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Homework Help: Engineering Project Question

  1. Jun 8, 2015 #1
    Hi im asked to make 40 page report about a new total knee replacement with wireless technology as a final assignment. This is what i thought of:

    The total knee replacement will have 5 sensors on each part of the knee upper part and lower part(femoral and tibial) each of the 5 will be connected to a microchip.

    The microchip has a lithium/iodine battery connected right next to it. also the microchip has two wires connected to each sensor. One that transmit power and the other that receives signals from the sensor. This may seem silly but i was going to say the wire that is going to receive signals is a nano fibre optic cable.

    The knee replacement will be made from polyurethane instead of the ones used today like titanium and cobalt chromium.

    the upper part of the knee is made by this process:

    1. connect all the sensors and wires.
    2. leave a gap between the sensors and wires by something.......
    3. put the system in a housing
    4. pour polyurethane in there (potting)
    5. leave dent to place microchip and battery during surgery
    6. use surface grinding to make the part as smooth as possible.

    same procedure for lower part of the knee

    so they will slide on each other

    It doesnt have to be practical but i want something fancy. so is the fibre optic embbeded in the polyurethane a good choice to transmit data from the sensors? since polyurethane is sterilizable.
    The fibre optic will be totally embbeded in the knee replacement ( no contact with body parts and fluids). or is there another better material to transmit signals?

    Also the data collected by the microchip will be sent to a monitor that is encased in a brace by RFID. This brace can be wrapped around the knee. then the monitor will send this data to the users device via bluetooth.
  2. jcsd
  3. Jun 8, 2015 #2


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    Are you sure you are interpreting the "wireless" part of the project correctly? It makes no sense to do anything wireless in close proximity around the knee inside the tissue of the leg. It makes good sense to do wireless communication between the controlling microcontroller (uC) and the outside world's logging circuitry. It probably also makes sense to do wireless charging of the small battery power source inside the leg tissue.

    Also, why would anybody use a permanently implanted monitoring circuit after a knee replacement? I can see maybe using such a sensor system for the first year or so after the replacement to monitor and track recovery and help guide physical therapy (PT), but IMO the is no reason for a permanently implanted monitoring circuit.

    So, can you provide more information on your project? What clinical evidence is there for such an implant (either for 1 year of recovery or for permanent monitoring)? Do you agree that your wireless boundaries are misplaced in your original post, or am I misunderstanding something? What reading have you been doing about knee replacements (can you provide links)?

    Fun project, BTW :smile:
  4. Jun 8, 2015 #3
    I know it doesnt make such sense i wanted to talk about a simple cobalt chromium design with a microcontroller that fits in the tibial part something like this ( http://www.gizmag.com/go/6435/ ) but my group members wanted something new and different.

    Answering you quesntions:
    1. 1. sensors---->microchip
    2. microchip---> monitor by RFID ( monitor is in brace something like: http://www.betterbraces.com.au/knee-braces ) brace can be taken off.
    3. monitor ---> to device ( computer or phone ) via bluetooth.
    2. its nano technology can be used if another injury occured or failure of implant or for yearly visits or he can just do monthly checks or 3 months checks to check if everything is good.
    3. Im currently reading about mems technology https://www.mems-exchange.org/MEMS/what-is.html (these are the sensors used).

    Its a new design i now it hardly makes sense but its im already half way through the project. The only thing i can do now is change how the sensors and microchip communicate. I want some kind of nano cable or wire that can transmit signals or codes and can be put in the human body. any ideas ?
  5. Jun 8, 2015 #4


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    Staff: Mentor

    Can you post the original project statement? What were you given as your project objective exactly?
  6. Jun 8, 2015 #5
    Ive done the requirements document and the design document and now i have the final project report.

    This was given to us at the beginning of the semester:


    Australia maintains one of the world’s most reliable databanks on joint replacements, so much so that the US FDA relies on Australia’s data rather than duplicating its own for the success, failure, degradation, and replacement of worn artificial joints. However, accumulating data on the wear-and-tear of the joints is time-consuming and expensive as it normally requires the patient to have a formal series of appointments to a surgery and imaging centre involving MRIs, CT scans or other costly procedures. Worse, yet, it is highly desirable to provide warning of catastrophic failures as far in advance as possible.

    We are publishing this Request For Proposal (RFP) for a complete system that involves electronics, mechanical, mechatronic, telecommunications and software as part of the solution. First we would like to include wireless sensors as part of the current knee replacement procedure that can be queried by a smartphone, or a similar sized (or smaller) device, to help monitor the long-term health of the artificial joint in terms of its most typical failure modes, both early on (infant mortality) and for the life of the joint (long term maintenance).

    In addition to the implanted and external monitoring capability, a test jig is required which will allow for simulating in hardware the operation of the monitoring gear with an artificial knee. The test jig should simulate loaded and loaded knee actuation and should allow for several degrees of freedom of positioning the mechanical knee joint relative to the sensors and/or the features that the sensors are meant to monitor.
  7. Jun 11, 2015 #6


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    The problem with using fibre is the need for wires to power the sensor. I think I'd be looking at a serial bus of some sort that can do both with just two wires. Will there be sensors in both parts of the knee? I'm wondering about the lifetime of the wire/fibre that has to cross the joint and flex with it. Could you use two batteries one either side of the joint? Better still.. would it be possible to use RFID to power and talk to the sensors directly and eliminate the need for the implanted wires/fibre, micro and battery/charging?

    Google found there are projects using RFID sensors to monitor tyre pressure....


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