98 SYNTHESIS OF POLYETHYLENE MAGNETIC NANOPARTICLES J. Chatterjee 1 , Y. Haik 1 & C.-J. Chen 1 1 Biomagnetic Engineering Lab , FAMU-FSU College of Engineering, Tallahassee, FL 32310 INTRODUCTION: Polymer-based nanoparticles have been synthesized in the last few decades for biomedical applications, mostly in drug delivery, immunoassay and cell separation. Non-magnetic and water-insoluble polyethylene, polypropylene and polystyrene particles are being used as components in cleansing agents in the cosmetic industry and to study the effect of body fluids on polymer particles in vitro. In most cases polymer composite particles and encapsulated particles are prepared by emulsion polymerization, solvent evaporation, hot melt method etc. A convenient way of forming encapsulated particles is to dissolve the polymer and the inorganic particles in a solvent or water and then forming an oil in water emulsion and stabilizing the particles either by chemical crosslinking or by heat. Recently a method has been described by Wunder et al [1] to prepare UHMWPE particles to be used for in vitro study. Their method was based on the concept of nonsolvent and temperature induced crystallization. This method is much easier and less complicated for the preparation of particles with crystalline polymers. In this study the above method is modified to produce composite particles. A method of solvent-nonsolvent temperature induced crystallization, coupled with ultrasonication using an ultrasound probe is reported in this paper. No direct interaction of sound field with molecular species takes place during ultrasound application; moreover, the acoustic cavitations at the transient high temperature and high pressure cause chemical effects and give rise to nanostructured materials. Ultrasound mixing of the polymer with maghemite in the solvent and further mixing with the nonsolvent caused the formation of a homogeneous emulsion with a well-dispersed phase of polymer with maghemite. Initially, the emulsion was formed by mixing the solvent, polymer with maghemite and nonsolvent at high temperature using ultrasound. The ultrasonication caused the formation of micro- droplets, which formed a microphase-separated system while cooled rapidly and consequently a macrophase-separated system was formed separating two liquids. Polymer crystallized with lowering of temperature and the polymer along with magnetic particle was distributed in the nonsolvent medium separating two liquids. Our study focuses on the effect of different solvents and amplitudes of sonication during particle formation. The two solvents with high boiling points were Decalin and OMCTS and the nonsolvent was tetraglyme. The polymer used in this study was low molecular weight polyethylene with broad distribution. The polymer had a wax like appearance and softness. The particles formed with this polymer are non-toxic and can be used for in vitro applications and also as an efficient medium for transdermal drug delivery. These polyethylene magnetic particles were further modified to bind avidin for biomedical applications such as cell separation and immunoassays. The protein coupling efficiency was measured. The magnetic properties were also investigated, since these submicron composite particles are designed for biomedical applications where an external magnetic field will induce a force to separate them. METHODS: Very low molecular weight polyethylene wax (number average molecular weight 700 g/mole) was obtained from the Honeywell Corporation. This product is not hazardous under OSHA Hazard communication. Decalin and tetraglyme were obtained from Sigma- Aldrich, octamethylcyclotetrasiloxane from Dow Chemical Company, sodium oleate from Sigma- Aldrich. All solvents and nonsolvents were used as received. Iron oxide particles with an average diameter range of 5 nm -10 nm were synthesized by a combination of the widely used coprecipitation method along with ultrasonication [2]. These particles were modified with sodium oleate (an anionic surfactant) to attach them to polyethylene. Iron oxide powder was mixed with sodium oleate (30% of weight of polymer) in water, stirred at moderate speed for about 2 hours, dried and then used in a mixture with the polyethylene wax. A dilute (0.05% w/w) solution (10 ml) of the polyethylene wax and iron oxide mixture was made using Decalin at 150 o C in a 25 ml screw cap scintillation vial by ultrasonication. Ten ml of tetraglyme at same temperature was added and sonicated at 50% amplitude for 30 seconds. After dissolution and mixing at 150 o C, the mixture was immediately cooled at 0 o C temperature. An emulsion formed within a few minutes. Within 45 minutes to one hour at room temperature, European Cells and Materials Vol. 3. Suppl. 2, 2002 (pages 98-101) ISSN 1473-2262