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1.
Materials (Basel) ; 12(20)2019 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-31635254

RESUMO

In this work, it is demonstrated that direct laser interference patterning (DLIP) is a method capable of producing microtextured metallic molds for hot embossing processes. Three different metals (Cr, Ni, and Cu), relevant for the mold production used in nanoimprinting systems, are patterned by DLIP using a picosecond laser source emitting at a 532 nm wavelength. The results show that the quality and surface topography of the produced hole-like micropatterns are determined by the laser processing parameters, such as irradiated energy density and the number of pulses. Laser-induced periodic surface structures (LIPSS) are also observed on the treated surfaces, whose shapes, periodicities, and orientations are strongly dependent on the accumulated fluence. Finally, the three structured metals are used as embossing molds to imprint microlenses on polymethyl methacrylate (PMMA) foils using an electrohydraulic press. Topographical profiles demonstrate that the obtained structures are comparable to the masters showing a satisfactory reproduction of the texture. The polymeric microlens arrays that showed the best surface homogeneity and overall quality were those embossed with the Cr molds.

2.
Sci Rep ; 9(1): 13944, 2019 Sep 26.
Artigo em Inglês | MEDLINE | ID: mdl-31558749

RESUMO

Fabricating aluminium surfaces with superhydrophobic and ice-repellent properties present nowadays a challenging task. In this work, multifunctional structures are manufactured by direct laser writing and direct laser interference patterning methods using pulsed infrared laser radiation (1064 nm). Different periodic patterns with feature sizes ranging from 7.0 to 50.0 µm are produced. In addition, hierarchical textures are produced combining both mentioned laser based methods. Water contact angle tests at room temperature showed that all produced patterns reached the superhydrophobic state after 13 to 16 days. In addition, these experiments were repeated at substrate temperatures from -30 °C to 80 °C allowing to determine three wettability behaviours as a function of the temperature. The patterned surfaces also showed ice-repellent properties characterized by a near three-fold increase in the droplets freezing times compared to the untreated samples. Using finite element simulations, it was found that the main reason behind the ice-prevention is the change in the droplet geometrical shape due to the hydrophobic nature of the treated surfaces. Finally, dynamic tests of droplets imping the treated aluminium surfaces cooled down to -20 °C revealed that only on the hierarchically patterned surface, the droplets were able to bounce off the substrate.

3.
Materials (Basel) ; 12(17)2019 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-31461830

RESUMO

Superhydrophobic natural surfaces usually have multiple levels of structure hierarchy, particularly microstructures covered with nano-roughness. The multi-scale nature of such a surface reduces the wetting of water and oils, and supports self-cleaning properties. In this work, in order to broaden our understanding of the wetting properties of technical surfaces, biomimetic surface patterns were fabricated on stainless steel with single and multi-scale periodic structures using direct laser interference patterning (DLIP). Micropillars with a spatial period of 5.5 µm and a structural depth of 4.2 µm were fabricated and covered by a sub-micro roughness by using ultrashort laser pulses, thus obtaining a hierarchical geometry. In order to distinguish the influence of the different features on the wettability behavior, a nanosecond laser source was used to melt the nano-roughness, and thus to obtain single-scale patterns. Then, a systematic comparison between the single- and multi-scale structures was performed. Although, the treated surfaces showed hydrophilic behavior directly after the laser treatment, over time they reached a steady-state hydrophobic condition. However, the multi-scale structured metal showed a contact angle 31° higher than the single-scale geometry when the steady-state conditions were reached. Furthermore, the impact of the surface chemistry was investigated by energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analyses. Finally, a hydrophobizing agent was applied to the laser treated samples in order to further enhance the water contact angles and to determine the pure contribution of the surface topography. In the latter case, the multi-scale periodic microstructures reached static contact angles of 152° ± 2° and a contact angle hysteresis of only 4° ± 2°, while the single-scale structures did not show superhydrophobic behavior. These results definitely suggest that multi-scale DLIP structures in conjunction with a surface chemistry modification can promote a superhydrophobic regime.

4.
Materials (Basel) ; 12(14)2019 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-31337017

RESUMO

Many laser material processing applications require an optimized beam profile, e.g., ring shape or Top-Hat profiles with homogeneous intensity distribution. In this study, we show a beam shaping concept leading to a phase shifting element with binary height profile as well as a very low periodicity with near diffraction limited spot size. Further advantages of so-called Fundamental Beam Mode Shaping (FBS) elements are the simplified handling, and a high efficiency and homogeneity. The calculated height profile of FBS elements are transferred in fused silica substrates using a combination of microlithography technologies, reactive ion etching (RIE) and ion beam etching (IBE). The experiments demonstrated a linear relation between the etching depth after RIE and IBE. The optical evaluation of the manufactured FBS beam mode shaper confirmed the presented concept design.

5.
Sci Rep ; 9(1): 7801, 2019 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-31127183

RESUMO

This study focuses on the development of a strategy to produce periodic structures with a variable spatial period for increasing the homogeneity of structural colours by means of direct laser interference patterning. Using a four-beam interference configuration, hole-like periodic arrays are produced on stainless steel with a 70 ps pulsed laser source operating at 532 nm laser wavelength. The laser processing parameters are optimised for obtaining patterns with the highest possible diffraction efficiency and thus showing the highest possible colour intensity. A model for calculating the required spatial period to obtain a defined colour under specific conditions of illumination and observation angles is presented. A very good agreement between the captured structural colour spectrum and the real visible spectrum of light was obtained. In addition, a strategy for mixing holographic colours, in particular for obtaining the white colour is developed. Finally, the developed model is successfully integrated into machine software, in order to automatically process images that exhibit required colours at certain viewing conditions. The produced patterns are characterised using confocal microscopy and the efficiency of the first diffraction order was measured by optical spectroscopy.

6.
Sci Rep ; 9(1): 6721, 2019 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-31040334

RESUMO

Textured implant surfaces with micrometer and sub-micrometer features can improve contact properties like cell adhesion and bacteria repellency. A critical point of these surfaces is their mechanical stability during implantation. Therefore, strategies capable to provide both biocompatibility for an improved implant healing and resistance to wear for protecting the functional surface are required. In this work, laser-based fabrication methods have been used to produce hierarchical patterns on titanium surfaces. Using Direct Laser Writing with a nanosecond pulsed laser, crater-like structures with a separation distance of 50 µm are produced on unpolished titanium surfaces. Directly on this texture, a hole-like pattern with 5 µm spatial period is generated using Direct Laser Interference Patterning with picosecond pulses. While the smaller features should reduce the bacterial adhesion, the larger geometry was designed to protect the smaller features from wear. On the multifunctional surface, the adherence of E. Coli bacteria is reduced by 30% compared to the untreated reference. In addition, wear test performed on the multiple-scale patterns demonstrated the possibility to protect the smaller features by the larger craters. Also, the influence of the laser treatment on the growth of a titanium oxide layer was evaluated using Energy Dispersive X-Ray Spectroscopy analysis.

7.
Materials (Basel) ; 12(9)2019 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-31067815

RESUMO

This work addresses the fabrication of hydrophobic surface structures by means of direct laser interference patterning using an optical setup optimized for high throughput processing. The developed optical assembly is used to shape the laser beam intensity as well as to obtain the two sub beams required for creating the interference pattern. The resulting beam profile consists of an elongated rectangular laser spot with 5.0 mm × 0.1 mm size, which enables the optimized utilization of the laser fluence available from an ns-pulsed laser with a wavelength of 1064 nm. Depending on the pulse repetition rate applied, heating of the substrate volume generated by heat accumulation encouraged exceptionally high aspect ratios of the trench structures due to melt flow dynamic material deformation. Finally, water contact angle measurements of the produced structures permitted the demonstration of the capability of controlling the wetting angle, in which this effect does not only depend on the height of the generated surface structures but also on their morphology.

8.
Materials (Basel) ; 12(7)2019 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-30934782

RESUMO

Controlling laser induced surface morphology is essential for developing specialized functional surfaces. This work presents novel, multi-scale periodic patterns with two-dimensional symmetry generated on stainless steel, polyimide and sapphire. The microstructures were realized by combining Direct Laser Interference Patterning with the generation of Laser Induced Periodic Surface Structures in a one-step process. An industrial, fiber femtosecond laser source emitting at 1030 nm with a pulse duration of 500 fs was utilized for the experiments. In the case of stainless steel, it was possible to create line-like or pillar-like surface patterns by rotating the polarization orientation with respect to the interference pattern. In the case of polyimide and sapphire, the absorption of the laser radiation was promoted by a multiphoton mechanism. In polyimide, grooves and pillars of several microns in depth were produced over an area much larger than the spot size. Finally, for sapphire, the simultaneous generation of interference-like pattern and laser induced periodic surface structures was realized. The results reported here provide valuable data on the feasibility to combine two state-of-the-art techniques with an industrial apparatus, to control the induced surface morphology.

9.
Sci Rep ; 9(1): 5455, 2019 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-30931990

RESUMO

The direct fabrication of microstructures, having a non-symmetrical morphology with controllable inclination, presents nowadays a challenging task. Natural examples of surfaces with inclined topographies have shown to provide anisotropic functionalities, which have attracted the interest of several researchers in the last years. This work presents a microfabrication technique for producing microstructures with a determined and controllable inclination angle using two-beam Direct Laser Interference Patterning. Polyimide foils are irradiated with a 4 ns UV (266 nm) laser source producing line-like structures with a period varying from 4.6 µm to 16.5 µm. The inclinations, retrieved by tilting the sample with respect to the optical axis of the setup, are changed from 0° to 75°, introducing a well controllable and defined inclination of the structure walls. The structuring parameters (laser fluence, number of laser pulses and interference period) as well as the inclination of the microstructures are correlated with the global tilting of the sample. As a result, a determined laser fluence and number of pulses are necessary to observe a remarkable non-symmetrical morphology of the structures. In addition, the presence of structural undercuts is reported, which opens the possibility for developing new direction-dependent properties on polymeric materials. As an example, preliminary results on light diffraction are presented, showing a similar behavior as blazed diffraction gratings.

10.
J Biomed Opt ; 23(12): 1-5, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30569671

RESUMO

The scattering properties of biological tissue are highly dependent on the structure size, refractive index, and wavelength of the incident light. Furthermore, these scattering characteristics are strongly influenced by movements of the scattering objects. A method is developed to determine the angular- and spectral-resolved scattering properties that enabled the characterization of biological nano- and microscaled cell structures. Nanosecond pulses from a spectrally filtered supercontinuum light source are captured and time-resolved to depress background noise and minimize disruptive effects of the biological cells. The scattering characteristics of a monolayer of mouse fibroblast L929 cells are measured at defined wavelengths in a standard cell culture plate. Because of the size and distribution of the scattering structures, a Fourier transform-based Mie scattering scheme is used to analyze the data. The system is tested to detect structural changes of mouse fibroblast L929 cells before and after poisoning with Triton X100. The final result is the development of a contamination-free method to study pathological changes in cell cultures, necrosis, or other cell-damaging effects.


Assuntos
Morte Celular/fisiologia , Fibroblastos/citologia , Espalhamento de Radiação , Análise Espectral/métodos , Animais , Linhagem Celular , Luz , Camundongos , Necrose
11.
Opt Express ; 25(19): 22959-22970, 2017 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-29041601

RESUMO

Product piracy impacts wide areas of the global economy resulting in multi-billion dollar losses per year. Therefore, product protection technologies are required to produce security elements with high flexibility and complexity. In this work, the fabrication of diffraction-based security elements, so called grating cell arrays, using direct laser interference patterning is presented. Ultraviolet two-beam interference patterning is used to structure line-like gratings into 80 µm in diameter spots with spatial periods ranging from 0.7 µm to 2.2 µm on PET substrates. The developed grating cell arrays are generated by the combination of several holographic surface gratings with variable spatial period and pattern orientation. The stored security information can be visualized by illumination with a coherent light source such as a laser pointer.

12.
Opt Express ; 25(9): 9603-9616, 2017 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-28468343

RESUMO

This study investigates the general mechanism of Direct Laser Interference Patterning (DLIP) involved in the structuring process of polymer materials. An empirical model is developed taking into account experimental observations of DLIP-treated pigmented and transparent polycarbonate substrates with UV (263 nm) and IR (1053 nm) laser radiation. Depending on the used laser processing conditions, the type of material as well as the spatial period of the interference pattern, four different structuring mechanisms can be identified. The treated surfaces are investigated using confocal microscopy, scanning electron microscopy and focus ion beam and as a result from the experimental data analysis, the developed model predicts the material surface topography after the patterning process, by means of a set of material-dependent coefficients.

13.
Micromachines (Basel) ; 8(8)2017 Aug 11.
Artigo em Inglês | MEDLINE | ID: mdl-30400437

RESUMO

Micro Physiological Systems (MPS), also known as Multi-Organ-Chip, Organ-on-a-Chip, or Body-on-a-Chip, are advanced microfluidic systems that allow the cultivation of different types of cells and tissue in just one common circuit. Furthermore, they thus can also adjust the interaction of these different tissues. Perspectival MPS will replace animal testing. For fast and flexible manufacturing and marking of MPS, a concept for a universal micromachining platform has been developed which provides the following latest key technologies: laser micro cutting of polymer foils, laser micro- and sub-micro-structuring of polymer foils, 3D printing of polymer components as well as optical inspection and online process control. The combination of different laser sources, processing optics, inspection systems, and print heads on multiple axes allows the change and exactly positioning to the workpiece during the process. Therewith, the realization of MPS including 3D printed components as well as direct laser interference patterned surfaces for well-defined cell adhesion and product protection is possible. Additional basic technologies for the generation of periodical line-like structures at polycarbonate foils using special Direct Laser Interference Patterning (DLIP) optics as well as for the 3D printing of fluid-tight cell culture reservoirs made of Acrylonitrile Butadiene Styrene directly onto polycarbonate microfluidics were established. A first prototype of the universal micromachining platform combining different lasers with Direct Laser Writing and DLIP is shown. With this laser micro cutting as well as laser micro-structuring of polycarbonate (PC) foils and therewith functionalization for MPS application could be successfully demonstrated.

14.
Adv Healthc Mater ; 6(3)2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27930868

RESUMO

Direct laser interference patterning (DLIP) is used to produce periodic line-like patterns on titanium surfaces. An Nd:YAG laser operating at 532 nm wavelength with a pulse duration of 8 ns is used for the laser patterning process. The generated periodic patterns with spatial periods of 5, 10, and 20 µm are produced with energy densities between 0.44 and 2.6 J cm-2 with a single laser pulse. With variation of energy density, different shapes of the arising topography are observed due to the development of the solidification front of the molten material at the maxima positions. Characterization of the surface chemistry shows that the DLIP treatment enhances the content of nitrogen of the titanium reactive layer from 3.9% up to 23.4%. The structural analysis near the titanium surface shows no changes in microstructure after the laser treatment. Contact angles between 65° and 79° are measured on both structured and turned reference surfaces. Cell viability of human osteoblasts on line-like patterned surfaces after 7 d in cultivation medium is 16% higher compared to the grit-blasted and acid-etched references. Finally, the possibility of patterning complex 3D dental implants is shown.


Assuntos
Implantes Dentários , Lasers , Teste de Materiais , Osteoblastos/metabolismo , Titânio/química , Linhagem Celular , Humanos , Osteoblastos/citologia , Propriedades de Superfície
15.
Opt Express ; 24(6): A553-68, 2016 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-27136876

RESUMO

In the search for alternative materials to replace indium-tin-oxide in transparent electrodes we have structured copper and aluminum thin films (between 5 an 40 nm) for tailoring their optical properties. Micrometer scaled holes were produced using the direct laser interference patterning (DLIP) technique. We compared the optical and electrical parameters of nanosecond and picosecond processed thin films. It was found that the optical transmittance of the structured layers was relatively increased between 25 to 125% while the electrical resistance was marginally influenced. In addition, the laser treatment enhanced the diffuse to total transmission ratio (HAZE) by values ranging from 30 to 82% (relative) as a potential advantage of µm structuring. The results also show that both of the studied metals succeed to match the target which is set by typical applications of indium thin oxide (ITO) films. Furthermore, numerical simulations are performed in order to understand the ablation process of thin film material for ps and ns pulses.

16.
Biomater Sci ; 4(7): 1074-8, 2016 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-27232637

RESUMO

Substrate topography can have profound effects on initial bacterial adhesion during biofilm formation. We applied Staphylococcus epidermidis and Escherichia coli cells onto periodically structured substrates with different structure dimensions, structure types and wetting properties. We found a strong dependence of cell retention on the structure dimensions of the applied substrates. Periodicities in the range of the cell size increased, whereas smaller periodicities decreased cell retention, independent of contact time (minutes to hours) and hydrophobicity. These novel insights on the role of surface topography on bacterial retention might facilitate the development of non-fouling surfaces in the future.


Assuntos
Aderência Bacteriana , Escherichia coli/fisiologia , Staphylococcus epidermidis/fisiologia , Biofilmes , Interações Hidrofóbicas e Hidrofílicas , Molhabilidade
17.
Macromol Biosci ; 15(8): 1060-9, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-25914260

RESUMO

Modification of the biomaterial surface topography is a promising strategy to prevent bacterial adhesion and biofilm formation. In this study, we use direct laser interference patterning (DLIP) to modify polystyrene surface topography at sub-micrometer scale. The results revealed that three-dimensional micrometer structures have a profound impact on bacterial adhesion. Thus, line- and pillar-like patterns enhanced S. aureus adhesion, whereas complex lamella microtopography reduced S. aureus adhesion in static and continuous flow culture conditions. Interestingly, lamella-like textured surfaces retained the capacity to inhibit S. aureus adhesion both when the surface is coated with human serum proteins and when the material is implanted subcutaneously in a foreign-body associated infection model.


Assuntos
Aderência Bacteriana/efeitos dos fármacos , Biofilmes/efeitos dos fármacos , Poliestirenos/química , Staphylococcus aureus/efeitos dos fármacos , Materiais Biocompatíveis/química , Materiais Biocompatíveis/farmacologia , Incrustação Biológica , Proteínas Sanguíneas/química , Humanos , Lasers , Poliestirenos/farmacologia , Staphylococcus aureus/química , Staphylococcus aureus/patogenicidade , Propriedades de Superfície
18.
Adv Healthc Mater ; 4(4): 516-21, 2015 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-25323149

RESUMO

Matrix-metalloproteinase and photosensitive peptide units are combined with heparin and poly(ethylene glycol) into a light-sensitive multicomponent hydrogel material. Localized degradation of the hydrogel matrix allows the creation of defined spatial constraints and adhesive patterning for cells grown in culture. Using this matrix system, it is demonstrated that the degree of confinement determines the fate of neural precursor cells in vitro.


Assuntos
Células-Tronco Adultas/citologia , Hidrogéis/farmacologia , Luz , Células-Tronco Neurais/citologia , Células-Tronco Adultas/efeitos dos fármacos , Animais , Proliferação de Células/efeitos dos fármacos , Vidro/química , Heparina/química , Camundongos , Células-Tronco Neurais/efeitos dos fármacos , Polietilenoglicóis/síntese química , Polietilenoglicóis/química
19.
Adv Mater ; 24(7): 906-10, 2012 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-22403830

RESUMO

Direct laser interference patterning (DLIP) is used to fabricate large area, two-dimensional periodic surface patterns on polyethylene terephthalate (PET) substrates to enhance the performance of ZnPc:C60 solar cells by light concentration in the absorber layer. Comparing the power conversion efficiencies to the reference cell on flat PET, a relative increase of 21% is observed for the hexagonal pattern with 0.7 µm period, depicted in the figure.


Assuntos
Lasers , Compostos Orgânicos/química , Energia Solar , Absorção , Eletrodos , Fulerenos/química , Indóis/química , Compostos Organometálicos/química , Polietilenotereftalatos/química , Poliestirenos/química , Tiofenos/química
20.
Nanotechnology ; 23(1): 015304, 2012 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-22155970

RESUMO

A simple approach for creating periodic nano-cavities and periodic stripes of nano-cavity arrays on poly (3,4-ethylene dioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) thin films using a combination of optical near-field enhancement through self-assembled silica nanospheres and laser interference lithography is presented. Monolayers of close-packed silica nanospheres (800, 600, and 430 nm in diameter) are self-assembled on 2 µm thick PEDOT-PSS electropolymerized films and are subsequently irradiated with 10 ns pulses of 355 nm wavelength laser light. Over areas spanning 2 cm(2), circular nano-cavities with central holes of size 50-200 nm and surrounding craters of size 100-400 nm are formed in the PEDOT-PSS films directly underneath the nanospheres due to strong enhancement (11-18 fold) of the incident light in the near-field, which is confirmed through Mie scattering theory. Predictions from theoretical simulations examining the combined effects of near-field enhancement and interference are in good agreement with the experimental results. The results illustrate the versatility of the described technique for creating nano-cavity arrays or nano-pores in PEDOT-PSS over large areas with designed periodicity and hole size.

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