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week 5 Flashcards

1
Q

Ceramic definition

A

inorganic/non-metallic compositions.

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2
Q

few ceramic compositions have achieved clinical success:

A

Example of implantable inert bioceramics:

Al2O3, ZrO2,( clinical success) TiO2.

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3
Q

Ceramics are (treatment response)

A

refractory (resistant to treatment) polycrystalline compounds

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4
Q

Ceramics properties

A
  1. Usually inorganic
  2. Highly inert
  3. Hard and brittle
  4. High compressive strength
  5. Generally good electric and thermal insulators
  6. Good aesthetic appearance
  7. Good tribological properties (wear, friction)
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5
Q

Tissue composition

A

Tissue = organic polymer fibers + mineral + living cells

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6
Q

ceramic classification based on crystallinity

Type of bond

A
  1. amorphous ceramics that are generally referred to as ‘glasses’
  2. Crystalline ceramics, which may be single phase materials like alumina
  3. Semi-Crystalline:

Ionic bonds

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7
Q

Mineral component (ceramic) bone:

A
  • hydroxyapatite (HA); Ca5(PO4)3OH
  1. Mineralization under biological conditions: - many elemental substitutions
    • protein directed crystallization
    • unique characteristics: crystal morphology and solubility
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8
Q

Types of bioceramics (3):

A
  1. Bioinert: Alumina (Al2O3), Zirconia (ZrO3), Pyrolytic carbon.
  2. Bioactive: Bioglass (Na2OCaOP2O3-SiO), Hydroxyapatite (Ca10(PO4)6(OH)2) (sintered at high temperature)
  3. Resrobable or biodegradable: Hydroxyapatite (sintered at low temperature) Tricalcium phosphate.
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9
Q

Biocompatibility vs bioactivity vs biodegradability:

A
  1. Biocompatibility: Minimize inflammatory responses and toxic effects. (eg. head of articulations)
  2. Bioactivity: Characteristic that allows the material to form a bond with living tissue (Hench 1971).
    • Ability of a material to stimulate healing and trick the tissue system into responding as if it were a natural tissue (Hench 2002).
    • Advantages: bone-tissue-implant interface, enhanced healing* response, *extended implant life.
  3. Biodegradability: Breakdown of implant due to chemical or cellular actions, enzymes.
    • If timed to rate of tissue healing transforms implant to scaffold for tissue regeneration.
    • Mitigates issues of **stress shielding, implant loosening, long term stability. (eg. Low bearing appliacations) **
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10
Q

Types of bioceramics (4)

A
  1. Type 1: bioinert == Fully dense and inert: zirconia/alumina
  2. Type 2: porous inert == Porous/inert: porous alumina/zirconia
  3. Type 3: surface reactive == Fully dense and bioactive: hydroxyapatite
  4. Type 4: resorbable materials == Porous/bioactive/resorbable: scaffolds for tissue engineering
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11
Q

Are there materials implanted in the body tha are completely inert?

A

no type of material implanted in the body is completely inert because **they will elicit a response from living tissues. **

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12
Q

The success of ceramic/bioglass-based implantation depends on:

A
  1.  Achieving a stable attachment to connective tissue when used as a bulk implant.
  2. Stimulating repair and regeneration of bone when used as particulates for bone grafting.
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13
Q

Types of implant-Tissue Response

A

1) If the material is toxic, the surrounding tissue dies.
2) If the material is nontoxic and biologically inactive (nearly inert), a fibrous tissue of variable thickness forms.
3) If the material is nontoxic and biologically active (bioactive), an interfacial bond forrns.
4) If the material is nontoxic and dissolves, the **surrounding tissue replaces it. **

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14
Q

Types of bioceramics Tissue attachments

A
  1. Dense, nonporous nearly inert cerarnics attach by bone growth into surface irregularities by cementing the device into the tissues. or by press-fitting into a defect. flermed Morphoiogicai Fiation)
    • AI2O3, (Single Ctystal and Polycrystalline)
  2. For porous inert implants bone ingrowth occurs, which mechanicaliy attaches the bone to the material. (termed Biological Fixation)
    • Al203 (Porous Polycrystalline) Hydroxylapatilecoated Porous Metals
  3. _Dense, nonporous surface-reactive cerarnics, glasses, and glass-cerarnics _attach directly by chemical bonding with the bone. (Termed Bioactive Fixation)
    • Bioactive glasses Bioactive glass-cerarnics Hydroxylapatite
  4. Dense, nonporous (or porous) resorbable cerarnics are designed to be slowly replace by bone.
    • Calciurn Sulphate (Plaster of Paris) TricalciurnPhosphate Calciurn-Phosphate Salts
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15
Q

Ceramic Type 1: Bioinert

Describe means of attachment.

A
  1. Interface is not chemically or biologically bonded.
  2. o Relative movement. –> **deformation due to fibrous layer formation that reduces flexibility. –> modular and encapsulation **
  3. o Progressive development of** fibrous capsule in soft and hard tissues **
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16
Q

Type 2: Porous inert:

Describe means of attachment.

A
  1. Tissue ingrowth
  2. o Biological fixation
  3. o Increased interfacial area tissue-implant
  4. o Reduced movement- withstands more complex **stresses **
17
Q

 Type 3: Surface reactive:

Describe means of attachment.

A
  1. Attach by chemical bonds with tissue
  2. o Slow rate of degradation if any
  3. o Induce bone formation
  4. o Intermediate between bioinert and resorbable.
18
Q

Type 4: Resorbable materials

Describe means of attachment

A
  1. Degrade gradually over a period of time to be replaced by tissue
  2. o Leads to a thin, if any, interfacial layer
  3. o Optimal solution if requirements of strength and short-term performance can be met. Problems??? need screws and inmobilization in order to give enough time to bone to grow.
19
Q

Problems with each of the 4 types of bioceramics

A
  1. Type one: Fibrous layers formation that goes away but if too thick will interfere with movement
  2. Type 2: Pore size needs to be ideal at least 50 um potential removal of implant is a problem.
  3. Type 3: behaves more like a bioinert; also pore size is important for vascularization. Mechanical properties are an issue.
  4. Type 4: degrades too quickly
20
Q

processing of bioceramics result in 5 different microstructures:

A

  1. Glass
  2. Cast or plasma-sprayed polycrystalline ceramic
  3. Liquid-phase sintered (vitrified ceramic)
  4. solid-state sintered ceramic
  5. Polycrystalline glass- ceramic
21
Q

Strengthening mechanisms:

A
  1. ** Ion exchange:** to get compressive strength – introduction of bigger cations within structure.
  2. Quenching of glass: glass transformation temperature.

heating —> expansion —-> cooling (upon cooling surface is put into compression

ceramics Fractures easily under tension.

  1.  In ceramics strengthening means to prevent fracture or inhibit crack propagation.
  2. To improve strength:
    • polishing: etch (**electropolishing) or fire polish. **
22
Q

Surface residual stresses:

A

o Early crack nucleation and propagation can occur if a ceramic specimen is put under tension.

23
Q

Failure is probabilistic in ceramics it depends on:

A
  1. o It depends on flaw distribution.
  2. o It depends on **crystal size. **
  3. It depends on **porosity: 3% porosity will result in 10x decrease in strength of ceramics. **

Stress = k (d-1/3) —> d = diameter of crystals

24
Q

Nearly inert crystalline ceramic: Aluminum oxides (Alumina)

Advantages:

Disadvantages:

Applications:

A
  1.  Combination of attractive properties.
  2.  Bioinertness – low immune response.
  3.  Alumina-on-alumina implants have been cleared by the FDA.
  4.  Implantations, since 1987, have been successful.
  5.  Small grain size and porosity – higher strength.
  6.  Stress shielding may be a problem.
  7.  High hardness, low wear.

Disadvantages:

  1.  Minimal bone ingrowth.
  2.  Interfacial failure and loss of implant may be a problem.

Applications:

  1.  Orthopedics: Femoral heads, bone screws and plates, porous coatings for femoral stems, porous spacers (revision), knee prosthesis.
  2.  Dental crowns and bridges.
25
Q

Porous ceramics

A
  1. Inertness combined with the mechanical stability of a highly convoluted interface that develops when bone grows into the pores of the ceramic.
  2.  Implant serve as a structural bridge or scaffold for bone formation (>50 - 150 microns pore size).
26
Q

How to decrease fractures in ceramics

A
  1. Make small grains
  2. Use sintering agent + MO (Molibdenium oxide) but this changes the purity of the ceramic
  3. Eliminate flaws = inclusions –> reduction of [stress] [] by polishing reduction of flaws
  • Electromechanical —> electrochemical
  • Etching
  • Temperature treatment (annealing decreases the stress resigual
  • Ion Exchange
27
Q

Bioactive glasses and glass-ceramics:

A
  1.  Bioactive: direct chemical bonding with the host biological tissue
  2.  Some compositions will bond to soft tissues as well as to bone = formation of carbonated HA layer.

Glass:

  1.  An inorganic melt cooled to solid form without crystallization.
  2. ** An amorphous solid.**
  3.  Possesses short range atomic order – it is brittle.

Glass-ceramic:

  1.  Polycrystalline solid prepared by controlled crystallization of glass.
  2.  Stimulatory effects on bone building cells.
28
Q

Calcium-phosphate ceramics:

Factors that influence rate of resorption of an implant are: o physical factors

A
  1.  Naturally occurring in the body.
  2.  Composition of bone.
  3.  The main crystalline component of the mineral phase of bone is a calcium deficient carbonate HA.
  4.  Speed of hydrolysis increase with a decreasing Ca/P ratio.

_ Factors that influence rate of resorption of an implant are:_

  1. o chemical factors
  2. o biological factors
  3. o physical factors
29
Q

Calcium-phosphate ceramics applications:

A
    • bone grafting applications.
    • porous component to **non-major load bearing parts of the skeleton. **
30
Q

The most employed method for ceramic coating is

A

plasma spraying.

  •  Mechanical mismatch between the coating and the substrate can lead to high levels of **residual interfacial stress. **
31
Q

Calcium-phosphate ceramics mechanical behavior :

A
  1. Poor mechanical behavior of calcium phosphate ceramics greatly restrict its use as implants.
  2. Tensile, compressive strength and fatigue resistance depend on the total volume of porosity.
  3. Low reliability under tensile loads, consequently in clinical practice, calcium phosphate bioceramics should be used as:
  •  powders
  •  in small, unloaded implants
  •  with reinforcing metal posts
  •  coatings
  •  fillers (composites)
  •  in porous implants where bone
  • growth acts as the reinforcing phase
32
Q

Resorbable calcium-phosphate:

Calcium-phosphate bone cements:

A

Resorbable calcium-phosphate:

  1.  Biodegradation caused by three factors: physiochemical dissolution, physical disintegration, and biological factors.
  2.  Degradation or resorption of calcium phosphate in vivo occurs by a combination of phagocytosis of particles and the production of acids.
  3.  All calcium phosphate ceramics biodegrade to varying degrees.

** Calcium-phosphate bone cements:**

  1.  Requirements are injectability and moldability.
  2.  Different combinations of calcium compounds (alpha-TCP, dicalcium phosphate).
  3.  Considerable interest in the potential use of these materials for drug delivery.
33
Q

Hydroxyapatites ceramics bioactivity, application

A
  1. Bioactive + osteoconductive.
  2. Broadly used as coating or orthopedic implants.
  3. Successful clinical application in polymer composites.
  4. Approaches were developed to produce bioactive and either** bioresorbable or biodurable composites**.
  5. _Substitution of hydroxyl and/or phosphate groups by carbonate increases apatite solubility. _
34
Q

Calcium - phosphate ceramics depend on the ratio of

Give examples:

A

Calcium to phosphate

  1. If ratio Ca-P = 1 —-> ceramic degrades too fast
  2. If ratio Ca-P = 2 —-> ceramic degrade very slowly
  3. If ratio Ca-P = 1.43 —-> ceramic degrades in 3 months (slow but not too slow)
  4. Ceramics Type 3 and 4 have a ratio of Ca-P close to 1.
  5. Ceramics Type 1 and 2 have a ratio of Ca-P close to 2.
35
Q

4 strengthening methods used for ceramics.

A
  1. Ion exchange : provides **compressive strength **
  2. polishing : to make surface smooth –> to **eliminate flaws or cracking **
  3. Quenching of glass heating and cooling: giving compressive strength. When it is cooled the surface is put under compressive stress.
  4. **Annealing: make small grains **controlled heating rates –> need phase diagram to achieve ideal temperature and cooling rates to achieve small grains
36
Q

calcium-phosphate ceramics. What state of matter are they used?

A

Pastes for bone augmentation and powders for sintering

Biomedical (9 decks)

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