ARTICLE Kinetics of In Vivo Bone Deposition by Bone Marrow Stromal Cells Within a Resorbable Porous Calcium Phosphate Scaffold: An X-Ray Computed Microtomography Study A. Papadimitropoulos, 1 M. Mastrogiacomo, 2 F. Peyrin, 3,4 E. Molinari, 1 V.S. Komlev, 5,6 F. Rustichelli, 2 R. Cancedda 2 1 Dipartimento di Informatica, Sistemistica e Telematica, Universita ` degli Studi di Genova, Genova, Italy 2 Istituto Nazionale per la Ricerca sul Cancro, Dipartimento di Oncologia, Biologia e Genetica dell’Universita’ di Genova, Largo Rosanna Benzi 10, 16132 Genova, Italy; telephone: þ39-0105737398; fax: þ39-0105737257; e-mail: ranieri.cancedda@unige.it 3 European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex, France 4 CREATIS, UMR CNRS 5515, Ba ˆt. Blaise Pascal, INSA, Lyon, France 5 Dipartimento di Scienze Applicate ai Sistemi Complessi, Universita’ Politecnica delle Marche and CNISM, Via Breccee Bianche, Ancona, Italy 6 Institute for Physical Chemistry of Ceramics, Russian Academy of Sciences, Ozernaya, Moscow, Russia Received 28 November 2006; accepted 26 February 2007 Published online 9 March 2007 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/bit.21418 ABSTRACT: Resorbable ceramic scaffolds based on Silicon stabilized tricalcium phosphate (Si-TCP) were seeded with bone marrow stromal cells (BMSC) and ectopically implanted for 2, 4, and 6 months in immunodeficient mice. Qualitative and quantitative evaluation of the scaffold material was performed by X-ray synchrotron radiation computed microtomography (microCT) with a spatial reso- lution lower than 5 mm. Unique to these experiments was that microCT data were first collected on the scaffolds before implantation and then on the same scaffolds after they were seeded with BMSC, implanted in the mice and rescued after different times. Volume fraction, mean thickness and thick- ness distribution were evaluated for both new bone and scaffold phases as a function of the implantation time. New bone thickness increased from week 8 to week 16. Data for the implanted scaffolds were compared with those derived from the analysis of the same scaffolds prior to implantation and with data derived from 100% hydroxyapatite (HA) scaffold treated and analyzed in the same way. At variance with findings with the 100% HA scaffolds a significant variation in the density of the different Si-TCP scaffold regions in the pre- and post-implantation samples was observed. In particular a post-implantation decrease in the density of the scaffolds, together with major changes in the scaffold phase composition, was noticeable in areas adjacent to newly formed bone. Histology confirmed a better integration between new bone and scaffold in the Si-TCP composites in comparison to 100% HA composites where new bone and scaffold phases remained well distinct. Biotechnol. Bioeng. 2007;98: 271–281. ß 2007 Wiley Periodicals, Inc. KEYWORDS: synchrotron MicroCT; bone substitute; bone tissue engineering Introduction Orthopedic surgeons have major difficulties to confront with, when it comes to replacing or restoring large segmental skeletal bone defects such as the ones resulting from trauma or resection of bone tumors. Current treatments for bone defects include the use of autografts, allografts, and metallic implants (Hatano et al., 2005; Perry, 1999). Autologous bone grafts are considered the gold standard because of their osteoconductive, osteogenic and osteoinductive properties. However, limitations in the quantity, which can be harvested from the iliac crest or other sites together with complications Correspondence to: R. Cancedda ß 2007 Wiley Periodicals, Inc. Biotechnology and Bioengineering, Vol. 98, No. 1, September 1, 2007 271