Biomimetic soft lithography on curved nanostructured surfaces

In this paper a nano-molding process using a nature-created master is demonstrated. The eye of night moth Agotis exclamationis having 100 nm-scale structures on a curved surface is used as biomimetic master mold from which nanostructures are replicated onto a flat substrate. Suitable conditions of this simple and cost-efficient process allows for minimal texture damage. The fabrication consists of two steps: first, a negative PDMS mold of the curved eye surface is made, and second, the flexible mold is replicated into a hybrid UV sensitive polymer, on a flat substrate. An accurate copy of the master surface with dense arrays of 200 nm high and 100–120 nm wide posts are generated, thus preserving the integrity of the nanostructures. The known anti-reflecting optical properties of the moth eye were reproduced with a reflectivity reduced by a factor of 2

Characterization of Ferrofluid-Based Stimuli-Responsive Elastomers

Stimuli-responsive materials undergo physicochemical and/or structural changes when a specific actuation is applied. They are heterogeneous composites, consisting of a non-responsive matrix where functionality is provided by the filler. Surprisingly, the synthesis of polydimethylsiloxane (PDMS)-based stimuli-responsive elastomers (SRE) has seldomly been presented. Here, we present the structural, biological, optical, magnetic, and mechanical properties of several magnetic SRE (M-SRE) obtained by combining PDMS and isoparafin-based ferrofluid (FF). Independently of the FF concentration, results have shown a similar aggregation level, with the nanoparticles mostly isolated (>60%). In addition to the superparamagnetic behavior, the samples show no cytotoxicity except the sample with the highest FF concentration. Spectral response shows FF concentrations where both optical readout and magnetic actuation can simultaneously be used. The Young’s modulus increases with the FF concentration until the highest FF concentration is used. Our results demonstrate that PDMS can host up to 24.6% FF (corresponding to 2.8% weight of Fe3O4 nanoparticles concentration). Such M-SRE are used to define microsystems – also called soft microsystems due to the use of soft materials as main mechanical structures. In that scenario, a large displacement for relatively low magnetic fields (<0.3 T) is achieved. The herein presented M-SRE characterization can be used for a large number of disciplines where magnetic actuation can be combined with optical detection, mechanical elements, and biological sample

Recent progress in lab-on-a-chip systems for the monitoring of metabolites for mammalian and microbial cell research

Lab-on-a-chip sensing technologies have changed how cell biology research is conducted. This review summarises the progress in the lab-on-a-chip devices implemented for the detection of cellular metabolites. The review is divided into two subsections according to the methods used for the metabolite detection. Each section includes a table which summarises the relevant literature and also elaborates the advantages of, and the challenges faced with that particular method. The review continues with a section discussing the achievements attained due to using lab-on-a-chip devices within the specific context. Finally, a concluding section summarises what is to be resolved and discusses the future perspectives

Fabrication of polymeric micro structures by controlled drop on demand inkjet printing

Well controlled spherical microstructures could enable several novel MEMS devices. However, micro machining of spherical shapes has proven to be difficult with conventional planar microfabrication processes [1]. This paper presents a method allowing to fabricate controlled micro spherical structures. Drops of approximately 30 picoliters of polymeric solution were accurately inkjet printed on rounded platforms. The deposited volume is confined by rim of these platforms, thus allowing a fine control of the spherical cap edge angle as well as the volume and the radius of curvature. The process proposed allowed to fabricate large arrays of micro spherical shapes, with a controlled edge angle between 25° and 110°. Several arrays of 30 by 30 micro hemispheres with an edge angle of 90° have been successfully fabricated with a yield above 98%

Transflective holographic film for head worn display

A display panel assembly comprises a transflective holographic screen, i.e., a transparent screen that reflects light from a projection system, comprising at least a volume hologram, a first protective element and a second protective element, each arranged in contact with the volume hologram such that the volume hologram is sandwiched between the first protective element and the second protective element. The display panel assembly further comprises a projection system focusing an image on the volume hologram comprising at least projection optics, mounting means arranged to fixedly mount the projection system relatively to the transflective holographic screen. The volume hologram comprises a plurality of diffractive patterns disposed in sequence across the volume hologram, each of the plurality of diffractive patterns being configured to diffuse the light rays from the projection system in a determined direction corresponding to the specific diffractive pattern and oriented towards a position of an intended eye of a user wearing the display panel assembly

Fabrication of epoxy spherical microstructures by controlled drop-on-demand inkjet printing

Well-controlled spherical microstructures open new possibilities for several MEMS devices, such as hemispherical microfluidic channels or micro-optical elements. However, machining of micro-spherical shapes has proven to be difficult with conventional planar micro-fabrication processes. This paper presents a fabrication method allowing the fabrication of controlled micro-spherical cap structures with defined edge angles. Drops of 30 pL of an epoxy solution were accurately inkjet printed on circular platforms. The deposited volume is confined by the rim of the platforms. This allows a fine tuning of the spherical cap edge angle as well as its height and radius of curvature. The presented method allowed fabricating large arrays of well-controlled micro-spherical shapes of different diameters, ranging from 50 to 930 μm, with a maximum controlled edge angle tuning of 85°. Theoretical investigations of the underlying phenomena are also presented. Good agreement between experimental results and theoretical expectations has been observed, with standard deviations below 3%. Using the proposed method, several 2D arrays up to 900 micro hemispheres with an edge angle of 90° ± 2° have been fabricated with a yield above 98%

High-resolution 1D moirés as counterfeit security features

A moire is an interference pattern that appears when two different periodic structures are overlaid. The image created is extremely sensitive to small variations in the original layers and is thus very interesting for anti-counterfeit protection. We present a microfabricated 1D moire enabling complex high-resolution patterns as a significantly improved security feature that cannot be reproduced using standard printing methods. Furthermore, we demonstrate, theoretically and experimentally, that a microscopic deviation from the original design results in a macroscopic variation in the moire that is clearly visible to the naked eye. The record resolution achieved in the elements fabricated and the increased design freedom, make these high-resolution moires excellent candidates for a variety of visually appealing security applications

Inkjet-printed hemispherical microcapsules and silicon chip embedding

Planar lithography techniques are not effective for precise fabrication of microdevices with hemispherical shapes. Drop-on-demand (DOD) inkjet printing (IJP) of photo-curable ink is a more appropriate fabrication approach as it takes advantage of the surface tension as well as of the delivery of a well-defined ink volume. Described is a DOD IJP technique onto geometrically-patterned silicon substrates enabling the controlled fabrication of SU-8 hemispherical microcapsules. Open half capsules of 100 µm in diameter with inner cavity volumes of 5, 20 and 45 pl with a printing yield above 96% are demonstrated. The same technique is directly adapted to the fabrication of microcapsules embedding silicon microchips. The reported findings open new paths for controlled encapsulation of liquids into smart microsystems.info:eu-repo/semantics/publishe