Flexible high-aspect-ratio microneedles penetrating brain tissue.
Credit:
(c) Toyohashi University Of Technology
(August 10, 2015)
Microscale needle-electrode array technology has enhanced brain science
and engineering applications, such as electrophysiological studies, drug and
chemical delivery systems, and optogenetics.
However, one challenge is reducing the tissue/neuron damage
associated with needle penetration, particularly for chronic insert experiment
and future medical applications. A solution strategy is to use
microscale-diameter needles (e.g., < 5 μm) with flexible properties.
However, such physically limited needles cannot penetrate the brain and other
biological tissues because of needle buckling or fracturing on penetration.
A research team in the Department of Electrical and
Electronic Information Engineering and the Electronics-Inspired
Interdisciplinary Research Institute (EIIRIS) at Toyohashi University of
Technology has developed a methodology to temporarily enhance the stiffness of
a long, high-aspect-ratio flexible microneedle (e.g., < 5 μm in diameter and
> 500 μm in length), without affecting the needle diameter and flexibility
in tissue. This has been accomplished by embedding a needle base in a film
scaffold, which dissolves upon contact with biological tissue. Silk fibroin is
used as the dissolvable film because it has high biocompatibility, and is a
known biomaterial used in implantable devices.
"We investigated preparation of a silk base scaffold
for a microneedle, quantitatively analyzed needle stiffness, and evaluated the
penetration capability by using mouse brains in vitro/in vivo. In addition, as
an actual needle application, we demonstrated fluorescenctce particle depth
injection into the brain in vivo,and confirm that by observing fluorescenctce
confocal microscope" explained the first author, master's degree student
Satoshi Yagi, and co-author PhD candidate Shota Yamagiwa.