David T. Gethin

3D Bioprinting of Carboxymethylated-Periodate Oxidized Nanocellulose Constructs for Wound Dressing Applications

Nanocellulose has a variety of advantages, which make the material most suitable for use in biomedical devices such as wound dressings. The material is strong, allows for production of transparent films, provides a moist wound healing environment, and can form elastic gels with bioresponsive characteristics. In this study, we explore the application of nanocellulose as a bioink for modifying film surfaces by a bioprinting process. Two different nanocelluloses were used, prepared with TEMPO mediated oxidation and a combination of carboxymethylation and periodate oxidation. The combination of carboxymethylation and periodate oxidation produced a homogeneous material with short nanofibrils, having widths <20 nm and lengths <200 nm. The small dimensions of the nanofibrils reduced the viscosity of the nanocellulose, thus yielding a material with good rheological properties for use as a bioink. The nanocellulose bioink was thus used for printing 3D porous structures, which is exemplified in this study. We also demonstrated that both nanocelluloses did not support bacterial growth, which is an interesting property of these novel materials.

Design optimisation of aluminium recycling processes using Taguchi technique

Abstract In this paper, a robust design method is developed for reducing cost and improving quality in aluminium recycling. An experimental investigation into the process parameter effects is presented to determine the optimum configuration of design parameters for performance, quality and cost. The Taguchi method is applied initially to plan a minimum number of experiments. Orthogonal array techniques are used to investigate the simultaneous variation of several parameters and the investigation of interactions between parameters. Matrix experiments using standard L4 and L9 orthogonal arrays are employed to evaluate the effects of parameters in recycling of aluminium dross and scrap materials. A statistical analysis of signal-to-noise ratio is followed by performing an analysis of variance (ANOVA), in order to estimate the optimum levels and determine the relative magnitude of the effect of various factors. Finally, a historical data analysis based on the response surface methodology is carried out using a Taguchi orthogonal analysis. Experimental results are shown for an L18 orthogonal array illustrating a good agreement between the optimum factor levels suggested by the signal-to-noise ratios and those obtained from the response surfaces.

Nature's moisture harvesters: a comparative review

Nature has adapted different methods for surviving dry, arid, xeric conditions. It is the focus of this comparative review to pull together the relevant information gleaned from the literature that could be utilized to design moisture harvesting devices informed by biomimetics. Most water harvesting devices in current use are not informed by nature and those that do are usually based on a biomimetic principle that has been based on one species only. This review draws on the published literature to establish a list of species (animals (vertebrates/invertebrates) and plants) whose habitat is in mainly dry or arid regions and that are known to harvest airborne moisture. Key findings have been outlined and review comments and discussion set out. Following this, surface feature convergences have been identified, namely hexagonal microstructures, groove-like and cone-like geometries. This has been coupled with direction of water flow that is driven by surface energy. As far as the authors are aware, this convergent evolution has not been brought together in this manner before. In the future this information could be translated into an engineered device for collecting water from airborne sources.

Three-dimensional unstructured mesh generation: Part 2. Surface meshes

Abstract This paper deals with surface patches and surface meshing. Triangular and quadrilateral patches in linear and quadratic forms, and Non-Uniform Rational B-Spline (NURBS) patch have been used to define surface geometry. From the real application of view, data conversion between the mesh generator and some existing CAD packages has been considered. As a result of this study, converters from a graphics data standard and several CAD data formats have been implemented. The quality improvement of surface meshes has been discussed in terms of parametric plane stretching, diagonal swapping and smoothing procedures. Furthermore, a scheme of visual representation is introduced to utilize colour effect in validating the geometry and its surface meshes.

Numerical comparison of a deformable discrete element model and an equivalent continuum analysis for the compaction of ductile porous material

Abstract The combined finite and discrete element technique has been considered for the compaction of an assembly of particles. Each particle is mapped with finite elements and the interaction between particles is solved using a discrete element technique. Compaction of a few particles in two dimensions using the combined discrete/finite element method is shown to be equivalent to the Gurson model in the continuum analysis. Results generated from both analyses are compared and found to be in good agreement up to 95% densification. The work demonstrates the potential applicability of the deformable discrete element method for particulate analysis or powder compaction in particular.

Three-dimensional unstructured mesh generation: Part 3. Volume meshes

Abstract Volume meshes are generated through three-dimensional triangulation and interior point creation based on the surface meshes. To deal with non-convex geometries, boundary surface conformity is gained via edge swapping, boundary edge and surface recovery, and the robustness of the algorithm has been discussed in terms of the accuracy of geometric judgements. The performane of the mesh generator has been investigated by means of numerical experiments, and examples have been tested to validate the mesh generator. The possibility of extension of this mesh generator to incorporate with analysis programs, in terms of adaptive analysis, has been explored. This paper is also designed to briefly address mesh quality measures, quality statistics and mesh smoothing techniques. Using mesh quality metrics, visual quality assessment has been discussed. Furthermore, several general ways of visual representation of volume meshes have been introduced.

A discrete deformable element approach for the compaction of powder systems

The paper describes the application of a discrete deformable element modelling approach to simulate the compaction of a mixture of ductile and brittle powders together with an exploration of its suitability to establish the yield characteristics of powders. Two-dimensional rod models comprising ductile and brittle particles are assembled and subject to uniaxial compression in a rigid die. The utility of the method to represent the yielding of the powder is also explored by the application of a biaxial loading sequence. The model was found to be capable of modelling the behaviour of powder mixtures successfully. It captured ductile–brittle failure mechanisms in the case of brittle particles and demonstrated the effectiveness of a proportion of ductile particles in preventing the fragmentation of brittle particles in a mixture, illustrating agreement with experimental observation. The exploration of yield surface prediction was subject to a number of assumptions driven by the two-dimensional nature of the simulation, coupled with the high initial density level enforced by the particle packing. Despite these constraints, the results were encouraging when compared with experimental measurement of yield characteristics. Further work is required to establish more realistic initial density and to develop the capability to include a larger number of particles within the simulation.

Three-dimensional unstructured mesh generation: Part 1. Fundamental aspects of triangulation and point creation

Abstract The present paper introduces an alternative approach for Delaunay triangulation, in which the triangulation is mapped from an equivalent convex hull in a higher dimension. Furthermore, some fundamental aspects of a point creation algorithm for unstructured mesh generation have been addressed based on numerical experiments. A point spacing tensor and point insertion criterion have been introduced aiming to deal with anisotropic meshes.

Flexographic printing of graphene nanoplatelet ink to replace platinum as counter electrode catalyst in flexible dye sensitised solar cell

Abstract A semitransparent catalytically active graphene nanoplatelet (GNP) ink was developed suitable for roll to roll printing onto a flexible indium tin oxide substrate at a speed of 0·4 m s−1. Dye sensitised solar cells using this ink as a catalyst demonstrated efficiencies of 2·0%, compared with 2·6% for sputtered platinum. Given further optimisation, GNP inks have the potential to replace chemically reduced or sputtered platinum. This would have the benefit of replacing the chemical reduction or sputtering operations as well as providing potential material cost benefits.

A finite element model of the squeeze casting process

Purpose – To present a numerical model of squeeze casting process.Design/methodology/approach – The modelling consists of two parts, namely, the mould filling and the subsequent thermal stress analysis during and after solidification. Mould filling is described by the Navier‐Stokes equations discretized using the Galerkin finite element method. The free surface is followed using a front tracking procedure. A thermal stress analysis is carried out, assuming that a coupling exists between the thermal problem and the mechanical one. The mechanical problem is described as an elasto‐visco‐plastic formulation in an updated Lagrangian frame. A microstructural solidification model is also incorporated for the mould filling and thermal stress analysis. The thermal problem is solved using enthalpy method.Findings – During the mould‐filling process a quasi‐static arbitrary Lagrangian‐Eulerian (ALE) approach and a microstructural solidification model were found to be applicable. For the case of the thermal stress ana...