biomaterials...25 2. ceramics as biomaterials bioactive ceramics, active glasses and glass-ceramics...
TRANSCRIPT
Ming Li, Ph.D.
Professor of Materials Science and Engineering
Central South University
E-mail:[email protected]
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
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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
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
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
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Contents
• Properties of ceramics
• Ceramics as biomaterials
Inert ceramics
Porous ceramics
Bioactive Ceramics, Active Glasses
and Glass Ceramics
Biodegradable ceramics
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 <7 μm
Alumina (Al2O3)
2. Ceramics as biomaterials: Inert Ceramics
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Crystal structure of alumina (○: aluminum; ●: oxygen)
2. Ceramics as biomaterials: Inert Ceramics
Rhombohedral structure (a = 4.758 Å
and c = 12.991 Å)
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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
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Total hip
replacement
implants
Total knee
replacement
implants Ceramic
Dental
ImplantsBIOLOX®* 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
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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
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• 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
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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.
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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
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Glasses and Glass-ceramics
2. Ceramics as Biomaterials: Bioactive Ceramics,
Active Glasses and Glass-Ceramics
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.
Mineral name, chemical name, and composition of various phases
of calcium phosphates
2. Ceramics as Biomaterials: Bioactive Ceramics,
Active Glasses and Glass-Ceramics
32
Hydroxyapatite(Ca10(PO4)6(OH)2), HAP
2. Ceramics as Biomaterials: Bioactive Ceramics,
Active Glasses and Glass-Ceramics
35
Raman FTIR
poorly crystalline HAP
bovine cortical bone
HAP ceramic
highly crystalline HAP
Hydroxyapatite
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Biodegradable bioceramics
Degradation Mechanism:
Degradation = chemical breakdown of the bulk materials
1. Physiochemical dissolution
2. Physical disintegration into small particles at grain
boundaries
3. Biological factors, such as phagocytosis
2. Ceramics as Biomaterials
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❑ All calcium phosphate ceramics biodegrade to varying degrees;
the rate of biodegradation increases as:
1. Decreasing Ca/P ratio
2. Surface area increases (powders > porous solid >dense solid);
3. Crystallinity decreases;
4. Crystal perfection decreases;
5. Crystal and grain size decrease;
6. There are ionic substitutions of CO32-, Mg2+, and Sr2+ in HA.
❑ Factors that tend to decrease the rate of biodegradation include:
(1) F− substitution in HA;
(2) Mg2+ substitution in β-TCP; and
(3) lower β-TCP/HA ratios in biphasic calcium phosphates.
2. Ceramics as Biomaterials: biodegradable bioceramics
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Degradation of ceramic biomaterials
Osteoclasts (bone-resorbing cells) mediate true degradation of
the ceramic component of bone
Takeway is that osteoclasts "eat"crystal fragments, which are
then metabolized intracellularly
2. Ceramics as Biomaterials: biodegradable bioceramics
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α-TCP:
• dissolution speed limits usage
β-TCP:
• Osteoinductive degradation similar to
bone resorption
Tricalcium phosphates (TCP)
2. Ceramics as Biomaterials: biodegradable bioceramics
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• preservation of strength
• degradation speed = regeneration speed
• degradation products
Challenges for degradable ceramics
2. Ceramics as Biomaterials: biodegradable bioceramics
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Reading Materials:
Book: Biomaterials Science: An Introduction to Materials
in Medicine (3rd Edition, 2013)
• Ceramics, Glasses, and Glass-Ceramics: Basic Principles