Whole-cell based hybrid materials for green energy production, environmental remediation and smart cell-therapy

This critical review highlights the advances that have been made over recent years in the domain of whole-cell immobilisation and encapsulation for applications relating to the environment and human health, particularly focusing on examples of photosynthetic plant cells, bacteria and algae as well as animal cells. Evidence that encapsulated photosynthetic cells remain active in terms of CO(2) sequestration and biotransformation (solar driven conversion of CO(2) into biofuels, drugs, fine chemicals etc.), coupled with the most recent advances made in the field of cell therapy, reveals the need to develop novel devices based on the preservation of living cells within abiotic porous frameworks. This review shall corroborate this statement by selecting precise examples that unambiguously demonstrate the necessity and the benefits of such smart materials. As will be described, the handling and exploitation of photosynthetic cells are enhanced by entrapment or encapsulation since the cells are physically separated from the liquid medium, thereby facilitating the recovery of the metabolites produced. In the case of animal cells, their encapsulation within a matrix is essential in order to create a physical barrier that can protect the cells auto-immune defenders upon implantation into a living body. For these two research axes, the key parameters that have to be kept in mind when designing hybrid materials will be identified, concentrating on essential aspects such as biocompatibility, mechanical strength and controlled porosity (264 references).     

Prolonging the lifetime and activity of silica immobilised Cyanidium caldarium

Over the past few years the idea of living photosynthetic materials has advanced from concept to reality. This work outlines the improvements made in the immobilisation of the thermotolerant acidophile Cyanidium caldarium (Tilden) Geitler SAG 16.91 within porous and transparent silica gels with the view to targeting photochemical materials that can be used to mitigate rising CO(2) emissions. Our results suggest that the immobilised cells are autofluorescent for at least 75 days post encapsulation and can maintain a steady oxygen production rate over a similar timeframe corroborating the viability and physiological activity of silica immobilised C. caldarium.     

Cell polarisation model: The 1D case

We study the dynamics of a one-dimensional non-linear and non-local drift-diffusion equation set in the half-line, with the coupling involving the trace value on the boundary. The initial mass M of the density determines the behaviour of the equation: attraction to self-similar profile, to a steady state of finite time, blow-up for supercritical mass. Using the logarithmic Sobolev and the HWI inequalities we obtain a rate of convergence for the sub-critical and critical mass cases. Moreover, we prove a comparison principle on the equation obtained after space integration. This concentration-comparison principle allows proving blow-up of solutions for large initial data without any monotonicity assumption on the initial data.     

Enhancement of the transverse conductance in DNA nucleotides

We theoretically study the electron transport properties of DNA nucleotides placed in the gap between two single-wall carbon nanotubes capped or terminated with H or N. We show that in the case of C-cap and H-termination the current at low electric bias is dominated by nonresonant tunneling, similarly to the cases of gold electrodes. In nitrogen-terminated nanotube electrodes, the nature of current is primarily quasiresonant tunneling and is increased by several orders of magnitude. We discuss the consequence of our result on the possibility of recognition at the level of single molecule.     

Paintshop, odd cycles and necklace splitting

The following problem has been presented in [T. Epping, W. Hochstättler, P. Oertel, Complexity results on a paint shop problem, Discrete Applied Mathematics 136 (2004) 217-226] by Epping, Hochstättler and Oertel: cars have to be painted in two colors in a sequence where each car occurs twice; assign the two colors to the two occurrences of each car so as to minimize the number of color changes. More generally, the “paint shop scheduling problem” is defined with an arbitrary multiset of colors given for each car, where this multiset has the same size as the number of occurrences of the car; the mentioned article states two conjectures about the general problem and proves its NP-hardness. In a subsequent paper in [P. Bonsma, Th. Epping, W. Hochstättler, Complexity results for restricted instances of a paint shop problem for words, Discrete Applied Mathematics 154 (2006) 1335-1343], Bonsma, Epping and Hochstättler proved its APX-hardness and noticed the applicability of some classical results in special cases.We first identify the problem concerning two colors as a minimum odd circuit cover problem in particular graphs, exactly situating the problem. A resulting two-way reduction to a special minimum uncut problem leads to polynomial algorithms for subproblems, to observing APX-hardness through MAX CUT in 3-regular graphs, and to a solution with at most 3/4th of all possible remaining color changes (when all obliged color changes have been made).For the general problem concerning an arbitrary number of colors, we realize that the two aforementioned conjectures are corollaries of the celebrated “necklace splitting” theorem of Alon, Goldberg and West.     

Mechanism for spherical dome and microvoid formation in polycarbonate using nanojoule femtosecond laser pulses

Spherical domes are created on the surface of polycarbonate samples, and microvoids are formed within the bulk using only a femtosecond oscillator with pulse energy of just 0.47?nJ. Size of spherical domes and shape of microvoids are controlled by changing the laser focus inside the material. Their formation is explained by a combination of heat accumulation and dome formation dynamics, where the dome acts as a microlens shifting the laser focus within the sample. The technique described here provides a simple avenue for fabricating smooth microlens arrays of various sizes and opens the possibility for direct fabrication of complex three-dimensional microfluidic channels in transparent materials.