Type I collagen is one of the most vital proteins in our bodies and serves a number of structural roles. Despite collagen’s importance, little is known about its nanoscale morphology in tissues and how morphology relates to mechanical function. This study directly probes nanoscale structure and mechanics in collagen as a function of hydration utilizing atomic force microscopy investigations of the mouse tail tendon. We demonstrate that collagen morphology and mechanical properties at the nanoscale change with dehydration, indicating that hydration is a factor which must be considered when performing studies at any length scale in collagen-based tissues. Studies are underway to further investigate this phenomenon and to determine how these properties change with disease in tendon and other Type I collagen-based tissues.

It has been reported [1] that microwave radiation can enhance many of the mechanical properties of Bombyx mori silkworm cocoon silk, as measured in constant strain rate tensile tests to failure and in stress relaxation tests. The consequences of microwave radiation will affect decisions about the use of silk in settings subjected to significant microwave exposure – for example, as a reinforcing fiber in an epoxy matrix composite that may be microwave cured, or as a component in aircraft radomes.

There are two possible mechanisms by which microwave radiation may affect a material [2]: (i) the radiation may enable chemical and/or microstructural changes – and therefore property changes – in the same way that conventional heating would, or (ii) the high heating rates that are achievable by microwaving may selectively favor changes that would be masked under conventional conditions, where heating rates are low enough to give preference to changes that have a lower activation energy. Here we explore the former possibility for silk.

We characterized several mechanical properties of degummed and subsequently annealed B. mori silk, and compared them to the corresponding properties of degummed B. mori silk that was not annealed. The annealing treatment was carried out at 140 °C for 7 hours (conditions that optimally increased crystal size in an unrelated study of B. mori silk [3]), and then the fibers were allowed to cool gradually to room temperature over the course of an hour. Comparison of mechanical properties revealed no differences between the materials that we tested. Thus, for annealed silk, we do not observe the enhancements that can be achieved by microwaving. We conclude that in cases where microwaving affects the properties of silk, those changes are not a simple consequence of annealing by the microwaves.

Biologically relevant lipid bilayers supported on highly ordered pyrolytic graphite (HOPG) were probed both mechanically and electrically with a Conductive Atomic Force Microscope (C-AFM) capable of measuring ultra-low currents. Results show that these membranes undergo an elastic response up to 26 nN on average when compressed with an AFM tip. Measuring the films with a low contact force demonstrates that contact mode AFM can be used repeatedly to image without damaging the film. Based on current-voltage measurements made with the C-AFM, it is shown that apparently high resistances seen for the films could be the result of variable electrical contact between the tip and surface. As a result, the paper proposes that the deflection of the cantilever should always be measured in order to ensure knowledge of the location of the tip during all electrical measurements.

Geckos can cling to almost any surface using dense arrays of microscopic hierarchical hairs called setae. The flat, regular, terminal branches of the setae adhere by the van der Waals dispersion force, and the mechanics of the gecko attachment scheme are a current topic among biologists and researchers in smart materials for adhesion. We studied the friction behavior of natural gecko arrays. Our experiments demonstrate the presence of velocity strengthening dynamic friction over the range of velocities from 5×10–4 to 158 mm/s and a range of specimen elastic moduli from 1.1 to 3.6 GPa. From these dynamic experiments, we calculate low-v activation volumes between 1500 and 3000 nm3. Since these volumes are 3 orders of magnitude larger then are typical for bulk materials, we conclude that there is weak coupling between individual sliding contacts in the gecko system.

We show a novel, bioengineered, moldable platform for bone regeneration composed of porous bionanocomposite scaffolds made of components that are normally found in bone tissue (calcium, collagen, carbonate, sodium, and phosphorous). To accommodate high- or low-stress environments, the hardness and modulus (stiffness) of these scaffolds can be tuned in a wide range in Megapascal (MPa) to Gigapascal (GPa) regions, while maintaining the required viscoelasticity. Our approach to control the mechanical properties is based on a new formulation of mineralized bioscaffolds by incorporation of calcium carbonate in which, calcium and phosphorous are in the form of calcite, calcium polyphosphate (CPP) and hydroxyapatite (HAP). The variation in the calcium carbonate concentration allows tuning of calcite/CPP contents in the bioscaffold to tailor the degree of mineralization and mechanical and viscoelastic properties that closely match those of natural bone. Our results demonstrate an ideal framework for new bone scaffold designs for advanced bone substitute applications.

Atomic layer deposition (ALD) was used to coat cellulose nanocrystal (CNC) aerogel scaffolds with a thin conformal layer of Al2O3. Electron probe microanalysis indicates that the penetration of Al2O3 into the aerogel was greater than 50 μm. Thermogravimetric analysis (TGA) shows that Al2O3 coated CNC aerogel composites have improved temperature and oxidation resistance.

Bioactive glass is an attractive scaffold material for use in filling bone defects because of its widely recognized ability to support the growth of bone cells and to bond firmly with hard and soft tissue. Use of bioactive glasses in the form of porous three-dimensional scaffolds for bone repair applications has been receiving considerable interest in recent years. However, bioactive glass scaffolds have been limited to the repair of low-load bone defects because of their low strength. In the present work, porous and strong bioactive glass scaffolds with an oriented microstructure were prepared by unidirectional freezing of camphene-based suspensions, and evaluated for their ability to regenerate bone in a non-healing rat calvarial defect model. Scaffolds of 13-93 glass (53SiO2, 6Na2O, 12K2O, 5MgO, 20CaO, 4P2O5; wt%) with a porosity of 50% and columnar pores of diameter 50–150 μm showed a compressive strength of 47 ± 5 MPa and an elastic modulus of 11 ± 3 GPa. Total bone regeneration in the oriented scaffolds, 18% after implantation for 12 weeks to 24% after 24 weeks, was not significantly different from that in 13-93 scaffolds with a microstructure similar to that of dry human trabecular bone (control group). The results indicated that these oriented bioactive glass (13-93) scaffolds could potentially be used in the regeneration of loaded bone.

Vaterite is one of the thermodynamically less stable polymorphs of calcium carbonate. Under ambient conditions it transforms into calcite, the most stable form of calcium carbonate. Organisms are able to stabilize minerals such as vaterite by means of organic molecules. The exact mechanisms how biomineralization proteins interact with metastable mineral phases are, however, less well understood. Many in vitro studies were performed using calcite as a model system. A deeper understanding of the interaction of organic molecules with metastable mineral phases would make them useful as a tool to control mineralization processes in vitro. In this study, we report on the co-precipitation of a natively soluble histidine-tagged GFP (green fluorecent protein) with a metastable vaterite phase and the subsequent insolubility of the fluorescent organic matrix in a 30μl calcium carbonate precipitation assay. The intrinsic fluorescence of GFP is conserved during the interaction with the mineral phase, indicating proper folding even in the insoluble state. This experiment can be extended to obtain deeper insights into some mechanistic models of biomineralization proteins by tracking native and modified GFP proteins microscopically during various stages of mineral precipitation and dissolution.

Bacteriophytochromes (Bphs) are red-light photoreceptors found in photosynthetic and non-photosynthetic bacteria that have been engineered into infrared fluorescent protein markers. Bphs are composed of a photosensory module that is covalently linked to an effector/regulatory module, usually a histidine kinase (HK) domain. Light-induced, global structural changes are proposed to originate within the covalently attached biliverdin chromophore, a linear tetrapyrrole, and propagate through the protein. Bphs undergo reversible photoconversion between two distinct red and far-red light absorbing states, denoted Pr and Pfr respectively. For most Bphs, Pr is the dark-adapted state. The energy dissipated during Pr/Pfr photoconversion is proposed to directly impact the infrared fluorescence quantum yield. At this time, only structures of three different Bphs have been published, all of truncated proteins in their respective dark-adapted states. We have utilized scanning probe microscopy (SPM) to investigate the structure of intact Bphs in the light-adapted state in order to gain new insight into the mechanism of photoconversion and fluorescence. Scanning tunneling microscopy (STM) analysis of a pair of Bphs from photosynthetic bacterium R. palustris, RpBphP2 (P2) and RpBphP3 (P3) in their light-adapted states is presented in these proceedings. The concentration of the depositing protein has a key role in the molecular arrangements observed on the highly-ordered pyrolytic graphite (HOPG) surface. For example, at a high protein concentration, a hexagonal lattice of Bphs is observed by STM on a HOPG surface. Upon dilution, the photoreceptors self-organize into fiber-like structures on the surface. In these fibers, the dimer interface and the individual domains of the Bphs can be assigned and directly compared to a structural model of the intact, full-length proteins. In summary, SPM has potential to be an effective method for gaining new insight into Bph structure and dynamics.

How the molecular structure of proteins in solution correlates with the mechanical properties of the solution at different length scales is not known. Using optical-tweezers based microrheology, we investigate a key physical property, viscoelasticity, of collagen solutions. To do this, we measure short-range thermal fluctuations of probe particles to obtain elastic and viscous moduli of their surrounding medium, and validate our measurement and analysis techniques using the previously studied system of polyethylene oxide. Probing the concentration dependence of viscoelasticity, we find that collagen solutions exhibit elasticity of comparable strength to viscosity when the concentration reaches ∼5 mg/ml. We also find that the presence of telopeptides alters the viscoelasticity of collagen solutions, particularly at high frequencies