Biomedical Engineering Reference
In-Depth Information
A
Table 3.2.11-2 Surface finish (R
a
, average, and R
q
, root mean
square) of pyrolytic carbon heat valve components
a
Specimen
R
a
(nm)
R
q
(nm)
Comments
Glass microscope
slide
17.14
26.80
On-X leaflet
33.95
42.12
Clinical
Sorin Bicarbon
leaflet
40.12
50.63
Nonclinical
SJM leaflet
49.71
62.74
Clinical
CMI (SJM)
leaflet
67.98
85.56
Nonclinical
Sorin Monoleaflet
99.59
128.10
Clinical
B
DeBakey-Surgitool
ball
129.78
157.93
Nonclinical
As-coated slab
389.07
503.72
a
Components/prepared by: On-X/Medical Carbon Research Institute, Austin, TX;
Sorin/Sorin Biomedica, Saluggia, Italy; SJM/Saint Jude Medical, Saint Paul, MN;
CMI (SJM)/CarboMedics, Austin, TX; DeBakey-S/CarboMedics, San Diego (circa
1968). ''Clinical'' was from as-packaged valve; ''nonclinical'' lacks component
traceability.
eliminate components with subsurface flaws. With the
advent of bed size control, which allows coating to exact
final dimensions, the concerns about flaws introduced
during the machining and grinding operation have been
eliminated.
The polished and inspected components, thus pre-
pared, are now ready for assembly into devices, or are
packaged and sterilized in the case of stand-alone devices.
Shown in
Fig. 3.2.11-9
are the three pyrolytic carbon
components for a bileaflet mechanical heart valve. The
Fig. 3.2.11-8 Scanning electron microscope micrographs of
(A) as-coated and (B) as-polished surfaces.
and Haubold, 1996), the surfaces of polished pyrolytic
carbon (30-50 nm) are an order of magnitude smoother
than the as-deposited surfaces (300-500 nm).
Once the desired surface quality is achieved, compo-
nents are again inspected. The final component in-
spection may include measurement of dimensions, X-ray
inspection in two orientations to verify coating thickness,
and visual inspection for surface quality and flaws. In
many cases, automated inspection methods with com-
puter-controlled coordinate measurement machines are
used. X-ray inspection can be used to ensure that mini-
mum coating thickness requirements are met. Two or-
thogonal views ensure that machining and grinding of the
coating was achieved uniformly and that the coating is
symmetrical. The machining and grinding operation after
coating is not without the risk of inducing cracks or flaws
in the coating, which may subsequently affect the service
life of the component. Such surface flaws are detected
visually or with the aid of dye-penetrant techniques.
Components may also be proof-tested to detect and
Fig. 3.2.11-9 Components for On-X bileaflet heart valve.
