Experimental Study On Poly Lactic-Co-Glycolic Acid Microbubble Ultrasonic Contrast Agent Preparation

Objectives: Prepare poly lactic-co-glycolic acid (PLGA) microbubble ultrasonic contrast agent and evaluate its physicochemical and acoustic properties; Develop the technique and formula of preparation of stable and effective microbubbles containing hydrophilic drugs and evaluate its safety on contrast echocardiography.Methods: The poly lactic-co-glycolic acid microbubbles were prepared by double emulsion. Light microscope, scanning electron microscope,Laser Particle Size Analyses and Coulter counter analyzed the appearance, diameter, size distribution and concentrations. PLGA microbubbles with varied ratios of lactic to glycolic acid were prepared and stored separately in common temperature (<250C) and cold closet (40C) in state of freeze drying powder and suspension(PBS). Inspect the physicochemical properties (concentration, PH value,size distribution) in different time respectively. The acoustic properties of the polymer ultrasound contrast agent were evaluated in vitro under different doses with ultrasound energy at a variety of MI values (from 0.03 to 1.2). Left ventricle contrast images were recorded after injection of contrast agent. Prepare EB-PLGA microbubbles and evaluate its drug loading and burst release to choose the best technique and formula. The morphology of EB-PLGA was observed by light and fluorescence microscope. The diagnostic safety of the polymer contrast agent on contrast echocardiograph was preliminary evaluated.Result: PLGA microbubbles were white powder, present suspension after dissolved in saline or PBS. Under microscope, microbubbles had uniform size and preferable dispersing with PH value of suspension 6.5士0.3. The microbubble suspension contained 2.0～4.0×109 /ml microbubbles, with mean diameter of 1.2um. There were no significantly differences on concentration, diameter and PH value compared the group of 40C with the group at common temperature. Microbubble suspension kept in common temperature was soon deformed with PH value descending. In vitro study this kind of echo-contrast agent showed high echogenicity and acoustic intensity had a linear relation with MI. Whlie injected in animals provide a MI-dependent opacification of the left ventricle. There was no significant adverse effect on myocardial permeability while practice polymer ultrasound agent into contrast echocardiograph.Conclusion: The hollow microbubble contrast agent was formulated by double emulsion using biodegradable high molecular polymer of PLGA. The agent had an ideal size and narrow distribution with higher resonance frequency. Low temperature drying conservation could help keep the agent stably. The agent can successfully pass through pulmonary circulation and develop the left ventricle. Optimizing formula could elevate drug loading and decrease burst release unusually. There was no significant adverse effect on myocardial permeability while using EB-PLGA microbubble on contrast echocardiograph. The above results suggest PLGA microbubble is a promising ultrasound contrast agent for its high echogenicity, outstanding stability, and superordinary hydrophilic drugs carrier.