A simple method for implanting free-floating microdevices into the nervous tissue

Abstract

Objective. Free-floating implantable neural interfaces are an emerging powerful paradigm for mapping and modulation of brain activity. Minuscule wirelessly-powered devices have the potential to provide minimally-invasive interactions with neurons in chronic research and medical applications. However, these devices face a seemingly simple problem—how can they be placed into nervous tissue rapidly, efficiently and in an essentially arbitrary location? Approach. We introduce a novel injection tool and describe a controlled injection approach that minimizes damage to the tissue. Main results. To validate the needle injectable tool and the presented delivery approach, we evaluate the spatial precision and rotational alignment of the microdevices injected into agarose, brain, and sciatic nerve with the aid of tissue clearing and MRI imaging. In this research, we limited the number of injections into the brain to four per rat as we are using microdevices that are designed for an adult head size on a rat model. We then present immunohistology data to assess the damage caused by the needle. Significance. By virtue of its simplicity, the proposed injection method can be used to inject microdevices of all sizes and shapes and will do so in a fast, minimally-invasive, and cost-effective manner. As a result, the introduced technique can be broadly used to accelerate the validation of these next-generation types of electrodes in animal models.

Tracking the Migration of Injectable Microdevices in the Rodent Brain Using a 9.4T Magnetic Resonance Imaging Scanner

“…We have previously shown that the spatial precision of our injection method was excellent as the microdevice reached within 200 µm of its target location 91% of the time (Khalifa et al, 2021). In this study, all 11 microdevices in all five rats reached their target site.…”

“…The microdevices were injected using a custom-made novel injection tool described in detail in Khalifa et al (2021). The main components of the injection tool are a 22G (or thin wall 23G) needle, and 350 µm stainless steel cylindrical rod (OrthoTechnology, FL, United States; Figure 2B).…”

“…Unlike bulky implantable electronics, injectable microdevices require only minimally invasive superficial surgeries. Our group (Khalifa et al, 2021) and others (Zhou et al, 2017) have shown that a small immune response was caused when inserting a syringe into the brain.…”

“…It has been shown in many research studies that floating implants that are not otherwise anchored to the skull or in contact with meningeal tissue mitigate injury responses (Biran et al, 2007;Kim et al, 2013;Ersen et al, 2015). Lastly, intracortical microdevices are compatible with minimally invasive intracranial insertion techniques (Cortese et al, 2020;Sigurdsson et al, 2020;Khalifa et al, 2021), which leads to reduced surgical complications and faster recovery. Unlike bulky implantable electronics, injectable microdevices require only minimally invasive superficial surgeries.…”

Injectable wireless microdevices: challenges and opportunities

“…The microbead was fully implanted in the sciatic nerve of a rat to confirm its ability to elicit action potentials in axons. Its injection tool and approach are described in detail in (Khalifa et al 2021a ). The main components of the injection tool are a 23G needle and a stainless-steel cylindrical rod, where PEG is used to temporarily affix the microdevice to the tip of the rod.…”