Animal, vegetable or mineral? A continuum of form
Professor Stephen Hyde, Australian National University, Australia
The morphologies of biological materials — from body shapes to membranes within cells -- are typically curvaceous and flexible, in contrast to the angular, facetted shapes of inorganic matter. An alternative dichotomy has it that biomolecules typically assemble into aperiodic structures in vivo, in contrast to inorganic crystals. This lecture will explore the evolution of our understanding of structures across the spectrum of materials, from living to inanimate, driven by those naive beliefs. The idea that there is a clear distinction between these two classes of matter has waxed and waned in popularity through past centuries. Our current understanding, driven largely by detailed exploration of biomolecular structures at the sub-cellular level and more recent explorations of sterile soft matter, makes it clear that this is a false dichotomy. Liquid crystals and other soft materials are common to both living and inanimate materials. The older picture of disjoint universes of forms is better understood as a continuum of forms, with significant overlap and common features unifying biological and inorganic matter. In addition to the philosophical relevance of this perspective, there are important ramifications for science. For example, the debates surrounding extra-terrestrial life, the oldest terrestrial fossils and consequent dating of the emergence of life on earth rests to some degree on prejudices inferred from the supposed dichotomy between life-forms and the rest.
Living crystals: the enigmatic functions of biological cubic membranes
Professor Yuru Deng, Institute of Biomedical Engineering and Health Sciences, Changzhou University, China
Biological cubic membranes (CM) represent an ordered 3-dimensional fold of typically 2-dimensionally extended flat lipid bilayer structures that occur in all living systems and that function to partition intracellular compartments. CM follow mathematically well-defined geometries but are, nevertheless, highly dynamic structures that respond to environmental cues. While the specific functions of CM are still a matter of discussion, an increasing body of evidence suggests a vital and protective role for CM in stressed or diseased cells. The perhaps best-characterized CM transition has been observed in the mitochondrial inner membranes of free-living giant amoeba (Chaos carolinense). In this ancient organism, cells are able to survive under rather extreme conditions such as lack of food, fluctuations of ambient temperature or osmolarity, or oxidative stress. Upon food depletion, mitochondrial inner membranes in this organism undergo rapid and reversible changes in 3D organization, providing a valuable model to study sub-cellular organelle adaptations. In mammalian cells, CM are frequently observed in conjunction with viral infections, leading to the proposition that they may represent a platform for virus particle assembly, perhaps triggered by reprogramming of host lipid (cholesterol) metabolism. Last but not least, I will discuss a potential role of CM in mitochondria of retintal photoreceptor cone cells of small mammals treeshrews (Tupaia belangeri) that may serve as UV filter, micro-lens and/or wave-guide, based on theoretical simulations.
Fedorov coined the aphorism 'crystallization is death'. Instead, crystalized CM may indeed be indispensable to ensure stressed cell survival and bear a fascinating potential for technological and biomedical exploitation.
Bio-mimetics and soft robotics
Professor George Whitesides, Harvard University, USA
Biomimicry can occur an any scale, from that of molecules to that of macroscopic organisms. This talk will discuss structures fabricated in organic elastomers (so-called “soft robots”) that mimic some of the motions of invertebrates (starfish, insects, squid), and the possible applications of these structures.
Biomimetic adhesive microstructures as an approach to understand functioning biological systems
Professor Stanislav Gorb, Kiel University, Germany
Biological hairy attachment systems have robust adhesion and high reliability of contact. Previous comparative experimental studies on biological systems showed the way to development of novel glue-free adhesives. While producing the reversible adhesives, mimicking the gecko attachment system, still remains the main direction of research in the field, very convincing results have been achieved in manufacturing adhesive microstructures inspired by male chrysomelid beetles. Comparative studies on microstructures with different contact geometries showed that beetle-inspired mushroom-shaped adhesive microstructure (MSAMS) even outperform the gecko-inspired spatula-shaped geometry under certain conditions. Adhesion of MSAMS is reversible and even stronger under water. MSAMS demonstrated stick-slip free friction and lower impact of contamination by particles. MSAMS can keep its adhesive capability over thousands of attachment cycles. On rough substrates, their performance can be enhanced by the introduction of fluid into the contact zone. Additionally, the development of MSAMS provides an opportunity for biologists to run experiments, which would be otherwise only hardly possible with real biological system. The present lecture discusses how the knowledge obtained from studies on MSAMS can be applied to understanding function of biological adhesive systems of insects.
Fluid Dynamics and Self-Organization of Cytoplasmic Streaming
Professor Ray Goldstein FRS, University of Cambridge, UK
Organisms show a remarkable range of sizes, yet the dimensions of a single cell rarely exceed 100 microns. While the physical and biological origins of this constraint remain poorly understood, exceptions to this rule give valuable insights. A well-known counterexample is the aquatic plant Chara, whose cells can exceed 10 cm in length and 1 mm in diameter. Two spiraling bands of molecular motors at the cell periphery drive the cellular fluid up and down at speeds up to 100 microns/s, motion that has been hypothesized to mitigate the slowness of metabolite transport on these scales and to aid in homeostasis. This is the most organized instance of a broad class of continuous motions known as “cytoplasmic streaming", found in a wide range of eukaryotic organisms - alga, plants, amoebae, nematodes, and flies - often in unusually large cells. In this overview of the physics of this phenomenon, we examine the interplay between streaming, transport and cell size, and discuss the possible role of self-organization phenomena in establishing the observed patterns of streaming.
Photosynthesis-inspired redesign of membrane protein architectures for capturing and storing solar energy
Professor Neil Hunter FRS, University of Sheffield, UK
Photosynthesis, the ultimate source of all food and most energy resources on Earth, starts with the absorption of solar energy. However, sunlight is a diffuse energy source so an extensive light-harvesting (LH) antenna, consisting of thousands of pigment molecules, is required to absorb this energy and funnel it to specialised chlorophyll (Chl)-protein complexes called reaction centres (RCs). Here, the absorbed energy initiates a series of electron transfer reactions that capture some of the solar energy, prior to its storage in a chemical form that powers cellular metabolism. The antenna consists of repeating protein components called light-harvesting complexes that hold chlorophylls and carotenoid pigments in specific orientations and in close proximity to one another, ensuring efficient energy transfer to the RC. LH and RC complexes are 5-30 nanometres (nm) in size, forming energy trapping macromolecular membrane assemblies that extend to ~500 nm. The timescales are correspondingly short, and solar energy is transiently stored as a charge separation within 100 picoseconds of light capture.
Extensive spectroscopic and structural research has told us a great deal about these early events in photosynthesis, and computational models are addressing the collective energy transfer and trapping behavior of large-scale protein arrays, identifying desirable design motifs for artificial photosynthetic systems. New architectures for coupled energy transfer and trapping, consisting of mesoscale arrays of photosynthetic complexes, have been fabricated on a variety of surfaces using several lithographic approaches. The aim is to advance our understanding of natural energy-converting systems and to guide the design and production of proof-of-principle devices for biomimetic systems to capture, convert and store solar energy. Ultimately, we can envisage the design and construction of new proteins, cells and organisms with enhanced energy capturing functions.
Bioinspired genotype-phenotype linkages: mimicking cellular compartmentalisation for the engineering of functional proteins
Dr Florian Hollfelder, University of Cambridge, UK
The idea of compartmentalization of genotype and phenotype in cells is key for enabling Darwinian evolution. This contribution describes bioinspired systems that use in vitro compartments – water-in-oil droplets and gel-shell beads - for the directed evolution of functional proteins. Technologies based on these principles promise to provide easier access to protein-based therapeutics, reagents for processes involving enzyme catalysis, parts for synthetic biology and materials with biological components.
Climbing with adhesion: from bio-inspiration to bio-understanding
Professor Mark Cutkosky, Stanford University, USA
Bio-inspiration is an increasingly popular design paradigm, especially as robots venture out of the laboratory into the world. Animals are adept at coping with the variability that the world imposes. With advances in scientific tools for understanding biological structures in detail, we are increasingly able to identify design features that account for animals' robust performance. In parallel, advances in fabrication methods and materials are allowing us to engineer artificial structures with similar properties. The resulting robots become a useful platform for testing hypotheses about which principles are most important. Taking gecko-inspired climbing as an example, we show that the process of extracting principles from animals and adapting them to robots provides insights for both robotics and biology.
Bio-inspired membrane-based systems for a physical approach of cell organization and dynamics: usefulness and limitations
Professor Patricia Bassereau, Institut Curie, France
Being at the periphery of each cell compartments as well as of the entire cells and interacting with a large part of cell components, cell membranes participate to most of their vital functions. Biologists have worked for a long time on deciphering how membranes are organized, how they contribute to trafficking, motility, cytokinesis, cell-cell communications, information transport etc..., using top-down approaches and always more advanced techniques. In contrast, physicists have developed bottom-up approaches and minimal model membrane systems of growing complexity in order to build-up general models that explain how cell membranes work and their interactions with proteins or cytoskeleton. We will review the different model membrane systems that are currently available, how they can help deciphering cell functioning but also list their limitations. Model membrane systems are also used in synthetic biology and can have potential applications. We will eventually discuss the possible synergy between the development of complex in vitro membrane systems in a biological context and for technological applications. Questions that could also be discussed are: what can we still do with synthetic systems, where do we stop building-up and which are the alternative solutions?