ADSORPTION AND RELEASE OF STRONTIUM FROM HYDROXYAPATITE CRYSTALS DEVELOPED IN SIMULATED BODY FLUID (SBF) ON POLY (2-hydroxyethyl) METHACRYLATE SUBSTRATES

Poly (2-hydroxy ethyl) methacrylate (PHEMA) is a polymer that can be carboxymethylated to induce calcification on its surface. This mimics the calcification of bone matrix since the polymer surface induces the deposit of large hydroxyapatite calcospherites. We investigated the effect of Sr on hydroxyapatite crystals developed on PHEMA pellets. Pellets were incubated for 1 week in a synthetic body fluid (SBF) to induce mineralization, then 2 weeks in SBF containing 0, 130, 260 or 390 μM of Sr allowing growth and maturation of calcospherites. Calcospherites were dissolved in HCl and Ca, PO4 and Sr content was measured. Sr release was assessed by transferring other pellets in saline which was collected at regular intervals to measure Sr release. Hydroxyapatite was characterized by SEM, X-ray diffraction, FTIR and Raman microspectroscopy. After the maturation period, Sr was incorporated into hydroxyapatite crystals as a function of its concentration in SBF. However, size of the calcospherites decreased as a function of the strontium concentration. During the release phase, the slope of Sr elution was progressive and similar independently of the initial concentration; ~30% Sr was released after 61 days. XRD showed that incorporation of Sr produced no significant change in crystal lattice parameters or cristallinity. A progressive release of Sroccurred from the crystals. Strontium can be adsorbed rapidly on hydroxyapatite crystals and can be released easily. Carboxymethylated PHEMA can be used to study the effect of chemical compounds on the growth of hydroxyapatite nodules and their release in a second time.