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JOUR T1 - JO - VL - 6 IS - 12 SP - 4457 EP - 4475 PY - 2010/12// T2 - AU - SN - 1742-7061 DO - http://dx.doi.org/10.1016/j.actbio.2010.06.031 UR - http://www.sciencedirect.com/science/article/pii/S1742706110002977

Preparation tricalcium phosphate (added to article)
It is generally believed that tricalcium phosphate cannot be precipitated directly from aqueous solution. Typically a double decomposition reaction involving a soluble phosphate and calcium salts (e.g. (NH4)2HPO4+ Ca(NO3)2) is performed under carefully controlled pH conditions. The precipitate will either be "amorphous tricalcium phosphate", ATCP, or calcium deficient hydroxypatite, CDHA, Ca9(HPO4)(PO4)5(OH), (note CDHA is sometimes termed apatitic calcium triphosphate). 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 a wet procedure is to heat a dry mixture of a calcium phosphate and calcium carbonate which has an overall Ca/P ratio of 3:2, for example:


 * CaCO3 + Ca2P2O7 → Ca3(PO4)2 + CO2

Structure added to article
Tricalcium phosphate has three recognised polymorphs, the rhombohedral β- form, 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 They all have complex structures and have been described as containing "columns" of cations and anions. The β-form has two types of columns, each containing calcium and phosphate ions. The high temperature forms each have two types of columns, one containing only calcium ions and the other both calcium and phosphate.

There are differences in chemical and biological properties between the beta and alpha forms, the alpha form is more soluble and biodegradeable. Both forms are avalable commercially and are present in formulations used in medical and dental applications.

Crystal structure of β-tricalcium phosphate
α-TCP

Amorphous tricalcium phosphate, ATCP
Structurally ATCP has short term ordering of anions and cations, and it has been proposed that small clusters termed Posner's clusters" with a composition Ca?(PO4)?  are present. ATCP is difficult to prepare in a pure form, it readily takes up other ions, e,.g CO32– and  HPO42–. ??amorphous TCP composition?? CaxHy(PO4)x

Biphasic tricalcium phosphate, BCP
TY - JOUR T1 - Synthesis and characterisation of calcium deficient apatite JO - Solid State Ionics VL - 101–103, Part 2 IS - 0 SP - 1279 EP - 1285 PY - 1997/11// T2 - International Symposium on the Reactivity of Solids AU - Vallet-Regí, M. AU  - Rodríguez-Lorenzo, L.M. AU  - Salinas, A.J. SN  - 0167-2738 DO - http://dx.doi.org/10.1016/S0167-2738(97)00213-0 UR - http://www.sciencedirect.com/science/article/pii/S0167273897002130

TY - CHAP AU - Daculsi, G. AU  - Legeros, R. T1  - 17 - Tricalcium phosphate/hydroxyapatite biphasic ceramics A2 - Kokubo, Tadashi BT - Bioceramics and their Clinical Applications PB - Woodhead Publishing CY - PY - 2008/// SP - 395 EP - 423 T2 - Woodhead Publishing Series in Biomaterials SN - 978-1-84569-204-9 DO - http://dx.doi.org/10.1533/9781845694227.2.395 UR - http://www.sciencedirect.com/science/article/pii/B978184569204950017X

Biphasic tricalcium phosphate, BCP
Biphasic tricalcium 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. It is a ceramic. Preparation involves the sintering causing the irreversible decomposition of calcium deficient apatites alternatively termed non-stoichiometric apatites or basic calcium phosphate :, an example is:


 * Ca10-δ(PO4)6-δ(HPO4)δ(OH)2-δ → (1-δ)Ca10(PO4)6(OH)2 + 3δCa3(PO4)2

β-TCP can contain impurities, for example calcium pyrophosphate, CaP2O7 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.

T1 - Chapter A2 - BT - PB - PY - /// VL - SP - 111 EP - 189 T2 - Structure and Chemistry of the Apatites and Other Calcium Orthophosphates SN - DO - http://dx.doi.org/ UR -

Tetracalcium phosphate
TY - JOUR T1 - Tetracalcium phosphate: Synthesis, properties and biomedical applications JO - Acta Biomaterialia VL - 6 IS - 10 SP - 3815 EP - 3823 PY - 2010/10// T2 - AU - Moseke, C. AU  - Gbureck, U. SN  - 1742-7061 DO - http://dx.doi.org/10.1016/j.actbio.2010.04.020 

Act Cryst 1973 10.1107/S0567740873006102

Tetracalcium phosphate is the compound Ca4(PO4)2O,(4CaO.P2O5). It is the most basic of the calcium phosphates, and has a Ca/P ratio of 2, making it the most phosphorus rich phosphate. Tetracalcium phosphate is used to make calcium phosphate cements for medical use.

Preparation and reactions
Tetracalcium phosphate cannot be prepared in aqueous solution, any precipitates having the correct Ca/P ratio contain hydroxide ions and contain apatitic phases. Solid state reactions are used, one example is:


 * 2CaHPO4 + 2CaCO3 → Ca4(PO4)2O + CO2 +H2O (1450-1500 °C for up to 12 hours)

As tetracalcium phosphate is metastable the molten reaction mixture has to be quenched rapidly reducing the temperature and preventing the formation of other compounds such as Ca3(PO4)2, CaO, CaCO3 and Ca5(PO4)3(OH).

Unwanted tetracalcium phosphate can be formed when metal alloy implants (orthopaedic and dental) are plasma spayed with hydroxyapatite.

Tetracalcium phosphate is stable in water at room temperature for up to four weeks, but at higher temperatures hydrolyses to hydroxyapatite and calcium hydroxide:
 * 3Ca4(PO4)2O + 3H2O → 2Ca5(PO4)3(OH) +2Ca(OH)2

Tetracalcium phosphate is a component used in the formation of some hydroxyapatite calcium phosphate cements that used for the repair of bone defects. One example of a cement forming reaction is that of tetracalcium phosphate and dicalcium diphosphate dihydrate:


 * Ca4(PO4)2O + CaHPO4.2H2O → Ca5(PO4)3(OH) + 2H2O

Structure
Crystalline tetracalcium phosphate is monoclinic, and has close similarities to hydroxyapatite. The similarity is such that it has been suggested that there is an epitactic relationship between the structures enabling direct conversion of tetracalcium phosphate to hydroxyapatite.

Uses
Cements TY - JOUR T1 - Fibre-reinforced calcium phosphate cements: A review JO - Journal of the Mechanical Behavior of Biomedical Materials VL - 4 IS - 8 SP - 1658 EP - 1671 PY - 2011/11// T2 - Special Issue Soft Tissues Special Issue Section on Soft Tissue 3d Strain AU - Canal, C. AU  - Ginebra, M.P. SN  - 1751-6161 DO - http://dx.doi.org/10.1016/j.jmbbm.2011.06.023 UR - http://www.sciencedirect.com/science/article/pii/S1751616111001810

TY - JOUR T1 - Technological issues for the development of more efficient calcium phosphate bone cements: A critical assessment JO - Biomaterials VL - 26 IS - 33 SP - 6423 EP - 6429 PY - 2005/11// T2 - AU - Bohner, M. AU  - Gbureck, U. AU  - Barralet, J.E. SN  - 0142-9612 DO - http://dx.doi.org/10.1016/j.biomaterials.2005.03.049 UR - http://www.sciencedirect.com/science/article/pii/S0142961205003844


 * Drug delivery

TY - JOUR T1 - Calcium phosphate cements as drug delivery materials JO - Advanced Drug Delivery Reviews VL - 64 IS - 12 SP - 1090 EP - 1110 PY - 2012/9// T2 - Targeted delivery of therapeutics to bone and connective tissues AU - Ginebra, Maria-Pau AU - Canal, Cristina AU - Espanol, Montserrat AU - Pastorino, David AU - Montufar, Edgar B. SN  - 0169-409X DO - http://dx.doi.org/10.1016/j.addr.2012.01.008 UR - http://www.sciencedirect.com/science/article/pii/S0169409X12000117


 * Reactivity and prep of cements

author ="Bohner, Marc", title ="", journal ="J. Mater. Chem.", year ="2007", volume ="17", issue ="38", pages ="3980-3986", publisher ="The Royal Society of Chemistry", doi ="10.1039/B706411J", url ="http://dx.doi.org/10.1039/B706411J",

author ="Sugawara, Akiyoshi and Asaoka, Kenzo and Ding, Shinn-Jyh", title ="Calcium phosphate-based cements: clinical needs and recent progress", journal ="J. Mater. Chem. B", year ="2013", volume ="1", issue ="8", pages ="1081-1089", publisher ="The Royal Society of Chemistry", doi ="10.1039/C2TB00061J", url ="http://dx.doi.org/10.1039/C2TB00061J",