Organ rejection is a concern that can happen at any stage after a kidney transplant, and it often occurs without clear symptoms. People with a transplanted kidney have to keep a constant eye on its health. Currently, the simplest way to do this is by measuring levels of markers like creatinine and blood urea nitrogen in the blood. However, these markers can fluctuate for reasons that aren't related to organ rejection, making them unreliable indicators that can result in false positives or negatives. Additional blood markers can help but are not perfectly reliable either. The current gold standard for identifying organ rejection is a biopsy, but it's an invasive procedure with its own set of risks. Now, a first-ever device to monitor transplanted organs can sense warning signs of rejection up to three weeks earlier than current methods.

Researchers at Northwestern University (Evanston, IL, USA) have created the first electronic device designed to continuously monitor the health of a transplanted organ in real time. This soft, ultrathin implant sits directly on the transplanted kidney and monitors temperature fluctuations, which are often related to inflammation and other bodily reactions that can indicate transplant rejection. Since inflammation is usually accompanied by a rise in temperature, the researchers reasoned that unusual temperature increases could act as early indicators of potential rejection issues. The device then sends this data wirelessly to a nearby smartphone or tablet, alerting the patient or medical professionals.

In a new study, the team tested this implant on a small animal model with transplanted kidneys. They found that the device could pick up early signs of organ rejection up to three weeks before traditional monitoring methods could. Specifically, they observed that the temperature of a transplanted kidney could rise by up to 0.6 degrees Celsius before any signs of rejection appeared. In animals not taking immunosuppressive drugs, this temperature increase occurred a few days before any changes in blood biomarkers were noticeable. For animals on immunosuppressive medication, not only did the temperature rise, but it also showed other irregularities, even three weeks before creatinine and blood urea nitrogen levels changed. The new device, therefore, not only identifies the early signs of rejection but also provides continuous, real-time monitoring.

“We imagine that a surgeon could implant the device immediately following the transplant surgery, while the patient is still in the operating room,” said Northwestern’s John A. Rogers, a bioelectronics pioneer who led the device development. “Then, it can monitor the kidney without requiring additional procedures.”

“All electronic components are encased in a soft, biocompatible plastic that is gentle and flexible against the kidney’s delicate tissues,” said Surabhi Madhvapathy, a graduate student in Rogers’ laboratory. “The surgical insertion of the entire system, which is smaller than a quarter, is a quick and easy procedure.” 

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