1. MASE 542/Chem 442
Ceramics and Glasses
Cont.

2. Ceramics Usually inorganic nonmetallic materials refractory
polycrystalline
Composition:
ınorganic silicates, metallic oxides, carbides and various refractory hydrides, sulfides, and selenides.
Oxides such as Al2O3, MgO, SiO2, and ZrO2 contain metallic and
covalently bonded ceramics such as diamond and carbonaceous structures like graphite and pyrolized carbons

3. Ceramics
Ionic nature prevents plastic shear (Unlike metals and polymers)
Fracture after crack
non-ductile
Hard and brittle
almost zero creep at room temperature
susceptible to notches or microcracks
low tensile strength.
If a ceramic is flawless, it is very strong even when subjected to tension.
At the crack tip the stress could be many times higher than the stress in the material away from the tip, resulting in a stress concentration which weakens the material considerably. So, it is difficult to predict the tensile strength of the material
(ceramic).
Flawless glass fibers have twice the tensile strengths of high strength steel (~7 GPa)

4. Ceramics high melting temperatures
generally hard;
Diamond is the hardest (hardness index : 10 Moh’s scale)
Talc (Mg3Si3O10COH) is the softest ceramic (1 )
Alumina (Al2O3; hardness 9)
Quartz (SiO; hardness 8)
apatite (Ca5P3O12F; hardness 5)
high melting temperatures
low conductivity of electricity and heat.
in fact, the measurement of hardness is calibrated against ceramic
materials.

5. Advantages of Ceramics:
inert in body (or bioactive in body)
Chemically inert in many environments
high wear resistance (orthopedic & dental applications)
high modulus (stiffness) & compressive strength
Comparable to metals
esthetic for dental applications

6. Disadvantages of Ceramics
brittle (low impact/fracture resistance, flaw tolerance)
low tensile strength (fibers are exception)
poor fatigue resistance (relates to flaw tolerance)
properties difficult to reproduce, difficulties in processing and fabrication

7. Desired Properties of Implantable Bioceramics
1. Should be nontoxic. 2. Should be noncarcinogenic. 3. Should be nonallergic. 4. Should be noninflammatory. 5. Should be biocompatible. 6. Should be biofunctional for its lifetime in the host.

8. Types of Implant–Tissue Response
If the material is toxic, the surrounding tissue dies.
If the material is nontoxic and biologically inactive (nearly inert), a fibrous tissue of variable thickness forms.
If the material is nontoxic and biologically active (bioactive), an interfacial bond forms.
If the material is nontoxic and dissolves, the surrounding tissue replaces it.
RATNER

9. TABLE 2 Types of Bioceramic–Tissue Attachment and Their Classification
Example
Al2O3 (Single crystal
and polycrystalline)
Al2O3 (Polycrystalline)
Hydroxyapatite-coated
porous metals
Bioactive glasses
Bioactive glass-ceramics
Hydroxyapatite
Calcium sulfate (Plaster
of Paris)
Tricalcium phosphate
Calcium-phosphate salts
Type of attachment
1. Dense, nonporous, nearly inert
ceramics attach by bone growth into
surface irregularities by cementing the device into the tissues or by
press-fitting into a defect
(“morphological fixation”).
2. For porous inert implants, bone
ingrowth occurs that mechanically
attaches the bone to the material
(termed “biological fixation”).
3. Dense, nonporous surface-reactive
ceramics, glasses, and glass-ceramics attach directly by chemical bonding with the bone (termed “bioactive fixation”).
4. Dense, nonporous (or porous)
resorbable ceramics are designed to be slowly replaced by bone.

10. Type 1. Inert Ceramics
Dense, nonporous ceramics attach by bone growth into surface irregularities by cementing the device into the tissues or by press-fitting into a defect (“morphological fixation”).
Example:
dense and porous aluminum oxides( Al2O3 (Single crystal and polycrystalline)
zirconia ceramics
calcium aluminates
If mechanically fit and used under compression: Fine
If interfacial movement:LOOSENing
CAPSULE FORMATION IN MOTION

11. Type 1. Inert Ceramics
maintain their physical and mechanical properties while in the host.
resist corrosion and wear
Uses:
as structural-support implants
bone plates, bone screws, and femoral acetabular cups
Nonstructural support
ventilation tubes, sterilization devices, drug delivery

12. Alumina (Al2O3): single crystal alumina referred to as “Sapphire”
“Ruby” is alumina with about 1% of Al3+ replaced by Cr3+; yields red color
“Blue sapphire” is alumina with impurities of Fe and Ti; various shades of blue

13. Alumina (Al2O3) & Zirconia (ZrO2)
Most commonly used structural bioceramics.
Primarily used as modular heads on femoral stem hip components.
Wear less than metal components, and the wear particles are generally better tolerated.
Need polished surface (ball&sucket)

14. Alumina Hip
the alumina ball and socket in a hip prosthesis are polished together and used as a pair.
wear on alumina-articulating surfaces being nearly 10 times lower than metal–polyethylene surfaces
alumina noncemented cups press-fitted into the acetabulum of the hip.
The cups are stabilized by the growth of bone into grooves.
Long-term results in general are good, especially for younger patients.

15. problems stress shielding due to the high elastic modulus of alumina,
cancellous bone atrophy and loosening of the acetabular cup
in old patients with osteoporosis or rheumatoid arthritis.
Consequently, it is essential that the age of the patient, nature before any prosthesis is used

16. Characteristic Features of Ceramic Biomaterials
Trends Biomater. Artif. Organs, Vol 18 (1), pp 9-17 (2004)
Characteristic Features of Ceramic Biomaterials
Material Young’s (GPa) Compr. (MPa) Bond (GPa) Hardness Density Modulus Strength strength Inert Al2O >3.9 ZrO ≈ Graphite NA NA Pyrolitic Carbon NA Vitreous Carbon NA Bioactive HAP Bioglass ≈ NA 2.5 Bone NA NA
The variation in Young's Modulus noted for some of the materials listed is due to variation in density of test specimens.
PS - Partially Stabilized; HA - Hydroxyapatite; NA - Not Available; AW - Apatite-Wallastonite; HV - Vickers Hardness; DPH - Diamond Pyramid Hardness

17. Alumina (Al2O3): High-density, high-purity (>199.5%) alumina
most widely used form is polycrystalline
excellent corrosion resistance
good biocompatibility
High wear resistance (Low coefficient of friction)
Excellent compressive strength
Resistance to fatigue (dynamic and impact)
Resist crack growth
USED IN
load-bearing hip prostheses and dental implants

18. Fabrication of Biomedical devices from Al2O3 & (ZrO2):
devices are produced by pressing and sintering fine powders at temperatures between 1600 to 1700ºC.
Fine grains polycrystalline (average grain size less than 4 micron)
Additives such as MgO added (<0.5%) to limit grain growth
Grain size and sintering aid is critical to properties

20. Alumina orthopedic surgery for nearly 20 years
excellent biocompatibility
very thin capsule formation
which permits cementless fixation of prostheses
exceptionally low coefficients of friction and wear

21. Zirconia (ZrO2)
Zirconia is also used as the articulating ball in total hip prostheses/load-bearing prostheses
Alumina Zirconia
Elastic modulus (GPa)
Flexural strength (GPa) >
Hardness, Mohs
Density (g/cm3)
Grain size (μm)
Note: Both ceramics contain 3 mole % Y2O3.
Source: J.B. Park, personal communication, 1993

22. Dental Porcelain:
ternary Composition = Mixture of K2O-Al2O3-SiO2 made by mixing clays, feldspars, and quartz
CLAY = Hydrated alumino silicate
FELDSPAR = Anhydrous alumino silicate
QUARTZ = Anydrous Silicate

23. Type 2. Porous Ceramics
bone ingrowth occurs, mechanically attaches the bone to the material (“biological fixation”).
Example: Al2O3 (Polycrystalline), Hydroxyapatite-coated porous metals
Ingrowth of tissue
increases the resistance to movement of the device in tissue
serves as a structural bridge or scaffold for bone formation.
An interface is formed “biological fixation”
Withstand more complex stress states

24. Porous Ceramics Limitation:
To keeep tissue viable and healty pores need to be larger than um
To provide blood to the new inborn tissue
Not only size but also connectivity
No vascularization in less than 100um
POROUS= large surface area….
corrosion, metal leaching
Decreases mechanical strength
when load-bearing is not a primary requirement-provide a functional implant.

25. Porous Ceramics
Porous materials are weaker than the equivalent bulk form
porosity increases, the strength of the material decreases rapidly.
Much surface area is also exposed,
environment on decreasing the strength become much more important than for dense, nonporous materials.
The aging (subsequent decrease in strength) requires bone ingrowth to stabilize the structure of the implant.

26. Type 3. Bioactive glass and glass-ceramics
Glass ceramics are polycrystalline ceramics made by controlled crystallization of glasses developed by
Dense, nonporous , surface-reactive ceramics, glasses, and glass-ceramics attach directly by chemical bonding with the bone (“bioactive fixation”).
a time-dependent, kinetic modification of the surface that occurs upon implantation.
Example :Bioactive glasses, Bioactive glass-ceramics, Hydroxyapatite

27. Bioactive glass and glass-ceramics
Creates a specific biological response at the interface
Bond formation between the material and the tissue
Bioactive coating on metal….
Increase interfacial stability, resist mechanical forces
Adhesion may be equal to or more than the adhesive strength of the implant or the tissue
but can not solve other mechanical problems related to porosity
Works as a coating or unloaded space fillers (cement)

28. Bioactive glass and glass-ceramics
Be careful about :
the time dependence of bonding
the strength of bond
the mechanism of bonding
the thickness of the bonding zone differ for the various materials.

29. Bioactive Glass Composition includes SiO2, CaO and Na2O
Bioactivity depends on the relative amounts of SiO2, CaO and Na2O
Cannot be used for load bearing applications
Ideal as bone cement filler and coating due to its biological activity

30. USES For coating of metal prostheses
In reconstruction of dental defects.
For filling space vacated by bone screws, donor bone, excised tumors, and diseased bone loss.
As bone plates and screws.
As replacements of middle ear ossicles.
For correcting periodontal defects.
In replacing subperiosteal teeth.

31. Approximate regions of the tissue-glass-ceramic bonding for the SiO2-CaO-Na2O system
Nonbonding;
reactivity is too low
Bonding within 30 days
Billotte, W. G. “Ceramic Biomaterials.” The Biomedical Engineering Handbook: Second Edition. Ed. Joseph D. Bronzino Boca Raton: CRC Press LLC, 2000
Bonding does not form glass.

32. Surface interaction of bioactive glass/glass ceramic
High silica content: surface hydration layer
Inert glass and vitrous silica (region B)
SiO2 rich: surface SiOH condensation
Protect further attack (region B)
Commercial silica glass
Si–OH+ OH– Si → Si–O–Si + H2O
Ion exchange of alkali ions and with protons or hydronum ions (region C)
Thick and porous , non-protecting SiO2 rich surface layer
Rapid dissolution of silica at high pH(region C)

33. Bioactive glass
The bonding to bone is related to the simultaneous formation of a calcium phosphate and SiO2-rich film layer on the surface
If a SiO2-rich layer forms first and a calcium phosphate film develops later (46 to 55 mol % SiO2 samples) or no phosphate film is formed (60 mole % SiO2) then direct bonding with bone does not occur

34. Ceravital glass ceramic
Low alkali Bioglass SiO2
In order to control the dissolution rate: Al2O3, TiO2, Ta2O5 are added
Inhibit bone bonding
fine grains
Advantages over glasses and ceramics.
very low thermal coefficient of expansion
controlled grain size and improved resistance to surface damage= the tensile strength of these materials can be increased by at least a factor of two, from about 100 to 200 MPa.
The resistance to scratching and abrasion of glass ceramics is similar to that of sapphire
The resistance
to scratching and abrasion of glass ceramics is similar to that of sapphire

35. Glass-ceramic: Cons… Brittle
limitations on the compositions used for producing a biocompatibile (or osteoconductive) glass ceramic hinders the production of a glass ceramic which has substantially higher mechanical strength.
NO load-bearing implants such as joint implants
But OKEY for fillers for bone cement, dental restorative composites, and coating material
A glass ceramic with 36 wt% of magnetite in a β-wollastonite- and CaOSiO2-based glassy matrix :treating bone tumors by hyperthermia [Kokubo et al., 1992].

36. Type 4. Resorbable Ceramics
Dense, nonporous (or porous) resorbable ceramics are designed to be slowly replaced by bone.
Example: Calcium sulfate (Plaster of Paris), Tricalcium phosphate, Calcium-phosphate salts
Almost all bioresorbable ceramics are variations of calcium phosphate

37. Type 4. Resorbable Ceramics
Degrade over time and replaced by the natural tissue
Very thin or no interfacial tissue
Complications:
maintenance of strength and the stability of the interface during the degradation period and replacement by the natural host tissue
matching resorption rates to the repair rates of body tissues
Degredation products should be metabolically acceptable

38. resorbable ceramics Ex:
poly(lactic acid) and poly(glycolic acid) : sutures (CO2 and H2O)
Porous or particulate tricalcium phosphate (TCP) : resorbable hard tissue replacements when low loads are applied to the material.

39. Calcium Phosphates
Ca : P Mineral name Formula Chemical name 1.0 Monetite CaHPO4 Dicalcium phosphate (DCP) 1.0 Brushite CaHPO4·2H2O Dicalcium phosphate Dihydrate (DCPD) 1.33 — Ca8(HPO4)2(PO4)4·5H2O Octocalcium phosphate (OCP) 1.43 Whitlockite Ca10(HPO4)(PO4)6 1.5 — Ca3(PO4)2 Tricalcium phosphate (TCP) 1.67 Hydroxyapatite Ca10(PO4)6(OH)2 2.0 Ca4P2O9 Tetracalcium phosphate

40. Calcium Phosphate Ceramics
Bone composition: ( by weight )
25% water, 15% organic materials and 60% mineral phases.
The mineral phase:
Primarily calcium and phosphate ions
traces of magnesium, carbonate, hydroxyl, chloride, fluoride, and citrate ions.
calcium phosphates occur naturally in the body
past 20–30 years: use as a biomaterial
Depends on their solubility and speed of hydrolysis which increase with a decreasing calcium-to-phosphorus ratio.
Ca/P ratio of less than 1 : 1 are not suitable for biological implantation.

41. Calcium Phosphate Ceramics
rate of resorption
physical factors (e.g., surface area, crystallite size)
chemical factors (atomic and ionic substitutions in the lattice)
biological factors (types of cells surrounding the implant and location, age, species, sex, and hormone levels.)

42. Calcium Phosphates
• Hydroxyapatite (HA :Ca10(PO4)6(OH) • Weak in tension • Used primarily as powders, small unloaded implants, coatings, porous implants for bone ingrowth • Good material for bone tissue engineering • Can be easily degraded if conditions are correct – pH, chemical attack, phagocytosis • Pure HA degrades rapidly

43. Physical Properties of Calcium Phosphate
Properties Values
Elastic modulus (GPa) 4.0–117
Compressive strength (MPa) 294
Bending strength (MPa) 147
Hardness (Vickers, GPa)
Poisson’s ratio
Density (theoretical, g/cm3) 3.16
Source: Park JB and Lakes RS Ceramic Implant
Materials In: Biomaterials An Introduction, 2nd ed., p 125.
Plenum Press, New York.

44. Resorption or biodegradation of calcium phosphate ceramics
In fluenced by
Physiochemical dissolution
depends on the solubility product of the material
As Ca/P decreases, solubility increases
local pH of its environmen
Causes formation of new surface phases : amorphous calcium phosphate, dicalcium phosphate dihydrate, octacalcium phosphate, and anionic substituted HA.
Physical disintegration into small particles as a result of preferential chemical attack of grain boundaries.
Biological factors, such as phagocytosis, which causes a decrease in local pH concentrations
Ideally, one would wish for a replacement material to be
slowly resorbed by the body once its task of acting as a scaffold
for new bone has been completed. Degradation or resorption of
calcium phosphates in vivo occurs by a combination of phagocytosis
of particles and the production of acids.

45. The rate of biodegradation increases as:
Surface area increases (powders > porous solid > dense solid)
Crystallinity decreases
Crystal perfection decreases
Crystal and grain size decrease
There are ionic substitutions of CO−32 , Mg2+, and Sr2+ in HA

46. Factors that tend to decrease the rate of biodegradation
F− substitution in HA
Mg2+ substitution in β-TCP, and
lower β-TCP/HA ratios in biphasic calcium phosphates.

47. HA gained acceptance as bone substitute repair of
bony defects
periodontal defects
maintenance or augmentation of ear implant, eye implant, spine fusion, adjuvant to uncoated implants.

48. HA
Bone growth in or near implanted HA is more rapid than what is found with control implants.
In the literature HA is sometimes referred to as an "osteoinductive“ material.

49. HA elastic modulus (Gpa) Polycrystalline hydroxyapatite: 40 -117
Enamel (stiffest hard tissue)
Dentin
compact bone
Polycrystalline hydroxyapatite has a high elastic modulus (40 to 117 GPa). Hard tissue such as bone,
dentin, and dental enamel are natural composites which contain hydroxyapatite (or a similar mineral),
as well as protein, other organic materials, and water. Enamel is the stiffest hard tissue, with an elastic
modulus of 74 GPa, and contains the most mineral. Dentin ( E
= 21 GPa) and compact bone (
= 12 to
18 GPa) contain comparatively less mineral. The Poisson’s ratio for the mineral or synthetic hydroxyapatite
is about 0.27 which is close to that of bone ( ≈
0.3) [Park and Lakes, 1992].
The ideal Ca:P ratio of hydroxyapatite is 10:6 and the calculated density is g/cm 3
. Substitution
of OH with fluoride gives the apatite greater chemical stability due to the closer coordination of fluoride
(symmetric shape) as compared to the hydroxyl (asymmetric, two atoms) by the nearest calcium. This
is why fluoridation of drinking water helps in resisting caries of the teeth.

50. Bioceramic Coatings
Coatings of hydroxyapatite are often applied to metallic implants (most commonly titanium/titanium alloys and stainless steels) to alter the surface properties.
In this manner the body sees hydroxyapatite-type material which it appears more willing to accept.
Without the coating the body would see a foreign body and work in such a way as to isolate it from surrounding tissues.
To date, the only commercially accepted method of applying hydroxyapatite coatings to metallic implants is plasma spraying.

51. Bone Fillers
Hydroxyapatite may be employed in forms such as powders, porous blocks or beads to fill bone defects or voids.
These may arise when large sections of bone have had to be removed (e.g. bone cancers) or when bone augmentations are required (e.g bone reconstructions or dental applications).
The bone filler will provide a scaffold and encourage the rapid filling of the void by naturally forming bone and provides an alternative to bone grafts.
It will also become part of the bone structure and will reduce healing times

52. Tissue Interactions with Bioceramics
Toxic: Tissue dies
Inert: Capsule forms
Bioactive: Interfacial bond forms
Dissolves: Replaced by tissue

53. Basic Applications of Ceramics:
Orthopedics
Dentistry
inner ear implants
drug delivery devices
ocular implants
heart valves

54. Orthopedics bone plates and screws
total & partial hip components (femoral head)
coatings (of metal prostheses) for controlled implant/tissue interfacial response
space filling of diseased bone
vertebral prostheses, vertebra spacers, iliac crest prostheses

55. Dentistry: dental restorations (crown and bridge)
implant applications (implants, implant coatings)
orthodontics (brackets)
glass ionomer cements and adhesives

56. Veneers

57. Deterioration of Ceramics
Fatigue
Accelarated flaws or impurities
source of crack initiation and growth under stress
the rate of degradation in vivo
presence of water may reduce stregth
Accelerates crack growth

58. FIGURE Transmission electron micrograph of well-mineralized bone (b) juxtaposed to the glass-ceramic (c) which fractured during sectioning. X51,500. Insert a is the diffraction pattern from ceramic area and b is from bone area. (Source: Beckham CA, Greenlee TK Jr, Crebo AR Bone Formation at a Ceramic Implant Interfaces, Calc. Tiss. Res. 8:165–171.) Bioglass glass ceramic implanted in the femur of rats for six weeks showed intimate contacts between the mineralized bone and the Bioglass . The mechanical strength of the interfacial bond between bone and Bioglass ceramic is on the same order of magnitude as the strength of the bulk glass ceramic (83.3 MPa), which is about three-fourths that of the host bone strength [Park and Lakes, 1992].

59. Characteristic Features of Ceramic Biomaterials
Trends Biomater. Artif. Organs, Vol 18 (1), pp 9-17 (2004)
Characteristic Features of Ceramic Biomaterials
Material Young’s (GPa) Compr. (MPa) Bond (GPa) Hardness Density Modulus Strength strength Inert Al2O >3.9 ZrO2 (PS) ≈ Graphite NA NA Pyrolitic Carbon NA Vitreous Carbon NA Bioactive HAP Bioglass ≈ NA 2.5 Bone NA NA
The variation in Young's Modulus noted for some of the materials listed is due to variation in density of test specimens.
PS - Partially Stabilized; HA - Hydroxyapatite; NA - Not Available; AW - Apatite-Wallastonite; HV - Vickers Hardness; DPH - Diamond Pyramid Hardness