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Flexible and Stretchable Devices for Human-Machine Interfaces
Published in Muhammad Mustafa Hussain, Nazek El-Atab, Handbook of Flexible and Stretchable Electronics, 2019
Irmandy Wicaksono, Canan Dagdeviren
Instead of using an LED with patterned metal interconnects on a long strip of polymer, research performed by Lu et al. (2017) and Canales et al. (2015) exploited thermal drawing techniques to develop flexible and stretchable fiber-based neural probes. The thermal drawing of a polycarbonate and cyclic olefin copolymer (COC) with the introduction of a conductive polymer composite resulted in a flexible multi-modal all-polymer fiber probe (Figure 18.23d,e). The implantable, fiber-based neural probe facilitates in vivo optical stimulation, drug delivery, and electrophysiological recording through the delicate regions of the brain with pinpoint accuracy. Figure 18.23f shows a long-term trial of the fiber probes in freely moving Thy1-ChR2-YFP mice. They retain both recording and stimulation capabilities for 2 months. These multi-modal injectrodes have the potentials to advance tools for manipulation and analysis of brain circuits, particularly for the treatment of neurodegenerative disorders. For instance, they could be integrated with wirelessly controlled pumps that could deliver micro-liters dose of drugs on-demand (Dagdeviren et al. 2018).
Diffractive optical elements
Published in Neil Collings, Fourier Optics in Image Processing, 2018
In order to realise low-cost optical systems, it is important to be able to replicate the DOEs. A variety of embossing, moulding and casting techniques have been developed for optical elements. Embossing is the process of pushing a seal into hot wax. A silicon or quartz seal is called a stamp. Copies of silicon or quartz stamps can be made in nickel, and the resulting elements are called nickel shims. Companies, such as NIL Technology, and EV Group make stamps and shims for nanoimprint lithography. CDA GmbH have teamed up with Holoeye Photonics AG to offer a design and fabrication competence for embossing DOEs into either Polymethyl Methacrylate (PMMA), Polycarbonate (PC), Cyclic Olefin Copolymer (COC), or Cyclic Olefin Polymer (COP). Moulding describes the process of using fluid materials to fill the space between the mould and a reference surface, so that, when cool, the injected material takes the form of the mould. Nickel shims, fabricated from the lithographically mastered DOE, are used for injected moulding [192]. Companies, such as NIL Technology, Temicon, and Rothtec will fabricate shims to customer specifications. Casting is a higher quality process than either injection moulding or embossing. The UV-curable or sol-gel materials are introduced between the mould and a substrate, and subsequently cured by either UV light or thermal curing. The replica formed by one of the above techniques is now a low-cost component for the optical system, provided that the quantity required is sufficient to justify the expense of replication.
Natural Fibres-Based Hybrid Towpregs
Published in R. Alagirusamy, Flexible Towpregs and Their Thermoplastic Composites, 2022
Epoxy is one of the most popular resins used for composite manufacturing. Fibre reinforced epoxy composites have found wide application in the areas of automotive, aerospace, construction etc. Epoxy has excellent mechanical and thermal properties but due to its high density of cross-linkages, the ductility and fracture toughness of epoxy is very poor (Sultan and McGarry 1973). Hayes et al. (2007) have dissolved a thermoplastic polymer (polybisphenol-A-co-epichlorohydrin) in an epoxy resin to create a miscible blend and have used that blend as a matrix for glass fibre-reinforced laminates. They have observed that the blended polymer reinforced glass composite can heal the internal damage if the damaged sample is heated at 130°C. There is much similar literature available where an amorphous or semi crystalline thermoplastic polymer such as cyclic olefin copolymer (Mahmood, Dorigato, and Pegoretti 2020), poly(ε-caprolactone) (Luo et al. 2009), poly (ethylene-co-(methacrylic acid)) (Meure, Wu, and Furman 2009) etc. are added to epoxy resin and the polymer blend is used as a self-healing composite matrix. Intrinsic self-healing systems are based on specific molecular structures that may induce crack healing with the need of external stimuli such as heat, light, UV etc. (Garcia 2014; Wu, Meure, and Solomon 2008; Van der Zwaag et al. 2014; Zhong and Post 2015). Reddy et al. (2020) have developed a hybrid composite by reinforcing an epoxy/polyester blend with alkali-treated cordia dichotoma fibre and granite powder. The above composite exhibits very good tensile, flexural and impact properties and is thermally stable up to a temperature of 430°C.
Recent developments in hot embossing – a review
Published in Materials and Manufacturing Processes, 2021
Swarup S. Deshmukh, Arjyajyoti Goswami
The whole embossing setup was placed in a closed chamber in which compressed nitrogen gas was charged during the embossing stage. The sealing film (silicone) was placed within the two chambers, and the sectional image of the whole setup is shown in Fig. 12 (b). The temperature distribution was measured through an infrared (IR) camera, and it was found that a maximum of 10°C variation is observed in the heating of the substrate. Three different types of microstructures, namely, micro-lenses array, micro-cylindrical array, and V grooves, were fabricated on the Polycarbonate (PC), Polylactic acid (PLA), and Cyclic olefin copolymer respectively. In order to characterize the heating rate, the heating rate was measured by a variation of the input voltage. In this study, the input voltage was varied from 28 V to 48 V, and variation in temperature at 9 points of the polymer substrate was observed. It was observed that in the case of 48 V, only 13 seconds were needed to increases the temperature from 40°C to 180°C. Next, the heating rate was measured by varying the heating area, and for the smaller area, the higher heating rate was observed.[150]