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BIOMATERIALS ENT 219

BIOMATERIALS ENT 219. Lecture 9 Ceramic Material. 1.0 INTRODUCTION. Ceramics are inorganic materials composed of non-directional ionic bonds between electron donating and electron –accepting elements. Mechanical properties of ceramics: Hard Brittle

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BIOMATERIALS ENT 219

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  1. BIOMATERIALSENT 219 Lecture 9 Ceramic Material

  2. 1.0 INTRODUCTION • Ceramics are inorganic materials composed of non-directional ionic bonds between electron donating and electron –accepting elements. • Mechanical properties of ceramics: • Hard • Brittle • Allow for little deformation before failure • Can withstand high compression stress

  3. 1.0 INTRODUCTION • WHY CHOOSE CERAMIC AS BIOMATERIALS? • Have an appropriate mechanical properties for particular medical application such as dental crowns. • Biocompatible: • Relative inertness to the body fluid. • More resistant to degradation. • Have a similar chemistry and mechanical properties with natural bone → more often used as a part of orthopaedic implant (coating material) or as dental materials (crowns, dentures). • High wear resistance

  4. 2.0 STRUCTURE OF CERAMIC • Ceramic may contain crystal or non-crystalline (amorphous) glassess.

  5. 2.0 CRYSTAL STRUCTURE OF CERAMIC • Crystal structure in ceramic materials are composed of ions rather than atoms. • The ions are arranged in an orderly repeating pattern in three dimension. • The repeating elements or subdivisions of the crystal called unit cells. The unit cell for an ionic crystal having a sodium chloride structure

  6. Ceramic Crystal Structures Two characteristic of the component ions in crystalline ceramic materials that influence the crystal structure: • The magnitude of the electrical charge on each of the components ions. • The crystal must be electrically neutral • The crystal must be balanced by an equal number of anion –ve charges • The relative size of the cations and anions • This involves the sizes or ionic radii, rC & rA respectively • The ratio of rC/rA is less than unity due to cation size that is small. This is caused by the metallic elements give up electrons when ionized

  7. AX- TYPE CRYSTAL STRUCTURE • Ceramic materials which have equal number of cations and anoins. • AX compounds • A = cation • X = anion • Consists of : • Rock Salt/ Sodium Chloride (NaCl ) structure • Cesium Chloride Structure • Zinc Blende Structure

  8. AX- Crystal Structure: Rock Salt Structure Same concepts can be applied to ionic solids in general. Example: Sodium Chloride (NaCl ) / rock salt structure rNa = 0.102 nm rCl = 0.181 nm • rNa/rCl = 0.564 • cations prefer OHsites The coordination number is 6 Adapted from Fig. 12.2, Callister 7e.

  9. AX-Crystal Structure :Rock Salt Structure MgO and FeO also have the NaCl structure O2- rO = 0.140 nm Mg2+ rMg = 0.072 nm • rMg/rO = 0.514 • cations prefer OHsites Adapted from Fig. 12.2, Callister 7e. So each oxygen has 6 neighboring Mg2+

  10. AX-Crystal Structures: Cesium Chloride Structure Cesium Chloride structure:  cubicsites preferred So each Cs+ has 8 neighboring Cl- Adapted from Fig. 12.3, Callister 7e.

  11. AX-Crystal Structures: Zinc Blende Zinc Blende structure • Why is Zn2+ in TD sites? • bonding hybridization of zinc favors TD sites • Size arguments predict Zn2+ in OHsites, • In observed structure Zn2+ in TD sites So each Zn2+ has 4 neighboring O2- Adapted from Fig. 12.4, Callister 7e. Ex: ZnO, ZnS, SiC

  12. AX2 Type Crystal Structures • Charges of cation and anions are not the same Fluorite structure • Calcium Fluorite (CaF2) • cations in cubic sites • UO2, ThO2, ZrO2, CeO2 • antifluorite structure – • cations and anions • reversed Adapted from Fig. 12.5, Callister 7e.

  13. ABX3 Crystal Structures • Ceramic compound have more than one type of cation • Perovskite Ex: complex oxide BaTiO3 (Barium Titanate) Adapted from Fig. 12.6, Callister 7e.

  14. Crystal Structure of Ceramic

  15. 2.2 MICROSTRUCTURE OF CERAMIC

  16. MICROSTRUCTURAL FEATURES 2.2 MICROSTRUCTURE OF CERAMIC

  17. 3.0 BIOMEDICAL APPLICATION • DENTISTRY • Dental filling, Dental crown, dentures • Why widely used in dentistry • Relatively inert to body fluid • High compressive strength • Aesthetically pleasing apparent

  18. 3.0 BIOMEDICAL APPLICATION • ORTHOPAEDIC IMPLANT • Femoral head/ball of hip implant • Coating of hip stem • Acetabular inner cup of hip implant

  19. Acetabular component • Inner cup (Polymer or ceramic) • Outer cup (Metal) • Femoral component • femoral stem (metal) • neck (metal) • head/ball (metal or ceramic)

  20. 4.0 DESIRED PROPERTIES OF BIOCERAMICS In orderto be classified as a bioceramic, the ceramic material must exceed such properties: • Should be nontoxic • Should be noncarcinogenic • Should be nonallergic • Should be non inflammatory • Should be biocompatible • Should be biofunctional for its lifetime in host

  21. 5.0 TYPE OF BIOCERAMICS 5.1 RELATIVELY INERT (NON-ABSORBABLE) BIOCERAMICS 5.2 NON-INERT BIOCERAMICS (RESORBABLE) BIOCERAMICS 5.3 SURFACE REACTIVE (SEMI-INERT) BIOCERAMICS Notes Absorbable : Capable of being absorbed or taken in through the pores of a surface

  22. 5.0 TYPE OF BIOCERAMICS • Relative reactivity of bioceramics in physiological enviroments: Non-inert bioceramic Surface reactive bioceramic

  23. 5.0 TYPE OF BIOCERAMICS • Some typical room temperature properties of bioceramics and corticol bone

  24. 5.1 RELATIVELY INERT (NON-ABSORBABLE) BIOCERAMICS • Maintain their physical and mechanical properties while in host. • Resist corrosion and wear • Have all the six (6) desired properties of implantable bioceramics. • Have a reasonable fracture toughness. • Typically used as structural-support implant such as bone plates, bone screw and femoral heads.

  25. 5.1 RELATIVELY INERT (NON-ABSORBABLE) BIOCERAMICS 5.1.1 ALUMINA or Aliminum oxides (Al203) • The main source of alumina or aluminium oxide is bauxite and native corundum. • Highly stable oxide – very chemically inert • Low fracture toughness and tensile strength – high compression strength • Very low wear resistance • Quite hard material, varies from 20 to 30 GPa. Notes Bauxite and corundum is type of minerals

  26. 5.1 RELATIVELY INERT (NON-ABSORBABLE) BIOCERAMICS • Mechanical properties requirement: • Compressive strength: 4 -5 Gpa • Flexural strength : > 400MPa • Elastic modulus: 380 GPa • Density : 3.8 – 3.9 g/cm3 • Generally quite hard : 20 to 30 GPa

  27. 5.1 RELATIVELY INERT (NON-ABSORBABLE) BIOCERAMICS ALUMINA High hardness + low friction + low wear+ inert to in vivo environment Ideal material for use in: • Orthopaedic joint replacement component, e.g. femoral head of hip implant • Orthopaedic load-bearing implant • Implant coating • Dental implants

  28. 5.1 RELATIVELY INERT (NON-ABSORBABLE) BIOCERAMICS 5.1.2 ZIRCONIA (Zr202) • Pure zirconia can be obtained from chemical conversion of zircon, which is an abundant mineral deposit.

  29. 5.1 RELATIVELY INERT (NON-ABSORBABLE) BIOCERAMICS • Has a high melting temperature and chemical stability. • The bending strength and fracture toughness are 2-3 and 2 times greater than alumina.

  30. 5.1 RELATIVELY INERT (NON-ABSORBABLE) BIOCERAMICS • The improved mechanical properties plus excellent biocompatibility and wear properties make this material the best choice the new generation of orthopaedic implant. • Has already widely use to replace alumina and metals.

  31. 5.1 RELATIVELY INERT (NON-ABSORBABLE) BIOCERAMICS 5.1.3 CARBON • Carbon can be made in many allotropic forms: • Crystalline diamond • Graphite • Nanocrystalline glassy carbon • Quasicrystalline pyrolitic carbon • Only pyrolitic carbon is widely utilized for implant fabrication. • Normally used as surface coating

  32. 5.2 NON-INERT BIOCERAMICS (RESORBABLE) BIOCERAMICS • Chemically broken down by the body and degrade • The resorbed material is replaced by endogenous tissue • Chemicals produced as the ceramic is resorbed must be able to be processed through the normal metabolic pathways of the body without evoking any deleterious effect. • Synthesize from chemical (synthetic ceramic) or natural sources (natural ceramic)

  33. 5.2 NON-INERT BIOCERAMICS (RESORBABLE) BIOCERAMICS • Examples of Resorbable Bioceramics • Calcium phosphate • Calcium sulfate, including plaster of Paris • Hydroxyapatite • Tricalcium phosphate • Ferric-calcium-phosphorous oxides • Corals

  34. 5.2 NON-INERT BIOCERAMICS (RESORBABLE) BIOCERAMICS 5.2.1 Synthetic ceramic 5.2.1.1 Calcium phosphate and Hydroxyapatite • Can be crystallized into salts such as Hydroxyapatite. • Hydroxyapatite (HAP) has a similar properties with mineral phase of bone and teeth. • Important properties of HAP: • Excellent biocompatibility • Form a direct chemical bond with hard tissue

  35. 5.2 NON-INERT BIOCERAMICS (RESORBABLE) BIOCERAMICS • Low values of mechanical strength and fracture toughness, thus cannot be used in load bearing materials.

  36. 5.2 NON-INERT BIOCERAMICS (RESORBABLE) BIOCERAMICS • Application: • Bone graft substitute in a granular or a solid block.

  37. 5.2 NON-INERT BIOCERAMICS (RESORBABLE) BIOCERAMICS • Application (cont): • Temporary scaffold which is gradually replaced by tissue • Orthopaedic and dental implant coating • Dental implant materials • Drawback: • Complicated fabrication process and difficult to shape

  38. 5.2 NON-INERT BIOCERAMICS (RESORBABLE) BIOCERAMICS 5.2.1.2 Tricalcium phosphate • Composition similar to hydroxyapatite • Degrades faster than calcium phosphate • More soluble than synthetic HAP • Allow good bone in growth and eventually is replaced by endogenous tissue.

  39. 5.2 NON-INERT BIOCERAMICS (RESORBABLE) BIOCERAMICS 5.2.2 Natural ceramic 5.2.2.1 Coral, Seashells • Corals/Seashells transformed into HAP • Biocompatible • Facilitate bone growth • Used to repair traumatized bone, replaced disease bone and correct various bone defect. • Bone scaffold

  40. 5.3 SURFACE REACTIVE (SEMI-INERT) BIOCERAMICS • Direct and strong chemical bond with tissue • Fixation of implants in the skeletal system • Low mechanical strength and fracture toughness • Examples: • Glass ceramics • Hydroxyapatite • Dense nonporous glasses

  41. 5.3 SURFACE REACTIVE (SEMI-INERT) BIOCERAMICS 5.3.1 Glass ceramics • Glass-ceramics are crystalline materials obtained by the controlled crystallization of an amorphous parent glass. • Controlled crystallisation requires: • specific compositions • usually a two-stage heat-treatmen • Controlled nucleation • Controlled crystallization will growth of crystal of small uniform size

  42. 5.3 SURFACE REACTIVE (SEMI-INERT) BIOCERAMICS • Type of glass ceramic • Bioglass • Ceravital • Both are SiO2, CaO, Na2O and P2O5 systems • Bioglass composition manipulated to induce direct bonding with the bone • Must simultaneously form a calcium phosphate and SiO2 – rich film layer on surface of ceramic for this to happen • With correct composition will bond with bone in approximately 30 days

  43. Bioglass structure

  44. 5.3 SURFACE REACTIVE (SEMI-INERT) BIOCERAMICS • Glass ceramic properties

  45. 5.3 SURFACE REACTIVE (SEMI-INERT) BIOCERAMICS

  46. 5.3 SURFACE REACTIVE (SEMI-INERT) BIOCERAMICS

  47. 5.3 SURFACE REACTIVE (SEMI-INERT) BIOCERAMICS • Application of Glass Ceramic • Orthopaedic and dental implant coating • Dental implant • Facial reconstruction components • Bone graft substitute material • Main limitation: • Brittleness • Cannot be used for making major load bearing implant such as joint implant

  48. 6.0 BIODEGRADATION OF CERAMIC DEFINITION • Biodegradation: chemical breakdown of a material mediated by any component of the physiological environment ( such as water, ions, cells, proteins, and bacteria).

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