Outstanding Energy Storage Performance of NBT-Based Ceramics under Moderate Electric Field Achieved via Antiferroelectric Engineering.

Ultrahigh energy-storage performance of dielectric ceramic capacitors is generally achieved under high electric fields (HEFs). However, the HEFs strongly limit the miniaturization, integration, and lifetime of the dielectric energy-storage capacitors. Thus, it is necessary to develop new energy-storage materials with excellent energy-storage densities under moderate electric fields (MEFs). Herein, the antiferroelectric material Ag0.9Ca0.05NbO3 (ACN) was used to modify the relaxor ferroelectric material 0.6Na0.5Bi0.5TiO3-0.4Sr0.7Bi0.2TiO3 (NBT-SBT). The introduction of ACN results in high polarization strength, regulated composition of rhombohedral (R3c) and tetragonal (P4bm), nanodomains, and refined grain size. An outstanding recoverable energy density (Wrec = 4.6 J/cm3) and high efficiency (η = 82%) were realized under an MEF of 260 kV/cm in 4 mol % ACN-modified NBT-SBT ceramic. The first-principles calculation reveals that the interaction between Bi and O is the intrinsic mechanism of the increased polarization. A new parameter ΔP/Eb was proposed to be used as the figure of merit to measure the energy-storage performance under MEFs (∼200-300 kV/cm). This work paves a new way to explore energy-storage materials with excellent-performance MEFs.

Magnetic resonance imaging interactions with a sacral neuromodulation system.

AIMS: Sacral neuromodulation (SNM) has successfully treated patients with functional urinary and/or bowel disorders for more than two decades. Historically, patients with the InterStim system (Medtronic) were contraindicated for Magnetic Resonance Imaging (MRI) scans. In 2012, Medtronic obtained Food and Drug Administration (FDA) approval for allowing 1.5 Tesla (T) MRI head scans. In September 2019, the Axonics System (Axonics) received FDA approval for 1.5 T full-body MR Conditional labeling and then 3 T full-body MR Conditional labeling in July 2020. In August 2020, Medtronic received 1.5 and 3 T full-body MR Conditional labeling from the FDA for their new SNM systems (InterStim II and Micro devices with SureScanTM  leads). With the advancements in MRI technology and availability of full-body MRI eligible SNM systems, it is important for physicians to better understand MRI safety for these systems. METHODS: This paper explains the fundamentals of MRI physics, its interactions with active implantable medical devices (AIMDs), the subsequent potential safety hazards with emphasis on radio frequency (RF)-related safety, and the risks associated with "Off-label" scans, including abandoned and broken leads. RESULTS: MRI guidelines provided by the AIMD device manufacturer should be followed to ensure MRI scan safety and avoid any unnecessary risk to patients. CONCLUSIONS: MRI guidelines provided by the device manufacturer are the best resource for guidance for performing safe MRI scanning. Specific conditions should be fully understood and generalizations on MRI safety claims based on partial analysis or case studies should be avoided.

Biomimetic synthesis of calcium carbonate with different morphologies and polymorphs in the presence of bovine serum albumin and soluble starch.

Calcium carbonate has been synthesized by the reaction of Na2CO3 and CaCl2 in the presence of bovine serum albumin (BSA) and soluble starch. Effects of various bovine serum albumin (BSA) and soluble starch on the polymorph and morphology of CaCO3 crystals were investigated. Crystallization of vaterite is favored in the presence of BSA and soluble starch, respectively, while calcite is favored in the presence of a mixture of BSA and soluble starch. The morphologies of CaCO3 particles in the presence of mixture of BSA and soluble starch are mainly rod-like, suggesting that the BSA, soluble and their assemblies play key roles in stabilizing and directing the CaCO3 crystal growth.

Accelerated life-test methods and results for implantable electronic devices with adhesive encapsulation.

We have developed and applied new methods to estimate the functional life of miniature, implantable, wireless electronic devices that rely on non-hermetic, adhesive encapsulants such as epoxy. A comb pattern board with a high density of interdigitated electrodes (IDE) could be used to detect incipient failure from water vapor condensation. Inductive coupling of an RF magnetic field was used to provide DC bias and to detect deterioration of an encapsulated comb pattern. Diodes in the implant converted part of the received energy into DC bias on the comb pattern. The capacitance of the comb pattern forms a resonant circuit with the inductor by which the implant receives power. Any moisture affects both the resonant frequency and the Q-factor of the resonance of the circuitry, which was detected wirelessly by its effects on the coupling between two orthogonal RF coils placed around the device. Various defects were introduced into the comb pattern devices to demonstrate sensitivity to failures and to correlate these signals with visual inspection of failures. Optimized encapsulation procedures were validated in accelerated life tests of both comb patterns and a functional neuromuscular stimulator under development. Strong adhesive bonding between epoxy and electronic circuitry proved to be necessary and sufficient to predict 1 year packaging reliability of 99.97% for the neuromuscular stimulator.

Neurostimulation Strategy for Stress Urinary Incontinence.

We have developed a percutaneously implantable and wireless microstimulator (NuStim) to exercise the pelvic floor muscles for the treatment of stress urinary incontinence. It produces a wide range of charge-regulated electrical stimulation pulses and trains of pulses using a simple electronic circuit that receives power and timing information from an externally generated RF magnetic field. The complete system was validated in vitro and in vivo in preclinical studies demonstrating that the NuStim can be successfully implanted into an effective, low threshold location, and the implant can be operated chronically to produce effective and well-tolerated contractions of skeletal muscle.

Design and Testing of a Transcutaneous RF Recharging System for a Fetal Micropacemaker.

We have developed a rechargeable fetal micropacemaker in order to treat severe fetal bradycardia with comorbid hydrops fetalis. The necessarily small form factor of the device, small patient population, and fetal anatomy put unique constraints on the design of the recharging system. To overcome these constraints, a custom high power field generator was built and the recharging process was controlled by utilizing pacing rate as a measure of battery state, a feature of the relaxation oscillator used to generate stimuli. The design and in vitro and in vivo verification of the recharging system is presented here, showing successful generation of recharging current in a fetal lamb model.

High-Temperature Dielectrics in BNT-BT-Based Solid Solution.

Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT)-based ternary solid solutions were investigated for high-temperature capacitor applications. Through a comprehensive investigation of the (1 - x )(0.92Bi0.5Na0.5TiO3-0.08BaTiO3)- x NaNbO3 [(1 - x )(BNT-BT)- x NN, x = 0 -0.45] system, 0.85(BNT-BT)-0.15NN was selected as the parent matrix due to its relatively high permittivity (>1800) and favorable energy-storage density (0.56 J/cm3 at 7 kV/mm). The effect of bismuth substitution on the dielectric properties of the matrix was further characterized. The introduction of bismuth greatly broadened the operational temperature range of 0.85(BNT-BT)-0.15Na1-3yBiyNbO3 ceramics to over 327 °C for a ±15% tolerance. The dc resistivities were of the order of 108 - [Formula: see text] magnitude from room temperature to 300 °C. An activation energy of 1.1-1.2 eV in 200-350 °C was obtained from dc resistivity data, suggesting that the conduction process in this temperature range may be associated with oxygen vacancy migration. Furthermore, the energy-storage properties were largely improved by the addition of bismuth. When the substitution of Bi over Na achieved was up to 7%, the energy-storage density and efficiency reached 0.62 J/cm3 and 88% at 7 kV/mm, respectively. These results confirm that a BNT-BT-based solid solution is a promising candidate for lead-free high-temperature capacitor applications.

Minimally invasive implantable fetal micropacemaker: mechanical testing and technical refinements.

This paper discusses the technical and safety requirements for cardiac pacing of a human fetus with heart failure and hydrops fetalis secondary to complete heart block. Engineering strategies to meet specific technical requirements were integrated into a systematic design and implementation consisting of a novel fetal micropacemaker, a percutaneous implantation system, and a sterile package that enables device storage and recharging maintenance in a clinical setting. We further analyzed observed problems on myocardial fixation and pacing lead fatigue previously reported in earlier preclinical trials. This paper describes the technical refinements of the implantable fetal micropacemaker to overcome these challenges. The mechanical performance has been extensively tested to verify the improvement of reliability and safety margins of the implantation system.