Abstract
While wireless monitoring of intracardiac pressure using implants is essential for the management of heart
failure, miniaturizing these implants is critical for reducing their associated complications. Current implants mainly
consist of an electromagnetic antenna, electronics, and energy-storage and conversion units. However, these
units contain toxic materials, and a large antenna is necessary to transmit the large wavelengths (>5 cm) of
electromagnetic waves. The size and inorganic components of the current implants increase the risk of
complications for patients.
Ultrasound technology is promising to replace electromagnetic waves for in vivo wireless communications. It is
safe, does not interfere with other electromagnetic signals, has lower in vivo signal attenuation, and permits the
use of significantly smaller antennas and implants due to its sub-millimeter wavelength. Therefore,
communication through ultrasound is ideal for use in minimally invasive pressure monitoring implants. The long-
term objective is to develop an ultrasound-based, wireless technology that will miniaturize intracardiac implants
by eliminating both the electromagnetic antenna and the energy storage and conversion units. The objective of
this project is to utilize flexible, acoustic microresonators (100 to 500 µm thick films) with compressible
microcavities for physiological pressure measurements of atriums and ventricles.
Our central hypothesis is that the post-processing of echo signals from the resonators and their resonant
frequencies can detect intracardiac pressure changes. Our rationale is that micro-fabricated films made from
polydimethylsiloxane (PDMS) form acoustic resonators. Incorporating gas/void filled microcavities into the PDMS
film creates a resonator that is sensitive to the pressure difference between the inside and outside. Changing
the differential pressure causes deformations of the resonator. These deformations shift the film's resonant
frequency allowing for the detection of pressure changes.
Our specific aims are to 1) prove the measurement sensitivity of the resonator underwater at the ventricular and
atrial physiological pressures with the resolution of ~1mmHg and temporal resolution of 40 (ms); 2) demonstrate
the safety of an implantable device in vitro by incorporating hemocompatible materials, testing a device's
durability, and testing in a specially designed phantom; and 3) prove that the implant is suitable for a minimally
invasive delivery (transseptal procedure) on a benchtop test setup. Upon project completion, the technology can
be immediately employed to create safer next-generation in vivo pressure monitoring implants that operate solely
using acoustic waves. This contribution is significant because it can aid over 6 million Americans who live with
Heart Failure (HF), resulting in chronic hospitalizations that cost $16 billion. The proposed research is innovative
because this technology employs only acoustic waves; avoids energy conversion, storage units, and
electromagnetic antennas; and significantly reduces an implant's size and complications.
