The stretchable sensor, which operates without batteries, would be wrapped around stents or diverters implanted to control blood flow in vessels affected by the aneurysms. To reduce costs and accelerate manufacturing, fabrication of the stretchable sensors uses aerosol jet 3D printing to create conductive silver traces on elastomeric substrates. The 3D additive manufacturing technique allows production of very small electronic features in a single step, without using traditional multi-step lithography processes in a cleanroom. The device is believed to be the first demonstration of aerosol jet 3D printing to produce an implantable, stretchable sensing system for wireless monitoring.
Inserted using a catheter system, the sensor would use inductive coupling of signals to allow wireless detection of biomimetic cerebral aneurysm hemodynamics. Monitoring the progress of cerebral aneurysms now requires repeated angiogram imaging using contrast materials that can have harmful side effects. Because of the cost and potential negative effects, use of the imaging technique must be limited. However, a sensor placed in a blood vessel could allow more frequent evaluations without the use of imaging dyes.
The six-layer sensor is fabricated from biocompatible polyimide, two separate layers of a mesh pattern produced from silver nanoparticles, a dielectric, and soft polymer-encapsulating material. The sensor would be wrapped around the stent or flow diverter, which must be less than two or three millimeters in diameter to fit into the blood vessels. The sensor includes a coil to pick up electromagnetic energy transmitted from another coil located outside the body. Blood flowing through the implanted sensor changes the capacitance, which alters the signals passing through the sensor on their way to a third coil located outside the body. In the laboratory, the researchers have measured capacitance changes six centimeters away from a sensor implanted in meat to simulate brain tissue. Their measurements indicated that the flow rate correlates well with the measured capacitance change.
Use of the aerosol jet 3D printing technique was essential to producing the stretchable and flexible electronics necessary for the sensor. The technique uses a spray of aerosol particles to create patterns, allowing narrower feature sizes than conventional inkjet printing. The printing speed, the printing width, and the amount of material being jetted can all be controlled. And the parameters can be optimized for each material over a broad range of viscosities. Also, because the sensor can be fabricated in a single step without costly cleanroom facilities, it could be manufactured in higher volume at lower cost.
In the next phase of development of the aneurysm sensor, it will be able to measure blood pressure in the vessel along with the flow rates. That would allow the device to be used for other applications, such as intracranial pressure measurements.
The team has also developed a flexible and wearable health monitor able to provide ECG and other information. The success of this monitoring technique demonstrates the potential for smart and connected wireless soft electronics based on nanomaterials, stretchable mechanics, and machine learning algorithms.