There is currently a lack of waveguides that are compliant and elastic enough to be suitable for a variety of implantation applications. High refractive index silicones have the mechanical and optical properties that might make them useful as an implantable waveguide. A high refractive index silicone from the optical encapsulant category of silicones (Gelest OE50) was fabricated into simple waveguides and its potential as an implantable waveguide was investigated. It was found that while the elasticity and stiffness of the Gelest OE50 was not affected by exposure to an environment simulating that of the body, the optical clarity was. The attenuation coefficent was found to increase from 0.1165 dB/mm to 0.2081 dB/mm, a increase significant enough to make it difficult to recommend for use as a material for implantable waveguides.

Abstract Emerging neurotechnologies such as brain-computer interfaces and implantable sensors offer considerable promise in the treatment of a broad range of neurological conditions. The key challenges are reducing the implant size, powering it, and confirming long-term accuracy and safety. Here we report the development of a novel type of implantable medical device that measures intracranial pressure long term and which weighs only 0.28 g. Currently the management of hydrocephalus patients relies heavily on non-specific symptoms e.g. headache and there is a lack of actionable data to drive decisions that are not solely hospital based such as imaging. The implant is designed to sit within the cerebral cortex. In a group of 10 adults and 10 children with hydrocephalus we demonstrated that the device was safe and capable of remotely monitoring intracranial pressure in patients at home for up to 18 months (ClinicalTrial.gov NCT06402786). In several children shunt failures occurred and these were associated with raised ICP. Instead of relying on non-specific symptoms such as headache, physicians were able to obtain real-time intracranial pressure readings that can lead to changes in the management of these complex patients.

Reliable communication and robust power supply are critical requirements for medical implants. However, the achievable data rates are constrained by the large time constant due to the system's high quality (Q) factor. Additionally, achieving high data rates through PSK modulation can significantly reduce the average transfer power to the implant during phase shifts. This paper introduces M-PSK modulation and power injection compensation to enhance data rates and ensure reliable power transfer during communication. A lead-lag phase detector is implemented to demodulate the received signal. In a benchtop experiment, the IPT system (Qp=78.4) transmitted a 32-bit data sequence at 222kbps at 6.667MHz with zero error. The compensation improves the average load power from 79.7% to 101.2% of the unmodulated value.

This article presents a system-on-a-chip (SoC) for pressure sensors in 180-nm CMOS technology. It can interface with a capacitive pressure sensor with an inductive wireless power supply and data transmission via load-shift keying (LSK). It integrates an analog front end (AFE), bandgap references (BGRs), delta-sigma ADC, I2C, RC oscillator, low-dropout regulators (LDOs), shorting control switches, and full-bridge rectifier (Rct). An external coil receives wireless power, which is rectified and regulated to 1.8 V by the full-bridge Rct and LDOs. The AFE samples the capacitance change of the pressure sensor to a voltage that is converted into 19-bit digital data by the delta-sigma ADC, which is then converted into 43 Hz per sample serial data by the I2C block. A temperature sensor is included, and 19-bit measurements are transmitted in serial with capacitance data. Serial data are transmitted wirelessly using LSK. This SoC has a measured accuracy of 1 mmHg between 575- and 900-mmHg absolute with a wireless power supply and wireless data transfer.

Phase shift keying (PSK) is a modulation scheme which allows a single inductive link to achieve simultaneous wireless power and data transmission (SWPDT). However, the phase shift modulation may result in significant power reduction during the period where the link settles to a new steady state after each phase shift. In this paper, a power injection compensation method is developed to temporarily increase the duty cycle such that power transfer is controlled at the correct average level during PSK modulation. This paper presents a design method for power injection compensation based on an approximated transient model of IPT system. The design method is tested in an experimental converter operating a 1.0MHz. The experimental results show that for 90˚ phase modulation, the power injection control system increases the average load power from 72% to 98% of the unmodulated value. This is done without communication and compensation from the secondary side showing that the compensation technique can be implied to the primary converter to compensate for power transfer reduction during high modulation rates where feedback delays from the secondary limit performance.

Positive surgical margin. Video OCT cross-sectional images of a positive tumor margin from the in vivo resection bed of a 72 year-old female WLE patient with invasive ductal carcinoma as the surgeon sweeps the handheld probe along the margin.

Abstract High Q coils are required by inductive power transfer (IPT) links to attain reasonable levels of power transfer especially for loosely coupled links such as those used for small, deeply implanted medical devices. However, the high Q feature makes IPT systems strongly dependent on operating frequency which must be matched in the primary and secondary resonant tanks. Consequently, power transfer is sensitive to resonant frequency shifts due to component aging and environmental factors. Here, a switched capacitor (SC) network is developed to maintain tight matching and enhance system robustness. The combination of high voltage and high frequency required to achieve power transfer to deeply implanted devices makes the SC network design challenging. High frequencies require small tuning capacitance and high voltage requires MOSFETS with large output capacitance (COSS) resulting in COSS having a significant effect on tuning frequency. This paper proposes a parameter design method incorporating COSS to eliminate the uncertainty of voltage related COSS. In the experiment, the SC network broadens the effective bandwidth from 37 to 585 kHz at the centre frequency of 6.50 MHz. Across a frequency sweep, the worst case in transfer power drop is −0.43 dB, which demonstrates sufficient immunity to parameter deviations.

<p>Negative surgical margin. Video OCT cross-sectional images of a negative tumor margin from the in vivo resection bed of a 72 year-old female WLE patient with invasive ductal carcinoma as the surgeon sweeps the handheld probe along the margin.</p>

Technological advancements in electronics and micromachining now allow the development of discrete wireless brain implantable micro-devices. Applications of such devices include stimulation or sensing and could enable direct placement near regions of interest within the brain without the need for electrode leads or separate battery compartments that are at increased risk of breakage and infection. Clinical use of leadless brain implants is accompanied by novel risks, such as migration of the implant. Additionally, the encapsulation material of the implants plays an important role in mitigating unwanted tissue reactions. These risks have the potential to cause harm or reduce the service of life of the implant. In the present study, we have assessed post-implantation tissue reaction and migration of borosilicate glass-encapsulated micro-implants within the cortex of the brain. Twenty borosilicate glass-encapsulated devices (2 × 3.5 × 20 mm) were implanted into the parenchyma of 10 sheep for 6 months. Radiographs were taken directly post-surgery and at 3 and 6 months. Subsequently, sheep were euthanized, and GFAP and IBA-1 histological analysis was performed. The migration of the implants was tracked by reference to two stainless steel screws placed in the skull. We found no significant difference in fluoroscopy intensity of GFAP and a small difference in IBA-1 between implanted tissue and control. There was no glial scar formation found at the site of the implant’s track wall. Furthermore, we observed movement of up to 4.6 mm in a subset of implants in the first 3 months of implantation and no movement in any implant during the 3–6-month period of implantation. Subsequent histological analysis revealed no evidence of a migration track or tissue damage. We conclude that the implantation of this discrete micro-implant within the brain does not present additional risk due to migration.

Background: Electrical stimulation applied to individual organs, peripheral nerves, or specific brain regions has been used to treat a range of medical conditions. In cardiovascular disease, autonomic dysfunction contributes to the disease progression and electrical stimulation of the vagus nerve has been pursued as a treatment for the purpose of restoring the autonomic balance. However, this approach lacks selectivity in activating function- and organ-specific vagal fibers and, despite promising results of many preclinical studies, has so far failed to translate into a clinical treatment of cardiovascular disease. Objective: Here we report a successful application of optogenetics for selective stimulation of vagal efferent activity in a large animal model (sheep). Methods and results: Twelve weeks after viral transduction of a subset of vagal motoneurons, strong axonal membrane expression of the excitatory light-sensitive ion channel ChIEF was achieved in the efferent projections innervating thoracic organs and reaching beyond the level of the diaphragm. Blue laser or LED light (>10 mW mm−2; 1 ms pulses) applied to the cervical vagus triggered precisely timed, strong bursts of efferent activity with evoked action potentials propagating at speeds of ∼6 m s−1. Conclusions: These findings demonstrate that in species with a large, multi-fascicled vagus nerve, it is possible to stimulate a specific sub-population of efferent fibers using light at a site remote from the vector delivery, marking an important step towards eventual clinical use of optogenetic technology for autonomic neuromodulation.

This paper presents a new capacitance to voltage analog-front end (AFE) designed in 180 rim CMOS technology for wireless implantable applications. This AFE consists of a Low-dropout regulator (LDO), bandgap reference (BGR), switched-capacitor (SC) sampler, SC op-amp and oscillator. The LDO regulates the wireless power supply coming from an off-chip rectifier and provides a stable and accurate DC voltage. Capacitance is converted to a discrete voltage by a SC sampling circuit and then amplified by a SC op-amp. Both of SC sampling and SC op amp circuits form a correlated double sampling scheme. This AFE is designed to sense a capacitance range from 6 pF to 7 pF (300-1000 mmHg) corresponding to a 0.68 V-1.07 V discrete output voltage with a sampling frequency of 1.63 KHz. This AFE has a sensitivity of 0.39 mV/fF, average power consumption of 201 mu W and 3.25% accuracy operating over a 2.1 V-3.3 V rectified wireless supply voltage and similar to 40 degrees C similar to 125 degrees C temperature range.

Current generation left ventricular assist devices (LVADs) are powered by a percutaneous driveline. The high prevalence of driveline infections has motivated the development of transcutaneous energy transfer (TET) systems which eliminate driveline associated complications by wirelessly delivering power across the skin. Destination therapy (DT) requires long-term reliable operation of the TET electronics suggesting the use of hermetic packaging techniques as used in all other chronically implanted devices. TET coils dissipate heat during operation and in order for the technology to be suitable for patient use, sufficient power must be delivered while maintaining temperatures at levels deemed safe. The heating of a TET system designed for DT which uses hermetic packaging technology was evaluated in silico and in vivo. A numerical model was used to evaluate the temperature of the TET coils. The TET system was fabricated and assessed in vivo using an ovine model. The receiving coil was implanted subcutaneously in a sheep and the transmission coil placed in contact with the skin and concentric to the implanted coil. Temperatures of the system were measured using sensors fixed to the surface of the coils. Numerical modeling indicated that the maximum temperatures of the primary and secondary coil surfaces were 38.13°C and 38.41°C, respectively, when delivering 10 W continuously. Stable temperatures were observed in vivo after 70 minutes and the maximum skin and implant surface temperatures were 37.73°C and 38.31°C, respectively. This study showed that a hermetic, chronically implantable TET system is thermally safe when continuously delivering 10 W of power, sufficient to power modern LVADs.

Miniaturised biomedical implants, such as neural stimulators and leadless pacemakers are becoming increasingly popular. As of yet, access to a reliable power source has been one of the major obstacles towards creating miniature devices with extended functionalities. Batteries tend to take up 80% room while offering a limited lifespan. Moreover, transcutaneous energy transfer systems (TET) designed to deliver power to implants without a physical link require a receiving coil that requires a generous real estate. This research proposes a new transcutaneous energy transfer (TET) method to deliver power to miniaturised deeply implanted biomedical devices.

Deeply implanted biomedical devices (DIBDs) are a challenging application of wireless power transfer because of the requirement for miniaturization while minimizing patient exposure to tissue heating. This article proposes a capacitively coupled conductive power transfer method for DIBDs, which allows for the safe transfer of power into the body while using minimum implant volume. The method uses parallel insulated capacitive electrodes to couple uniform current flow into the tissue and implants. Analytical analyses are presented, which result in a two-port network that describes circuit operation. The two-port network is further simplified for typical DIBD applications where coupling to the external electrodes is low. This results in a simple circuit model of power transfer for which the parameters are easily obtained by experimental measurements. The proposed circuit model has been validated using circuit coupled finite-element analysis (COMSOL) and benchtop experiments using a tissue phantom. In addition, the safety aspect of the method has been evaluated via COMSOL simulation of the specific absorption rate for various implanted receiver dimensions and implantation depths. Finally, a completed power supply, unaffected by the implantation depth, running at 6.78 MHz, delivering 10 mW deep into the body while meeting the IEEE C95.1 basic restriction is presented.

This paper presents a capacitive pressure sensor interface circuit design in 180 nm XH018 CMOS technology for an implantable capacitive pressure sensor, which has a wireless power supply and wireless data transfer function. It integrates full-bridge rectifiers, shorting control switches, low-dropout regulators, bandgap references, analog front end, single slope analog to digital converter (ADC), I2C, and an RC oscillator. The low-dropout regulators regulate the wireless power supply coming from the rectifier and provide a stable and accurate 1.8 V DC voltage to other blocks. The capacitance of the pressure sensor is sampled to a discrete voltage by the analog front end. The single slope ADC converts the discrete voltage into 11 bits of digital data, which is then converted into 1 kbps serial data out by the I2C block. The “1” of serial data is modulated to a 500 kHz digital signal that is used to control the shorting switch for wireless data transfer via inductive back scatter. This capacitive pressure sensor interface IC has a resolution of 0.98 mmHg (1.4 fF), average total power consumption of 7.8 mW, and ±3.2% accuracy at the worst case under a −20 to 80 °C temperature range, which improves to ±0.86% when operated between 20 and 60 °C.

Implanted electronics require protection from the body's fluids to avoid moisture induced failure. This study presents an injection molded liquid crystal polymer (LCP) package to protect active implantable devices for chronic applications, such as in optogenetic research. The technology is applied and assessed through a custom package for a fully implantable optogenetic stimulation system, built on a versatile telemetry system that can incorporate additional stimulating and recording channels. An adapted quasi-steady state model predicts the lifetime of an enclosure, where the definition of the lifetime is the time before the internal relative humidity (RH) reaches a time constant, or 63%RH, a conservative limit to minimize the risk of corrosion. The lifetime of the LCP optogenetic device is 94 days, and can be extended to 326 days with the inclusion of 5% w/v silica gel desiccant. Samples of the LCP optogenetic device containing humidity sensors testing in saline at 38 °C support the RH change predictions. Desiccants inside the implant enclosure can store permeating moisture and prolong the life expectancy of LCP-based implants to years or decades. The results of this study demonstrates the feasibility of providing reliable protection for chronic optogenetic implants, and the technology can be transferred to other applications as an easily-manufactured, cost-effective, radiofrequency compatible alternative to hermetic packaging for chronic studies.

We present a capacitance to frequency converter (CFC) implemented in 180nm CMOS technology intended for pressure monitoring in the body. It is designed to sense pressure changes from 300mmHg to 1000mHg (capacitance range from 6pF to 7 pF) corresponding to a frequency output range of 1.8MHz to 13.4MHz. The frequency output is modulated with a 1.63KHz clock and the number of cycles per period is counted. This readout circuit has a resolution of 0.28fF (0.196mmHg) with a power consumption of 72μW at 1.8 V supply.