Effect of added NaHCO3 on the basic properties of apatite cement

Evaluation of highly carbonated hydroxyapatite bioceramic implant coatings with hierarchical micro-/nanorod topography optimized for osseointegration

Background

Optimal osseointegration has been recognized as a pivotal factor in determining the long-term success of biomedical implants.

Materials and methods

In the current study, highly carbonated hydroxyapatite (CHA) with carbonate contents of 8, 12 and 16 wt% and pure hydroxyapatite (HA) were fabricated via a novel hydrothermal method and deposited on the titanium substrates to generate corresponding CHA bioceramic coatings (designated as C8, C12 and C16, respectively) and HA bioceramic coatings (designated as C0).

Results

C8, C12 and C16 were endowed with nanoscale, hierarchical hybrid micro-/nanoscale and microscale surface topographies with rod-like superstructures, respectively. Compared with C0, the micro-/nanotextured CHA bioceramic coatings (C8, C12 and C16) possessed excellent surface bioactivity and biocompatibility, as well as better wettability, which mediated improved protein adsorption, giving rise to simultaneous enhancement of a biological cascade of events of rat bone-marrow-derived mesenchymal stem cells including cell adhesion, proliferation, osteogenic differentiation and, notably, the production of the pro-angiogenic growth factor, vascular endothelial growth factor-A. In particular, C12 with biomimetic hierarchical hybrid micro-/nanorod topography exhibited superior fractal property and predominant performance of protein adsorption, cell adhesion, proliferation and osteogenesis concomitant with angiogenesis.

Conclusion

All these results suggest that the 12 wt% CHA bioceramic coating with synergistic modification of surface chemistry and topography has great prospect for future use as implant coating to achieve optimum osseointegration for orthopedic and dental applications.

Photocurable bioactive bone cement based on hydroxyethyl methacrylate-poly(acrylic/maleic) acid resin and mesoporous sol gel-derived bioactive glass

This paper reports on strong and bioactive bone cement based on ternary bioactive SiO2-CaO-P2O5 glass particles and a photocurable resin comprising hydroxyethyl methacrylate (HEMA) and poly(acrylic/maleic) acid. The as-cured composite represented a compressive strength of about 95 MPa but it weakened during soaking in simulated body fluid, SBF, qua its compressive strength reached to about 20 MPa after immersing for 30 days. Biodegradability of the composite was confirmed by reducing its initial weight (~32%) as well as decreasing the molecular weight of early cured resin during the soaking procedure. The composite exhibited in vitro calcium phosphate precipitation in the form of nanosized carbonated hydroxyapatite, which indicates its bone bonding ability. Proliferation of calvarium-derived newborn rat osteoblasts seeded on top of the composite was observed during incubation at 37 °C, meanwhile, an adequate cell supporting ability was found. Consequently, it seems that the produced composite is an appropriate alternative for bone defect injuries, because of its good cell responses, high compressive strength and ongoing biodegradability, though more in vivo experiments are essential to confirm this assumption.

Direct and interactive influence of explanatory variables on properties of a calcium phosphate cement for vertebral body augmentation

We used the response surface methodology to investigate the direct and interactive effects of three explanatory variables on three properties of a calcium phosphate cement (CPC) for use in vertebroplasty (VP) and balloon kyphoplasty (BKP). The variables were poly(ethylene glycol) content of the cement liquid (PEG), powder-to-liquid ratio (PLR), and the amount of Na2HPO4 added to an aqueous solution of 4 wt/wt% poly(acrylic acid) (as the cement liquid) (SPC). The properties were injectability (I), final setting time (F), and 5-day compressive strength (UCS). We found that (1) there was an interactive effect between the variables on I and F but not on UCS; (2) the maximum I (98%) was obtained with PEG = 20 wt/wt% and PLR = 2 g mL(-1); (3) F = 15 min (the proposed optimum value for a CPC for use in VP and BKP) was obtained with PEG = 4 wt/wt% and PLR = 2.9 g mL(-1); and (4) the maximum UCS (39 MPa) was obtained with SPC = 0 and PLR = 3.5 g mL(-1).

Influence of mixing blood with calcium phosphate bone paste on hardening

Calcium phosphate bone paste (CPP) has been recently introduced as a reconstructive material in craniofacial surgery. However, we observed that mixing of blood and CPP tended to interfere with CPP hardening. In addition, CPP mixed with blood tended to be absorbed postoperatively. Hence, we used a rabbit model and applied CPP mixed with blood over defects in the skull to investigate the influence of blood on CPP. Calcium phosphate bone paste was mixed with blood for 1 minute and applied to the defects in the calvarial bone of rabbits. At 4 and 24 postoperative weeks, we histologically evaluated morphologic changes in the hydroxyapatite (HA). Our study revealed that HA was not absorbed when a small quantity of blood (15%) was mixed with CPP. However, HA was absorbed almost entirely when a large quantity of blood (30%) was mixed with CPP. In addition, we found that the porosity of HA was increased by the mixture of a small quantity of blood into CPP, and this addition stimulated osteogenesis in HA.

Deriving fast setting properties of tetracalcium phosphate/dicalcium phosphate anhydrous bone cement with nanocrystallites on the reactant surfaces

OBJECTIVE

This study attempts to reveal how nanocrystallites on the ceramic surfaces of non-dispersive calcium phosphate cement (nd-CPC) participate in setting processes as compared with conventional CPC (c-CPC).

METHODS

The compositions and morphologies of CPC during the early setting reactions were studied with X-ray diffraction and a scanning transmission electron microscope equipped with an energy dispersive spectroscopy system. The pH values and dispersive properties of CPC during the early setting reactions were investigated as well as the compressive strength of nd-CPC after 24h of immersion with varying liquid to powder ratios.

RESULTS

The mechanical strength of nd-CPC was approximately 60MPa after a 24h immersion in simulate body solution with a P/L ratio between 3.3 and 4.2g/mL. The nanocrystallites on the particle surfaces of nd-CPC were shown to grow rapidly and provided interlocking sites that allowed rapid development of the apatite phase in the cement, and were also shown to be non-dispersive in solution as determined by an injection test of c-CPC.

CONCLUSIONS

The interlocking particles produced by whisker growth on the ceramic particles or new crystallites formed between the ceramic particles caused the cement to be non-dispersive in solution. The particles of reactants with nanocrystallites on surfaces also gave this cement the ability to be shaped easily as a paste during an operation or to be injected into a cavity.

Effects of carbonate on hydroxyapatite formed from CaHPO(4) and Ca(4)(PO(4))(2)O

Carbonated hydroxyapatites were formed via reactions in NaHCO(3)/NaH(2)PO(4) solutions from a mixture of particulate tetracalcium phosphate (TetCP) and anhydrous dicalcium phosphate (DCPA). Reactions were followed by determinations of pH and ion concentrations. The solids formed were analyzed by XRD and FTIR. Rates of heat evolution were established by isothermal calorimetry. Reactions in the absence of NaH(2)PO(4) did not reach completion within 24 h. Constitution of reactants to achieve a DCPA-to-NaHCO(3) ratio of 1, in conjunction with the presence of NaH(2)PO(4) as a buffer, was found to be optimal for formation of apatite with no remaining reactant. The amount of carbonate incorporated in this apatite was 4-5 wt%. Calorimetry indicated the reaction mechanism to depend on the bicarbonate concentration in solution. The presence of NaH(2)PO(4) was found to increase the reaction rate but decrease the extent of carbonate uptake.

Cephalexin-loaded injectable macroporous calcium phosphate bone cement

Different types of calcium phosphate cements (CPCs) have been studied as potential matrices for incorporating different types of antibiotics. All of these matrices were morphologically microporous whereas macroporosity is essential for rapid cement resorption and bone replacement. In this study, liberation of cephalexin monohydrate (CMH) from a macroporous CPC was investigated over 0.5-300 h in simulated body fluid and some mathematical models were fitted to the release profiles. Macroporosity was introduced into the cement matrix by using sodium dodecyl sulfate molecules as air-entraining agents and the effect of both surfactant and CMH on basic properties of the CPC was studied. Incorporation of CMH into the CPC composition increased the setting time, decreased the crystallinity of the formed apatite phase, and improved the injectability of the paste. The use of both CMH and sodium dodecyl sulfate did not affect the rate of conversion of the reactants into apatite phase while soaking the cements in simulated body fluid. Results showed that the liberation rate of the drug from porous CPC was higher than that of the nonporous CPC but same release patterns were experienced in both types of cements, that is, like to nonporous CPC, a time-dependent controlled release of the incorporated drug was obtained from macroporous CPC. The Weibull model was the best fitting-equation for release profiles of all cements. The liberated CMH was as active as fresh cephalexin. It is concluded that this macroporous CPC can be successfully used as drug carrier with controlled release profile for the treatment of bone infections.

The influence of the acidic component of the gas-foaming porogen used in preparing an injectable porous calcium phosphate cement on its properties: acetic acid versus citric acid

In the present study, macroporous calcium phosphate cements (CPCs) were prepared using a porogen; that is, the gas-foaming technique. The objective was to investigate the influence of the acidic component of the porogen (acetic acid versus citric acid) on several properties of a specified CPC. In all of the cements prepared, the basic component of the porogen was the same, namely, NaHCO(3), and it was added to the powder phase of the cement, while the acidic component of the porogen was dissolved in the liquid phase of the cement. The cements were characterized in terms of initial setting time, porosity, crystallinity, injectability and compressive strength. Also, XRD, FTIR, and SEM techniques were employed to evaluate the phase composition, the chemical groups and the morphological aspects of the porous cements during setting. It was found that the presence of a porogen in a CPC led to significant decreases in both its initial setting time and compressive strength. A CPC made using acetic acid contained a larger amount of the apatite phase but was significantly less injectable and less porous than when citric acid was used.

Phase evaluation of an effervescent-added apatitic calcium phosphate bone cement

Development of macroporosity during setting would allow fast bone ingrowth and good osteointegration of the implant. The interconnected macropores could be created in calcium phosphate cements (CPCs) through the addition of an effervescent porogen mixture to the component of the cements. But this addition could also affect other characteristics of CPCs, such as setting time, mechanical strength, extent of conversion of reactant to apatite phase, crystallinity, and chemical composition of apatite lattice. In this study, these properties were investigated in an effervescent-added calcium phosphate bone cement. From 0 to 20 wt % of an effervescent mixture was added to calcium phosphate cement (CPC) components and phase evaluations were performed after 24 h incubation at 37 degrees C and 28% relative humidity and 1, 3, 7, and 14 days immersion in a specific simulated body fluid. XRD and FTIR techniques were used to characterize the cement composition, crystallinity, and chemical groups in final CPCs. The results showed that addition of effervescent porogen affects the extent of conversion of reactant to apatite phase and crystallinity. In other words, using the effervescent porogen in CPCs could accelerate the rate of conversion of TTCP/DCPA reactant to apatite phase with smaller crystallites, so that it was the predominant phase (about 67%) after only 3 days soaking in SBF solution. The content of carbonate groups substituted for phosphate groups in apatite lattice increased when the effervescent additive was further added. The compressive strength of the set calcium phosphate cement decreased significantly with the addition of the effervescent agent and reached from 8 MPa for additive-free CPC to 1.3 MPa for 20% effervescent-added CPC. The compressive strength was improved after 3 days immersing of CPC in the simulated body fluid solution.

Alkali ion substituted calcium phosphate cement formation from mechanically activated reactants

Potassium and sodium containing nanoapatite cements were produced from Ca2KNa(PO4)2 by prolonged high energy ball milling of the compound for up to 24 h. This mechanical treatment resulted in the decrease of the crystal size and a partial amorphisation of the cement reactant as shown by X-ray diffraction analysis and the appearance of strong exothermic peaks in differential scanning calorimetry measurements. The pH of water saturated with Ca2KNa(PO4)2 was 12.5 when the material was mechanically activated but was only 9.5 for the untreated compound suggesting an increase in solubility following milling. The cements set following mixing with a 2.5% Na2HPO4 solution in clinically acceptable times between 5-12 min and showed compressive strengths of up to 11 MPa after 24 h setting. The strong alkaline pH value of the cements may provide antimicrobial potential for an application in dentistry as pulp capping agents or cavity liners or for the treatment of infected bone sites.

Transmission electron microscopic study on setting mechanism of tetracalcium phosphate/dicalcium phosphate anhydrous-based calcium phosphate cement

This work studied transmission electron microscopy on the setting mechanism of tetracalcium phosphate/dicalcium phosphate anhydrous (TTCP/DCPA)-based calcium phosphate cement. The results suggest the process for early-stage apatite formation as the follows: when TTCP and DCPA powders are mixed in the phosphate-containing solution, the TTCP powder is quickly dissolved because of its higher solubility in the acidic solution. The dissolved calcium and phosphate ions, along with those ions readily in the solution, are then precipitated predominantly on the surface of DCPA particles. Few apatite crystals were observed on the surface of TTCP powder. During the later stages of reaction, the extensive growth of apatite crystals/whiskers, with a calcium/phosphorous ratio very close to that of hydroxyapatite, effectively linked DCPA particles together and also bridged the larger TTCP particles. It is suggested that, when the large TTCP particles are locked in place by the bridging apatite crystals/whiskers, the CPC is set and would not dissolve when immersed in Hanks' solution after 20-40 min of reaction.

The Ca/P range of nanoapatitic calcium phosphate cements

Nanoapatites are apatites consisting of nanometer size crystals. The commercial calcium phosphate cements set by the precipitation of nanoapatitic calcium phosphates in the range 1.5 < or = Ca/P < 1.8. In this study it is shown that a continuum of nanoapatites can precipitate in the range 0.8 < Ca/P< or = 1.5. In order to be formed these nanoapatites need to incorporate K+ ions. In addition they can incorporate some Na+ ions. Upon immersion in aqueous solutions these nanoapatites loose phosphate, K+ and Na+ so that in an open system they are transformed into calcium deficient hydroxyapatite Ca9(HPO4)(PO4)5OH within about 2 months.