We describe a protocol to rapidly and reliably visualize blood vessels in experimental animals. Blood vessels are directly labeled by cardiac perfusion using a specially formulated aqueous solution containing 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), a lipophilic carbocyanine dye, which incorporates into endothelial cell membranes upon contact. By lateral diffusion, DiI also stains membrane structures, including angiogenic sprouts and pseudopodial processes that are not in direct contact. Tissues can be immediately examined by conventional and confocal fluorescence microscopy. High-quality serial optical sections using confocal microscopy are obtainable from thick tissue sections, especially at low magnification, for three-dimensional reconstruction. It takes less than 1 h to stain the vasculature in a whole animal. Compared with alternative techniques to visualize blood vessels, including space-occupying materials such as India ink or fluorescent dye-conjugated dextran, the corrosion casting technique, endothelial cell-specific markers and lectins, the present method simplifies the visualization of blood vessels and data analysis.

Herein, we describe a method for targeting to and retaining intravenously (IV) injected nanoparticles at the site of acute myocardial infarction (MI) in a rat model. Enzyme-responsive peptide-polymer amphiphiles (PPAs) were prepared and assembled as spherical micellar nanoparticles. The resulting nanoparticles respond to matrix metalloproteineases (MMP-2 and MMP-9) that are upregulated in heart tissue post-myocardial infarction. The nanoparticles undergo a morphological transition from spherical-shaped, discrete materials to network-like assemblies when acted upon by MMPs. We show that 15–20 nm, responsive nanoparticles can be injected IV, undergoing reaction with MMPs in the heart after MI, with the resulting assemblies remaining within the infarct for up to 28 days. The initial studies reported here set the stage for the development of targeting systems for therapeutic delivery for acute MI. Critically, with this development, injection of materials is possible via the IV route immediately following MI, resulting in targeted accumulation and long term retention at the site of MI.

Recently, the development of polydopamine (PDA) has demonstrated many excellent performances such as free radical scavenging, UV shielding, photothermal conversion, and biocompatibility. These unique properties make PDA widely designed as...