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week 5 Flashcards

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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.

Study These Flashcards
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.

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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

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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

Study These Flashcards
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:

Study These Flashcards
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:

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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:

Study These Flashcards
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:

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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:

Study These Flashcards
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
Porous ceramics
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
How to decrease fractures in ceramics
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
Bioactive glasses and glass-ceramics:
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
Calcium-phosphate ceramics: Factors that influence rate of resorption of an implant are: o physical factors
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
Calcium-phosphate ceramics applications:
1. - **bone grafting** applications. 2. - porous component to **non-major load bearing parts of the skeleton. **
30
The most employed method for ceramic coating is
**plasma spraying.** * ** Mechanical mismatch** between the _coating_ and the _substrate_ can lead to high levels of **residual interfacial stress. **
31
Calcium-phosphate ceramics mechanical behavior :
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
Resorbable calcium-phosphate: Calcium-phosphate bone cements:
**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
Hydroxyapatites ceramics bioactivity, application
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
Calcium - phosphate ceramics depend on the ratio of Give examples:
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
4 strengthening methods used for ceramics.
1. Ion exchange : provides **compressive strength ** 2. **p**olishing : 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
calcium-phosphate ceramics. What state of matter are they used?
Pastes for bone augmentation and powders for sintering

Biomedical (9 decks)

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