Synthesis and characterization of spherical magnetite/biodegradable polymer composite particles

A method for preparing colloidal particles formed by a magnetite nucleus an d a biodegradable poly(DL-lactide) polymer coating is first described. The method is based on the so-called double-emulsion technique, employed to obt ain polymeric spheres loaded with therapeutic drugs, to be used as drug del ivery vectors. The aim of this work was to obtain, in a reproducible and ra ther simple way, colloidal particles that were both magnetic field responsi ve, and useful as drug delivery systems. In order to investigate to what ex tent is this target achieved, we compare the structure, chemical compositio n, and surface properties of the composite particles with those of the nucl eus and the coating material. Although the surface properties of the magnet ite core are not completely masked, this preliminary study shows that the s ynthetic new material displays a behavior intermediate between that of magn etite and poly (DL-lactide) spheres. Thus, electrophoresis measurements as a function of pH shows that the isoelectric point (pH(iep) = 5.2) of core/s hell colloids is in between those of magnetite (pH(iep) = 7) and polymer (p H(iep) < 2). A similar conclusion is reached when a surface thermodynamic s tudy is performed on the three types of particles: the electron-donor compo nent of the surface free energy of the solids is the quantity that appears to be most sensitive to the surface composition. The fact that poly(DL-lact ide) is close to being a nonpolar material gives rise to a measurable decre ase in the electron-donor component of the surface free energy, although th e effect of coating is also observable in the electron-acceptor and the apo lar van der Waals component. (C) 2001 Academic Press.