Silica formation aided by polypeptides is being actively investigated for a wide range of applications including biomaterials synthesis, ceramics and controlled release systems. We envision that biocatalyzed mineralization could have application as a dental material where in situ formation of mineral layers could provide needed wear-resistance or sealing capability. The approach would be more clinically relevant, if a polymer host could be used to carry and specifically position the biocatalyst on a surface and additionally maintain the catalyst activity.

Accordingly, we studied the influence of simple catalytic polypeptides on silica formation from prehydrolyzed alkoxide precursor solutions onto a surface. The polypeptides were localized on to the surface as multilayered thin films using the layer-by-layer (LbL) assembly of polyelectrolytes. Polylysine (PLL) or another biocatalytic polycation, poly(ethyleneimine) (PEI), was adsorbed layer-by-layer up to 10 bilayers on silicon wafers in combination with a negatively charged polyelectrolyte polymer host, poly(sodium-4-styrene sulfonate) (PSS) to prepare PEI-(PLL/PSS)10, PEI-(PEI/PSS)10 and PEI-(PEI/PSS/PLL/PSS)10 multilayer films. Pre-hydrolyzed alkoxysilane solutions were placed dropwise on the catalytic films for silicification. Additionally, the effects of precursor concentration, solvent and drying were evaluated. The morphology, roughness and contact mechanical stiffness of the formed silica were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM).

The resulting silica morphology was plate-like or spherical, and porous with average particle size depending on the catalyst and its positions on the surface. Without a catalyst the silica formed over longer times with a fine, gel-like appearance. The morphology of silica produced on the substrate was different from that of particles catalyzed in solution with the same polypeptide catalyst. Additionally, it was found that the homogeneity of PEI-(PLL/PSS)10 films increased with drying temperature, silica precursor concentration and the presence of ethanol. The contact mechanical stiffness of the silica particles (40 N/m) catalyzed from PEI-(PLL/PSS)10 films was lower than the non-silicified areas (48 N/m) suggesting that regions of the silica were amorphous and hydrated. These results show that a polypeptide applied to a surface as a multiple layer with an oppositely charged polymer host (PSS) maintains its activity for silicification. The generally coherent nature of the mineral coating suggests its potential for enhancing critical restorative dental interfaces; however properties like porosity, hydration and their effect on hardness and permeability will need further study.

Chemo-mechanical protein aggregates in plants, e.g. the forisomes of legumes, transform the chemical free energy of their reaction with calcium ions into mechanical energy. Light and scanning electron microscopy analyses demonstrated that the spindle-shaped bodies with lengths between 25 and 40 μm consist of fiber bundle units which change their length and diameter during a reversible switching reaction induced by either calcium, barium, strontium ions or by changes of the pH value. For the determination of forces generated during the switching reaction a force measurement in vitro system based on the bending of thin glass fiber was developed. By using this set-up, dynamical forces of forisomes, in the presence of different alkaline ions, in the range up to 180 nN were measured.

Bone plays a key role in the paleontological and archeological records and can provide insight into the biology, ecology and the environment of ancient vertebrates. Examination of bone at the tissue level reveals a definitive relationship between nanomechanical properties and the local organic content, mineral content, and microstructural organization. However, it is unclear as to how these properties change following fossilization, or diagenesis, where the organic phase is rapidly removed and the remaining mineral phase is reinforced by the deposition of apatites, calcites, and other minerals. While the process of diagenesis is poorly understood, its outcome clearly results in the potential for dramatic alteration of the mechanical response of biological tissues. In this study, fossilized specimens of mammalian long bones, collected from Colorado and Wyoming, were studied for mechanical variations. Nanoindentation performed in both longitudinal and transverse directions revealed preservation of bone's natural anisotropy as transverse modulus values were consistently smaller than longitudinal values. Additionally modulus values of fossilized bone from 35.0 to 89.1 GPa increased linearly with logarithm of the sample's age. Future studies will aim to clarify what mechanical and material elements of bone are retained during diagenesis as bone becomes part of the geologic milieu.

A multi-scale analysis for unit cells of human cortical bone is presented. Two studies are conducted: the first study concerns the effect of aging over the structural and mechanical properties of human cortical bone; the second study is devoted to the failure mechanism and the development of cracks in cortical bone under various loading conditions. Experiments are conducted on human specimen of different ages in order to measure relevant geometrical and mechanical parameters and obtain microscopic data that will be injected into finite element models. First a continuum FEM model will compute macroscopic information that will be validated through comparison with the experimental measurements. For the failure mechanism study, an XFEM model will be developed in order to allow the growth of multiple cracks until complete failure of the cell. An elastic-damage criterion will be used in order to place the initial cracks in maximum strain locations. To follow the global response of the cell, the stress intensity factors are computed at each crack tip and a load parameter is adjusted so that the stress intensity factors remain at the critical value. In the case of competitive crack tips, a stability analysis is performed by computing the second derivative of the potential energy for each crack. Fatigue loading will be also investigated. The discretization utilizes the eXtended Finite Element Method and requires no remeshing as the cracks grow. The crack geometries are arbitrary with respect to the mesh, and are described by a vector level set. Special boundary conditions and the algorithm for detecting crack bridging and crack entering Haversian canals which allows the cracks to grow until maximum failure and/or percolation is presented.

Osteocalcin (OC) and osteopontin (OPN) are among the most abundant non-collagenous bone matrix proteins. Both have drawn interest from investigators studying their function in osteoporosis and it is known that mutations of these proteins can also have dramatic effects on the properties of bone. Other proteins including fibrillin 1 and 2 (FBN2) have been less widely studied, but can be mutated in some individuals resulting in connective tissue disorders. It has been reported that abnormal fibrillin may play a role in decreased bone mass. In this study bones from osteopontin (OPN), osteocalcin (OC) and fibrillin-2 (FBN2) knockout mice have been investigated. The study has identified how these proteins affect the bone's nanomechanical properties (hardness and elastic modulus). Nanoindentation tests were performed on the radial axis of cortical femora bones from the knockout mice and their wildtype controls. The results showed that young (age< 12 weeks) OPN knock-out bones have significantly lower mechanical properties than wild-type bones indicate a crucial role for OPN in early bone mineralization. After 12 weeks of age, the OPN knockout and wild-type control bones did not show any statistical difference. In OC deficient mice the mechanical properties were found to increase in the cortical mid-shaft of femora from 1 year old mice, suggesting an increase in bone mineralization, but 3 month old FBN2 deficient mice bones showed a decrease in mechanical properties across the cortical radial axis of the mid- femora.

Calcium phosphates materials are widely used to treat the bones defects. HA bioceramics traditionally used in medicine has some serious disadvantage – week resorbility properties. Calcium phosphate cements seems to be promising compounds to replace conventional ceramics. High macroporosity of hardened materials leads to low mechanical strength. The main objective of present work was a development of new chemically bonded materials based on α-tricalcium phosphate (α-TCP) and hydroxylapatite phase. The main idea was to combine the benefit of ceramics technology (compacting of powders to reduce the starting macroporosity) to improve the materials strength with advantages of cement product (small resorbable calcium phosphate particles). α-Ca3(PO4)2-based biocements were synthesized with initial composition of HA, α- and β-TCP containing 80% wt. of TCP phase. The rate of α-TCP transformation to apatite phase during setting reaction was about 20% wt. in case of cylindrical samples (8mm × 8 mm) at 60°C for 50 hours. The fabricated TCP – bio-composites demonstrated high mechanical strength and stiffness characteristic. Most efficient results were achieved with chitosan biopolymer containing samples (σc = 120 MPa).

Geckos have extraordinary ability to move on vertical surfaces and ceilings. The secret of the climbing ability stems from their foot pads, a special hierarchical hairy structure. Mimicking such structure would lead to dry adhesives for many applications. Recent experiments showed that the adhesion of multiwalled carbon nanotubes is larger than that of a gecko foot-hair. To explore the adhesive mechanisms of the nanotubes, we have developed a multiscale approach to simulate the adhesion process of carbon nanotubes. A molecular dynamics is used to simulate the deformation and damage of the nanotubes when contacting with a rough surface at atomic scale. A coarse graining method is developed to predict the interactions and adhesion of larger scale nanotube array. The parameters used in the coarse graining method are determined by the detailed molecular dynamics. The preliminary results show that the nanotube bending under pre-applied pressure increases the contact area and therefore enhances the adhesion. The nanotube breakage during pre-loading will reduce the adhesion in post cycles. These results are consistent with the experiments found in literature.

Wood exhibits a highly diversified microstructure. It appears as a solid-type composite material at a length scale of some micrometers, while it resembles an assembly of plate-like elements arranged in a honeycomb fashion at the length scale of some hundreds of micrometers. These structural features of wood result in different load carrying mechanisms at different observation scales and at different loading conditions. In this paper, we elucidate the main load carrying mechanisms by means of a micromechanical model for wood across different species, based on tissue-independent stiffness properties of cellulose, lignin, and water. The model comprises three homogenization steps, two based on continuum micromechanics and one on the unit cell method. The latter represents plate-like bending and shear of the cell walls, due to transverse shear loading and axial straining in the tangential direction Accurate representation of these deformation modes results in accurate (orthotropic) stiffness estimates, which deviate, on average, by less than 10 % from corresponding experimental results, across a variety of softwood species.

The hydroxyapatite (HA) based bioceramic materials are usually prepared at high sintering temperatures to attain suitable mechanical properties. The sintering process usually results in a material which is compositionally and morphologically different from nonstoichiometric nano-crystalline HA phase of hard tissue. At the same time, HA particulates used as precursors in ceramic manufacturing are often very similar to the natural HA nanocrystals. It has been shown that synthetic nanoparticle HA (nanoHA) based materials improve the biological response in vitro and in vivo, but the information on mechanical properties of these materials is scarce.

In this work we studied the HA nanoparticle (10 – 80 nm mean size) coatings with 30 – 70% porosity prepared by a dip-coating technique on Ti and TiN substrates. It has been found that the mechanical properties of HA nanoparticle coatings are strongly influenced by the initial size, morphology, and surface treatment of nanoparticles. The nanoindentation Young's modulus and hardness of as–deposited nanoHA coatings were in the range of 2.5 – 6.9 GPa and 80 – 230 MPa, respectively. The coatings were stable after annealing up to at least 600 °C, reaching the Young's modulus up to 23 GPa and hardness up to 540 MPa, as well as in simulated body fluids.