Viktor N. Bagratashvili

The fibre optic reflectometer: A new and simple probe for refractive index and phase separation measurements in gases, liquids and supercritical fluids

A fibre optic reflectometer (FOR) has been developed to monitor refractive index (n) and density (ρ) changes in gases, liquids and supercritical fluids (SCFs). The key operating principle is the measurement of the intensity of light from a light emitting diode, LED, which is reflected from the end of a fibre immersed in the medium. The amount of reflected light depends on the difference between the refractive indices of the fibre and the medium. The refractive index of the medium is related in turn to its density. The FOR is particularly sensitive to phase separation, a key aspect of supercritical fluid systems, because of the density discontinuity which accompanies the separation. This device allows the collection of data with a high spatial (9 μm-fibre diameter) and time (∼0.02 s) resolution. The small size of the fibre optic probe means that it can be put into operating reactors and even catalyst beds. Experiments are described with pure CO2 and CHF3, and mixtures CO2u2006+u2006cyclohexane and CO2u2006+u2006MeOH over wide pressure and temperatures ranges. The measurements are in excellent agreement with published data for these systems.

Osteogenic differentiation of human mesenchymal stem cells in 3-D Zr-Si organic-inorganic scaffolds produced by two-photon polymerization technique.

Two-photon polymerization (2PP) is applied for the fabrication of 3-D Zr-Si scaffolds for bone tissue engineering. Zr-Si scaffolds with 150, 200, and 250 μm pore sizes are seeded with human bone marrow stem cells (hBMSCs) and human adipose tissue derived stem cells (hASCs) and cultured in osteoinductive and control media for three weeks. Osteogenic differentiation of hASCs and hBMSCs and formation of bone matrix is comparatively analyzed via alkaline phosphatase activity (ALP), calcium quantification, osteocalcin staining and scanning electron microscopy (SEM). It is observed that the 150 μm pore size Zr-Si scaffolds support the strongest matrix mineralization, as confirmed by calcium deposition. Analysis of ALP activity, osteocalcin staining and SEM observations of matrix mineralization reveal that mesenchymal stem cells cultured on 3-D scaffolds without osteogenic stimulation spontaneously differentiate towards osteogenic lineage. Nanoindentation measurements show that aging of the 2PP-produced Zr-Si scaffolds in aqueous or alcohol media results in an increase in the scaffold Young’s modulus and hardness. Moreover, accelerated formation of bone matrix by hASCs is noted, when cultured on the scaffolds with lower Young’s moduli and hardness values (non aged scaffolds) compared to the cells cultured on scaffolds with higher Young’s modulus and hardness values (aged scaffolds). Presented results support the potential application of Zr-Si scaffolds for autologous bone tissue engineering.

Novel biodegradable star-shaped polylactide scaffolds for bone regeneration fabricated by two-photon polymerization

AIMnTo assess the properties of 3D biodegradable scaffolds fabricated from novel star-shaped poly(D,L-lactide) (SSL) materials for bone tissue regeneration.nnnMATERIALS & METHODSnThe SSL polymer was synthesized using an optimized synthetic procedure and applied for scaffold fabrication by the two-photon polymerization technique. The osteogenic differentiation was controlled using human adipose-derived stem cells cultured for 28 days. The SSL scaffolds with or without murine MSCs were implanted into the cranial bone of C57/Bl6 mice.nnnRESULTSnThe SSL scaffolds supported differentiation of human adipose-derived stem cells toward the osteogenic lineage in vitro. The SSL scaffolds with murine MSCs enhanced the mineralized tissue formation.nnnCONCLUSIONnThe SSL scaffolds provide a beneficial microenvironment for the osteogenic MSCs differentiation in vitro and support de novo bone formation in vivo.

A route to diffusion embedding of CdSe/CdS quantum dots in fluoropolymer microparticles

A green and efficient synthetic approach has been developed using supercritical carbon dioxide as a transport medium for the diffusion embedding of core shell CdSe/CdS quantum dots (QD) into polytetrafluorethylene (PTFE) microparticles, leading to matrix immobilisation of QD in PTFE. Transmission electron microscopy and photoluminescence spectroscopy probes show that the products are fine dispersive photoluminescent nanocomposites with QD being homogeneously isolated throughout the polymer microparticle volume. Up to 3 × 105 QD can be embedded into a single ∼1 μm PTFE microparticle by this technique without degradation of the microparticulate structure. A further photoluminescence study of thermally heated and laser irradiated CdSe/CdS/PTFE microparticles reveals excellent optical performance and stability over the 20–80 °C temperature range.

Compatibility of cells of the nervous system with structured biodegradable chitosan-based hydrogel matrices

Hydrogel matrices for cell cultivation have been generated by two-photon laser polymerization of unsaturated chitosan derivatives and methacrylated hyaluronic acid. The adhesive and toxic properties of the matrices have been assessed, and the matrices have been shown to have a good compatibility with primary hippocampal cell cultures. The formation of morphologically normal neural networks by cells of the nervous system cultured on the surface of hydrogel matrices has been observed. The metabolic status of dissociated hippocampal cells cultured on the matrices was similar to that of the control cultures, as shown by the results of MTT reductase activity assay. Thus, matrices based on unsaturated polysaccharide derivatives crosslinked by laser irradiation showed good compatibility with differentiated cells of the nervous system and considerable potential for use in neurotransplantation.

Fabrication of microstructured materials based on chitosan and D,L-lactide copolymers using laser-induced microstereolithography

The graft copolymers of chitosan and oligo(D,L-lactide) obtained by solid-phase synthesis have been used as the basis of photosensitive compositions for the fabrication of three-dimensional microstructures by laser-induced stereolithography. The electronic absorption spectra of the copolymers are close to the sum of the spectra of native chitosan and polylactide, which has been chosen as a model of grafted oligolactide chains. The fundamental absorption bands of the copolymers lie in a range to 500 nm, and their contribution to the absorption intensity of a photosensitive composition based on the copolymers at second harmonic laser frequency is insignificant. Depending on the macromolecular characteristics of the copolymers, the three-dimensional crosslinking of photosensitive compositions on their basis in the course of microstructuring occurs with different efficiency.