The Small World of Osteocytes: Connectomics of the Lacuno-Canalicular Network in Bone

Osteocytes and their cell processes reside in a large, interconnected network of voids pervading the mineralized bone matrix of most vertebrates. This osteocyte lacuno-canalicular network (OLCN) is believed to play important roles in mechanosensing, mineral homeostasis, and for the mechanical properties of bone. While the extracellular matrix structure of bone is extensively studied on ultrastructural and macroscopic scales, there is a lack of quantitative knowledge on how the cellular network is organized. Using a recently introduced imaging and quantification approach, we analyze the OLCN in different bone types from mouse and sheep that exhibit different degrees of structural organization not only of the cell network but also of the fibrous matrix deposited by the cells. We define a number of robust, quantitative measures that are derived from the theory of complex networks. These measures enable us to gain insights into how efficient the network is organized with regard to intercellular transport and communication. Our analysis shows that the cell network in regularly organized, slow-growing bone tissue from sheep is less connected, but more efficiently organized compared to irregular and fast-growing bone tissue from mice. On the level of statistical topological properties (edges per node, edge length and degree distribution), both network types are indistinguishable, highlighting that despite pronounced differences at the tissue level, the topological architecture of the osteocyte canalicular network at the subcellular level may be independent of species and bone type. Our results suggest a universal mechanism underlying the self-organization of individual cells into a large, interconnected network during bone formation and mineralization

Accelerated Growth Plate Mineralization and Foreshortened Proximal Limb Bones in Fetuin-A Knockout Mice

PMCID: PMC3473050This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Passive and active mechanics of Banksia seed pods

Biological materials consist of only a few basic building blocks, namely sugars, proteins and a few minerals which are assembled into structurally complex materials to ensure (multi)functionality for the particular organism. Prominent examples are bone or nacre, composites of mineral and protein possessing high stiffness and strength. Apart from mineralized materials, protein- and sugar-based materials such as spider dragline silk or plant fibres achieve similarly high values. On the other end of the scale are soft materials with 3 to 4 magnitude lower stiffness and strength values (eg. parenchymatic tissue or artery). Common concept for all biological materials is that a wide range of material properties is achieved by structuring rather than changing their chemical components and frequently materials combine high strength and toughness when needed. A comprehensive understanding of the structure function relationships of biological materials requires measurements of mechanical properties at a range of different length scales, often in combination with other techniques (eg. X-rays, microscopy, spectroscopy). This approach will be illustrated on the example of plants and especially dead but multifunctional tissues such as the seed pods of Banksia attenuata, a native Australian species. The seed storing pods can remain on the plant for up to 15 years without metabolism before they open upon elevated temperatures (eg. caused by bush fires). During the storage period the seed pod material must passively resist weathering, microbial degradation and attacks by bird beaks. Interestingly, the seed pods do not open at uniform temperatures. Instead, opening temperatures change gradually along a climatic South-North gradient increasing towards North. We were able to identify the “temperature sensor” of the seed pods: the inner curvature of the layered follicles gradually increases providing Northern seed pods with a higher flexural rigidity. Opening is activated by a temperature-dependent decrease of the elastic modulus of the inner resistance layer, allowing pre-stresses to be released. However, the initial opening is not sufficient to release the seeds, further opening is fueled by moisture changes which lead to directional swelling and at the same time to changing mechanical properties in different layers of the seed pod. The findings on Banksia seed pods provide inspiration for self-sensing, moving and actuating materials and systems. We expect a comparably easy transfer into technical application because metabolism and biological signaling is not required for functionality. Since the material consists only of a few basic building blocks, namely cellulose, hemicelluloses, lignin, tannins and waxes, recycling and sustainable material use seem to be much easier compared to multi-component composites

Osmotic pressure induced tensile forces in tendon collagen

Water is an important component of collagen in tendons, but its role for the function of this load-carrying protein structure is poorly understood. Here we use a combination of multi-scale experimentation and computation to show that water is an integral part of the collagen molecule, which changes conformation upon water removal. The consequence is a shortening of the molecule that translates into tensile stresses in the range of several to almost 100 MPa, largely surpassing those of about 0.3 MPa generated by contractile muscles. Although a complete drying of collagen would be relevant for technical applications, such as the fabrication of leather or parchment, stresses comparable to muscle contraction already occur at small osmotic pressures common in biological environments. We suggest, therefore, that water-generated tensile stresses may play a role in living collagen-based materials such as tendon or bone.United States. Office of Naval Research. Presidential Early Career Award for Scientists and EngineersNational Institutes of Health (U.S.) (U01-EB016422

Special issue: bioinspired architectural and architected materials

Peer Reviewe

An Introduction into the Physics of Self-folding Thin Structures

Preprint. The article was published in: Friedman, Michael/Schäffner, Wolfgang (eds.) (2016): On Folding. Towards a New Field of Interdisciplinary Research. Bielefeld: transcript, pp. 175–210

Self-organized rod undulations on pre-stretched textiles

Textile technology is a traditional approach to additive manufacturing based on one-dimensional yarn. Printing solid rods onto pre-stretched textiles creates internal stresses upon relaxation of the pre-stretch, which leads to buckling-induced out-of-plane deformation of the textile. Similar behaviours are well known to occur also in biological systems where differential growth leads to internal stresses that are responsible for the folding or wrinkling of leaves, for example. Our goal was to get a quantitative understanding of this wrinkling by a systematic experimental and numerical investigation of parallel rods printed onto a pre-stretched textile. We vary rod thickness and spacing to obtain wavelength and phase coherence of the wrinkles as a function of these parameters. We also derive a simple analytical description to rationalize these observations. The result is a simple analytical estimate for the phase diagram of behaviours that may be used for design purposes or to describe wrinkling phenomena in biological or bioinspired systems.Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659Peer Reviewe

The Earth\u27s Lithosphere Inspires Materials Design

Structural patterns found in living organisms have long been inspiring biomimetic materials design. Here, it is suggested that a rich palette of patterns occurring in inanimate Nature, and especially in the Earth\u27s lithosphere, could be not less inspirational for design of novel architectured materials. This materials design paradigm is referred to as lithomimetics and it is demonstrated that some of the patterns found in the lithosphere can be emulated by established processes of severe plastic deformation. This opens up interesting avenues for materials design in which potentially promising structural patterns are borrowed from the lithosphere\u27s repository. The key aim here is to promulgate the “lithomimetics” paradigm as a promising approach to developing novel architectured materials

Three-dimensional lattice-Boltzmann simulations of critical spinodal decomposition in binary immiscible fluids

We use a modified Shan-Chen, noiseless lattice-BGK model for binary immiscible, incompressible, athermal fluids in three dimensions to simulate the coarsening of domains following a deep quench below the spinodal point from a symmetric and homogeneous mixture into a two-phase configuration. We find the average domain size growing with time as $t^\gamma$, where $\gamma$ increases in the range $0.545 < \gamma < 0.717$, consistent with a crossover between diffusive $t^{1/3}$ and hydrodynamic viscous, $t^{1.0}$, behaviour. We find good collapse onto a single scaling function, yet the domain growth exponents differ from others' works' for similar values of the unique characteristic length and time that can be constructed out of the fluid's parameters. This rebuts claims of universality for the dynamical scaling hypothesis. At early times, we also find a crossover from $q^2$ to $q^4$ in the scaled structure function, which disappears when the dynamical scaling reasonably improves at later times. This excludes noise as the cause for a $q^2$ behaviour, as proposed by others. We also observe exponential temporal growth of the structure function during the initial stages of the dynamics and for wavenumbers less than a threshold value.Comment: 45 pages, 18 figures. Accepted for publication in Physical Review

New Materials through Bioinspiration and Nanoscience

Chemistry and Chemical Biolog