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.

Getting in shape: DNA‐brush copolymer amphiphiles assemble into micelles with morphologies determined by selective interactions that allow manipulation of the magnitude of steric and electrostatic repulsions in the micelle shells. Cylinder‐to‐sphere phase transitions occur when an input DNA sequence is added to the micelles (see picture).

Micelles were prepared from polymer-peptide block copolymer amphiphiles containing substrates for protein kinase A, protein phosphatase-1 and matrix metalloproteinases 2 and 9. We examine reversible switching of the morphology of these micelles through a phosphorylation-dephosphorylation cycle and study peptide-sequence directed changes in morphology in response to proteolysis. Furthermore, the exceptional uniformity of these polymer-peptide particles makes them amenable to cryo-TEM reconstruction techniques lending insight into their internal structure.

In this paper we present in situ transmission electron microscopy (TEM) of synthetic polymeric nanoparticles with emphasis on capturing motion in a solvated, aqueous state. The nanoparticles studied were obtained from the direct polymerization of a Pt(II)-containing monomer. The resulting structures provided sufficient contrast for facile imaging in situ. We contend that this technique will quickly become essential in the characterization of analogous systems, especially where dynamics are of interest in the solvated state. We describe the preparation of the synthetic micellar nanoparticles together with their characterization and motion in liquid water with comparison to conventional electron microscopy analyses.