Study On Fabrication And Controlled Release Of Magnetic-responsive Microcapsules

Recently, stimuli-responsive materials are finding an increasingly large number ofapplications in surface coatings, optoelectronics, corrosion protection, and biomedicine anddrug delivery, and the latter fields constitute growing outreach and importance. The optimumgoal of microencapsulation technique is to release the core content at the right time, rightplace and in a controlled manner in order to achieve the desired functionality. However, theconventional release method is either based on passive slow diffusion, or completedestruction of the microcapsule shell.In the present study, hydrothemal method was employed for the preparation ofmonodispersed ferrite nanospheres, followed by coating with silica by a modified St bermethod. Magnetic nanoparticles were embeded into the polyelectrolyte capsules fabricatedvia layer-by-layer assembly. Finally, magnetic-responsive microcapsules with a magneticcore and various magnetic nanoparticles in the shell were obtained after dissolving the silicatemplate. The size of the monodispersed magnetic nanoparticles is tunable by varying thetemperature of the precusor’s solution and the volume ratio of ethylene glycol anddiethylene glycol. By varying the amount of TMAH in the TEOS hydrolysis step, it wasfound that adding1.6mL of TMAH gave the best silica coating on the surface of themagnetic particles, and the size of the cavity of microcapsules can be tuned by varying theamount of TEOS. The increase of ironic strength results the disassembly of polyelectrolytesand nanoparticles.In the release test, it was found that the amount of release is41%,80%and96%in80min when the magnetic field intensity is0,4000and5800G, respectively. With a4000Gmagnetic field, it only needs25min to reach the amount of41%. Similarly, it only take37min to release80%of the core material under a magnetic field of5800G. Compared to therelease curve of the microcapsules with no magnetic nanoparticles embedded in the shell, theattraction between microcapsules and the magnet which causes the deformation ofmicrocapsules plays the main role in accelerating the release speed of the core material,while the deformation of microcapsules caused by the alignment of the magneticnanoparticles embedded in the shell has little effect in controlling the release of themicrocapsule.Compared with previous controlled release methods, this is a novel and proactive release mechanism which the release can be better controlled. In addition, the microcapsulesare reusable. At the side of other pressure-induced release, magnetic-responsivemicrocapsules with good biocompatibility can be controlled remotely. Our work opens a newvenue in targeted drug delivery and controlled release applications.