Micromechanical Properties of Microstructured Elastomeric Hydrogels

Local, micromechanical environment is known to influence cellular function in heterogeneous hydrogels, and knowledge gained in micromechanics will facilitate the improved design of biomaterials for tissue regeneration. In this study, a system comprising microstructured resilin‐like polypeptide (RLP)–poly(ethylene glycol) (PEG) hydrogels is utilized. The micromechanical properties of RLP‐PEG hydrogels are evaluated with oscillatory shear rheometry, compression dynamic mechanic analysis, small‐strain microindentation, and large‐strain indentation and puncture over a range of different deformation length scales. The measured elastic moduli are consistent with volume averaging models, indicating that volume fraction, not domain size, plays a dominant role in determining the low strain mechanical response. Large‐strain indentation under a confocal microscope enables the visualization of the microstructured hydrogel micromechanical deformation, emphasizing the translation, rotation, and deformation of RLP‐rich domains. The fracture initiation energy results demonstrate that failure of the composite hydrogels is controlled by the RLP‐rich phase, and their independence with domain size suggested that failure initiation is controlled by multiple domains within the strained volume. This approach and findings provide new quantitative insight into the micromechanical response of soft hydrogel composites and highlight the opportunities in employing these methods to understand the physical origins of mechanical properties of soft synthetic and biological materials.     

Continuous wave NMR of submonolayer 3He adsorbed on grafoil

NMR linewidths and magnetic susceptibilities of ³He adsorbed on Grafoil have been measured by a continuous wave technique between 0.40 K to 4.21 K for five fractional monolayer coverages, x, between 0.20 and 0.96. Interpretations in terms of the phases of the submonolayers are presented.     

Generation and propagation of a picosecond acoustic pulse at a buried interface: time-resolved x-ray diffraction measurements

We report on the propagation of coherent acoustic wave packets in (001) surface oriented Al0.3Ga0.7As/GaAs heterostructure, generated through localized femtosecond photoexcitation of the GaAs. Transient structural changes in both the substrate and film are measured with picosecond time-resolved x-ray diffraction. The data indicate an elastic response consisting of unipolar compression pulses of a few hundred picosecond duration traveling along [001] and [001] directions that are produced by predominately impulsive stress. The transmission and reflection of the strain pulses are in agreement with an acoustic mismatch model of the heterostructure and free-space interfaces.     

The method of lines applied to nonlinear nonlocal functional differential equations

This paper discusses nonlinear functional differential equation in a real reflexive Banach space with nonlocal history condition. By using the method of lines, the existence and uniqueness of a strong solution are established. Finally, some applications of the abstract results are presented.     

Electrodeposition and characterization Zn-Co alloy

The present work details optimization of a stable acid chloride bath for electroplating of bright Zn-Co alloy on mild steel using gelatin and glycine as additives. It was found that the addition of gelatin along with glycine changed the deposition pattern markedly. A suitable bath has been formulated using conventional Hull cell experiments. The bath under plating conditions were found to exhibit anomalous codeposition with preferential deposition of less noble (zinc) over more noble (cobalt) as characterized by Zn-Fe group metal alloys. Investigation revealed that the current density (c.d.), temperature, and pH of the bath have strong effect on the composition of the deposit. Influence of bath constituents and operating parameters on appearance and composition of deposits were studied as measure of their performance against corrosion. A variety of deposits were obtained and their corrosion resistances were measured by Tafel method with/without chrome passivation. Experimental results demonstrated the fact that the corrosion resistances of Zn-Co alloys increased with percent of Co in the deposit except at very high c.d. This is due to the fact at very high c.d. the deposit becomes very porous and thick as evidenced by SEM image. The formation of Zn-Co alloy is confirmed by EDAX analysis. A stable chloride bath for Zn-Co alloy deposition has been proposed and discussed. The formation of passive film on chromatization is indicated by almost same E _corr value of all Zn-Co electroplates irrespective of the current densities at which they have been deposited. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 811–816. The text is published in the original.     

Sonochemical synthesis of Ce(1-x)Fe(x)O(2-δ) (0 ≤ x ≤ 0.45) and Ce(0.65)Fe(0.33)Pd(0.02)O(2-δ) nanocrystallites: oxygen storage material, CO oxidation and water gas shift catalyst

Nanocrystalline Ce(1-x)Fe(x)O(2-δ) (0 ≤ x ≤ 0.45) and Ce(0.65)Fe(0.33)Pd(0.02)O(2-δ) of ~4 nm sizes were synthesized by a sonochemical method using diethyletriamine (DETA) as a complexing agent. Compounds were characterized by powder X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and transmission electron microscopy (TEM). Ce(1-x)Fe(x)O(2-δ) (0 ≤ x ≤ 0.45) and Ce(0.65)Fe(0.33)Pd(0.02)O(2-δ) crystallize in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe(3+) ion in CeO(2), lattice oxygen is activated and 33% Fe substituted CeO(2)i.e. Ce(0.67)Fe(0.33)O(1.835) reversibly releases 0.31[O] up to 600 °C which is higher or comparable to the oxygen storage capacity of CeO(2)-ZrO(2) based solid solutions (Catal. Today 2002, 74, 225-234). Due to interaction of redox potentials of Pd(2+/0)(0.89 V) and Fe(3+/2+) (0.77 V) with Ce(4+/3+) (1.61 V), Pd ion accelerates the electron transfer from Fe(2+) to Ce(4+) in Ce(0.65)Fe(0.33)Pd(0.02)O(1.815), making it a high oxygen storage material as well as a highly active catalyst for CO oxidation and water gas shift reaction. The activation energy for CO oxidation with Ce(0.65)Fe(0.33)Pd(0.02)O(1.815) is found to be as low as 38 kJ mol(-1). Ce(0.67)Fe(0.33)O(1.835) and Ce(0.65)Fe(0.33)Pd(0.02)O(1.815) have also shown high activity for the water gas shift reaction. CO conversion to CO(2) is 100% H(2) specific with these catalysts and conversion rate was found to be as high 27.2 μmoles g(-1) s(-1) and the activation energy was found to be 46.4 kJ mol(-1) for Ce(0.65)Fe(0.33)Pd(0.02)O(1.815).     

VEGFR-2 targeted cellular delivery of doxorubicin by gold nanoparticles for potential antiangiogenic therapy

We report a novel gold nanobioconjugate system that achieves targeted delivery of the small molecule drug doxorubicin to endothelial cells using anti-VEGFR-2 antibody conjugated gold nanoparticles (GNPs). The reported nanobioconjugate system combines the inherent ability of GNPs to undergo high levels of derivatization with the precision of antibody recognition of a cell surface antigen. Transmission electron microscopy (TEM) and surface-enhanced Raman spectroscopy (SERS) confirmed intracellular presence of the GNPs. Using a VEGFR-2 expressing cell line and a cell line that is negative for the receptor, in combination with competition assay we established the cell specific targeted delivery of the nanobioconjugate. The nanobioconjugate system described here may have potential drug delivery applications for antiangiogenic cancer therapy.     

Principal eigenvector field segmentation for reproducible diffusion tensor tractography of white matter structures

The study was aimed to test the feasibility of utilizing an algorithmically determinable stable fiber mass (SFM) map obtained by an unsupervised principal eigenvector field segmentation (PEVFS) for automatic delineation of 18 white matter (WM) tracts: (1) corpus callosum (CC), (2) tapetum (TP), (3) inferior longitudinal fasciculus (ILF), (4) uncinate fasciculus (UNC), (5) inferior fronto-occipital fasciculus (IFO), (6) optic pathways (OP), (7) superior longitudinal fasciculus (SLF), (8) arcuate fasciculus (AF), (9) fornix (FX), (10) cingulum (CG), (11) anterior thalamic radiation (ATR), (12) superior thalamic radiation (STR), (13) posterior thalamic radiation (PTR), (14) corticospinal/corticopontine tract (CST/CPT), (15) medial lemniscus (ML), (16) superior cerebellar peduncle (SCP), (17) middle cerebellar peduncle (MCP) and (18) inferior cerebellar peduncle (ICP). Diffusion tensor imaging (DTI)-derived fractional anisotropy (FA) and the principal eigenvector field have been used to create the SFM consisting of a collection of linear voxel structures which are grouped together by color-coding them into seven natural classes to provide PEVFS signature segments which greatly facilitate the selection of regions of interest (ROIs) for fiber tractography using just a single mouse click, as compared with a manual drawing of ROIs in the classical approach. All the 18 fiber bundles have been successfully reconstructed, in all the subjects, using the single ROIs provided by the SFM approach, with their reproducibility characterized by the fact that the ROI selection is user independent. The essentially automatic PEVFS method is robust, efficient and compares favorably with the classical ROI methods for diffusion tensor tractography (DTT).     

Approximations of solutions to neutral functional differential equations with nonlocal history conditions

This work is concerned with a class of neutral functional differential equations with nonlocal history conditions in a Hilbert space. The approximation of solution to a class of such problems is studied. Moreover, the convergence of Faedo-Galerkin approximation of solution is shown. For illustration, an example is worked out.