BIOMATERIALS ... 25 2. Ceramics as Biomaterials Bioactive Ceramics, Active Glasses and...

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Transcript of BIOMATERIALS ... 25 2. Ceramics as Biomaterials Bioactive Ceramics, Active Glasses and...

  • Ming Li, Ph.D.

    Professor of Materials Science and Engineering

    Central South University

    E-mail:liming0823@csu.edu.cn

    Office: Room 308, Chemistry Building, Main Campus

    BIOMATERIALS

    Lecture 4: Ceramics, Glasses, and Glass- Ceramics

    Sept. 18, 2019

  • 2

    Book: Biomaterials Science: An Introduction to Materials

    in Medicine (3rd Edition, 2013)

    • Two points for each error found

    in the book

    • Only count for the first person

    who finds the error

    NOTE

  • 3

    Last Lecture

    • Properties and challenges

    • Commonly used metals

    Stainless steel

    Titanium

    Cobalt alloys

    • Smart metal biomaterials

    Shape memory metals

    Magnetostrictive materials

  • 4

    Contents

    • Properties of ceramics

    • Ceramics as biomaterials

    Inert ceramics

    Porous ceramics

    Bioactive Ceramics, Active

    Glasses and Glass Ceramics

    Biodegradable ceramics

  • 5

    Contents

    • Properties of ceramics

    • Ceramics as biomaterials

    Inert ceramics

    Porous ceramics

    Bioactive Ceramics, Active

    Glasses and Glass Ceramics

    Biodegradable ceramics

  • 6

    Ceramic biomaterials

    ❑ Ceramics are refractory polycrystalline compounds;

    • Inorganic • Hard and brittle • High compressive strength ❑ Applications:

    • Orthopaedic load-bearing coatings • Dental implants • Bone graft substitutes • Bone cements

    1. Properties of ceramics

  • 7

    1. Inert (Al2O3, ZrO2)

    2. Nearly inert, porous (hydroxyapatite)

    3. Bioactive (bioglass)

    4. Resorbable/degradable (Ca3(PO4)2)

    Types of ceramic biomaterials

    Bioactive compound is a compound that has an effect on a

    living organism, tissue or cell.

    Bioresorbable compounds are designed to degrade safely

    within the body.

    1. Properties of ceramics

  • 8

    Definitions

    If the material is...

    • toxic surrounding tissue dies

    • nontoxic and biologically inactive (nearly inert)

    fibrous tissue of variable thickness forms

    • nontoxic and biologically active (bioactive): an

    interfacial bond form

    • nontoxic and dissolves: surrounding tissue

    replaces it

    1. Properties of ceramics

  • 9

    Pros:

    1. inert or bioactive

    2. high wear resistance

    3. high stiffness and compression strength

    4. aesthetic (dental)

    Cons:

    1. brittle

    2. low tensile strength

    3. low fatigue strength

    Ceramic biomaterials

    1. Properties of ceramics

  • 10

    1. Properties of ceramics

    Types of ceramic biomaterials

  • 11

    Bioactivity spectra for

    various bioceramic implants

    (A) Relative rate of bioreactivity

    (B) Time-dependence of

    formation of bone bonding at

    an implant interface.

    1. Properties of ceramics

  • 12

    Ceramic Biomaterials

    1. Properties of ceramics

    BIOLOX®* delta ceramic femoral head

  • 13

    Natural hard tissues are ceramic-polymer composites

    • Bones, Teeth, Shells

    Hydroxyapatite Ca5(PO4)3OH gives teeth and bones their

    hardness!

    Hard tissues

  • 14

    Bonding structure

    The extent to which a ceramic lattice is ionic or covalent in

    nature will depend on the electro-negativities of the atoms

    involved

  • 15

    Contents

    • Properties of ceramics

    • Ceramics as biomaterials

    Inert ceramics

    Porous ceramics

    Bioactive Ceramics, Active Glasses

    and Glass Ceramics

    Biodegradable ceramics

  • 16

    Inert Ceramics

    Alumina (Al2O3) and Zirconia (ZrO2)

    2. Ceramics as biomaterials

  • 17

    Used in total hip arthroplasty since 1970

    • high-purity alumina (around 99.7%)

    • MgO controls grain size during the

    sintering process

    Alumina used in orthopaedic applications

    should have a grain size

  • 18

    Crystal structure of alumina (○: aluminum; ●: oxygen)

    2. Ceramics as biomaterials: Inert Ceramics

    Rhombohedral structure (a = 4.758 Å

    and c = 12.991 Å)

  • 19

    Production of Alumina

    Three stages:

    1. Extraction: The aluminum-bearing minerals in bauxite are

    selectively extracted from the insoluble components by

    dissolving them in a solution of sodium hydroxide.

    Al(OH)3 + Na + + OH− → Al(OH)4

    − + Na+

    2. Precipitation: Crystalline aluminum trihydroxide is precipitated.

    This is the reverse of the extraction process, except the

    chemistries are well-controlled.

    Al(OH)4 − + Na+ → Al(OH)3 + Na

    + + OH−

    3. Calcination: Aluminum trihydroxide is calcined to form

    alumina. The water is driven off to form alumina. This process

    dictates the properties of the final product.

    2Al(OH)3 → Al2O3 + 3H2O

  • 20

    Total hip

    replacement

    implants

    Total knee

    replacement

    implants Ceramic

    Dental

    Implants BIOLOX®* delta

    ceramic femoral

    head.

    Alumina: Applications

    2. Ceramics as biomaterials: Inert Ceramics

  • 21

    Zirconia (ZrO2)

    Yttrium stabilizes the tetragonal phase

    2. Ceramics as biomaterials: Inert Ceramics

  • 22

    Zirconia failures

    Long term tension and moisture...

    Monoclinic content from 1%→30% on the surface

    →Surface roughness from 0.006 m up to 0.12 μm

    2. Ceramics as biomaterials: Inert Ceramics

  • 23

    Zirconia

    Still widely used in dental applications

    2. Ceramics as biomaterials: Inert Ceramics

  • 24

    • Good mechanical tissue-implant fixation

    • Poor mechanical properties

    Porous Ceramics

    When pore sizes exceed 100 µm, bone will grow within the

    interconnecting pore channels near the surface and maintain

    its vascularity and long-term viability.

    2. Ceramics as biomaterials

  • 25

    2. Ceramics as Biomaterials

    Bioactive Ceramics, Active

    Glasses and Glass-Ceramics

    • Bonding to bone was first demonstrated for a compositional range of

    bioactive glasses that contained SiO2, Na2O, CaO, and P2O5 in specific

    proportions

    • Many bioactive silica glasses are based upon the formula called 45S5,

    signifying 45 wt.% SiO2 (S = the network former) and 5:1 ratio of CaO

    to P2O5.

    • Glasses with lower ratios of CaO to P2O5 do not bond to bone.

    Substitutions in the 45S5 formula of 5–15wt.% B2O3 for SiO2 or 12.5

    wt.% CaF2 for CaO or heat treating the bioactive glass compositions to

    form glass-ceramics have no measurable effect on the ability of the

    material to form a bone bond. However, adding as little as 3 wt.% Al2O3 to the 45S5 formula prevents bonding to bone.

  • 26

    The compositional dependence of bone and soft tissue bonding

    on the Na2O–CaO–P2O5–SiO2 glasses

    Compositional dependence (in wt.%) of

    bone bonding and soft tissue bonding of

    bioactive glasses and glass-ceramics. All

    compositions in region A have a constant

    6 wt.% of P2O5. A-W glass ceramic has

    higher P2O5 content. IB, Index of

    bioactivity.

    2. Ceramics as Biomaterials: Bioactive Ceramics,

    Active Glasses and Glass-Ceramics

    • All the glasses contain a constant 6 wt.% of

    P2O5.

    • Compositions in the middle of the diagram

    (region A) form a bond with bone.

    • Consequently, region A is termed the

    bioactive bone bonding boundary.

    • Silicate glasses within region B (e.g.,

    window or bottle glass or microscope

    slides) behave as nearly inert materials and

    elicit a fibrous capsule at the implant–tissue

    interface.

    • Glasses within region C are resorbable and

    disappear within 10 to 30 days of

    implantation.

    • Glasses within region D are not technically

    practical, and therefore have not been

    tested as implants

  • 27

    Glasses and Glass-ceramics

    2. Ceramics as Biomaterials: Bioactive Ceramics,

    Active Glasses and Glass-Ceramics

  • 28

    Types of silicate glass interfaces with

    aqueous or physiological solutions

  • 29

  • 30

    Calcium Phosphate Ceramics • Bone typically consists by weight of 25% water, 15% organic materials,

    and 60% mineral phases. The mineral phase consists primarily of calcium

    and phosphate ions, with traces of magnesium, carbonate, hydroxyl,

    chloride, fluoride, and citrate ions.

    • Calcium phosphates occur naturally in the body

    • But they also occur within nature as mineral rocks, and certain

    compounds can be synthesized in the laboratory.

    M