Zugl.: Marburg, Univ., Diss., 2003. / Computerdatei im Fernzugriff.

Zugl.: Marburg, University, Diss., 2003.

Cell patterning platforms support diverse research goals including tissue engineering, the study of cell physiology, and the development of biosensors. Patterning and interfacing with neurons is a particular challenge, being approached via various bioengineering approaches. Such constructs, when optimised, can inform our understanding of neuronal computation and learning, and ultimately aid the development of intelligent neuroprostheses. A fundamental pre-requisite is the ability to dictate the spatial organization and topography of patterned neuronal cells. This thesis details efforts to pattern neurons using photolithographically defined arrays of the polymer parylene-C, printed upon oxidised silicon wafers. Initial work focused on exploring the parylene-C:SiO2 construct as a wide-ranging cell-patterning platform, assessing cell adhesion from both substrate- and cell-centric perspectives. Next, the LUHMES (Lund Human Mesencephalic) cell line was used to explore the potential for construction of interrogatable, topographically-defined neuronal networks. In isolation, LUHMES neurons failed to pattern and did not show any morphological signs of cellular differentiation. However, in the context of a cellular template (the HEK 293 cell line which was found to pattern reliably), LUHMES were able to adhere secondarily on-chip. This co-culture environment promoted morphological differentiation of neurons. As such, HEK 293 cells fulfilled a role analogous to glia, dictating neuronal cell adhesion and generating an environment conducive to neuronal survival. Neurites extended between islands of adherent cell somata. The geometry and configuration of parylene-C influenced the organisation of neurites. With appropriate designs, orthogonal neuronal networks could be created. The dominant guidance cue for neurite growth direction appears to be a diffusible chemotactic agent. HEK 293 cells were later replaced with slower growing human glioma-derived precursors, extracted during tumour debulking surgery. These primary cells patterned accurately on parylene-C and provided a similarly effective, and longer lasting, scaffold for neuronal adhesion.

No description available.

No description available.

Over the 1980’s, the introduction of Additive Manufacturing (AM) technologies has provided alternative methods for the fabrication of complex three-dimensional (3D) synthetic bone tissue implant scaffolds. However, implants are still unable to provide post surgery feedback. Implants often loosen due to mismatched mechanical properties of implant material and host bone. The aim of this PhD research is to fabricate an integrated strain gauge that is able to monitor implant strain for diagnosis of the bone healing process. The research work presents a method of fabricating electrical resistance strain gauge sensors using rapid and mask-less process by experimental development (design of experiment) using the nScrypt 3Dn-300 micro dispensing direct write (MDDW) system. Silver and carbon electrical resistance strain gauges were fabricated and characterised. Carbon resistive strain gauges with gauge factor values greater than 16 were measured using a proven cantilever bending arrangement. This represented a seven to eight fold increase in sensitivity over commercial gauges that would be glued to the implant materials. The strain sensor fabrication process was specifically developed for directly fabricating resistive strain sensor structures on synthetic bone implant surface (ceramic and titanium) without the use of glue and to provide feedback for medical diagnosis. The reported novel approach employed a biocompatible parylene C as a dielectric layer between the electric conductive titanium and the strain gauge. Work also showed that parylene C could be used as an encapsulation material over strain gauges fabricated on ceramic without modifying the performance of the strain gauge. It was found that the strain gauges fabricated on titanium had a gauge factor of 10.0±0.7 with a near linear response to a maximum of 200 micro strain applied. In addition, the encapsulated ceramic strain gauge produced a gauge factor of 9.8±0.6. Both reported strain gauges had a much greater sensitivity than that of standard commercially available resistive strain gauges.

Wireless networks face ever-changing demands on their spectrum and infrastructure resources such as, increased communication bands, capacity-intensive data applications, and the steady growth of worldwide wireless subscribers. This rapid increase in the use of wireless communication and the dependence on a reliable connectivity leads manufacturers to seek systems which are ever smaller, low power, provide long range, and high bandwidth, whilst giving higher reliable technologies. In modern communication systems MEMS is now finding its way, replacing older more high power and non-linear systems. One of the important components of RF MEMS technology is the implementation of MEMS phase shifters for phased array applications that require better performance than arrays of conventional phase shifters. An important example is where RF MEMS devices can be applied to vary the characteristics of an antenna, such as beam steering or tuning in a multiband antenna. The core of this thesis is the development and fabrication of a novel Parylene based MEMS phase shifter. This is the first novel application of Parylene as the strength member of the MEMS bridge. The implementation provided MEMS devices with lower actuation voltage of < 25 V. The fabricated phases shifters provide higher RF performance such as < 1 dB insertion loss, linearity of > 65 dBm, and return loss of < -15 dB. The reliability of the fabricated devices were tested beyond 2 billion switching cycles. This is higher than competing MEMS capacitive devices with a maximum lifetime of 500 million cycles. The fabricated device provides a maximum phase shift of 16.82° at 2.5 GHz, whilst the nominal value of phase shift was 5.4° at 2.5 GHz within the stable region of operation. The fabricated device provides comparable results with respect to reference DMTL designs. The research carried out in this thesis has lead to a number of international publications and four granted patents. The generic nature of this technology can open new opportunities in the conception and application of new MEMS devices in communication and sensing applications. The ability to deliver miniature, low power and high efficiency MEMS capacitive devices, will revolutionise the next generation of tuneable RF components suitable for mobile and handheld devices of the future.

ZnO nanowires (NWs) are good candidates for chemical sensing because of their high surface-to-volume ratio. In this work, ZnO nanobridge sensors were fabricated utilizing a novel method which uses carbonized photoresist (C-PR) as a nucleation layer. The use of C-PR allows simultaneous growth and integration of NWs to lithographically-defined features. The nanobridge sensors are shown to be sensitive to the presence of O₂, H₂O, CO, and H₂/N₂ gas. However, since ZnO dissolves in water, a protective layer is necessary for these sensors to be used in the liquid or vapor phase. A chemical vapor deposition (CVD) process for amino-[2,2]paracyclophane (parylene-A) was developed and used to successfully protect the NWs. Gas sensing measurements were performed on bare and parylene-A coated devices with and without UV illumination. The parylene-A layer was found to attenuate sensitivity to O₂ and H₂O, and UV illumination was found to decrease the response time. / Graduation date: 2012

Neural probes are a promising tool in understanding the brain, alleviating symptoms of various diseases like Parkinson’s Disease and allowing for applications like controlling prosthetics directly using the mind. However, current probes suffer from deleterious glial tissue buildup, poor insulation and low electrode yield. In this work, to improve upon current probes, ultra-compliant probes are fabricated and integrated with biodissolvable needles. Mechanically compliant probes allow for reduction in the body’s immune response chronically whereas biodissolvable needles provide sufficient stiffness during insertion. To achieve this, contributions are made in the categories of probe design concepts, device level processes, and processes in support of final probe assembly. Major contributions include incorporation of interleaved atomic layer deposited ceramics to create hybrid materials that provide better insulation properties, reducing the distance between the electrode and the site-of-interest by developing a gray scale lithography based technique to fabricate protruding electrodes and creating probes that improve electrode yield by integrating liquid crystal polymers into the parylene-C probe structure, which allows the parylene-C probe to actuate. To allow for integration of the biodissolvable needle with the probe, a peel-based process is developed that controls the adhesion between parylene-C to Si using different HMDS conditions and a transfer based process is developed that enables hightemperature annealing. In addition, a generalized design of neural probes using meandering interconnect structures is developed, allowing for rapid mechanical design of probes. This is key for neural probes because of the application specific nature of neural probe design.

This diploma thesis is focused on preparation and characterization of parylene C barrier properties. The layers were prepared by chemical vapour deposition (CVD). The interest in characterization of those layers is huge mainly because of their possible use in museology for the protection of the museum archives against the corrosion. Chlorinated dimer of para-xylylene was used as a precursor. Polypropylene foils, metal sheets and silica wafers were used as tested substrates for thin film preparation. Polypropylene foils were used for oxygen transmission rate measurements, metal sheets were used for corrosion tests and silica wafers were used for Fourier transform infrared spectroscopy (FTIR), confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) and stylus profilometry.