Coil Antennas for Cochlear Implants

A Cochlear implant is a neuro-prosthetic medical device that is surgically placed underneath the skin consisting of a multi-electrode array that stretches into the inner ear or cochlea. The multi-electrode array electrically stimulates the hair cells or nerve cells within the cochlea to produce the sensation of sound. This implant is paired with an external unit that is worn on the ear and resembles a hearing aid. These two units communicate wirelessly with each other through a set of transmitting and receiving antennas over a transcutaneous electromagnetic radio link. The receiving antenna within the Cochlear implant body is the main focus of my work, the project in collaboration with Cochlear Limited, Sydney, under the ARC Industrial Transformation Training Centres (ITTC) hub. Currently, the receiving antennas within the Cochlear implant body are made of a simple multi-stranded platinum wire that is twisted into a circular loop encapsulated in silicone casing. The use of platinum as the core antenna conductor has disadvantages of high impedance at radio frequencies (RF) along with reported long-term cytotoxicity of platinum based electrodes in Cochlear implants. The Cochlear implants including the receiver coil antennas are manufactured through a manual method where each component is hand assembled. The high cost of Cochlear Implants which is between USD 30,000-50,000 stems from the manual hand assembling process. As such, the main idea behind the project is to change the production approach. Within this broad idea and direction from Cochlear Limited, Sydney, the scope of this thesis is limited to examining rapid prototyping and fabrication methods for constructing an electrode layout in the form of a coil antenna for the application of wirelessly powering the implant. The fabrication methods evaluated for the construction of the coil antenna are also suggested to be applied for constructing the multi-electrode array (MEAs) of the cochlear implant, which is made from the same material as the receiving coil antenna. However, unlike the coil antenna, these MEAs are exposed to the biological cells for electrical stimulation and without the silicone casing. These present limitations of the Cochlear implant, including antenna component within the implant, are discussed in detail in chapter 1 with the literature review. This PhD thesis presents the design and fabrication of alternate spiral coil antenna for the Cochlear implants produced through different additive and subtractive manufacturing routes. Suitable conducting materials for fabricating the core conductor of the antenna are identified along with coherent manufacturing strategy for rapid prototyping of the alternate antennas. Chapter 2 presents a general summary of the reagent materials and methods adopted for the fabrication of spiral coil antenna. The coil antenna design including the simulated geometrical dimension and electrical parameters are presented. The chapters following report on the experimentally fabricated spiral coil antennas. In chapter 3, two different additive manufacturing methods of inkjet and extrusion printing are used for the fabrication of gold nanoparticle-based coil antennas on the polydimethylsiloxane (PDMS) substrate. These two methods are compared in terms of ease of fabrication of the coil antenna and thus prepared coil antennas are electrically assessed through impedance measurements. Chapter 4 presents gold-based coil antennas fabricated on flexible PDMS and acrylic Perspex substrates using a laser engraving process. The gold layer is sputter coated onto a chemically treated PDMS surface and acrylic Perspex and through laser engraving process, the gold-coated layer is carved into a functional coil antenna. The coil antennas fabricated using this method are used to evaluate the effect of substrate and deposited conductor compatibility and its subsequent effect on its electrical characteristics. In chapter 5, a laser induced graphene-based coil antenna is constructed on a flexible polyimide (PI) substrate produced through a laser ablation process as an alternative to gold-based coil antennas. Here, the laser light is irradiated on the polymer substrate that locally increases the temperature of the substrate, breaking the chemical bonds to produce graphene. The structural build of all the fabricated coil antennas is assessed through scanning electron microscopy (SEM) and optical microscopy measurements. The printed coil antennas are also used as wireless signal receivers by coupling with a Qi based transmitting module operating at 100-125 KHz frequency for demonstrating its capability as a wireless receiver. This method of producing graphene is also applied for PDMS sheets. The graphene produced on the surface of the PDMS is tested for biocompatibility and assessed as a potential bioelectrode by culturing live cells on it. Finally, chapter 6 discusses the conclusion and future work for the experimental works carried out in the previous chapters and provides future direction

Novel Collagen Surgical Patches for Local Delivery of Multiple Drugs

Effective control of post-operative inflammation after tissue repair remains a clinical challenge. A tissue repair patch that could appropriately integrate into the surrounding tissue and control inflammatory responses would improve tissue healing. A collagen-based hybrid tissue repair patch has been developed in this work for the local delivery of an anti-inflammatory drug. Dexamethasone (DEX) was encapsulated into PLGA microspheres and then co-electrocompacted into a collagen membrane. Using a simple process, multiple drugs can be loaded into and released from this hybrid composite material simultaneously, and the ratio between each drug is controllable. Anti-inflammatory DEX and the anti-epileptic phenytoin (PHT) were co-encapsulated and released to validate the dual drug delivery ability of this versatile composite material. Furthermore, the Young’s modulus of this drug-loaded collagen patch was increased to 20 KPa using a biocompatible riboflavin (vitamin B2)-induced UV light cross-linking strategy. This versatile composite material has a wide range of potential applications which deserve exploration in further research

Proving Scalability of an Organic Semiconductor To Print a TFT-Active Matrix Using a Roll-to-Roll Gravure

Organic semiconductor-based thin-film transistors’ (TFTs) charge-carrier mobility has been enhanced up to 25 cm²/V s through the improvement of fabrication methods and greater understanding of the microstructure charge-transport mechanism. To expand the practical feasibility of organic semiconductor-based TFTs, their electrical properties should be easily accessed from the fully printed devices through a scalable printing method, such as a roll-to-roll (R2R) gravure. In this study, four commercially available organic semiconductors were separately formulated into gravure inks. They were then employed in the R2R gravure system (silver ink for printing gate and drain–source electrodes and BaTiO₃ ink for printing dielectric layers) for printing 20 × 20 TFT-active matrix with the resolution of 10 pixels per inch on poly­(ethylene terephthalate) (PET) foils to attain electrical properties of organic semiconductors a practical printing method. Electrical characteristics (mobility, on–off current ratio, threshold voltage, and transconductance) of the R2R gravure-printed 20 × 20 TFT-active matrices fabricated with organic semiconducting ink were analyzed statistically, and the results showed more than 98% device yield and 50 % electrical variations in the R2R gravure TFT-active matrices along the PET web