ABSTRACT
A systematic study has been carried out to develop a material with significant protection properties from galactic cosmic radiation and solar energetic particles. The research focused on the development of hydrogen-rich benzoxazines, which are particularly effective for shielding against such radiation. Newly developed benzoxazine resin can be polymerized at 120 °C, which meets the low-temperature processing requirements for use with ultrahigh molecular weight polyethylene (UHMWPE) fiber, a hydrogen-rich composite reinforcement. This highly reactive benzoxazine resin also exhibits low viscosity and good shelf-life. The structure of the benzoxazine monomer is confirmed by proton nuclear magnetic resonance and Fourier transform infrared spectroscopy. Polymerization behavior and thermal properties are evaluated by differential scanning calorimetry and thermogravimetric analysis. Dynamic mechanical analysis is used to study chemorheological properties of the benzoxazine monomer, rheological properties of the cross-linked polybenzoxazine, and rheological properties of UHMWPE-reinforced polybenzoxazine composites. The theoretical radiation shielding capability of the composite is also evaluated using computer-based simulations.
ABSTRACT
Implant-assisted targeting of magnetic particles under the influence of an external magnetic field has previously been verified through mathematical modeling, in vitro studies, and in vivo studies on rat carotid arteries as a feasible method for localized drug delivery. The present study focuses on the development of nanoparticles for the treatment of in-stent thrombosis. Magnetic nanoparticles in the size-range 10-30 nm were synthesized in a one-pot procedure by precipitation of ferrous hydroxide followed by oxidation to magnetite. The nanoparticles were silanized with tetraethyl orthosilicate in the presence of triethylene glycol and/or polyethylene glycol. The surface coated magnetite nanoparticles were activated with either N-hydroxysulfosuccinimide or tresyl chloride for covalent immobilization of tissue plasminogen activator (tPA). Hysteresis loops showed saturation magnetizations of 55.8, 44.1, and 43.0 emu/g for the naked nanoparticles, the surface coated nanoparticles, and the tPA-nanoparticle conjugates, respectively. The hemolytic activity of the nanoparticles in blood was negligible. An initial in vivo biocompatibility test in pig, carried out by intravascular injection of the nanoparticles in a stented brachial artery, showed no short-term adverse effects. In vitro evaluation in a flow-through model proved that the nanoparticles were captured efficiently to the surface of a ferromagnetic coiled wire at the fluid velocities typical for human arteries. A preliminary test of the tPA-nanoparticle conjugates in a pig model suggested that the conjugates may be used for treatment of in-stent thrombosis in coronary arteries.
