A new method to prepare porous silk fibroin (SF) membranes without dialysis is proposed. Silk fibers were degummed to remove sericin and the resultant fibroin was dissolved in a CaCl 2 -CH 3 CH 2 OH-H 2 O ternary solvent. Rather than undergoing dialysis, a fibroin salty solution was diluted in water and then submitted to a mechanical agitation that led to a phase separation through foam formation on the solution surface. This foam was continually collected and then compacted between plates to remove the excess of water. The membranes presented large pores with diameters of greater than 100 lm (as shown by scanning electron microscopy -SEM), porosity of 68% and water content of 91% w/w. X-ray diffraction (XRD) and infrared spectroscopy (FTIR-ATR) indicated that the membranes present SF in a b-sheet structure even before the ethanol treatment. A typical elastic deformation profile and degradation under temperature were observed using calorimetric analysis (DSC), thermal gravimetric analysis (TGA) and mechanical tests. As indicated by the in vitro cytotoxicity tests, these membranes present potential for use as scaffolds.
Silk fibroin is a fibrous protein that has been extensively studied for application in the biomedical field, and has been used as a scaffold for bone tissue engineering. Biomaterials made of proteins are prone to physical and chemical degradation during storage; lyophilization, a drying method that consists of freezing and drying steps, is known to promote minimal changes in structure and biological activity of biomaterials. This study evaluates the effect of freezing methods on the properties of lyophilized porous silk fibroin membranes. The membranes were obtained from silk fibroin solution, frozen in liquid nitrogen or ultrafreezer, lyophilized, and then characterized by XRD, FTIR, TGA, DSC and SEM. Although the membranes presented similar physical, chemical and microstructural characteristics, quench freezing with liquid nitrogen, followed by lyophilization, promoted collapse of the membranes, while slow cooling performed by ultrafreezer preserved membrane integrity.
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.
This paper presents the results of an evaluation of the main characteristics of landforms located at Araguari County where stabilized slime have been scattered over the soil surface. These characteristics have special importance to determine the soil capacity of assimilation nutrients and other minerals that exist in this kind of slime provided by frigorific. Keywords: relief and toposequence analysis, infiltration capacity, soil materials
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