Tricalcium phosphate (sometimes abbreviated TCP), more commonly known as Calcium phosphate, is a calciumsaltofphosphoric acid with the chemical formulaCa3(PO4)2. It is also known as tribasic calcium phosphate and bone phosphate of lime (BPL). It is a white solid of low solubility. Most commercial samples of "tricalcium phosphate" are in fact hydroxyapatite.[4][5]
It exists as three crystalline polymorphs α, α′, and β. The α and α′ states are stable at high temperatures.
Calcium phosphate refers to numerous materials consisting of calcium ions (Ca2+) together with orthophosphates (PO3− 4), metaphosphatesorpyrophosphates (P 2O4− 7) and occasionally oxide and hydroxide ions. Especially, the common mineral apatite has formula Ca5(PO4)3X, where XisF, Cl, OH, or a mixture; it is hydroxyapatite if the extra ion is mainly hydroxide. Much of the "tricalcium phosphate" on the market is actually powdered hydroxyapatite.[5]
It cannot be precipitated directly from aqueous solution. Typically double decomposition reactions are employed, involving a soluble phosphate and calcium salts, e.g. (NH4)2HPO4 + Ca(NO3)2.[6] is performed under carefully controlled pH conditions. The precipitate will either be "amorphous tricalcium phosphate", ATCP, or calcium deficient hydroxyapatite, CDHA, Ca9(HPO4)(PO4)5(OH), (note CDHA is sometimes termed apatitic calcium triphosphate).[6][7][8] Crystalline tricalcium phosphate can be obtained by calcining the precipitate. β-Ca3(PO4)2 is generally formed, higher temperatures are required to produce α-Ca3(PO4)2.
An alternative to the wet procedure entails heating a mixture of a calcium pyrophosphate and calcium carbonate:[7]
CaCO3 + Ca2P2O7 → Ca3(PO4)2 + CO2
Structure of β-, α- and α′- Ca3(PO4)2 polymorphs[edit]
Tricalcium phosphate has three recognised polymorphs, the rhombohedral β form (shown above), and two high temperature forms, monoclinic α and hexagonal α′. β-Tricalcium phosphate has a crystallographic density of 3.066 g cm−3 while the high temperature forms are less dense, α-tricalcium phosphate has a density of 2.866 g cm−3 and α′-tricalcium phosphate has a density of 2.702 g cm−3 All forms have complex structures consisting of tetrahedral phosphate centers linked through oxygen to the calcium ions.[9] The high temperature forms each have two types of columns, one containing only calcium ions and the other both calcium and phosphate.[10]
There are differences in chemical and biological properties between the β and α forms, the α form is more soluble and biodegradable. Both forms are available commercially and are present in formulations used in medical and dental applications.[10]
Calcium phosphate is one of the main combustion products of bone (see bone ash). Calcium phosphate is also commonly derived from inorganic sources such as mineral rock.[11]
Tricalcium phosphate occurs naturally in several forms, including:
as a rock in Morocco, Israel, Philippines, Egypt, and Kola (Russia) and in smaller quantities in some other countries. The natural form is not completely pure, and there are some other components like sand and lime which can change the composition. The content of P2O5 in most calcium phosphate rocks is 30% to 40% P2O5 by weight.
Biphasic calcium phosphate, BCP, was originally reported as tricalcium phosphate, but X-Ray diffraction techniques showed that the material was an intimate mixture of two phases, hydroxyapatite (HA) and β-tricalcium phosphate.[12] It is a ceramic.[13]
Preparation involves sintering, causing irreversible decomposition of calcium deficient apatites[7] alternatively termed non-stoichiometric apatites or basic calcium phosphate.[14] An example is:[15]
β-TCP can contain impurities, for example calcium pyrophosphate, Ca2P2O7 and apatite. β-TCP is bioresorbable. The biodegradation of BCP involves faster dissolution of the β-TCP phase followed by elimination of HA crystals. β-TCP does not dissolve in body fluids at physiological pH levels, dissolution requires cell activity producing acidic pH.[7]
Tricalcium phosphate is used in powdered spices as an anticaking agent, e.g. to prevent table salt from caking. The calcium phosphates have been assigned European food additive number E341.
^Yashima, M.; Sakai, A.; Kamiyama, T.; Hoshikawa, A. (2003). "Crystal structure analysis of β-tricalcium phosphate Ca3(PO4)2 by neutron powder diffraction". RNAl of Solid State Chemistry. 175 (2): 272–277. Bibcode:2003JSSCh.175..272Y. doi:10.1016/S0022-4596(03)00279-2.
^ abCarrodeguas, R.G.; De Aza, S. (2011). "α-Tricalcium phosphate: Synthesis, properties and biomedical applications". Acta Biomaterialia. 7 (10): 3536–3546. doi:10.1016/j.actbio.2011.06.019. PMID21712105.
^Daculsi, G.; Legeros, R. (2008). "17 – Tricalcium phosphate / hydroxyapatite biphasic ceramics". In Kokubo, Tadashi (ed.). Bioceramics and their Clinical Applications. Woodhead Publishing. pp. 395–423. doi:10.1533/9781845694227.2.395. ISBN978-1-84569-204-9.
^Salinas, Antonio J.; Vallet-Regi, Maria (2013). "Bioactive ceramics: from bone grafts to tissue engineering". RSC Advances. 3 (28): 11116–11131. Bibcode:2013RSCAd...311116S. doi:10.1039/C3RA00166K.
^Vallet-Regí, M.; Rodríguez-Lorenzo, L.M. (November 1997). "Synthesis and characterisation of calcium deficient apatite". Solid State Ionics. 101–103, Part 2: 1279–1285. doi:10.1016/S0167-2738(97)00213-0.
^Straub DA (June 2007). "Calcium supplementation in clinical practice: a review of forms, doses, and indications". Nutr Clin Pract. 22 (3): 286–296. doi:10.1177/0115426507022003286. PMID17507729.
^Cao H, Kuboyama N (September 2009). "A biodegradable porous composite scaffold of PGA/β-TCP for bone tissue engineering". Bone. 46 (2): 386–395. doi:10.1016/j.bone.2009.09.031. PMID19800045.
^Kundu, B; Lemos A; Soundrapandian C; Sen PS; Datta S; Ferreira JMF; Basu D (2010). "Development of porous HAp and β-TCP scaffolds by starch consolidation with foaming method and drug-chitosan bilayered scaffold based drug delivery system". J. Mater. Sci. Mater. Med. 21 (11): 2955–2969. doi:10.1007/s10856-010-4127-0. PMID20644982. S2CID6483779.
