Influences of biosilica content from Amazonian freshwater sponge on calcium phosphates

Abstract

In this work, hydroxyapatite (HA) reinforced with biogenic silica from Amazonian freshwater sponge, collected at Negro River, Amazonas, was produced using different percentages of the sponges after a calcination process. These freshwater sponges are composed by silicon dioxide (silica) and an organic matrix. It is known that silicon dioxide, when incorporated to the hydroxyapatite structure, shows a tendency to partially or totally replace the (PO4)3− groups. In the present study, hydroxyapatite (HA) was synthesized by an aqueous solution precipitation method, and freshwater sponges were added after heat treatment. The XRD and FTIR results for the samples with 2 wt% and 4 wt% of silica added to hydroxyapatite presented HA and quartz phases, while the samples containing 8 wt%, 15 wt%, and 25 wt% of added silica presented quartz, cristobalite, and a partial HA partially decomposed into β-TCP, as well as whitlockite. XPS analysis showed bands corresponding to silicon for the samples with 8 wt%, 15 wt%, and 25 wt% of added silicon to HA. The increase in calcium/phosphorous (Ca/P) atomic ratio with increasing silicon content indicated the partial substitution of phosphate by silicate groups. Morphological analyses were also performed and showed the preferential presence of a new phase in grain boundaries, differing from pure HA pellets, which probably occurred due to the addition of silicon from freshwater sponge. The unique nanometric morphology for the sample with 25 wt% of silica in hydroxyapatite matrix, with nanometric porosity on the entire surface of the samples, has never been previously reported.