Papers by Author: Nilce C.C. da Rocha

Abstract: Polymeric sponges coated with hydroxyapatite were used in lead and cadmium uptake experiments in order to mimetizes heavy metal incorporation by bone tissue. The hydroxyapatite-coated sponges (S-HA) were obtained by hydrothermal alkali conversion from monetite. The results showed that S-HA were efficient in immobilizing Pb and Cd. The uptake experiments using hydroxyapatite powder (HA) removed almost 100% of Pb2+ and 59% of Cd2+. When polymeric sponges coated with hydroxyapatite were used, the removal of Cd2+ and Pb2+ decreased, respectively, to closely 14 % and 74%, after 24 hours sorption. Before and after sorption experiment MEV analysis indicated precipitation of pyromorphite on hydroxyapatite-coated sponges.

Abstract: In this study, the insulin adsorption ability by synthetic hydroxyapatite was investigated. Hydroxyapatite before thermal treatment and heated at 900°C and 1100°C were incubated in a solution containing 32 mg insulin/gHA. Adsorption and desorption experiments were carried out at 37°C under constant and slowly stirring. From FTIR results it was observed that insulin was tightly attached to HA surface after 96 hours adsorption experiment. Thermal pre-treatment on HA samples had no effect on insulin adsorption. However, protein desorption was more pronounced on samples not submitted to thermal treatment.

Abstract: Micrometric sphere beads of HA-alginate composite were produced to remove Pb2+ and Cd2+ from contaminated gastric fluid. It was shown that the composite was effective in Pb2+ and Cd2+ immobilization from high-contaminated simulated gastric fluid. X-ray diffraction and scanning electron microscope analyses performed on HA-alginate beads after the Pb2+ uptake showed that lead phosphate, (Pb10-x Cax (PO4)6Cl2), was precipitated on beads surface. X-ray diffraction patterns of HA powder after Cd2+ sorption experiments showed no evidence of other phases, however, dispersive energy spectrometer analyses of the HA-alginate confirmed the presence of Cd2+ on the composite surface. Desorption experiments in simulated enteric fluid showed that composite beads containing Pb2+ and Cd2+ remained stables for one hour in simulated gastrointestinal fluid. The results reinforce the hypothesis that HA-alginate composite can be a very efficient system for Pb2+ and Cd2+ uptake from contaminated gastrointestinal fluid preventing systemic contamination by bloody stream uptake.

Abstract: Adsorption experiments of bovine serum albumin on hydroxyapatite previously annealed at temperatures up to 1100°C was performed at 37°C and phosphate buffer, pH 6.0. Kinetic process was very efficient and irreversible for low phosphate buffer concentration. Thermal treatment contributed to the decrease of bovine serum albumin immobilization indicating that sorption process depended on HA specific surface area and the number of surface active sites. However, it was verified that particle size was also an important parameter for bovine serum albumin immobilization.

Abstract: Cadmium uptake by hydroxyapatite from aqueous solution was studied in time intervals between 2 minutes and 96 hours, using different Cd2+ concentrations (21 to 768 mg L-1). The solution pH after Cd2+ uptake was assessed. Dissolution experiments at fixed pH were performed in order to evaluate the ion exchange process. Cd2+sorption by hydroxyapatite is fast and it happens simultaneously by different mechanisms. Ion exchange is the main mechanism, where mechanism Cd2+ present in aqueous solution replaces Ca2+ from hydroxyapatite structure.