CC BY
3The 30th International Conference on Advanced Laser Technologies ALT'23
B-O-8
Formation of composite nanostructures by multiphoton lithography
for biomedical applications
D. Murashko1, E. Otsupko1, U. Kurilova2, A.Gerasimenko1'2, S.Selishchev1
1- National Research University of Electronic Technology MIET, Institute of Biomedical System, Bld. 1, Shokin
Square, Zelenograd, Moscow 124498, Russia 2- I.M. Sechenov First Moscow State Medical University, 8 Trubetskay str., Moscow 119991, Russia
skorden@outlook. com
Two-photon lithography, also known as multiphoton laser lithography, is a technique that allows direct laser writing in a volume with a resolution of less than 100 nm. When exposed to a near-infrared laser, the source material photopolymerises in the focal volume region to form complex micro- and nanostructures. Two-photon lithography is used in bioelectronics [1], labs-on-a-chip [2], and cell and tissue engineering [3,4]. Most synthetic photoresists and photoinitiators are not used in biological applications due to their cytotoxicity. To create a biocompatible structure, polysaccharides and proteins, which are the main elements of the extracellular matrix, are usually used. We chose bovine serum albumin (BSA) as a biopolymer because of its wide availability and well-studied properties, elasticity and enzymatic degradation. The organic dye riboflavin mononucleotide was used as the photoinitiator.
Despite their excellent biocompatibility and wide availability, natural polymers have inferior physical and chemical properties compared to synthetic photoresists. Therefore, single-walled carbon nanotubes (SWNTs) "TUBALL" were added to the material to improve the mechanical properties and provide electrical conductivity. The tubes have an average outer diameter of 16 nm and a length of more than 5 ^m. The carbon nanotubes were dissolved in 5 g/l distilled water. BSA, riboflavin and SWNTs were dissolved in phosphate buffer saline (pH = 7.4) to avoid rapid aggregation of the protein.
The structure was formed using a femtosecond pulsed Ti:sapphire laser. The irradiation wavelength was 736 nm, the pulse duration was 140 fs, the repetition frequency was 80 MHz and the irradiation power was 30 mW. An 0AGP-10-S optical attenuator with a Glan prism was used to control the irradiation power. The laser beam was focused on the sample using a optical microscope with 60x magnification (NA = 0.65). The samples were moved under the radiation using an XY 8MTF motorised scanning stage at a scanning speed of 5 ^m/s. The average dimensions of the nanostructures formed were 40 ^m x 40 ^m, with a height of 15 ^m. The mechanical properties of the nanostructures were investigated by indentation using a Nanoscan-4D Compact nanohardness tester. Measurements were made using a Berkovich trihedral pyramid indenter, with Poisson's ratio set at 0.3. The average modulus of elasticity of the BSA samples with SWNTs was 5.9 GPa and the hardness was 0.26 GPa. While for a BSA sample the value of Young's modulus was 0.86 MPa, the hardness was 75.16 MPa. The results showed that the addition of SWNTs improved the mechanical properties of the structures compared to the BSA material without filler. The nanotubes also ensured the electrical conductivity of the nanostructure. The addition of SWNTs reduced the resistance to 30 kQ compared to BSA alone (1 GQ). The studies were carried out using the Van der Pauw method.
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[2] Sima F. et al., Three-dimensional femtosecond laser processing for lab-on-a-chip applications, Nanophotonics, vol. 7, pp. 613-634, (2018).
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