An experimental and theoretical approach on stability towards hydrolysis of triethyl phosphate and its effects on the microstructure of sol-gel-derived bioactive silicate glass.

The sol-gel method is versatile and one of the well-established synthetic approaches for preparing bioactive glass with improved microstructure. In a successful approach, alkoxide precursors undergo rapid hydrolysis, followed by immediate condensation leading to the formation of three-dimensional gels. On the other hand, a slow kinetics rate for hydrolysis of one or more alkoxide precursors generates a mismatch in the progression of the consecutive reactions of the sol-gel process, which makes it difficult to form homogeneous multicomponent glass products. The amorphous phase separation (APS) into the gel is thermodynamically unstable and tends to transform into a crystalline form during the calcination step of xerogel. In the present study, we report a combined experimental and theoretical method to investigate the stability towards hydrolysis of triethyl phosphate (TEP) and its effects on the mechanism leading to phase separation in 58S bioactive glass obtained via sol-gel route. A multitechnical approach for the experimental characterization combined with calculations of functional density theory (DFT) suggest that TEP should not undergo hydrolysis by water under acidic conditions during the formation of the sol or even in the gel phase. The activation energy barrier (ΔG‡) showed a height of about 20 kcal·mol-1 for the three stages of hydrolysis and the reaction rates calculated for each stage of TEP hydrolysis were kFHR = 7.0 × 10-3s-1, kSHR = 6.8 × 10-3s-1 and kTHR = 3.5 × 10-3s-1. These results show that TEP remains in the non-hydrolyzed form segregated within the xerogel matrix until its thermal decomposition in the calcination step, when P species preferentially associate with calcium ions (labile species) and other phosphate groups present nearby, forming crystalline domains of calcium pyrophosphates permeated by the silica-rich glass matrix. Together, our data expand the knowledge about the synthesis by the sol-gel method of bioactive glass and establishes a mechanism that explains the role played by the precursor source of phosphorus (TEP) in the phase separation, an event commonly observed for these biomaterials.

Investigation of citric acid-assisted sol-gel synthesis coupled to the self-propagating combustion method for preparing bioactive glass with high structural homogeneity.

In this research, the mechanism of an efficient strategy for the synthesis of 58S bioglass with high structural homogeneity by a citric acid assisted sol-gel route was investigated. This is an interesting approach to prepare bioactive glass via the sol-gel method with application potential in bone tissue engineering and also for the development of new biomedical devices. Herein, 58S bioglass was synthesized by two routes: conventional sol-gel method (CSG) and citric acid assisted sol-gel route coupled to the self-propagating combustion method (SPC). The effects of citric acid on the temperature required for 58S vitreous consolidation, long- and short-range ordering were investigated by several analysis techniques. Results suggested that citric acid molecules serve as an effective molecular template formed by molecular network raised from intermolecular forces, especially the hydrogen bonds, resulting from the chemical interactions between the COOH and hydroxyl groups (water, ethanol, POH, SiOH). In this scenario, citric acid controls the phase segregation during the drying and combustion steps of the gel in the SPC method by establishing chemical interactions (hydrogen bonds) with the superficial silanol groups present on the small-sized silica nanoparticles present in the sol governing their growth. Besides these mentioned features, the self-propagating combustion behavior exhibited by the nitrate-citrate in the SPC xerogel during the combustion step allowed the removal of the organic load and the consolidation of the vitreous structure at a temperature considerably lower than the sample obtained by the CSG method. Consequently, the SPC method leads to the formation of a glass structure with high homogeneity for the 58S, whereas the conventional sol-gel method produces a matrix enriched with calcium phosphate crystalline nuclei - glass-ceramic.

Comprehensive in vitro and in vivo studies of novel melt-derived Nb-substituted 45S5 bioglass reveal its enhanced bioactive properties for bone healing.

The present work presents and discusses the results of a comprehensive study on the bioactive properties of Nb-substituted silicate glass derived from 45S5 bioglass. In vitro and in vivo experiments were performed. We undertook three different types of in vitro analyses: (i) investigation of the kinetics of chemical reactivity and the bioactivity of Nb-substituted glass in simulated body fluid (SBF) by 31P MASNMR spectroscopy, (ii) determination of ionic leaching profiles in buffered solution by inductively coupled plasma optical emission spectrometry (ICP-OES), and (iii) assessment of the compatibility and osteogenic differentiation of human embryonic stem cells (hESCs) treated with dissolution products of different compositions of Nb-substituted glass. The results revealed that Nb-substituted glass is not toxic to hESCs. Moreover, adding up to 1.3 mol% of Nb2O5 to 45S5 bioglass significantly enhanced its osteogenic capacity. For the in vivo experiments, trial glass rods were implanted into circular defects in rat tibia in order to evaluate their biocompatibility and bioactivity. Results showed all Nb-containing glass was biocompatible and that the addition of 1.3 mol% of Nb2O5, replacing phosphorous, increases the osteostimulation of bioglass. Therefore, these results support the assertion that Nb-substituted glass is suitable for biomedical applications.

Electrically wired enzyme/TiO2 composite for glucose detection.

TiO2, glucose oxidase and carbon nanotube microparticles were ultrasonically formed to provide a large surface area for enzyme immobilisation and a favorable microenvironment for direct electron transfer. This simple architecture nanostructure was used to construct a glucose oxidase biosensor, which demonstrated good analytical performance with high reproducibility, and good detection for pathological glucose level.

Facile and innovative method for bioglass surface modification: Optimization studies.

In this work it is presented a facile and novel method for modification of bioglass surface based on (Camolten salt bath2+|Naglass+) ion exchange by immersion in molten salt bath. This method allows changing selectively the chemical composition of a surface layer of glass, creating a new and more reactive bioglass in a shell that surrounds the unchanged bulk of the original BG45S5 bioglass (core-shell type system). The modified bioglass conserves the non-crystalline structure of BG45S5 bioglass and presents a significant increase of surface reactivity in comparison with BG45S5. Melt-derived bioactive glasses BG45S5 with the nominal composition of 46.1mol% SiO2, 24.4mol% Na2O, 26.9mol% CaO, and 2.6mol% P2O5 have been subjected to ion exchange at 480°C in molten mixture of Ca(NO3)2 and NaNO3 with molar ratio of 70:30 for different time periods ranging from 0 to 60min. The optimization studies by using XRF and XRD showed that ion exchange time of 30min is enough to achieve higher changes on the glass surface without alters its non-crystalline structure. The chemical composition, morphology and structure of BG45S5 and bioglass with modified surface were studied by using several analytical techniques. FTIR and O1s XPS results showed that the modification of glass surface favors the formation of Si-ONBO groups at the expense of SiOBOSi bonds. 29Si MAS-NMR studies showed that the connectivity of SiQn species decreases from cross-linked SiQ3 units to chain-like SiQ2 units and finally to depolymerized SiQ1 and SiQ0 units after ion exchange. This result is consistent with the chemical model based on the enrichment with calcium ions of the bioglass surface such that the excess of positive charges is balanced by depolymerization of silicate network. The pH changes in the early steps of reaction of bioactive glasses BG45S5 and BG45Ca30, in deionized water or solutions buffered with HEPES were investigated. BG45Ca30 bioactive glass exhibited a significant increase in the pH during the early steps of the reaction compared to BG45S5.

Hierarchical structures of ß-TCP/45S5 bioglass hybrid scaffolds prepared by gelcasting.

This paper investigates the microstructure and the mechanical properties of ß-tricalcium phosphate (ß-TCP) three-dimensional (3D) porous materials reinforced with 45S5 bioactive glass (BG). ß-TCP and ß-TCP/x%-BG scaffolds with interconnected pores networks, suitable for bone regeneration, were fabricated by gel-casting method. Mechanical properties, porosity, and morphological characteristics were evaluated by compressive strength test, scanning electron microscopy (SEM) and X-ray microtomography analysis, whereas the structures were fully explored by XRD, and Raman spectroscopy. To the best of our knowledge, this is the first time where the mechanism for understanding the effect of bioglass on the mechanical properties and microstruture of ß-TCP/45S5-BG scaffolds has been systematically studied. The findings showed that ionic product lixiviated from 45S5 bioactive glass, rich in silicon species and sodium ion, catalyzes a phase transition from ß-TCP to Si-TCP by replacement of phosphorus for silicon and contributes to the improvement of scaffolds mechanical properties. The compressive strength of ß-TCP/5%-BG and ß-TCP/7.5%-BG was improved around 200% in comparison to pure ß-TCP. Osteoblast-like cells (MG 63) were exposed to the materials for 24h through the use of medium conditioned by ß-tricalcium phosphate/bioactive glass. Cell viability was measured by MTT assay in the cells and the data obtained were submitted to ANOVA, Tukey׳s multiple comparison (p<0.05). The ß-TCP/7.5-BG promoted an increase of cell proliferation. The results suggest that compositions and processing method studied may provide appropriate materials for tissue engineering.

Adesão do paciente à terapia medicamentosa da hipertensão arterial: revisão da literatura / Patient adherence to drug therapy of hypertension: literature review

Este estudo teve por objetivo avaliar, por meio de uma revisão da literatura, a adesão medicamentosa de pacientes com Hipertensão Arterial Sistêmica (HAS). Foram selecionados artigos nas bases de dados: Biblioteca Científica Eletrônica Online (ScientificElectronic Library Online - SciELO), Google Acadêmico e Centro Latino-americano e do Caribe de Informação em Ciências da Saúde (BIREME). Na busca foram excluídos os artigos que não apresentavam o conteúdo sob o ponto de vista da falta de adesão à terapia medicamentosa da HAS. Foram observados, na pesquisa, fatores relacionados: a) ao paciente e à doença: socioeconômicos, cronicidade, assintomatologia e sensação de ?cura? da doença; b) ao tratamento: a complexidade do esquema terapêutico, efeitos colaterais, alto custo dos medicamentos e interrupção e receio das medidas prescritas; c) aos serviços de saúde: profissionais, a organização e fortalecimento do tipo de política de saúde para a resolutividade dos problemas, estrutura dos serviços de saúde, a educação permanente e atenção prioritária à comunicação médico-paciente-equipe de saúde. O apoio social e da família, assim como o envolvimento do cuidador no processo de tratamento para o hipertenso, também foram relatados nos artigos. A falta de adesão ao tratamento medicamentoso da terapia da hipertensão arterial é uma condição multifatorial e não deve ser creditada apenas ao paciente. Fatores ligados à própria doença, ao tratamento e aos serviços de saúde, incluindo seus profissionais, interferem na forma como essa adesão ocorre

This study aimed to describe and analyze what reasons lead the patient not adhering to Hypertension drug therapy. As this study is a literature review, articles were surveyed by active search for information in databases. It was observed that the articles presented main points related to: a) patient and disease factors, such as socioeconomic factors, education level, gender, ethnicity and age, as well as chronic, no symptomatology, and sense of disease ?cure?; b) treatment, such as complexity of therapeutic regimen, side effects and the high cost of medicines, as well as disruption and fear the prescribed measures; c) health services, including their employees, which pointed out the organization and strengthening of the type of health policy for solving the problems, the best structure of health services, continuing education of employees and priority attention to medical communication / patient / health team. The social and family support, as well as the caregiver?s involvement in the process of treatment for hypertension have also been reported in the articles. The lack of adherence to drug treatment of high blood pressure therapy is a multifactorial condition and should not be credited only to the patient. Factors linked to the disease, treatment and health services, including their professionals, interfere in how this adhesion occurs

Electrocatalytic Oxygen Reduction Performance of Silver Nanoparticle Decorated Electrochemically Exfoliated Graphene.

We have developed a potentiostatic double-pulse technique for silver nanoparticle (Ag NP) deposition on graphene (GRn) with superior electronic and ionic conductivity. This approach yielded a two-dimensional electrocatalyst with a homogeneous Ag NP spatial distribution having remarkable performance in the oxygen reduction reaction (ORR). GRn sheets were reproducibly prepared by the electrochemical exfoliation of graphite (GRp) at high yield and purity with a low degree of oxidation. Polystyrenesulfonate added during exfoliation enhanced the stability of the GRn solution by preventing the restacking of the graphene sheets and increased its ionic conductivity. The potentiostatic double-pulse technique is generally used to electrodeposit Pt nanoparticles and remains challenging for silver metal that exhibits nucleation and growth potentials relatively close to each other. We judiciously exploited this narrow margin of potential, and for the first time we report Ag NP electrodeposited onto graphene with the subsequent ability to control both the density and the size of metallic nanoparticles. Considering the high activity along with the lower cost of Ag compared to Pt, these findings are highly relevant to the successful commercialization of fuel cells and other electrochemical energy devices.