The concept of an electronic visual prosthesis has been investigated since the early 20th century. While the first generation of long-term implantable devices were defined by the turn of the millennium, the greatest progress has been achieved in the past decade. This review describes the current state of the art of visual prosthesis investigated by more than two dozen active groups in this field of research. The focus is on technological solutions in regard to long-term safety of materials, electrode-tissue interfaces and encapsulation technologies. Furthermore, we critically assess the maximum number of stimulating electrodes each technological approach is likely to provide.

Polymer optics have gained increasing importance in recent years. With advancing requirements for the optical components, the fabrication process remains a challenge. In particular, the fabrication of the mold inserts for the replication process is crucial for obtaining high-quality optical components. This review focuses on fabrication technologies for optical mold inserts. Thereby, two main types of technologies can be distinguished: fabrication methods to create mold inserts with optical surface quality and methods to create optical microstructures. Since optical mold inserts usually require outstanding form accuracies and surface qualities, a focus is placed on these factors. This review aims to give an overview of available methods as well as support the selection process when a fabrication technology is needed for a defined application. Furthermore, references are given to detailed descriptions of each technology if a deeper understanding of the processes is required.

No abstract

Abstract:Polymer optics are widely used in various applications, replacing traditional glass lenses. The ability to create free-form and micro-structured optics, as well as fast replication, gives them major advantages over traditional glass lenses. However, the fabrication of complex optical components requires full process control and understanding of influencing factors on the quality of the polymer optical parts. In this work, a curved diffractive optical element (DOE) is fabricated using injection compression molding. Different gate designs were evaluated and the movement of the compression stamper was optimized to obtain good filling behavior. The process stability was analyzed and improved by controlling the melt temperature precisely. Finally, the molding parameters were optimized, focusing on the mold temperature, melt temperature and compression force. Curved diffractive optical elements were replicated with feature sizes of 1.6 µm. The experiments showed that all aspects of the molding process have to be controlled perfectly to produce complex polymer optics. High mold temperatures and compression force are necessary to replicate micro-structured features. The work presents a broad investigation and description of the fabrication process and their influences.

Standard interconnection technologies are reviewed in respect to their applicability to electrically and mechanically connect laser-patterned nerve electrodes made from silicone rubber and platinum foil to wires and screen printed alumina substrates. Laser welding, gap welding, microflex ball bonding, and soldering are evaluated. Corresponding processes were established and evaluated in respect to their mechanical strength. Best results were obtained by soldering. If soldering cannot be used because of regulatory reasons, parallel gap welding and microflex are recommended. Laser welding provides weaker interconnects with only moderate reproducibility.