Papers by Author: Grínia M. Nogueira

Abstract: 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.

Abstract: The requirements for scaffolds for bone tissue engineering include appropriate chemistry, morphology and structure to promote cell adhesion and synthesis of new bone matrix. Silk fibroin (SF) represents an important biomaterial for biomedical application, due to its suitable mechanical properties, biodegradability, biocompatibility, and versatility in processing. Our group has developed a new method to obtain a porous SF membrane, and the study of its potential for use as a scaffold for bone regeneration was the aim of this study. Porous membranes were obtained from SF solution, through the compression of a material generated by phase separation. For in vitro calcification experiments, porous SF membrane samples were immersed in SBF at pH 7.4 placed in polyethylene flasks. The experiments were carried out for seven days, at 36.5±0.5 °C. After 48 and 96h, the solutions were changed for fresh SBF with the ion concentration 1.5-fold higher than that of the standard one, to accelerate the calcification process. The characterization of morphology and composition of samples was performed by using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The SEM micrographs indicated that the porous SF membranes presented calcium phosphate deposits after undergoing in vitro calcification. These results were confirmed by EDS spectra, which showed a stoichiometric molar Ca/P ratio ranging from 1.27 to 1.52. This fact may suggest that calcification deposits consisted of mixtures of HAP (Ca/P ratio = 1.67) and transient HAP precursor phases, such as octacalcium phosphate (Ca/P = 1.33) and dicalcium phosphate dehydrate (Ca/P = 1), indicating early stage mineralization. The porous silk fibroin membrane analysed in the current study is a promising material to be used as scaffolds for bone regeneration.

Abstract: 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.