(416c) Reactive Nanoparticles For Biomedical Cements And Construction Materials

In solid/gas- or solid/liquid-reactions reactive particles strongly influence important parameters such as reaction rate, mechanism and product stability (e.g. fuels, cements, catalysis). The reactivity of particles strongly depends on the availability of surface area of the starting material, which ideally consists of well characterized homogenous nanoparticles. The present contribution investigates how such materials can be manufactured and explores their use as rapidly binding biomedical cements. Recent advances in the synthesis of nanoparticles by flame spray synthesis made not only a wide variety of oxides accessible to the flame process, but also reactive salts (calcium phosphates, gypsum, cement, limestone) [1] and even metal nanoparticles [2]. Tricalcium phosphate (TCP) is a very promising candidate to find application as a bone substitute material. We show that nanoparticulate amorphous TCP produced in the flame exhibit extremely fast reaction times, as required for a clinical application [3]. Furthermore, a similar reactivity was found for both, nanoparticulate gypsum (anhydrous calcium sulphate) and Portland cement derived from flame processing. Thereby, the gypsum showed a strongly increased hardness when compared to commercially available Alabaster [4]. We compare the gain in reactivity of biomedical cements, gypsum and Portland cement if nanoparticles are used instead of conventional micron-sized starting materials. The use of online monitoring systems such as isothermal calorimetry allowed studying the reactivity in detail. Based on these experimental finding, we developed a physical model describing the cement hardening process.

References: [1] S. Loher, W.J. Stark, M. Maciejewski, A. Baiker, S.E. Pratsinis, D. Reichardt, F. Maspero, D. Günther, Fluoro-apatite and calcium phosphate nanoparticles by flame synthesis, Chem. Mater. 17 (1), 36-42 (2005).

[2] R. N. Grass, W.J. Stark, Gas phase synthesis of fcc-cobalt nanoparticles, J. Mater. Chem., 16, 1825-30 (2006).

[3] T.J. Brunner, M. Bohner, C. Dora, C. Gerber, W.J. Stark, Comparison of amorphous TCP nanoparticles to micron-sized alpha-TCP as starting materials for calcium phosphate cements, J. Biomed. Mater. Res. Part B: Appl Biomater, published online (2007).

[4] N. Osterwalder, S. Loher, R. N. Grass, T.J. Brunner, L. K. Limbach, S. C. Halim, W. J. Stark, Preparation of nano-gypsum from anhydrite nanoparticles: Strongly increased Vickers hardness and formation of calcium sulfate nano-needles, J. Nanopart. Res., 9, 275-81 (2007).