Ultra-long-term reliable encapsulation using an atomic layer deposited Hfo2/Al2o3/Hfo2 triple-interlayer for biomedical implants

Long-term packaging of miniaturized, flexible implantable medical devices is essential for the next generation of medical devices. Polymer materials that are biocompatible and flexible have attracted extensive interest for the packaging of implantable medical devices, however realizing these devices with long-term hermeticity up to several years remains a great challenge. Here, polyimide (PI) based hermetic encapsulation was greatly improved by atomic layer deposition (ALD) of a nanoscale-thin, biocompatible sandwich stack of HfO2/Al2O3/HfO2 (ALD-3) between two polyimide layers. A thin copper film covered with a PI/ALD-3/PI barrier maintained excellent electrochemical performance over 1028 days (2.8 years) during acceleration tests at 60 °C in phosphate buffered saline solution (PBS). This stability is equivalent to approximately 14 years at 37 °C. The coatings were monitored in situ through electrochemical impedance spectroscopy (EIS), were inspected by microscope, and were further analyzed using equivalent circuit modeling. The failure mode of ALD Al2O3, ALD-3, and PI soaking in PBS is discussed. Encapsulation using ultrathin ALD-3 combined with PI for the packaging of implantable medical devices is robust at the acceleration temperature condition for more than 2.8 years, showing that it has great potential as reliable packaging for long-term implantable devices

Fully Integrated Biochip Platforms for Advanced Healthcare

Recent advances in microelectronics and biosensors are enabling developments of innovative biochips for advanced healthcare by providing fully integrated platforms for continuous monitoring of a large set of human disease biomarkers. Continuous monitoring of several human metabolites can be addressed by using fully integrated and minimally invasive devices located in the sub-cutis, typically in the peritoneal region. This extends the techniques of continuous monitoring of glucose currently being pursued with diabetic patients. However, several issues have to be considered in order to succeed in developing fully integrated and minimally invasive implantable devices. These innovative devices require a high-degree of integration, minimal invasive surgery, long-term biocompatibility, security and privacy in data transmission, high reliability, high reproducibility, high specificity, low detection limit and high sensitivity. Recent advances in the field have already proposed possible solutions for several of these issues. The aim of the present paper is to present a broad spectrum of recent results and to propose future directions of development in order to obtain fully implantable systems for the continuous monitoring of the human metabolism in advanced healthcare applications

Magnetic Resonance Imaging Compatibility of the Polymer-based Cochlear Implant

ObjectivesIn this study, we compared the magnetic resonance (MR) image artifacts caused by a conventional metal-based cochlear implant and a newly developed liquid crystal polymer (LCP)-based device.MethodsThe metal-based cochlear implant system (Nurobiosys Co.) was attached to side of the head of a subject and the LCP-based device was attached to opposite side. In both devices, alignment magnets were removed for safety. Magnetic resonance imaging (MRI) was performed on a widely used 3.0 T and an ultra-high 7.0 T MRI machine. 3.0 and 7.0 T MR images were acquired using T1- and T2*-weighted gradient echo sequences, respectively.ResultsIn the 3.0 T images, the metal-based device on the left side generated the significant amount of artifacts. The MR images in the proximity of the metal package were obscured by the artifacts in both axial and sagittal views. On the other hand, the MR images near the LCP-based device were relatively free from the artifacts and clearly showed the brain structures. 7.0 T MR images showed the more severe distortion in the both sides but the metal-based cochlear implant system caused a much larger obscure area than the LCP-based system.ConclusionThe novel LCP-based cochlear implant provides a good MRI compatibility beyond present-day cochlear implants. Thus, MR images can be obtained from the subjects even with the implanted LCP-based neural prosthetic systems providing useful diagnostic information. Furthermore, it will be also useful for functional MRI studies of the auditory perception mechanism after cochlear implantations as well as for positron emission tomography-MRI hybrid imaging

Doctor of Philosophy

dissertationBiomedical implantable devices have been developed for both research and clinical applications, to stimulate and record physiological signals in vivo. Chronic use of biomedical devices with thin-film-based encapsulation in large scale is impeded by their lack of long-term functionality and stability. Biostable, biocompatible, conformal, and electrically insulating coatings that sustain chronic implantation are essential for chip-scale implantable electronic systems. Even though many materials have been studied to for this purpose, to date, no encapsulation method has been thoroughly characterized or qualified as a broadly applicable long-term hermetic encapsulation for biomedical implantable devices. In this work, atomic layer deposited Al2O3 and Parylene C bi-layer was investigated as encapsulation for biomedical devices. The combination of ALD Al2O3 and CVD Parylene C encapsulation extended the lifetime of coated interdigitated electrodes (IDEs) to up to 72 months (to date) with low leakage current of ~ 15 pA. The long lifetime was achieved by significantly reducing moisture permeation due to the ALD Al2O3 layer. Moreover, the bi-layer encapsulation separates the permeated moisture (mostly at the Al2O3 and Parylene interface) from the surface contaminants (mostly at the device and Al2O3 interface), preventing the formation of localized electrolyte through condensation. Al2O3 works as an inner moisture barrier and Parylene works as an external ion barrier, preventing contact of AI2O3 with liquid water, and slowing the kinetics of alumina corrosion. Selective removal of encapsulation materials is required to expose the active sites for interacting with physiological environment. A self-aligned mask process with three steps was developed to expose active sites, composed of laser ablation, oxygen plasma etching, and BOE etching. Al2O3 layer was found to prevent the formation of microcracks in the iridium oxide film during laser ablation. Bi-layer encapsulated iridium oxide had higher charge injection capacity and similar electrochemical impedance compared with Parylene C coated iridium oxide film after deinsulation. The Al2O3 and Parylene C bi-layer encapsulation was applied to Utah electrode array (UEA)-based neural interfaces to study its long-term performance. The median tip impedance of the bi-layer encapsulated wired Utah electrode array increased slowly during the 960 days of equivalent soak testing at 37 °C. Impedance for Parylene coated UEA dropped 50% to 75% within 6 months. In addition, bi-layer coated fully integrated Utah array-based wireless neural interfaces had stable power-up frequencies at ~910 MHz and constant RF signal strength of -50 dBm during the 1044 days of equivalent soaking time at 37 °C. This is much longer than lifetime achieved with Parylene C coating, which was about one year at room temperature

Wafer-Level Parylene Packaging With Integrated RF Electronics for Wireless Retinal Prostheses

This paper presents an embedded chip integration technology that incorporates silicon housings and flexible Parylene-based microelectromechanical systems (MEMS) devices. Accelerated-lifetime soak testing is performed in saline at elevated temperatures to study the packaging performance of Parylene C thin films. Experimental results show that the silicon chip under test is well protected by Parylene, and the lifetime of Parylenecoated metal at body temperature (37°C) is more than 60 years, indicating that Parylene C is an excellent structural and packaging material for biomedical applications. To demonstrate the proposed packaging technology, a flexible MEMS radio-frequency (RF) coil has been integrated with an RF identification (RFID) circuit die. The coil has an inductance of 16 μH with two layers of metal completely encapsulated in Parylene C, which is microfabricated using a Parylene–metal–Parylene thin-film technology. The chip is a commercially available read-only RFID chip with a typical operating frequency of 125 kHz. The functionality of the embedded chip has been tested using an RFID reader module in both air and saline, demonstrating successful power and data transmission through the MEMS coil

Nanofilament Scaffold For Tissue Regeneration

A scaffold for tissue regeneration is provided. In a preferred embodiment, the scaffold is implantable in a patient in need of nerve or other tissue regeneration and includes a structure which has a plurality of uniaxially oriented nanofibers made of at least one synthetic polymer. Preferably, at least 75% of the nanofibers are oriented within 20 degrees of the uniaxial orientation. The scaffold beneficially provides directional cues for cell and tissue regeneration, presumably by mimicking the natural strategy using filamentous structures during development and regeneration.Georgia Tech Research Corporatio

Polymer-to-Carbon Conversion: From Nature to Technology

Glassy carbon is derived from synthetic organic polymers that undergo the process of coking during their pyrolysis. Polymer-to-carbon conversion (hereafter referred to as PolyCar) also takes place in nature, and is indeed responsible for the formation of various naturally occurring carbon allotropes. In the last few decades the PolyCar concept has been utilized in technological applications, i.e., specific polymers are patterned into the desired shapes and intentionally converted into carbon by a controlled heat-treatment. Device fabrication using glassy carbon is an excellent example of the use of the PolyCar process in technology, which has rapidly progressed from conventional to micro- and nanomanufacturing. While the technique itself is simple, one must have a good understanding of the carbonization mechanism of the polymer, which in turn determines whether or not the resulting material will be glassy carbon. Publications that comprise this special issue shed light on several aspects of the formation, properties and performance of glassy carbon in the cutting-edge technological applications. The results of detailed material characterization pertaining to two important research areas, namely neural electrodes and precision glass molding, are presented as examples. I hope that the readers will enjoy as well as benefit from this collection