Magnetically targetable microcapsules display subtle changes in permeability and drug release in response to a biologically compatible low frequency alternating magnetic field

High frequency alternating magnetic fields (AMF) have been widely used as a non-invasive method to induce local hyperthermia for antitumor treatment and to efficiently trigger drug release from various carriers. However, few studies have exploited the potential of targeted drug delivery to healthy cells or tissue and the use of low frequency AMF (LF-AMF) for intracellular triggered release. To achieve this goal, doxycycline was delivered with the layer-by-layer (LbL) assembled magnetic microcapsules, and AMF with low frequency (50 Hz) was applied. The low frequency AMF had little effect on morphology of microcapsules, which upon exposure for 360 min caused no significant damage and had the advantage of minimizing heating effects. Nonetheless, microcapsule permeability increased as a function of exposure time when assessed using FITC-dextran (70 kDa) with the number of permeable microcapsules increased from 13.5% (20 min) to 52.8% (360 min). Increased permeability also enhanced in vitro doxycycline release in genetically engineered myoblast cells where EGFP expression is regulated by the tetracycline system, while targeted EGFP expression was observed by magnetically navigating the microcapsules to a site of interest. Upon LF-AMF exposure of 30 min, no cytotoxicity was observed, but intracellular doxycycline release was promoted and enhanced EGFP expression as demonstrated by EGFP fluorescence intensity measurement. This study reveals the possibility of targeted drug delivery and using LF-AMF as a non-cytotoxic intracellular trigger of drug release from microcapsules without alteration in cell viability.