BENCHTOP DEVELOPMENT

In order to establish the viability of the MBP, PKC has recently completed its Pathfinder prototype using off-the-shelf electronics, micropumps and flexible Tygon tubing, as shown in Figure 3. For the implant electronics, we selected a low-power microcontroller, wireless chip, analog-to-digital converter (ADC) and power supply using evaluation boards that are readily available. We focused on the software development to validate delivery of fluids, detection of VEGF samples using light spectroscopy as well as wireless monitoring and reconfiguration of the delivery regimes using the state-of-the-art Medical Implant Communication Service (MICS) wireless chip. We also developed the physician monitoring and control software on a PC that communicates wirelessly with the implant unit. The accuracy of pump rate was verified by a precision weight scale.

In the experiment, the implant control unit was able to react to the changes in VEGF level when samples of reconstituted recombinant VEGF protein were introduced into the system. One of the two pumps was always actuated, circulating the body fluid between the weight scale and spectrometer. Because this circulation is a closed loop, no change in measurement was detected on the weight scale. The VEGF spectrometer produced a voltage output corresponding to the absorption of UV light at 280 nm. The voltage signal was acquired by the implant control unit and compared against a predetermined threshold level. If a VEGF absorption level greater than the threshold is detected by the microcontroller, the second pump is actuated to bring the drug from reservoir into the main circulation.  The pump rate was determined by the orientation level detected by the accelerometer due to the fact that the control unit at the chest level will have to pump with greater or lesser force depending the patient’s body position (i.e., supine vs. upright).