIPAM networks (MPNIPAM) and thereby physically regulating the harmonics (swelling and shrinking) of the polymer monolith inside the microchannel. Magnetic properties in terms of saturation magnetization, remanence and coercivity of the designed system have been extracted for data accuracy. The optimum concentration of NIPAM monomer in the polymer matrix and the embedded nanoparticles yield ∼80% volume shrinkage inside the microchannel, which is close to the undoped PNIPAM system, without compromising the oscillating field induced heating. Very importantly, the oscillating field-actuated de-swelling response time is ∼3 s, which is significantly faster than the thermal actuation, and in addition the microvalve exhibits a faster response time compared with the macrovalve (MPNIPAM monolith inside 1500 µm diameter channel). The enhanced shrinkage rate and the actuation efficiency might be ideal for many biomedical applications, including synergistic application of heat and sustained releasing capability of chemotherapeutic agents.

A remotely operated drug delivery system with an electrolytic pump and a thermo-responsive valve

“…We found that the size of the iron particles we used did not negatively affect the valve's function, yet they are considerably more cost efficient than nano-sized beads like the ones used previously. 10 The serpentine micro-channel (width: 0.4 mm and depth: 0.3 mm) was made on a PMMA substrate using a laser cutter (Universal PLS6.75). This serpentine structure helps keeping the PNIPAM in place, and has an increased area efficiency compared to a straight channel.…”

“…This serpentine structure helps keeping the PNIPAM in place, and has an increased area efficiency compared to a straight channel. 10 After uniformly distributing 3 mg of the iron micro-particles into the micro-channel, the PMMA substrate was bonded to another PMMA substrate using a thermal-compression bonding system (INSTRON Dual Column Testing Systems). The PNIPAM hydrogel was formed by mixing equal volumes of two different solutions.…”

“…In the previous work, a thermo-responsive poly (N-Isopropylacrylamide) (PNIPAM) valve was developed, which was controlled by inductive heating with an alternating-currentdriven electromagnetic field. 10 PNIPAM is a thermo-responsive hydrogel, and its volume changes with temperature. By expelling or absorbing water molecules, depending on whether it is above or below a designed lower critical solution temperature (LCST), 11,12 respectively, the polymer in the valve channel seals the valve or allows the drug to flow through it.…”

Recent developments in microfluidic large scale integration

“…Potential replacement technologies include electrostatic [10], magnetic [11], torque generated [12], Braille pin [13], thermal [14,15] and shape memory alloy (SMA) [3] actuation.…”

Smart Drug Delivery Strategies Based on Porous Nanostructure Materials

“…Due to its controlled size, morphology and release, and excellent biocompatibility, biodegradable organic/inorganic micro/nano-particles have been studied extensively [2][3][4][5]. In fact, stimuli-responsive systems could facilitate drug release to reach a target environment.…”