Design and fabrication of a next generation regenerative neural interface

A Spiral Peripheral Neural Interface (SPNI) is an electrode array that has been previously presented as a regenerative neural interface capable of receiving information from, and transmitting information to nerves. The SPNI has previously been proven in concept, however, when stimulating nerves in the device, the electrodes areinsufficiently isolated from each other and stimulations can trigger unwanted neural activity in neighbouring channels of the SPNI. Along with this, neural interfaces generally, suffer from chronic viability problems, due to biological rejection. These issues were addressed in this thesis, by the addition of a PDMS silicone membrane, into the structure of the SPNI. Improvements to the understanding and performance of structural, electrical and biocompatibility aspects of the SPNI are addressed, with the addition of the PDMS film, which is used to electrically seal SPNI channels whilst not hindering conductor integrity. The inclusion ofPDMS also provides a platform which may enable drug delivery. This work dramatically improves SPNI performance whilst providing routes to improved biocompatibility. This thesis addresses the main issues previously presented in the SPNI and brings the device up to a new standard which can once again be tested for its viability in vivo

Liquid Metal-Enabled Filtering Switches and Switchplexers

The via-pad-slot (VPS) structure, as the switchable element, has been used to demonstrate a single-pole-triple-throw (SPTT) filtering switch and a switchplexer. The VPS can be flexibily switched using liquid metal (LM) or high dielectric constant materials to either cover or uncover the slot. Since the LM only moves on the surface of the VPS and the substrate-integrated waveguide (SIW), the implementation and actuation of the LM is simple and does not cause excessive loss on the device. In the switchplexer design, all channels can be switched on and off to form filters or multiplexers of various channel combinations. Additional transmission zeros (TZs) can be generated by the loaded, partially switched-off channel. The generation of the TZs was discussed and analyzed using coupling matrix approach. The demonstrated &lt;italic&gt;X&lt;/italic&gt;-band (9.56&amp;#x2013;10.44 GHz) cross-shaped SPTT fifth-order filtering switch exhibits a suppression level of better than 40 dB at 8 and 12 GHz, an insertion loss (IL) of 1.55 dB at 10 GHz, and an isolation level of 58 dB at 10 GHz. The &lt;italic&gt;X&lt;/italic&gt;-band switchplexer operates at three frequency bands, e.g., 11.08&amp;#x2013;11.55 GHz, 10.61&amp;#x2013;10.99 GHz, and 9.76&amp;#x2013;10.33 GHz. The LM-enabled VPS-based switchable element can be integrated with other multifunctional circuits and systems for channel control and reconfiguration.</p

Liquid Metal-Based Tunable Linear Phase Shifters With Low Insertion Loss, High Phase Resolution, and Low Dispersion

A linear, tunable, and self-compensating phase shifter based on liquid metal (LM) is proposed in this article using a half-mode substrate-integrated waveguide (HMSIW). The key phase shifting element is a via-pad-slot (VPS) structure where a thru via is attached to a pad surrounded by an annular slot. This is equivalent to a shunt capacitance and inductance loaded on the HMSIW. Phase shift is achieved when the annular slot is covered by the LM that runs in microfluidic channels on the surface of the HMSIW. This allows easy implementation and convenient manipulation of the LM without incurring excessive losses. A self-compensation structure, based on multiple rows of VPSs, is proposed to achieve a low phase deviation with frequency (low dispersion). The design method to ensure a linear and small phase step over a large phase range is presented. Two phase shifters have been designed and experimentally verified. Phase shifter-I, with two VPS rows, provides a phase shift from 0&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt; to 41&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt; with &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\pm$&lt;/tex-math&gt; &lt;/inline-formula&gt;1&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt; phase deviation with frequency over 9.5&amp;#x2013;12.5 GHz. The average phase resolution is 1&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt;. The measured insertion loss (IL) is 0.8 &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\pm$&lt;/tex-math&gt; &lt;/inline-formula&gt; 0.1 dB, with a figure of merit of 45.6&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt;/dB. Phase shifter-II uses three VPS rows to provide a phase shift from 0&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt; to 180&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt; with a phase resolution of 1.68&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt;. The achieved phase deviation with frequency is within &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\pm$&lt;/tex-math&gt; &lt;/inline-formula&gt;2&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}\mathbf{}$&lt;/tex-math&gt; &lt;/inline-formula&gt; over 10&amp;#x2013;12.5 GHz and within &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\pm$&lt;/tex-math&gt; &lt;/inline-formula&gt;5&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt; over 9&amp;#x2013;13 GHz. The measured IL is 1.1 &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\pm$&lt;/tex-math&gt; &lt;/inline-formula&gt; 0.1 dB with a competitively high figure of merit of 163.6&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$^{\circ}$&lt;/tex-math&gt; &lt;/inline-formula&gt;/dB. Unlike many other phase shifters, the loss of the proposed phase shifters does not increase with the phase shift. The measurements are in very good agreement with the circuit analysis and simulations. The proposed linear phase shifter has demonstrated high performance and very attractive features such as low IL that does not strongly depend on the phase shift, linear phase change, high phase resolution, and low phase dispersion with frequency. Compared with other LM-enabled phase shifters, it has the advantage of easy implementation and control. This LM-based phase shifter also potentially has high power handling capability.</p

Biofouling resistant materials based on micro‐structured surfaces with liquid‐repellent properties

Adhesion of contaminants on various polymer-based devices during fluid-substrate interactions is a common problem that can cause biofouling andcorrosion. In this study, hierarchical structures with submicron features onpolypropylene (PP), high-density polyethylene (HDPE), and polycarbonate (PC)are fabricated by femtosecond laser ablation. The effect of the hierarchicalstructures on surface wettability, droplet impact, and bacterial attachment hasbeen examined. Our results demonstrate that the structured polymeric sub-strates facilitate large contact angles and minimal interfacial adhesion, allowingdroplets to roll off at a low angle of inclination below 5◦. Further, rendering thehierarchicalstructureswithalow-surface-energycoatingcanenablethesurfacesto exhibit superamphiphobic properties. The low interfacial adhesion properties,as accounted by the large contact angles and small contact angle hysteresis, ofsuch surfaces prevent bacterial attachment and biofilm formation. The findingsprovide a design principle for creating affordable biofouling resistant surfaceswith a submicron topography hat can be used for engineering and biomedical devices

Wettability and Bactericidal Properties of Bioinspired ZnO Nanopillar Surfaces

Nanomaterials of zinc oxide (ZnO) exhibit antibacterial activities under ambient illumination that result in cell membrane permeability and disorganization, representing an important opportunity for health-related applications. However, the development of antibiofouling surfaces incorporating ZnO nanomaterials has remained limited. In this work, we fabricate superhydrophobic surfaces based on ZnO nanopillars. Water droplets on these superhydrophobic surfaces exhibit small contact angle hysteresis (within 2-3°) and a minimal tilting angle of 1°. Further, falling droplets bounce off when impacting the superhydrophobic ZnO surfaces with a range of Weber numbers (8-46), demonstrating that the surface facilitates a robust Cassie-Baxter wetting state. In addition, the antibiofouling efficacy of the surfaces has been established against model pathogenic Gram-positive bacteria Staphylococcus aureus (S. aureus) and Gram-negative bacteria Escherichia coli (E. coli). No viable colonies of E. coli were recoverable on the superhydrophobic surfaces of ZnO nanopillars incubated with cultured bacterial solutions for 18 h. Further, our tests demonstrate a substantial reduction in the quantity of S. aureus that attached to the superhydrophobic ZnO nanopillars. Thus, the superhydrophobic ZnO surfaces offer a viable design of antibiofouling materials that do not require additional UV illumination or antimicrobial agents.</p