Self-Localized Liquid Crystal Micro-Droplet Arrays on Chemically Patterned Surfaces

Liquid crystal (LC) micro-droplet arrays are elegant systems that have a range of applications, such as chemical and biological sensing, due to a sensitivity to changes in surface properties and strong optical activity. In this work, we utilize self-assembled monolayers (SAMs) to chemically micro-pattern surfaces with preferred regions for LC occupation. Exploiting discontinuous dewetting, dragging a drop of fluid over the patterned surfaces demonstrates a novel, high-yield method of confining LC in chemically defined regions. The broad applicability of this method is demonstrated by varying the size and LC phase of the droplets. Although the optical textures of the droplets are dictated by topological constraints, the additional SAM interface is shown to lock in inhomogeneous alignment. The surface effects are highly dependent on size, where larger droplets exhibit asymmetric director configurations in nematic droplets and highly knotted structures in cholesteric droplets.

Fabrication of hydrophobic surfaces on Titanium using Micro-EDM exhibiting antibacterial properties

Microbial contamination on medical assistive devices has been the major challenge for biomedical industries. The present work is focused on producing patterned surfaces on commercially pure Titanium (cp-Ti) using Micro-Electrical Discharge Machining (Micro-EDM) technique, and the feasibility of patterned surface in restricting bacterial growth. Geometrical patterning in form of micro-holes have been produced on cp-Ti biomaterials with Micro-EDM in two forms, one with 20 µm inter-distance forming a dense pattern and the other with 60 µm inter-distance forming a sparse pattern. The patterned surface establishes the degree of hydrophobicity as 130° and 106° for densely patterned and sparsely patterned surfaces respectively. Further, the effect of bacterial adhesion over the textured cp-Ti surfaces are challenged with model bacteria gram negative Escherichia coli (e.coli) in Luria broth (LB) agar media. The Colony Forming Unit (CFU) count obtained for densely patterned surface compared with that of non-patterned surface reflects 90% reduced bacterial growth. The instances of pattern formation and bacterial growth have been observed with Scanning Electron Microscopy. The enhanced material properties with micro-patterning that combat microbial activities on the biomaterial surface proves its efficacy in adoption for biomedical applications, with significant reduction in bacterial contamination on medical devices or implants, leading toward reduced healthcare risks and issues related to bacterial infections on the biomaterials.

Microbowls with controlled concavity for accurate microscale mass spectrometry

Patterned surfaces can enhance the sensitivity of laser desorption ionization mass spectrometry by segregating and concentrating analytes, but their fabrication can be challenging. Here, we describe a simple method to fabricate substrates patterned with micron-scale wells that yield more accurate and sensitive mass spectrometry measurements compared to flat surfaces. The wells can also concentrate and localize cells and beads for cell-based assays.

Impact of Pre-Patterned Structures on Features of Laser-Induced Periodic Surface Structures

The efficiency of light coupling to surface plasmon polariton (SPP) represents a very important issue in plasmonics and laser fabrication of topographies in various solids. To illustrate the role of pre-patterned surfaces and impact of laser polarisation in the excitation of electromagnetic modes and periodic pattern formation, Nickel surfaces are irradiated with femtosecond laser pulses of polarisation perpendicular or parallel to the orientation of the pre-pattern ridges. Experimental results indicate that for polarisation parallel to the ridges, laser induced periodic surface structures (LIPSS) are formed perpendicularly to the pre-pattern with a frequency that is independent of the distance between the ridges and periodicities close to the wavelength of the excited SPP. By contrast, for polarisation perpendicular to the pre-pattern, the periodicities of the LIPSS are closely correlated to the distance between the ridges for pre-pattern distance larger than the laser wavelength. The experimental observations are interpreted through a multi-scale physical model in which the impact of the interference of the electromagnetic modes is revealed.

Stochastic Adsorption of Diluted Solute Molecules at Interfaces

<div> <p>Here an analytical solution of Fick’s 2^nd law is used to predict the diffusion and the stochastic adsorption of single diluted solute molecules on flat and patterned surfaces. The equations are then compared to the results of several numerical Monte Carlo simulations using a random walk model. The 1D diffusion simulations clarify that the dependence of the solute-surface collision rate on the observation-time (measurement time resolution) is because of the multiple collisions of the same molecules over different time regions. It also surprisingly suggests that due to the self-mimetic fractal function of diffusion, the equation should be corrected by a factor of two. The absorption rate of solute on an adsorptive surface is found to follow a power-law decay function due to an evolving concentration gradient near the surface along with the depletion of the bulk solute molecules on the surface, for example, in a self-assembled monolayer adsorption kinetics. Thus, the analytical equations developed to calculate the collision at a fixed measuring frequency can be extended to map the whole curve over time. In the last section of this work, 3D diffusion simulations suggest that the analytical solution is valid to predict the adsorption rate of the bulk solute to a small group of adsorptive target molecules/area on a bouncing surface, which is a critical process in analyzing the kinetics of many bio-sensing platforms.</p> </div>

Spatial Control of Neuronal Adhesion on Diamond-Like Carbon

This study reports a route to spatial control of neuronal adhesion onto Diamond-Like Carbon (DLC) by surface functionalisation by poly (oligo-ethyleneglycol methacrylate) (pOEGMA) and consequent laser ablation to produce cell adhesive tracks. DLC can be deposited as a tough and low friction coating on implantable devices and surgical instruments and has favourable properties for use as a biomaterial. The pOEGMA surface coating renders the DLC surface antifouling and the laser ablation creates graphitised tracks on the surface. The surfaces were coated with laminin, which adhered preferentially to the ablation tracks. The patterned surfaces were investigated for neuronal cell growth with NG108-15 cells for short term culture and rat neural stem cells for longer term culture. The cells initially adhered highly selectively to the ablation tracks while longer term cell culture revealed a more uniform cell coverage of the surface.

Mechanically Switchable Wetting Petal Effect in Self-Patterned Nanocolumnar Films on Poly(dimethylsiloxane)

Switchable mechanically induced changes in the wetting behavior of surfaces are of paramount importance for advanced microfluidic, self-cleaning and biomedical applications. In this work we show that the well-known polydimethylsiloxane (PDMS) elastomer develops self-patterning when it is coated with nanostructured TiO2 films prepared by physical vapor deposition at glancing angles and subsequently subjected to a mechanical deformation. Thus, unlike the disordered wrinkled surfaces typically created by deformation of the bare elastomer, well-ordered and aligned micro-scaled grooves form on TiO2/PDMS after the first post-deposition bending or stretching event. These regularly patterned surfaces can be reversibly modified by mechanical deformation, thereby inducing a switchable and reversible wetting petal effect and the sliding of liquid droplets. When performed in a dynamic way, this mechanical actuation produces a unique capacity of liquid droplets (water and diiodomethane) transport and tweezing, this latter through their selective capture and release depending on their volume and chemical characteristics. Scanning electron and atomic force microscopy studies of the strained samples showed that a dual-scale roughness, a parallel alignment of patterned grooves and their reversible widening upon deformation, are critical factors controlling this singular sliding behavior and the possibility to tailor their response by the appropriate manufacturing of surface structures.