Medical Design Briefs - August 2024 - 11

Fig. 4 - Piezoelectric hemispheres or focus
bowls for therapeutic ultrasound. (Credit: PI)
Targeted Drug Delivery with Sound Waves
Ultrasound makes the targeted release or activation of
drugs at a specific location in the body possible. Various
mechanisms are suitable. The basic method is the injection of
microspheres filled with medication or gas, which are distributed
in the patient's bloodstream during treatment and can
only be used where they are in the sound field focus. An unstable
cavitation generated by ultrasound causes the microspheres
to burst in a targeted way. If the small spheres are
filled with drugs, active substances can be released locally in
the body directly at their destination.
In order to increase the uptake of therapeutic substances in
specific tissues, gas-filled microspheres can be injected. The stable
oscillation of these microspheres, which is generated using
ultrasound, produces micro streams, which in combination
with the mechanical energy of the acoustic waves, increase the
permeability, for example, of the blood vessel walls for the active
substance in the blood. This mechanism is called sonoporation,
and is used, for example, in the reversible opening of
the blood-brain barrier, a process that can improve the medical
therapy of neurodegenerative diseases such as Parkinson's or
Alzheimer's significantly.
In sonodynamic therapy, focused ultrasound waves induce
the formation of reactive oxygen species (ROS) which act cytotoxically
on cells, such as, in cancer tumors.
Intravascular Therapy with Piezo Components
An intravascular application of ultrasound is used in a minimally
invasive way to reduce atherosclerotic plaques in blood vessels
or at the heart valves as well as with life-threatening vascular constrictions
(stenosis). In intravascular lithotripsy, ultrasound waves
increase the permeability of the blood vessel wall (sonoporation)
allowing the medication to more easily penetrate and induce the
dissolution of plaques. If a blood clot (thrombus) has already
formed, its structure can be loosened with the help of mechanical
ultrasound energy. Drugs can then more easily penetrate the
thrombus and dissolve it. In this way, the flow of blood to vital
organs is ensured and embolisms are prevented.
Medical Design Briefs, August 2024
Why Piezoelectric Transducers?
Generating and detecting ultrasound is a classic piezo application
of piezoelectric transducers. When an AC voltage is
applied, the piezo elements start to oscillate at the frequency
used. Ultrasound generation benefits from the short response
times and the high dynamics of this motion. Piezo elements
(see Figure 4) are suitable for various ultrasound applications
- especially in power ultrasound since they generate considerable
power densities of up to several kW/cm², which can be
Target
organ
Target
lesion
Fig. 5 - HIFU transducer with fixed ultrasound focus. (Credit: PI)
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Medical Design Briefs - August 2024

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