Although the implantation of a flow diverter stents has proved to be a highly effective, less invasive treatment for aneurysms (protuberances in blood vessels), its applicability has been encumbered by the frequent monitoring which it requires. However, a team of researchers from a number of reputable universities have devised a highly flexible sensor that could be fused with the flow diverter to allow for easier and more cost-effective monitoring of hemodynamics in a blood vessel.
The flow diverter is a tubed wire mesh, 10mm long at best. It treats an aneurysm by expanding inside the heart blood vessels to redirect blow flow away from the bulging section of a blood vessel. In doing so, it facilitates the growth of local blood clot that fills up the aneurysm sac.
However, the restoration of the damaged section of a heart blood vessel can take months or even years, and the flow diverter must be monitored throughout this period via MRI and angiogram technology. To reduce the cost and increase the time-efficiency of the monitoring protocols, the team of researchers from a number of universities are developing a sensor that can simplify the monitoring protocols.
The sensors measure blood flow by tracking changes in capacitance. The sensors have proved to measure blood flow with a high degree of accuracy in animal blood vessels in vitro. The team is now looking to make the sensors operate wirelessly to allow for in vivo testing.
The Evolution of Endovascular Treatments for Damaged Heart Blood Vessels
Over the past few years, the most widely used treatment for damaged heart blood vessels has been the endovascular therapy. The standard endovascular therapy involves the use of platinum coils to augment the aneurysm sac.
However, recent developments in this area have brought about the use of a flow diverter that entails the insertion of a hyper-expansible porous stent through the cross-section of an aneurysm to prevent blood flow from whirling inside the bulged section of the artery wall and to facilitate local blood clot within the bulge.
But the major challenge has been how to monitor the blood flow fluxes, especially because the restoration of the damaged artery can take months or even years. Now, the team of researchers is looking to develop a sensor that simplifies the monitoring processes. With this sensor, a doctor can measure blood flow changes in the sac by sending electromagnetic energy via a wireless inductive coil to the sensor, and then measure the changes in the energy’s resonant frequency as it passes through the sensor.
The Schematics of the Flow Diverter Sensor
The length and diameter of flow diverters are usually no more than 5-10mm and a few millimeters respectively, hence the infusion of standard sensors with elaborate electric circuits in the flow diverters is untenable. This sensor developed by the team of researchers is a batteryless, wireless, highly-elastic device that is small enough to fit into the blood vessel, where it can be deployed without causing any damage.
Made with nanofabrication and material transfer printing techniques, the sensor is only just a few hundred nanometers thick. The device comes with a structure that allows it to be compressed during placement, and then expanded 300% – 400% during deployment. It is composed of a dielectric material encapsulated in an elastomeric material with a dual-layered micro-membrane made of two metals. The sensor is designed to encapsulate the flow diverter.
When blood flows through the diverter, the membrane deflects according to the strength of the flow, so that the level of deflection indicates the velocity difference in the flow. The distance between the two metal layers correlates inversely to the capacitance, hence the level of deflection can be measured by the determination of changes in capacitance.
Gold, magnesium, and the nickel-titanium alloy called nitinol were three test materials for the sensors, all of which are safe for the body. But since magnesium dissolves into the bloodstream after it serves its intended purpose, it became the primary metal component.
In the studies, the proof-of-principle sensor was deployed in a vitro-testing that involves the connection of the sensor to a guide wire. The researchers are now working on a wireless application that allows for the implantation of wireless sensors in heart blood vessels of lab animals.
With a nanotechnology-based sensor system, the new flow diverter offers patients with heart blood vessel anomalies the potential of less invasive aneurysm treatment and highly tenable monitoring regimes. The integrated system will also allow doctors to easily monitor the efficacy of flow diverters after surgery.