Targeted polymer ultrasound contrast agents for molecular imaging

Cardiovascular disease (CVD) is a complex pathology that begins at the molecular and cellular levels, but typically manifests itself via high blood pressure, stroke or heart failure. Detecting CVD early in the disease process would allow for more effective treatment. Ultrasound provides inexpensive, real-time imaging of the body but needs to be coupled with a disease targeted ultrasound contrast agent (USCA) to provide insight into molecular events at specific pathologic tissues. Therefore, the specific goals of this work were to fabricate, and characterize a peptide-targeted polymer ultrasound contrast agent (USCA) designed to bind to Human Umbilical Vein Endothelial Cells (HUVECs) under flow conditions.;Spherical polymer UCSAs (average diameters ranging from 1-3 mum) were fabricated using a modified double emulsion technique by optimizing relevant processing parameters. The internal structure of the fabricated USCAs was classified as hollow or solid by correlating high frequency measurements of the normalized backscatter coefficient (NBC) with the expected differences from theoretical predictions of scattering by solid and hollow spheres. The fabricated polymer USCAs that were deemed hollow also exhibited high levels of echogenicity when exposed to diagnostic frequencies (5-10 MHz) of ultrasound. This process was selected for creating targeted USCAs.;A targeting strategy of physically incorporating the lipid-based ligand was investigated using a known polymer microsphere system in which the microspheres were characterized morphologically by SEM, proton nuclear magnetic resonance (HNMR), and zeta potential measurements. The surface architecture that led to significant binding was composed of 2000 Da molecular weight unliganded PEG-lipids and 3350 Da molecular weight liganded PEG-lipids. The mixed surface architecture was used in the polymer USCA system for coupling biotinylated peptide RGD (Arg-Gly-Asp) through avidin-biotin-bridging. RGD-targeted polymer USCA adhered to HUVEC after 30 min of static incubation. Under flow conditions at shear rates of 46, 62, and 108 s-1, the adherence of RGD-targeted polymer USCA increased with shear rate from 3 USCA/cell to 8 USCA/cell.;In conclusion, methods were developed to produce, and characterize polymer USCAs functionalized with physical incorporation techniques. These site-targeted polymer USCAs attached to HUVEC surfaces under flow. Thus, these targeted USCAs have demonstrated potential for molecular imaging of CVD.