A variety of materials capable of programmed shape and size changes are found in biological systems, from allosteric enzymes to pseudopodium formation during chemotaxis, and endosomes during cell-uptake processes. By contrast, programmable synthetic supramolecular assemblies of this type are in their infancy, but are expected to have broad utility in a range of applications including targeted delivery and detection. One of the keys to developing these types of materials is understanding how the morphology of the materials affects their properties and interactions with biological systems. This thesis focuses on how to unite two different morphology-dependent properties into a single system. This has allowed access to materials that can be optimized to perform two parallel or competing functions such as longer circulation time in vivo coupled with higher cellular uptake. The first chapter of this thesis describes the importance of developing biohybrid polymeric nanoparticles that use nucleic acids or peptides as biological building blocks incorporated into polymeric nanomaterials. These materials were programmed to undergo well-defined changes in structural features, properties and/or morphology in response to stimuli associated with a given tissue or disease state of interest. Chapter 2 describes the development of DNA-polymeric nanoparticles and their morphologically switchable properties are further applied in programmable pharmacokinetics control in the in vivo system. Chapter 3 describes the development of peptide- hybrid nanoparticles that can undergo morphological switching in response to enzymes. This morphologically switchable peptide-hybrid nanoparticle was applied in targeted accumulation within tumor tissue or myocardial infarcted (MI) tissue. Both of which express inflammatory enzymes to which the particles respond. Chapter 4 describes new methods to characterize or expand the use of the nanoparticle systems described in Chapters 2 and 3, including a new strategy for nanowire fabrication and a new way of determining critical aggregation concentration (CAC) in micelles. Finally, Chapter 5 describes the high- resolution characterization of nanoparticles via an unprecedented super resolution fluorescence imaging technique to characterize the sizes of nanoscale particles in in vivo systems and in ex vivo tissue slices

Matrix metalloproteinase enzymes, overexpressed in HT-1080 human fibrocarcinoma tumors, were used to guide the accumulation and retention of an enzyme-responsive nanoparticle in a xenograft mouse model. The nanoparticles were prepared as micelles from amphiphilic block copolymers bearing a simple hydrophobic block and a hydrophilic peptide brush. The polymers were end-labeled with Alexa Fluor 647 dyes leading to the formation of labeled micelles upon dialysis of the polymers from DMSO/DMF to aqueous buffer. This dye-labeling strategy allowed the presence of the retained material to be visualized via whole animal imaging in vivo and in ex vivo organ analysis following intratumoral injection into HT-1080 xenograft tumors. We propose that the material is retained by virtue of an enzyme-induced accumulation process whereby particles change morphology from 20 nm spherical micelles to micrometer-scale aggregates, kinetically trapping them within the tumor. This hypothesis is tested here via an unprecedented super-resolution fluorescence analysis of ex vivo tissue slices confirming a particle size increase occurs concomitantly with extended retention of responsive particles compared to unresponsive controls.

A method for targeting to and retaining intravenously injected nanoparticles at the site of acute myocardial infarction in a rat model is described. Enzyme-responsive peptide-polymer amphiphiles are assembled as spherical micellar nanoparticles, and undergo a morphological transition from spherical-shaped, discrete materials to network-like assemblies when acted upon by matrix metalloproteinases (MMP-2 and MMP-9), which are up-regulated in heart tissue post-myocardial infarction.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are a promising platform for cardiac studies in vitro, and possibly for tissue repair in humans. However, hiPSC-CM cells tend to retain morphology, metabolism, patterns of gene expression, and electrophysiology similar to that of embryonic cardiomyocytes. We grew hiPSC-CM in patterned islands of different sizes and shapes, and measured the effect of island geometry on action potential waveform and calcium dynamics using optical recordings of voltage and calcium from 970 islands of different sizes. hiPSC-CM in larger islands showed electrical and calcium dynamics indicative of greater functional maturity. We then compared transcriptional signatures of the small and large islands against a developmental time course of cardiac differentiation. Although island size had little effect on expression of most genes whose levels differed between hiPSC-CM and adult primary CM, we identified a subset of genes for which island size drove the majority (58%) of the changes associated with functional maturation. Finally, we patterned hiPSC-CM on islands with a variety of shapes to probe the relative contributions of soluble factors, electrical coupling, and direct cell-cell contacts to the functional maturation. Collectively, our data show that optical electrophysiology is a powerful tool for assaying hiPSC-CM maturation, and that island size powerfully drives activation of a subset of genes involved in cardiac maturation.

In this paper we present in situ transmission electron microscopy 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.