Detection of Blood Clots Using a Whole Stent as an Active Implantable Biosensor.

Many cardiovascular problems stem from blockages that form within the vasculature and often treatment includes fitting a stent through percutaneous coronary intervention. This offers a minimally invasive therapy but re-occlusion through restenosis or thrombosis formation often occurs post-deployment. Research is ongoing into the creation of smart stents that can detect the occurrence of further problems. In this study, it is shown that selectively metalizing a non-conductive stent can create a set of electrodes that are capable of detecting a build-up of material around the stent. The associated increase in electrical impedance across the electrodes is measured, testing the stent with blood clot to mimic thrombosis. It is shown that the device is capable of sensing different amounts of occlusion. The stent can reproducibly sense the presence of clot showing a 16% +/-3% increase in impedance which is sufficient to reliably detect the clot when surrounded by explanted aorta (one sample t-test, p = 0.009, n = 9). It is demonstrated that this approach can be extended beyond the 3D printed prototypes by showing that it can be applied to a commercially available stent and it is believed that it can be further utilized by other types of medical implants.

Implantable Self-Reporting Stents for Detecting In-Stent Restenosis and Cardiac Functional Dynamics.

Despite the increasing number of stents implanted each year worldwide, patients remain at high risk for developing in-stent restenosis. Various self-reporting stents have been developed to address this challenge, but their practical utility has been limited by low sensitivity and limited data collection. Herein, we propose a next-generation self-reporting stent that can monitor blood pressure and blood flow inside the blood arteries. This proposed self-reporting stent utilizes a larger inductor coil encapsulated on the entire surface of the stent strut, resulting in a 2-fold increase in the sensing resolution and coupling distance between the sensor and external antenna. The dual-pressure sensors enable the detection of blood flow in situ. The feasibility of the proposed self-reporting stent is successfully demonstrated through in vivo analysis in rats, verifying its biocompatibility and multifunctional utilities. This multifunctional self-reporting stent has the potential to greatly improve cardiovascular care by providing real-time monitoring and unprecedented insight into the functional dynamics of the heart.

A Single-Connector Stent Antenna for Intravascular Monitoring Applications.

Recently, smart stents have been developed by integrating various sensors with intravascular stents for detecting vascular restenosis or monitoring intravascular biomedical conditions such as blood pressure or blood flow velocity. The information on biomedical signals is then transmitted to external monitoring systems via wireless communications. Due to the limited volumes of blood vessels and limited influence of blood flow, antennas with good radiation performance are required for intravascular applications. In this paper, we propose a stent antenna composed of multiple rings containing crowns and struts, where each ring is connected with one connector. Unlike a conventional stent, wherein each ring is connected with several connectors, the single connector prevents the random distribution of electrical current and thus achieves good radiation performance. The implantable stent antenna is designed for the frequency range of 2 to 3 GHz for minimum penetration loss in the human body and tissues. Mechanical FEM simulations were conducted to ensure that the mechanical deformation was within specific limits during balloon expansions. A prototype was fabricated with laser cutting techniques and its radiation performance experimentally characterized. It was demonstrated that the fabricated stent antenna had an omnidirectional radiation pattern for arbitrary receiving angles, a gain of 1.38 dBi, and a radiation efficiency of 74.5% at a resonant frequency of 2.07 GHz. The main contribution of this work was the manipulation of the current distributions of the stent for good EM radiation performances which needed to be further examined while inserted inside human bodies. These research results should contribute to the further development of implantable wireless communications and intravascular monitoring of biomedical signals such as blood pressure and blood flow velocity.