Peptide Brush Polymers and Nanoparticles with Enzyme-Regulated Structure and Charge for Inducing or Evading Macrophage Cell Uptake

Cellular uptake by macrophages and ensuing clearance by the mononuclear phagocyte system stands as a significant biological barrier for nanoparticle therapeutics. While there is a growing body of work investigating the design principles essential for imparting nanomaterials with long-circulating characteristics and macrophage evasion, there is still a widespread need for examining stimuli-responsive systems, particularly well-characterized soft materials, which differ in their physiochemical properties prior to and after an applied stimulus. In this work, we describe the synthesis and formulation of polymeric nanoparticles (NPs) and soluble homopolymers (Ps) encoded with multiple copies of a peptide substrate for proteases. We examined the macrophage cell uptake of these materials, which vary in their peptide charge and conjugation (<i>via</i> the N- or C-terminus). Following treatment with a model protease, thermolysin, the NPs and Ps undergo changes in their morphology and charge. After proteolysis, zwitterionic NPs showed significant cellular uptake, with the C-terminus NP displaying higher internalization than its N-terminus analogue. Enzyme-cleaved homopolymers generally avoided assembly and uptake, though at higher concentrations, enzyme-cleaved N-terminus homopolymers assembled into discrete cylindrical structures, whereas C-terminus homopolymers remained dispersed. Overall, these studies highlight that maintaining control over NP and polymer design parameters can lead to well-defined biological responses

Dye Encapsulation in Polynorbornene Micelles

The encapsulation efficiency of high-<i>T</i>_g polynorbornene micelles was probed with a hydrophobic dye 2,6-diiodoboron-dipyrromethene (BODIPY). Changes in the visible absorption spectra of aggregated versus monomeric dye molecules provided a probe for assessing encapsulation. Polynorbornene micelles are found to be capable of loading up to one BODIPY dye per ten polymers. As the hydrophilic block size increased in the polymeric amphiphiles, more of the dye was incorporated within the micelles. This result is consistent with the dye associating with the polymer backbone in the shell of the micelles. The encapsulation rate varied significantly with temperature, and a slight dependence on micellar morphology was also noted. Additionally, we report a 740 μs triplet lifetime for the encapsulated BODIPY dye. The lifetime is the longest ever recorded for a BODIPY triplet excited state at room temperature and is attributed to hindered triplet–triplet annihilation in the high-viscosity micellar shell