Dissolvable material expands opportunities for flexible microneedles used for brain penetrations
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 fluorescence particle depth injection into the brain in vivo,and confirm[ed] that by observing [with a] fluorescence confocal microscope" explained the first author, master's degree student Satoshi Yagi, and co-author PhD candidate Shota Yamagiwa.
The leader of the research team, Associate Professor Takeshi Kawano said: "Preparation of the dissolvable base scaffold is very simple, but this methodology promises powerful tissue penetrations using numerous high-aspect-ratio flexible microneedles, including recording/stimulation electrodes, glass pipettes, and optogenetic fibers." He added: "This has the potential to reduce invasiveness drastically and provide safer tissue penetration than conventional approaches."
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Kawano T et al. Dissolvable Base Scaffolds Allow Tissue Penetration of High-Aspect-Ratio Flexible Microneedles. Advanced Healthcare Materials, Published Online August 2 2015. doi: 10.1002/adhm.201500305