Biomaterials Science

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Biomaterials Science
Thomas Cleij Organische en polymere
scheikunde thomas.cleij_at_luc.ac.be D 155
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Biomaterials Science

• Six classes on the chemical aspects of
  bioelectronics and nanotechnology
• Introduction to materials
• Carbon based materials
• Mechanical properties
• Polymer chemistry
• Properties of functional materials
• Biocompatibility

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Biomaterials Science

• Emphasis on
• Chemical properties
• Synthesis
• Functional properties
• Base text Biomaterials Science An Introduction
  to Materials in Medicine by Buddy Ratner et al.
• Some information on the slides of today The
  Science and Engineering of Materials by Donald
  Askeland and Pradeep P. Phulé

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Biomaterials Science
Focus of materials science in general
on Compositionthe chemical make-up of
materials Structurea description of the
arrangements of atoms or ions in
materials Synthesisthe process by which
materials are made from naturally occurring or
other chemicals Processingdifferent ways for
shaping materials into useful components or
changing their properties
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Classification of Materials

• Metals and Alloys
• Ceramics and glasses
• Polymers (plastics)
• Semiconductors
• Composites
• Differences amongst others based on strength and
  solid state bonding properties

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Classification of Materials
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Classification of Materials

• Chemical bonding the classical model
• Ionic bonding
• One or more electrons transfer from a metallic
  donor atom to a non-metallic acceptor atom

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Classification of Materials
Many crystalstructures/latticespossible
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Classification of Materials
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Classification of Materials

• Chemical bonding the classical model
• Covalent bonding
• Sharing of valence electrons

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Classification of Materials
Graphite
Polymers
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Classification of Materials

• Chemical bonding the classical model
• Metallic bonding
• Free electron modelelectrons are sharedwith
  all neighbors!

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Classification of Materials

• Chemical bonding the classical model
• Weak bonding
• London forces(dispersion interactions)
• Dipole-induced dipole interaction
• Dipole-dipole interaction
• Hydrogen bonding

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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 - Ferrous metals and alloys -
  Nonferrous metals and alloys

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Metals
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Metals
Stainless steel A group of ferrous alloys that
contain at least 11 Cr, providing extraordinary
corrosion resistance. Categories of stainless
steelsferritic, martensitic and austenitic
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Metals
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Metals
ASTM 316L 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
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Metals

• Many alloys are developed for Improved surface
  characteristics or mechanical properties.
• Cobalt based alloys
• Often made using casting
• Disadvantages
• Formation of interdendritic regions during
  melting
• Large grain size
• Casting defects
• Solution Hot isostatic pressing

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Metals

• Other materials
• Titanium-based alloys
• 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).

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Metals
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Metals
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Ceramics and glasses

• Ceramics are usually solid inorganic materials
• Combination of ionic and covalent bonding
• Typical 4-fold coordination of covalent
  materials
• Charge neutrality of ionic solids
• Complex crystal structures
• Good wear resistance and strength
• Sometimes brittle

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Ceramics and glasses
Common ceramics
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Ceramics and glasses
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Ceramics and glasses
Ceramic processing Green ceramicA ceramic
that has been shaped into a desired form but has
not yet been sintered.
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Ceramics and glasses

• Two most common bioceramics
• Al2O3 (orthopedics, dental, cardiovascular,
  etc.)
• Calcium phosphates (coatings for chemical
  bonding, temporary bone space fillers, dental,
  etc.)
• Properties of calcium phosphates depends on CaP
  ratio
• 1.671 Ca10(PO4)6(OH)2 Hydroxyapatite (HA)

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Ceramics and glasses

• Tissue attachment to bioceramics
• Morphological fixation (cementing)
• Biological fixation (bone ingrowth)
• Bioactive fixation (chemical bonding)
• Resorbable ceramics (ceramics are slowly replaced
  by bone
• Critical Interfacial thickness

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Ceramics and glasses
Tissue attachment to bioceramics
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Ceramics and glasses

• Glasses
• Cooled molten ceramics which have not developed a
  crystal structure no long distance order
• Glass temperature Tg The temperature below which
  an undercooled liquid becomes a glass.
• Glass formers Oxides with a high-bond strength
  that easily produce a glass during processing.
• Intermediates Oxides that, when added to a
  glass, help to extend the glassy network
  although the oxides normally do not form a glass
  themselves.

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Ceramics and glasses
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Ceramics and glasses
Glass-ceramics Intermediate between glasses and
ceramics achieved by careful processing (small
crystalline regions in glass matrix
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Ceramics and glasses
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Polymers

• Organic (carbon containing) long molecular chains
  or networks
• Characterized by covalent bonds
• Thermosetting (cures and forms a 3D network)
• Thermoplastic (remains somewhat flexible
  dependent on the temperature)

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Composites

• Advanced materials with improved properties
• Alloys are mixtures of metals or polymers on a
  molecular level.
• Blends are mixtures of polymer phases on a
  molecular level.
• Composites consist of a continuous and a
  discontinuous phase, i.e. mixtures on a
  macroscopic scale.

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Composites
A macroscopic combination of two or more distinct
materials that have readily discernable
interfaces between them. Often two phases 1)
The matrix 2) The reinforcement Composites are
mainly developed for structural applications
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Composites

• Classification based on form of reinforcement
• Fiber
• Particulate
• Flake
• Laminate
• Formulation of composites based on a mixture of
  science/engineering and trial-and-error.
• Orientation is key to mechanical properties.

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Composites
Lamination
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Composites
Fiber containing composites Most important class
of composites, which was initially developed for
aerospace industry Typical properties- High
tensile strength- High Youngs modulus- Good
resistance to weathering Fibers -
Polycrystalline or amorphous - Continuous
production - Typical diameter 2-25 mm
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Composites
Typical fibers Aramid (Kevlar or Twaron tensile
strength up to 3.6 GPa and modulus up to 190
GPa) Glass Graphite Silicon carbide Aluminum
oxide Carbon (tensile strength up to 4.5 GPa and
modulus up to 900 GPa)
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A relationship exists between the ideal length
and the amount of adhesion
Not enough adhesion
Optimal
Tensile Strength Test
Too much adhesion
Catastrophic failure
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Composites
Typical biomedical composites Epoxides Carbon
fibers Polyethylene HA Polyurethane
Bioglass Etc.
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Sources of Pictures and Text
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/3_conditions_treated/hip_resurfacing.htm http//w
ww.outokumpu.com/ http//www.atlas-hip.com/an/bien
venue.htm http//www.orthogastonia.com/patient_ed/
html_pages/hand/hand_cmc_arthroplasty.html http//
www.bg.ic.ac.uk/Lectures/Hench/BioGlass/cal3.htm h
ttp//www.ami.co.il/html/aesthetic/in-aestetic/mal
ar.htm http//www.sptimes.com/2003/10/17/Citytimes
/Beyond_skin_deep.shtml