Biomedical Engineering Reference
In-Depth Information
and the biological solder. However, selection of the best agents is not easy.
In the proposed studies, graphite was utilized, because of its limitations
as a biocompatible or biodegradable material, and because it is cheap and easy
to use.
For these initial experiments different concentrations of albumin were first
tested. The results showed that as the concentration of albumin increased, the
microwave time required to cause coagulation decreased. The coagulation,
similar to that of egg whites could be easily observed. One disadvantage of a
high albumin concentration is that the biological solder becomes a thick paste.
This thick paste is hard to apply to an artery. Thus, for practical reasons, we
used a 40% albumin solution for the remainder of our experiments.
We then examined two different doping materials: graphite and ferric oxide.
We tested the time required to coagulate the biological solder with different
concentrations of graphite and ferric oxide added to the solution. Adding
either graphite or ferric oxide greatly decreased the time to coagulation;
however, this effect was not linear. The biggest changes occurred with the
addition of small concentrations of graphite or ferric oxide. Higher concen-
trations had less effect on shortening the coagulation time further. Thus, we
selected a 1-2% concentration of graphite or ferric oxide for the rest of the
experiments.
We also measured the temperature in the biological solder. The solder was
placed on the outside of the artery, and the microwave antenna/catheter was
placed within the artery. A thermocouple was placed in the biological solder.
The thermocouple was positioned perpendicular to the microwave antenna to
prevent interference. A number of power settings and times were examined.
The temperature of the solder rose quickly when the microwave energy was
applied. In several initial studies, we noticed that the artery was getting warm.
Thus, we started to infuse deionized, distilled water through the artery while
applying the microwave energy. We also redesigned our antenna/catheter
system so that the microwave energy only radiated in one direction. These
simple procedures kept the artery cool.
In Vitro Vessel Anastomosis
Canine carotid arteries were anastomosed end
to end with microwaves using 40% albumin and 1% ferric oxide as solder. The
tear strength of microwave anastomosis compared was to the hand-sewing
anastomosis. The tear strength of the microwave anastomosis was 954
±
132 g
152 g for the hand-sewn anastomosis. There were problems,
however: While we were able to create strong anastomoses in vitro with this
approach, the volume of material that was needed to surround and secure the
artery anastomoses would likely generate significant inflammatory responses
in vivo. Thus, we abandoned this approach.
We then hypothesized that by placing the vessels side by side, we could in
effect create an end-to-end anastomosis. This approach would provide the
needed large surface area for anastomosis strength without use of the extra
material. This anastomosis approach is depicted in Figures 6.25 and 6.26.
versus 795
±
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