Quantitative, label-free characterization of stem cell differentiation at the single-cell level by broadband coherent anti-Stokes Raman scattering microscopy.

We use broadband coherent anti-Stokes Raman scattering (BCARS) microscopy to characterize lineage commitment of individual human mesenchymal stem cells cultured in adipogenic, osteogenic, and basal culture media. We treat hyperspectral images obtained by BCARS in two independent ways, obtaining robust metrics for differentiation. In one approach, pixel counts corresponding to functional markers, lipids, and minerals, are used to classify individual cells as belonging to one of the three lineage groups: adipocytes, osteoblasts, and undifferentiated stem cells. In the second approach, we use multivariate analysis of Raman spectra averaged exclusively over cytosol regions of individual cells to classify the cells into the same three groups, with consistent results. The exceptionally high speed of spectral imaging with BCARS allows us to chemically map a large number of cells with high spatial resolution, revealing not only the phenotype of individual cells, but also population heterogeneity in the degree of phenotype commitment.

LTB4 is a signal-relay molecule during neutrophil chemotaxis.

Neutrophil recruitment to inflammation sites purportedly depends on sequential waves of chemoattractants. Current models propose that leukotriene B(4) (LTB(4)), a secondary chemoattractant secreted by neutrophils in response to primary chemoattractants such as formyl peptides, is important in initiating the inflammation process. In this study we demonstrate that LTB(4) plays a central role in neutrophil activation and migration to formyl peptides. We show that LTB(4) production dramatically amplifies formyl peptide-mediated neutrophil polarization and chemotaxis by regulating specific signaling pathways acting upstream of actin polymerization and MyoII phosphorylation. Importantly, by analyzing the migration of neutrophils isolated from wild-type mice and mice lacking the formyl peptide receptor 1, we demonstrate that LTB(4) acts as a signal to relay information from cell to cell over long distances. Together, our findings imply that LTB(4) is a signal-relay molecule that exquisitely regulates neutrophil chemotaxis to formyl peptides, which are produced at the core of inflammation sites.

A Surrogate for Debye-Waller Factors from Dynamic Stokes Shifts.

We show that the short-time behavior of time-resolved fluorescence Stokes shifts (TRSS) are similar to that of the intermediate scattering function obtained from neutron scattering at q near the peak in the static structure factor for glycerol. This allows us to extract a Debye-Waller (DW) factor analog from TRSS data at times as short as 1 ps in a relatively simple way. Using the time-domain relaxation data obtained by this method we show that DW factors evaluated at times ≥ 40 ps can be directly influenced by α relaxation and thus should be used with caution when evaluating relationships between fast and slow dynamics in glassforming systems.

Label-free cellular imaging by broadband coherent anti-Stokes Raman scattering microscopy.

Raman microspectroscopy can provide the chemical contrast needed to characterize the complex intracellular environment and macromolecular organization in cells without exogenous labels. It has shown a remarkable ability to detect chemical changes underlying cell differentiation and pathology-related chemical changes in tissues but has not been widely adopted for imaging, largely due to low signal levels. Broadband coherent anti-Stokes Raman scattering (B-CARS) offers the same inherent chemical contrast as spontaneous Raman but with increased acquisition rates. To date, however, only spectrally resolved signals from the strong CH-related vibrations have been used for CARS imaging. Here, we obtain Raman spectral images of single cells with a spectral range of 600-3200 cm⁻¹, including signatures from weakly scattering modes as well as CH vibrations. We also show that B-CARS imaging can be used to measure spectral signatures of individual cells at least fivefold faster than spontaneous Raman microspectroscopy and can be used to generate maps of biochemical species in cells. This improved spectral range and signal intensity opens the door for more widespread use of vibrational spectroscopic imaging in biology and clinical diagnostics.

Metal-ligand-containing polymers: terpyridine as the supramolecular unit.

New and interesting properties can be obtained from macromolecular architectures functionalized with supramolecular moieties, particularly metal-ligand complexes. Self-assembly, based on the selective control of noncovalent interactions, guides the creation of hierarchically ordered materials providing access to novel structures and new properties. This field has expanded significantly in the last two decades, and one of the most ubiquitous functionalities is terpyridine. Despite its wide-spread use, much basic knowledge regarding the binding of terpyridine with metal ions remains unknown. Here, the binding constants of PEG-substituted terpyridine in relation to other literature reports are studied and a few examples of supramolecular materials from our laboratory are summarized.

Impact of polymer-bound iodine on fibronectin adsorption and osteoblast cell morphology in radiopaque medical polymers: tyrosine-derived polycarbonate blends as a model system.

Imaging of polymer implants during surgical implantations is challenging in that most materials lack sufficient X-ray contrast. Synthetic derivatization with iodine serves to increase the scattering contrast but results in distinct physicochemical properties in the material which influence subsequent protein adsorption and cell morphology behavior. Herein we report the impact of increasing iodine inclusion on the cell morphology (cell area and shape) of MC3T3-E1 osteoblasts on a series of homopolymers and discrete blend thin films of poly(desaminotyrosyl tyrosine ethyl ester carbonate), poly(DTE carbonate), and an iodinated analogue poly(I(2)-DTE carbonate). Cell morphology is correlated to film chemical composition via measuring fibronectin (FN) adhesion protein adsorption profile on these films. FN exhibits up to 2-fold greater adsorption affinity for poly(I(2)-DTE carbonate) than (poly(DTE carbonate)). A correlation was established between cell area, roundness, and the measured FN adsorption profile on the blend films up to 75% by mass poly(I(2)-DTE carbonate). Data suggest that incorporation of iodine within the polymer backbone has a distinct impact on the way FN proteins adsorb to the surface and within the studied blend systems; the effect is composition dependent.

Thin Film Elastic Modulus of Degradable Tyrosine-Derived Polycarbonate Biomaterials and Their Blends.

The integrity, function, and performance of biomedical devices having thin polymeric coatings are critically dependent on the mechanical properties of the film, including the elastic modulus. In this report, the elastic moduli of several tyrosine-derived polycarbonate thin films, specifically desaminotyrosyl ethyl tyrosine polycarbonates p(DTE carbonate), an iodinated derivative p(I(2)-DTE carbonate), and several discrete blends are measured using a method based on surface wrinkling. The data shows that the elastic modulus does not vary significantly with the blend composition as the weight percentage of p(I(2)-DTE carbonate) increases for films of uniform thickness in the range of 67 to 200 nm. As a function of film thickness, the observed elastic moduli of p(DTE carbonate), p(I(2)-DTE carbonate) and their 50:50 by mass blend show little variation over the range 30 to 200 nm.

A highly selective colorimetric aqueous sensor for mercury.

A new colorimetric mercury sensor is reported based on binding to terpyridine derivatives. It is able to selectively detect Hg II ions over a number of environmentally relevant ions including Ca II, Pb II, Zn II, Cd II, Ni II, Cu II, and others. The response time upon exposure to Hg II is instantaneous. By the "naked eye," the detection limit of Hg II is 2 ppm (25 microM) in solution. With a spectrometer, this detection limit is increased down to 2 ppb (25 nM), which is the current EPA standard for drinking water. The significant problem of mercury poisoning requires new methods of detection that are sensitive and selective. Here we report a new simple system that takes advantage of the unique optical properties generated by terpyiridine-Hg complexes.

Rheological studies of PLLA-PEO-PLLA triblock copolymer hydrogels.

We report detailed rheological data on aqueous gels formed from triblock copolymers of L-lactide and ethylene oxide including the dependence of the viscoelastic moduli on frequency and applied stress of these systems for the first time. We are able to create strong gels with elastic moduli greater than 10,000 Pa, which is an order of magnitude higher than previously achieved with related biocompatible physically associated gels of similar chemistry. Moreover, the value of the elastic modulus strongly depends on PLLA block length, offering a mechanism to control the mechanical properties as desired for particular applications. At the gel point, we observe scaling that is characteristic of a percolated network, G' approximately G" approximately omega(Delta), but with an exponent that is lower than predicted by percolation, Delta=0.36. Our results have implications for the design of new materials for soft tissue engineering, where native tissues have moduli in the kPa range.