Raman microspectrometry studies of brushite cement: In vivo evolution in asheep model

Calcium phosphate hydraulic cements are promising synthetic bone grafting m aterials. Brushite-based cements were implanted for 6 and 12 months in the distal condyle of sheep femur, and their in vivo evolution was investigated by Raman microspectrometry. This new technique can probe small volumes in the cubic micrometer range. Its resolution allows a very fine analysis of c rystalline changes in calcium phosphate mixtures at the microscopic level. First, Raman spectra of pure brushite, monetite, and beta-tricalcium phosph ate (beta-TCP) were recorded, in order to set a data base for the basic com ponents of brushite cements. These spectra show significant differences in the vibration mode v(1) for the phosphate ion (988 and 878 cm(-1) for brush ite, 988 and 900 cm(-1) for monetite, 968 and 948 cm(-1) for beta-TCP), The se differences are strong enough as to allow the qualitative and quantitati ve analysis of these crystalline phases in the cement, Implanted sheep femu r samples were harvested after 24 and 52 weeks post-op, and prepared for Ra man analysis in the form of 1-mm-thick sections. Implants at 24 weeks show a core of residual cement isolated from the surrounding bone by fibroconnec tive tissue. No trace of brushite was detected by micro-Raman analysis in t his area, but instead, a mixture of beta-TCP and Type-B carbonated apatite, the latter being very close in composition and structure to the mineral fr action of normal bone in the vicinity of the implant. Implants recovered af ter 52 weeks show a decrease of the bone/residual cement perimeter, whereas new trabeculations are formed in the implanted zone; the small amounts of residual cement still present are substantially transformed into Type-Il ca rbonated apatite containing small amounts of proteins. In the same area, so me beta-TCP particles are also detected showing that, contrary to brushite, the excess beta-TCP originally present in the cement is not completely met abolized. In the implanted zone already converted into trabecular bone, Ram an microspectrometry shows the characteristic spectrum of normal bone. (Bon e 25: 81S-84S; 1999) (C) 1999 by Elsevier Science Inc. All rights reserved.