A Novel Subcutaneously Implanted Device for Cardiovascular Assessment

Feasibility Study on Subcutaneously Implanted Devices in Male Rodents for Cardiovascular Assessment Through Near-Field Communication Interface

Hamlyn researchers proposed a novel implanted device for cardiovascular assessment (this work was selected as the latest AIS inside back cover story).

Implantable devices are natural substitutes for wearable monitoring platforms currently in use today. Intra-body monitoring offers a direct connection to the body at the cellular and tissue levels that has no precedent in wearable technology.

When it comes to cardiovascular assessment, monitoring of intra-body cardiovascular parameters can benefit from implantation of miniature devices close to anatomical targets. It thus overcomes the signal attenuation barriers related to the propagation towards body surface while allowing localised sensing at the target site with higher precision.

With proper electronic miniaturisation, packaging, robustness, and power consumption reduction, such implantable devices can harvest enough energy from the surrounding environment for proper operation.

Contextualization image for device implantation inside a rodent at the subcutaneous level — Contextualisation image for device implantation inside a rodent at the subcutaneous level, with wireless transmission of power and data from an external mobile phone, and main device components exhibited inside the image inset: microcontroller unit, amplifier for biopotential detection (wire-electrodes), RED and infrared (IR) light sources, and respective light detector.

With the hope to contribute towards the development of implantable devices for cardiovascular monitoring, our researchers at the Hamlyn Centre proposed a novel near-field communication (NFC)-powered implantable device with acquisition channels for electrocardiogram, arterial pulse, and temperature measurements.

The electronic components responsible for the interface with the biological tissues are assembled on a different board layer (bottom) relative to the control and communication (on top). An additional layer of transparent elastomer covers the entire device for mechanical stability and biocompatibility with the animal tissues (See the illustration image on the cover photo).

Implantable device design, packaging, and channel characterisation. a) Simplified electronic schematic for the developed implantable device with main electronic modules enclosed by boxes. b) Mobile phone’s app developed to receive, visualise, and store signals sent by the implantable device through NFC. c) Scanning electron microscopy (SEM) image of device’s structure protected by PDMS. d) Calibration curve obtained for the internal temperature channel of the device using a hotplate with controlled-temperature settings. e) Linear fit obtained between the SpO2 levels calculated by the proposed device and a commercial pulse oximeter (reference).

Animal Trial Intervention and Follow-up

Implantation of the devices on the rodents took place inside a controlled trial experiment, with subcutaneous deployment of two equivalent devices on opposite sides of the dorsal region of the animals through surgery.

During surgical intervention, the animals remained anaesthetised in the prone position over the operation table, with isoflurane and oxygen supplied through a close-fitting mask. After surgical site closure, immediate NFC readings were taken externally by a phone in-close contact with the dorsal body surface of the animal.

Experimental setups devised for NFC transmission efficiency characterization and the animal trial — Experimental setups devised for NFC transmission efficiency characterisation and the animal trial. a) Diagram and referential axes used for the calculation of the harvested voltage level for the system mobile phone—implantable device by magnetic induction. b) Evaluation of antenna’s efficiency (implantable device) with on-axis distance by comparison with a standard-sized loop antenna in the open-air propagation and PDMS blockage scenarios (center alignment). c) Geometry and disposition of the implantable antenna used as references for the estimation of the harvested voltage levels during planar bending. d) Respective harvested levels obtained by planar bending the implantable antenna relative to the x- and y-axes (angle) at different heights from the transmission antenna (in the z-direction). e) Schematisation of the two implant sites located subcutaneously at the back of the rodent (with attached wire-electrodes) and used as reference during surgery. f ) SEM image revealing details of the outer surface for the encapsulation layer protecting the implantable device after surgical explantation from the rodent. g) Similar SEM image taken at a deeper scale and reduced field-of-view.

The inside back cover of Advanced Intelligent Systems in June 2021

The implanted device has been successfully deployed inside rodents for a 72-hour trial period to assess external powering and data communication in living animals.

Overall, the experimental results obtained by this device demonstrated the potential for providing more reliable diagnostic information than that of external wearable devices.

This feasibility study on subcutaneously implanted devices in male rodents for cardiovascular assessment through NFC Interface has been selected as the inside back cover story of the latest Advanced Intelligent Systems Journal in June 2021.

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This research was supported by EPSRC Programme Grant “Micro-robotics for Surgery (EP/P012779/1)” and EPSRC "Smart Sensing for Surgery (EP/L014149/1)" (Bruno Gil Rosa, Salzitsa Anastasova-Ivanova and Guang-Zhong Yang, "Feasibility Study on Subcutaneously Implanted Devices in Male Rodents for Cardiovascular Assessment Through Near-Field Communication Interface", Advanced Intelligent Systems, 3 (6), June 2021).