Stretchable Wireless Sensor Designed to Track Healing of Cerebral Aneurysms

An extremely small wireless sensor fixed in the blood vessels of the human brain could help clinicians assess the healing of aneurysms—bulges that can be fatal or cause serious harm if they burst.

The stretchable sensor, which works without batteries, would be wrapped around diverters or stents implanted to regulate blood flow in vessels damaged by the aneurysms.

To decrease costs and fast-track manufacturing, fabrication of the stretchable sensors makes use of aerosol jet 3D printing to produce conductive silver traces on elastomeric substrates. The 3D additive manufacturing method enables the production of tiny electronic features in one step, without using conventional multi-step lithography processes in a cleanroom.

The device is supposed to be the first demonstration of aerosol jet 3D printing to create an implantable, stretchable sensing system for wireless monitoring.

“The beauty of our sensor is that it can be seamlessly integrated onto existing medical stents or flow diverters that clinicians are already using to treat aneurysms,” said Woon-Hong Yeo, an assistant professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering and the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. “We could use it to measure an incoming blood flow to the aneurysm sac to determine how well the aneurysm is healing, and to alert doctors if blood flow changes.”

The sensor is inserted using a catheter system and would use inductive coupling of signals to enable wireless detection of biomimetic cerebral aneurysm hemodynamics. The research was published on August 7^th, 2019 in the journal Advanced Science.

Tracking the development of cerebral aneurysms currently requires repeated angiogram imaging using contrast materials that can have adverse side effects. Due to the cost and potential negative effects, use of the imaging method must be restricted. However, a sensor positioned in a blood vessel could permit more recurrent evaluations without the use of imaging dyes.

For patients who have had a procedure done, we would be able to tell if the aneurysm is occluding as it should without using any imaging tools. We will be able to accurately measure blood flow to detect changes as small as 0.05 meters per second.

Woon-Hong Yeo, Assistant Professor, George W. Woodruff School of Mechanical Engineering, Georgia Tech

The six-layer sensor is made from biocompatible polyimide, two individual layers of a mesh pattern created from silver nanoparticles, a dielectric and soft polymer-encapsulating material. The sensor would be wrapped around the flow diverter or stent, which has to be less than 2 or 3 mm in diameter to fit into the blood vessels.

The sensor comprises a coil to collect electromagnetic energy conveyed from another coil based outside the body. Blood flowing via the implanted sensor changes its capacitance, which modifies the signals passing via the sensor on their way to a third coil situated outside the body. In the lab, Yeo and his collaborators have measured capacitance variations 6 cm away from a sensor fixed in meat to mimic brain tissue.

“The flow rate is correlated really well with the capacitance change that we can measure,” Yeo said. “We have made the sensor very thin and deformable so it can respond to small changes in blood flow.”

Application of the aerosol jet 3D printing method was vital to creating the stretchable and flexible electronics essential for the sensor. The method uses a spray of aerosol particles to develop patterns, allowing slimmer feature sizes than traditional inkjet printing.

We can control the printing speed, the printing width, and the amount of material being jetted. The parameters can be optimized for each material, and we can use materials that have a broad range of viscosities.

Woon-Hong Yeo, Assistant Professor, George W. Woodruff School of Mechanical Engineering, Georgia Tech

Since the sensor can be created in a single step without expensive cleanroom facilities, it could be factory-made in higher volume at a reasonable cost.

The subsequent phase of the aneurysm sensor will be able to compute blood pressure in the vessel together with the flow rates. “We will be able to measure how pressure contributes to flow change,” Yeo explained. “That would allow the device to be used for other applications, such as intracranial pressure measurements.”

Yeo’s study team has also built a flexible and wearable health monitor able to deliver ECG and other data. He says the success of the monitoring method reveals the potential for smart and connected wireless soft electronics based on stretchable mechanics, nanomaterials, and machine learning algorithms.

We are excited that people are now recognizing the potential of this technology. There are a lot of opportunities to integrate this sensing mechanism into ultrathin membranes that are implantable within the body.

Woon-Hong Yeo, Assistant Professor, George W. Woodruff School of Mechanical Engineering, Georgia Tech