Andrés Lasagni

Rapid prototyping of microstructured hydrogels via laser direct-write and laser interference photopolymerisation

We present recent results on fabrication of micrometre- and sub-micrometre-scale structures in polyethylene glycol diacrylate (PEG-DA), a biocompatible hydrogel, useful in biomedical applications. The hydrogel structures were fabricated using two laser-based techniques; laser direct-write photopolymerisation, and multiple-beam laser interference photopolymerisation using continuous wave, nanosecond pulsed and femtosecond pulsed lasers, with light wavelengths of 266 nm, 355 nm, 532 nm and 800 nm. Through these techniques, we demonstrated the ability to fabricate fine structures over large areas without the use of templates or masks. Such structures can be useful for a variety of applications including cell biological studies, tissue engineering and drug delivery.

The fabrication of high aspect ratio carbon nanotube arrays by direct laser interference patterning

High aspect ratio periodic carbon nanotube arrays were fabricated using direct laser interference patterning with a frequency tripled Nd:YAG (YAG: yttrium aluminium garnet) laser (lambda = 355 nm) emitting 10 ns laser pulses. The depth of the fabricated arrays could be adjusted by controlling the number of laser pulses. Application of successive laser pulses (10-20) induced pattern distortion, resulting in the formation of conical organized arrays. The number of laser pulses necessary to produce this distortion is proportional to the spatial period of the interference pattern. Raman spectroscopy analyses confirmed that the chemical form of the carbon nanotubes was preserved after patterning.

Rapid fabrication of pentaerythritol triacrylate periodic structures on large areas by laser interference patterning with nanosecond pulses

We report on rapid fabrication of two-dimensional periodic structures in pentaerythritol triacrylate (PETIA) through laser interference patterning with 10 ns pulses from a frequency-tripled Nd:YAG laser emitting at 355 nm. Different periodic arrays including line-, cross-, honeycomb-, and dotlike structures were fabricated using two and three interfering laser beams. The composition of the photoinitiator was changed from 2% to 15% w/w to determine the threshold laser fluences necessary to photopolymerize the PETIA solution. The effects of the PETIA layer thickness and periodic geometries on the mechanical stability of the fabricated structures as well as self-organization processes are reported.

Rapid fabrication of biocompatible hydrogels microdevices using laser interference lithography

We report on fabrication of periodic arrays of polyethylene glycol diacrylate (PEG-DA), a biocompatible hydrogel, useful in biomedical applications. The structures were produced by means of multi beam laser interference lithography with both nanosecond (266 and 355 nm of wavelengths with pulses lasting 10 ns) and femtosecond pulsed lasers (800 nm of wavelength and 90 fs laser pulses). Configurations involving two, four and five laser beams were utilized obtaining a wide variety of patterns with different feature sizes in the micrometer scale. Through this technique, we demonstrated the ability to fabricate high feature density patterns over large areas without the use of templates or masks. In addition, resolution and geometrical characteristic of the periodic arrays are discussed as function of pulse duration and laser processing parameters. The photopolymerization nature of the process was also investigated.

Macroscopic 2D Design of Micro/Nano Grain Architectures by Laser Interference Metallurgy

Tailoring of micro/nano structures and surface functionalization are key goals in surface processing of materials. A new technology for a unique geometric precise 2D micro/nano design of grain architectures is presented. By means of super lateral grain growth crystalline lattice patterns such as line-, dot- and cross-like patterns were generated. The grain dimensions may be selected between a few nanometers and about 10 micrometers. The phase and grain formation was characterized by Electron Backscatter Diffraction with regard to orientation distribution and texture formation. Furthermore, dynamic aspects of this laser induced recrystallization process are studied, such as the heat transport in the films, comparing the vertical with the lateral solidification velocities by two-dimensional finite element method (FEM) simulations. Finally, the mechanical properties of the tailored thin films have been determined using nanoindentation experiments.

Micro/Nano Fabrication of Surface Architectures on Polymers and Copolymers Using Direct Laser Interference Patterning

Novel surface engineering techniques of polymeric materials are essential to produce advanced topographies which could for example serve to modulate cell and tissue response in bio-materials. Direct Laser Interference Patterning (DLIP) permits the fabrication of repetitive arrays and microstructures by irradiation of the sample surface with coherent beams of light. Furthermore, the most important advantage of this method is that no additional process steps are required in comparison with other top-down or bottom-up techniques. In this study, we report a novel method for the advanced design of architectures in polymers using a single step process, as well as photo-activation of polymers with low absorption coefficient using a second polymer with relative high absorption coefficient. Previously calculated interference patterns using the well known interference theory could be directly produced on polymeric surface. Moreover, the cross-section of the structured polymers changes depending on the intensity of the laser beams, and photomachinability of polymers is highly influenced by laser wavelength. High absorbance of the polymeric materials at specific wavelengths allows the reduction of the laser intensity required to achieve a determined structure depth. For (60:40 %) polymethylmetacrylate/polystyrene copolymer substrate, different structures types were observed depending on the laser intensity including swelling and ablation of the material.