Comparative evaluation of push-out bond strength of Neo MTA Plus with Biodentine and white ProRoot MTA

Objective: The aim of this in vitro study was to evaluate the bond strength of a new calcium silicate cement, Neo MTA Plus (Avalon Biomed Inc. Bradenton, FL, U.S.A) by comparing ProRoot MTA and Biodentine.

Material and Methods: Sixty dentin slices were instrumented to achieve a diameter of 1.3 mm. Group 1: white ProRoot MTA, group 2: Biodentine, group 3: Neo MTA Plus – G (powder mixed with gel), group 4: Neo MTA Plus – W (powder mixed with distilled water) were loaded into cavities. The push-out bond strength values were measured. Data were analyzed using Welch ANOVA with Bonferroni correction p = 0.05. Failure modes (adhesive, cohesive, and mixture) were analyzed.

Results: The highest bond strength value was recorded in Neo MTA Plus mixed with gel (5.23 ± 1.78 MPa), whereas white ProRoot MTA (2.57 ± 0.66 MPa) had the lowest. Bond strength values of Neo MTA Plus mixed either with gel or with distilled water were statistically different from both white ProRoot MTA and Biodentine (2.61 ± 0.70 MPa) (p < 0.05). Adhesive failure was predominantly observed in all groups.

Conclusion: Neo MTA Plus could be considered as alternatives to the ProRoot MTA and Biodentine due to its better performance in bonding to root dentin.     

Isothermal crystallization kinetics and mechanical properties of polycaprolactone composites with zinc oxide,oleic acid,and glycerol monooleate

The isothermal crystallization and mechanical behavior of polycaprolactone (PCL) with zinc oxide (ZnO) with oleic acid and glycerol monooleate (GMO) were studied. Theoretical melting points calculated by the Flory–Huggins and Thompson–Gibbs models were thoroughly compared with differential scanning calorimetry experimental observations. The isothermal crystallization kinetic parameters by Avrami analysis showed that crystallization was controlled by nucleation, crystal growth was spherical, and the nucleation type changed between thermal and athermal nucleation. X‐ray diffraction showed that when the additives were used together both the crystal thickness and the degree of crystallinity increased. A multiple‐response regression analysis was made with the ZnO, oleic acid, and GMO concentrations as variables and the crystallinity as output. Interaction parameters by the Pukanzky model were calculated from the tensile strength at the yield point and indicated that the addition of oleic acid or GMO improved the interface between the ZnO particles and PCL. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1259‐1275, 2013     

Utilization of multiple graphene layers in fuel cells. 1. An improved technique for the exfoliation of graphene-based nanosheets from graphite

An improved, safer and mild method was proposed for the exfoliation of graphene like sheets from graphite to be used in fuel cells. The major aim in the proposed method is to reduce the number of layers in the graphite material and to produce large quantities of graphene bundles to be used as catalyst support in polymer electrolyte membrane fuel cells. Graphite oxide was prepared using potassium dichromate/sulfuric acid as oxidant and acetic anhydride as intercalating agent. The oxidation process seemed to create expanded and leafy structures of graphite oxide layers. Heat treatment of samples led to the thermal decomposition of acetic anhydride into carbondioxide and water vapor which further swelled the layered graphitic structure. Sonication of graphite oxide samples created more separated structures. Morphology of the sonicated graphite oxide samples exhibited expanded the layer structures and formed some tulle-like translucent and crumpled graphite oxide sheets. The mild procedure applied was capable of reducing the average number of graphene sheets from 86 in the raw graphite to nine in graphene-based nanosheets. Raman spectroscopy analysis showed the significant reduction in size of the in-plane sp² domains of graphene nanosheets obtained after the reduction of graphite oxide.     

Directed Evolution of an Antitumor Drug (Arginine Deiminase PpADI) for Increased Activity at Physiological pH

Arginine deiminase (ADI; EC 3.5.3.6) has been studied as a potential antitumor drug for the treatment of arginine‐auxotrophic tumors, such as hepatocellular carcinomas (HCCs) and melanomas. Studies with human lymphatic leukemia cell lines confirmed that ADI is an antiangiogenic agent for treating leukemia. The main limitation of ADI from Pseudomonas plecoglossicida (PpADI) lies in its pH‐dependent activity profile, its pH optimum is at 6.5. A pH shift from 6.5 to 7.5 results in an approximately 80 % drop in activity. (The pH of human plasma is 7.35 to 7.45.) In order to shift the PpADI pH optimum, a directed‐evolution protocol based on an adapted citrulline‐screening protocol in microtiter‐plate format was developed and validated. A proof of concept for ADI engineering resulted in a pH optimum of pH 7.0 and increased resistance under physiological and slightly alkaline conditions. At pH 7.4, variant M2 (K5T/D44E/H404R) is four times faster than the wild‐type PpADI and retains ～50 % of its activity relative to its pH optimum, compared to ～10 % in the case of the wild‐type PpADI.     

pH-dependent swelling of hydrogels containing highly branched polyamine macromonomers

We examine the pH-dependent swelling of end-linked hydrogels containing high concentrations of amine-functional macromonomers. Gels are formed by end-linking of epoxide-terminated, linear poly(ethylene glycol) (PEG) to either amine-terminated poly(amidoamine) (PAMAM) dendrimers or highly branched poly(ethyleneimine) (PEI). After extraction in neutral water, the hydrogels are swollen in aqueous solutions of HCl or NH₄OH to vary the external pH. Equilibrium volume swelling ratios (Q_s) pass through a maximum value (Q_max) at an external pH denoted as pH^∗ which is approximately 4-5 for the gels studied. The swelling behavior is modeled using Donnan equilibrium theory to describe the ion swelling pressure, with the Flory-Rehner phantom network expression representing the elastic and mixing contributions to the free energy. The model accurately predicts the maximum in swelling near pH = 4-5, but overestimates Q_max for several of the gels due to neglecting the finite extensibility of the short linear PEG chains.     

Hollow core mesoporous shell carbon supported Pt electrocatalysts with high Pt loading for PEMFCs

The aim of this study is to synthesize mesoporous carbon supports and prepare their corresponding electrocatalysts with microwave irradiation method and also increasing the Pt loading over the carbon support by using some additional reducing agents. Pt loadings on hollow core mesoporous shell (HCMS) and commercial Vulcan XC72 carbon supports up to 34% and 44%, respectively, were achieved via polyol process with microwave irradiation method. When hydrazine or sodium borohydride was used in addition to ethylene glycol, Pt loading over the HCMS carbon support was increased. Characterization of the prepared electrocatalysts was performed by ex situ (BET, XRD, SEM, TGA and Cyclic Voltammetry) and in situ (PEM fuel cell tests) analysis. PEM fuel cell performance tests showed that 44% Pt/Vulcan XC72 and 28% Pt/HCMS electrocatalysts exhibited improved fuel cell performances. The results revealed that as the Pt loading increased PEM fuel cell performance was also increased.     

Examination of 2-methacryloyloxyethyl phosphorylcholine polymer coated acrylic resin denture base material: surface characteristics and <Emphasis Type="BoldItalic">Candida albicans</Emphasis> adhesion

The aim of this study is to evaluate the effects of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer coating with various concentrations onto acrylic resin denture base material on surface characteristics such as contact angle and surface roughness and on Candida albicans adhesion which is the major factor of denture stomatitis. Specimens, prepared from heat-polymerized acrylic denture base material, were divided into control and three test groups, randomly. Surfaces of the specimens in test groups were coated with poly(MPC) (PMPC) by graft polymerization of MPC in different concentrations (0.25?mol/L; 0.50?mol/L and 0.75?mol/L), while no surface treatment was applied to the control group. Contact angles and surface roughness were examined, and chemical composition of the surfaces was analyzed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (FTIR) to verify the presence of PMPC coatings. Then, specimens were incubated with C. albicans for 18?h and the number of adhered cells was determined. Upon PMPC coating, the contact angle values statistically decreased, but no difference was found in surface roughness values. A statistically significant decrease was observed in C. albicans adhesion in parallel with the increase in the MPC polymer concentration. There was no significant difference between 0.50?mol/L and 0.75?mol/L groups in terms of adhesion. These findings indicated that graft polymerization of MPC on acrylic denture base material reduces the adhesion of C. albicans, and may be evaluated as a coating for prevention of denture stomatitis.     

Integration of strategic and tactical decisions for vendor selection under capacity constraints

We examine a generalized vendor selection problem of a multi-store firm where the goal is the simultaneous determination of (i) the set of vendors the firm should work with and (ii) how much each store should order from the selected vendors. In addition to the typical costs associated with vendor selection and delivery between the vendors and their assigned stores, we explicitly consider the inventory-related costs and decisions of the stores. We emphasize the relationship between facility location applications and the problem at hand, and we propose an integrated vendor selection and inventory optimization model. Also, arguing that our model creates a venue for precise incorporation of realistic capacity constraints, we model throughput and dispatch capacities, explicitly. The model is a challenging mixed integer nonlinear program for which we propose an efficient solution approach that relies on Generalized Benders Decomposition (GBD).