Reinventing biointegrated devices
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Citation
Ghaffari, Roozbeh, Benjamin L. Schlatka, Guive Balooch,
Yonggang Huang, and John A. Rogers. “Reinventing
biointegrated devices.” Materials Today 16, no. 5 (May 2013):
156-157. © 2013 Elsevier Ltd.
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http://dx.doi.org/10.1016/j.mattod.2013.05.001
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Elsevier B.V.
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http://hdl.handle.net/1721.1/81263
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Materials Today Volume 16, Number 5 May 2013
COMMENT
Comment
Roozbeh Ghaffari
MC10 Inc. & Massachusetts Institute of
Technology
rghaffari@mc10inc.com
Benjamin L. Schlatka
MC10 Inc.
Guive Balooch
L’Oreal Research and Innovation
Yonggang Huang
Northwestern University
John A. Rogers
University of Illinois at Urbana-Champaign
Reinventing
biointegrated devices
Roozbeh Ghaffari discusses siliconbased nanomaterials configured in
flexible and stretchable formats, and
their potential to rapidly transform
the medical landscape
The curved surfaces and complex geometries of the human body
create challenges in achieving soft conformal contact at the cellular scale with many existing classes of wearable health monitors,
surgical tools and minimally-invasive medical devices. This size
156
mismatch is pervasive in cardiology, where existing implantable
and cardiac ablation catheters contain several orders fewer microelectrodes than there are addressable cardiomyocytes, fibroblasts,
and smooth muscle cells in the heart. A similar tradeoff exists in
systems designed for a brain–computer interface (BCI). To date,
bio-integrated devices that interface with the curvilinear surface of
the brain have largely relied on arrays of rigid microelectrodes in
planar or needle-like configurations. Although successful for simple clinical practice, most conventional bio-integrated devices in
use today contain widely spaced electrodes (0.5–1 cm), are stiff
(gigapascal modulus levels for devices compared to megapascal
and kilopascal ranges for soft tissue), and thus are limited to
achieving poor interfacial contact at low spatial resolution. For
catheter mapping systems, in particular, the large millimeter-scale
size of electrodes leads to significant under-sampling of electrophysiological signals, thereby limiting the ability to identify
regions of disease.
A more powerful approach involves the fabrication of siliconbased integrated circuits, associated electronics and distributed
sensors in ultrathin formats onboard surgical and medical devices,
allowing for flexibility or even stretching [1–3]. Flexible/stretchable electronics, as this new class of systems has been referred to in
the research literature, exploit monocrystalline silicon (Si). These
Si-based electronics maintain the same high performance processing power of conventional silicon wafers to achieve multiplexing
at high sampling rates and high temporal resolution. However,
they also are processed to be strikingly soft and elastic compared to
conventional rigid/brittle Si wafers. Their high performance, relative to organic semiconductors, coupled with their extremely low
bending stiffness, therefore allows for a new class of biointegrated
devices to seamlessly laminate onto deformable biological tissues
for mapping electrical, mechanical, chemical and thermal properties at the cellular level [1].
Several important innovations in materials science underlie
these advances in emerging biointegrated devices. The first relies
on a dramatic reduction in the thickness profile of semiconductor
materials (e.g. Si nanoribbons) and interconnecting metals down
to the nanoscale (250 nm) via anisotropic wet and dry etching
techniques of silicon-on-insulator (SOI) wafers [1–4]. The second
depends on strategies to spatially configure discrete chiplets
of silicon and passive elements in distributed arrays based on
1369-7021/06/$ - see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mattod.2013.05.001
analytical and numerical modeling simulations [2]. Finally, these
distributed arrays of nanomaterials are embedded on unusual
substrates – deflectable catheters, elastic sheets, or bio-resorbable
protein layers through wet and dry surface treatment techniques
using transfer printing tools that facilitate strong adhesion
between two dissimilar surfaces. The end result is a new class of
bio-integrated devices containing ultrathin complementary metal
oxide semiconductor (CMOS) transistors, filters, amplifiers and
multiplexor circuits, matching the performance of conventional
wafer-based systems, but with extreme rubber band-like mechanical characteristics. These features are useful for cardiovascular and
neural applications, and may also fundamentally change the way
devices are designed and integrated on human skin for health
monitoring and point of care diagnostic applications [4].
In cardiac rhythm management, integration of high-density
electrodes containing platinum and gold interfacing metals, with
local amplifiers (for improved signal quality) and nearby multiplexing (to reduce the number of routed wires) provide routes to
map and treat (via cardiac ablation) complex arrhythmias, including persistent atrial fibrillation. The new devices born out of this
technology allow for much higher definition mapping of activation
patterns, with substantially less interpolation processing between
neighboring electrodes compared to conventional basket catheters with millimeter electrode spacing. Electrograms collected at
high sampling rates (2 kHz per electrode) and combined
spatiotemporally across 60–300 electrodes yield voltage
and isochronal activation maps, demonstrating the natural
COMMENT
electrophysiology of the heart, with very little to no interpolation
[1–3] and with little to no mechanical loading side effects. These
advances over conventional systems offer new ways to seamlessly
integrate with the heart and to clearly visualize complex arrhythmia patterns.
Much like the biointegrated systems constructed for the heart,
BCI devices that localize aberrant activity on the surface of the
brain have recently revealed important new insight into the
mechanisms underlying micro-seizures and epilepsy triggers
[2]. This technology is similar in form and implementation to
cardiac devices in the sheet-based design, but for BCI, the devices
have been specifically tuned to match the mechanical properties
and shape of the brain. The promise of new BCI devices is to
permit precise spatial localization of neurological disease triggers
in order to minimize excessive resection of brain matter during
therapy.
For skin-based and point-of-care health diagnostics, there are
many applications ranging from tracking heart rate and measuring
brain activity to hydration measurements from light-based assessment of bioanalytes in sweat secreted through skin pores. Skin
based systems also have brought to the forefront ultrathin, flexible
antenna designs and stretchable batteries to power such systems
during continuous and/or intermittent use [4,5].
Advances in biointegrated devices described in this comment
highlight important innovations in semiconductor and polymer
fabrication processes that were once limited to the microchip and
computer industries. New mechanics optimization and integration strategies for distributed nanosensors, actuators and flexible/
stretchable electronics onboard existing medical device platforms
have led to new breakthroughs in translational medicine. Despite
the necessary clinical trials being pursued to assure biocompatibility and overall safety, it is apparent from the number of clinical
applications underway in cardiac, neural, and health monitoring
applications that systems containing active electronics mounted
on sheets and catheters will bring forth new generations of devices
in many areas of healthcare over the next decade.
Further reading
[1]
[2]
[3]
[4]
[5]
D.H. Kim, et al. Proc. Natl. Acad. Sci. U. S. A. 109 (49) (2012) 19910–19915.
D.H. Kim, et al. Annu. Rev. Biomed. Eng. 14 (2012) 113–128.
J. Viventi, et al. Sci. Transl. Med. 2 (2010) 24ra22.
D.H. Kim, et al. Science 333 (2011) 838–843.
S. Xu, et al. Nature Commun. (2013), http://dx.doi.org/10.1038/ncomms2553.
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Materials Today Volume 16, Number 5 May 2013