Superductile,Wavy Silica Nanostructures Inspired by Diatom Algae

Biology implements intriguing structural design principles that allow for attractive mechanical properties—such as high strength, toughness, and extensibility despite being made of weak and brittle constituents, as observed in biomineralized structures. For example, diatom algae contain nanoporous hierarchical silicified shells, called frustules, which provide mechanical protection from predators and virus penetration. These frustules generally have a morphology resembling honeycombs within honeycombs, meshes, or wavy shapes, and are surprisingly tough when compared to bulk silica, which is one of the most brittle materials known. However, the reason for its extreme extensibility has not been explained from a molecular level upwards. By carrying out a series of molecular dynamics simulations with the first principles‐based reactive force field ReaxFF, the mechanical response of the structures is elucidated and correlated with underlying deformation mechanisms. Specifically, it is shown that for wavy silica, unfolding mechanisms are achieved for increasing amplitude and allow for greater ductility of up to 270% strain. This mechanism is reminiscent to the uncoiling of hidden length from proteins that allows for enhanced energy dissipation capacity and, as a result, toughness. We report the development of an analytical continuum model that captures the results from atomistic simulations and can be used in multiscale models to bridge to larger scales. Our results demonstrate that tuning the geometric parameters of amplitude and width in wavy silica nanostructures are beneficial in improving the mechanical properties, including enhanced deformability, effectively overcoming the intrinsic shortcomings of the base material that features extreme brittleness.     

Upper Body Detection and Tracking in Extended Signing Sequences

The goal of this work is to detect and track the articulated pose of a human in signing videos of more than one hour in length. In particular we wish to accurately localise hands and arms, despite fast motion and a cluttered and changing background.     

Maximizing Transfection Efficiency of Vertically Aligned Silicon Nanowire Arrays

Vertically aligned silicon nanowire (VA‐SiNW) arrays are emerging as a powerful new tool for gene delivery by means of mechanical transfection. In order to utilize this tool efficiently, uncertainties around the required design parameters need to be removed. Here, a combination of nanosphere lithography and templated metal‐assisted wet chemical etching is used to fabricate VA‐SiNW arrays with a range of diameters, heights, and densities. This fabrication strategy allows identification of critical parameters of surface topography and consequently the design of SiNW arrays that deliver plasmid with high transfection efficiency into a diverse range of human cells whilst maintaining high cell viability. These results illuminate the cell‐materials interactions that mediate VA‐SiNW transfection and have the potential to transform gene therapy and underpin future treatment modalities.     

Shaky foundations of hierarchical biological materials

It is popular stance that successful growth – be it structural, economic or biological – requires a stable foundation. The hierarchical structure of native biological materials and tissues introduces variations in form and function across a multitude of scales. Yet, many synthetic scaffolds and substrates in which such materials are assembled, the foundation, are designed at a single scale. The result is an uncertain or shaky foundation for material assembly and tissue growth, where changes in the scaffold properties and architecture result in unpredictable behaviors in tissue development, and proven, reliable scaffolds for one tissue type may be completely unsuitable for another. This is in contrast to the behavior of foundations for civil engineering structures, which provide a decoupling of the foundation from the building design since different foundations can support equivalent functional structures. Current advancements in the design of biologically active foundations shed light on proven scaffolds and substrates, but cannot be used to design and predict success from the bottom-up. This is because while the phenomenological coupling between materials and substrates has been well investigated and has yielded methodologies for biomaterial synthesis, the underlying mechanisms of self-assembly and growth are not fully understood. A potential solution lies in the utilization of hierarchical material foundations, with molecular, fibrillar and other interactions designed across all length- and time-scales with engineered, predictive, and repeatable outcomes. The potential to realize such hierarchical multiscale scaffolds can be found in the exploitation of responsive, or mutable, polymer systems that exhibit precise control and variegated chemical functionalities for applications in diverse areas such as regenerative medicine, cancer treatment or drug delivery.     

Vaults engineered for hydrophobic drug delivery

The vault nanoparticle is one of the largest known ribonucleoprotein complexes in the sub-100 nm range. Highly conserved and almost ubiquitously expressed in eukaryotes, vaults form a large nanocapsule with a barrel-shaped morphology surrounding a large hollow interior. These properties make vaults an ideal candidate for development into a drug delivery vehicle. In this study, the first example of using vaults towards this goal is reported. Recombinant vaults are engineered to encapsulate the highly insoluble and toxic hydrophobic compound all-trans retinoic acid (ATRA) using a vault-binding lipoprotein complex that forms a lipid bilayer nanodisk. These recombinant vaults offer protection to the encapsulated ATRA from external elements. Furthermore, a cryo-electron tomography (cryo-ET) reconstruction shows the vault-binding lipoprotein complex sequestered within the vault lumen. Finally, these ATRA-loaded vaults show enhanced cytotoxicity against the hepatocellular carcinoma cell line HepG2. The ability to package therapeutic compounds into the vault is an important achievement toward their development into a viable and versatile platform for drug delivery.     

A study of the gold acceptor in a silicon p+n junction and an n-type MOS capacitor by thermally stimulated current and capacitance measurements

The thermally stimulated current and capacitance responses of a gold doped p⁺n junction and n-type MOS capacitor were measured experimentally and modeled theoretically for the case of majority-carrier defect charging. The gold acceptor atoms are initially charged with electrons at low temperatures, and during the heating cycle, excess electrons are released from the gold atoms. The thermally stimulated current response for this phase is similar in both structures and has a distinctive peak-and-valley shape and an emission temperature about 220 K. During the steady-state phase, a current peak occurs in the MOS capacitance response. A physical model was developed and the influence of various parameters on the current and capacitance measurements was quantified. Various analytical schemes are described which allow rapid identification of the gold defect center and rapid computation of its density. A simple and inexpensive apparatus is described which is capable of heating rates as high as 10 K/s.     

Spectrally resolved fluorescence correlation spectroscopy based on global analysis

Multicolor fluorescence correlation spectroscopy has been recently developed to study chemical interactions of multiple chemical species labeled with spectrally distinct fluorophores. In the presence of spectral overlap, there exists a lower detectability limit for reaction products with multicolor fluorophores. In addition, the ability to separate bound product from reactants allows thermodynamic properties such as dissociation constants to be measured for chemical reactions. In this report, we utilize a spectrally resolved two-photon microscope with single-photon counting sensitivity to acquire spectral and temporal information from multiple chemical species. Further, we have developed a global fitting analysis algorithm that simultaneously analyzes all distinct auto- and cross-correlation functions from 15 independent spectral channels. We have demonstrated that the global analysis approach allows the concentration and diffusion coefficients of fluorescent particles to be resolved despite the presence of overlapping emission spectra.     

Geometric confinement governs the rupture strength of H-bond assemblies at a critical length scale

The ultrastructure of protein materials such as spider silk, muscle tissue, or amyloid fibers consists primarily of beta-sheets structures, composed of hierarchical assemblies of H-bonds. Despite the weakness of H-bond interactions, which have intermolecular bonds 100 to 1000 times weaker than those in ceramics or metals, these materials combine exceptional strength, robustness, and resilience. We discover that the rupture strength of H-bond assemblies is governed by geometric confinement effects, suggesting that clusters of at most 3-4 H-bonds break concurrently, even under uniform shear loading of a much larger number of H-bonds. This universally valid result leads to an intrinsic strength limitation that suggests that shorter strands with less H-bonds achieve the highest shear strength at a critical length scale. The hypothesis is confirmed by direct large-scale full-atomistic MD simulation studies of beta-sheet structures in explicit solvent. Our finding explains how the intrinsic strength limitation of H-bonds can be overcome by the formation of a nanocomposite structure of H-bond clusters, thereby enabling the formation of larger and much stronger beta-sheet structures. Our results explain recent experimental proteomics data, suggesting a correlation between the shear strength and the prevalence of beta-strand lengths in biology.