Three-dimensional (3D) micro/nano-structuring of photo-resists is systematically studied at the close-to-dielectric- breakdown irradiance. It is demonstrated that avalanche absorption is playing a major part in free electron generation and chemical bond breaking at these conditions. The steps of photo-initiation and chemical bond breaking in propagation of polymerization are altered as compared with photo-polymerization at low-irradiance and one-photon stereo-lithography. The avalanche dominates radical generation and promotion of polymerization at tight focusing and a high approximately TW/cm(2) irradiance. The rates of electron generation by two-photon absorption and avalanche are calculated for the experimental conditions. Simulation results are corroborated by 3D polymerization in three resists with different photo-initiators at two different wavelengths and pulse durations. The smallest feature sizes of 3D polymerized logpile structures are consistent with spectral dependencies of the two photon nonlinearities. Implications of these findings for achieving sub-100 nm resolution in 3D structuring of photo-polymers are presented.

Femtosecond Laser Induced Polymerization is an attractive direct writing technique for rapid three-dimensional (3D) micro and nanofabrication in diverse applications. Recently, it has been successfully applied for 3D scaffold fabrication required in biomedicine applications. However, there are still a lot of investigations to be done before it can be used for practical applications in tissue engineering or regenerative medicine. In this work, experimental results on production of artificial polymeric scaffolds for stem cell growth are presented. Parameters (average laser power, sample scanning speed, and developing conditions) for microfabrication in biocompatible photopolymers AKRE (AKRE37) and ORMOSIL (SZ2080) are experimentally determined. 3D custom form and size artificial scaffolds were successfully microfabricated. Adult stem cell growth on them was investigated in order to test their biocompatibility. The results of myogenic stem cell culture expansion were compared to the control growth of the same cells on the scaffolds manufactured out of commonly used biocompatible photopolymers ORMOCER (Ormocore b59) and Poly-Ethylen Glycol Di-Acrylate (PEG-DA-258). Preliminary results show FLIP technique to have potential in fabrication of artificial 3D polymeric scaffolds for cell proliferation experiments. These are the first steps in transferring FLIP fabrication method from laboratory tests to flexible manufacturing of individual scaffolds out of biocompatible and biodegradable polymers.

Laser Two-Photon Polymerization (LTPP) is a technique enabling formation of 3D nanostructures in photosensitive resins with sub-wavelength resolution and unmatched flexibility. However, controllable fabrication of sub-100 nm features by this technique is still a challenge. Self-polymerization, also known as non-local polymerization, is considered to be promising in this ultra-high resolution structure formation. Recent observation of fragile self-polymerized fibres with diameter within tens of nanometres (nano-fibres) encourages the use of self-polymerization to produce nanometre scale structures other than fibres and to define the conditions for controllable fabrication. "X"-shaped polymerized supports are used as rigid structures to produce suspended self-polymerized features of different nature (shape and dimensionality) in-between the walls of "X". By laser writing lines parallel to the substrate and perpendicular to the long symmetry axis of "X" under different conditions, selfformation of periodic nano-fibres (diameter <100 nm) and nano-membranes is induced in acrylate photopolymer AKRE37. Depending on introduced exposure dose, spatial density threshold behaviour of non-structure, nano-fibre, nano-membrane, and laser written lines is deduced. Preliminary model including laser intensity, concentration of radicals, collapse force, and distance between supports as variables having threshold effect on final self-polymerized structure's geometry is proposed to explain non-local self-polymerization.

This work reports for the first time the development of enhanced conductivity, graphenedoped photo-patternable hybrid organic-inorganic ionogels and the effect of the subsequent materials condensation on the conductivity and mechanical stability of threedimensional microstructures fabricated by multi-photon polymerisation (MPP). Ionogels were based on photocurable silicon/zirconium hybrid sol-gel materials and phosphonium (trihexyltetradecylphosphonium dicyanamide [P6,6,6,14][DCA] ionic liquid (IL). To optimise the dispersion of graphene within the ionogel matrices, aqueous solutions of graphene were prepared, as opposed to the conventional graphene powder approach, and employed as catalysts of hydrolysis and condensation reactions occurring in the sol-gel process.Ionogels were prepared via a two step process by varying the hydrolysis degree from 25 to 50%, IL content between 0-50 w/w%, and the inorganic modifier (zirconate complex) concentration from 30 to 60 mol.% against the photocurable ormosil and they were characterised via Raman, Electrochemical Impedance Spectroscopy and Transmission Electron Microscopy. MPP was performed on the hybrid ionogels, resulting in threedimensional microstructures that were characterised using scanning electron microscopy.It is clearly demonstrated that the molecular formulation of the ionogels, including the concentration of graphene and the zirconate network modifier, play a critical role in the conductivity of the ionogels and influence the resulting mechanical stability of the fabricated three-dimensional microstructures. This work aims to establish for the first time the relationship between the molecular design and condensation of materials in the physico-chemistry and dynamic of ionogels.3

Laser-Micro/Nanofabricated 3D Polymers for Tissue Engineering ApplicationsA multi-photon polymerization system has been designed based on a pulsed irradiation light source (diode-pumped solid state femtosecond laser Yb:KGW, 300 fs, 1030 nm, 1-200 kHz) in combination with large working area and high precision linear motor driven stages (100×100×50 mm3). The system is intended for high resolution and throughput 3D micro- and nanofabrication and enables manufacturing the polymeric templates up to 1 cm2areas with sub-micrometer resolution. These can be used for producing 3D artificial polymeric scaffolds to be applied for growing cells, specifically, in the tissue engineering. The bio-compatibility of different acrylate, hybrid organic-inorganic and biodegradable polymeric materials is evaluated experimentallyin vitro. Variously sized and shaped polymeric scaffolds of biocompatible photopolymers with intricate 3D geometry were successfully fabricated. Proliferation tests for adult rabbit myogenic stem cells have shown the applicability of artificial scaffolds in biomedicine practice.