Microstructuring of polymer films by inkjet etching

Bubble-Patterned Films by Inkjet Printing and Gas Foaming

The micropatterning of thin films represents a challenging task, even for additive manufacturing techniques. In this work, we introduce the use of inkjet-printing technology coupled with a gas-foaming process, to produce patterned porosities on polymeric thin films, to develop a bubble-writing method. Inkjet printing of an aqueous solution of poly (vinyl alcohol) (PVA), a well-known gas-barrier polymer, allows the selective coating of a thin poly (lactic acid) (PLA) film, which is, successively, exposed to a gas-foaming process. The foaming of the thin PLA film is effective, only when PVA is printed on top, since the PVA barrier hinders the premature loss of the gas, thus allowing the formation of cavities (bubbles) in the covered areas; then, removing the PVA coating by water washing forms a bubble pattern. As a proof of concept, the surface-morphology features of the patterned porous PLA films have been proven effective at driving endothelial cell growth. A new technological platform is, hence, introduced in the field of tissue engineering and, in general, in fields involving thin films, where a patterned porous structure may add value.

Wetting and Evaporation of Solvents on Thin Soluble Substrates

In this work, the wetting and evaporation behaviour of non-polar solvent droplets on thin soluble coatings is investigated experimentally. The wetting process on spin-coated polymer layers by toluene is captured using shadowgraphy. Initial spontaneous dynamic wetting as well as later stages of wetting are recorded and evaluated. Furthermore, structures obtained by wetting and subsequent evaporation of solvents on polymer coatings are studied by confocal microscopy. The solubility of the substrate has been varied by using polymers with different molecular masses. We observe that initial spreading dynamics does not depend on the molar mass in the studied range. However, we find a strong influence of the molar mass on the late stage wetting dynamics and on the surface structure after solvent evaporation.

"Print-to-pattern": Silk-Based Water Lithography

The requirement of nontoxic and versatile manufacturing frameworks for biologically relevant applications has imposed significant constraints on the choice of functional materials and the complementary fabrication tools. In this context, silk is actively studied, thanks to its mechanical robustness, biocompatibility, wide availability, aqueous processing conditions, and ease of functionalization. The inherent matching between the water solubility of silk and the aqueous inks of the inkjet printing (IJP) process has derived a biofriendly and versatile "print-to-pattern" scheme-termed silk-based water lithography-toward scalable functional biomanufacturing. The deposition mode of IJP and the etching effect of silk film by water features a dual tone fabrication where functional molecules are dispensed additively, while the silk film is patterned in a "subtractive" fashion. Such versatility and scalability pave the way to a wide range of opportunities in the biomedical field.

Evaluation of the PMMA microlens efficiency for the realization of a solar micro-concentrator array

In order to assess the performance of solar micro-concentrators, specific methods and protocols need to be developed, tested, and applied. In detail, as in conventional concentration modules, one of the fundamental parameters to consider is the efficiency of optical concentrators. In fact, optical concentrators give fundamental information on the current potentially generated from solar microcells that receive the concentrated light radiation. To develop a measurement method for micrometer-size optical components, a suitable optical system was implemented and used. Moreover, the potential application of the printed microstructures in an optical system for solar micro-concentrators was demonstrated.

Inkjet Etching of Polymers and Its Applications in Organic Electronic Devices

Inkjet printing techniques for the etching of polymers and their application to the fabrication of organic electronic devices are reviewed. A mechanism is proposed for the formation of via holes in polymer layers through inkjet printing with solvent, and recent achievements in the fabrication with inkjet etching of various three-dimensional microstructures (i.e., microwells, microgrooves, hexagonal holes, and concave structures) are discussed. In addition, organic electronic devices are presented that use inkjet-etched subtractive patterns as platforms for the selective depositions of an emissive material, a liquid crystal, an organic conductor, an organic insulator, and an organic semiconductor, and as an optical waveguide.

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.

An inverse method for determining the spatially resolved properties of viscoelastic-viscoplastic three-dimensional printed materials

A method using experimental nanoindentation and inverse finite-element analysis (FEA) has been developed that enables the spatial variation of material constitutive properties to be accurately determined. The method was used to measure property variation in a three-dimensional printed (3DP) polymeric material. The accuracy of the method is dependent on the applicability of the constitutive model used in the inverse FEA, hence four potential material models: viscoelastic, viscoelastic–viscoplastic, nonlinear viscoelastic and nonlinear viscoelastic–viscoplastic were evaluated, with the latter enabling the best fit to experimental data. Significant changes in material properties were seen in the depth direction of the 3DP sample, which could be linked to the degree of cross-linking within the material, a feature inherent in a UV-cured layer-by-layer construction method. It is proposed that the method is a powerful tool in the analysis of manufacturing processes with potential spatial property variation that will also enable the accurate prediction of final manufactured part performance.

Flow through ring resonator sensing platform

Polymeric microring resonator platform employing a flow-through approach is realized. A reduction of more than one order of magnitude of the sensor response time respect to standard flow-over approach is obtained.

Graded-size microlens array by the pyro-electrohydrodynamic continuous printing method

In the present work, the pyro-electrohydrodynamic technique was used for the realization of tunable-size microlens arrays. Poly(methyl methacrylate) dissolved in different solvent mixtures was used as the polymeric material for the realization of the microstructures. By controlling the experimental parameters and in particular, the volume of the drop reservoir, graded-size square arrays of tens of microlenses with focal length in the range 1.5-3 mm were produced. Moreover, the optical quality and geometrical features were investigated by profilometric and interferometric analysis.

Printing of polymer microlenses by a pyroelectrohydrodynamic dispensing approach

The investigation of a method for fabricating microlenses by a nozzle-free inkjet printing approach is reported. The new method, based on a pyroelectrohydrodynamic mechanism, is also able to dispense viscous liquids and to draw liquid phase drops directly from the reservoir. Specifically, by dispensing optical grade polymer dissolved in different solvent mixtures, microlenses were printed with a pattern defined directly through this deposition method. The reliability of the microlenses and the tunability of their focal properties were demonstrated through profilometric and inteferometric analyses.