Bioceramics Lecture 7

8/16/2019 Bioceramics Lecture 7

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Bioceramics

Materials in medical Science

lecture 7


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Types of Bioceramics


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Comparative mechanical properties


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Natural Ceramic materials


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BioactivityVs.Biocompatibility


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Relatively Bioinert Ceramics

• Relatively bioinert ceramics maintain their physicaland mechanical properties while in the host.

• They resist corrosion and wear.

• !amples of relatively bioinert ceramics are denseand porous aluminium o!ides" #irconia ceramics"and sin$le phase calcium aluminates

• Relatively bioinert ceramics are typically used asstructural%support implants. Some of these are

bone plates" bone screws" and femoral heads.!amples of non%structural support uses areventilation tubes" sterili#ation devices and dru$delivery devices


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&ses of Bioinert Ceramics


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'lumina('l)*+,

• The main source of hi$h purity alumina(aluminium o!ide, is bau!ite and nativecorundum.

•

The commonly available alumina (alpha"-, canbe prepared by calcinin$ alumina trihydrate

• The 'merican Society for Testin$ andMaterials ('STM, species that alumina for

implant use should contain//.01 pure aluminaand less than *.21 combined Si3) and al4ali

o!ides (mostly Na)3,


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Characteristics of 'lumina


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Characteristics of 'lumina

• The stren$th of polycrystalline alumina dependson its $rain si#e and porosity. 5enerally" thesmaller the $rains" the lower the porosity andthe hi$her the stren$th .

• The 'STM standards (6*+%78, re9uires a:e!ural stren$th $reater than ;** MSapphire.


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5ems

• ?iamond@Carbon

• Ruby= 'lumina with chromiumimpurity

• Sapphire= 'lumina

• merald=Be+'l)(Si3+,"

Ruby

Blue Sapphire

merald

?iamond


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'lumina

• Both polycrystalline and sin$le crystal alumina have beenused clinically. The hi$h hardness is accompanied by lowfriction and wear and inertness to the in vivo environment. These properties ma4e alumina an ideal material for usein Aoint replacements. 3ne of the most popular uses for

aluminium o!ide is in total hip prostheses.

• 'luminium o!ide hip prostheses with an ultra%hi$hmolecular wei$ht polyethylene (&M


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Firconia(Fr3),

•


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3ther uses of Firconia

'lthou$h low%9uality #irconia is used as an abrasive in hu$e9uantities" tou$h" wear resistant" refractory #irconiaceramics are used to manufacture parts operatin$ ina$$ressive environments" li4e e!trusion dyes" valves andport liners for combustion en$ines" low corrosion" thermalshoc4 resistant refractory liners or valve parts in foundries.Firconia blades are used to cut Hevlar" ma$netic tapes. i$htemperature ionic conductivity ma4es #irconia ceramicssuitable as solid electrolytes in fuel cells and in o!y$ensensors. 5ood chemical and dimensional stability"mechanical stren$th and tou$hness" coupled with a Koun$Lsmodulus in the same order of ma$nitude of stainless steelalloys was the ori$in of the interest in usin$ #irconia as aceramic biomaterial.


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Characteristics of Firconia


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Carbon=


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Carbon=


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5lassy Carbon

• 5lassy carbon" also called vitreous carbon" is an advanced material of purecarbon combinin$ $lassy and ceramic properties with these of $raphite. &nli4e$raphite" $lassy carbon has a fullerene%related microstructure. This leads to a$reat variety of uni9ue material properties.

i$h temperature resistance in inert $as or vacuum up to +***C

i$h purity

!treme corrosion resistance

Impermeability to $as and li9uids" no open porosity

No wettin$ by melts

i$h hardness and stren$th

Gow density

i$h surface 9uality" no particle $eneration

Gow thermal e!pansion

!treme resistance to thermal shoc4

Isotropy of physical and chemical properties

5ood electrical conductivity

Biocompatibility


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5lassy carbon

• &nli4e all other ceramic and metallic hi$htemperature materials" $lassy carbon increase instren$th with a rise in temperature up to )7** H.5lassy carbon shows at )7** H compared to room

temperature the double stren$th. Compared toceramic and metallic materials" $lassy carbonshows even at hi$h temperatures noembrittlement.

•

?ue to the hi$h purity the catalytic action of forei$nelements (reaction centres, concernin$ o!idationand corrosion is limited to a minimum.

• Mainly electrode and biosensor application


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Carbon

• 5raphite and $lassy carbon have amuch lower mechanical stren$ththan


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Carbon

• Carbons e!hibit e!cellentcompatibility with tissue.Compatibility of


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?istribution of minerals in hardtissues


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Mechanical properties of Tissues


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Biode$radable or ResorbableCeramics

• 'lthou$h


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Calcium


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Calcium cm+. Substitution of 3 with :uoride

$ives the apatite $reater chemicalstability due to the closer coordination of:uoride (symmetric shape, as comparedto the hydro!yl (asymmetric" two atoms,

by the nearest calcium. This is why:uoridation of drin4in$ water helps inresistin$ caries of the teeth.


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Calcium


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'mon$ the most important properties of hydro!yapatite as a biomaterial is itse!cellent biocomaptibility. ydro!yapatite appears to form a direct chemicalbond with hard tissues D


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hitloc4ite

• hitloc4ite is a mineral" an unusual form of calcium phosphate. Its formula is Ca/(M$6e,(


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Bioactive or Surface%ReactiveCeramics

• &pon implantation in the host" surfacereactive ceramics form stron$ bonds withadAacent tissue. !amples of surface

reactive ceramics are dense nonporous$lasses" Bio$lass and Ceravital" andhydro!yapatites. 3ne of their many usesis the coatin$ of metal prostheses. This

coatin$ provides a stron$er bondin$ tothe adAacent tissues" which is veryimportant for prostheses.


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5lass Ceramics

• 5lass ceramics are polycrystallineceramics made by controlledcrystalli#ation of $lasses .

• The formation of $lass ceramics isin:uenced by the nucleation and $rowthof small (Q2 m diameter, crystals as wellas the si#e distribution of these crystals. It

is estimated that about 2* 2) to 2* 20 nuclei per cubic centimeter are re9uired toachieve such small crystals.


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5lass Ceramics

• The $lass ceramics developed for implantation are Si3)

%Ca3%Na)3%


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5lass Ceramics

• 5lass ceramics have several desirable properties compared to$lasses and ceramics. The thermal coefcient of e!pansion isvery low" typically 2* U7 to 2* U0 C U2 " and in some cases it caneven be made ne$ative. ?ue to the controlled $rain si#e andimproved resistance to surface dama$e" the tensile stren$th of thesematerials can be increased by at least a factor of two" from about2** to )** M

Bioceramics Lecture 7

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