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Multisite neural probes are a fundamental tool to study brain function. Hybrid silicon/polymer neural probes combine rigid silicon and flexible polymer parts into one single device and allow, for example, the precise integration of complex probe geometries, such as multishank designs, with flexible biocompatible cabling. Despite these advantages and benefiting from highly reproducible fabrication methods on both silicon and polymer substrates, they have not been widely available. This paper presents the development, fabrication, characterization, and in vivo electrophysiological assessment of a hybrid multisite multishank silicon probe with a monolithically integrated polyimide flexible interconnect cable. The fabrication process was optimized at wafer level, and several neural probes with 64 gold electrode sites equally distributed along 8 shanks with an integrated 8 µm thick highly flexible polyimide interconnect cable were produced. The monolithic integration of the polyimide cable in the same fabrication process removed the necessity of the postfabrication bonding of the cable to the probe. This is the highest electrode site density and thinnest flexible cable ever reported for a hybrid silicon/polymer probe. Additionally, to avoid the time-consuming bonding of the probe to definitive packaging, the flexible cable was designed to terminate in a connector pad that can mate with commercial zero-insertion force (ZIF) connectors for electronics interfacing. This allows great experimental flexibility because interchangeable packaging can be used according to experimental demands. High-density distributed in vivo electrophysiological recordings were obtained from the hybrid neural probes with low intrinsic noise and high signal-to-noise ratio (SNR).

Superhydrophobic surfaces (SHS), with their exceptional water‐repellent properties, have attracted great interest due to their versatile applications. The robustness of SHS has emerged as an essential issue for practical applications, as SHS are directly exposed to various harsh environments, such as continuous raindrop impact, corrosive media, and extreme temperatures. Polyimide (PI) is an ideal candidate for robust SHS due to its superior mechanical, thermal, and chemical properties. However, the low processability of PI in surface microstructuring has limited its application in SHS. In this study, a high‐yield and cost‐effective fabrication method for constructing high‐aspect‐ratio PI microstructures has been developed by controlling the template surface treatment, precursor molecular weight, and vacuum process. This approach achieves an exceptional yield rate of 99.8% and an aspect ratio of 10.7, enabling the construction of various microstructures. The SHS is demonstrated by fabricating microstructures on PI surfaces using the proposed method. The PI SHS exhibits a water contact angle of up to 162° and a roll‐off angle of less than 9°. The water repellency withstands 100 tape peeling tests and remains stable after continuous exposure to temperatures up to 250 °C and various chemical reagents for 60 days, which presents excellent robustness against environmental factors. This study presents robust polyimide superhydrophobic surfaces with excellent mechanical durability, thermal stability, and chemical stability. A high‐yield and cost‐effective method to fabricate high‐aspect‐ratio polyimide surface microstructures is developed by controlling the template surface treatment, precursor molecular weight, and vacuum process time. The proposed method is applied for the realization of robust superhydrophobic surfaces.

Implantable sensors capable of real-time measurements are powerful tools to diagnose disease and maintain health by providing continuous or regular biometric monitoring. In this paper, we present a dental implantable temperature sensor that can send early warning signals in real time before the implant fails. Using a microfabrication process on a flexible polyimide film, we successfully fabricated a multi-channel temperature sensor that can be wrapped around a dental implant abutment wing. In addition, the feasibility, durability, and implantability of the sensor were investigated. First, high linearity and repeatability between electrical resistance and temperature confirmed the feasibility of the sensor with a temperature coefficient of resistance (TCR) value of 3.33 × 10–3/°C between 20 and 100 °C. Second, constant TCR values and robust optical images without damage validated sufficient thermal, chemical, and mechanical durability in the sensor’s performance and structures. Lastly, the elastic response of the sensor’s flexible substrate film to thermal and humidity variations, simulating in the oral environment, suggested its successful long-term implantability. Based on these findings, we have successfully developed a polymer-based flexible temperature sensor for dental implant systems.

Flexible polymer neural probes are an attractive emerging approach for invasive brain recordings, given that they can minimize the risks of brain damage or glial scaring. However, densely packed electrode sites, which can facilitate neuronal data analysis, are not widely available in flexible probes. Here, we present a new flexible polyimide neural probe, based on standard and low-cost lithography processes, which has 32 closely spaced 10 μm diameter gold electrode sites at two different depths from the probe surface arranged in a matrix, with inter-site distances of only 5 μm. The double-layer design and fabrication approach implemented also provides additional stiffening just sufficient to prevent probe buckling during brain insertion. This approach avoids typical laborious augmentation strategies used to increase flexible probes’ mechanical rigidity while allowing a small brain insertion footprint. Chemical composition analysis and metrology of structural, mechanical, and electrical properties demonstrated the viability of this fabrication approach. Finally, in vivo functional assessment tests in the mouse cortex were performed as well as histological assessment of the insertion footprint, validating the biological applicability of this flexible neural probe for acquiring high quality neuronal recordings with high signal to noise ratio (SNR) and reduced acute trauma.

Demands for neural interfaces around functionality, high spatial resolution, and longevity have recently increased. These requirements can be met with sophisticated silicon-based integrated circuits. Embedding miniaturized dice in flexible polymer substrates significantly improves their adaptation to the mechanical environment in the body, thus improving the systems’ structural biocompatibility and ability to cover larger areas of the brain. This work addresses the main challenges in developing a hybrid chip-in-foil neural implant. Assessments considered (1) the mechanical compliance to the recipient tissue that allows a long-term application and (2) the suitable design that allows the implant’s scaling and modular adaptation of chip arrangement. Finite element model studies were performed to identify design rules regarding die geometry, interconnect routing, and positions for contact pads on dice. Providing edge fillets in the die base shape proved an effective measure to improve die-substrate integrity and increase the area available for contact pads. Furthermore, routing of interconnects in the immediate vicinity of die corners should be avoided, as the substrate in these areas is prone to mechanical stress concentration. Contact pads on dice should be placed with a clearance from the die rim to avoid delamination when the implant conforms to a curvilinear body. A microfabrication process was developed to transfer, align, and electrically interconnect multiple dice into conformable polyimide-based substrates. The process enabled arbitrary die shape and size over independent target positions on the conformable substrate based on the die position on the fabrication wafer.

Advances in micromachining technology have provided the opportunity to explore possibilities of creating life-sized physical models of the cochlea. The physical model of the cochlea consists of two fluid-filled channels separated by an elastic partition. The partition is micromachined from silicon and uses a 36-mm linearly tapered polyimide plate with a width of 100 µm at the basal end and 500 µm at the apex to represent the basilar membrane. Thicknesses from 1 to 5 µm have been fabricated. Discrete aluminum fibers (1.5 µm in width) are machined to create direction-dependent properties. A 0.5 × 0.5 mm opening represents the helicotrema. The fluid channels are machined from plexiglas using conventional machining methods. A magnet-coil system excites the fluid channel. Measurements on a model with thickness 4.75 µm show a velocity gain of 4 and phase of 3.5 π radians at a location 23 mm from the base. Mathematical modeling using a 3-D formulation confirm the general characteristics of the measured response.

Fabrication techniques have been developed to produce a perforated polymer microtube as a drug delivery device. The technique consists of first forming a silicon platform with trenches and alignment marks to hold the tubes for subsequent processing. Photolithography and reactive ion etching with an inductively coupled plasma source were used to fabricate micro holes on the surface of polyimide tubes. Several materials have been used to form the etching mask, including titanium film deposited by e-beam evaporation and SiO 2 and SiN x films deposited by high-density plasma chemical vapor deposition (HDPCVD). Three equidistant holes of 20 μm in diameter were fabricated on polyimide tubes (I.D. = 125 μm). The perforated tubes were loaded with ethinyl estradiol and tested for drug release in phosphate buffered saline (pH = 7.1) at 37°C. Zero order release was observed over a period of 30 days with a potential to be extended to 4 years.

The materials that have been employed for the construction of microfluidic devices have been diverse, ranging from traditional materials, such as silicon and glass, to newer polymeric materials. Similarly, the methods for microfabrication have included lithography, casting, injection molding and hot embossing, to name a few. In this chapter, we provide an overview of the various materials and methods that have been used in a diverse range of microfluidic applications. Details on the physical and chemical properties of the materials, as well as the performance characteristics of the microfabrication methods, are provided.