ORCID Profile
0000-0001-5093-415X
Current Organisations
Murdoch University
,
Australian National University
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Animal Physiology - Biophysics | Soft Condensed Matter | Condensed Matter Physics | Physiology |
Expanding Knowledge in the Biological Sciences | Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Technology
Publisher: The Optical Society
Date: 06-01-2014
DOI: 10.1364/OE.22.000689
Publisher: MDPI AG
Date: 18-04-2020
DOI: 10.3390/GELS6020013
Abstract: Hydrogels composed of calcium cross-linked alginate are under investigation as bioinks for tissue engineering scaffolds due to their variable viscoelasticity, biocompatibility, and erodibility. Here, pyrrole was oxidatively polymerized in the presence of sodium alginate solutions to form ionomeric composites of various compositions. The IR spectroscopy shows that mild base is required to prevent the oxidant from attacking the alginate during the polymerization reaction. The resulting composites were isolated as dried thin films or cross-linked hydrogels and aerogels. The products were characterized by elemental analysis to determine polypyrrole incorporation, electrical conductivity measurements, and by SEM to determine changes in morphology or large-scale phase separation. Polypyrrole incorporation of up to twice the alginate (monomer versus monomer) provided materials amenable to 3D extrusion printing. The PC12 neuronal cells adhered and proliferated on the composites, demonstrating their biocompatibility and potential for tissue engineering applications.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 10-11-2021
Publisher: The Royal Society
Date: 16-06-2017
Abstract: We investigate the equilibrium properties of a single area-minimizing bubble trapped between two narrowly separated parallel curved plates. We begin with the case of a bubble trapped between concentric spherical plates. We develop a model which shows that the surface energy of the bubble is lower when confined between spherical plates than between flat plates. We confirm our findings by comparing against Surface Evolver simulations. We then derive a simple model for a bubble between arbitrarily curved parallel plates. The energy is found to be higher when the local Gaussian curvature of the plates is negative and lower when the curvature is positive. To check the validity of the model, we consider a bubble trapped between concentric tori. In the toroidal case, we find that the sensitivity of the bubble's energy to the local curvature acts as a geometric potential capable of driving bubbles from regions with negative to positive curvature.
Publisher: Informa UK Limited
Date: 16-09-2013
Publisher: IOP Publishing
Date: 06-2013
Publisher: American Physical Society (APS)
Date: 28-12-2012
Publisher: The Royal Society
Date: 08-08-2012
Publisher: American Association for the Advancement of Science (AAAS)
Date: 07-04-2017
Abstract: High-resolution microscopy of hierarchically organized solid gyroid nanostructures sheds light on the underlying dynamic formation process.
Publisher: Elsevier BV
Date: 12-2017
Publisher: Elsevier BV
Date: 02-2009
Publisher: IOP Publishing
Date: 09-2001
Publisher: Elsevier BV
Date: 03-2015
Publisher: American Physical Society (APS)
Date: 11-03-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4SM01932F
Abstract: The structure of the P 6 3 /mcm phase in gemini surfactants is the tri-continuous 3etc(193) geometry, and this represents a nearly stable morphology also in diblock copolymer melts.
Publisher: American Chemical Society (ACS)
Date: 23-10-2014
DOI: 10.1021/MA5016352
Publisher: Walter de Gruyter GmbH
Date: 12-01-2014
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0FD00108B
Abstract: The field of ‘biological and bio-inspired optics’ has led to a solid understanding of the materials properties of photonic and nanostructured biological materials. Future progress may result from a greater focus on living tissue and biology.
Publisher: The Optical Society
Date: 15-10-2015
DOI: 10.1364/OL.40.004795
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9SM01460H
Abstract: Star copolymers on a sphere self-assemble into patchy particles with structure and coordination corresponding to those found in the famous Thomson problem.
Publisher: IOP Publishing
Date: 29-04-2015
Publisher: American Physical Society (APS)
Date: 06-03-2012
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3BM00012E
Publisher: Wiley
Date: 04-08-2011
Publisher: IOP Publishing
Date: 07-2015
Publisher: Wiley
Date: 26-05-2017
DOI: 10.1002/MP.12280
Abstract: Structure-property relations, which relate the shape of the microstructure to physical properties such as transport or mechanical properties, need sensitive measures of structure. What are suitable fabric tensors to quantify the shape of anisotropic heterogeneous materials? The mean intercept length is among the most commonly used characteristics of anisotropy in porous media, e.g., of trabecular bone in medical physics. Yet, in this series of two papers we demonstrate that it has conceptual shortcomings that limit the validity of its results. We test the validity of general assumptions regarding the properties of the mean-intercept length tensor using analytical formulas for the mean-intercept lengths in anisotropic Boolean models (derived in part I of this series), augmented by numerical simulations. We discuss in detail the functional form of the mean intercept length as a function of the test line orientations. As the most prominent result, we find that, at least for the ex le of overlapping grains modeling porous media, the polar plot of the mean intercept length is in general not an ellipse and hence not represented by a second-rank tensor. This is in stark contrast to the common understanding that for a large collection of grains the mean intercept length figure averages to an ellipse. The standard mean intercept length tensor defined by a least-square fit of an ellipse is based on a model mismatch, which causes an intrinsic lack of accuracy. Our analysis reveals several shortcomings of the mean intercept length tensor analysis that pose conceptual problems and limitations on the information content of this commonly used analysis method. We suggest the Minkowski tensors from integral geometry as alternative sensitive measures of anisotropy. The Minkowski tensors allow for a robust, comprehensive, and systematic approach to quantify various aspects of structural anisotropy. We show the Minkowski tensors to be more sensitive, in the sense, that they can quantify the remnant anisotropy of structures not captured by the mean intercept length analysis. If applied to porous tissue and microstructures, this improved structure characterization can yield new insights into the relationships between geometry and material properties.
Publisher: Wiley
Date: 26-05-2017
DOI: 10.1002/MP.12281
Abstract: Structure-property relations, which relate the shape of the microstructure to physical properties such as transport or mechanical properties, need sensitive measures of structure. What are suitable fabric tensors that quantify the shape of anisotropic heterogeneous materials? The mean intercept length is among the most commonly used characteristics of anisotropy in porous media, for ex le, of trabecular bone in medical physics. We analyze the orientation-biased Boolean model, a versatile stochastic model that represents microstructures as overlapping grains with an orientation bias towards a preferred direction. This model is an extension of the isotropic Boolean model, which has been shown to truthfully reproduce multi-functional properties of isotropic porous media. We explain the close relationship between the concept of intersections with test lines to the elaborate mathematical theory of queues, and how explicit results from the latter can be directly applied to characterize microstructures. In this series of two papers, we provide analytic formulas for the anisotropic Boolean model and demonstrate often overlooked conceptual shortcomings of this approach. Queuing theory is used to derive simple and illustrative formulas for the mean intercept length. It separates into an intensity-dependent and an orientation-dependent factor. The global average of the mean intercept length can be expressed by local characteristics of a single grain alone. We thus identify which shape information about the random process the mean intercept length contains. The connection between global and local quantities helps to interpret observations and provides insights into the possibilities and limitations of the analysis. In the second paper of this series, we discuss, based on the findings in this paper, short-comings of the mean intercept analysis for (bone-)microstructure characterization. We will suggest alternative and better defined sensitive anisotropy measures from integral geometry.
Publisher: Wiley
Date: 05-10-2016
DOI: 10.1002/ADV.21571
Publisher: MDPI AG
Date: 13-01-2022
Abstract: Melt-electrowriting (MEW) is an emerging method that combines electrospinning and extrusion printing, allowing the fabrication of micron-scale structures suitable for tissue engineering. Compared to other additive fabrication methods, melt-electro written structures can offer more appropriate substrates for cell culture due to filament size and mechanical characteristics of the fabricated scaffolds. In this study, polycaprolactone (PCL)/graphene composites were investigated for fabrication of micron-size scaffolds through MEW. It was demonstrated that the addition of graphene can considerably improve the processability of PCL to fabricate micron-scale scaffolds with enhanced resolution. The tensile strength of the scaffold prepared from PCL/graphene composite (with only 0.5 wt.% graphene) was proved significantly (by more than 270%), better than that of the pristine PCL scaffold. Furthermore, graphene was demonstrated to be a suitable material for tailoring the degradation process to avoid undesirable bulk degradation, rapid mass loss and damage to the internal matrix of the polymer. The findings of this study offer a promising route for the fabrication of high-resolution scaffolds with micron-scale resolution for tissue engineering.
Publisher: SPIE
Date: 07-12-2013
DOI: 10.1117/12.2033820
Publisher: Springer Science and Business Media LLC
Date: 09-2007
Publisher: The Optical Society
Date: 06-05-2011
DOI: 10.1364/OE.19.010001
Publisher: Springer Science and Business Media LLC
Date: 18-07-2016
DOI: 10.1038/LSA.2016.192
Publisher: Elsevier BV
Date: 09-2012
Publisher: Springer Science and Business Media LLC
Date: 11-2001
Publisher: IOP Publishing
Date: 25-05-2011
DOI: 10.1088/0953-8984/23/23/234120
Abstract: We investigate the dynamics of a single tracer exploring a course of fixed obstacles in the vicinity of the percolation transition for particles confined to the infinite cluster. The mean-square displacement displays anomalous transport, which extends to infinite times precisely at the critical obstacle density. The slowing down of the diffusion coefficient exhibits power-law behavior for densities close to the critical point and we show that the mean-square displacement fulfills a scaling hypothesis. Furthermore, we calculate the dynamic conductivity as a response to an alternating electric field. Last, we discuss the non-gaussian parameter as an indicator for heterogeneous dynamics.
Publisher: The Optical Society
Date: 14-02-2018
DOI: 10.1364/OL.43.000863
Publisher: Springer Berlin Heidelberg
Date: 2001
Publisher: IOP Publishing
Date: 16-02-2017
Publisher: Springer Berlin Heidelberg
Date: 2001
Publisher: Wiley
Date: 20-06-2019
Abstract: Amphiphilic lipids aggregate in aqueous solution into a variety of structural arrangements. Among the plethora of ordered structures that have been reported, many have also been observed in nature. In addition, due to their unique morphologies, the hydrophilic and hydrophobic domains, very high internal interfacial surface area, and the multitude of possible order-order transitions depending on environmental changes, very promising applications have been developed for these systems in recent years. These include crystallization in inverse bicontinuous cubic phases for membrane protein structure determination, generation of advanced materials, sustained release of bioactive molecules, and control of chemical reactions. The outstanding erse functionalities of lyotropic liquid crystalline phases found in nature and industry are closely related to the topology, including how their nanoscopic domains are organized. This leads to notable ex les of correlation between structure and macroscopic properties, which is itself central to the performance of materials in general. The physical origin of the formation of the known classes of lipidic lyotropic liquid crystalline phases, their structure, and their occurrence in nature are described, and their application in materials science and engineering, biology, medical, and pharmaceutical products, and food science and technology are exemplified.
Publisher: AIP Publishing
Date: 20-07-2020
DOI: 10.1063/5.0007286
Abstract: The role of particle shape in self-assembly processes is a double-edged sword. On the one hand, particle shape and particle elongation are often considered the most fundamental determinants of soft matter structure formation. On the other hand, structure formation is often highly sensitive to details of shape. Here, we address the question of particle shape sensitivity for the self-assembly of hard pear-shaped particles by studying two models for this system: (a) the pear hard Gaussian overlap (PHGO) and (b) the hard pears of revolution (HPR) model. Hard pear-shaped particles, given by the PHGO model, are known to form a bicontinuous gyroid phase spontaneously. However, this model does not replicate an additive object perfectly and, hence, varies slightly in shape from a “true” pear-shape. Therefore, we investigate in the first part of this series the stability of the gyroid phase in pear-shaped particle systems. We show, based on the HPR phase diagram, that the gyroid phase does not form in pears with such a “true” hard pear-shaped potential. Moreover, we acquire first indications from the HPR and PHGO pair-correlation functions that the formation of the gyroid is probably attributed to the small non-additive properties of the PHGO potential.
Publisher: AIP Publishing
Date: 20-07-2020
DOI: 10.1063/5.0007287
Abstract: We consider depletion effects of a pear-shaped colloidal particle in a hard-sphere solvent for two different model realizations of the pear-shaped colloidal particle. The two models are the pear hard Gaussian overlap (PHGO) particles and the hard pears of revolution (HPR). The motivation for this study is to provide a microscopic understanding for the substantially different mesoscopic self-assembly properties of these pear-shaped colloids, in dense suspensions, that have been reported in the previous studies. This is done by determining their differing depletion attractions via Monte Carlo simulations of PHGO and HPR particles in a pool of hard spheres and comparing them with excluded volume calculations of numerically obtained ideal configurations on the microscopic level. While the HPR model behaves as predicted by the analysis of excluded volumes, the PHGO model showcases a preference for splay between neighboring particles, which can be attributed to the special non-additive characteristics of the PHGO contact function. Lastly, we propose a potentially experimentally realizable pear-shaped particle model, the non-additive hard pear of revolution model, which is based on the HPR model but also features non-additive traits similar to those of PHGO particles to mimic their depletion behavior.
Publisher: Elsevier BV
Date: 03-2022
Publisher: American Physical Society (APS)
Date: 11-12-2013
Publisher: Elsevier BV
Date: 2011
Publisher: International Union of Crystallography (IUCr)
Date: 15-02-2007
Publisher: Walter de Gruyter GmbH
Date: 14-01-2015
Publisher: IOP Publishing
Date: 08-10-2018
Publisher: Wiley
Date: 04-2010
DOI: 10.1111/J.1365-2818.2009.03331.X
Abstract: Quantitative measures for anisotropic characteristics of spatial structure are needed when relating the morphology of microstructured heterogeneous materials to tensorial physical properties such as elasticity, permeability and conductance. Tensor-valued Minkowski functionals, defined in the framework of integral geometry, provide a concise set of descriptors of anisotropic morphology. In this article, we describe the robust computation of these measures for microscopy images and polygonal shapes. We demonstrate their relevance for shape description, their versatility and their robustness by applying them to experimental data sets, specifically microscopy data sets of non-equilibrium stationary Turing patterns and the shapes of ice grains from Antarctic cores.
Publisher: Elsevier BV
Date: 2010
Publisher: Wiley
Date: 24-02-2020
Publisher: Elsevier BV
Date: 03-2003
Publisher: EDP Sciences
Date: 2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C2FD20112G
Abstract: Inverse bicontinuous cubic phases with two aqueous network domains separated by a smooth bilayer are firmly established as equilibrium phases in lipid/water systems. The purpose of this article is to highlight the generalisations of these bicontinuous geometries to polycontinuous geometries, which could be realised as lipid mesophases with three or more network-like aqueous domains separated by a branched bilayer. An analysis of structural homogeneity in terms of bilayer width variations reveals that ordered polycontinuous geometries are likely candidates for lipid mesophase structures, with similar chain packing characteristics to the inverse micellar phases (that once were believed not to exist due to high packing frustration). The average molecular shape required by global geometry to form these multi-network phases is quantified by the surfactant shape parameter, v/(al) we find that it adopts values close to those of the known lipid phases. We specifically analyse the 3etc(187 193) structure of hexagonal symmetry P6(3) /mcm with three aqueous domains, the 3dia(24 220) structure of cubic symmetry I43d composed of three distorted diamond networks, the cubic chiral 4srs(24 208) with cubic symmetry P4232 and the achiral 4srs(5 133) structure of symmetry P42/nbc, each consisting of four intergrown undistorted copies of the srs net (the same net as in the QII(G) gyroid phase). Structural homogeneity is analysed by a medial surface approach assuming that the headgroup interfaces are constant mean curvature surfaces. To facilitate future experimental identification, we provide simulated SAXS scattering patterns that, for the 4srs(24 208) and 3dia(24 220) structures, bear remarkable similarity to those of bicontinuous QII(G)-gyroid and QII(D)-diamond phases, with comparable lattice parameters and only a single peak that cannot be indexed to the well-established structures. While polycontinuous lipid phases have, to date, not been reported, the likelihood of their formation is further indicated by the reported observation of a solid tricontinuous mesoporous silicate structure, termed IBN-9, which formed in the presence of surfactants [Han et al., Nat. Chem., 2009, 1, 123].
Publisher: Elsevier BV
Date: 12-2020
Publisher: AIP
Date: 2013
DOI: 10.1063/1.4811946
Publisher: American Physical Society (APS)
Date: 16-04-2015
Publisher: American Physical Society (APS)
Date: 14-04-2015
Publisher: Springer Berlin Heidelberg
Date: 2013
Publisher: AIP Publishing
Date: 22-01-2013
DOI: 10.1063/1.4774084
Abstract: Local structure characterization with the bond-orientational order parameters q4, q6, … introduced by Steinhardt et al. [Phys. Rev. B 28, 784 (1983)10.1103/PhysRevB.28.784] has become a standard tool in condensed matter physics, with applications including glass, jamming, melting or crystallization transitions, and cluster formation. Here, we discuss two fundamental flaws in the definition of these parameters that significantly affect their interpretation for studies of disordered systems, and offer a remedy. First, the definition of the bond-orientational order parameters considers the geometrical arrangement of a set of nearest neighboring (NN) spheres, NN(p), around a given central particle p we show that the choice of neighborhood definition can have a bigger influence on both the numerical values and qualitative trend of ql than a change of the physical parameters, such as packing fraction. Second, the discrete nature of neighborhood implies that NN(p) is not a continuous function of the particle coordinates this discontinuity, inherited by ql, leads to a lack of robustness of the ql as structure metrics. Both issues can be avoided by a morphometric approach leading to the robust Minkowski structure metrics \\documentclass[12pt]{minimal}\\begin{document}$q_l^{\\prime }$\\end{document}ql′. These \\documentclass[12pt]{minimal}\\begin{document}$q_l^{\\prime }$\\end{document}ql′ are of a similar mathematical form as the conventional bond-orientational order parameters and are mathematically equivalent to the recently introduced Minkowski tensors [G. E. Schröder-Turk et al., Europhys. Lett. 90, 34001 (2010)10.1209/0295-5075/90/34001 S. Kapfer et al., Phys. Rev. E 85, 030301–R (2012)10.1103/PhysRevE.85.030301].
Publisher: Frontiers Media SA
Date: 09-05-2019
Publisher: Elsevier BV
Date: 08-2004
Publisher: OSA
Date: 2012
Publisher: Elsevier BV
Date: 12-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9SM01067J
Abstract: In this paper, we analysed the geometrical effects in ellipse assemblies over the range of packing fractions and elongations.
Publisher: Elsevier BV
Date: 05-2012
Publisher: Elsevier BV
Date: 03-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6NR07516A
Publisher: IOP Publishing
Date: 15-04-2019
Publisher: AIP
Date: 2013
DOI: 10.1063/1.4811939
Publisher: Elsevier BV
Date: 12-2016
Publisher: The Royal Society
Date: 16-06-2017
Publisher: Elsevier BV
Date: 02-2010
Publisher: Elsevier BV
Date: 12-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4TB01636J
Abstract: Electrically conductive, mechanically improved graphene/chitosan/lactic acid composites were synthesised and could be easily processed into multi-layer scaffolds using additive fabrication techniques.
Publisher: IOP Publishing
Date: 24-08-0024
Publisher: American Physical Society (APS)
Date: 24-09-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B916340A
Abstract: This paper presents the first examination of the potential for bicontinuous structures such as the gyroid structure to produce high efficiency solar cells based on conjugated polymers. The solar cell characteristics are predicted by a simulation model that shows how the morphology influences device performance through integration of all the processes occurring in organic photocells in a specified morphology. In bicontinuous phases, the surface defining the interface between the electron and hole transporting phases ides the volume into two disjoint subvolumes. Exciton loss is reduced because the interface at which charge separation occurs permeates the device so excitons have only a short distance to reach the interface. As each of the component phases is connected, charges will be able to reach the electrodes more easily. In simulations of the current-voltage characteristics of organic cells with gyroid, disordered blend and vertical rod (rods normal to the electrodes) morphologies, we find that gyroids have a lower than anticipated performance advantage over disordered blends, and that vertical rods are superior. These results are explored thoroughly, with geminate recombination, i.e. recombination of charges originating from the same exciton, identified as the primary source of loss. Thus, if an appropriate materials choice could reduce geminate recombination, gyroids show great promise for future research and applications.
Publisher: American Chemical Society (ACS)
Date: 04-08-2011
DOI: 10.1021/LA201718A
Abstract: We report that a specific realization of Schwarz's triply periodic hexagonal minimal surface is isotropic with respect to the Doi-Ohta interface tensor and simultaneously has minimal packing and stretching frustration similar to those of the commonly found cubic bicontinuous mesophases. This hexagonal surface, of symmetry P6(3)/mmc with a lattice ratio of c/a = 0.832, is therefore a likely candidate geometry for self-assembled lipid/surfactant or copolymer mesophases. Furthermore, both the peak position ratios in its powder diffraction pattern and the elastic moduli closely resemble those of the cubic bicontinuous phases. We therefore argue that a genuine possibility of experimental misidentification exists.
Publisher: Springer International Publishing
Date: 2017
Publisher: Elsevier BV
Date: 10-2011
DOI: 10.1016/J.BIOMATERIALS.2011.06.012
Abstract: Triply-periodic minimal surfaces are shown to be a more versatile source of biomorphic scaffold designs than currently reported in the tissue engineering literature. A scaffold architecture with sheetlike morphology based on minimal surfaces is discussed, with significant structural and mechanical advantages over conventional designs. These sheet solids are porous solids obtained by inflation of cubic minimal surfaces to sheets of finite thickness, as opposed to the conventional network solids where the minimal surface forms the solid/void interface. Using a finite-element approach, the mechanical stiffness of sheet solids is shown to exceed that of conventional network solids for a wide range of volume fractions and material parameters. We further discuss structure-property relationships for mechanical properties useful for custom-designed fabrication by rapid prototyping. Transport properties of the scaffolds are analyzed using Lattice-Boltzmann computations of the fluid permeability. The large number of different minimal surfaces, each of which can be realized as sheet or network solids and at different volume fractions, provides design flexibility essential for the optimization of competing design targets.
Publisher: Springer Science and Business Media LLC
Date: 04-10-2023
Publisher: Elsevier BV
Date: 12-2008
Publisher: American Physical Society (APS)
Date: 04-02-2015
Publisher: American Chemical Society (ACS)
Date: 11-02-2022
Publisher: IOP Publishing
Date: 13-02-2017
Publisher: The Royal Society
Date: 06-06-2012
Abstract: A fundamental understanding of the formation and properties of a complex spatial structure relies on robust quantitative tools to characterize morphology. A systematic approach to the characterization of average properties of anisotropic complex interfacial geometries is provided by integral geometry which furnishes a family of morphological descriptors known as tensorial Minkowski functionals. These functionals are curvature-weighted integrals of tensor products of position vectors and surface normal vectors over the interfacial surface. We here demonstrate their use by application to non-cubic triply periodic minimal surface model geometries, whose Weierstrass parametrizations allow for accurate numerical computation of the Minkowski tensors.
Publisher: MDPI AG
Date: 05-01-2015
DOI: 10.3390/CRYST5010014
Publisher: Elsevier BV
Date: 09-2019
DOI: 10.1016/J.CUB.2019.07.005
Abstract: The wings of butterflies and moths generate some of the most spectacular visual displays observed in nature [1-3]. Particularly striking effects are seen when light interferes with nanostructure materials in the wing scales, generating bright, directional colors that often serve as dynamic visual signals [4]. Structural coloration is not known in night-flying Lepidoptera, yet here we show a highly unusual form of wing coloration in a nocturnal, sexually dimorphic moth, Eudocima materna (Noctuidae). Males feature three dark wing patches on the dorsal forewings, and the apparent size of these patches strongly varies depending on the angle of the wing to the viewer. These optical special effects are generated using specialized wing scales that are tilted on the wing and behave like mirrors. At near-normal incidence of light, these "mirror scales" act as thin-film reflectors to produce a sparkly effect, but when light is incident at ∼20°-30° from normal, the reflectance spectrum is dominated by the diffuse scattering of the underlying, black melanin-containing scales, causing a shape-shifting effect. The strong sexual dimorphism in the arrangement and architecture of the scale nanostructures suggests that these patterns might function for sexual signaling. Flickering of the male's wings would yield a flashing, supernormal visual stimulus [5] to a viewer located 20°-30° away from the vertical, while being invisible to a viewer directly above the animal. Our findings reveal a novel use of structural coloration in nature that yields a dynamic, time-dependent achromatic optical signal that may be optimized for visual signaling in dim light.
Publisher: Wiley
Date: 15-02-2023
Abstract: Surface curvature both emerges from, and influences the behavior of, living objects at length scales ranging from cell membranes to single cells to tissues and organs. The relevance of surface curvature in biology is supported by numerous experimental and theoretical investigations in recent years. In this review, first, a brief introduction to the key ideas of surface curvature in the context of biological systems is given and the challenges that arise when measuring surface curvature are discussed. Giving an overview of the emergence of curvature in biological systems, its significance at different length scales becomes apparent. On the other hand, summarizing current findings also shows that both single cells and entire cell sheets, tissues or organisms respond to curvature by modulating their shape and their migration behavior. Finally, the interplay between the distribution of morphogens or micro‐organisms and the emergence of curvature across length scales is addressed with ex les demonstrating these key mechanistic principles of morphogenesis. Overall, this review highlights that curved interfaces are not merely a passive by‐product of the chemical, biological, and mechanical processes but that curvature acts also as a signal that co‐determines these processes.
Publisher: Springer Science and Business Media LLC
Date: 08-08-2023
Publisher: Springer Science and Business Media LLC
Date: 10-2003
Publisher: Elsevier BV
Date: 05-2011
DOI: 10.1016/J.JSB.2011.01.004
Abstract: The structure of the porous three-dimensional reticulated pattern in the wing scales of the butterfly Callophrys rubi (the Green Hairstreak) is explored in detail, via scanning and transmission electron microscopy. A full 3D tomographic reconstruction of a section of this material reveals that the predominantly chitin material is assembled in the wing scale to form a structure whose geometry bears a remarkable correspondence to the srs net, well-known in solid state chemistry and soft materials science. The porous solid is bounded to an excellent approximation by a parallel surface to the Gyroid, a three-periodic minimal surface with cubic crystallographic symmetry I4₁32, as foreshadowed by Stavenga and Michielson. The scale of the structure is commensurate with the wavelength of visible light, with an edge of the conventional cubic unit cell of the parallel-Gyroid of approximately 310 nm. The genesis of this structure is discussed, and we suggest it affords a remarkable ex le of templating of a chiral material via soft matter, analogous to the formation of mesoporous silica via surfactant assemblies in solution. In the butterfly, the templating is achieved by the lipid-protein membranes within the smooth endoplasmic reticulum (while it remains in the chrysalis), that likely form cubic membranes, folded according to the form of the Gyroid. The subsequent formation of the chiral hard chitin framework is suggested to be driven by the gradual polymerisation of the chitin precursors, whose inherent chiral assembly in solution (during growth) promotes the formation of a single enantiomer.
Publisher: SPIE
Date: 29-04-2017
DOI: 10.1117/12.2270120
Publisher: Wiley
Date: 16-06-2011
Abstract: Predicting physical properties of materials with spatially complex structures is one of the most challenging problems in material science. One key to a better understanding of such materials is the geometric characterization of their spatial structure. Minkowski tensors are tensorial shape indices that allow quantitative characterization of the anisotropy of complex materials and are particularly well suited for developing structure‐property relationships for tensor‐valued or orientation‐dependent physical properties. They are fundamental shape indices, in some sense being the simplest generalization of the concepts of volume, surface and integral curvatures to tensor‐valued quantities. Minkowski tensors are based on a solid mathematical foundation provided by integral and stochastic geometry, and are endowed with strong robustness and completeness theorems. The versatile definition of Minkowski tensors applies widely to different types of morphologies, including ordered and disordered structures. Fast linear‐time algorithms are available for their computation. This article provides a practical overview of the different uses of Minkowski tensors to extract quantitative physically‐relevant spatial structure information from experimental and simulated data, both in 2D and 3D. Applications are presented that quantify (a) alignment of co‐polymer films by an electric field imaged by surface force microscopy (b) local cell anisotropy of spherical bead pack models for granular matter and of closed‐cell liquid foam models (c) surface orientation in open‐cell solid foams studied by X‐ray tomography and (d) defect densities and locations in molecular dynamics simulations of crystalline copper.
Publisher: Wiley
Date: 21-09-2012
Abstract: Tuning mechanical properties of and fluid flow through open‐cell solid structures is a challenge for material science, in particular for the design of porous structures used as artificial bone scaffolds in tissue engineering. We present a method to tune the effective elastic properties of custom‐designed open‐cell solid foams and bone scaffold geometries by almost an order of magnitude while approximately preserving the pore space geometry and hence fluid transport properties. This strong response is achieved by a change of topology and node coordination of a network‐like geometry underlying the scaffold design. Each node of a four‐coordinated network is disconnected with probability p into two two‐coordinated nodes, yielding network geometries that change continuously from foam‐ or network‐like cellular structures to entangled fiber bundles. We demonstrate that increasing p leads to a strong, approximately exponential decay of mechanical stiffness while leaving the pore space geometry largely unchanged. This result is obtained by both voxel‐based finite element methods and compression experiments on laser sintered models. The physical effects of randomizing network topology suggest a new design paradigm for solid foams, with adjustable mechanical properties.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5SM03114A
Abstract: Granular heaps of particles created by deposition of mono-disperse particles raining from an extended source of finite size are characterized by a non-homogeneous field of density. It was speculated that this inhomogeneity is due to the transient shape of the sediment during the process of construction of the heap, thus reflecting the history of the creation of the heap. By comparison of structural characteristics of the heap with sediments created on top of inclined planes exploiting the method of Minkowski tensors, we provide further evidence to support this hypothesis. Moreover, for the case of sediments generated by homogeneous rain on surfaces, we provide relationships between the inclination of the surface and the Minkowski measures characterizing the isotropy of local particle environments.
Publisher: AIP Publishing
Date: 23-03-2018
DOI: 10.1063/1.5023011
Abstract: We develop a density functional for hard particles with a smooth uniaxial shape (including non-inversion-symmetric particles) within the framework of fundamental measure theory. By applying it to a system of tapered, aspherical liquid-crystal formers, reminiscent of pears, we analyse their behaviour near a hard substrate. The theory predicts a complex orientational ordering close to the substrate, which can be directly related to the particle shape, in good agreement with our simulation results. Furthermore, the lack of particle inversion-symmetry implies the possibility of alternating orientations in subsequent layers as found in a smectic/lamellar phase of such particles. Both theory and Monte Carlo simulations confirm that such ordering occurs in our system. Our results are relevant for adsorption processes of asymmetric colloidal particles and molecules at hard interfaces and show once again that tapering strongly affects the properties of orientationally ordered phases.
Publisher: Public Library of Science (PLoS)
Date: 11-06-2014
Publisher: Elsevier BV
Date: 08-2012
Publisher: Springer Science and Business Media LLC
Date: 09-2013
Publisher: Cold Spring Harbor Laboratory
Date: 29-04-2021
DOI: 10.1101/2021.04.28.441812
Abstract: Bicontinuous membranes in cell organelles epitomise nature’s ability to create complex functional nanostructures. Like their synthetic counterparts, these membranes are characterised by continuous membrane sheets draped onto topologically complex saddle-shaped surfaces with a periodic network-like structure. In cell organelles, their structure sizes around 50–500 nm and fluid nature make Transmission Electron Microscopy (TEM) the analysis method of choice to decipher nanostructural features. Here we present a tool to identify bicontinuous structures from TEM sections by comparison to mathematical “nodal surface” models, including the hexagonal lonsdaleite geometry. Our approach, following pioneering work by Deng and Mieczkowski (1998), creates synthetic TEM images of known bicontinuous geometries for interactive structure identification. We apply the method to the inner membrane network in plant cell chloroplast precursors and achieve a robust identification of the bicontinuous diamond surface as the dominant geometry in several plant species. This represents an important step in understanding their as yet elusive structure-function relationship.
Publisher: IOP Publishing
Date: 23-03-2016
Publisher: American Physical Society (APS)
Date: 12-02-2016
Publisher: The Optical Society
Date: 24-02-2017
DOI: 10.1364/OE.25.005001
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D2SM00922F
Abstract: In a tomographic study of a bidisperse mixture of ellipsoidal placebo pills, a simple mixture distribution is found to reproduce the local packing fraction distributions.
Publisher: IOP Publishing
Date: 02-11-2010
Publisher: The Royal Society
Date: 16-06-2017
Abstract: We investigate a model of hard pear-shaped particles which forms the bicontinuous Ia d structure by entropic self-assembly, extending the previous observations of Barmes et al. (2003 Phys. Rev. E 68 , 021708. ( doi:10.1103/PhysRevE.68.021708 )) and Ellison et al. (2006 Phys. Rev. Lett. 97 , 237801. ( doi:10.1103/PhysRevLett.97.237801 )). We specifically provide the complete phase diagram of this system, with global density and particle shape as the two variable parameters, incorporating the gyroid phase as well as disordered isotropic, smectic and nematic phases. The phase diagram is obtained by two methods, one being a compression–decompression study and the other being a continuous change of the particle shape parameter at constant density. Additionally, we probe the mechanism by which interdigitating sheets of pears in these systems create surfaces with negative Gauss curvature, which is needed to form the gyroid minimal surface. This is achieved by the use of Voronoi tessellation, whereby both the shape and volume of Voronoi cells can be assessed in regard to the local Gauss curvature of the gyroid minimal surface. Through this, we show that the mechanisms prevalent in this entropy-driven system differ from those found in systems which form gyroid structures in nature (lipid bilayers) and from synthesized materials (di-block copolymers) and where the formation of the gyroid is enthalpically driven. We further argue that the gyroid phase formed in these systems is a realization of a modulated splay-bend phase in which the conventional nematic has been predicted to be destabilized at the mesoscale due to molecular-scale coupling of polar and orientational degrees of freedom.
Publisher: EDP Sciences
Date: 2017
Publisher: Elsevier BV
Date: 2010
Publisher: Elsevier BV
Date: 2014
Publisher: IOP Publishing
Date: 05-2010
Publisher: The Royal Society
Date: 08-01-2013
Abstract: We systematically analyse the mechanical deformation behaviour, in particular Poisson's ratio, of floppy bar-and-joint frameworks based on periodic tessellations of the plane. For frameworks with more than one deformation mode, crystallographic symmetry constraints or minimization of an angular vertex energy functional are used to lift this ambiguity. Our analysis allows for systematic searches for auxetic mechanisms in archives of tessellations applied to the class of one- or two-uniform tessellations by regular or star polygons, we find two auxetic structures of hexagonal symmetry and demonstrate that several other tessellations become auxetic when retaining symmetries during the deformation, in some cases with large negative Poisson ratios ν −1 for a specific lattice direction. We often find a transition to negative Poisson ratios at finite deformations for several tessellations, even if the undeformed tessellation is infinitesimally non-auxetic. Our numerical scheme is based on a solution of the quadratic equations enforcing constant edge lengths by a Newton method, with periodicity enforced by boundary conditions.
Publisher: American Physical Society (APS)
Date: 06-2012
Publisher: Proceedings of the National Academy of Sciences
Date: 05-10-2015
Abstract: Arthropod biophotonic nanostructures provide a plethora of complex geometries. Although the variety of geometric forms observed reflects those found in hiphilic self-assembly, the biological formation principles are more complex. This paper addresses the chiral single gyroid in the Green Hairstreak butterfly Callophrys rubi , robustly showing that the formation process produces both the left- and right-handed enantiomers but with distinctly different likelihood. An interpretation excludes the molecular chirality of chitin as the determining feature of the enantiomeric type, emphasizing the need to identify other chirality-specific factors within the membrane-based biological formation model. These findings contribute to an understanding of nature’s ability to control secondary features of the structure formation, such as enantiomeric type and crystallographic texture, informing bioinspired self-assembly strategies.
Publisher: Springer Science and Business Media LLC
Date: 12-2006
Publisher: Springer Science and Business Media LLC
Date: 02-2019
DOI: 10.1557/MRS.2019.21
Publisher: AIP Publishing
Date: 21-12-2020
DOI: 10.1063/5.0029301
Abstract: The quantizer problem is a tessellation optimization problem where point configurations are identified such that the Voronoi cells minimize the second moment of the volume distribution. While the ground state (optimal state) in 3D is almost certainly the body-centered cubic lattice, disordered and effectively hyperuniform states with energies very close to the ground state exist that result as stable states in an evolution through the geometric Lloyd’s algorithm [M. A. Klatt et al. Nat. Commun. 10, 811 (2019)]. When considered as a statistical mechanics problem at finite temperature, the same system has been termed the “Voronoi liquid” by Ruscher, Baschnagel, and Farago [Europhys. Lett. 112, 66003 (2015)]. Here, we investigate the cooling behavior of the Voronoi liquid with a particular view to the stability of the effectively hyperuniform disordered state. As a confirmation of the results by Ruscher et al., we observe, by both molecular dynamics and Monte Carlo simulations, that upon slow quasi-static equilibrium cooling, the Voronoi liquid crystallizes from a disordered configuration into the body-centered cubic configuration. By contrast, upon sufficiently fast non-equilibrium cooling (and not just in the limit of a maximally fast quench), the Voronoi liquid adopts similar states as the effectively hyperuniform inherent structures identified by Klatt et al. and prevents the ordering transition into a body-centered cubic ordered structure. This result is in line with the geometric intuition that the geometric Lloyd’s algorithm corresponds to a type of fast quench.
Publisher: Springer Science and Business Media LLC
Date: 18-02-2019
DOI: 10.1038/S41467-019-08360-5
Abstract: Partitioning space into cells with certain extreme geometrical properties is a central problem in many fields of science and technology. Here we investigate the Quantizer problem, defined as the optimisation of the moment of inertia of Voronoi cells, i.e., similarly-sized ‘sphere-like’ polyhedra that tile space are preferred. We employ Lloyd’s centroidal Voronoi diagram algorithm to solve this problem and find that it converges to disordered states associated with deep local minima. These states are universal in the sense that their structure factors are characterised by a complete independence of a wide class of initial conditions they evolved from. They moreover exhibit an anomalous suppression of long-wavelength density fluctuations and quickly become effectively hyperuniform. Our findings warrant the search for novel amorphous hyperuniform phases and cellular materials with unique physical properties.
Publisher: Elsevier BV
Date: 03-2007
Publisher: American Physical Society (APS)
Date: 30-10-2015
Publisher: The Royal Society
Date: 16-06-2017
Abstract: Biological membranes do not only occur as planar bilayer structures, but depending on the lipid composition, can also curve into intriguing three-dimensional structures. In order to fully understand the biological implications as well as to reveal the full potential for applications, e.g. for drug delivery and other biomedical devices, of such structures, well-defined model systems are required. Here, we discuss the formation of lipid non-lamellar liquid crystalline (LC) surface layers spin-coated from the constituting lipids followed by hydration of the lipid layer. We demonstrate that hybrid lipid polymer films can be formed with different properties compared with the neat lipid LC layers. The nanostructure and morphologies of the lipid films formed reflect those in the bulk. Most notably, mixed lipid layers, which are composed of glycerol monooleate and diglycerol monooleate with poly( N -isopropylacrylamide) nanogels, can form films of reverse cubic phases that are capable of responding to temperature stimulus. Owing to the presence of the nanogel particles, changing the temperature not only regulates the hydration of the cubic phase lipid films, but also the lateral organization of the lipid domains within the lipid self-assembled film. This opens up the possibility for new nanostructured materials based on lipid–polymer responsive layers.
Publisher: Wiley
Date: 21-04-2011
Abstract: It appears that most models for micro‐structured materials with auxetic deformations were found by clever intuition, possibly combined with optimization tools, rather than by systematic searches of existing structure archives. Here we review our recent approach of finding micro‐structured materials with auxetic mechanisms within the vast repositories of planar tessellations. This approach has produced two previously unknown auxetic mechanisms, which have Poisson's ratio ν ss = ‐1 when realized as a skeletal structure of stiff incompressible struts pivoting freely at common vertices. One of these, baptized Triangle‐Square Wheels , has been produced as a linear‐elastic cellular structure from Ti‐6Al‐4V alloy by selective electron beam melting. Its linear‐elastic properties were measured by tensile experiments and yield an effective Poisson's ratio ν LE ≈ ‐0.75, also in agreement with finite element modeling. The similarity between the Poisson's ratios ν SS of the skeletal structure and ν LE of the linear‐elastic cellular structure emphasizes the fundamental role of geometry for deformation behavior, regardless of the mechanical details of the system. The approach of exploiting structure archives as candidate geometries for auxetic materials also applies to spatial networks and tessellations and can aid the quest for inherently three‐dimensional auxetic mechanisms.
Publisher: Wiley
Date: 16-06-2011
Abstract: The effective linear‐elastic moduli of disordered network solids are analyzed by voxel‐based finite element calculations. We analyze network solids given by Poisson‐Voronoi processes and by the structure of collagen fiber networks imaged by confocal microscopy. The solid volume fraction ϕ is varied by adjusting the fiber radius, while keeping the structural mesh or pore size of the underlying network fixed. For intermediate ϕ , the bulk and shear modulus are approximated by empirical power‐laws $ K(\\phi) \\propto \\phi^n$ and $ G(\\phi) \\propto \\phi^m$ with n ≈ 1.4 and m ≈ 1.7. The exponents for the collagen and the Poisson‐Voronoi network solids are similar, and are close to the values n = 1.22 and m = 2.11 found in a previous voxel‐based finite element study of Poisson‐Voronoi systems with different boundary conditions. However, the exponents of these empirical power‐laws are at odds with the analytic values of n = 1 and m = 2, valid for low‐density cellular structures in the limit of thin beams. We propose a functional form for K ( ϕ ) that models the cross‐over from a power‐law at low densities to a porous solid at high densities a fit of the data to this functional form yields the asymptotic exponent n ≈ 1.00, as expected. Further, both the intensity of the Poisson‐Voronoi process and the collagen concentration in the s les, both of which alter the typical pore or mesh size, affect the effective moduli only by the resulting change of the solid volume fraction. These findings suggest that a network solid with the structure of the collagen networks can be modeled in quantitative agreement by a Poisson‐Voronoi process.
Publisher: Emerald
Date: 07-12-2015
DOI: 10.1108/ETPC-07-2015-0055
Abstract: – The purpose of this paper is to consider the growing interest in oracy and to propose the pedagogy of process drama as an ideal model for the dialogic classroom. – This paper takes the form of an explanatory case study where the author draws on a successful drama/oracy project in a primary school in Brisbane, Australia, to illustrate the connections between Alexander’s five indicators of a dialogic classroom and the process drama in which the students participated. – The application of this process drama as pedagogy for the teaching and learning of oracy has contributed positively to students’ oral communication skills and intercultural awareness. In addition, parents provide positive feedback about student engagement in school and developing self-confidence because “they have something to say”. – There was no formal pre-post test for the oral communication skills on this study, instead the researchers developed a draft “oracy” checklist which deserves further interrogation and development. – There are implications for the use of process drama as a means of creating and sustaining the dialogic classroom. Teacher professional development would be required to assist the planning and delivery of dramas that allow for the deep and complex learning evidenced in this study. – This is an ideal vehicle for assisting in the development of empathy, collaboration, emotional intelligence and intercultural understanding. – This is an ex le of an extremely high-quality curriculum plan and implementation. The importance of engaging in implicit and explicit instruction of oral communication for the twenty-first century should not be underestimated. The process drama allows oral language to be foregrounded, with additional learning opportunities from a range of other learning areas, brought together in a coherent and complex model of practice.
Start Date: 2018
End Date: 12-2021
Amount: $392,664.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2021
End Date: 12-2024
Amount: $369,000.00
Funder: Australian Research Council
View Funded Activity