Cassiano Gomes Aimoli

Natural and prosthetic heart valve calcification: morphology and chemical composition characterization.

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.

Influence of Acetylation on In Vitro Chitosan Membrane Biomineralization

In a previous work of this research group, we studied the in vitro calcification of dense and porous chitosan membranes. Chemical modifications had been promoted, but fur ther investigations were needed to better understand the role of some chemi cal groups in the process of calcification. In the present study, we proposed the acetylation of the already-molded chitosan membranes, producing a “pseudo-chitin”, to be used in calcification. The ac etylated chitosan was submitted to mineralization by soaking the membranes in simulated body fluids (SBF) with 1x and 1.5x the concentration of ions found in human serum, for 7 days at 36.5 C. Morphological characterization was performed using SEM and compositional analyses wer done using SEM-EDX and FTIR-ATR techniques. The results showed that acetyl groups induce calcification, forming deposits that present a Ca:P ratio different of those formed on pristine chitosan.

In Vitro Calcification of Silk Fibroin Hydrogel

Silk fibroin hydrogels were prepared and their potential to deposit calcium phosphates in vitro was observed. Pristine and lyophilized samples were tested in 1xSBF and 1.5xSBF. The results showed that silk fibroin hydrogels can induce calcium phosphate deposits both in the pristine and lyophilized form. However, the pristine silk fibroin hydrogel after calcification presented a fragile structure making it difficult to handle, while the lyophilized samples presented better resistance to handling. Calcium phosphates deposits were intense in samples submitted to tests in 1.5xSBF, however, few and isolated deposits were observed on samples submitted to tests in 1xSBF. The 3-D porous structure and the ability to deposit calcium phosphates, turn silk fibroin hydrogel a potential material suitable to use in biomimetic processes.

An EXAFS Study Of The Binding Of Chromium, Mercury And Copper On Natural, Crosslinked And Multilayer Chitosan Films

The coordination environment of metal atoms involved in their adsorption on chitosan was studied by using EXAFS technique. Chromium, mercury and copper complexes were gotten on natural, crosslinked and multilayer chitosan films and the spectra of the distribution of neighbor atoms around the adsorbed central atom were obtained. All spectra were obtained in transmission mode and were collected around Hg (12284 eV) L edge, Cr (5989 eV) and Cu (8987 eV) K edges. For chromium ions, it was possible to observe that metal interaction is mainly performed on amino groups, on the other hand, it was not possible to distinguish if the metal interaction takes place preferentially on amino or hydroxyl group, for mercury and copper.

Study of Morphology of Cardiac Valves (Human and Bovine Pericardium) after In Vivo Calcification

Pathologic calcification can lead to failure or deterioration of cardiac valves. Several researchers have tried alternatives to construct these devices, such as the incorporation or utilization of new biomaterials able to inhibit or decrease the calcification process. In vitro calcification tests can be used to screen new biomaterials regarding their potential to calcify in vivo. However, the mechanisms involved in both cases are not completely understood. In order to collect more information about the calcification process of implanted materials, morphology and elemental analyses of calcified cardiac valve fragments explanted from different patients were investigated and compared to previous reports of in vitro calcification tests. Scanning Electron Microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses indicated that the calcium phosphate deposits from both bovine pericardium and human cardiac valves calcified in vivo were similar to the deposits obtained from in vitro calcification samples as previously reported in the literature.