Sima Rekštytė

Preclinical study of SZ2080 material 3D microstructured scaffolds for cartilage tissue engineering made by femtosecond direct laser writing lithography

Over the last decade DLW employing ultrafast pulsed lasers has become a well-established technique for the creation of custom-made free-form three-dimensional (3D) microscaffolds out of a variety of materials ranging from proteins to biocompatible glasses. Its potential applications for manufacturing a patients specific scaffold seem unlimited in terms of spatial resolution and geometry complexity. However, despite few exceptions in which live cells or primitive organisms were encapsulated into a polymer matrix, no demonstration of an in vivo study case of scaffolds generated with the use of such a method was performed. Here, we report a preclinical study of 3D artificial microstructured scaffolds out of hybrid organic-inorganic (HOI) material SZ2080 fabricated using the DLW technique. The created 2.1 × 2.1 × 0.21 mm(3) membrane constructs are tested both in vitro by growing isolated allogeneic rabbit chondrocytes (Cho) and in vivo by implanting them into rabbit organisms for one, three and six months. An ex vivo histological examination shows that certain pore geometry and the pre-growing of Cho prior to implantation significantly improves the performance of the created 3D scaffolds. The achieved biocompatibility is comparable to the commercially available collagen membranes. The successful outcome of this study supports the idea that hexagonal-pore-shaped HOI microstructured scaffolds in combination with Cho seeding may be successfully implemented for cartilage tissue engineering.

Nano-groove and 3D fabrication by controlled avalanche using femtosecond laser pulses

We report fabrication of sub-100 nm resolution structures by ablation on the surface of sapphire using femtosecond laser pulses. A single 50–70 nm wide groove was recorded by laser ablation via a controlled ripple formation on the surface. Ripples are created by breakdown due to a sphere-to-plane formation of an ionisation below surface in a similar way as the bulk ripples. Different thresholds for the ripples formed parallel and perpendicular to direction of the laser scan were observed. In a sol-gel photo-polymer SZ2080 and thermo-polymer polydimethylsiloxane, free-standing 3D structures were formed without use of two-photon absorbing photo-sensitizers. Both cases of the surface and bulk structuring were achieved via a controlled avalanche, which dominated ionisation of materials.

Three-dimensional laser micro-sculpturing of silicone: towards bio-compatible scaffolds

Possibility to form three-dimensional (3D) micro-structures in silicone elastomer (polydimethylsiloxane; PDMS) doped with different photo-initiators was systematically investigated using direct laser writing with femtosecond laser pulses at different exposure conditions. Accuracy of the 3D structuring with resolution of ~5 μm and a fabrication throughput of ~720 μm(3)/s, which is exceeding the previously reported values by ~ 300(×), was achieved. Practical recording velocities of ~ 1 mm/s were used in PDMS with isopropyl-9H-thioxanthen-9-one (ISO) and thioxanthen-9-one (THIO) photo-initiators which both have absorption at around 360 nm wavelength. The 3D laser fabrication in PDMS without any photo-initiator resulting in a fully bio-compatible material has been achieved for the first time. Rates of multi-photon absorption and avalanche for the structuring of silicone are revealed: the two-photon absorption is seeding the avalanche of a radical generation for subsequent cross-linking. Direct writing enables a maskless manufacturing of molds for soft-lithography and 3D components for microfluidics as well as scaffolds for grafts in biomedical applications.

Nanoscale Precision of 3D Polymerization via Polarization Control

NATO SPS-985048 “Nanostructures for Highly Effi cient Infrared Detection” grant is acknowledged. D.G. is grateful for the fi nancial support by “FOKER” (Grant No. MIP-14459) grant from the Research Council of Lithuania.

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.

Microactuation and sensing using reversible deformations of laser-written polymeric structures

We investigate reversible deformations of polymeric microstructures fabricated using direct laser writing three-dimensional lithography upon immersion in various solvents. Swelling and shrinkage of sub-micrometre size features are induced by interaction with surrounding solvent and such deformations can be exploited to create larger structures whose size, shape, and other structural parameters depend on the surroundings. We describe diffractive optical elements, micro-mechanical sensors and also hybrid deformable structures, that can be used to implement micro-actuation, micro-sensing, and other functionalities highly sought for micro-optical, micro-mechanical, and micro-fluidic systems.

Synthesis, characterization and 3D micro-structuring via 2-photon polymerization of poly(glycerol sebacate)-methacrylate-an elastomeric degradable polymer

Poly(glycerol sebacate) (PGS) has been utilised in numerous biomaterial applications over recent years. This elastomeric and rapidly degradable polymer is cytocompatible and suited to various applications in soft tissue engineering and drug delivery. Although PGS is simple to synthesise as an insoluble prepolymer, it requires the application of high temperatures for extended periods of time to produce an insoluble matrix. This places limitations on the processing capabilities of PGS and its possible applications. Here, we present a photocurable form of PGS with improved processing capabilities: PGS-methacrylate (PGS-M). By methacrylating the secondary hydroxyl groups of the glycerol units in the PGS prepolymer chains, the material was rendered photocurable and, in combination with a photoinitiator, crosslinked rapidly on exposure to UV light at ambient temperatures. The polymer’s molecular weight and the degree of methacrylation could be controlled independently and the mechanical properties of the crosslinked material tailored. The polymer also displayed rapid degradation under physiological conditions and cytocompatibility with various primary cell types. As a demonstration of the processing capabilities of PGS-M, µm scale 3D scaffold structures were fabricated using 2-photon polymerisation and used for 3D cell culture. The tunable properties of PGS-M coupled with its enhanced processing capabilities make the polymer an attractive potential biomaterial for various future applications.

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.

Femtosecond pulsed light polarization induced effects in direct laser writing 3D nanolithography

We demonstrate how the coupling between (i) polarization of the writing laser beam, (ii) tight focusing and (iii) heat conduction affects the size, shape and absorption in the laser-affected area and therefore the polymerization process. It is possible to control the sizes of 3D laser-produced structure at the scale of several nanometers. Specifically we were able to tune the aspect ratio of 3D suspended line up to 20% in hybrid SZ2080 resist. The focal spot of tightly focused linearly polarized beam has an elliptical form with the long axis in the field direction. It is shown here that this effect is enhanced by increase in the electronic heat conduction when polarization coincide with temperature gradient along with the absorption. Overlapping of three effects (i- iii) results in the difference of several tens of nanometers between two axes of the focal ellipse. Narrow line appears when polarization and scan direction coincide, while the wide line is produced when these directions are perpendicular to each other. The effect scales with the laser intensity giving a possibility to control the width of the structure on nanometer scale as demonstrated experimentally in this work. These effects are of general nature and can be observed in any laser-matter interaction experiments where plasma produced by using tight focusing of linear-polarized light.