Final Design

The fully assembled Kidney Perfusion device 2 is shown in Figure 1 with the heating system, packaging, electronics box, GUI, fluid path (tubes, oxygenator, and reservoir), chamber, and sensors.

Figure 1. Fully Assembled Kidney NMP

To summarize, the key functional requirements of the Kidney perfusion device are to provide a steady 100-150ml/min flow of oxygenated 37 °C blood through a kidney. The device must have sensors in the blood flow line for Temperature, Pressure, and flow to ensure these requirements are met. The system must have inlet and outlet ports within the flow to allow the users to input medicines to the kidney and remove perfusate samples to test biomarkers such as oxygenation. Visualizing live data from these sensors is also an essential function for ensuring perfusions are functioning properly and studying the kidney’s biological functions.

Figure 2: Critical Component overview 

Key component description

The full system consists of 5 main components supporting a perfusate fluid line (Figure 2). 

1. A Kamoer DIP 1500 peristaltic pump (Amazon): The previously mentioned first iteration of this system tested this component and found no issues with it supporting perfusion flow rates, tubing requirements, and durability. This component is relatively inexpensive at $200 and easily procurable. It also offers remote control over 485 Modbus to integrate with the GUI. Peristaltic pumps do not contact the fluid line, thus making replacements of disposable components straightforward, as only a tubing swap is necessary. 

2. Medtronic Pixie Oxygenator and Heat Exchanger: This is the most expensive disposable component for each perfusion at $600. They are standard for this device in its prior iterations with no performance issues. They are packaged together and readily available as standard medical components. 

3. The heat exchanger on the oxygenator is supplied with hot water from a heating water loop. This water is targeted at slightly above the 34-37 °C perfusate temperature setpoint. But it can be changed through the GUI over a range from ambient room temperatures to 37 °C.

4. In-line monitoring and control: The perfusate is measured through a sensor suite. 

1. Teensy 4.1 microcontroller (DigiKey) and custom PCB (JLCPCB) with sensor chips for the sensors, as well as 485 Modbus pump control and connections for the heating system safety board and temperature control SSR. 

2. DweyerOmega 13mm ⅛ NPT Threaded Platinum 100 Ohm resistance temperature detector (RTD PT100) (DigiKey) monitors the temperature in line with a Tee connector. Communicates over a MAX31865 board.

3. XY-Tech CG038NS (XY-Tech) ultrasonic clamp-on flow sensor. Integrated over 485 MODBUS

4. Deltran DPT-100 disposable pressure sensor (Utah Medical) mounted in line through a Tee monitors pressure. Integrated with an HX711 ADC chip.

5. Generic Luer stopcocks available from Cole-Parmer or Amazon.

6. 10k Ohm thermistor (Amazon) measures the temperature of the perfusate exiting the kidney or is movable to the kidney surface. 

5. The kidney is housed within a plastic chamber that collects blood as it drains out through a silicone mesh screen. The kidney sits on blood that enters through a cannula connected to the kidney, and urine is collected in a bag next to the ureter. 

Mechanical Packaging: 

The system is housed within an aluminum T-slot framed enclosure with clear acrylic shelves. This packaging allows for benchtop use or for the system to be placed on a wheeled cart. It places disposable components such as the tubing, reservoir, and oxygenator up front for easy access and replacement. For the two systems, the packaging was iterated on slightly, with system 1. Using 30mm T-slot framing, and system 2 using 20mm framing with 2 flat sizes. This was done to improve portability, reduce weight, and decrease crevices that need to be cleaned each perfusion.

Figure 3. (a) CAD of Device 1 and (b) CAD of Device 2

The integrated system was validated on both a water loop and an extended human-kidney perfusion. Pump flow was controllable across the operating range over RS-485 Modbus, and the pressure channel resolved downstream resistance changes from 0 mmHg up to 400 mmHg, well beyond the 65–95 mmHg operating window. Under closed-loop PID control, the heating system held the perfusate within ±0.2 °C of the 34–37 °C setpoint. In a 100-minute perfusion of a discarded human kidney on Device 1, flow held at a ~107 mL/min mean and mean arterial pressure stayed in the ~90–103 mmHg range, with the organ visibly transitioning from pale to uniformly reperfused. Two complete devices were delivered to the sponsors; the one remaining task is gravimetric calibration of the flow sensor on perfusate at the operating temperature.