David C. Green

Interfacial Assembly of Protein-polymer Nano-conjugates into Stimulus-Responsive Biomimetic Protocells

The mechanism of spontaneous assembly of microscale compartments is a central question for the origin of life, and has technological repercussions in diverse areas such as materials science, catalysis, biotechnology and biomedicine. Such compartments need to be semi-permeable, structurally robust and capable of housing assemblages of functional components for internalized chemical transformations. In principle, proteins should be ideal building blocks for the construction of membrane-bound compartments but protein vesicles with cell-like properties are extremely rare. Here we present an approach to the interfacial assembly of protein-based micro-compartments (proteinosomes) that are delineated by a semi-permeable, stimulus-responsive, enzymatically active, elastic membrane consisting of a closely packed monolayer of conjugated protein-polymer building blocks. The proteinosomes can be dispersed in oil or water, thermally cycled to temperatures of 70u2009°C, and partially dried and re-inflated without loss of structural integrity. As a consequence, they exhibit protocellular properties such as guest molecule encapsulation, selective permeability, gene-directed protein synthesis and membrane-gated internalized enzyme catalysis.

In vitro gene expression and enzyme catalysis in bio-inorganic protocells

Silica n nanoparticles with a balance of hydrophilic and hydrophobic surface properties exhibit surfactant-like behaviour, and as a consequence can strongly adsorb at oil/water interfaces to stabilize the formation of water micro-droplets. Here we exploit this strategy to construct a model of a primitive bio-inorganic protocell, which unlike conventional paradigms based on self-assembled vesicles, is structurally delineated by a porous inorganic membrane rather than a lipid-based bilayer. As proof-of-principle we show that the nanoparticle-stabilized droplets (colloidosomes) can support a range of functionally active biomolecules and bio-machinery related to metabolic and informational processing. Specifically, we demonstrate that the rate of cell-free in vitrogene expression of enhanced green fluorescent protein (eGFP) is essentially the same within the colloidosome interior as in bulk aqueous solution. In addition, we report considerable enhancements in the specific activity of enzymes such as lipoprotein lipase, chymotrypsin or alkaline phosphatase when entrapped within the nanoparticle-stabilized water droplets. Our results suggest that artificial protocells based on the construction of biological/inorganic nanoscale components could have considerable potential in areas such as synthetic biology and bionanotechnology. In a wider perspective, studies on bio-inorganic protocells could provide alternative models for evaluating potential prebiotic pathways prior to the emergence of lipid-based compartmentalization on the early Earth.

A New General Synthetic Strategy for Phase‐Pure Complex Functional Materials

The ability of ionic liquids to solvate inorganic salts completely has to date never been employed in the synthesis of complex inorganic materials. Here, we demonstrate that complex functional oxides, even those traditionally considered extremely difficult to synthesize in bulk, such as quinternary superconductors, are produced with no impurity phases and on timescales that are much shorter than other synthetic techniques.

Tensile failure due to interaction between fibre breaks

A new explanation for tensile strength of unidirectional composites is proposed based on the linking of fibre breaks in adjacent fibres if they are within a critical axial distance. No stress concentrations are included in the model. The probability of obtaining a given number of fibre breaks sufficiently close to interact is estimated by scanning an array of fibres for clusters of broken fibres. Using a simple energy balance approach it is shown that a bundle of failed fibres of a certain critical size can pull out from the rest of the composite by shear failure around the edge of the bundle, and this can be expected to lead to catastrophic fracture. Tensile strengths are obtained which are comparable with experimental data for unidirectional carbon fibre/epoxy, suggesting that it may be the interaction of fibre breaks rather than the stress concentrations associated with the breaks which is critical in determining composite tensile strength.

Discussing Ethical Issues in School Science: An investigation into the opportunities to practise and develop arguments offered by online and face‐to‐face discussions

Recent changes in UK science curricula mean that it is now expected that pupils are taught about socio‐scientific applications and implications of science; however, finding time to incorporate associated discussions and to set up forums for debate is challenging for teachers. This paper reports on a project to investigate different approaches to engaging students in argument and discussion including online debate outside lesson time. The project involved incorporating different types of discussion into sixth form (students aged 16–17) biology lessons. An opportunity sample of six experienced teachers and their classes (totalling 84 students) was recruited. In all, five online discussions between schools, one online within school discussion and four face‐to‐face discussions were analysed for their quality of argument. Results indicate that, within this sample, the dialogue in online discussions demonstrated higher levels of argumentation than those in face‐to‐face discussions. Students in the face‐to‐face discussions volunteered less evidence to support their arguments and were less likely to challenge each other’s points. Students reported they learned slightly more from online discussion than from face‐to‐face discussion; this was confirmed by their teachers. Whilst this study is clearly limited by size and the unanticipated events within school that limited the amount of data collected, it was concluded that online discussion is worth further investigation by education practitioners. It offers opportunities to bring students together across time and space to practise justifying and defending their point of view.

Quantitative microstructural analysis of a continuous fibre composite

Abstract A micrograph of a carbon fibre-reinforced PEEK prepreg has been analysed to determine the fibre distribution and the results compared with the probability density of the theoretical distribution obtained using a spatial statistical model. The close agreement indicates that the model may be used with confidence for the predictive modelling of high performance continuous fibre composites of around 50% volume fraction.

3D visualization of additive occlusion and tunable full-spectrum fluorescence in calcite

From biomineralization to synthesis, organic additives provide an effective means of controlling crystallization processes. There is growing evidence that these additives are often occluded within the crystal lattice. This promises an elegant means of creating nanocomposites and tuning physical properties. Here we use the incorporation of sulfonated fluorescent dyes to gain new understanding of additive occlusion in calcite (CaCO3), and to link morphological changes to occlusion mechanisms. We demonstrate that these additives are incorporated within specific zones, as defined by the growth conditions, and show how occlusion can govern changes in crystal shape. Fluorescence spectroscopy and lifetime imaging microscopy also show that the dyes experience unique local environments within different zones. Our strategy is then extended to simultaneously incorporate mixtures of dyes, whose fluorescence cascade creates calcite nanoparticles that fluoresce white. This offers a simple strategy for generating biocompatible and stable fluorescent nanoparticles whose output can be tuned as required.

Designed 3D architectures of high-temperature superconductors

Self-supporting superconducting replicas of pasta shapes are reported, yielding products of differing 3D architectures. Functioning high-temperature superconductor wires are developed and refined from replicas of spaghetti, demonstrating a unique sol-gel processing technique for the design and synthesis of novel macroscopic morphologies of complex functional materials.