Linas Jonušauskas

Optically Clear and Resilient Free-Form µ-Optics 3D-Printed via Ultrafast Laser Lithography

We introduce optically clear and resilient free-form micro-optical components of pure (non-photosensitized) organic-inorganic SZ2080 material made by femtosecond 3D laser lithography (3DLL). This is advantageous for rapid printing of 3D micro-/nano-optics, including their integration directly onto optical fibers. A systematic study of the fabrication peculiarities and quality of resultant structures is performed. Comparison of microlens resiliency to continuous wave (CW) and femtosecond pulsed exposure is determined. Experimental results prove that pure SZ2080 is ∼20 fold more resistant to high irradiance as compared with standard lithographic material (SU8) and can sustain up to 1.91 GW/cm2 intensity. 3DLL is a promising manufacturing approach for high-intensity micro-optics for emerging fields in astro-photonics and atto-second pulse generation. Additionally, pyrolysis is employed to homogeneously shrink structures up to 40% by removing organic SZ2080 constituents. This opens a promising route towards downscaling photonic lattices and the creation of mechanically robust glass-ceramic microstructures.

Augmentation of direct laser writing fabrication throughput for three-dimensional structures by varying focusing conditions

Abstract. We propose a laser fabrication approach for single monolith structure by varying beam focusing lenses (NA1=1.4 and NA2=0.45). With this, we show great improvement of the manufacturing throughput while keeping the desired spatial resolution and feature definition. To quantitatively evaluate its efficiency, we theoretically calculate and experimentally measure the polymerized volume using different focusing conditions and show that the augmentation can reach more than sevenfold. Based on this, sample structures of hybrid organic-inorganic SZ2080 and hydrogel polyethylene (glycol) diacrylate photopolymers were successfully manufactured. These three-dimensional structures included prototype scaffolds for cell growth and microfluidic components. Their quality was assessed and possible difficulties as well as limitations that arose were discussed. The new structures were compared to alternative direct laser writing throughput increasing techniques. Finally, we discussed potential applications in manufacturing various elements for regenerative medicine and microfluidics.

Nanophotonic lithography: a versatile tool for manufacturing functional three-dimensional micro-/nano-objects

In this paper, an overview of literature supported by original experimental results on direct laser polymerization of three-dimensional micro-/nano-structuring of various photopolymers is presented. Alternative technologies, principles of threshold based direct laser writing in polymers employing ultrafast lasers, issues of optimization of the laser structuring parameters for increasing fabrication resolution and production throughput are presented and discussed. Examples of woodpile templates and nanogratings are shown as well as an opto-fluidic sensor design for usage in lab-on-chip type devices is demonstrated and its performance is characterized. Additionally, a possibility to produce a three-dimensional electric circuit is introduced.

Fabrication of a composite of nanocrystalline carbonated hydroxyapatite (cHAP) with polylactic acid (PLA) and its surface topographical structuring with direct laser writing (DLW)

Correction for ‘Fabrication of a composite of nanocrystalline carbonated hydroxyapatite (cHAP) with polylactic acid (PLA) and its surface topographical structuring with direct laser writing (DLW)’ by E. Garskaite et al., RSC Adv., 2016, 6, 72733–72743.The fabrication of polylactic acid (PLA)-carbonated hydroxyapatite (cHAP) composite material from synthesised phase pure nano-cHAP and melted PLA by mechanical mixing at 220-235{\deg}C has been developed in this study. Topographical structuring of PLA-cHAP composite surfaces was performed by direct laser writing (DLW). Microstructured surfaces and the apatite distribution within the composite and formed grooves were evaluated by optical and scanning electron microscopies. The influence of the dopant concentration as well as the laser power and translation velocity on the composite surface morphology is discussed. The synthesis of carbonated hydroxyapatite (cHAP) nanocrystalline powders via wet chemistry approach from calcium acetate and diammonium hydrogen phosphate precursors together with crosslinking and complexing agents of polyethylene glycol, poly(vinyl alcohol) and triethanolamine is also reported. Thermal decomposition of the gels and formation of nanocrystalline cHAP were evaluated by thermal analysis, mass spectrometry and dilatometry measurements. The effect of organic additives on the formation and morphological features of cHAP was investigated. The phase purity and crystallinity of the carbonated apatite powders were evaluated by X-ray diffraction analysis and FT-IR spectroscopy.

Hybrid subtractive-additive-welding microfabrication for lab-on-chip applications via single amplified femtosecond laser source

Abstract. An approach employing ultrafast laser hybrid subtractive-additive microfabrication, which combines ablation, three-dimensional nanolithography, and welding, is proposed for the realization of a lab-on-chip (LOC) device. A single amplified Yb:KGW femtosecond (fs)-pulsed laser source is shown to be suitable for fabricating microgrooves in glass slabs, polymerization of fine-meshes microfilter out of hybrid organic–inorganic photopolymer SZ2080 inside them, and, finally, sealing the whole chip with cover glass into a single monolithic piece. The created microfluidic device proved its particle sorting function by separating 1- and 10-μm polystyrene spheres in an aqueous mixture. All together, this proves that laser microfabrication based on a single amplified fs laser source is a flexible and versatile approach for the hybrid subtractive-additive manufacturing of functional mesoscale multimaterial LOC devices.

Mesoscale 3D manufacturing: varying focusing conditions for efficient direct laser writing of polymers

In this paper, we report a novel approach for efficient fabrication of mesoscale polymer 3D microstructures. It is implemented by direct laser writing varying exposure beam focusing conditions. By carefully optimizing the fabrication parameters (laser intensity, scanning velocity/exposure time, changing objective lens) complex 3D geometries of the microstructures can be obtained rapidly. Additionally, we demonstrate this without the use of the photoinitiator as photosensitizer doped in the pre-polymer material (SZ2080). At femtosecond pulsed irradiation ~TW/cm² intensities the localized free radical polymerization is achieved via avalanche induced bond braking. Such microstructures have unique biocompatibility and optical transparency as well as optical damage threshold value. By creating the bulk part of the structure using low-NA (0.45) objective and subsequently fabricating the fine features using oil immersion high-NA (1.4) objective the manufacturing time is reduced dramatically (30x is demonstrated). Using this two objective method a prototype of functional microdevice was produced: 80 and 85 µm diameter microfluidic tubes with the fine filter consisting of 4 µm period grating structure that has 400 nm wide threads, which corresponds to a feature precision aspect ratio of ~200. Therefore, such method has great potential as a polymer fabrication tool for mesoscale optical, photonic and biomedical applications as well as highly integrated 3D µ-systems. Furthermore, the proposed approach is not limited to lithography and can be implemented in a more general type of laser writing, such as inscription within transparent materials or substractive manufacturing by ablation.

Fabrication, replication, and characterization of microlenses for optofluidic applications

Here we report Direct Laser Writing (DLW) based fabrication of aspheric microlenses out of hybrid organicinorganic photopolymer ORMOSIL. Using the advantages of the flexible manufacturing technique the produced microlenses are embedded inside a fluidic channel. Applying the soft-lithography molding technique the structures are transferred to the elastomer PDMS and hydrogel PEG-DA-258 materials. Measurements show that such replica transferring can reproduce the initial structures into other materials on desired substrates with no noticeable losses of quality. Furthermore, it makes femtosecond laser redundant once the original structure is made. The embedded structures are immersed into several liquid media (acetone, methanol) and the focusing performance corresponding to the change of the optical path length of the microlenses is obtained. It well matches with the estimated values. In conclusion, we report a combination of laser fabrication and replication methods as an efficient way to produce optofluidic components, which can be used for light based sensing, trapping or other applications such as MOEMS devices.

Lithographic microfabrication of biocompatible polymers for tissue engineering and lab-on-a-chip applications

In this work, a combination of Direct Laser Writing (DLW), PoliDiMethylSiloxane (PDMS) soft lithography and UV lithography was used to create cm- scale microstructured polymer scaolds for cell culture experiments out of dierent biocompatible materials: novel hybrid organic-inorganic SZ2080, PDMS elastomer, biodegradable PEG- DA-258 and SU-8. Rabbit muscle-derived stem cells were seeded on the fabricated dierent periodicity scaolds to evaluate if the relief surface had any eect on cell proliferation. An array of microlenses was fabricated using DLW out of SZ2080 and replicated in PDMS and PEG-DA-258, showing good potential applicability of the used techniques in many other elds like micro- and nano- uidics, photonics, and MicroElectroMechanical Systems (MEMS). The synergetic employment of three dierent fabrication techniques allowed to produce desired objects with low cost, high throughput and precision as well as use materials that are dicult to process by other means (PDMS and PEG-DA-258). DLW is a relatively slow fabrication method, since the object has to be written point-by-point. By applying PDMS soft lithography, we were enabled to replicate laser-fabricated scaolds for stem cell growth and micro-optical elements for lab-on-a-chip applications with high speed, low cost and good reproducible quality.

Fabrication of flexible microporous 3D scaffolds via stereolithography and optimization of their biocompatibility

In this work the principles of fabrication of 3D scaffolds via stereolithography and scaffolds’ biocompatibility are investigated. Cells can be seeded into 3D printer-formed structures and artificial tissue or organ can be grown and implanted into human body. In this work the requirements of reproducing the original environment of cells in such bioscaffolds are used in order to create and test mechanically flexible microporous structures. New materials and suitable scaffolds’ geometries might bring desired features in tissue engineering. The scaffolds were fabricated using the tabletop 3D printer Autodesk Ember. Commercial photoresin Formlabs Flexible was used for this task. Optimization steps presented in this paper allowed to increase the biocompabaility of the scaffolds by 48% in comparison to unoptimized ones.

Bioresists from renewable resources as sustainable photoresins for 3D laser microlithography: material synthesis, cross-linking rate and characterization of the structures

Stereolithography (SLA) allows rapid and accurate materialization of computer aided design (CAD) models into real objects out of photoreactive resin. Nowadays this technology has evolved to a widespread simple and flexible personal tabletop devices - three dimensional (3D) optical printers. However, most 3D SLA printers use commercially available resins which are not cheap and of limited applicability, often of unknown chemical ingredients and fixed to certain mechanical properties. For advanced research, it is important to have bio-resin appropriate to 3D print microscaffolds for cell proliferation and tissue engineering. To fill these requirements would be to use sources from bio-based resins, which can be made of naturally derived oils. Chosen substances glycerol diglycidyl ether and epoxidized linseed oil can be obtained from renewable recourses, are biodegradable and can be synthesized as sustainable photosensitive materials.1 UV (ff=365 nm) lithography was employed to determine their photocross-linking rate and cured material properties. After exposing material to UV radiation through a micro-patterned amplitude mask selective photopolymerization was observed. Acetone was used as a solvent to dissolve UV unaffected area and leaving only exposed microstructures on the substrate. The resins were compared to FormLabs Form Clear and Autodesk Ember PR48 as standard stereolithography materials. Finally, 3D microporous woodpile scaffolds were printed out of commercial resins and cells adhesion in them were explored.