Miniature sensor implant can relay patient healthcare status to a smartphone

Tiny, implantable sensors have been developed that can be used to give doctors an indication about internal health problems of patients before they may be aware of them.

They are able to detect a person’s developing health problems, indicate the most effective type of exercise for an individual athlete, or even help triage wounded soldiers.

“Other implantable sensors currently on the market have a significant drawback,” said Natalie A Wisniewski of Profusa, who worked on the project.

“They often provoke a ‘foreign body’ immune response that coats the sensor with inflammatory cells or scar tissue.” That coating can wall off the device from capillaries and prevent it from sensing chemical changes accurately, so it stops working after a few weeks or months.

This problem was solved by fooling the body so it can’t recognise their sensors as foreign objects.

The sensors are smaller than a grain of rice and are made of a hydrogel scaffold that’s as flexible as a contact lens.

The researchers also made sure their sensor lacks any flat surfaces which can prompt the body to detect it as unnatural and expel it.

As a result, cells and capillaries grow into the sensor’s porous structure without triggering the undesirable immune response. The first of their sensors implanted in human volunteers are still functioning after more than four years.

The researchers implanted dye molecules into the hydrogel scaffold that respond to the concentration of an analyte in the blood.

The type of dye molecule attached to the hydrogel determines the analyte, such as oxygen, carbon dioxide, glucose or lactate, that a particular sensor can recognise.

A small detector held against the skin, or stuck to it as a patch, shines near-infrared light through the skin, causing the dye molecules to fluoresce more or less brightly depending on the concentration of the analyte.

Although this fluorescent light is not visible to human eyes, it can be seen by the detector, which then wirelessly transmits the measurement to a computer or cell phone to record the change in brightness as the analyte concentration fluctuates over time.

The device has been shown to report tissue oxygen levels in patients under treatment for peripheral artery disease, which affects millions of people worldwide.

The disease reduces the flow of oxygenated blood in arms and legs, in some cases leading to amputation. The device is being used to help prevent amputations by informing physicians about declining oxygen levels in a patient’s limbs.

The researchers are also developing sensors for other analytes, such as glucose, so they can broaden applications for the devices and they eventually hope to have a single sensor that detects multiple body chemistries at the same time.

“The sensors would provide a continuous record of your analytes relative to your personal baseline,” Wisniewski said. “Then if something goes off kilter, it’s flagged early, before you feel symptoms, so you can get to the doctor in time for treatment.”

The researchers are presenting details of their work at the current national meeting of the American Chemical Society.

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