15 th International Symposium on MICROENCAPSULATION, Parma (Italy), September 18-21, 2005 NOVEL POLYMERIC PARTICLES AS CONTRAST AGENTS FOR ULTRASOUND IMAGING Emilia Pisani 1,2 , Nicolas Tsapis 1 , Juliane Paris 1 , Valerie Nicolas 3 , Erol Kurtisovski 4 , W. Urbach 4 , Elias Fattal 1 1. UMR CNRS 8612, School of Pharmacy, Université Paris Sud, France. 2. Facoltà di Farmacia,Università degli Studi di Torino, Torino, Italy 3. IFR75-ISIT, Plateau technique-Imagerie cellulaire, Université Paris Sud, France. 4. UMR CNRS 7623, Laboratoire d'Imagerie Paramétrique, Université Paris VI, France. E-mail:emilia.pisani@cep.u-psud.fr Key words: POLYMERIC PARTICLES, CONTRAST AGENTS, ULTRASOUND IMAGING INTRODUCTION The use of ultrasounds as a diagnostic tool has increased in recent years. Advantages of ultrasound are numerous: low cost of the exam, wide availability, portability, low cost of the equipment and absence of ionizing radiation. Unfortunately, ultrasound signal to noise ratio is usually small. Ultrasound contrast agents are therefore used to enhance the signal to noise ratio. Ultrasound contrast agents are usually water dispersions of biocompatible microparticles or microbubles that backscatter ultrasonic waves. The use of ultrasound contrast agents help image delineation of organs, including chambers of the heart or assist in imaging the blood flow. Commercial ultrasound contrast agents (USCA) usually suffer from a poor stability with time in solution with a mean half life of a few hours. The elaboration of more stable USCA would lead to a more widespread clinical use, and take full benefits of harmonic imaging, which enhances considerably the signal to noise ratio [1,3]. Contrast agents are subjected to insonation, and ultrasound energy has been shown to have a role in increasing polymer degradation rates and therefore drug delivery. The ability to externally control degradation and drug release rates opens many possibilities to non-invasive, targeted drug delivery systems. Additionally, ultrasound is a relatively safe triggering mechanism. These systems have great potential for targeted treatment of diseases such as cancer, for which current systemic treatments have severe toxic side effects. We have developed a product candidate for ultrasound contrast agent based on biodegradable polymer encapsulating liquid perfluorocarbons. EXPERIMENTAL METHODS We use a modified solvent evaporation method from a simple oil-in-water emulsion to obtain cavity- containing particles: Poly(lactide-co-glycolide) (RG502, Boehringer-Ingelheim, Germany) is dissolved into methylene chloride along with liquid perfluorocarbon. The organic solution is then emulsified into 20 ml of a 0.5% polyvinyl alcohol (w/v) aqueous solution (MW 30 000-70 000, 89% hydrolyzed, Sigma-Aldrich) using an Ultra-turrax T25 (IKA) operating at a velocity comprised between 8000 and 24500 RPM. Emulsification is performed in a beaker placed over ice for 2 minutes. Methylene chloride is then evaporated by magnetic stirring for about 3 hours at 500RPM in a thermostated bath (20ºC). For fluorescent or confocal microscopy, red nile (Sigma-Aldrich) is added to the organic solution prior to emulsification. Particles have been characterized by laser diffraction (granulometry) or light scattering for size distribution and polydispersity. Shell thickness has been measured on confocal slices and transmission electron microscopy images. Particles morphology has been studied by scanning electron microscopy (SEM). The echogenic properties of microparticles are verified by in vitro measurements performed in pulse-echo mode. RESULTS AND DISCUSSION We have developed a contrast agent candidate based on encapsulation of liquid perfluorocarbon within a biodegradable and biocompatible polymeric shell. Fluorescent optical microscopy and confocal microscopy show spherical particles with an undyed cavity inside. Undyed cavities are well centred within the particles and the shell thickness is homogeneous for each particle (Figure 1). Figure 1: Confocal microscopy image (scale bar =10 µm). PLGA is dyed in red. 443