1 Mass spectrometric monitoring of Sr enriched bone cements - from in vitro to in vivo Marcus Rohnke 1* , Anja Henss 1 , Julia Kokesch-Himmelreich 1 , Matthias Schumacher 2 , Seemun Ray 3 , Volker Alt 3,4 , Michael Gelinsky 2 and Juergen Janek 1 1) Institute for Physical Chemistry, Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 58, 35392 Giessen, Germany 2) Centre for Translational Bone, Joint and Soft Tissue Research, Technische Universität Dresden, Fetscherstrasse 74, 01307 Dresden, Germany 3) Laboratory of Experimental Trauma Surgery, University of Giessen, Kerkraderstrasse 9, 35394 Giessen, Germany 4) Department of Trauma Surgery, University Hospital of Giessen-Marburg, Rudolf-Buchheim- Str. 7, 35385 Giessen, Germany *Corresponding author. Tel.: +49 641 99 34502. Fax: +49 641 99 34509. Email address: Marcus.Rohnke@phys.chemie.uni-giessen.de Abstract Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a well-established technique in materials science, but is now increasingly applied also in the life sciences. Here we demonstrate the potential of this analytical technique for use in the development of new bone implant materials. We tracked strontium enriched calcium phosphate cements, which were developed for the treatment of osteoporotic bone, from in vitro to in vivo. Essentially the spatial distribution of strontium in two different types of strontium-modified calcium phosphate cements is analysed by SIMS depth profiling. To gain information about the strontium release kinetics the cements were immersed for 3,7,14 and 21 days in -MEM and TRIS-solution and analysed afterwards by ToF-SIMS depth profiling. For cements stored in -MEM solution an inhibited strontium release was observed. By using principal component analysis to evaluate TOF-SIMS surface spectra, we are able to prove the adsorption of proteins on the cement surface, which inhibit the release kinetics. Cell experiments with human osteoblast-like cells cultured on the strontium-modified cements and subsequent mass spectrometric analysis of the mineralised extracellular matrix (mECM) prove clearly that strontium is incorporated into the mECM by the osteoblast-like cells. Finally, in an animal experiment the strontium-doped cements are implanted into the femur of osteoporotic rats. After 6 weeks only a slight release of strontium was found in the vicinity of the implant material. By using ToF-SIMS it is proven that strontium is localised in regions of newly formed bone but also within the pre-existing tissue. Keywords: Sr enriched Calcium phosphate cements, time of flight secondary ion mass spectrometry, osteoporosis, bone imaging, bone implant interface