Controlled actuation of biocompatible, multifunctional magnetic hydrogel nanocomposites for lab-on-a-chip applications.
Santaneel Ghosh*, and Tong Cai**.
- Southeast Missouri State University; **University of North Texas
Externally tunable magnetic hydrogel nanocomposites hold great therapeutic potential for magnetic resonance imaging, organelle specific binding, intracellular spatial control, sequential release of drug molecules and flow path regulation in micro-fluidic devices. Smart polymers, conventionally poly(N-isopropylacrylamide) (PNIPAM) or polyethylene glycol (PEG) analogue-based systems are attractive for device fabrication because of their perceived intelligence to external stimuli, i.e., possession of lower critical solution transition (LCST) behavior at ~30-40C, close to normal physiological temperature. Alternating magnetic field can be applied to change the phase of the nano-magnet doped polymeric structures as the magnetic nanodots act as nano sources of heat when exposed to the oscillating magnetic field. Efficiency of the induced heat generation inside the colloidal medium can be controlled intrinsically by changing the size, concentration and composition of the nano-magnets or extrinsically by tuning the frequency and intensity of the applied magnetic fields. Recent studies have reported various magnetic hydrogel nano-composites and temperature regulation induced by remotely applied ac magnetic excitations. DC magnetic field induced bending has also been investigated. However, although, dc field initiates bending, it is not possible to change the phase of the polymer monolith, i.e., bending and shrinkage are not simultaneous. Remote controlled bending actuation is one of the key requirements for practical use of these systems in lab-on-a-chip applications or as soft actuators in switching devices. As ac magnetic field induced controlled modulation of the polymer networks can directly transform the absorbed energy into bending and shrinkage simultaneously, 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 sensors, artificial muscles, drug delivery systems, and film separation devices.
In this work, a performance enhanced, alternating magnetic field responsive hydrogel nanocomposite system has been designed. The system is capable of producing fast mechanical response in an alternating magnetic field (bending from sides) over a wide range of field and frequency domains. The equilibrium bending angle of the polymer monolith was influenced by several factors: mechanical strength of the monolith, ac field induced temperature regulation and the surface evaporation. In addition, we found that both de-swelling and LCST were not affected due to the nanoparticle incorporation. Combined bending and shrinkage response, especially at the micro-scale indicates its great potential for application in micro-sensors and actuators, particularly in lab-on-a-chip applications. To our knowledge, this is the first time that quantitative oscillating field modulated bending actuation has been investigated for a tunable nano-composite system.
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