Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
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Chapter 1.<br />
Polylactide Based Bio-Materials<br />
cells in <str<strong>on</strong>g>the</str<strong>on</strong>g> dermis stop producing as much HA and increase <str<strong>on</strong>g>the</str<strong>on</strong>g> rate <str<strong>on</strong>g>of</str<strong>on</strong>g> its degradati<strong>on</strong>. HA degradati<strong>on</strong><br />
products also accumulate in <str<strong>on</strong>g>the</str<strong>on</strong>g> skin after UV exposure [Averbeck et al., 2006].<br />
Due to its high biocompatibility and its natural presence in <str<strong>on</strong>g>the</str<strong>on</strong>g> extracellular matrix <str<strong>on</strong>g>of</str<strong>on</strong>g> tissues, HA<br />
is gaining popularity as a biomaterial scaffold in tissue engineering research. In some cancers, HA levels<br />
correlate well with malignancy and poor prognosis. HA is thus <str<strong>on</strong>g>of</str<strong>on</strong>g>ten used as a tumor marker for prostate and<br />
breast cancer. It may also be used to m<strong>on</strong>itor <str<strong>on</strong>g>the</str<strong>on</strong>g> progressi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> disease.<br />
3.2 Calcium Phosphates and Tricalcium Phosphates<br />
Seventy percent <str<strong>on</strong>g>of</str<strong>on</strong>g> b<strong>on</strong>e is made up <str<strong>on</strong>g>of</str<strong>on</strong>g> hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ], tooth enamel is also<br />
largely calcium phosphate. Like o<str<strong>on</strong>g>the</str<strong>on</strong>g>r apatites, it has a calcium and phosphate comp<strong>on</strong>ent in a ratio <str<strong>on</strong>g>of</str<strong>on</strong>g> 1.67<br />
(Ca/P ratio) but is associated with a hydroxyl group. <strong>The</strong>re are several o<str<strong>on</strong>g>the</str<strong>on</strong>g>r n<strong>on</strong>-apatitic calcium phosphates<br />
that are distinguished from <strong>on</strong>e ano<str<strong>on</strong>g>the</str<strong>on</strong>g>r by <str<strong>on</strong>g>the</str<strong>on</strong>g>ir molecular formulae, Ca/P ratios that differ from 1.67, crystal<br />
structures and solubilities, which have higher dissoluti<strong>on</strong> rates than stoichiometric hydroxyapatite.<br />
3.2.1 Structures <str<strong>on</strong>g>of</str<strong>on</strong>g> Calcium Phosphate<br />
Calcium phosphate Ca 3 (PO 4 ) 2 is <str<strong>on</strong>g>the</str<strong>on</strong>g> name given to a family <str<strong>on</strong>g>of</str<strong>on</strong>g> minerals c<strong>on</strong>taining calcium i<strong>on</strong>s<br />
(Ca 2+ ) toge<str<strong>on</strong>g>the</str<strong>on</strong>g>r with orthophosphates (PO 4 3- ). Tricalcium phosphates (TCP) are am<strong>on</strong>g <str<strong>on</strong>g>the</str<strong>on</strong>g> most comm<strong>on</strong>lyused<br />
calcium phosphates compounds in implant materials. <strong>The</strong>y are found in ceramic b<strong>on</strong>e substitutes,<br />
metallic pros<str<strong>on</strong>g>the</str<strong>on</strong>g>sis coatings, cements and composite materials. From a strict chemical point <str<strong>on</strong>g>of</str<strong>on</strong>g> view,<br />
‘tricalcium phosphate’ refers to a compositi<strong>on</strong>, even though, in <str<strong>on</strong>g>the</str<strong>on</strong>g> minds <str<strong>on</strong>g>of</str<strong>on</strong>g> many users, this term is used to<br />
describe a structure, generally that <str<strong>on</strong>g>of</str<strong>on</strong>g> β tricalcium phosphate (βTCP). Tricalcium phosphates exist in four<br />
different forms:<br />
<br />
<br />
ATCP will hereby designate amorphous tricalcium phosphate;<br />
Ap TCP: apatitic tricalcium phosphate: Ca 9 (HPO 4 )(PO 4 ) 5 (OH);<br />
TCP: <str<strong>on</strong>g>the</str<strong>on</strong>g> most widely used member <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> TCP family having a crystalline structure: -Ca 3 (PO 4 ) 2 ;<br />
TCP: <str<strong>on</strong>g>the</str<strong>on</strong>g> metastable high-temperature crystalline structure: α-Ca 3 (PO 4 ) 2 .<br />
Amorphous tricalcium phosphate (ATCP) and apatitic tricalcium phosphate (Ap TCP) are low<br />
temperature, unstable phases generally obtained by precipitati<strong>on</strong>, whereas and tricalcium phosphates (<br />
and TCP) are high-temperature crystalline phases.<br />
3.2.2 Syn<str<strong>on</strong>g>the</str<strong>on</strong>g>sis <str<strong>on</strong>g>of</str<strong>on</strong>g> Different Calcium Phosphate Phases<br />
<strong>The</strong> producti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> tricalcium phosphate-based ceramics generally involves TCP powder<br />
preparati<strong>on</strong> and, in a successive stage, powder processing in order to obtain cohesive biomaterials in <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
form <str<strong>on</strong>g>of</str<strong>on</strong>g> dense or macro-porous ceramics, coatings, cements or composites for b<strong>on</strong>e filling, substituti<strong>on</strong><br />
and/or rec<strong>on</strong>structi<strong>on</strong> applicati<strong>on</strong>s. In several cases, however, calcium phosphate phases form during<br />
processing, as, for example, in <str<strong>on</strong>g>the</str<strong>on</strong>g> case <str<strong>on</strong>g>of</str<strong>on</strong>g> hydroxyapatite (HAp) plasma spraying. We will focus <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
elaborati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> different tricalcium phosphate phases (amorphous, and polymorphic forms), <str<strong>on</strong>g>the</str<strong>on</strong>g>ir<br />
structure, and main physicochemical properties and <str<strong>on</strong>g>the</str<strong>on</strong>g>ir processing.<br />
3.2.2.1 Amorphous TriCalcium Phosphate (ATCP)<br />
One <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> most c<strong>on</strong>venient preparati<strong>on</strong> methods is double decompositi<strong>on</strong> between a calcium salt<br />
soluti<strong>on</strong> and a hydrogen phosphate salt soluti<strong>on</strong> in aqueous media, at ambient temperature and at a pH close<br />
to 10 [Somrani et al., 2005; Heughebaert and M<strong>on</strong>tel, 1982]. It can also be obtained in hydroalcoholic<br />
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