CNR ExploRA

Articolo in rivista, 2021, ENG, 10.1039/d1tb00601k

Thermal crystallization of amorphous calcium phosphate combined with citrate and fluoride doping: a novel route to produce hydroxyapatite bioceramics

Degli Esposti L.; Markovic S.; Ignjatovic N.; Panseri S.; Montesi M.; Adamiano A.; Fosca M.; Rau J.V.; Uskokovic V.; Iafisco M.

Institute of Science and Technology for Ceramics (ISTEC), National Research Council (CNR), Via Granarolo 64, Faenza, 48018, Institute of Science and Technology for Ceramics (ISTEC), National Research Council (CNR), Via Granarolo 64, 48018 Faenza, Italy, , , Italy; Institute of Science and Technology for Ceramics (ISTEC), National Research Council (CNR), Via Granarolo 64, Faenza, 48018, Institute of Science and Technology for Ceramics (ISTEC), National Research Council (CNR), Via Granarolo 64, 48018 Faenza, Italy, , , Italy; Institute of Technical Sciences of the Serbian Academy of Science and Arts, Knez Mihailova 35/IV, P. O. Box 377, Belgrade, 11000, Institute of Technical Sciences of the Serbian Academy of Science and Arts, Knez Mihailova 35/IV, P. O. Box 377, 11000 Belgrade, Serbia, , , Serbia; Institute of Technical Sciences of the Serbian Academy of Science and Arts, Knez Mihailova 35/IV, P. O. Box 377, Belgrade, 11000, Institute of Technical Sciences of the Serbian Academy of Science and Arts, Knez Mihailova 35/IV, P. O. Box 377, 11000 Belgrade, Serbia, , , Serbia; Institute of Structure of Matter (ISM), National Research Council (CNR), Via del Fosso del Cavaliere 100, Rome, 00133, Institute of Structure of Matter (ISM), National Research Council (CNR), Via del Fosso del Cavaliere 100, 00133 Rome, Italy, , Italy; Sechenov First Moscow State Medical University, Institute of Pharmacy, Department of Analytical, Physical and Colloid Chemistry, Trubetskaya 8, Build. 2, Moscow, 119991, Sechenov First Moscow State Medical University, Institute of Pharmacy, Department of Analytical, Physical and Colloid Chemistry, Trubetskaya 8, Build. 2, 119991 Moscow, Russia, , Russian Federation; TardigradeNano LLC, Irvine, CA, 92604, TardigradeNano LLC, Irvine, CA, 92604, USA, , United States

Amorphous calcium phosphate (ACP) is a material of high interest for dentistry, orthopedics, and other biomedical sectors. Being intrinsically metastable, the process of transformation of ACP into a crystalline phase upon heating is of high relevance for the development of innovative bioceramics. Here we have first studied the thermal behavior of a citrate-stabilized ACP (Cit-ACP) also doped with fluoride ions (Cit-FACP) prepared at three different nominal Cit/Ca ratios (i.e.4, 2, 1) by differential thermal analysis. Next, the physico-chemical features of the crystalline products as well as thein vitrocell response to the materials were investigated. A citrate and fluoride free ACP sample was also tested as the blank. We have found that the activation energy of crystallization of Cit-(F)ACP samples is lower in comparison to the blank ACP and this is influenced by the nominal Cit/Ca molar ratio. Interestingly, we have discovered that the thermal treatment of Cit-(F)ACP at 800 °C yields hydroxyapatite (HA) or fluorapatite (FHA) as the main products differently from blank ACP that, like most of the ACPs reported in the literature, yields ?-tricalcium phosphate. This was attributed to the Ca/P ratio of Cit-(F)ACP, which is similar to HA. A study of the crystalline products has revealed that all the (F)HA samples were non-cytotoxic, and retained carbonate ions in the crystal structure despite the heat treatment that should have induced decarbonation. The morphology of the products is influenced by the nominal Cit/Ca ratio and the presence of fluoride, ranging from spherical nanoparticles to micrometric hexagonal rods. Overall, our results prove that the thermal crystallization of Cit-(F)ACP is markedly different from classic ACP based materials and the thermal treatment of Cit-(F)ACP represents an attractive route for producing pure bioactive HA ceramics.

Journal of Materials Chemistry B 9 , pp. 4832–4845