Interstitial pressure inside a tumor is often quite high compared to normal body tissue and may impede the delivery of chemotherapeutic agents as well as decrease the effectiveness of radiation therapy. Medications can temporarily decrease tumor pressure, but identifying the optimal time to initiate treatment, when tumor pressure is lowest, can be very difficult. Now, a team of scientists from Purdue University, West Lafayette, IN, has developed a unique sensor that can wirelessly relay pressure readings from inside a tumor.

Wireless interstitial fluid pressure sensor shown to scale on a dime. (Credit: Babak Ziaie, PhD, Purdue University)

As tumors grow, blood vessels from surrounding tissue grow into the tumor to nourish it. But, the newly formed blood vessels tend to be twisty and leaky, and it’s thought that these abnormal blood vessels, which leak fluid and proteins into the interstitial space between tumor cells, are the cause of the high pressure observed in tumors.

Patients who have tumors with high interstitial pressure often receive a less than adequate dose of chemotherapy or other types of anti-cancer drugs. In addition, high interstitial pressure can also contribute to low oxygen levels in tumors, which can negate the effects of radiation therapy.

Currently, the only option for measuring pressure is to stick a needle inside the tumor, which is not practical for clinical applications. So the team created a novel sensor that can be implanted into a tumor to wirelessly transmit interstitial fluid pressure readings. The sensor is an adaptation of a technology developed in the 1950s called the Guyton capsule, which is a perforated capsule that, once implanted, allows interstitial fluid to flow through it. Subsequent insertion of a needle into the capsule provides direct access to the interstitial fluid for pressure measurements.

Using special microfabrication techniques, the team created a miniaturized wireless pressure sensor and combined it with a Guyton-like capsule so that it could generate interstitial pressure readings without the use of a needle and that could be read remotely.

They tested the device by implanting it into pancreatic tumors in mice and were able to show a decrease in interstitial tumor pressure following administration of an angiogenic inhibitor.