Atomic Magnetometer
Our group proposes to use an atomic magnetometer for our device to detect action potentials traveling down the arm. The atomic magnetometer is a small chip-like device that is highly sensitive to magnetic fields. The atomic magnetometer will be located right under the shoulder and will be mounted around the bicep. The magnetometer measures the action potential in order to the electronic neuromodulator to cancel them out. The atomic magnetometer is a critical component of our design as it is the non-invasive component of our design.
An atomic magnetometer is a sensor chip that can detect the electromagnetic waves associated to action potentials traveling through neurons. The device consists of a small glass container with the vapor of an alkali metal found within it. The alkali metal is usually cesium (Cs) because it is measured well at 20 – 37°C (body temperature/room temperature). Cesium is then polarized by a laser pump, resulting in polarized cesium atoms. The magnetometer then uses a laser to probe the polarized molecules and measure their magnetic resonance frequency which is directly proportional to the magnetic field strength [14].
Figure 1. Diagram of the inner workings of the magnetometer using Rb as the alkali metal vapor [7]
The magnetic field strength of the action potential must be measured in order for the neuromodulator to detect it and cancel it out. This involves the magnetic spin (in the x-y-z plane) of the charged cesium atoms and the spin of the magnetic field produced by the nerves. When cesium vapor is probed in a direction along the x-y-z plane, the nerve creates a perpendicular transverse spin component which will be the component being measured. This component is measured optically using a light shined in the direction of the transverse spin component. The waves can be measured in pulse intervals where the light measuring the wave can be sent out in certain time intervals [15]. This method of measurement is ideal for us because we are looking for the atomic magnetometer to measure the action potentials every 10 seconds. A computer chip will then process these measurements and develop an algorithm in those 10 seconds. If there is an irregular wave pattern that does not match the wave pattern, that wave gets canceled out by the electronic neuromodulator.
The materials we need to construct the magnetometer consist of a laser pump, a light probe, a magnetic shield, a polarizing beam splitter (PBS), a small glass tube, and a polarizing beam detector [15]. The laser pump and probe are necessary to allow the polarization and probing of the cesium metal vapor found within the magnetometer. The PBS is needed for splitting the probed light beam to be measured by the detectors. The small glass tube, of about 1.9mm allows the flow of the probed light beam. The entire device is encapsulated in a magnetic shield of 10mm to prevent any outside forces from interacting with the system. We plan to use low-density polyethylene to encapsulate the magnetometer system since it is highly durable while being thin enough to detect electromagnetic wave frequencies.
Electronic Neuromodulation Unit
In addition to the atomic magnetometer, we will incorporate the electronic neuromodulator, a morphing electronic. Neuromodulation will allow us to target the neuronal stimulation responsible for the pill-rolling tremors and inhibit the targeted signals [16]. The electronic neuromodulator will be located above the median nerve, and near the atomic magnetometer. The neuromodulator will be implanted underneath the skin, so minimally invasive surgery will be performed. To successfully accomplish our design, we will use soft materials with low bending stiffness with increased thickness, which is to operate during surgery. Device materials can be deposited directly on the soft material, which will act as a base [17]. Most devices, such as the electrodes in DBS, have a fixed shape and are unable to create a seamless neural interface. However, most bio-electronic systems have the same Young’s moduli E of biological tissue which ranges from 100 Pa to 10 MPa. A mismatch in the material and tissue surroundings can deteriorate the function of the device in the long run [17]. In past studies, visco-plastic conductive polymer proved to have a self-healable property and biocompatible glycerol that had unique mechanical properties such as high conductivity.
Additionally, the polymer acted as a liquid at a strain rate similar to the tissue growth rate and acted as a solid at higher strain rates because the polymer has a lower Young’s Modulus than most bioelectronics. Therefore, the implanted device can withstand any exterior body movements and unpredictable variations/movements during surgery [16]. A key design criterion is the safety of the electrodes that will be implanted into the device, which is linked to biocompatibility and preventing the buildup of harmful electrochemical products. Another part of biocompatibility is the size of the electrode, which should not exceed 0.1 mm. The greater the size of the electrode, the more emphasis should be placed on supplying a safe charge that the electrode can withstand per unit surface area [16].
The electronic neuromodulator (bio-electronic) will have similar properties to the surrounding biological tissue, thus biocompatible. The neuromodulator will utilize electrodes that will not exceed 0.1 mm and are connected to cuffs that wrap around the target nerve fiber. The cuffs will have a magnetic bore that will prevent excessive thermal conduction and will be
MRI compatible. The neuromodulator cuff will be made of a viscoplastic polymer with low bending stiffness that encourages long-term biocompatibility.