Neural Stimulation for less than a Dollar

Written by Andrea de Kock

August 8, 2019

A new study published in Frontiers of Neuroscience has shocked the Neuroscience community with its low-cost neural stimulation device. In their research they designed and manufactured an effective multi-channel stimulation device from common electrical hardware and a 3D printer. The device cost a mere 1 USD and can be assembled within 20 minutes!

Why design a new stimulation device?

The implantation of electrodes with the aim of alleviating symptoms of various disorders and diseases is a widely used method in humans since the 1950s. Similarly, it is a common tool for many animal studies on new cell mechanisms, neurological disorders and treatments. There has been a wide variety of electrode devices developed for this preclinical research, particularly in rodents, which vary in cost, functionality and size. Many have reported on either wireless battery-operated stimulators or devices with self-generated power. Other researchers further focused on creating multi-functional and flexible probes with cutting-edge features for stimulating and recording. Whilst these designs make research on freely moving animals and chronic recordings easier, they are very complex and costly to develop and manufacture. Besides, most of these stimulators were designed specifically for use in rats and are, therefore, too large for efficient use in mice.

3D printing offers a much better approach not only for improved adhesion, but also in manufacturing exact replicas of the device

While more advanced features in some cases might be ideal to incorporate into the design, some experiments rather require low-cost and readily available devices. There is a desire for surgeries to be scheduled and completed without any delays and for low-cost devices with quick and easy assembly. Researchers want to reduce the time spent in testing and improve the rate of quality data output. However, there has been little focus on advancing the more basic electrode device designs, which would be more affordable but also reliable and easily accessible by most researchers.

 

For this reason, researchers from the University of Toronto, Canada, designed a 2-channel stimulating device that can easily be made by 3D printing, for high turnover experiments. The amount of materials used in the process is minimised by their specific design. Moreover, the customisability of 3D printing enables the device’s connector base to be matched with the curvature of the mouse skull. This ensures both the production of a small and ultra-lightweight device and an improved adhesion to the skull for enhanced efficiency during the experiment.

 

Many previous studies have tried to improve on electrode device adhesion to the mouse skull, by way of using flexible material, applying more adhesive, as well as limiting the size of the flat base, or cutting a curve into the base with scissors. However, in using a 3D printable design, one is more able to customise different aspects of the design to enhance its performance even further than with the abovementioned optimisations. The 3D printing offers a much better approach not only for improved adhesion, but also in manufacturing exact replicas of the device with the same adhesion characteristics, which would not be possible through manual alterations.

Design and 3D Printing

Figure 1: 3D Printing of the neural stimulation device

As depicted in Figure 1, each connector was designed with a flat top surface and a concave bottom for improved adhesion to the curvature of the mouse skull. The base dimensions (Fig 1D) were 5 mm by 4.5 mm and the base height 3 mm (with the concave curvature reaching the lowest point at 2.4 mm). Two parallel channels extended through the connector with a 2.1 mm diameter each, with their centre axes only 2 mm apart (Fig 1D). Small grooves (0.5 mm by 0.5 mm) were further incorporated in the design for the placement of wire electrodes along the front of each connector (Fig 1A).

 

For improved efficacy in printing, the connectors were arranged in an array of four with 1.5 mm length supporting columns on a 3 mm thick supporting platform (Fig 1E). These were then further duplicated into a 3 by 3 array with 5 mm spacing in between each supporting platform (Fig 1F). This resulted in a total of 36 connectors being printed with each print job. Printing was done with the desktop stereolithographic 3D printer Form 2 (Formlabs Inc., US) and designing was done in SOLIDWORKS 2017 (Dassault Systèmes).

 

Connectors were 3D printed in the liquid photopolymer resin “Clear” (FLGPCL04) in the highest resolution, which took approximately 3 hours to complete. Within 30 minutes after printing, the connectors were removed and immediately transferred to a bath of isopropanol for about 20 minutes. After the first 10 minutes in the bath, vigorous manual agitation removed any excess uncured resin. The connectors were then dried and cured under UV light at 60 degrees Celsius for 2 hours. Supporting components such as the columns and platforms that the connectors were arranged on for printing were only removed after curing, with standard wire cutters.

Device Assembly

Figure 2: Assembly of the Neural Stimulation Device

Assembly of the devices is depicted in Figure 2. The exciting part of this assembly process is that anyone can complete it. Assembly takes approximately 20 minutes per device, but when practiced it can be as short as 17 minutes per device. The only real skill involved is basic soldering of the wire and pin, but this is easy once you get the hang of it.

 

The fully assembled electrical stimulation device weighed only 143 ± 8 mg, which is well under the weight limit for ultra-lightweight designs (2 g). With a 3 mm height it can also be considered ultra-low size. This is actually a very important factor in designing these stimulation devices. When studying freely moving animals and behaviour in rodents, it is necessary to ensure comfort in the wearing of head-mounted devices, as this can confound the data recorded.

Total Time and Cost for Manufacturing Each Device

Figure 3: Total Costs of Neural Stimulation Device

In their publication, the University of Toronto researchers indicated that the total cost for each of the devices is just under 1 US dollar. Even with a fail rate of 6% for each print job, the total cost would still be only a dollar to produce. This then confirms that the manufacturing of these electrode stimulating devices is affordable to any researcher and in any sized study.

 

With regards to the time constraint for the manufacturing, they confirmed that apart from the assembly time, which is about 17 to 20 minutes, no further active time is required for the manufacturing. To recap, printing takes approximately 3.5 hours, washing in the isopropanol bath requires 20 minutes, curing under UV light 2 hours and drying of the glue between 3 and 12 hours. All of this can, however, be planned and prepared ahead of time and can be done in bulk quantities to ensure stimulating devices are readily available prior to planned surgeries.

 

In Vivo Stimulation Test

The new device was tested in vivo on mice and it passed with flying colours. The electrical and mechanical properties of the device was suitable for the intended application and did not heighten the brain inflammatory response.

Figure 4: Experimental Design and Implant in Mouse

 

As depicted in Figure 4, two days passed between the implantation surgery and the stimulation test. Stimulation was done for 1 hour on Day 1. No abnormal limb movements or twitches were observed during the stimulation period or thereafter. Between Day 1 and Day 3, further tests were performed to determine if the stimulation device impacted on any astrogliotic or inflammatory responses. No changes were seen in the quantity of mature neurons, GFAP+ astrocytes or in Iba1+ cells between control and study groups over time, which usually indicates trauma to the brain and/or inflammation. They further demonstrated that no changes were evident in implanted versus non-implanted hemispheres. In conclusion, over the short time of their study the immune response was not significant enough to impede the experiment or stimulation. The researchers stated that chronic implantation, however, might reveal a greater glial and immune response.

 

What is the outcome of such a low-cost stimulating device?

The result of this study is a device that is not only easy and cost-effective to manufacture, but also robust, with minimal risk of device failure, and it saves time in research. Plus, there are the bonuses of less animals sacrificed due to reactions to implantation and more versatility for future research offered by 3D printing.

The researchers from Toronto are now keen on making their design for a low-cost, low-weight and quick manufacturing 3D printed device for electrical stimulation in mice, readily available for furthering various research paradigms. They included some ideas in their publication, for future alterations in the design that will be suitable in various studies (Fig 5 below). Some of the variations included: adding more channels; increasing the distance between electrodes; customising the base for implantation on various sites; enlarging the device for rats; and increasing the stimulation area.

Figure 5: Further recommendations for stimulation device designs

This tiny electrical stimulation device has not failed in over 60 consecutive surgeries and each device costs only 1 US dollar. You will require access to a 3D printer if you want to follow in the Toronto researchers’ footsteps, but your possibilities for future research paradigms will be endless.

 

References

Morrison TJ, Sefton E, Marquez-Chin M, Popovic MR, Morshead CM and Naguib HE (2019) A 3D Printed Device for Low Cost Neural Stimulation in Mice. Front. Neurosci.13:784. doi: 10.3389/fnins.2019.00784

Shinkman PG (2001) International Encyclopedia of the Social & Behavioural Sciences. Brain Stimulation in Human Patients.