We demonstrate capability to structure photo-polymers with sub-wavelength resolution, ∼200-500 nm, and retrieve three-dimensional (3D) structures using a picosecond laser exposure. This alternative to commonly used ultra-short femtosecond lasers extends accessibility of 3D direct write. A popular hybrid sol-gel resist SZ2080 was used for quantitative determination of structuring resolution at 1064 nm and 532 nm wavelengths and for pulses of 8-25 ps duration at the repetition rates of 0.2-1 MHz. Systematic study of feature size dependence of 3D suspended nano-rods shows that linear power dependence of photopolymerization on the dose-per-pulse becomes dominant at higher repetition rates (≥0.5 MHz) while the two-photon nonlinear absorption is still distinguishable at rates lower than 0.2 MHz and shorter pulses (≤8 ps). Thermal accumulation defines polymerization when cooling time of the focal volume is larger than separation between pulses. Photopolymerization and its scaling mechanisms, quality, and fidelity at tight focusing of fs-, ps-, and cw-laser radiation are revealed and explained. 3D scaffolds for biomedicine and microlenses for optical applications are fabricated by the ps-laser direct write.

No abstract

A series of π-expanded coumarins comprising of 4–5 conjugated rings were designed and synthesized. The strategic placement of two dialkylamino groups containing long alkyl chains attached to the peripheral ends of bis-coumarins resulted in dyes with superb solubility. As α,β-unsaturated ketones, these compounds display properties of donor–acceptor–donor (D–A–D)-type chromophores. Photophysical studies of the new functional dyes revealed a combination of favorable properties: strong absorption of blue and green light, weak fluorescence, reasonable two-photon absorption (2PA) cross-section, and complete solubility in nonpolar solvents. The fluorescence lifetimes of coumarin-derived α,β-unsaturated ketones were measured for the first time. The placement of two amine groups at peripheral positions of the dyes produced two-photon absorption cross-section values at the level of 150–400 GM around 800 nm, which generated two-photon photoinitiation. The highest 2PA cross-section was approximately 400 GM for the derivative of 4-methylcyclohexanone. Directly using these compounds as sensitizer or initiator, two (2D)- and three-dimensional (3D) nanopatterns were successfully fabricated by two-photon initiated polymerization. 3,3′-Carbonyl-biscoumarin, which contains two dihexylamino substituents at positions 7 and 7′ possesses the largest fabrication window. MC3T3-E1 preosteoblastic cells exhibited strong adherence to all π-expanded coumarins and the same spindle-shaped morphology as the tissue culture treated polystyrene control surface. Additionally, our results showed an increase in cell proliferation after 3 and 7 days in culture, as well as a high cell viability of approximately 100% on all materials compared to the control surface. These findings confirm that D–A–D-type ketocoumarin derivatives used as potential photoinitiators are noncytotoxic and can be used in the fabrication of biomaterial scaffolds for tissue engineering applications.

This work presents the latest results on direct laser writing of polymeric materials for tissue engineering applications. A femtosecond Yb:KGW laser (300 fs, 200 kHz, 515 nm) was used as a light source for non-linear lithography. Fabrication was implemented in various photosensitive polymeric materials, such as: hybrid organic-inorganic sol-gel based on silicon-zirconium oxides, commercial ORMOCER® class photoresins. These materials were structured via multi-photon polymerization technique with submicron resolution. Porous three-dimensional scaffolds for artificial tissue engineering were fabricated with constructed system and were up to several millimeters in overall size with 10 to 100 μm internal pores. Biocompatibility of the used materials was tested in primary rabbit muscle-derived stem cell culture in vitro and using laboratory rats in vivo. This interdisciplinary study suggests that proposed technique and materials are suitable for tissue engineering applications.