Histological, chemical, and crystallographic analysis of four calcium phosphate cements in different rabbit osseous sites

Abstract

Four calcium phosphate cement formulations were implanted in the rabbit distal femoral metaphysis and middiaphysis. Chemical, crystallographic, and histological analyses were made at 2, 4, and 8 weeks after implantation. When implanted into the metaphysis, part of the brushite cement was converted into carbonated apatite by 2 weeks. Some of the brushite cement was removed by mononuclear macrophages prior to its conversion into apatite. Osteoclastlike cell mediated remodeling was predominant at 8 weeks after brushite had converted to apatite. The same histological results were seen for brushite plus calcite aggregate cement, except with calcite aggregates still present at 8 weeks. However, when implanted in the diaphysis, brushite and brushite plus calcite aggregate did not convert to another calcium phosphate phase by 4 weeks. Carbonated apatite cement implanted in the metaphysis did not transform to another calcium phosphate phase. There was no evidence of adverse foreign body reaction. Osteoclastlike cell mediated remodeling was predominant at 8 weeks. The apatite plus calcite aggregate cement implanted in the metaphysis that was not remodeled remained as poorly crystalline apatite. Calcite aggregates were still present at 8 weeks. There was no evidence of foreign body reaction. Osteoclastlike cell remodeling was predominant at 8 weeks. Response to brushite cements prior to conversion to apatite was macrophage dominated, and response to apatite cements was osteoclast dominated. Mineralogy, chemical composition, and osseous implantation site of these calcium phosphates significantly affected their in vivo host response.

Phytic acid as alternative setting retarder enhanced biological performance of dicalcium phosphate cement in vitro

“…4). The release of phosphate in conjunction with the adsorption of Ca 2+ and Mg 2+ is related to the well know tendency of brushite cements to convert into calcium phosphate phases with a higher Ca: P ratio 44–47 . Surprisingly, sodium pyrophosphate and phytic acid behaved differently and expressed both Ca 2+ and phosphate ions.…”

Mechanisms of in Vivo Degradation and Resorption of Calcium Phosphate Based Biomaterials

“…CaP biomaterials once implanted adsorb various proteins (soluble growth factor, serum proteins, and extracellular matrix proteins) onto their surfaces which alter the interfacial properties resulting in enhanced in vivo degradation [2,56]. Brushite cements are shown to resorb at a much faster rate when compared to apatite cements [57,58,59]. This difference can be explained by the compositional difference observed for the final products of these cements.…”

“…Therefore, if brushite cement grafts contain large amounts of unreacted TCP then the dicalcium phosphate dehydrate (DCPD) get resorbed leaving behind long standing β-TCP material [67,92]. Another factor that limits the rate and extent of brushite resorption is the phase conversion phenomenon [57,93]. After demonstrating fast degradation post implantation, the remaining brushite cement converts to less soluble apatites (octacalcium phosphate OCP and hydroxyapatite HA) [94,95,96].…”

“…After demonstrating fast degradation post implantation, the remaining brushite cement converts to less soluble apatites (octacalcium phosphate OCP and hydroxyapatite HA) [94,95,96]. These result in no or very slow resorption from this point onwards mediated solely by osteoclasts, rather than macrophagic phagocytosis [57,65]. Other dicalcium phosphate materials such as monetite show greater resorption and bone formation in vivo when compared with brushite cements [97].…”

Biomaterials for Craniofacial Bone Regeneration

“…The discovery of bone cements constituted of CaP phases that can be formed at room temperature (calcium deficient HA, brushite, octacalcium phosphate and monetite) opened up a wide range of possibilities in the manufacture of new CaP bone scaffold materials [12–15]. Importantly, these materials have much lower solubility rates and have been shown to transform into a more stable HA phase upon implantation [16–18]. In fact it has been suggested that these less crystalline phases with lower solubility than sintered CaPs have superior biological properties [19].…”