Smart Breast Clip: A Wireless Implant for Continuous Molecular Sensing of Breast Masses

Over 40,000 women die of breast cancer each year in the US due to some form of chemoresistance. To try and combat this, we have developed a novel “Smart Breast Clip” sensor for a patient-specific and response-guided breast cancer treatment. Our sensor is a diffuse optical spectroscopy implant that can be placed into a tumor with a 12G breast biopsy needle. While adaptable to sense additional molecular targets, our sensor currently uses red (680 nm) and near-infrared light (850 nm) to measure changes in tumor concentrations of oxy- and deoxy-hemoglobin; markers that have been shown to predict pathologic complete response to chemotherapy in breast cancer patients.

The minimally invasive 10 mm x 2 mm sensor contains two vertical cavity surface emitting lasers (VCSELs) at 680 nm and 850 nm that output up to 5 mW of optical power and a photodiode that is controlled by an off-the-shelf analog front end integrated circuit with integrated transimpedance amplifier. This ultralow powered sensor is wirelessly powered using near-field resonant inductive coupling at 6.58 MHz and communicates via backscattered load shift keying. Monte Carlo photon simulations reveal a sensor interrogation volume of up to 4 cm3 at the source and detector separation used, around the diameter of average breast tumors.

Sensor characterization using in vitro liquid tissue mimicking ink phantoms showed sensitivity to absorption concentrations ranging from 0 to 0.025 mm−1, consistent with estimated tumor hemoglobin absorptions. Furthermore using bovine hemoglobin at concentrations expected in breast tumors, we have successfully wirelessly powered our “smart breast clip”; simultaneously and temporally collecting changes in oxy-and deoxy-hemoglobin within in vitro liquid tissue mimicking blood phantoms. Subsequently, we used an in vivo immunocompetent murine model of human breast cancer (BALB/cByJ) to characterize the biocompatibility of our implant. The sensor was injected into 10 mm diameter 4T1 murine breast cancer tumors (N = 10) and both the implant and tumor tissue were evaluated after the tumor progressed to 25 mm. No adverse effects were observed from the hematoxylin and eosin tissue staining. A pilot study of 5 BALB/cByJ mice was conducted, without the introduction of 4T1 murine breast cancer cells, and demonstrated functionality of our prototype wired smart breast clip within an in vivo environment.