Controlled actuation of alternating magnetic field-sensitive tunable hydrogels

Abstract

The feasibility of using tunable magnetic nano-particles embedded in cylindrical hydrogel materials for guided actuation via controlled modulation of oscillating magnetic field and frequency is investigated. Ferromagnetic nano-particles (Fe3O4) encapsulated within a thermo-sensitive polymer network [-poly(N-isopropylacrylamide) (PNIPAM)] were polymerized inside 1.5 mm diameter capillary tubes. Inside alternating magnetic field (25–70 Oe, 150–280 kHz), the polymer monolith quickly bends along the longitudinal axis. The bending behaviour of the polymer monolith was influenced by the following factors: (a) mechanical strength of the monolith, (b) ac field-induced temperature regulation and (c) the surface evaporation. The equilibrium bending angle reached a maximum value of 74° at 30 Oe, 200 kHz, between 15% and 35% relative humidity conditions. In addition, we found that micro-scale monolith (300 µm diameter) exhibited significantly faster actuation response compared with the 1500 µm diameter hydrogel cylinder. Both de-swelling efficiency and volumetric transition temperature were not affected due to the nano-magnet incorporation. As ac magnetic field-induced controlled modulation can directly transform the absorbed energy into bending and shrinkage simultaneously for temperature sensitive polymers, i.e. the absorbed energy is converted into mechanical work, this novel approach may lead to a new category of magnetically responsive polymeric structures for potential applications in the field of smart gel-based devices, such as micro-sensors and actuators, and particularly in biomedical fields.

Novel magneto-responsive membrane for remote control switchable molecular sieving

“…Besides better heat generation, the relatively big size was also expected to prevent the leaching out from the hydrogel network during filtration, because mesh size of such gel is typically less than 20 nm. 35,41,50,51 The temperature changes for water and MNP dispersion after 5 minutes of AMF exposure are shown in Table 1. The SLP calculated using eqn (3) is 672 W g À1 and it correlates well with the reported SLP of iron oxide nanoparticles with similar size and under similar field conditions (magnetosome: diameter 30-40 nm, f = 410 kHz, H = 10 kA m À1 , SLP = 960 W g À1 ), 36 indicating the relatively good heating efficiency of the particles and AMF conditions used in this study.…”

Functionalization of hybrid poly(n‐isopropylacrylamide) hydrogels for Escherichia coli cell capture via adsorbed intermediate dye molecule

“…Our method may also be used to attach carbon nanotubes to the surface of the hydrogel, with potential significance in the improvement of hydrogel mechanics, as well as in areas of biosensing and biotechnology . For instance, carbon‐based hybrid PNIPAM hydrogels have been shown to increase conductivity and improve shrinking/swelling kinetics in hydrogels . Magnetic Fe 3 O 4 powder has been used to synthesize magnetic hybrid hydrogels that are capable of being easily manipulated structurally, which has ramifications in biotechnology, specifically in the areas of direct drug delivery, hypothermia treatment and microvalve construction .…”

“…For instance, carbon‐based hybrid PNIPAM hydrogels have been shown to increase conductivity and improve shrinking/swelling kinetics in hydrogels . Magnetic Fe 3 O 4 powder has been used to synthesize magnetic hybrid hydrogels that are capable of being easily manipulated structurally, which has ramifications in biotechnology, specifically in the areas of direct drug delivery, hypothermia treatment and microvalve construction . Other microbe capturing materials such as immunomagnetic beads may be attached directly to the surface of the hybrid hydrogel using this method .…”

A Magnetically Tunable Check Valve Applied to a Lab-on-Chip Nitrite Sensor

“…The reported systems use oscillating magnetic fields to drive an on-chip piston with two ball-style check valves to pump fluid. Other groups in the biomedical field have researched magnetic hydrogels [25,26,27] to create magnetically actuated microvalves [28,29]. These systems, however, are intended for use in benchtop applications and are not likely to withstand extreme pressure environments.…”