Bioinert

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Ceramic Biomaterials (Bioceramics)
Bioinert a. Alumina (Al2O3) femoral ball, cap
(sometimes) harder vs. zirconia b. Zirconia
(ZrO2) femoral ball (sometimes) c. Pyrolitic
carbon (PyC) heart valve leaflets allotrope of
C Egraphite _______,
EPyC _________ Excellent
blood-compatibility Bioactive Glass
amorphous Glass-Ceramic polycrystalline
material formed as a glass and then crystallized
via heat treatment 3 Key Compositional
Components (in general) for Bioactivity 1.
SiO2 lt 60 2. High CaO NaO content 3. High
CaO/P2O5 Examples Carbonated hydroxy apatite
(HCA) Ca10(PO4)6(OH)2 Bioglass
45S5 Ceravital
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Some Allotropes of Carbon
graphite
diamond
C60 Buckyball
Pyrolytic carbon (PyC)
carbon nanotube
Montreals 1067 Expo American pavilion at night
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Terminology
Prosthesis artificial substitute for missing
body part Exoprosthesis exists outside of the
body Endoprosthesis exists inside the body
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• Heart Valves
• Maintains uni-directional flow of blood by
  opening and closing, depending on the
  differences in pressure on each side.
• History of Heart Valves
• Biological Heart Valves or Bioprotheses
• (made of biological tissues)
• - First were homo- or allografts
• - transplanted from another patient (cadaver)
• - poor durability
• - immune response
• - low availability
• - Next, hetero- or xenografts
• - Introduced in 1965
• - transplanted from another species
• - typically pig (porcine) or bovine
• - tissue is treated with _________________ ?
  __________________ ? stabilizes tissue ?
  increased ________________

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Heart Valve Maintains uni-directional flow of
blood by opening and closing, depending on the
differences in pressure on each side.
Xenotransplant Porcine heart valve
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• Carpentier-Edwards Valve (Baxter Health Care)
• STENT
• The wire is bent to form three U-shaped prongs.
• Provides support to preserve the valve in the
  natural shape and achieve normal opening and
  closing.
• - Co-Ni alloy
• SEWING RING A Dacron or Gortex cloth sewing
  skirt is attached to the base of the wire stent,
  and then the stents themselves are also covered
  with cloth. Porcine valves have good durability
  and usually last for ten to fifteen years.
• b. Hancock Valve (Medtronic)
• STENT PP and Co-Cr alloy insert
• SEWING RING Dacron
• Properties of Biological vs. Mechanical Heart
  Valve
• Less prone to _________________
• More prone to calcification
• _________________________ (tear)
• more prone to structural deterioration (40 fail
  in 10 years)

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• Mechanical heart valves
• Implant
• a foreign or synthetic material is introduced
• Chemical Vapor Deposition in a fluidized bed (see
  slide)
• Used to make PyC-coated graphite leaflets
• chemical vapor deposition in a fluidized bed
  vertical tube containing a fine dispersion of
  refractory (high melting T) particles as well
  as the graphite parts which are levitated using
  an inert gas carrier (N2 or He)
• Early 1960s
• Vincent L. Gott (surgeon) and Jack Bokros
  (General Atomic Co)
• Ultra low temperature isotropic (ULTI) carbon
  deposited onto polymeric vascular grafts

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Graphite Heart Valves Coating with PyC-SiC

• Chemical vapor deposition in a fluidized bed
  vertical tube containing a fine dispersion of
  refractory (high melting T) particles (PyC and
  SiC) as well as the graphite parts which are
  levitated using an inert gas carrier (N2 or He)
• Silicon (up to 4-12 wt) is added to improve
  mechanical properties such as stiffness,
  hardness, and wear resistance, but with some
  _______________________________.

• Vertical tube heating coils Temp 1000 to 2400
  ?C
• Feed in hydrocarbon, silane carbide, and inert
  gases
• Graphite parts and refractory particles levitate
• Pyrolysis occurs and PyC containing SiC
  inclusions are deposited onto graphite parts
  (chemical vapor deposition)
• Can add W (tungsten) (up to 20 wt) to visualize
  in vivo

Heating coil
Graphite parts and bed particles float in gas
stream
inert gas (N2, He)
hydrocarbon gas
SiC gas
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Mechanical Heart Valves

• 1961 Starr-Edwards caged-ball
• cage Haynes 21 (Co-Cr-Mo)
• ball Silastic (crosslinked PDMS or silicone
  rubber)
• sewing ring silicone rubber inset under Dacron
  (PET) or Gortex (e-PTFE)
• --durable, flow pressure issues
• e. Late 1960s Tilting disc
• sewing ring Gortex
• disc polyacetal (Derlin) --durable, but can
  swell
• disc replaced with PyC-SiC alloy coated
  graphite disc
• -more flexible discs made of UHMWPE
• struts Ti-6Al-4V or Haynes 25 (Co-Cr-W-Ni), 21

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Mechanical Heart Valves

• 1977 St. Jude Bileaflet
• leaflets PyC-SiC alloy deposited onto graphite
  substrate
• ring Ti-6Al-4V (ASTM F136) coated with PyC
  (often pure PyC)
• sewing ring Dacron (PET) or Gortex (ePTFE)

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Vascular Graft tube which replaces/bypasses
part of a vessel (usually an artery) when it is
restricted/weakened due to disease or injury.
Manufactured by weaving or knitting multifilament
texturized polymeric yarns Dacron and Gortex.
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AUTOGRAFT
Introduced 1949
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a. Dacron Graft Poly(ethylene terephthalate)
(PET)
Woven
Knitted
Fewer leaks More rigid, difficult to
handle In-growth of new tissue prevented
First infuse with patients blood More flexible
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b. GORE-TEX Graft ePTFE (expanded
poly(tetrafluoroethylene)
PTFE is rapidly stretch to create a strong
microporous material known as expanded PTFE, or
ePTFE.
Woven ePTFE fibers