Use of Flavin-Related Cellular Autofluorescence to Monitor Processes in Microbial Biotechnology

Cellular autofluorescence is usually considered to be a negative phenomenon because it can affect the sensitivity of fluorescence microscopic or flow cytometric assays by interfering with the signal of various fluorescent probes. Nevertheless, in our work, we adopted a different approach, and green autofluorescence induced by flavins was used as a tool to monitor fermentation employing the bacterium Cupriavidus necator. The autofluorescence was used to distinguish microbial cells from abiotic particles in flow cytometry assays, and it was also used for the determination of viability or metabolic characteristics of the microbial cells. The analyses using two complementary techniques, namely fluorescence microscopy and flow cytometry, are simple and do not require labor sample preparation. Flavins and their autofluorescence can also be used in a combination with other fluorophores when the need for multi-parametrical analyses arises, but it is wise to use dyes that do not emit a green light in order to not interfere with flavins' emission band (500-550 nm).

Development of an Electroactive Hydrogel as a Scaffold for Excitable Tissues

For many cells used in tissue engineering applications, the scaffolds upon which they are seeded do not entirely mimic their native environment, particularly in the case of excitable tissues. For instance, muscle cells experience contraction and relaxation driven by the electrical input of an action potential. Electroactive materials can also deform in response to electrical input; however, few such materials are currently suitable as cell scaffolds. We previously described the development of poly(ethyelene glycol) diacrylate-poly(acrylic acid) as an electroactive scaffold. Although the scaffold itself supported cell growth and attachment, the voltage (20 V) required to actuate these scaffolds was cytotoxic. Here, we describe the further development of our hydrogels into scaffolds capable of actuation at voltages (5 V) that were not cytotoxic to seeded cells. This study describes the critical next steps towards the first functional electroactive tissue engineering scaffold.

Structural engineering to control density, conformation, and bioactivity of the poly(ethylene glycol)-grafted poly(urethane urea) scaffolds

Poly(urethane urea) scaffolds were fabricated through combined salt leaching and solvent casting methods. The scaffolds were then functionalized via aminolysis with poly(ethylene glycol) (PEG- g-PUU). To compare its bioactivity, gelatin was also grafted onto the aminolyzed poly(urethane urea) surface (Gel- g-PUU). Chemical changes at the surface were then monitored using quantitative/qualitative methods. Grafting with both gelatin and poly(ethylene glycol) remarkably enhanced the wettability of poly(urethane urea). Proliferation of human adipose–derived mesenchymal stem cells on poly(urethane urea) and the modified poly(urethane urea)s was evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay. The cell experiment results showed that both the modified poly(urethane urea)s enhanced the attachment and proliferation of human adipose–derived mesenchymal stem cells compared to pure poly(urethane urea). Based on previous reports, while a supportive role is observed at adequate poly(ethylene glycol) graft densities, cell adhesion and proliferation are inhibited at very high grafting densities. To correlate the cell data to poly(ethylene glycol) conformations, the surface tension was measured. Data on human adipose–derived mesenchymal stem cells’ attachment/proliferation and contact angle/surface free energy together showed that the grafting density of poly(ethylene glycol) was regulated by optimizing aminolysis conditions, careful selection of poly(ethylene glycol)’s molecular weight, and bulk properties of the matrix poly(urethane urea). As a result, surface overcrowding and brush conformation of the poly(ethylene glycol) chains were avoided, and human adipose–derived mesenchymal stem cell attachment and proliferation occurred on the PEG- g-PUU scaffold at a comparable level to the Gel- g-PUU.

Poly(3-hydroxybutyrate)/poly(ethylene glycol) scaffolds with different microstructure: the effect on growth of mesenchymal stem cells

Development of biocompatible 3D scaffolds is one of the most important challenges in tissue engineering. In this study, we developed polymer scaffolds of different design and microstructure to study cell growth in them. To obtain scaffolds of various microstructure, e.g., size of pores, we used double- and one-stage leaching methods using porogens with selected size of crystals. A composite of poly(3-hydroxybutyrate) (PHB) with poly(ethylene glycol) (PEG) (PHB/PEG) was used as polymer biomaterial for scaffolds. The morphology of scaffolds was analyzed by scanning electron microscopy; the Young modulus of scaffolds was measured by rheometry. The ability to support growth of mesenchymal stem cells (MSCs) in scaffolds was studied using the XTT assay; the phenotype of MSC was preliminarily confirmed by flow cytometry and the activity of alkaline phosphatase and expression level of CD45 marker was studied to test possible MSC osteogenic differentiation. The obtained scaffolds had different microstructure: the scaffolds with uniform pore size of about 125 µm (normal pores) and 45 µm (small pores) and scaffolds with broadly distributed pores size from about 50-100 µm. It was shown that PHB/PEG scaffolds with uniform pores of normal size did not support MSCs growth probably due to their marked spontaneous osteogenic differentiation in these scaffolds, whereas PHB/PEG scaffolds with diverse pore size promoted stem cells growth that was not accompanied by pronounced differentiation. In scaffolds with small pores (about 45 µm), the growth of MSC was the lowest and cell growth suppression was only partially related to stem cells differentiation. Thus, apparently, the broadly distributed pore size of PHB/PEG scaffolds promoted MSC growth in them, whereas uniform size of scaffold pores stimulated MSC osteogenic differentiation.

Tailoring barrier properties of thermoplastic corn starch-based films (TPCS) by means of a multilayer design

This work compares the effect of adding different biopolyester electrospun coatings made of polycaprolactone (PCL), polylactic acid (PLA) and polyhydroxybutyrate (PHB) on oxygen and water vapour barrier properties of a thermoplastic corn starch (TPCS) film. The morphology of the developed multilayer structures was also examined by Scanning Electron Microscopy (SEM). Results showed a positive linear relationship between the amount of the electrospun coatings deposited onto both sides of the TPCS film and the thickness of the coating. Interestingly, the addition of electrospun biopolyester coatings led to an exponential oxygen and water vapour permeability drop as the amount of the electrospun coating increased. This study demonstrated the versatility of the technology here proposed to tailor the barrier properties of food packaging materials according to the final intended use.

Chitosan as a Biomaterial: Influence of Degree of Deacetylation on Its Physiochemical, Material and Biological Properties

Chitosan is a biomaterial with a range of current and potential biomedical applications. Manipulation of chitosan degree of deacetylation (DDA) to achieve specific properties appears feasible, but studies investigating its influence on properties are often contradictory. With a view to the potential of chitosan in the regeneration of nerve tissue, the influence of DDA on the growth and health of olfactory ensheathing cells (OECs) was investigated. There was a linear increase in OEC proliferation as the DDA increased from 72 to 85%. This correlated with linear increases in average surface roughness (0.62 to 0.78 μm) and crystallinity (4.3 to 10.1%) of the chitosan films. Mitochondrial activity and membrane integrity of OECs was significantly different for OECs cultivated on chitosan with DDAs below 75%, while those on films with DDAs up to 85% were similar to cells in asynchronous growth. Apoptotic indices and cell cycle analysis also suggested that chitosan films with DDAs below 75% were cytocompatible but induced cellular stress, while OECs grown on films fabricated from chitosan with DDAs above 75% showed no significant differences compared to those in asynchronous growth. Tensile strength and elongation to break varied with DDA from 32.3 to 45.3 MPa and 3.6 to 7.1% respectively. DDA had no significant influence on abiotic and biotic degradation profiles of the chitosan films which showed approximately 8 and 20% weight loss respectively. Finally, perceived patterns in property changes are subject to change based on potential variations in DDA analysis. NMR examination of the chitosan samples here revealed significant differences depending upon which peaks were selected for integration; 6 to 13% in DDA values within individual samples. Furthermore, differences between DDA values determined here and those reported by the commercial suppliers were significant and this may also be a source of concern when selecting commercial chitosans for biomaterial research.

PEG-PHB-glutaminase nanoparticle inhibits cancer cell proliferation in vitro through glutamine deprivation

In this study, we demonstrate that L-glutaminase, a marine bacterial enzyme with a molecular weight of 37 kDa, inhibits cancer cell proliferation in vitro through glutamine deprivation. The concentration of the enzyme reducing the viability of HeLa cells to 50% was determined to be 12.5 μg/mL; the function of L-glutaminase in controlling cell proliferation was further analysed by BrdU assays. To increase its stability and bioavailability, the enzyme was immobilized on polyethyleneglycol (PEG)-polyhydroxybutyrate (PHB) nanoparticles. A dented anatomy of the HeLa cells was observed under fluorescence and confocal microscopy when they were incubated with L-glutaminase and in glutamine-free medium, as also a 3-fold increase in caspase-3 activity was observed under the same conditions. Blebbed cytoplasm and shrunken nuclei were observed in treated cells under transmission electron microscopy (TEM). Finally, the influence of the enzyme on cell cycle and DNA damage was evaluated using flow cytometry and DNA fragmentation assays. The results confirmed significant damage to the DNA of HeLa cells incubated with L-glutaminase and in glutamine-free medium. These studies attest to the significant role played by L-glutaminase against proliferation in cancer cells through glutamine deprivation.