Precipitation of calcium phosphate and calcium carbonate induced over chitosan membranes: A quick method to evaluate the influence of polymeric matrices in heterogeneous calcification

Precipitation of calcium compounds (phosphate and carbonate) was performed on chitosan porous and dense membranes. In order to observe the influence of acetyl groups on the nature of formed precipitates, some chitosan membranes were acetylated in methanol solution before undergoing calcification. Calcification experiments were performed more quickly than using SBF. In this method, a faster precipitation is induced by soaking the membranes in calcium chloride solutions and, in sequence, immersing the same membranes into sodium phosphate or carbonate solutions. This procedure induced the formation of calcium compound precipitates on membrane surfaces, which were analysed through optical microscopy, X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy with attenuated total reflection apparatus (FTIR-ATR) and small angle X-ray scattering (SAXS). The results indicated the biomimetic influence of the organic matrix on morphology, organization and composition of precipitates. The acetyl group induced the formation of organized calcium carbonate better than phosphate, which may correlate with the fact that these two compounds are commonly found together in nature in structures like shells and nacre. (C) 2006 Elsevier B.V. All rights reserved.531152

Investigation on the biomimetic influence of biopolymers on calcium phosphate precipitation-Part 1: Alginate

The understanding of how macromocules act in precipitation of inorganic phases is the key knowledge that is needed to establish the foundation to mimic nature and produce materials with high mechanical modulus besides Outstanding optical and thermal properties. This study investigated how addition of small amounts of alginate (7-70 ppm), that presents many carboxylic groups, affects phase distribution and morphology of calcium phosphates, obtained through precipitation and further submitted to calcination and sintering. The results lead to the Conclusion that alginate action is dynamic, where alginate molecules act as templates to nucleation, and most of the biopolymer remains in solution even when all calcium phosphate has precipitated. However, despite the effect on phase composition being mainly related to the system's kinetics, alginate does present thermodynamic interaction with the precipitates. It is probable that it acts by reducing the free energy Of nucleation, as in heterogeneous nucleation processes. (C) 2008 Elsevier B.V. All rights reserved.2941109111

Investigations into the early stages of "in vitro" calcification on chitosan films

This work investigated the mechanisms involved in the "in vitro" calcification of chitosan films. The calcification process on chitosan films is a phenomenon that has not been sufficiently studied, despite its importance in the understanding of many natural processes, such as bone and shell formation. Three different techniques were used in the present investigation: X-ray fluorescence (XRF), atomic force microscopy (AFM) and X-ray diffraction (XPD). Natural and acetylated chitosan films were used as substrates for calcification. The experiments were carried out by immersing chitosan membranes in simulated body fluid (SBF) or in a modified version of SBF, prepared without phosphate ions, during 30 min, 3 or 12 h. Calcium maps obtained by XRF showed that the initial calcium distribution on the chitosan surface was influenced by the acetylation treatment of chitosan films. AFM indicated the distribution pattern of calcium compound deposits at different times, obtained by film surface morphological analysis. The results suggest that the calcification mechanism is nucleation on membranes followed by the crystal growth of calcium compounds. AFM showed that the deposit formation is a function of immersion time: the deposits became more homogeneous and covered the surface more evenly with longer immersion times. XPD showed that the acetylated membranes produced more organized calcium deposits. (c) 2005 Elsevier B.V. All rights reserved.261788

In vitro mineralization on chitosan using solutions with excess of calcium and phosphate ions

Pseudo-simulated body fluids (SBFs) were used in in vitro experiments to promote chitosan porous membrane calcification. Common SBFs, which had concentrations of phosphate or calcium ions doubled, were so named because they do not replicate, by rigor, a genuine body fluid ion concentration. The objective of using such calcification fluids was to study the influence of phosphate and calcium excess in solution on mineralization deposit characteristics. SEM-EDS analyses showed that morphology and composition of deposits varies depending on which ion (phosphate or calcium) is in excess; x-ray diffractograms show that deposits are poorly crystalline (like biological apatites) but still show better crystallinity in deposits generated from P-rich SBF. This result, added to previous ones [such as those reported by Beppu and Santana Mater. Res. 5, 47 (2002)] where a difference in the interconnectivity of the inorganic and organic (matrix) phases was stressed, suggests different deposition processes for each C, Z situation.o TEXTO COMPLETO DESTE ARTIGO, ESTARÁ DISPONÍVEL À PARTIR DE AGOSTO DE 2015.20123303331

Chitosan membrane with patterned surface obtained through solution drying

Chitosan membranes with self-organized lines on surface were obtained. SEM and laser diffraction techniques showed that structures with peak-valley periods of about 5 +/- 2 mu m were observed in both porous and dense chitosan membranes. These unique patterns may be of special interest for applications where micro-mechanical interactions are important such as for biomaterials. The procedure used to produce these membranes consisted of casting, drying of a 2.5% chitosan solution, followed by coagulation using 1.0M NaOH solution. The analyses indicate that the drying step is the most important to shape the organized surface pattern. This is in agreement with literature that cites that when layers of polymer solutions undergo solvent evaporation and/or heating from below, the interface can become unstable, generating patterns, depending on the surface tension differences and density effects, fluid motion can be generated and amplified, through the known Marangoni effect. (c) 2005 Elsevier B.V. All rights reserved.2684169917517

Crosslinking of chitosan membranes using glutaraldehyde: Effect on ion permeability and water absorption

Many mass-transfer applications have used chitosan membranes in separation processes (e.g. filtration and adsorption). Chitosan can be crosslinked easily by dialdehydes, such as glutaraldehyde, and this process is able to change drastically some macro and micro properties: water absorption, ion permeability, chemical and mechanical properties. Dense membranes were produced by casting and drying of chitosan solution. Potentiometric titration, infrared spectroscopy (FTIR-ATR) and thermal gravimetric analyses (TGA) were used for chemical characterization, and to identify differences between pristine and crosslinked chitosan membranes. Diffusion experiments confirm some subtle changes in permeability of ions. All results indicate that chemical modification with glutaraldehyde turns chitosan more hydrophobic. (c) 2007 Elsevier B.V. All rights reserved.3014167112613

Lyophilized bovine pericardium treated with a phenethylamine-diepoxide as an alternative to preventing calcification of cardiovascular bioprosthesis: Preliminary calcification results

This study investigated the calcification process that occurred on chemically treated bovine pericardium substrata through tests with simulated body fluid solutions. The use of bovine pericardium bioprosthetic valves in heart valve surgery has a significant drawback due to the calcification processes. Thus, many routes such as chemical treatments in the substratum or the adoption of systemic therapies are considered in the literature with the intention to inhibit or to decelerate this process. The presented treatment using the two different phenetylamine-diepoxide solutions showed no effects on calcification experiments as showed by the tests. However, the lyophilized bovine pericardium samples, treated with both solutions, did not show any detectable phosphate deposits. The lyophilization of bovine pericardium before chemical treatments with cross-link agents as epoxy compounds may be an alternative to the conventional calcification prevention methods, but further investigations are recommended to check if the same behavior is found in all lyophilized systems.31427828

Natural and Prosthetic Heart Valve Calcification: Morphology and Chemical Composition Characterization

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Calcification is the most common cause of damage and subsequent failure of heart valves. Although it is a common phenomenon, little is known about it, and less about the inorganic phase obtained from this type of calcification. This article describes the scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy and Ca K-edge X-ray absorption near edge structure (XANES) characterization performed in natural and bioprosthetic heart valves calcified in vivo (in comparison to in vitro-calcified valves). SEM micrographs indicated the presence of deposits of similar morphology, and XANES results indicate, at a molecular level, that the calcification mechanism of both types of valves are probably similar, resulting in formation of poorly crystalline hydroxyapatite deposits, with Ca/P ratios that increase with time, depending on the maturation state. These findings may contribute to the search for long-term efficient anticalcification treatments.344311318Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP