Parylene photonics enable future optical biointerfaces

Date:
September 22, 2020
Source:
College of Engineering, Carnegie Mellon University
Summary:
Scientists have invented an optical platform that will likely
become the new standard in optical biointerfaces. They labeled
this new field of optical technology 'Parylene photonics.'


FULL STORY ========================================================================== Carnegie Mellon University's Maysam Chamanzar and his team have invented
an optical platform that will likely become the new standard in optical biointerfaces. He's labeled this new field of optical technology "Parylene photonics," demonstrated in a recent paper in Nature Microsystems and Nanoengineering.


========================================================================== There is a growing and unfulfilled demand for optical systems for
biomedical applications. Miniaturized and flexible optical tools
are needed to enable reliable ambulatory and on-demand imaging and
manipulation of biological events in the body. Integrated photonic
technology has mainly evolved around developing devices for optical communications. The advent of silicon photonics was a turning point in
bringing optical functionalities to the small form- factor of a chip.

Research in this field boomed in the past couple of decades. However,
silicon is a dangerously rigid material for interacting with soft tissue
in biomedical applications. This increases the risk for patients to
undergo tissue damage and scarring, especially due to the undulation
of soft tissue against the inflexible device caused by respiration and
other processes.

Chamanzar, an Assistant Professor of Electrical and Computer Engineering
(ECE) and Biomedical Engineering, saw the pressing need for an optical
platform tailored to biointerfaces with both optical capability and flexibility. His solution, Parylene photonics, is the first biocompatible
and fully flexible integrated photonic platform ever made.

To create this new photonic material class, Chamanzar's lab designed ultracompact optical waveguides by fabricating silicone (PDMS), an
organic polymer with a low refractive index, around a core of Parylene C,
a polymer with a much higher refractive index. The contrast in refractive
index allows the waveguide to pipe light effectively, while the materials themselves remain extremely pliant. The result is a platform that is
flexible, can operate over a broad spectrum of light, and is just 10
microns thick -- about 1/10 the thickness of a human hair.

"We were using Parylene C as a biocompatible insulation coating for
electrical implantable devices, when I noticed that this polymer is
optically transparent.

I became curious about its optical properties and did some basic
measurements," said Chamanzar. "I found that Parylene C has exceptional
optical properties.

This was the onset of thinking about Parylene photonics as a new research direction." Chamanzar's design was created with neural stimulation
in mind, allowing for targeted stimulation and monitoring of specific
neurons within the brain.

Crucial to this, is the creation of 45-degree embedded micromirrors. While prior optical biointerfaces have stimulated a large swath of the brain
tissue beyond what could be measured, these micromirrors create a tight
overlap between the volume being stimulated and the volume recorded. These micromirrors also enable integration of external light sources with the Parylene waveguides.



==========================================================================
ECE alumna Maya Lassiter (MS, '19), who was involved in the project,
said, "Optical packaging is an interesting problem to solve because the
best solutions need to be practical. We were able to package our Parylene photonic waveguides with discrete light sources using accessible packaging methods, to realize a compact device." The applications for Parylene
photonics range far beyond optical neural stimulation, and could one
day replace current technologies in virtually every area of optical biointerfaces. These tiny flexible optical devices can be inserted
into the tissue for short-term imaging or manipulation. They can also
be used as permanent implantable devices for long-term monitoring and therapeutic interventions.

Additionally, Chamanzar and his team are considering possible uses in wearables. Parylene photonic devices placed on the skin could be used to conform to difficult areas of the body and measure pulse rate, oxygen saturation, blood flow, cancer biomarkers, and other biometrics. As
further options for optical therapeutics are explored, such as laser
treatment for cancer cells, the applications for a more versatile optical biointerface will only continue to grow.

"The high index contrast between Parylene C and PDMS enables a low
bend loss," said ECE Ph.D. candidate Jay Reddy, who has been working on
this project.

"These devices retain 90% efficiency as they are tightly bent down to
a radius of almost half a millimeter, conforming tightly to anatomical
features such as the cochlea and nerve bundles." Another unconventional possibility for Parylene photonics is actually in communication links,
bringing Chamanzar's whole pursuit full circle. Current chip-to-chip interconnects usually use rather inflexible optical fibers, and any area
in which flexibility is needed requires transferring the signals to
the electrical domain, which significantly limits bandwidth. Flexible
Parylene photonic cables, however, provide a promising high bandwidth
solution that could replace both types of optical interconnects and
enable advances in optical interconnect design.

"So far, we have demonstrated low-loss, fully flexible Parylene
photonic waveguides with embedded micromirrors that enable input/output
light coupling over a broad range of optical wavelengths," said
Chamanzar. "In the future, other optical devices such as microresonators
and interferometers can also be implemented in this platform to enable a
whole gamut of new applications." With Chamanzar's recent publication
marking the debut of Parylene photonics, it's impossible to say just
how far reaching the effects of this technology could be. However, the implications of this work are more than likely to mark a new chapter
in the development of optical biointerfaces, similar to what silicon
photonics enabled in optical communications and processing.


========================================================================== Story Source: Materials provided by College_of_Engineering,_Carnegie_Mellon_University.

Original written by Dan Carroll. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Jay W. Reddy, Maya Lassiter, Maysamreza Chamanzar. Parylene
photonics: a
flexible, broadband optical waveguide platform with integrated
micromirrors for biointerfaces. Microsystems & Nanoengineering,
2020; 6 (1) DOI: 10.1038/s41378-020-00186-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200922172525.htm

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