High-Frequency
Vibration Driven Cutting
with Biological
Inspiration for Minimally Invasive Surgery
Abstract
Minimally Invasive
Surgery has become more and more important in the medical application. It
reduces the
operation danger
and also the ache of patient. In this process the small surgical utensils will
be inserted
through natural
pathways to the operation site, or one mobile micro robot moves firstly through
to make one
hole to the
operation site for the following action.
For the minimally
invasive surgery different working methods have been reported. Many use
electrically driven
cutter to execute
operation. Electrical energy brings ease, but although well protected, it is
still one great
danger for the
safety, especially for the operations at where nerves are densely located, for
example in spinal
disc surgery. For
this type of surgery, surgical utensils driven with high-frequency vibration are
much more
safer. There are
no sudden changes of effect at organism for vibrations with frequency below
40kHz.
The cutting
behavior of leaf-cutting ants makes use of high-frequency vibration produced
with an special
organ. When
harvesting fresh vegetation, leaf-cutting ants anchor with their hind legs on
the leaf edge and
rotate using the
legs as a pivot. During cutting, ants produce high-frequency vibrations that led
their
mandibles to
vibrate at about 1 kHz, with an amplitude of about 1 µm, a process that
mechanically facilitates
the cutting of the
leaf tissue. This method is especially suited for cutting tender leaves, and
ants have been
observed to reach
a cutting speed of 0.22mm/s [1].
The work in this
paper deals with transferring high-frequency vibration energy, or ultrasonic
energy with
conductor to the
operation site. Ultrasonic lithotriptor made of steel has been previously used
for the removal
of ureteric stones
[2]. But it will be difficult for solid conductor to transfer energy through
bends with high
curvature. Fluid
metal as the conductor for vibration was investigated.
Galinstan is one product of Geratherm [3]. It is one
mixture of Gallium, Indium and Titan, and has a melting
point of -20°C. At normal body and room temperature it
is in fluid state. It has the Density of 6,44g/cm⁄. And
with
Echo-Pulse-Method the propagation velocity of longitudinal sound wave has been
measured to amount
about 2950 m/s.
Thus it has an acoustic impedance of about 18.9´10 kg/(m◊s), which fits well
with the
acoustic impedance
of vibrator made of Titan (acoustic impedance 18,7´10 kg/(m◊s)). And it has also
low
absorption factor
of 20cm/20dB. Furthermore this material is harmless to the health.
For energy
transferring, fluid metal, Galinstan, was
filled in Teflon-tube with inner diameter of 0.7mm. At
proximal end the
tube was connected with vibrator. At distal end one small piston was stuck in
the tube. The
Teflon-tube bounds
the sound wave, and the vibration is transferred through Galinstan to drive the piston
reciprocating. The
tube could be bent with high curvature. Still there was no great energy output
loss at
piston. Two
methods of energy coupling between Galinstan
and vibrator and test results will also be
presented.
[1] J. Tautz, F.
Roces and B. Hölldobler: Use of a Sound-Based Vibratome by Leaf-Cutting Ants;
Science,
Vol 267,
6.January 1995, pp84-87.
[2] U. Stumpff:
Die Erzeugung und Übertragung von Ultraschalldehnwellen hoher Energiedichte in
flexiblen
Wellenleitern im
20 kHz-Bereich für therapeutische Anwendungen. Dissertation, 1978, RWTH
Aachen.
[3] Geratherm
GmbH Sicherheitsdatenblatt nach 93/112/EG, 1998, D-98716 Geschwenda
1147
Biomedical:
Biomedical