**6.1.7. Cobalt-substituted apatites**

The synthesis and the characterization of cobalt-substituted hydroxyapatite (Co-HAP) powders via the precipitation method were described by KRAMER et al [35]. Using a cobalt chloride solution and a simple soaking procedure, it is possible to prepare CoHAP with no apparent formation of second phases. Cobalt-substituted samples displayed paramagnetic properties as opposed to the diamagnetism of pure HA. The degradation studies showed that Co-HAP did not display markedly different degradation behavior from pure HAP, and the amount of cobaltreleased overthe course of a month was extremely low, alleviating the toxicity concerns. Cobalt-substituted hydroxyapatite nanoparticles, the biomaterial with magnetic properties, could be a promising material to be used in a variety of biomedical applications, including the magnetic imaging, drug delivery or hyperthermia-based cancer treatments.

Single crystals of chlorapatite [Ca5(PO4)3Cl] with the substitution of approximately 20% of Ca2+ by Co2+ (space group P63/M, *a* = 9.625(3) and *c* = 6.747(1) Å, *V* = 541.3 Å3 ) were prepared by ANDERSON and KOSTINER [36] via the flux techniques. Co ion is present at available six-coordi‐ nated cation site.
