The injectability of Portland cement (PC) with calcium chloride and calcium nitrate additives was investigated using a syringe with a 2 mm aperture for potential clinical applications such as vertebroplasty. Addition of either additive at 10 wt % increased the quantity of cement extruded through the syringe from approximately 25 wt % for the PC standard, to over 95 wt %. 10 wt % additions of either additive also decreased setting times from over 2 h to below 25 min. The compressive strength of the modified cements was all greater than the compressive strength of a human vertebral body. Decreasing either additive to 5 wt % generated compressive strengths after 24 h setting equal to polymethylmethacrylate, the cement used for the majority of vertebroplasty procedures. An initial early exotherm in the chloride cements was coupled with an X-ray diffraction (XRD) peak that indicated the early formation of the ettringite cement phase. In contrast, Fourier transform infrared (FTIR) spectroscopy and XRD data indicated that calcium nitrate may have stimulated early calcium silicate hydrate (CASAH) production (the main strength producing phase of PC). Combining the two additives produced a synergistic effect with cements having increased injectabilities and compressive strengths compared with either addition used individually. This study has demonstrated that by modifying PC with nonproprietary chemicals it was possible to significantly increase cement injectability and reduce setting times whilst maintaining compressive strengths, making PC suitable for potential orthopedic applications.
The injectability of Portland cement (PC) with several citrate additives was investigated for use in clinical applications such as vertebroplasty (stabilization of a fractured vertebra with bone cement) using a syringe. A 2-wt % addition of sodium or potassium citrate with PC significantly improved cement injectability, decreased cement setting times from over 2 h to below 25 min, while increasing the compressive strength to a maximum of 125 MPa. Zeta-potential measurements indicated that the citrate anion was binding to one or more of the positively charged species causing charged repulsion between cement particles which dispersed aggregates and caused the liquefying effect of the anion. Analysis of the hydrating phases of PC indicated that the early strength producing PC phase (ettringite) developed within the first 2 h of setting following addition of the citrate anion, while this did not occur in the control cement (PC only). Within 24 h ettringite developed in PC as well as calcium–silicate–hydrate (C–S–H), the major setting phase of PC, whereas cements containing citrate did not develop this phase. The evidence suggested that in the presence of citrate the cements limited water supply appeared to be utilized for ettringite formation, producing the early strength of the citrate cements. The present study has demonstrated that it is possible to modify PC with citrate to both improve the injectability and crucially reduce the setting times of PC while improving the strength of the cement. © 2014 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 1799–1808, 2014.
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