Magnetic properties and cytocompatibility of transition-metal-incorporated hydroxyapatite.

A detailed magnetization study, along with an assessment of the cellular proliferation, has been carried out on transition-metal-doped hydroxyapatite (HA), Ca10-x Mx (PO4 )6 (OH)2 , where M = Mn, Co, and Fe. In particular, a series of MnHA powder samples with an x value of 0.04 ≤ x ≤ 1.21, one CoHA (x = 0.48) and one FeHA sample (x = 1.06) were synthesized using a wet chemical method along with an ion-exchange procedure. Characterization by transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) indicated that the substitution of M elements does not change the morphology and crystalline structure of pure HA that showing a single phased HA nano-rod. In every case, the magnetization isotherms for 10 K ≤ T ≤ 300 K were linear through the origin characteristic of a paramagnetic response with no indication of superparamagnetic behavior, hysteresis, or magnetic ordering. The magnetic behavior for all samples could be fit to the Curie-Weiss law yielding values for the M ion magnetic moments. The Mn2+ magnetic moments were close to the spin-only value of S = 5/2 or 5.92 μB , while the Co2+ moment (4.41 μB ) was larger than the spin-only value for S = 3/2, indicating an orbital contribution due to incomplete quenching. The magnetic behavior for the FeHA sample showed a possible spin-state transition. In addition, no statistically significant differences were observed when cells were treated with the same dose of HA or MnHA up to 50 μg/mL, suggesting that the substituted Mn introduces no cytotoxicity to the HA powders.