Biological materials: Functional adaptations and bioinspired designs

Biological materials are typically multifunctional but many have evolved to optimize a chief mechanical function. These functions include impact or fracture resistance, armor and protection, sharp and cutting components, light weight for flight, or special nanomechanical/chemical extremities for reversible adhesive purposes. We illustrate these principles through examples from our own research as well as selected literature sources. We conduct this analysis connecting the structure (nano, micro, meso, and macro) to the mechanical properties important for a specific function. In particular, we address how biological systems respond and adapt to external mechanical stimuli. Biological materials can essentially be divided into mineralized and non-mineralized. In mineralized biological materials, the ceramics impart compressive strength, sharpness (cutting edges), and stiffness while the organic components impart tensile strength, toughness and ductility. Non-mineralized biological materials in general have higher tensile than compressive strength, since they are fibrous. Thus, the mineralized components operate optimally in compression and the organic components in tension. There is a trade-off between strength and toughness and the stiffness and density, with optimization. Mineralization provides load bearing capability (strength and stiffness) whereas the biopolymer constituents provide viscoelastic damping and toughness. The most important component of the nascent field of Biological Materials Science is the development of bioinspired materials and structures and understanding of the structure–property relationships across various length scales, from the macro-down to the molecular level. The most successful efforts at developing bioinspired materials that attempt to duplicate some of the outstanding properties are presented.     

Proteolysis in dry‐aged loins manufactured with sonicated pork and inoculated with Lactobacillus casei ŁOCK 0900 probiotic strain

Selected parameters related to proteolysis were evaluated in dry‐aged loins manufactured with sonicated pork and inoculated with Lactobacillus casei ?OCK 0900 probiotic strain. Dehydration, pH, water activity and total nitrogen content were not affected by ultrasound treatment. Neither sonication nor inoculation has an influence on L* and a* colour parameters. Sonication significantly influenced the pattern of proteolysis providing higher nonprotein nitrogen content (NPN) and proteolysis index (PI). The highest intensity of proteolysis, as assessed by NPN and PI, occurred in an inoculated sample. Neither sonication nor inoculation with L. casei had a significant effect on total viable counts. Loins inoculated with L. casei had the highest lactic acid bacteria count, followed by the sonicated and nonsonicated control. This research shows that sonication followed by inoculation with L. casei ?OCK 0900 could be used as an effective measure to speed up the proteolytic changes in dry‐aged meat cuts.     

Long-Ultraviolet-Excited White-Light Emission in Rare-Earth-Activated Yttrium-Oxyorthosilicate

White-light emission was achieved by activating yttrium oxyorthosilicate with two rare-earth elements, (Y_{1− m − n} Ce _m Tb _n )₂SiO₅. Ce³⁺ strongly absorbs at λ _ex =358 nm and produces a broad, mainly blue emission with a tail that extends out to 600 nm (orange), and transfers energy efficiently to Tb³⁺, which produces strong green-line emissions at 550 nm and some red emission around 650 nm. At λ_{e x} =358 nm, chromaticity coordinates of the optimally activated (Y_0.9625Ce_0.0075Tb_0.03)₂SiO₅ were found to be x =0.266, y =0.365 with a color temperature 8512 K. Upon mixing in another red-emitting phosphor, (Y_0.955Bi_0.005Eu_0.04)₂O₃, the chromaticity and color rendering index values were improved.     

DEM simulation of the packing structure and wall load in a 2-dimensional silo

The filling and discharge of a two-dimensional wedged-bottom silo holding circular objects was modelled using DEM technique to examine the influence of method of silo filling on distribution of orientations of unit vectors normal to contact points (contact normals) and normal contact forces. It was found that packing structure determined through method of generation of grain bedding significantly influenced distribution of contact normals. Nearly hexagonal network of contact normals was obtained for central filling of silo while sprinkle filling provided higher anisotropy of contact normals. The significance of frictional conditions and number of particles in system on distribution of contact normals was analysed. Increase in number of grains reduced disturbance from boundaries on behaviour of assembly. Distribution of loads on silo bottom obtained in simulation for different wall roughness was found in qualitative agreement with experimental data.     

Teaching elementary school students to identify story themes.

An instructional program focused on story theme was administered to 2nd and 3rd graders (high-, average-, and low-achieving students, including some with disabilities) in a high-poverty school. Compared with more traditional instruction, the program improved theme comprehension and the identification of instructed themes when they appeared in new stories. However, the program did not help students apply a theme to real-life situations or identify and apply noninstructed themes. Findings indicated that at-risk children (at all achievement levels, including those with disabilities) were able to achieve some degree of abstract, higher order comprehension when given instruction that combined structured lessons, a strategy, and discussion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relationships between post-failure state and compression strength of sudetic fractured rocks

The behaviour of the Sudetic crystalline rocks in a pre- and a post-critical state of stress is the topic of this work. The pre-and post-critical failure energy ratio has been discussed, and the regression lines of residual strength of fractured rocks has been detrmined, based on which the residual strength (R_rez) and the standard compression strength (R_e) relationship was empirically determined as R_rez=0.18R_c+5.6;     

Effect of fabrication temperature on strain‐sensing capacity of polypyrrole‐coated conductive fabrics

Textile strain sensors were made from polypyrrole‐coated stretchable fabrics by a method of screen printing with chemical vapor deposition. The effect of polymerization temperature on the sensing performances was studied. It was found that polymerization at low temperature significantly improved the electrical conductivity, strain sensitivity and environmental stability of the fabric sensors. The conductive fabrics were characterized using X‐ray diffraction, thermogravimetry, contact angle measurements, particle size analysis, scanning electron microscopy and scanning probe microscopy. Powders of pure polypyrrole prepared by the same fabrication method were characterized for a better understanding of the polypyrrole coating. Copyright © 2007 Society of Chemical Industry     

Search for optimal geometry of a conical turbine agitator for heat transfer in stirred vessels

Simultaneous measurements of power consumption P and heat transfer coefficient α for a jacketed, baffled, agitated vessel of diameter D = 0.45 m, equipped with a conical turbine, were carried out. The following geometric parameters of the agitator were tested: diameter d, blade width b and number Z, and distance from the bottom of the vessel to the lower edge of the blade h. The results of these investigations were generalized mathematically. On the basis of optimization, the best geometric parameters with respect to heat transfer are proposed for the conical turbine agitator.