Microscale needle-electrode array technology has been a true godsend for neuroscience and any number of engineering applications, such as electrophysiological studies, drug and chemical delivery systems, and optogenetics.
Inserting these tiny needles into brain tissue, however, is fairly problematic due to the damage they cause to surrounding neurons – an outcome that’s especially troubling in chronic-insert experiments and future medical applications.
To address this problem, researchers have come up with even thinner, microscale-diameter needles (less than 5 μm across) with flexible properties. The issue with these? They’re bendy. In other words, the very property thought to be of use in solving the dilemma – thinness – prevents these needles from penetrating biological tissue.
Nevertheless, the solution might be just around the corner. 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 technique capable of temporarily enhancing the stiffness of a long, high-aspect-ratio flexible micro-needle (less than 5 μm in diameter and more than 500 μm in length), without affecting its diameter or flexibility.
This has been achieved by embedding a needle base in a film scaffold, made from silk fibroin due to its high bio-compatibility, which dissolves upon contact with biological tissue.
“We investigated preparation of a silk base scaffold for a micro-needle, quantitatively analysed 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 that by observing fluorescence confocal microscope” explained the first author, master’s degree student Satoshi Yagi, and co-author Shota Yamagiwa, who’s currently a PhD candidate.
Associate Professor Takeshi Kawano, leader of the research team, said that while preparing the dissolvable base scaffold is very simple, it could prove highly useful in penetrating tissue with numerous high-aspect-ratio flexible micro-needles, including recording/stimulation electrodes, glass pipettes, and optogenetic fibres.
The new method would also drastically reduce invasiveness during brain science experiments and a host of medical procedures, as well as provide safer tissue penetration than current approaches.
A detailed account of developing the enhanced micro-needless has been released in the science journal Advanced Healthcare Materials.