S. H. Chen

Multiscale structure of calcium- and magnesium-silicate-hydrate gels

Concrete is the worlds most widely used building material. However, the production of CaO-based cements generates large amounts of anthropogenic emissions of CO2. Among different strategies to reduce CO2 emissions, newly developed MgO-based cements, though currently suffering from inferior mechanical properties, are some of the most promising and attractive options. By combining wide- and small-angle X-ray scattering and electron microscopy, we identified differences in the multiscale structure of the two main binding phases: the calcium-silicate-hydrate (C-S-H) gel for CaO-based cements and the magnesium-silicate-hydrate (M-S-H) gel for MgO-based cements. We found the primary unit at the nanoscale level of C-S-H to be a multilayer disk-like globule, whereas for M-S-H it is a spherical globule. These prominent differences result in diverse microstructures, leading to disparities in mechanical properties and durability for the associated cements. Modulating the M-S-H structure and enhancing the compatibility between C-S-H and M-S-H will be the key to improve the robustness of eco-friendly MgO-based binders.

Development of Secreted Protein and Acidic and Rich in Cysteine (SPARC) Targeted Nanoparticles for the Prognostic Molecular Imaging of Metastatic Prostate Cancer

Prostate cancer is the most commonly diagnosed non-skin malignancy in the United States and presents with a wide range of aggressiveness from extremely slow-growing to highly aggressive. There is a clinical need to determine the metastatic potential of the primary tumor to design the most appropriate treatment plan ranging from watchful waiting to more aggressive, invasive surgical treatments. In this study we have developed a nanoparticle based imaging agent that targets SPARC (Secreted Protein Acidic Rich in Cysteine), a molecular marker of prostate cancer metastatic potential. Previous studies by this group used phage display to identify a peptide with high binding affinity and specificity for SPARC. In this study, the SPARC-targeted peptide sequence was used to design a biomaterial with improved pharmacokinetic properties by attaching it to a biocompatible nanoparticle that is also coupled to a fluorophore for in vivo imaging. Prostate cancer cell lines with varying degrees of SPARC expression were used to show the ability of the targeted nanoparticle to bind specifically to SPARC in vitro and in vivo including the clinically relevant bone and lung metastases. We show that in vivo imaging information correlates with the metastatic potential of the prostate tumor. This prognostic information could enable doctors to stratify patients and design personalized treatment strategies.

A screening paradigm for the design of improved polymer-coated superparamagnetic iron oxide nanoparticles

Polymer-coated superparamagnetic iron oxide nanoparticles (NPs) have been used for a variety of biomedical applications, including as MRI contrast agents, for the treatment of iron anemias, and for ex vivo labeling of the cells used in cell-based therapies so that they can be tracked by MRI. Here we describe a three-stage screening paradigm to develop high potency (i.e., high relaxivity), stable, polymer-coated superparamagnetic iron oxide NPs. Each screen examined different facets of the interaction between iron oxides and polymers. First, an Ion Challenge Screen assessed whether a polymer interacted with the surface of the iron oxide. Second, a Synthesis Optimization Screen examined whether polymers that passed the Ion Challenge Screen were compatible with the synthetic method used to make NPs, and optimized the synthetic method for each polymer. Finally, a Heat Stress/Stability Screen assessed the stability of the optimized polymer-coated superparamagnetic iron oxides that passed the Synthesis Optimization Screen. A carboxymethyl dextran-coated superparamagnetic iron oxide nanoparticle (CMD-NP) with a transverse relaxivity (R2) of 271 mM−1 s−1 and a diameter of 47 nm by dynamic light scattering was obtained. A second NP, a carboxymethyl polyvinyl alcohol-coated nanoparticle (CMPVA-NP) had an R2 of 119 and diameter of 37 nm, but was less stable to heat stress than the CMD-NP. The CMD-NP is a polymer-coated superparamagnetic iron oxide NP with improved relaxivity and high stability achieved without the crosslinking procedure used in our cross-linked iron oxide (CLIO) NP.

Neutron scattering studies of dynamic crossover phenomena in a coupled system of biopolymer and its hydration water

We have observed a Fragile-to-Strong Dynamic Crossover (FSC) phenomenon of the α-relaxation time and self-diffusion constant in hydration water of three biopolymers: lysozyme, B-DNA and RNA. The mean squared displacement (MSD) of hydrogen atoms is measured by Elastic Neutron Scattering (ENS) experiments. The α-relaxation time is measured by Quasi-Elastic Neutron Scattering (QENS) experiments and the self-diffusion constant by Nuclear Magnetic Resonance (NMR) experiments. We discuss the active role of the FSC of the hydration water in initiating the dynamic crossover phenomenon (so-called glass transition) in the biopolymer. The latter transition controls the flexibility of the biopolymer and sets the low temperature limit of its biofunctionality. Finally, we show an MD simulation of a realistic hydrated powder model of lysozyme and demonstrate the agreement of the MD simulation with the experimental data on the FSC phenomenon in the plot of logarithm of the α-relaxation time vs. 1/T.

Glass States in Dense Attractive Micellar Systems

Recent mode coupling theory (MCT) studies show that if a short-range attractive interaction is added to the pure hard sphere system, one may observe a new type of glass. Within a certain volume fraction range where the two glass-forming mechanisms nearly balance each other, varying the external control parameter, the effective temperature, makes the glass-to-liquid-to-glass re-entrance and the glass-to-glass transitions possible. In this context, by using small angle neutron scattering and photon correlation measurements in a micellar system, the chapter presents evidence on this complex phase behavior. Finally, in agreement with MCT, an end point on the glass-to-glass transitions line is found, beyond which, the two glasses become identical in their local structure and the long time dynamics.