Medical Design Briefs - March 2023 - 37

and Japan-based ENEOS Corporation,
was published in the journal Advanced
Physics Research.
When ferroelectric materials are subjected
to an electric field, charge separation
(polarization) occurs. However, unlike
conventional paraelectric materials,
ferroelectrics retain their polarization
even after the removal of the electric
field, enabling them to maintain a high
number of accumulated charges at a low
voltage. Furthermore, since the polarization
of ferroelectric materials is independent
of the voltage, the generated force
is linearly proportional to the applied
voltage (see Figure 1).
" Ferroelectric media are superior to
ordinary paraelectric media for use in
electrostatic actuators in two respects.
One is that they can generate a higher
force by maintaining a large polarization
even at low voltage, and the other is that
their voltage response is almost linear,
resulting in good device controllability, "
says Prof. Nishimura.
The researchers used liquid crystals in
the special nematic phase (i.e., a phase
where the long axes of molecules are arranged
in parallel lines but not layers) as
a ferroelectric material. The material
was found to be able to flow like a liquid
at room temperature while possessing a
rod-shaped molecular structure like that
of solid crystals - necessary characteristics
that give these materials a large dipole
moment (i.e., magnitude of polarization)
and the fluidity required for
their use in artificial muscles.
In tests, the ferroelectric liquid crystal
was found to generate forces across electrodes
that were 1,200 times higher than
that of conventional paraelectric materials
such as insulating oils. With the ferroelectric
liquid crystals and a 3D printed
double-helical coil electrode, the researchers
developed an electrostatic actuator
capable of producing contraction
and expansion - like muscles would -
at low voltages (see Figure 2).
" When we applied an electric field of
0.25 MV m-1
, the device contracted by 6.3
mm, which is about 19 percent of its
original length, " says Prof. Nishimura.
" Visual observation showed that the device
moves when a voltage of 20 V is applied.
This means that even a dry cell
battery can power the present actuator. "
These findings demonstrate that ferroelectric
materials with spontaneous
polarization are promising for developing
electrostatic actuators suitable for
artificial muscles. The researchers are
now planning to optimize the viscoelasticity
of the liquid crystal material to further
improve the operation of the electrostatic
actuator.
For more information, visit www.
titech.ac.jp. Contact: Suzushi Nishimura,
nishimura.s.ai@m.titech.ac.jp.
The Promise of Mobile Photoacoustic Imaging
Mobile flexibility is helping
to advance medical
treatment.
OPOTEK
Carlsbad, CA
Preclinical laboratories at academic
facilities and contract research organizations
(CROs) have traditionally relied
on five main imaging modalities: optical,
acoustic, x-ray, MRI, and nuclear. Now,
photoacoustic imaging, which combines
optical and acoustic modalities, is enabling
some of the most promising medical
research, including providing images
of biological structures for increased visibility
during surgery and facilitating the
analysis of plaque composition to better
diagnose and treat coronary artery disease
(CAD).
With photoacoustic medical imaging,
nanosecond lasers
deliver
about the function of examined tissues
as well.
However, despite its promise, preclinical
researchers were limited to utilizing
large, fixed benchtop systems mounted
to immovable laser tables. Now, compact,
mobile photoacoustic platforms
are available and ready for use in preclinical
and clinical environments, including
commercial hospital settings.
Like an ultrasound machine, mobile
photoacoustic systems could be transported
to patient bedsides or to surgical
suites to render extremely detailed diagnostic
imaging tests for cardiovascular
diseases, cancer, chronic respiratory diseases,
and diabetes.
n Photoacoustic Systems for
Biomedical Imaging
light
pulses to specific biological tissues.
The laser's energy is absorbed and
converted into heat, which generates
an ultrasonic (sound) wave that can be
detected by a transducer and processed
to form an image. Due to the varied response
of components in biological tissue
based on user-defined laser parameters,
images can include information
Medical Design Briefs, March 2023
Although photoacoustic imaging
equipment has been available for a
few decades, the primary limiter to its
use has been the largest component in
the system, the nanosecond laser used
to transmit a pulse of laser light to the
area of interest. These lasers, which are
available in a wide range of wavelengths,
pulse energies, and repetition rates, generate
high peak powers and short pulse
widths, making them ideal for many
photoacoustic applications.
www.medicaldesignbriefs.com
However, fixed nanosecond wavelength
lasers like the Nd:YAG often
operate outside the ideal wavelengths
required to reach a usable depth in biological
tissue. These wavelengths are
usually within the water absorption
transparency window of 650 to 900 nm,
given that animals and humans are mostly
made of water.
For this reason, pulsed mode Nd:YAGs
that emit light at a fixed wavelength of
1064 nm require optical parametric oscillators
(OPO) to convert the Nd:YAG
fundamental wavelength to the optimal
frequency for photoacoustic diagnostic
analysis. These OPO lasers are generally
referred to as tunable lasers.
To enable required laser tunability,
manufacturers like Carlsbad, CA-based
OPOTEK have developed fast-tuning
technology that ensures that many wavelengths
can easily be produced to image
a variety of biological materials. Fast tuning
also helps to mitigate variations in
the field of view due to motion between
consecutive images, which allows for
more detailed imaging of moving biological
processes like blood flow.
OPOTEK, LLC, a global manufacturer
of tunable lasers for research and diagnostics,
offers solutions for specialized
applications including photoacoustic,
37
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Medical Design Briefs - March 2023

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