Abstract Body (Do not enter title and authors here): Introduction:
Implantable vascular electronics offer opportunities to improve patient monitoring and treatments. However, device manufacturability, alongside strict requirements of size, mechanics, and sensing capability, have hindered the development of implantable vascular sensors. Although stents are commonly used with over 3 million stents implanted in cardiovascular arteries every year, there have been minimal efforts to integrate sensing functionality with stents. A promising target for a stent-based electronic system is to monitor the progression of restenosis. Towards this, we report a stent-based sensor system utilizing an electronic stent and a soft sensor to wirelessly measure changes in arterial stiffness and monitor restenosis.

Methods:
A multi-step, rotational laser micromachining was developed to form an electronic stent with layers of stainless steel, polymer, gold, and parylene. Soft, capacitive sensors were printed with elastomer, polymer, and silver nanoparticles. Integrating a stent and sensor forms a passive, wireless sensor. An external loop antenna interrogates the implantable device to record a resonant frequency dependent on arterial strain. The device is evaluated in vitro with silicone models and ex vivo in an ovine coronary artery.

Results:
Figure 1a illustrates the device while the sensor and stent components are highlighted in Figures 1b and 1c. Capacitive strain sensor design was studied to achieve a gauge factor over 3 and the ability to measure strain changes as small as 0.15%. Stent design and fabrication strategies were developed to yield a stent that replicates conventional stent mechanics while offering wireless connectivity to an external antenna. Figure 1d shows the system before and after expansion with a balloon catheter. Once expanded, the device is operated via inductive coupling to wirelessly record changes in resonant frequency and measure changes in arterial strain or artery diameter (Figure 1e). Restenosis levels of 0% up to 90% were tested by thickening the artery wall along the length of the stent and are summarized in Figure 1f. Figure 1g shows the sensor implanted in the coronary artery of an ovine heart for ex vivo testing.

Conclusions:
We have demonstrated a vascular electronics system for the monitoring of arterial stiffness and restenosis. Collectively, our studies of vascular device fabrication and sensor design provide strategies to create vascular electronics for enhanced patient and disease monitoring.