Bioactive composites fabricated by freezing‐thawing method for bone regeneration applications

Hydrogels are widely used for controlled delivery of therapeutic agents. However, hydrogels lack bioactivity to encourage bone formation and mechanical integrity. Moreover, chemically crosslinked hydrogels exhibit cytotoxic effect. To overcome these limitations poly‐vinyl alcohol (PVA) and poly‐acrylic acid (PAA) blends were combined with ceramic materials based on β tricalcium phosphate, wollastonite, and magnesium silicate with different pore size distributions. The final 3D matrix was physically crosslinked using various freeze thawing (F/T) cycles. FTIR and SEM analysis showed that ceramics were dispersed within the polymer matrix and formed hydrogen bonds. Swelling studies in buffer solution pH 7.4 showed an increase in polymer swelling when ceramic was added. Furthermore, rheological testing demonstrated that incorporation of ceramics caused an increase in mechanical properties which varies with different pore size distributions of ceramics grains added. DSC thermograms showed increased T_g values for samples containing ceramics. Antimicrobial activity containing ciprofloxacin was tested against a pathogen associated with osteomyelitis and presented positive results with ciprofloxacin. The combination of increased strength and ability to encapsulate a clinically relevant antimicrobial agent indicates that the composite tested in this study has potential for the treatment of osteomyelitis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 761–773     

A Dual Colorimetric/Fluorescence System for Determining pH Based on the Nucleophilic Addition Reaction of an o‐Hydroxymerocyanine Dye

Owing to their ability to monitor pH in a precise and rapid manner, optical probes have widely been developed for biological and nonbiological applications. The strategies thus far employed to determine pH rely on two types of processes including reversible protonation of amine nitrogen atoms and deprotonation of phenols. We have developed a novel dual, colorimetric/fluorescence system for determining the pH of a solution. This system utilizes an o‐hydroxymerocyanine dye that undergoes a nucleophilic addition reaction that subsequently causes reversible structural changes interconverting a merocyanine to a spirocyanine and a spirocyanine to a spiropyran. It was demonstrated that the dye can be employed to measure the pH of solutions in the 2.5–5.75 and 9.6–11.8 ranges with color changes from yellow to dark blue and then to lavender. Moreover, the fluorescence response associated with the spirocyanine–spiropyran transformation of the dye occurring in alkaline solutions provides a precise method.     

Translating Bacterial Detection by DNAzymes into a Litmus Test

Microbial pathogens pose serious threats to public health and safety, and results in millions of illnesses and deaths as well as huge economic losses annually. Laborious and expensive pathogen tests often represent a significant hindrance to implementing effective front‐line preventative care, particularly in resource‐limited regions. Thus, there is a significant need to develop low‐cost and easy‐to‐use methods for pathogen detection. Herein, we present a simple and inexpensive litmus test for bacterial detection. The method takes advantage of a bacteria‐specific RNA‐cleaving DNAzyme probe as the molecular recognition element and the ability of urease to hydrolyze urea and elevate the pH value of the test solution. By coupling urease to the DNAzyme on magnetic beads, the detection of bacteria is translated into a pH increase, which can be readily detected using a litmus dye or pH paper. The simplicity, low cost, and broad adaptability make this litmus test attractive for field applications, particularly in the developing world.     

Modelling of a hydrogel diffraction grating used for pH-sensing

pH-Sensitive hydrogels are networks of polymers that can imbibe a solution and swell. They are used in many smart engineering devices. One of such applications is a diffractometric biochemical sensor. This sensor is composed of a hydrogel grating fixed on a hard substrate that can swell due to pH changes. The aim of the present study is to develop a numerical model of such a bi-material device used to measure pH value of a solution.     

关于带重力项一维渗流方程解的自由边界的C^k正则性的一点注记

本文研究带重力项的一维渗流方程 u_t=(u~m)_(xx)+(u~n)_x,m>1,n>1Cauchy问题解的自由边界的正则性.正如我们所知,此退化方程解的显著特征是满足有限传播速度:当初值u_0(x)具有紧支集时,自由边界x=ζ_i(t),(i=1,2)是两条Lipschitz连续曲线.本文进一步研究指出:当n≥m对压力v=m/(m-1)u~(m-1)有ζ'_1(t)=-limv_x(x,t),t∈(0,∞),且对ζ_1(t)的任何移动部份Γ是C~1正则的;当n-1/m-1≥k,k为正整数,则微商(1≤2l+j≤k)在Γ的每一侧附近是有界的;特别当n-1/m-1=k,则任意阶微商(l≥0,j≥0)在Γ的每一侧附近有界,从而v在Γ的每一侧是C~∞的。 本文只考虑i=1的情形,至于i=2可类似地加以考虑。     

A pitzer mixed electrolyte solution theory approach to assignment of pH to standard buffer solutions

The IUPAC recommendations for the pH scale for aqueous solutions are based on the Bates-Guggenheim (B-G) convention (1961) for the single ion activity coefficient of the chloride ion in the standard buffer(s). This convention was adopted as a reasonable estimate based on the Debye-Huckel theory and is limited in its application to ionic strengths less than 0.1 mol-kg^–1. This approach ignores the results of many workers over the years on the properties of mixed electrolyte solutions and their prediction on the basis of the theories of Harned, Scatchard, Guggenheim and more recently of Pitzer. The literature data of EMF measurements on appropriate weak acid systems have been reexamined to determine both the pK_a values and values of appropriate Pitzer interaction coefficients. The latter are used to calculate single chloride ion activity coefficients for the chosen compositions of pH standard buffers, and compared with the B-G convention values. Calculations were made to check the consistency of the pH values with determined pK_a values using the Pitzer treatment for all the required single ion activity coefficients. The overall aim was to remove the ionic strength restriction of the B-G convention and rationalize the approach to pH standardization for such diverse aqueous media as sea water, blood and acid-rain water.An account of this work was presented at the 12^th International Conference on Chemical Thermodynamics, Snowbird, Utah, August 1992.     

Influence of intersite modes on the exchange interaction in electron transfer at large distances

We consider the dependence of the exchange interaction in electron transfer processes on the intersite vibrational modes. We assume, in particular, that high-frequency intramolecular modes of proteins may play this role in biological processes. We compare our model with that for tunneling through a time dependent barrier and with other works which considered the dependence of the exchange interaction on the nuclear coordinates.Work partially supported by the Brazilian Agency CNPq and by the NSF (Grant PCM-8406049)On leave of absence from Institute de Física e Química de São Carlos, Universidade de São Paulo, 13560, São Carlos, SP, BrazilOn leave of absence from Departamento de Física, Universidade Federal de Pernambuco, 50000, Recife, Pe, BrazilContribution No. 7325     

Growth mode and interface structure of Ag on the HF-treated Si(111):H surface

A growth mode and interface structure analysis has been performed for Ag deposited at a high temperature of 300°C on the HF-treated Si(111):H surface by means of medium-energy ion scattering and elastic recoil detection analysis of hydrogen. The measurements show that Ag grows in the Volmer-Weber mode and that the Ag islands on the surface are epitaxial with respect to the substrate. The preferential azimuthal orientation is A-type only when Ag is deposited slowly. The interface does not reconstruct to the √3 × √3-Ag structure, which is normally observed for Ag deposition above 200°C on the Si(111)7 × 7 surface, but retain bulk-like structure. The presence of hydrogen at the interface is demonstrated after deposition of thick (1100 Å) Ag films. However, the amount of hydrogen at the interface is not a full monolayer. This partial desorption of hydrogen from the interface explains why the Schottky barrier heights of Ag/Si(111):H diodes are close to those of Ag/Si(111)7 × 7 and Ag/Si(111)2 × 1.     

Organotin compounds as energy-potentiated uncouplers of rat liver mitochondria

Triorganotins will titrate membrane potential (Δψ) and the accompanying pH gradient (ΔpH) in estimates of protonmotive force (Δp) in isolated rat liver mitochondria in an apparent concentrationdependent manner and in minimal halide media (5 μmol dm^?3). Under these conditions the concentrations of organotin required to produce a drop of 80–120mV in Δp approach or are in excess of those required to inhibit ATP-synthase activity, which are at least three-fold greater than those which inhibit ATP hydrolytic activity. The addition of exogenous chloride ion did not appreciably alter the steady-state or rate estimates of triorganotin-mediated membrane potential (Δψ) depolarization. The evidence indicates that triorganotins possess an uncoupling effect which is independent of halide/hydroxyl exchange or direct inhibition of the ATPase complex. The activity of various triorganotins may be best understood according to their abilities to uncouple or directly inhibit oxidative phosphorylation at the enzymic level, in the absence of halide/hydroxyl exchange.