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Local pH (local + ph)

Distribution by Scientific Domains
Polymers and Materials Science75%

Selected Abstracts

Electrolytic Deposition of Hydroxyapatite Coating on CoNiCrMo Substrates

ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010
Dong-Yang Lin
Hydroxyapatite (HA) coating was fabricated on CoNiCrMo alloy by electrolytic deposition (ELD). Different kinds of uncharged substrates were placed close to the cathode separately during the ELD process. Both CoNiCrMo and uncharged substrates were covered with uniform HA coatings composed of hexagonal prism crystals after 60,min deposition. The pH value of the bulk solution changed hardly while the local pH had a sharp increase after ELD. The results demonstrate the local pH plays a crucial role in the ELD process. [source]

Mesoporous Hydrous Manganese Dioxide Nanowall Arrays with Large Lithium Ion Energy Storage Capacities

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2009
Dawei Liu
Abstract Novel nanowall arrays of hydrous manganese dioxide MnO2,·,0.5H2O are deposited onto cathodic substrates by the potentiostatic method from a mixed aqueous solution of manganese acetate and sodium sulfate. The deposition is induced by a change of local pH resulting from electrolysis of H2O, and hierarchical mesoporous nanowall arrays are formed as a result of simultaneous precipitation of manganese hydroxide and release of hydrogen gas bubbles from the cathode. The morphology and lithium ion intercalation properties are found to change appreciably with the concentration of the precursor electrolyte, with a significant reduction in specific surface area with an increased precursor concentration. For example, mesoporous nanowall arrays deposited from 0.1,M solution possess a surface area of ,96,m2 g,1 and exhibit a stable high intercalation capacity of 256,mA hg,1 with a film of 0.5,µm in thickness, far exceeding the theoretical limit of 150,mA hg,1 for manganese dioxide bulk film. Such mesoporous nanowall arrays offer much greater energy storage capacity (e.g., ,230,mA hg,1 for films of ,2.5,µm) than that of anodic deposited films of the same thickness (,80,mA hg,1). Such high lithium ion intercalation capacity and excellent cyclic stability of the mesoporous nanowall arrays, especially for thicker films, are ascribed to the hierarchically structured macro- and mesoporosity of the MnO2,·,0.5H2O nanowall arrays, which offer large surface to volume ratio favoring interface Faradaic reactions, short solid-state diffusion paths, and freedom to permit volume change during lithium ion intercalation and de-intercalation. [source]

Bioceramic Bone Graft Substitutes: Influence of Porosity and Chemistry

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2005
Karin A. Hing
Bioceramics have been considered for use as synthetic bone graft substitutes (BGSs) for over 30 years, throughout which there have been two primary areas of research: (i) optimization of the physical pore structure and (ii) formulation of an appropriate bioceramic chemistry. While it is well recognized that both the rate of integration and the final volume of regenerated bone are primarily dependent on the macroporosity, there still seems to be some dispute regarding the optimum "type" of porosity. The rate and quality of bone integration have, in turn, been related to a dependence on pore size, porosity volume fraction, and interconnection size and interconnection density, both as a function of structural permeability and mechano-transduction. Moreover, the role of strut microstructure and pore geometry have been considered with respect to their influence on entrapment and recruitment of growth factors (GFs) in addition to its influence on scaffold mechanics. Deconvoluting the relative affects of these parameters is complicated by the use of both resorbable and nonresorbable bioactive bioceramics, which are believed to mediate bioactivity in the osseous environment through two principal mechanisms: (i) directly through dissolution and release of ionic products in vivo, elevating local concentrations of soluble species that interact directly with local cells or influence cell behavior by their effect on local pH, (ii) indirectly through the influence that surface chemistry will have on protein adsorption, GF entrapment, and subsequent cell attachment and function. This article aims to review some of the recent developments in bioceramic BGSs, with a view to understanding how the various physiochemical parameters may be optimized to promote bone healing. [source]

Mechanistic understanding of degradation in bioerodible polymers for drug delivery

AICHE JOURNAL, Issue 12 2002
Domenico Larobina
A new model was developed to understand the mechanism of erosion in bioerodible polymers, which is essential to accurately predict drug release and precisely design controlled release devices. This model takes into account the phenomenon of microphase separation observed for polyanhydrides of certain copolymer compositions, and assumes that erosion is dominated by degradation and, thus, in a system with a fast eroding and a slow eroding species, two rate constants,one for each species,essentially control the evolution of the polymer microstructure. Expressions were derived for the fraction of each monomer released, as well as for the porosity in the system. A partition coefficient accounts for thermodynamic partitioning of a drug into the microdomains. The solutions of the model equations were fitted to experimental data on monomer release kinetics from two polyanhydride systems to obtain the erosion rate constants. Drug release kinetics experiments are compared to the model solution for drug release, and the partition coefficient of the drug is obtained from the fits. The comparisons to the data are promising, while pointing out the limitations of the model. The model does not account for oligomer formation prior to monomer release or for the dependence of the rate constants on parameters such as the degree of crystallinity, the local pH, and the polymer molecular weight. [source]