Page 376 - Handbook of Biomechatronics

370 Lilach Bareket et al.

serving as return (Suaning et al., 2004). So far early versions of this device
with 14 channels in one layer were examined through acute stimulation
of arrays implanted in the suprachoroidal space in the eyes of cats (Wong
et al., 2008, 2009; Matteucci et al., 2013; Barriga-Rivera et al., 2016b,
2017) and sheep (Barriga-Rivera et al., 2015). Several stimulation paradigms
including monopolar, bipolar and hexapolar stimulation (Wong et al., 2009;
Habib et al., 2013; Matteucci et al., 2013, 2016), and the efficacy of new
array designs were examined (Barriga-Rivera et al., 2015, 2016a).
A nonactive Phoenix99 device has been chronically implanted in sheep
(manuscript in preparation).
The suprachoroidal system developed by the Korean group is based on
implementation of LCP films as means to achieve a miniaturized, integrated,
and entirely intraocular monolithic device (Jeong et al., 2012, 2016). Com-
pared with biopolymers such as PI, parylene, and PDMS, LCP films have
superior resistance to penetration of water and ions, potentially contributing
longevity of the implant (Jeong et al., 2012; Gwon et al., 2016). In addition,
there is no need to use adhesives as the films can be laminated to each other
by fusion bonding (combination of heat and pressure) (Lee et al., 2011).
Photolithography was used to define the electrode pattern and gold elec-
trodes were deposited via sputtering. Next, lamination of the LCP substrate
and precut cover layers was conducted via thermal-press bonding (Lee et al.,
2009). The researchers further suggested to overcome the fact that commer-
cially available LCP films are stiffer compared with PI, PDMS, and parylene
materials, by adapting a conformable fabrication scheme in which the LCP-
based device is molded into a curved shape to fit the eyeball through a
thermo-forming process (Jeong et al., 2012; Gwon et al., 2016).
The investigators were able to record cortical potentials in response to
electrical stimulation applied to the retina of rabbits via LCP-based arrays
with 8–16 channels (acute experiments) (Jeong et al., 2015; Lee et al.,
2009). OCT imaging and histological analysis, during 3–4 months post-
surgery, further confirm no adverse immune effects for the duration of
the study (up to 2.5 years and 4 months, respectively) (Lee et al., 2009;
Jeong et al., 2015, 2016). Later, an entire LCP packaged retinal implant
including a 16-electrode array (IrOx/Au), telemetry coils, and stimulator
circuitry was realized (Jeong et al., 2016). Further, extensive efforts are being
invested by the group to investigate the long-term reliability of LCP-based
retinal implants, and customize the fabrication process accordingly (Jeong
et al., 2011, 2016; Lee et al., 2009, 2011).