Photocatalytic Nanolithography of Self-Assembled Monolayers and Proteins

Self-assembled monolayers of alkylthiolates on gold and alkylsilanes on silicon dioxide have been patterned photocatalytically on sub-100 nm length-scales using both apertured near-field and apertureless methods. Apertured lithography was carried out by means of an argon ion laser (364 nm) coupled to cantilever-type near-field probes with a thin film of titania deposited over the aperture. Apertureless lithography was carried out with a helium–cadmium laser (325 nm) to excite titanium-coated, contact-mode atomic force microscope (AFM) probes. This latter approach is readily implementable on any commercial AFM system. Photodegradation occurred in both cases through the localized photocatalytic degradation of the monolayer. For alkanethiols, degradation of one thiol exposed the bare substrate, enabling refunctionalization of the bare gold by a second, contrasting thiol. For alkylsilanes, degradation of the adsorbate molecule provided a facile means for protein patterning. Lines were written in a protein-resistant film formed by the adsorption of oligo(ethylene glycol)-functionalized trichlorosilanes on glass, leading to the formation of sub-100 nm adhesive, aldehyde-functionalized regions. These were derivatized with aminobutylnitrilotriacetic acid, and complexed with Ni2+, enabling the binding of histidine-labeled green fluorescent protein, which yielded bright fluorescence from 70-nm-wide lines that could be imaged clearly in a confocal microscope

Achievable tolerances in robotic feature machining operations using a low-cost hexapod

Portable robotic machine tools potentially allow feature machining processes to be brought to large parts in various industries, creating an opportunity for capital expenditure and operating cost reduction. However, robots lack the machining capability of conventional equipment, which ultimately results in dimensional errors in parts. This work showcases a low-cost hexapod-based robotic machine tool and presents experimental research conducted to investigate how the widely researched robotic machining challenges, e.g. structural dynamics and kinematics, translate to achievable tolerance ranges in real-world production to highlight currently feasible applications and provide a context for considering technology improvements. Machining trials assess the total dimensional errors in the final part over multiple geometries. A key finding is error variation which is in the sub-millimetre range, although, in some cases, upper tolerance limits < 100 μm are achieved. Practical challenges are also noted. Most significantly, it is demonstrated that dimensional machining error is mainly systematic in nature and therefore that the total error can be dramatically reduced with in situ measurement and compensation. Potential is therefore found to achieve a flexible, high-performance robotic machining capability despite complex and diverse underlying scientific challenges. Overall, the work presented highlights achievable tolerances in low-cost robotic machining and opportunities for improvement, also providing a practical benchmark useful for process selection

OPTIMIZED SWITCH ALLOCATION TO IMPROVE THE RESTORATION ENERGY IN DISTRIBUTION SYSTEMS

In distribution networks switching devices play critical role in energy restoration and improving reliability indices. This paper presents a novel objective function to optimally allocate switches in electric power distribution systems. Identifying the optimized location of the switches is a nonlinear programming problem (NLP). In the proposed objective function a new auxiliary function is used to simplify the calculation of the objective function. The output of the auxiliary function is binary. The genetic algorithm (GA) optimization method is used to solve this optimization problem. The proposed method is applied to a real distribution network and the results reveal that the method is successful. K e y w o r d s: Power distribution systems, switches, restoration energy, genetic algorithm (GA

Nanopatterning proteins over large areas for biological applications

The recent decade has seen a rapid expansion in the ability to create and study nanometer scale objects and these new methods are being applied to the study of biological systems. The immobilisation of bioactive molecules has long been a goal in biomaterials and tissue engineering research, for use as stimulatory cues or model systems to study biointeractions. The advent of soft lithographic routes and efficient approaches to minimise non-specific protein interactions for example through immobilised polyethylene oxide coatings has lead to microscale pattens of proteins were routinely demonstrated and applied as model systems to study biological systems. While patterns at the micrometer scale of considerable interest and application, the size of and lengthscale at which proteins and other macromolecules are structured in vivo is in most cases at the nanoscale. Patterning biomolecules at the nanometer scale gives a significant potential for studying how biological systems function at the macromolecular length scale or to mimic the structure of biological interfaces with macromolecular resolution. A key requisite for the study of cellular biosystems is the ability to robustly generate large areas of patterns. In this work colloidal lithographic routes utilising electrostatic self assembly to generate dispersed monolayers of colloidal particles as masks for pattern generation have been used to generate nanostructured interfaces. Substrates with nanopatterned surface chemistry have been used as templates for generation of nanopatterns of proteins. Hydrophobically modified gold nanopatches in a silicon oxide background have been used to open up arrays of 100nm nanometer diameter regions within a protein rejecting background (based on PLL-g-PEG) and used to demonstrate nanopatterning of a number of protein systems (Laminin, Osteopontin and Ferritin). Nanostructured interfaces have also been fabricated on QCM-D sensors and used to study insitu protein and antibody binding at nanoscale patches while AFM microscopy of dried samples was used to quantify protein and antibody binding utilising height histograms. A combination of QCM-D, AFM and SPR derived data was used to establish the thickness and density of the adsorbed laminin layers at both nanoscale patches and homogeneous surfaces

Changes in fibroblast morphology in response to nano-columns produced by colloidal lithography

In designing new biomaterials, specific chemical and topographical cues will be important in guiding cell response. Filopodia are actin-driven structures produced by cells and speculated to be involved in cell sensing of the three-dimensional environment. This report quantifies filopodia response to cylindrical nano-columns (100 nm diameter, 160 nm high) produced by colloidal lithography. Also observed were actin cytoskeleton morphology by fluorescence microscopy and filopodia morphology by electron microscopy (scanning and transmission). The results showed that the fibroblasts used produced more filopodia per μm of cell perimeter and that filopodia could often be seen to interact with the cells’ nano-environment. By understanding as to which features evoke spatial reactions in cells, it may be possible to design better biomaterials

Use of nanotopography to study mechanotransduction in fibroblasts – methods and perspectives

The environment around a cell during in vitro culture is unlikely to mimic those in vivo. Preliminary experiments with nanotopography have shown that nanoscale features can strongly influence cell morphology, adhesion, proliferation and gene regulation, but the mechanisms mediating this cell response remain unclear. In this perspective article, we attempt to illustrate that a possible mechanism is direct transmittal of forces encountered by cells during spreading to the nucleus via the cytoskeleton. We further try to illustrate that this 'self – induced' mechanotransduction may alter gene expression by changing interphase chromosome positioning. Whilst the observations described here to show how we think nanotopography can be developed as a tool to look at mechanotransduction are preliminary, we feel they indicate that topography may give cell biologists a non-invasive tool with which to investigate in vitro cellular mechanisms