The mechanical properties of alginate hydrogels are critical to their successful use in tissue engineering. We hypothesized that combining alginates of differing molecular weights would allow one to readily control and decouple the viscosity of the pre-gel solution from the post-gel stiffness. To test this, binary hydrogels were prepared by incorporating low molecular weight (MW) alginate (Mn ~ 3.3 x 104 g/mol) into 1 %(w/w) alginate solutions composed of high MW alginate (Mn ~ 2.2 x 105 g/mol). The addition of low MW alginate had minimal effects on the solution viscosity, allowing high solids loading in the solution while maintaining a workable solution. However, the increased mass loading resulted in much higher stiffness gels following ionic cross-linking with calcium. These data may be interpreted in relation to the microstructure of the solution versus hydrogel.

Conductive polymers such as polypyrrole (Ppy) are potentially useful as an active interface for altering cellular processes and function. Their utilization in medically related applications however have been substantially held back by their non-degradable nature. Herein we report a novel approach to creation of bioerodible polypyrroles via modification of pyrrole beta-carbon with an ionizable moiety. It has been shown that the erosion rate of acid-bearing derivative of polypyrrole increases with pH, which is consistent with the pH dependent ionization of carboxylic acid group. The novel paradigm proposed for the creation of bioerodible polypyrroles allows for simple and efficient control over the erosion rate of the substrate independent of the polymer chain length, via the choice of the terminal ionizable group and its concentration along the polymer backbone.

Fourier Transform infrared spectroscopy has been employed to study the shells of two kind of mollusks, American oysters (Crassostrea virginica) and mussels (Ischadium recurvum). It is shown that it is possible to distinguish the different calcium carbonate lattice vibrations in each case, mussel shells present aragonite vibration frequencies, and the oyster shells present those corresponding to calcite. The superposition, shift and broadening of the infrared bands are discussed. Changes in the vibration modes due to successive thermal treatments are also reported.

Near field scanning optical microscopy (NSOM) and spectroscopy techniques were used to study the shape and the cell membrane details in bacteria. We present transmission and topo-graphic images for the bacteria Pseudomonas aeruginosa using the Aurora NSOM from ThermoMicroscopes. The P. aeruginosa has been widely studied due to its clinical importance in many infectious diseases. The samples were stained by the Gram method and we measured the absorption of laser light at 488 nm by the dye (Safranin) fixed at the bacteria membrane. To obtain good images we had to improve the sample preparation in order to obtain isolated bacteria at the microscope slab. This was achieved using individual colonies, from a dry growth procedure, diluted in physiologic solution. Comparison of the topographic and transmission images give information on the shape and details of the absorption of the laser light by the cell membrane. The results show patterns that depend on the thickness and shape of the membrane, thus revealing details of the cell membrane with nanometer resolution. These results could be an important tool for instance in studies of the effects of antibiotics on the cell membrane.

Maintenance of euglycemia is crucial because glucose is the sole nutrient that can be utilized by the brain, retina, and germinal epithelium in sufficient quantities to provide required levels of energy. Since carbohydrate reserves in neural tissue are limited, normal nerve cell function depends upon a continuous glucose supply. Neurons located in select brain sites, including the hindbrain nucleus tractus solitarius/area postrema complex (NTS/AP), exhibit unique electrophysiological and/or genomic responses to glucopenia, suggesting that regulatory signaling of this substrate fuel deficit originates within these select loci. Fundamental questions concerning the identification of monitored metabolic variables and the molecular mechanisms by which local sensor cells transduce energetic distributions into neural signals remain unresolved. The combination of microscopic particle induced x-ray emission (μPIXE) and scanning transmission ion microscopy (STIM) can permit quantitative multielemental mapping of the brain, at the single cell level, with part-per-million sensitivity while simultaneously providing structural information. Over the past year, the authors have investigated methods for utilization of μPIXE and STIM in conjunction with established neuroanatomical and pharmacological approaches in a novel strategy to characterize electrolytic indices of neuronal function. Micrometer-scale resolution of discrete brain sites is expected to yield critical information on intracellular levels of ions that regulate membrane potential and synaptic firing. This paper presents results on regional mapping for effects of metabolic manipulations deficits on the transmembrane flux of sodium, potassium, chlorine, and calcium ions. This research will significantly advance the current understanding of the cellular and molecular bases linking neuronal energetics with homeostatic regulation of metabolic substrate availability.

Growth factor delivery using polymer matrices is one exciting approach to replace or regenerate tissues. Most growth factor delivery systems, however, have been designed to operate under static conditions, regardless of dynamic environments in the body. Considering the dynamic environment of our body (e.g., bone, muscle, and blood vessel), mechanical stimulation is an important signal that could be readily exploited. We hypothesize that polymer matrices, which release growth factors in response to mechanical stimulation, could provide a novel approach to engineer tissues in mechanically stressed environments. We report here a model system, comprised of alginate hydrogel and vascular endothelial growth factor (VEGF), which upregulates the release of the growth factor in response to mechanical stimulation and subsequently promotes granulation tissue formation in animals. This approach may find a number of potential applications in tissue engineering, as well as in drug delivery.

The objective of the present in vitro study was to investigate the potential of carbon nanofibers, which have nanometer dimensions similar to hydroxyapatite crystals in physiological bone, for orthopedic applications. Studies of alkaline phosphatase activity and calcium deposition by osteoblasts (the bone-synthesizing cells) were performed on both nanophase (less than 100 nm) and conventional (greater than 100 nm) diameter carbon nanofibers. Results provided the first evidence of a strong correlation between decreased carbon fiber diameter and both increased alkaline phosphatase activity and increased calcium deposition by osteoblasts at early time points (specifically, 7 days), but not at later time points (specifically, 14 and 21 days). Results of early calcium deposition by osteoblasts on carbon nanofibers are promising and consistent with the desired rapid formation of natural bone at the implant interface.

Hydroxyapatite (HA) is a bone-like ceramic used as a coating for dental and orthopedic implants. It is well known for its good cytocompatibility properties, but is limited in use due to its high solubility within the body and mechanical properties that differ from surrounding tissue and bone. The present in vitro study investigated a variety of dopants as a way to further enhance the good cytocompatibility properties of HA as well as address these problematic properties. The dopants investigated were divalent (magnesium and zinc) and trivalent (yttrium, lanthanum, indium, and bismuth) ions. Of the trivalent ions, yttrium and indium have smaller ionic radii than calcium. The present study showed osteoblast adhesion to be statistically greater (p < 0.1) on yttrium-doped HA and indium-doped HA than on undoped HA. Since yttrium and indium are both trivalent ions of a smaller ionic radius than calcium, and other ions of different size and charge did not show significant changes in osteoblast adhesion, these results suggest that substituting divalent calcium with a trivalent ion of smaller size encourages osteoblast adhesion.

We studied the physico/chemical effects of deep UV irradiation of polystyrene, PMMA and polycarbonate with respect to cell adhesion and protein immobilization. Photochemical modifications of the polymer surfaces yielded unstable peroxides and carboxylic acid groups. Patterned protein adsorbates were realized by coupling via carbodiimid activation of the COOH moieties. We have immobilized enzymes and antibodies. It was observed that hepatoma cells (HepG2) and fibroblasts (L929) adhered in the presence of serum proteins in the culture medium on the irradiated regions of the substrate without any further treatment.

A novel system is described for determining physical properties, including bulk modulus and density, of small solid samples. The system consists of a chamber in which the sample weight is measured by a weighing device immersed in a gas of controllable density. Thus, the method of measuring density is based on Archimedes' principle where the weight of an object is reduced by the weight of the displaced fluid. This particular device has been designed for examining the density of disk-shaped samples 3 mm in diameter and 0.4 mm thick. The weighing device has a repeatability of 4 nN and sample densities can be determined to 0.5%.

A significant feature of this device is the ability to measure buoyancy forces at a plurality of gas densities, which allows one to capture nonlinear behaviors associated with closed-cell compressible media. Results are presented for a quasi-closed cell foam that experiences volume reduction as the gas pressure is increased. Volumetric strains are determined as the difference between the observed behavior and the linear behavior of incompressible media. Plots of hydrostatic stress versus volumetric strain are initially linear, as described by the bulk modulus, and exhibit a “kink” at high pressures, presumably due to the complete compression of internal cells.

Mineral nucleation at a Langmuir film interface has been studied by synchrotron x-ray scattering. Diluted calcium bicarbonate solutions were used as subphases for arachidic and stearic acid monolayers, compressed in a Langmuir trough. Self-assembly of the monolayer template is observed directly, and subsequent crystal growth monitored in-situ.

A series of ferromagnetic bioceramic samples in the system 45(CaO, P2O5), ySiO2xFe2O3 were synthesized with various processing parameters in order to study correlations between structure, magnetic properties and preparation variables. X-ray powder diffraction shows that the qualitative as well as the quantitative structure of the samples is strongly affected by processing parameters, including composition, annealing temperature and the chemical reactions. Magnetic measurements illustrate a strong correlation between the saturation magnetization, and hysteresis loss, with the processing parameters of the material.

The molecular deformation of both silkworm (Bombyx mori) and spider dragline (Nephila edulis) silks has been studied using a combination of mechanical testing and Raman spectroscopy. It was found that both materials have well-defined Raman spectra and that some of the bands in the spectra shift to lower wavenumber under the action of tensile stress or strain. The band shift was linearly dependent upon stress for both types of silk fiber for the 1085/1095 cm-1 band. This observation provides a unique insight into the effect of tensile deformation upon molecular structure and the relationship between structure and mechanical properties. The measurement of micromechanical deformation within samples of wood, flax and hemp fibers using Raman spectroscopy is also reported. Upon tensile deformation of the samples it was found that the characteristic Raman peak for cellulose, located at 1095 cm-1, shifted towards a lower wavenumber, indicating that the polymer chains within the cellulose were also being deformed. The magnitude of the shift with strain was found to be similar for all samples. No shift occurred of the peak that is characteristic of the non-load-bearing lignin (1600 cm-1) in the wood samples due to its amorphous structure. The similarities between the Raman band shifts in silk and cellulose are discussed.

There is intense current interest in the use of polymer and organic molecular materials for high technology devices including transistors, biosensors, and actuators [1]. In order for these materials to achieve their ultimate potential it is imperative to obtain detailed information about their microstructure, especially in the thin film forms central to technological applications. Our research group has been actively developing techniques for high-resolution electron optical examinations of polymers and organic materials, with particular emphasis on low dose high-resolution electron microscopy (HREM) [2]. While this method of examining organic materials' structure has proven to be particularly powerful, current generations of electron microscopes suffer from several problems. They are expensive, require considerable amounts of space, and are time-consuming and fairly difficult to operate. Furthermore, the high voltages normally used in conventional electron microscopes (200-400 kV) provide little contrast when imaging thin films composed of low atomic number components.

Calcium phosphate films were deposited on titanium electrodes cathodically from CaCl2·2H2O and Ca(H2PO4)2 · H2O aqueous solutions. In this study, H2O2 addition into electrolytes was applied to enhance the electrochemical process at the solution/electrode at a smaller cathodic potential than no H2O2 addition. Deposited films were analyzed by scanning electron microscopy (SEM) observation and X-ray diffraction (XRD). Cathodic current of the Ti electrode decreased once and increased in the solution with H2O2. It shows a cathodic current peak at c.a. 25 min in the case of potentiostatic condition at - 0.756 V (vs. Ag - AgCl, sat. KCl). The calcium phosphate film grows mainly with the decrease in current after the cathodic peak. The characteristics for the electrodeposited film such as crystal morphology depends on cathodic potential, solution pH, deposition temperature and amount of H2O2 addition. Dense calcium phosphate film composed of relatively good crystalline was obtained at pH 5.5 and – 0.756 V. Film adhesion on Ti appeared to be strong by peeling test. At larger cathodic potential of – 1.156 V, the film coverage on titanium plates was smaller and film adhesion worsened. Larger cathodic polarization of more than – 1.556 V was necessary to reduce water in case without H2O2 addition.

Natural composite bioceramics such as bone, teeth, carapaces and shells contain organic and inorganic moieties, with the organic matrix components directly involved in the precise formation of these structures. We have previously shown that chicken eggshell contains two main sulfated polymers (proteoglycans), referred to as mammillan and ovoglycan which are involved in nucleation and growth of the eggshell calcite crystals. They differ on their anionic properties due to the carboxylate and sulfate content of their glycosaminoglycan component. Based on biological and biochemical evidences, the putative role of mammillan, a keratan sulfate proteoglycan, is in the nucleation of the first calcite crystals, while that of ovoglycan, a dermatan sulfate proteoglycan, is to regulate the growth and orientation of the later forming crystals of the chicken eggshell. In this communication, a systematic study of the influence of variable concentrations of glycosaminoglycans differing in their sulfation status on the morphology, size and number of calcium carbonate crystals after crystallization on microbridges from a calcium chloride solution under an atmosphere of ammonium carbonate at different pH is presented. Depending on the pH and concentration, the variation of sulfation status drastically changed the morphology, size and number of calcite crystals. The produced calcite particles with various morphologies are promising candidates for some novel materials with desirable shape- and texture-depending properties.

High resolution triple axis X-ray diffraction has been used to monitor the effects of X-ray radiation damage in hen egg white lysozyme crystals. At long irradiation the expected decrease in peak intensity and increase in the angular extent of the peak breadth was seen. In contrast, both the intesi-ties and peak breadths exhibited more complex behavior during the initial stages of irradiation. Possible reasons for these observations are discussed.

In situ mineralization of hydroxyapatite (HAP) and the role of organics in initial nucleation and growth of HAP is critical for the resulting nano and microstructure of HAP. In situ mineralization of hydroxyapatite (HAP) in the presence of Ca binding polymers such as polyacrylic acid has shown some promise towards improvement of mechanical response of uniaxial compressed HAP/polymer composites to loading. This work represents fundamental studies on the nature of in situ HAP precipitation on resulting microstructure of the composite and bulk mechanical properties. Specifically, an experimental study, evaluating the role of initial stage mineralization of HAP on bulk mechanical responses is conducted. Fourier transform infrared (FT-IR) spectroscopic (with micro attenuated total reflectance) techniques are utilized to evaluate the association of polymer (polyacrylic acid) with HAP during mineralization of HAP. In situ HAP exhibits a faster mineralization as compared to the ex situ mineralization samples, This improved kinetics is responsible for altering the resulting micro and nanostructure of the HAP/polymer composite. Small spectral changes are detected in the absorbance spectra of in situ HAP as compared to ex situ samples. Changes in mechanical response to loading included improvement in strain-to-failure and resulting toughness characteristics of the in situ composite. The control and development of molecular-level associations of polymer with HAP is suggested to be critical for the resulting macro properties. Our results may have significant implications for design of nanocomposites for biomedical applications.

Polypeptide ultrathin films covalently grafted on solid substrates have attracted considerable attention in the interfacial polymer science community over the past couple of years. The potential applications of these films ranges from applications in liquid crystal displays, biosensors, optical devices, etc.. Their study may address important biocompatibility issues. We have synthesized polypeptide ultrathin films through the use of the physical vapor deposition technique. We expect to gain better insight into the polymerization process of the NCA monomers, as well as, possible control of the secondary structure.

Through use of the vapor deposition technique and the amino acid n-carboxy anhydride (NCA) benzyl serine we have been able to prepare polymeric amino acids for analysis. Benzyl serine NCA was evaporated in high vacuum at a temperature of 95-130°C. Different substrates have been used to examine the effects of chemical binding sites on polymerization and secondary structure formation. From IR-spectroscopy and optical microscopy it was evident that without a free amine initiator on the surface of the substrate, polymerization would not occur. Analysis of the films with IR and optical microscopy were used to determine optimum deposition and polymerization conditions. The methyl peak around 3000 cm-1, amide peak at 1650 cm-1 and the carbonyl stretching at 1750 cm-1 evidence of the monomer are greatly reduced or disappear in the deposition range of 40-100nm/min.

Analysis of the films with attenuated total reflectance (ATR) Infrared spectroscopy was used to examine the secondary structure. Values of amide 1 peak at 1632 cm-1, representing the carbonyl stretching, and the peak at 1530 cm-1, representing the carbon nitrogen stretching, match with literature values of beta sheet conformation.

The ability of Environmental Scanning Electron Microscopy (ESEM) to image insulating and/or moist specimens without the need for the removal of volatile components or the application of a conductive coating has significantly increased the potential range of experiments and observations that can be performed at the high resolution of electron microscopy. Such a technological advance has particularly important implications for the study of soft matter, complex fluids and biological specimens [1]. Thus an important field of research to which ESEM can be applied is the study of materials for biomedical applications such as tissue engineering. The bioactivity of these materials is dependent upon such factors as phase composition, chemical composition, surface activity, crystallinity and microstructure. Using ESEM it is possible to obtain surface-sensitive, specimen-dependent secondary electron images (in the absence of specimen coating), yielding potentially new perspectives on microstructure to complement information derived from other techniques. We have used ESEM to study the apposition of bone on hydroxyapatite-based biomedical materials, from both in vitro and in vivo investigations.