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Samenvatting Innovative Technology 3e bach BMW UHasselt

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Samenvatting van de hoorcolleges en ZSO's van het vak Innovative technology in diagnosis and therapeutics zoals gegeven in het academiejaar

Last document update: 6 year ago

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  • January 19, 2018
  • January 23, 2018
  • 31
  • 2017/2018
  • Summary

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ZSO1 BIOCOMPATIBILITY
Biomaterial science
Focus of materials science in general on:

1. Composition: the chemical make-up of materials
2. Properties: the functional characteristics of materials and analytical methods to measure these characteristics
3. Structure: a description of the arrangements of atoms or ions in materials

Biomaterials science focuses on:

 Materials of a biological origin
 Materials with an application in the biomedical sciences

Classification of materials
 Main classes
o Metals and alloys
o Ceramics and glasses
o Organic materials (Polymers and plastics)
 Subclasses
o Semiconductors
o Composites

Differences amongst others based on strength and solid state bonding properties

Strength
There is an elastic limit and stress limit (maximal tensile strength)




Solid state bonding properties
Ionic bonding
One or more electrons transfer from a metallic donor atom to a non-metallic acceptor atom




Simple cubic lattice Face centered cubic lattice

Many crystal structures/lattices possible.
Coulomb interaction between charges  Ionic materials are usually solids at room temperature

Purely ionic solids do not have many biomedical applications (However, glasses and ceramics do!)

,Covalent bonding




Characteristics of covalent bonding

 Octet rule (atoms in molecules strive to noble gas configurations)
 Emphasizes sharing of electrons
 Large variety in the arrangement of atoms is possible: unlimited number of molecules can exist
 No long range bonding: gasses, liquids and solids

Electronegativity




 Polar covalent bonds are not fully symmetrical
 Bond polarities are due to differences in electronegativity
 Inductive effect: the shift in electrons in a covalent bond due to the electronegativity of nearby atoms




 Small difference in electronegativity: non-polar covalent bond
 Difference of ~2 or less in electronegativity: polar covalent bond
 Difference of more than ~2 in electronegativity: ionic bond

Electronegativity is given on a relative scale developed by Linus Pauling.

Metallic bonding
Free electron model: electrons are shared with all neighbours!

Characteristics of metal bonding

 Long range bonding: usually solids at room temperature (sometimes liquids)
 Delocalized character of bonding gives strength to material
 Delocalized character of bonding allows deformations

Weak bonding
 London forces (dispersion interactions)
 Dipole-induced dipole interaction
 Dipole-dipole interaction
 Hydrogen bonding

,Classification of Materials (based on chemical bonding): metal, covalent, ionic

Classes of Materials: metals, polymers, ceramics and glasses composites etc.

Classes of Materials
Metals
 Usually FCC, HCP or BCC crystal lattice
 Good thermal and electrical conductors
 Produced from ores
 Often used in alloys
 Need surface treatment
 Two Classes:
o Ferrous metals and alloys
o Nonferrous metals and alloys

First step involves mostly chemistry and is often laborious




Example: Extraction of magnesium




Stainless steel
(very relevant for biomedical applications such as implants)

A group of ferrous alloys that contain at least 11% Cr, providing extraordinary corrosion resistance.

Categories of stainless steels:

 Ferritic  Mostly BCC (body-centered cubic) structure, poor alloy, only moderate improvements
 Martensitic  Complex structure, very strong, poor corrosi resistance
 Austenitic  FCC (face centered cubic) structure, most common, usually employed in biomedical sciences

, Often also used: 316L (L = low carbon)



ASTM 316L (American Society of Testing and Materials): alloy optimized for surface and bulk microstructure

 Fe Bulk metal
 Cr Gives corrosion resistant Cr2O3 surface
 Ni Stabilizes stronger austenitic FCC phase
 Low C Reduces formation of grain boundaries, improves corrosion resistance

Many other (non-ferrous) alloys have also been developed for improved surface characteristics or mechanical
properties.

Cobalt based alloys
(for example hip implants).
Often made using casting

 Disadvantages:
o Formation of interdendritic regions during melting
o Large grain size
o Casting defects
 Solution: Hot isostatic pressing

Titanium-based alloys
(for example dental implants)

Excellent corrosion resistance provides applications in chemical processing equipment, marine components and
biomedical implants.

Titanium alloys are considered biocompatible (i.e., they are not rejected by the
body). By developing porous coatings of bone-like ceramic compositions known as
hydroxyapatite, it may be possible to make titanium implants bioactive (i.e., the
natural bone can grow into the hydroxyapatite coating).


← α = HCP and β = BCC



Alpha-beta = ASTM F136 

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