Crystal polymer interaction with new injectable bone substitute; SEM and Hr TEM study

A composite constituted of calcium phosphate (CaP) granules and a hydrophil ic polymer as a carrier (hydroxy-propyl-methyl cellulose, HPMC) was develop ed to be an injectable bone substitute (IBS, CNRS patent). IBS is a composi te and not an ionic cement. The composite obtained is ready to use and ster ile. Chemical interactions between organic and inorganic components appeare d during the association of the two. The interactions of the CaP and the po lymer have been studied using scanning electron microscopy (SEM), electron microprobe (EDX), and high-resolution transmission electron microscopy (HrT EM) SEM revealed a degradation of the granules into smaller particles while EDX was unable to show significant changes in the Ca/P ratio during aging of the composite. With Hr TEM, however, we observed hydrolysis (process of dissolution and precipitation) from the surface to about 13 nm into the HA crystals and occasional dissolution with precipitation of beta-TCP crystals . In HA, the first zone of interaction consisted of a single layer of small globular crystals of 2 to 3 nm in diameter. Numerous lattice patterns in a ll three axes could be observed. Under the globular crystals zone, the inte r-reticular distances of the single crystals appeared enlarged by 1.2% (fro m 0.817 to 0.827 nm). The enlargement seems to correspond to diffusion of H PO4 into the crystal lattice. In beta-TCP crystals, dissolution was observe d to be several nanometers deep, but globular surface precipitation rarely was observed. With time or after steam sterilization, no changes were obser ved. These data demonstrate the strong interactions of the hydrophylic poly mer with calcium phosphate, but only in the first several nanometers of thi ckness. (C) 2000 John Wiley & Sons, inc.