Medical Design Briefs - December 2022 - 29

scribe their new GRIN lens, which they
incorporated into an endoscopy probe.
Experiments showed that the probe's
imaging properties are maintained even
when it is bent.
" The bendable nature of these GRIN
probes makes measurements in living
subjects, such as animals or human patients,
much more streamlined and practical, "
says Liu. " It could be useful for
precise, minimally invasive microscopyguided
placement of needles and catheters
for tissue biopsies and tumor ablation,
for example. "
n Imaging Through a Bent Lens
GRIN lenses are silica glass rods with
a continuously changing refractive index
that focuses light coming through
the rod without requiring a separate
focusing lens. Since their development
about 50 years ago, it has been generally
thought that GRIN lenses can only
be used as rigid imaging probes. In the
new work, the researchers challenged
this notion by finding out whether it
was possible to image through a bent
GRIN lens.
The researchers custom-designed a
GRIN lens 500 ┬Ám in diameter and
about 100 mm long. The lens' long,
thin shape and its lack of a rigid outer
casing gives it the flexibility to bend
about 10 degrees without breaking.
They then incorporated the new
GRIN lens into an endoscopic imaging
probe and tested it by performing
two-photon 3D fluorescence imaging
through it.
To simulate the real-world bending
that would be experienced deep inside
tissues, the lens was positioned vertically
and pushed to introduce the type of
beam deflection that would be experienced
if the probe was used in the working
channel of a needle used for a biopsy.
The experiment showed that the resolution
and signal level did not obviously
deteriorate when one end of the probe
was displaced laterally by 6 mm.
" When the lens is bent, the signal
lanes that carry the image through the
rod synergistically adapt by laterally shifting,
much like a car tends to shift toward
the outside of a slippery curved road, "
says Liu. " While the signal lanes distort a
bit while shifting, they largely keep their
properties such as order and shape. This
allows most of the resolution and signal
level to be retained. "
Medical Design Briefs, December 2022
Bendable
GRIN lens
The new GRIN-based endoscope is being used with an implantable microdevice designed to quickly
evaluate the effectiveness of various cancer therapies. (Credit: Guigen Liu, Harvard Medical School
and Brigham and Women's Hospital)
n A New Way to Screen
Cancer Drugs
Although further development and
testing would be needed to bring the
endoscope into the clinic, the device is
already finding applications in biomedical
research. Team lead and co-author
Oliver Jonas and colleagues are pairing
the endoscope with a new type of microdevice
to test a method for quickly evaluating
the effectiveness of various cancer
therapies.
The team's new microdevices are designed
to be implanted directly into a
tumor and carry small amounts of up to
20 drugs. To measure the effectiveness of
the various drugs without removing any
tumor tissue, the researchers insert a
GRIN-based endoscope directly into the
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microdevice where it can be used to image
fluorescence signals inside the tumor.
Although this setup is currently being
studied in mice, it could eventually
be used in patients to quickly figure out
which treatment options are best for
fighting each patient's specific tumor.
To move the probes toward clinical application,
the researchers are also working
to develop longer bendable GRIN
lenses to allow deeper imaging and more
flexibility. They also want to enhance the
mechanical durability of the optical
components using a thin polymer coating
that won't affect flexibility.
For more information, visit www.optica.
org. Contact: Guigen Liu, PhD, Harvard
Medical School and Brigham and Women's
Hospital, gliu19@bwh.harvard.edu.
29
Microdevice
3D image
http://www.optica http://www.medicaldesignbriefs.com

Medical Design Briefs - December 2022

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Medical Design Briefs - December 2022 - COV1A
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