Enabling Angioplasty-Ready "Smart" Stents to Detect In-Stent Restenosis and Occlusion

Abstract

Despite the multitude of stents implanted annually worldwide, the most common complication called in-stent restenosis still poses a significant risk to patients. Here, a "smart" stent equipped with microscale sensors and wireless interface is developed to enable continuous monitoring of restenosis through the implanted stent. This electrically active stent functions as a radiofrequency wireless pressure transducer to track local hemodynamic changes upon a renarrowing condition. The smart stent is devised and constructed to fulfill both engineering and clinical requirements while proving its compatibility with the standard angioplasty procedure. Prototypes pass testing through assembly on balloon catheters withstanding crimping forces of >100 N and balloon expansion pressure up to 16 atm, and show wireless sensing with a resolution of 12.4 mmHg. In a swine model, this device demonstrates wireless detection of blood clot formation, as well as real-time tracking of local blood pressure change over a range of 108 mmHg that well covers the range involved in human. The demonstrated results are expected to greatly advance smart stent technology toward its clinical practice.

Keywords: angioplasty; restenosis; smart medical implants; stents; wireless sensing.

Figure 1

Conceptual schematic of the smart stent and its functions. a) A pressure‐microsensor‐integrated wireless stent crimped on the balloon catheter is positioned at the targeted stenosis site in the artery. b) The smart stent is deployed by balloon inflation to start self‐diagnosing while scaffolding the narrowed artery after removal of the catheter; the stent's resonant frequency is at its nominal level (f ₁). c) In‐stent restenosis changes local blood pressure and shifts the stent's frequency (to f ₂) as a sign of the problem; the implant is continuously monitored through a handheld wireless reader that sends out a warning of restenosis upon occurrence.

Figure 2

Fabrication process and fabricated prototype. a) Optical image of fabricated MEMS capacitive pressure sensor chip (on a Canadian quarter, with an inset showing the sensor's design and structure) and two gold‐covered inductive stents with 30 mm length (upper) and 20 mm length (lower). b) Schematic of laser microwelding process joining the sensor chip onto the stent. c) Close‐up photographs (left and right) and scanning electron microscope image (middle) showing microwelded joint between the chip and the stent. d) Finalized smart stent device (showing 30 mm version).

Figure 3

Bench testing of smart stent. a) Mechanical crimping on the balloon catheter. b) Guiding the combined smart stent and balloon catheter through a sheath. c) Deployment of the stent into an artificial artery by inflating the balloon catheter. d) X‐ray imaging of the radiopaque stent device.

Figure 4

Measurement results from in vitro testing. a) Impedance phase dip comparison between bare and gold‐electroplated inductive stent connected with a 10 pF discrete capacitor. b) Impedance phase dips and serial resistances of two 30 mm long stents (4 mm in expanded diameter) joined with capacitive pressure microsensors by conductive epoxy and laser microwelding. c) Impedance phase dips of three differently sized microwelded smart stents in vascular grafts. d) Resonant frequency shifts of a 30 mm long microwelded smart stent (6 mm in expanded diameter) over varying applied pressure in water flow.

Figure 5

Wireless detection of in‐stent occlusion. a) Bypass surgery of the graft with deployed sensor‐integrated smart stents in the carotid artery of a swine model. b) Blood clot occurred inside the graft during test. c) Measured frequency response of functional and control stent devices to blood clot formation.

Figure 6

Wireless measurement results from the swine model test. a) Reflection spectra (on the monitor of the analyzer) showing the device's real‐time resonance tracked during the test. b) Plot of the normalized resonant frequency of the device observed for a MAP range over 100 mmHg varied through drug administration and eventual euthanasia.