Fungi, in particular, basidiomycetous fungi, are very successful in colonizing microconfined mazelike networks (for example, soil, wood, leaf litter, plant and animal tissues), a fact suggesting that they may be efficient solving agents of geometrical problems. We therefore evaluated the growth behavior and optimality of fungal space-searching algorithms in microfluidic mazes and networks. First, we found that fungal growth behavior was indeed strongly modulated by the geometry of microconfinement. Second, the fungus used a complex growth and space-searching strategy comprising two algorithmic subsets: 1) long-range directional memory of individual hyphae and 2) inducement of branching by physical obstruction. Third, stochastic simulations using experimentally measured parameters showed that this strategy maximizes both survival and biomass homogeneity in microconfined networks and produces optimal results only when both algorithms are synergistically used. This study suggests that even simple microorganisms have developed adequate strategies to solve nontrivial geometrical problems.
Micro-contact printing, μCP, is a well-established soft-lithography technique for printing biomolecules. μCP uses stamps made of Poly(dimethylsiloxane), PDMS, made by replicating a microstructured silicon master fabricated by semiconductor manufacturing processes. One of the problems of the μCP is the difficult control of the printing process, which, because of the high compressibility of PDMS, is very sensitive to minute changes in the applied pressure. This over-sensitive response leads to frequent and/or uncontrollable collapse of the stamps with high aspect ratios, thus decreasing the printing accuracy and reproducibility. Here we present a straightforward methodology of designing and fabricating PDMS structures with an architecture which uses the collapse of the stamp to reduce, rather than enlarge the variability of the printing. The PDMS stamp, organized as an array of pyramidal micro-posts, whose ceiling collapses when pressed on a flat surface, replicates the structure of the silicon master fabricated by anisotropic wet etching. Upon application of pressure, depending on the size of, and the pitch between, the PDMS pyramids, an air gap is formed surrounding either the entire array, or individual posts. The printing technology, which also exhibits a remarkably low background noise for fluorescence detection, may find applications when the clear demarcation of the shapes of protein patterns and the distance between them are critical, such as microarrays and studies of cell patterning.Electronic supplementary materialThe online version of this article (doi:10.1007/s10544-016-0036-4) contains supplementary material, which is available to authorized users.
This paper describes a novel technique for the fabrication of a multianalyte protein microassay on the basis of the creation of microwells that locally enhance the adsorption of proteins. The microwells are fabricated via a localized laser ablation of a protein-blocked thin gold layer (∼50 nm) deposited on a poly(methyl methacrylate) film. The microablation of gold induces local chemical and physical changes in the top surface of the polymer as well as a higher specific surface, which cooperate to achieve a higher and more reproducible surface concentration of proteins in microwells. The fabrication platform consists of a computer-controlled laser ablation system, comprising a research-grade inverted optical microscope, a pulsed nitrogen laser emitting at 337 nm, a programmable XYZ stage, and a picoliter pipet mounted on the XYZ stage. The microwells with diameters of 5−20 μm, 1−5 μm, and submicron widths are readily achieved by focusing through a 20× dry objective, a 40× dry objective, or a 100× oil immersion lens, respectively. One variant of the method uses a sequence of local ablation and “flood” coverage with protein solution. The second variant uses the microablation of the whole microassay followed by the “spatially addressable” deposition of different protein solution with a picoliter pipet mounted on the same fabrication platform. The analytical performance of the device required only a 2−7 μL volume of sample and a single dilution step. The results indicate that antibody arrays can be used to identify different proteins, yielding results within a few minutes of sample addition with acceptable assay repeatability. It was observed that the microassays comprising line-shaped microstructures offer a higher reproducibility as well as offering the opportunity to encode the information (e.g. type of antibody, concentration) through a combination of vertical lines in a “bar code”, “informationally addressable” mode and not in a 2D, spatially addressable mode like in the classical microarrays.
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