Abstract
Highly efficient magnetic release from nanocomposite microparticles is shown, which are made of Poly (N-isopropylacrylamide) hydrogel with embedded iron nanowires. A simple microfluidic technique was adopted to fabricate the microparticles with a high control of the nanowire concentration and in a relatively short time compared to chemical synthesis methods. The thermoresponsive microparticles were used for the remotely triggered release of Rhodamine (B). With a magnetic field of only 1 mT and 20 kHz a drug release of 6.5% and 70% was achieved in the continuous and pulsatile modes, respectively. Those release values are similar to the ones commonly obtained using superparamagnetic beads but accomplished with a magnetic field of five orders of magnitude lower power. The high efficiency is a result of the high remanent magnetization of the nanowires, which produce a large torque when exposed to a magnetic field. This causes the nanowires to vibrate, resulting in friction losses and heating. For comparison, microparticles with superparamagnetic beads were also fabricated and tested; while those worked at 73 mT and 600 kHz, no release was observed at the low field conditions. Cytotoxicity assays showed similar and high cell viability for microparticles with nanowires and beads.
Highlights
(N-isopropylacrylamide) (PNIPAM) is a stimuli-responsive or “smart” microgel that swells by uptaking a solvent below its transition temperature, called the lower critical solution temperature (LCST), and shrinks above this LCST by expelling the solvent[1]
We propose a new thermoresponsive nanocomposite material made of PNIPAM microparticles with embedded iron nanowires (NWs)
Magnetic heating is based on friction rather than magnetic losses (Néel relaxation and Brownian relaxation in case of NBs)[23], enabling heating of these nanowire composite (NWC) particles with only a fraction of the fields and frequencies required for nanobead composite (NBC) particles, made of PNIPAM with iron oxide NBs
Summary
Release Applications received: 27 November 2015 accepted: 06 June 2016 Published: 23 June 2016. Compared to externally applied direct thermal stimulation that heats the entire area of operation, or integrated heaters that require complex fabrication steps, utilizing magnetic losses from embedded magnetic nanobeads (NBs) provides highly localized and remotely controlled PNIPAM triggering While this approach has been successfully implemented for various applications, the drawback is primarily the low heating efficiency, i.e. the need for high magnetic fields (50 mT to 100 mT) and high frequencies (300 kHz to 1000 kHz)[19,20]. Compared to the values typically reported in literature for NBC particles the drug release from NWC particles is achieved with a magnetic field that is about five orders of magnitude lower in power This dramatic decrease in power requirement allows realizing applications and devices in a much more compact, efficient and cheaper way. While NBC(2.54) was used for comparison with NWC with the same concertation values, NBC(0.175) allows a comparison with NWC under the condition of similar heating power and timescales, when applying a high-power magnetic field of 73 mT and 600 kHz to the NBC particles and a low-power magnetic field of 1 mT and 20 kHz to the NWC particles
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