Fabrication of polymer micro-lens array with pneumatically diaphragm-driven drop-on-demand inkjet technology

Effects of surface patterning and topography on the cellular functions of tissue engineered scaffolds with special reference to 3D bioprinting

The extracellular matrix (ECM) of the tissue organ exhibits a topography from the nano to micrometer range, and the design of scaffolds has been inspired by the host environment. Modern bioprinting aims to replicate the host tissue environment to mimic the native physiological functions. A detailed discussion on the topographical features controlling cell attachment, proliferation, migration, differentiation, and the effect of geometrical design on the wettability and mechanical properties of the scaffold are presented in this review. Moreover, geometrical pattern-mediated stiffness and pore arrangement variations for guiding cell functions have also been discussed. This review also covers the application of designed patterns, gradients, or topographic modulation on 3D bioprinted structures in fabricating the anisotropic features. Finally, this review accounts for the tissue-specific requirements that can be adopted for topography-motivated enhancement of cellular functions during the fabrication process with a special thrust on bioprinting.

Printing Polymeric Convex Lenses to Boost the Sensitivity of a Graphene-Based UV Sensor

Ultraviolet (UV) is widely used in daily life as well as in industrial manufacturing. In this study, a single-step postprocess to improve the sensitivity of a graphene-based UV sensor is studied. We leverage the advantage of electric-field-assisted on-demand printing, which is simply applicable for mounting functional polymers onto various structures. Here, the facile printing process creates optical plano-convex geometry by accelerating and colliding a highly viscous droplet on a micropatterned graphene channel. The printed transparent lens refracts UV rays. The concentrated UV photon energy from a wide field of view enhances the photodesorption of electron-hole pairs between the lens and the graphene sensor channel, which is coupled with a large change in resistance. As a result, the one-step post-treatment has about a 4× higher sensitivity compared to bare sensors without the lenses. We verify the applicability of printing and the boosting mechanism by variation of lens dimensions, a series of UV exposure tests, and optical simulation. Moreover, the method contributes to UV sensing in acute angle or low irradiation. In addition, the catalytic lens provides about a 9× higher recovery rate, where water molecules inside the PEI lens deliver fast reassembly of the electron-hole pairs. The presented method with an ultimately simple fabrication step is expected to be applied to academic research and prototyping, including optoelectronic sensors, energy devices, and advanced manufacturing processes.

Naked-Eye 3D Display Based on Microlens Array Using Combined Micro-Nano Imprint and UV Offset Printing Methods

An optical film integrating microlens array (MLAs) and 3D micro-graphics is an important way to achieve the naked-eye 3D display effect. The 3D micro-graphics is traditionally generated by the micro-nano imprint technology based on precision engraving mold, which leads to high production cost and low production efficiency, and thus restricts the rapid response to production tasks and large-scale popularization and application. In this study, a process scheme for large-scale printing of 3D micro-graphics using UV offset printing based on presensitized (PS) plate was proposed, matching with the MLAs fabricated by micro-nano imprint process to achieve naked-eye 3D display effect. We used the laser confocal microscope to systematically measure and analyze the geometric and optical performance of the fabricated MLAs in terms of height, curvature radius, center distance, spacing, focal length, and numerical aperture, and evaluated the influence of the publishing resolution of the PS plate on the display effect of 3D micro-graphics. The printing quality and display effect of 3D micro-graphics were further improved by adjusting process parameters such as printing speed and printing pressure. The results of the current study demonstrate that the combined application of micro-nano imprint technology based on precision mold and UV offset printing technology based on PS plate can achieve an excellent naked-eye 3D display effect in 360° all angles, which is efficient, cost-saving, and highly flexible.

Printed cylindrical lens pair for application to the seam concealment in tiled displays

Seamless tiling of displays is one of the key enabling technologies for the next-generation large-area electronics applications. In this paper, we propose a facile method to demonstrate a seamless display using cylindrical lens pair (CLP) fabricated by dispenser printing method. Optical properties of the printed CLP and corresponding capability of concealing seam in the display are analyzed by a set of luminance simulation and measurement in terms of geometric parameters of the lens. The seamless display with an optimized CLP features a viewing angle of the seam concealment of 40°.

Nanoscale 2.5-dimensional surface patterning with plasmonic lithography

We report an extension of plasmonic lithography to nanoscale 2.5-dimensional (2.5D) surface patterning. To obtain the impulse response of a plasmonic lithography system, we described the field distribution of a point dipole source generated by a metallic ridge aperture with a theoretical model using the concepts of quasi-spherical waves and surface plasmon-polaritons. We performed deconvolution to construct an exposure map of a target shape for patterning. For practical applications, we fabricated several nanoscale and microscale structures, such as a cone, microlens array, nanoneedle, and a multiscale structure using the plasmonic lithography system. We verified the possibility of applying plasmonic lithography to multiscale structuring from a few tens of nanometres to a few micrometres in the lateral dimension. We obtained a root-mean-square error of 4.7 nm between the target shape and the patterned shape, and a surface roughness of 11.5 nm.

Replication of thermoplastic polymer spherical lens array using microforged molding technique

In this paper, we propose a replication method of thermoplastic polymer spherical lens array using a novel microforged mold. The Si₃N₄ ceramic balls, with 3.5 mm diameter, 10 nm surface roughness and 84 nm deviation from spherical profile, were utilized as indentor to generate aluminum alloy lens array mold. Upon the optimization of technical parameters, such as heating and de-molding temperature, indentation force and holding time, a high quality spherical lens array mold was obtained. The mold was used to fabricate spherical PMMA lens array by hot embossing, which showed excellent characteristics on dimensional stability, surface features and optical performances. Especially for the requirements of deep sag height and low f/#, the microforging technique reveals superior performance for low cost and high quality manufacture of spherical lenses. Compared to the previous complicated tools which requires precise calibration, the self-alignment mode of the balls and cavities can easily guarantee positioning accuracy. Accordingly, the pre-milled spherical cavity deformed uniformly in the process of microforging due to the symmetrical distribution of contact pressure and reduced the error caused by deformation. We believe the proposed microforging technique is an ideal mass production approach to the fabrication of thermoplastic polymer spherical lens array.

Inkjet Printing of Functional Materials for Optical and Photonic Applications

Inkjet printing, traditionally used in graphics, has been widely investigated as a valuable tool in the preparation of functional surfaces and devices. This review focuses on the use of inkjet printing technology for the manufacturing of different optical elements and photonic devices. The presented overview mainly surveys work done in the fabrication of micro-optical components such as microlenses, waveguides and integrated lasers; the manufacturing of large area light emitting diodes displays, liquid crystal displays and solar cells; as well as the preparation of liquid crystal and colloidal crystal based photonic devices working as lasers or optical sensors. Special emphasis is placed on reviewing the materials employed as well as in the relevance of inkjet in the manufacturing of the different devices showing in each of the revised technologies, main achievements, applications and challenges.

3D Lattice Structure Control of Ordered Macroporous Material by Self-Assembly of Liquid Droplets

Microfluidic devices, which can continuously fabricate single emulsion with monodispersed droplets having a pore diameter of more than 100 μm in large numbers, can be applied to manufacture ordered macroporous films. 3D ordered macroporous films with a diameter of more than 100 μm can be fabricated using ordered arrays of the monodispersed droplets as templates of the macropores, which are self-assembled in the space between two parallel flat glass plates. As the gap between the glass plates increases, the number of the layer increases. Furthermore, in the case with two or more layers, the lattice structure of the macroporous films also changes due to the confinement effects.

Extrusion printing for fabrication of spherical and cylindrical microlens arrays

In this paper, we present an extrusion printing technique for producing spherical and cylindrical plano-convex microlens arrays with controllable feature dimensions. This technique employs a robotic adhesive dispenser for robotically controlled microextrusion of ultraviolet (UV) curable polymer onto a glass substrate surface to directly deposit the microlens arrays. It provides a simple and flexible alternative to fabricate both spherical and cylindrical microlens arrays.

Rapid fabrication of thermoplastic polymer refractive microlens array using contactless hot embossing technology

A thermoplastic polymer refractive microlens array has been rapidly fabricated by contactless hot embossing technology through the stainless steel template with micro through-holes array, which has a diameter of 150 µm and a pitch of 185 µm. By optimizing the technical parameters including heating and demoulding temperature, loading pressure, loading and pressure holding time, a series of high quality microlenses arrays of different sags could be obtained. In addition, the sag and the radius of curvature of the microlens are controllable. The geometrical and optical properties of the microlenses are measured and the influence of temperature and pressure duration on the optical properties of the microlenses are analysed. The results show good surface features and optical performances. Unlike previous contactless hot embossing, a low cost and durable stainless steel template was utilized instead of silicon or nickel mold to avoid valuable equipments and complicated fabrication procedure. Besides, the whole contactless hot embossing process was absence of vacuum equipment. We think that the technology could be an attractive high flexibility method for enhancing efficiency and reducing cost.

Noncontact microembossing technology for fabricating thermoplastic optical polymer microlens array sheets

Thermoplastic optical polymers have replaced traditional optical glass for many applications, due to their superior optical performance, mechanical characteristics, low cost, and efficient production process. This paper investigates noncontact microembossing technology used for producing microlens arrays made out of PMMA (polymethyl methacrylate), PS (polyStyrene), and PC (polycarbonate) from a quartz mold, with microhole arrays. An array of planoconvex microlenses are formed because of surface tension caused by applying pressure to the edge of a hole at a certain glass transition temperature. We studied the principle of noncontact microembossing techniques using finite element analysis, in addition to the thermal and mechanical properties of the three polymers. Then, the independently developed hot-embossing equipment was used to fabricate microlens arrays on PMMA, PS, and PC sheets. This is a promising technique for fabricating diverse thermoplastic optical polymer microlens array sheets, with a simple technological process and low production costs.