Week 4: Aidan

 This week I dove into the world of magnetogenetics and Halbach arrays. Dr. Kaplitt is away, so I've been shadowing his post doc who is studying treatments for pain via magnetogenetics. Magnetogenetics in a nutshell is delivering a magnetic field sensitive transmembrane protein to a target nerve population (i.e., the dorsal root ganglion of the spine or the sciatic nerve) via a viral injection (i.e., Adeno-associated virus) to reduce pain or stimulate activity with external magnetic fields. The transmembrane construct that is currently being used (there are both inhibitory and excitatory versions) uses TRPV1 as the main structure (transmembrane protein found on pain receptors and detects capsaicin, which is what I worked with in the Daniel lab). It also has a region that binds to ferritin, a derivative of iron the body produces endogenously. In response to external magnetic fields, torque is applied to the ferritin tags, opening the TRVP1 transmembrane channel and either flooding Ca2+ or Cl- (depending on inhibitory/excitatory version of the construct). 

So far, this has mostly been performed using MRI to apply a strong and moving magnetic field. However, it would be very useful to be able to perform the behavior experiments without the need for the MRI, such as imaging the DRG. This week I have been leveraging the "engineer" half of biomedical engineer, and researching all things magnets so that I can build a benchtop device that can apply a magnetic field to a mouse. Initially I was looking at Helmholtz coils, but after scaling up to the necessary magnetic field strength and size dimensions, my simulations were suggesting a current draw that would cause significant heating and require a complicated cooling solution. Currently, I'm looking into the idea of Halbach arrays - which are arrangements of polar magnets such that their poles rotate causing constructive interference in one direction and destructive interference in the other. Magnets resist being in this orientation, so I have designed a part for 3D printing that I can press-fit the magnets into while building the array. This coming week I will be ordering/building the device, and the following week we can test out its effectiveness via the Von Frey test.