Medical Design Briefs - March 2024 - 31

cy, tissue can be processed faster, and
also more selectively, such as to protect
blood vessels in the surrounding area.
When working on soft tissue, such as
muscles, the targeted generation of
ultrasonic waves allows the blades of a
scalpel to oscillate in a defined manner
at very high frequencies.
Targeted heat generation - due
to friction between the tissue and
the surgical instrument - facilitates
rapid cutting of tissue with simultaneous
coagulation (see Figure 1),
which prevents severe bleeding and
promotes hemostasis. By applying
high energy densities at the surgical
instrument's point of contact, cutting
processes during surgery or biopsy are
significantly easier as lower mechanical
forces and pressure are required.
As a result, surgical incisions can be
made smaller and with less trauma to
the surrounding tissue. This results in
reduced postoperative pain as well as
shorter wound healing and thus improved
patient recovery.
Furthermore, ultrasonic instruments
can be used to gently break up hard concretions,
such as tartar or kidney stones,
with the aid of cavitation and the force of
acoustic waves. Soft tissue structures can
also be liquefied and suctioned in a targeted
and minimally invasive manner, like
during cataract operations (phacoemulsification)
or wound debridement.
Ultrasonic handpieces of this kind,
which are based on piezoceramics, are
generally referred to as scalers. Modern
scalers consist of a tool and typically
include additional functions, such as
a light, cooling water, gas supply and
suction, which can be integrated into
the handpiece and optionally switched
on and off as required. Typical applications
for ultrasonic scalers include:
* Ultrasonic scalpels and tissue sealing
tools, for example in vascular surgery
for coagulation.
* Laparoscopic ultrasonic dissection.
* Bone drills and saws, as used in orthopedics
and maxillofacial surgery.
* Tartar removal.
* Intracorporeal stone disruption.
* Ophthalmic phacoemulsification
* Ultrasound-assisted wound debridement.
For medical procedures in which hard
tissue is processed on a larger scale, rotary
tools (such as spiral drills) are used
as an alternative. To enable faster tissue
removal and reduce trauma to the surMedical
Design Briefs, March 2024
Ultrasonic handpiece for soft tissue dissection and coagulation. (Credit: Physik Instrumente)
Driver
Booster
Sonotrode
Fig. 1 - Structure of a scaler, consisting of the three components - piezoelectric driver, booster and
sonotrode.
Driver
Booster
Fig. 2 - Position of nodes and amplitudes of ultrasonic waves in a scaler.
rounding tissue, these tools can also be
supported with ultrasound.
General Structure
A scaler is a handheld, modular ultrasonic
transducer. Scalers usually consist
of a driver, a booster and a sonotrode
(see Figure 1). The driver, also called
the converter, generates ultrasonic
waves and usually consists of two or four
piezoceramic rings that are screwed towww.medicaldesignbriefs.com
gether.
To prevent overheating during
operation of the handpiece, low-loss
piezoelectric materials with a high mechanical
grade are used, e.g., PIC144,
PIC184, or PIC181. These constitute the
group of " hard " piezoceramics that are
particularly suitable for high-power ultrasonic
applications.
The booster serves both as a mechanical
amplifier and as a suspension mounting.
The gain value results from the
31
Sonotrode

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Medical Design Briefs - March 2024

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