A: redox reaction, B: Transducer, C: Op-Amp D: Microcontroller E: read-out

Transcription

1 Use of ph or glucose probes to diagnose compartment syndrome Client : Dr. Christopher Doro Advisor : Professor Walter Block Team : Alex Goodman Team Leader agoodman4@wisc.edu Kristina Geiger Communicator kgeiger4@wisc.edu Heather Barnwell BSAC hbarnwell@wisc.edu Will Bacon BPAG wbacon@wisc.edu Carly Rogers BWIG crogers6@wisc.edu Date: October 16th - October 22nd Alex Goodman: Research/Progress Summary I will begin to brainstorm possible designs for the circuit that will translate the current we receive from our glucose probe. Two electrodes, the working and reference probe will be connected to an operational amplifier This will generate a larger current for us to work with and interpret Using a current-to-voltage transducer, we will convert the current into voltage to work with The voltage read-out we receive should, in theory, be directly proportional to our glucose concentration A: redox reaction, B: Transducer, C: Op-Amp D: Microcontroller E: read-out

2 Transimpedance amplifier (TIA) Converts current to usable voltages current needs to be linearly proportional to source, peroxide in our case Positive input in grounded, negative input to source. A probe will produce a certain current into the op-amp, the op-amp will try to counter this with opposite current. The voltage required to produce this current is the V(out) of the the TIA NOTE: not exactly how this works, but it s a fine way to think about it TIA used in conjunction with working and reference electrode Another circuit design we need is a band filter - this will allow us to filter out unwanted voltages

3 Issues/Dilemmas Having never fabricated a circuit design before, I will required more time than usual to create a decent idea Unsure exactly how to set up electrodes in working order to eachother How do we display the output on a screen? Must develop further understanding of circuitry before continuing Advisor Meeting Agenda Discuss possibility of collaborating with electrical/computer engineers to design solid circuitry Kristina Geiger & Carly Rogers: Progress Summary We both will be focusing on the testing aspect of our design process, including everything from initial testing until final product testing, or as far as our team progresses Initial Testing Solution Testing Overview: This is the first and arguably the most important test we are going it conduct. Before we can move onto putting the probe in other materials and animals, we need to verify it will read the glucose level accurately, and make sure the probe works exactly how we need it to. The overall plan is to create multiple different buffer solutions in of known glucose concentrations to compare the probes readings in the solutions. Buffer solution concentration ranges should vary according to the levels Doctors/nurses will be testing for to test the accuracy of the probe in variations of glucose (Very Dead - 0 mg/dl, 20 mg/dl, 40 mg/dl, 60 mg/dl, 80 mg/dl, 100 mg/dl, >100 mg/dl - Healthy) Insert the probe into each solution and record the glucose reading, repeat at least 5 times for each solution and ensuring the probe is cleaned between readings Average reading data for each solution concentration Average the accuracy of the probe, and make adjustments to the probe and analyzer as needed Sponge Testing Overview: Soak separate pore-deficient sponges in the same known glucose concentration buffers. This test is designed to test the accuracy of the probe when inserted into a material rather than pure solution. The compartment will be more comparable to a sponge than pure liquid. Use the same known glucose concentration buffer solutions that were used during the solution testing, and thoroughly soak a sponge in each solution (approximately 5 min each depending on the density of the sponge.

4 Insert the probe into each sponge at varying depths and record the glucose reading (Take readings at 1 cm, 2cm, 3 cm, 4 cm, 5 cm, and 6 cm) Repeat at least 5 times for each sponge in a different known glucose concentration Average reading data for each sponge Average the accuracy of the probe, and make adjustments as needed to the probe, analyzer, and insertion method. How to make the known Glucose Solutions: There are 2 different solutions we could buy to make the known glucose solutions: The first is a 2g/L (200mg/dL) solution that would be fairly easy to dilute to our known concentrations. This solution is cheaper, and it would allow us to also make at least one solution over 100mg/dL. The second is a 1g/L (100mg/dL) solution that would be considerably easier to dilute to our desired concentrations. This solution is more expensive and would not allow us to make measurements over 100mg/dL. After we know the concentration of the solution we are dealing with we can take say a 50/50 mixture of the 200mg/dL solution and water to make our 100mg/dL solution and so forth. Solution Websites: Animal Testing Will develop more detailed processes once we reach this step in our design process Pig Testing: Use pigs scheduled for termination to test the accuracy of our probe in animal tissue that is most similar to human tissue. Their glucose levels will already be dropping so with a continuous glucose probe, we will actually be able to see the level of glucose drop in the pig s compartment. Dog Testing: Use the beagles available from Dr. Doro to test the accuracy of our probe in real animal tissue with induced compartment syndrome. This way we will have a situation of compartment syndrome to measure the decreasing glucose, instead of in the pig where it was just a dying muscle without the syndrome.

5 Timeline 10/22: Create a list of materials for fabrication and for testing 10/23: Send list of materials to Dr. Doro, and designate which materials they should order 10/27: Order materials that are less than $100 ourselves Before Thanksgiving: Fabrication of our probe 12/1: Initial Testing Issues/Dilemmas Glucose sensor technology may not be able to detect low glucose concentrations effectively, may have to adjust our sensor to more accurately read glucose concentrations more applicable to compartment syndrome. Probe has to be designed to work at a variation of depths (for patients with different sized limbs). Possibility of our materials not coming in in time to fabricate our design and test it before our poster presentations are due. The process of animal testing is very expensive and time consuming, and will require a lot of prior testing and work before we can even reach this point. Future Agenda Create a list of all possible materials needed for testing Order our own materials if < $100 Send Dr. Doro a list of all of our materials, and designate which ones they need to order for us Talk with Block about the pig testing to learn what we can and cannot do if we get to the point where our probe accurately detects glucose in known solutions and the sponges. Heather Barnwell: Research Summary Some CGMs use pen-like needle apparatuses Insert needle, push plunger to release wire and pull out Then connect transmitter, sensor, wire Easy insert for non-professionals

6 Facilitates safer insulin injections Also previous report contains research on peel-apart needle Future Agenda Order samples of plunge needle and peel-apart needle to determine which will work best with our mechanism Order materials for probe, fabricate device, choose insertion mechanism Will Bacon: Research Summary Moving forward, I will begin by acquiring materials and ultimately fabricating the glucose sensor, which consists of multiple parts listed below.

7 Electrode: The portion of the sensor to be inserted into the test solution or material. Platinum/Iridium electrode base Glucose oxidase coating to catalyze redox reaction Mediator to increase reaction selectivity and kinetic favorability Selectively permeable membrane around conductive portion (portion performing measurements) of electrode to increase selectivity Insulated coating for non-conductive portion of electrode outside desired measurement area. Insertion Device: A needle that will be used to allow the electrode access to the intracompartmental space (won t be necessary for solution testing) Pull away introducer needles already on market Arduino Uno/ Circuit: The test electrode and reference electrode will give us raw current data. It will be up to us to take this raw data and filter out unwanted noise (bandpass filter), amplify the signal (Operational Amplifier), and correlate the current to a specific glucose value (acquired via research and testing). Naturally Arduino code will also have to be written for this as well. Arduino Uno Operational Amplifier(s) Wires Soldering equipment Circuit Board Display: A display connected to the Arduino that will show the current glucose measurement. LED display Finding specific part numbers and protocols for fabrication will be the emphasis for this week. Having parts ordered as quickly as possible will be crucial, so that we aren t pressed for time at the end of the semester. Begin by: Ordering fingerstick blood glucose tests -- can be used to determine accuracy of our device via comparison Continuous Glucose Monitor -- Being able to get hands-on with a current CGM that works will be very beneficial. We can see exactly how the electrode, circuitry, and display interconnect. I believe this will be a more effective use of time than trying to come up with the electrode/circuitry/display interface from scratch. For items of a reasonable price (under $200), I will buy them immediately and get reimbursed after the fact. From current research, I believe almost all of our items will be under this limit, but purchasing lots of relatively inexpensive materials still adds up.

8 Issues/Dilemmas The circuitry aspect of fabricating the electrode seems to be fairly involved. We should seek advice from someone with more experience in the bioinstrumentation department. The calibration of converting a current from the electrode to a glucose concentration is not a constant for all glucose electrodes. It depends on the exact electrode specifications such as mediator used, selectively permeable membrane used, thickness of membrane, and amount of mediator/glucose oxidase used. Having precise control over the fabrication, so that we know all these variables is important. How precise would we need to be to get reasonable measurements? Advisor Meeting Agenda Discuss ordering parts Discuss potential bioinstrumentation resources