Properties of commonly used calcium phosphate cements in trauma and orthopaedic surgery

Calcium Phosphate Nanoparticles as Carriers of Low and High Molecular Weight Compounds

Nanoparticles could improve the bioavailability of active agents of various natures to human, animal, and plant tissues. In this work, we compared two methods on the synthesis of calcium phosphate nanoparticles (CaPs), differed by the synthesis temperature, pH, and concentration of the stabilizing agent, and explored the possibilities of incorporation of a low-molecular-weight peptide analogue enalaprilat, the enzyme superoxide dismutase 1 (SOD1), as well as DNA and dsRNA into these particles, by coprecipitation and sorption. CaPs obtained with and without cooling demonstrated the highest inclusion efficiency for enalaprilat upon coprecipitation: 250 ± 10 μg/mg of CaPs and 340 ± 30 μg/mg of CaPs, respectively. Enalaprilat sorption on the preliminarily formed CaPs was much less effective. SOD1 was only able to coprecipitate with CaPs upon cooling, with SOD1 loading 6.6 ± 2 μg/mg of CaPs. For the incorporation of DNA, the superiority of the sorption method was demonstrated, allowing loading of up to 88 μg/mg of CaPs. The ability of CaPs to incorporate dsRNa by sorption was also demonstrated by electrophoresis and atomic force microscopy. These results could have important implications for the development of the roots for incorporating substances of different natures into CaPs for agricultural and medical applications.

In vitro and in vivo analysis of the biocompatibility of two novel and injectable calcium phosphate cements

Calcium phosphate cements (CPCs) have been widely used as bone graft substitutes for many years. The aim of this study was to evaluate the biocompatibility of two novel injectable, bioactive cements: β-tricalcium phosphate (β-TCP)/CPC and chitosan microsphere/CPC in vitro and in vivo. This was accomplished by culturing mouse pre-osteoblastic cells (MC3T3-E1) on discs and pastes of CPCs. Cell growth, adhesion, proliferation and differentiation were assessed by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and alkaline phosphatase assays as well as by scanning electron microscopy and fluorescence. The effect of CPC paste curing was also evaluated. Implantation of two materials into the muscle tissue of rabbits was also studied and evaluated by histological analysis. Cell analysis indicated good biocompatibility in vitro. The fluorescence assay suggested that the cured material discs had no obvious effect on cell growth, while the curing process did. Histological examination showed no inflammatory cell infiltration into soft tissue. These data suggest that β-TCP/CPC and chitosan microsphere/CPC composites may be promising injectable material for bone tissue engineering.

Strontium-modified premixed calcium phosphate cements for the therapy of osteoporotic bone defects

In this study a premixed strontium-containing calcium phosphate bone cement for the application in osteoporotic bone defects has been developed and characterised regarding its material and in vitro properties as well as minimally invasive applicability in balloon kyphoplasty. Strontium was introduced into the cement by substitution of one precursor component, CaCO₃, with its strontium analogue, SrCO₃. Using a biocompatible oil phase as carrier liquid, a cement paste that only set upon contact with aqueous environment was obtained. Strontium modification resulted in an increased strength of set cements and radiographic contrast; and the cements released biologically relevant doses of Sr²⁺-ions that were shown to enhance osteoprogenitor cell proliferation and osteogenic differentiation. Finally, applicability of strontium-containing cement pastes in balloon kyphoplasty was demonstrated in a human cadaver spine procedure. The cement developed in this study may therefore be well suited for minimally invasive, osteoporosis-related bone defect treatment.

STATEMENT OF SIGNIFICANCE

Strontium-releasing calcium phosphate bone cements are promising materials for the clinical regeneration of osteoporosis-related bone defects since they have been shown to stimulate bone formation and at the same time limit osteoclastic bone resorption. Today clinical practice favours minimally invasive surgical techniques, e.g. for vertebral fracture treatment, posing special demands on such cements. We have therefore developed a premixed, strontium-releasing bone cement with enhanced mechanical properties and high radiographic visibility that releases biologically relevant strontium concentrations and thus stimulates cells of the osteogenic lineage. In a pilot experiment we also exemplify its excellent suitability for minimally invasive balloon kyphoplasty procedures.

Bioactive calcium phosphate cement with excellent injectability, mineralization capacity and drug-delivery properties for dental biomimetic reconstruction and minimum intervention therapy

CPC could be used as a promising biomaterial to reconstruct the breached enamel on exposed dentin through a biomimetic and minimally invasive way.

Self-setting calcium orthophosphate formulations

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.