10/20/2017
This week was short because Fall Break took up Monday and Tuesday. On Wednesday, we met with Dr. Klaesner to discuss some questions that we had about our preliminary report. Based on the discussion that took place, we are now adding the following design specification:
Our device should not add significant complexity or time to the existing procedure.
Furthermore, we are resolved to come up with multiple options as we begin thinking about our circuit designs, including non-resorbable options, as they may provide unforeseen benefits. One option that was mentioned by Dr. Klaesner was an implant placed just beneath the skin that could be removed in an outpatient surgery once it was no longer necessary. Despite our client favoring resorbable circuitry, we must keep in mind that resorbable devices have safety hazards and operational limitations that we may not be able to work around. Our goal is to develop 3-4 designs for each of the 4 components of our device: power supply circuit, current stimulation circuit, control circuit, and mechanical attachment.
Nathan, began to teach himself SPICE so that, as we develop circuit designs, we will be able to test different aspects, running simulations with different inputs and loads.
As we began brainstorming ideas to electrically isolate screws that are connected to the same rod, we realized that it might be worth pursuing a completely non-conducting rod that still provides the strength and benefits of the current titanium rods. This would have to be run by Dr.MacEwan, as the pedicle screw and rod system is part of his company’s trademark product package. If he is unwilling to change the material of the rod, this would not be a viable option.
Summary of current design solution:
This week was short because Fall Break took up Monday and Tuesday. On Wednesday, we met with Dr. Klaesner to discuss some questions that we had about our preliminary report. Based on the discussion that took place, we are now adding the following design specification:
Our device should not add significant complexity or time to the existing procedure.
Furthermore, we are resolved to come up with multiple options as we begin thinking about our circuit designs, including non-resorbable options, as they may provide unforeseen benefits. One option that was mentioned by Dr. Klaesner was an implant placed just beneath the skin that could be removed in an outpatient surgery once it was no longer necessary. Despite our client favoring resorbable circuitry, we must keep in mind that resorbable devices have safety hazards and operational limitations that we may not be able to work around. Our goal is to develop 3-4 designs for each of the 4 components of our device: power supply circuit, current stimulation circuit, control circuit, and mechanical attachment.
Nathan, began to teach himself SPICE so that, as we develop circuit designs, we will be able to test different aspects, running simulations with different inputs and loads.
As we began brainstorming ideas to electrically isolate screws that are connected to the same rod, we realized that it might be worth pursuing a completely non-conducting rod that still provides the strength and benefits of the current titanium rods. This would have to be run by Dr.MacEwan, as the pedicle screw and rod system is part of his company’s trademark product package. If he is unwilling to change the material of the rod, this would not be a viable option.
Summary of current design solution:
- Power supply circuit
- Inductive charging of a capacitor
- Battery – the existing solution used by Dr. MacEwan. This is believed to be too bulky, especially for animal studies in rats, and is likely the worst case scenario if no other power solution appears viable.
- Current stimulation circuit
- Currently no concrete solutions – will devise both resorbable and non-resorbable options if the client is open to this.
- Control circuit
- Microcontroller – resorbable: likely not within the capabilities of the lab at Northwestern
- Microcontroller – nonresorbable: would allow for ease of control and a more sophisticated interface with the device
- Binary counter – can be made resorbable and Dr. MacEwan has an unpublished paper on a prototype that somewhat successfully utilized this method to control current output, though the degree of accuracy was lacking and there was no 2-wayfeedback.
- Mechanical attachment
- Snap button-inspired attachment: would have the strength to withstand the procedural implantation but would pose issues for a resorbable circuit in terms of large floating particles within the body.
- Sleeve around the rod: ideal for resorbable circuitry. Multiple potential ways of getting the charge from the sleeve to the individual screw while bypassing the rod. More discussion necessary.