Technical Note The in vivo calcification capacity of a copolymer, based on methacryloyloxyethyl phosphate, does not favor osteoconduction I.C. Stancu, 1,2 R. Filmon, 2 F. Grizon, 2 C. Zaharia, 1 C. Cincu, 1 M.F. Basle ´, 2 D. Chappard 2 1 Department of Macromolecular Chemistry, Industrial Chemistry Faculty, University Politehnica, 71101 Bucharest, Romania 2 INSERM EMI 0335, LHEA, Faculte ´ de Me ´decine, 49045 Angers Ce ´dex, France Received 5 September 2003; revised 21 January 2004; accepted 9 February 2004 Published online 14 April 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.30036 Abstract: Polymers can be interesting alternatives to bone grafts; they must present suitable mechanical and osteocon- ductive properties. Biomimetic properties may be a key factor for the recognition by bone cells. Methacryloyloxy- ethyl phosphate (MOEP) was found to enhance hydroxyap- atite deposition. The copolymer containing MOEP and 1-vi- nyl-2-pyrrolidinone (50 –50%) binds large amounts of calcium. Particles of the copolymer were used to fill large cranial bone defects in the rat. After a 12-week healing period, the animals were euthanized and the skulls exam- ined by X-ray, histology, and electron microscopy (EM). The high phosphate content of the polymer conferred a marked calcium-binding capacity, and the particles were heavily calcified. They were embedded in a light fibrous stroma containing numerous capillaries and multinucleated giant cells. The osteoconductive properties were poor: only few trabeculae developed centripetally from the margins of the defects. There was no bone bonding and no osteoblast on the surface of the calcified material. Backscattered EM revealed that the degree of calcification was homogeneous in all particles. Calcium-phosphorus calcospherites were never observed. The material appeared to trap calcium but to impair nucleation because only small hydroxyapatite tablets were occasionally observed. Polyphosphated materials do not represent a suitable source of potentially usable bone substitutes. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 69A: 584 –589, 2004 Key words: methacryloyloxyethyl phosphate (MOEP); co- polymer; osteoconductive properties; polyphosphated ma- terials INTRODUCTION Skeletal defects are currently treated with natural bone grafts: autograft, allograft, or xenograft. Al- though usually effective in restoring the bone form and function, these natural bone grafts present several disadvantages. Autografts involve the use of healthy bone from another anatomical site for implantation in the defect site. The problems associated with this pro- cedure include limited availability, increased surgical times, donor site pain and morbidity, and potential donor site infection. 1 Allografts represent today the most common alternative to autogenic tissue; they consist of human cadaver bones or surgically removed femoral heads. They are less effective than autografts, and necessitate extensive microbiological and virolog- ical processing by bone banks. In addition, extensive delipidation is recommended; 2 the potential transmis- sion of disease (hepatitis, unconventional agents, i.e., prions, etc.) should not be forgotten, together with difficulties in reshaping the donor bone to fit the de- fect. Xenogeneic tissues are less used in bone grafting because of the necessity of extensive delipidation, dis- ease transmission, and rejection risk. 3 All of these aspects have led to extensive research in the field of synthetic bone substitutes, to obtain homogenous and unlimited industrially produced suitable biomaterials. Ceramics (calcium phosphate, bioactive glass) cur- rently used to fill skeletal defects exhibit poor mechan- ical properties for structural support during the heal- ing process. 4 Synthetic polymers can represent a favorable alternative as implantation materials due to their biomechanical properties similar to natural bone. Bone is a natural composite consisting of an organic matrix (collagen) and a mineral phase [hydroxyapatite Correspondence to: D. Chappard; e-mail: Daniel.chappard@ univ-angers.fr Contract grant sponsor: the Contrat de Plan Etat–Re ´gion “Pays de la Loire” © 2004 Wiley Periodicals, Inc.