Flexible parylene-based 3-D coiled cable

Prosthesis systems require reliable and flexible connecting cables from the sensing/stimulating electrode sites to processing circuitries. However, the limitations on the fabrication materials and processes restrict the cables' ability to stretch, resulting in breakage and failure of the implanted cabled device. Thus, a microfabricated and fully implantable 3-D parylene coiled cable for prosthesis application is presented. Compared to traditional flexible cables, this parylene coiled structure is able to be stretched by 100% of its original length and is also long-term biocompatible. In addition, the cable structure can be heat-formed in a mold to match muscle curvature and sharp turns in testing subjects and can also be directly integrated with flexible multi-electrodes arrays and neural probes

A generic packaging technique using fluidic isolation for low-drift implantable pressure sensors

This paper reports on a generic packaging method for reducing drift in implantable pressure sensors. The described technique uses fluidic isolation by encasing the pressure sensor in a liquid-filled medical-grade polyurethane balloon; thus, isolating it from surrounding aqueous environment that is the major source of baseline drift. In-vitro tests using commercial micromachined piezoresistive pressure sensors show an average baseline drift of 0.006 cmH2O/day (0.13 mmHg/month) for over 100 days of saline soak test, as compared to 0.101 cmH2O/day (2.23 mmHg/month) for a non-fluidic-isolated one soaked for 18 days. To our knowledge, this is the lowest reported drift for an implantable pressure sensor

Master of Science

thesisOver the past four decades, Multielectrode Array (MEA) devices have played a major role in electrophysiology by providing a simpler solution to simultaneous multi-site chronic extracellular recording: in vivo and in vitro. While a wide range of devices have been developed, almost all of them are limited to culturing and recording from one cell type, in vitro; and tissue surfaces, in vivo and in vitro. Most tissues are formed by different cell types that interact to maintain tissue function, like the heart which is composed mainly of cardio-myocytes and fibroblasts. Direct recording from such organs usually employs plunge-type electrodes which induce tissue damage and require better handling for sustenance. To better understand the functioning of such tissues, it is imperative to utilize recording systems that allow interactions between two or more cell types and at the same time sustain cultures with controlled cell number and distribution. In this thesis, the design, fabrication process, and characterization of an MEA device called the PerFlexMEA (Perforated Flexible MEA) is presented. It enables the generation and sustenance of a preparation with two cell types while recording their electrical activity. PerFlexMEA was developed using a thin (9?m) perforated Polycarbonate Track Etch (PCTE) membrane (3?m diam. pores, 200,000 pores/cm2) as substrate where cells can be cultured on both sides, allowing gap junction formation across the membrane via the pores. Cell number and distribution can be controlled on either side. The PerFlexMEA comprises a 4 × 5 array of square gold electrodes, each measuring 50 ?m × 50 ?m spaced 500 ?m apart. Parylene was patterned to insulate the leads (50 ?m thick) connecting the recording electrodes to the contact pads. A coinshaped device was designed to house the PerFlexMEA and to insulate its cell culture zone (wet) from contact pads (dry). Cardiomyocytes, isolated from neonatal mice were plated on the recording side of PerFlexMEA and electrical activity was recorded at a signal to noise ratio of 8.6 and peak to peak voltage of 200 ?V

Biocompatible microchannel scaffold with microwires for recording regenerative peripheral nerve neural spikes

A new process for the fabrication of a microchannel scaffold with microwires for peripheral nerve applications is presented. This microchannel scaffold implemented between the ends of nerves, the axons of which regenerate through microchannel in scaffold and fixed microelectrodes. This device is entirely handcrafted using commercially available materials such as microwires, PDMS film, liquid PDMS, dental cement, and epoxy glue. This device was implemented in the a Lewis rat sciatic nerve to better analyze the electrical signals of regenerated axons. 64-electrode microchannel scaffolds were developed for both peripheral nerve interfacing and peripheral nerve regeneration. The microwires were used for recording electrode to capture neural signal from the regenerated peripheral nerves. To further differentiate the methodology, the new addition of a ribbon cable will facilitate the transmission of the electrical signals. A total of eight devices have been developed, the nerve regeneration were examined four weeks after device implantation

Development of high-resolution shadow masks using thin membranes of parylene-C for patterning microelectronic devices

In order to fabricate microelectronic devices, patterning techniques such as photolithography or shadow mask patterning must be performed. This last technique uses a physical mask to block regions on the substrate during film deposition and its resolution is determined by the thickness of the mask and the fabrication procedures. This thesis reports the fabrication of Parylene-C thin shadow masks, 3 and 5 m, and their application in single-step and multi-step patterning and, on curved surfaces. The results for single-step patterning showed the possibility of defining features with a resolution of 10 m. When multi-step patterning the maximum resolution obtained in the produced masks was 20 m for separation between features and 40 m for lines where this resolution was limited by the photolithographic masks used. For the alignment, several strategies were tested but the one that presented the best results was the use of SU-8 pillars to align different shadow masks in order to pattern microelectronic devices with 10 m of tolerance. The produced shadow masks sets for TFT patterning were only one used one time and maintained the same yield from before patterning. For fiber patterning, the obtained results are promising since it showed the possibility of patterning in a curved surface using a simpler and low-cost technique. It was possible to deposit three material layers to fabricate a capacitor. It was possible to pattern a circle of 1 mm in diameter on a fiber with 750 m of diameter. This work allowed to fabricate ultra-thin masks in Parylene producing features of high resolution and features on curved surfaces showing how this material can be used as a complement in microelectronic device fabrication

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators

Conserving Waterlogged Rope: A Review of Traditional Methods and Experimental Research with Polyethylene Glycol

The excavation of Sieur de la Salle's ship, La Belle, yielded a large amount of waterlogged rope requiring conservation. A history of hemp and rope manufacture is reviewed to assist in the identification of the materials and rope-work recovered from the La Belle, as well as to assist in selecting an appropriate conservation treatment. A summary of several methods used to conserve cordage is presented. Time has shown that not all of these treatment methods have remained viable options, and that continued study and experimentation are needed so that the conservator has the tools to develop an appropriate conservation plan for each artifact. The majority of La Belle's cordage was conserved using the passivation polymers method developed by Dr. C. Wayne Smith and Dr. Donny L. Hamilton, both of Texas A&M University, in conjunction with Dow Corning Corporation, Midland, Michigan. An experiment applying knowledge gleaned from the passivation polymers process to polyethylene glycol (PEG) impregnation was conducted in an attempt to stabilize the PEG within the rope. The results were good; the rope retained some flexibility and appears stable with a slightly darker color than with silicone oil

Development of a novel intracortical electrode for chronic neural recordings

PhD ThesisMicromotion, attributable to the modulus mismatch between the brain and electrode materials, is a fundamental phenomenon contributing to electrode failure for invasive Brain-Machine Interfaces. Spike recording quality from conventional chronic electrode designs deteriorates over the weeks/months post-implantation, in terms of signal amplitude and single unit stability, due to glial cell activation by sustained mechanical trauma. Conventional electrode designs consist of a rigid straight shaft and sharp tip, which can augment mechanical trauma sustained due to micromotion. The sinusoidal probe has been fabricated to reduce micromotion related mechanical trauma. The electrode is microfabricated from flexible materials and has design measures such as a sinusoidal shaft, spheroid tip and a 3D polyimide ball anchor to restrict electrode movement relative to the surrounding brain tissue, thus theoretically minimising micromotion. The electrode was compared to standard microwire electrodes and was shown to have more stable chronic recordings in terms of SNR and LFP power. A longer chronic recording period was achieved with the sinusoidal probe for the first generation. Quantitative histology detecting microglia and astrocytes showed reduced neuronal tissue damage especially for the tip region between 6-24 months chronic indwelling period for the sinusoidal probe. This may be linked to the more stable chronic recordings. This is the first demonstration that electrode designs wholly incorporating micromotion- reducing measures may decrease the magnitude of gliosis, with possible chronic recording longevity enhancement

Design, manufacturing and characterisation of a wireless flexible pressure sensor system for the monitoring of the gastro-intestinal tract

Ingestible motility capsule (IMC) endoscopy holds a strong potential in providing advanced diagnostic capabilities within the small intestine with higher patient tolerance for pathologies such as irritable bowel syndrome, gastroparesis and chronic abdominal amongst others. Currently state-of-the art IMCs are limited by the use of obstructive off-the-shelf sensing modules that are unable to provide multi-site tactile monitoring of the Gastro-Intestinal tract. In this work a novel 12 mm in diameter by 30 mm in length IMC is presented that utilises custom-built flexible, thin-film, biocompatible, wireless and highly sensitive tactile pressure sensors arrays functionalising the capsule shell. The 150 μm thick, microstructured, PDMS flexible passive pressure sensors are wirelessly powered and interrogated, and are capable of detecting pressure values ranging from 0.1 kPa up to 30 kPa with a 0.1 kPa resolution. A novel bottom-up wafer-scale microfabrication process is presented which enables the development of these ultra-dense, self-aligned, scalable and uniquely addressable flexible wireless sensors with high yield (>80%). This thesis also presents an innovative metallisation microfabrication process on soft-elastomeric substrates capable to withstand without failure of the tracks 180o bending, folding and iterative deformation such as to allow conformable mapping of these sensors. A custom-built and low-cost reflectometer system was also designed, built and tested within the capsule that can provide a fast (100 ms) and accurate extraction (±0.1 kPa) of their response. In vitro and in vivo characterisation of the developed IMC device is also presented, facilitated respectively via the use of a biomimetic phantom gut and via live porcine subjects. The capsule device was found to successfully capture respiration, low-amplitude and peristaltic motility of the GI tract from multiple sites of the capsule.UK Engineering & Physical Sciences Research Council (EPSRC) through the Programme Grant Sonopill (EP/K034537/2)James Watt Scholarshi