Magnetorheological Fluids for Controlling Pharmaceutical Crystal Growth

Magnetorheological (MR) fluids are suspensions of magnet iron microparticles known as carbonyl iron (CI). MR fluids have the ability to increase in viscosity and display high yield stress with the application of an external magnetic field. Herein we explore the feasibility of using these materials to influence the crystallisations of active pharmaceutical ingredients in an attempt to affect crystal morphology. Within the context of this study, we developed a range of magnetorheological fluids by modifying carbonyl iron (CI) particle surfaces with a series of ligands. We used acid terminated PEG, oleic acid, carminic acid and 1-naphthaleneacetic acid as the functionalising ligands. We demonstrated control over crystal morphology in carbamazepine (CBZ) with the use of MR fluids. We managed to selectively crystallise form II of CBZ in PEG and carminic acid functionalised CI, and form III (commercially available/active form) with oleic acid and 1-naphthaleneacetic acid functionalities.

The second part of this study was concerned with improving the heat generation efficiency of iron oxide nanoparticles (NPs) for thermotherapy. Iron oxide NPs can generate heat loss through interaction with an alternating magnetic field (AMF). It was shown in the literature that a “tight” clustering of nanoparticle clusters can be used to increase heat generation efficiency. We therefore investigated the effect of coupling a temperature sensitive polymer (with a LCST of 32 ̊C), poly-N-isopropyl acrylamide (PNIPAM), to a “tight” clustering of magnetic iron oxide nanoparticles. The aim was that this coupling could produce a temperature induced aggregation of the NP clusters, concentrating them and therefore increasing the total heating power. Unfortunately, modification of PNIPAM for coupling resulted in an unknown product that failed to exhibit the desired properties.