Fluorescence imaging of cells using long-range electromagnetic surface waves for excitation

We present a depth-localized illumination technique for wide-field fluorescence microscopy, based on long-range optical surface waves. This technique allows one to excite the fluorescence only in a thin near-substrate layer of the specimen. Our experimental setup is compatible with both upright and inverted microscopes. It provides fluorescent microscopic images, which are superior to the epifluorescence ones in signal-to-noise ratio, contrast, and detail. We demonstrate the applicability of our technique for imaging both bacterial and eukaryotic cells (E. coli and HeLa, respectively).

Cell attachment on poly(3-hydroxybutyrate)-poly(ethylene glycol) copolymer produced by Azotobacter chroococcum 7B

BACKGROUND

The improvement of biomedical properties, e.g. biocompatibility, of poly(3-hydroxyalkanoates) (PHAs) by copolymerization is a promising trend in bioengineering. We used strain Azotobacter chroococcum 7B, an effective producer of PHAs, for biosynthesis of not only poly(3-hydroxybutyrate) (PHB) and its main copolymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV), but also alternative copolymer, poly(3-hydroxybutyrate)-poly(ethylene glycol) (PHB-PEG).

RESULTS

In biosynthesis we used sucrose as the primary carbon source and valeric acid or poly(ethylene glycol) 300 (PEG 300) as additional carbon sources. The chemical structure of PHB-PEG and PHB-HV was confirmed by 1H nuclear-magnetic resonance (1H NMR) analysis. The physico-chemical properties (molecular weight, crystallinity, hydrophilicity, surface energy) and surface morphology of films from PHB copolymers were studied. To study copolymers biocompatibility in vitro the protein adsorption and COS-1 fibroblasts growth on biopolymer films by XTT assay were analyzed. Both copolymers had changed physico-chemical properties compared to PHB homopolymer: PHB-HV and PHB-PEG had less crystallinity than PHB; PHB-HV was more hydrophobic than PHB in contrast to PHB-PEG appeared to have greater hydrophilicity than PHB; whereas the morphology of polymer films did not differ significantly. The protein adsorption to PHB-PEG was greater and more uniform than to PHB and PHB-PEG copolymer promoted better growth of COS-1 fibroblasts compared with PHB homopolymer.

CONCLUSIONS

Thus, despite low EG-monomers content in bacterial origin PHB-PEG copolymer, this polymer demonstrated significant improvement in biocompatibility in contrast to PHB and PHB-HV copolymers, which may be coupled with increased protein adsorption and hydrophilicity of PEG-containing copolymer.

The effects of confluency on cell mechanical properties

Mechanical properties of cells depend on various external and internal factors, like substrate stiffness and surface modifications, cell ageing and disease state. Some other currently unknown factors may exist. In this study we used force spectroscopy by AFM, confocal microscopy and flow cytometry to investigate the difference between single non-confluent and confluent (in monolayer) Vero cells. In all cases the stiffness values were fitted by log-normal rather than normal distribution. Log-normal distribution was also found for an amount of cortical actin in cells by flow cytometry. Cells in the monolayer were characterized by a significantly lower (1.4-1.7 times) Young's modulus and amount of cortical actin than in either of the single non-confluent cells or cells migrating in the experimental wound. Young's modulus as a function of indentation speed followed a weak power law for all the studied cell states, while the value of the exponent was higher for cells growing in monolayer. These results show that intercellular contacts and cell motile state significantly influence the cell mechanical properties.

[Atomic force microscopy of living cells: advances and future outlooks]

The advances of the method of atomic force microscopy for investigating the animal cells and an analysis of its development have been reviewed, with much attention being given to studies of living cells. The features and problems of the method have been considered, and a number of special methods based on the use of atomic force microscopy have been analyzed. The problems of choosing the geometry of probes for studies of animal cells, determination of cell adhesion on substrate, mapping of the cell surface using chemically modified cantilevers, and the distribution of molecular components inside the cell with the use of micro- and nanosurgical approaches have been discussed. The problems of combining the atomic force microscopy with optical and laser scanning confocal microscopy have been considered. Possible applications of the method in biotechnology and medicine are discussed.

[A study of lamellas of the web recombinant protein by atomic force microscopy]

Lamellas formed on the mica by protein 1F9, a recombinant analogue of the web protein, have been studied by atomic force microscopy. It has been shown that the molecules of 1F9 dissolved in strong solvents are capable of aggregating on the mica surface to form lamellas less than 1 nm in height and more than 1 microm in length. A model of a plane zigzag has been constructed to describe the conformation of 1F9 molecules on the mica surface.

[A comparative study of biodegradation kinetics of biopolymer systems based on poly(3-hydroxybutyrate)]

The aim of this study was to evaluate and to compare of long-term kinetics curves of biodegradation of poly(3-hydroxybutyrate) (PHB), its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and PHB/polylactic acid blend. The total weight loss and the change of average viscosity molecular weight were used as an index of biodegradation degree. The rate of biodegradation was analyzed in vitro in presence oflipase and in vivo when the films were implanted in animal tissues. The morphology of PHB films surface was studied by atomic force microscopy technique. It was shown that biodegradation of PHB is occurred by means of as polymer hydrolysis, and as its enzymatic biodegradation. The obtained data can be used for development of medical devices on the base of PHB.