Metallization of biologically inspired silica nanotubes

The desire and need for various types of nanostructures have been met with challenges of feasibility, reproducibility, and long fabrication time. To work towards improved bottom-up methods of nanofabrication, we use bacterial flagella as bio-templates for fabricating silica-mineralized nanotubes, which are ideal for the formation of metal nanoparticles or metal oxide nanoparticles. In this study, we show that silica nanotubes formed from flagella templates can be coated with gold, palladium, and iron oxide nanoparticles under mild aqueous conditions. The process was accomplished through reactions including reductive metallization or oxidative hydrolysis. Morphology and chemical composition were analyzed by transmission electron microscopy and energy dispersive X-ray spectroscopy, respectively. The results from these studies provide evidence for the complete coating of silica nanotubes with metal nanoparticles using a simple and fast procedure.     

Review and reappraisal of adaptive interfaces: Toward biologically inspired paradigms

The field of Adaptive Interfaces has been an active area of research for over 10 years. While there have been great advances, unresolved issues remain. The paper presents a reappraisal of adaptive interfaces with an eye toward addressing these issues using biologically inspired methods. We first define a general and theoretical model of adaptive interfaces based on a survey of existing research. Using our generalized adaptive interface model, we then proceed to build taxonomies of variables used for adaptation. The aim is to provide researchers, designers and builders a better understanding of the underlying mechanisms, processes and outcomes of adaptive interfaces. From our review, we propose design rules that address three primary elements of a generalized adaptive interface: the identification of variables that call for adaptation, the determination of necessary modifications to the interface, and the selection of the decision inference mechanism. We then turn to the investigation of an alternative method for adaptive interface design. To find a method that corresponds better to human decision-making, which has been characterized as situated and recognition-primed, we explored biologically inspired techniques. In particular, we focus on the correspondence between human decision-making behaviour and the concepts of emergence and self-organization. While our ruminations are speculative, the future of biologically inspired interfaces seems promising.     

A biologically inspired modular VLSI system for visual measurement of self-motion

We introduce a biologically inspired computational architecture for small-field detection and wide-field spatial integration of visual motion based on the general organizing principles of visual motion processing common to organisms from insects to primates. This highly parallel architecture begins with two-dimensional (2-D) image transduction and signal conditioning, performs small-field motion detection with a number of parallel motion arrays, and then spatially integrates the small-field motion units to synthesize units sensitive to complex wide-field patterns of visual motion. We present a theoretical analysis demonstrating the architecture's potential in discrimination of wide-field motion patterns such as those which might be generated by self-motion. A custom VLSI hardware implementation of this architecture is also described, incorporating both analog and digital circuitry. The individual custom VLSI elements are analyzed and characterized, and system-level test results demonstrate the ability of the system to selectively respond to certain motion patterns, such as those that might be encountered in self-motion, at the exclusion of others.     

Adhesion and sliding response of a biologically inspired fibrillar surface: experimental observations

Inspired by the adhesion mechanisms of several animal species such as geckos, beetles and flies, several efforts in designing and fabricating surface engineering strategies have been made recently to mimic the adhesive and frictional behaviour of biological foot pads. An important feature of such biological adhesion systems is the ability to switch between strong attachment and easy detachment, which is crucial for animal locomotion. Recent investigations have suggested that such a 'switching' mechanism can be achieved by the elastic anisotropy of the attachment pad, which renders the magnitude of the detachment force to be direction dependent. This suggestion is supported by the observations that the fibres of the foot pads in geckos and insects are oriented at an angle to the base and that geckos curl their toes backwards (digital hyperextension) while detaching from a surface. One of the promising bio-inspired architectures developed recently is a film-terminated fibrillar PDMS surface; this structure was demonstrated to result in superior detachment force and energy dissipation compared with a bulk PDMS surface. In this investigation, the film-terminated fibrillar architecture is modified by tilting the fibres to make the surface vertically more compliant and elastically anisotropic. The directional detachment and the sliding resistance between the tilted fibrillar surfaces and a spherical glass lens are measured: both show significant directional anisotropy. It is argued that the anisotropy introduced by the tilted fibres and the deformation-induced change in the compliance of the fibre layer are responsible for the observed anisotropy in the detachment force.     

Triangular core as a universal strategy for stiff nanostructures in biology and biologically inspired materials

Recent findings in protein structure prediction have revealed a new class of fibrous proteins called beta-solenoids. In stark resemblance to amyloid structures and prion proteins, these self-assembling peptides feature a triangular cross-sectional structure with non-specific biological significance. Using basic geometric and mechanical arguments and finite element simulations, here we point out that the equilateral triangle, as the most anisotropic regular convex polytope, is an ideal shape that leads to a maximum bending stiffness at minimum material usage. Considering the mechanical stability of the cell-puncture needle of the bacteriophage T4 virus and the extreme efficiency of aggregation in amyloids and prion proteins, possibly due to their capacity of acting as rigid binding and nucleation sites, we propose that the triangular core may reflect a universal biological paradigm for achieving exceptionally stiff nanostructures, overcoming the limitations of the underlying weak molecular interactions such as hydrogen bonds. Stiff nanostructures employing a triangular core geometry may be particularly useful for nanomechanical applications such as puncture and cutting devices where maximum rigidity has to be achieved using a minimal cross-sectional area.     

Crystallization behaviour of calcium aluminate glass fibres

Crystallization behaviour of as-spun and fully-nucleated calcium aluminate (CA) glass fibres produced via inviscid melt spinning (IMS), was studied. Differential thermal analysis (DTA) scans on the as-spun and fully-nucleated CA fibres were performed at different heating rates. By applying the Kissinger method to the DTA scan data the activation energy values for crystallization were determined to be 569 and 546 kJ mol–1, respectively for the as-spun and fully-nucleated CA fibres. The Ozawa analysis on the DTA scan data gave the Avrami parameters at 2.7 and 2.4, respectively, for the as-spun and fully-nucleated CA fibres, which indicates high tendency of bulk crystallization mode. The formation of equilibrium phases of Ca12Al14O33 and CaAl2O4 in the crystallized CA fibres was identified by using X-ray diffraction (XRD).     

Crystallization behavior of calcium phosphate glass powder

The crystallization behavior of calcium phosphate glass powder with the molar ratio [CaO]/[P₂O₅] = 0.88, to which 6.38 mol% TiO₂ and 10 mol% Al₂O₃ were added as nucleation agents, was investigated. The results indicate complex crystallization behavior which depends on the powder particle size and the crystallization temperature. In the crystallization temperature range T _c < 900°C the surface mechanism of crystallization dominates in the case of all particle sizes ranging from 0–1 mm and the -Ca₂P₂O₇ phase is formed. At very long annealing times volume crystallization occurs and the TiP₂O₇ and AlPO₄ phases are formed. In the temperature interval T _c > 900°C the dominant crystallization mechanism depends on the particle size. In the size range 0.15–0.5 mm the surface mechanism of crystallization is replaced by the volume one. In the range >0.5 mm the volume mechanism of crystallization is dominant. The phases -Ca₂P₂O₇, TiP₂O₇ and AlPO₄ are formed in that temperature interval for all particle sizes. The additives TiO₂ and Al₂O₃ influence the nucleation and formation of TiP₂O₇ and AlPO₄ but do not influence the formation of -Ca₂P₂O₇.     

Crystallization and structural properties of calcium malonate hydrate

Calcium malonate hydrate crystals were grown by the reaction method, with the aid of hydrosilica gel. Colourless and prismatic crystals up to 4.5 mm in size were obtained. Structural properties of the material were explored by employing X-ray diffraction (XRD), infrared (IR) absorption, laser Raman (LR), and thermogravimetric (TG) techniques. The IR spectrum indicates the presence of inequivalent water molecules in the structure of the compound. The thermal decomposition pattern of the sample suggests a three-stage decay scheme. About one-fifth of the weight is due to the presence of water of crystallization. The differential scanning calorimetric (DSC) study corroborates the presence of inequivalent water molecules in the structure.     

Morphological control of precipitated calcium carbonates and phosphates by colloidal additives

The precipitation of calcium carbonate and calcium phosphates from solutions with and without additives such as hydroxyethyl cellulose, colloidal silica and potato starch, has been studied by X-ray diffraction and scanning electron microscopy. A constant rate of 10^–6 mol s^–1 of reactant was added into the mixed solutions with and without additives. Nucleation frequency and morphology were dramatically altered by the addition of colloidal potato starch. It was found to be effective for non-specific nucleation of calcite and hydroxyapatite and specific nucleation of monetite. The nucleation frequency of calcite is increased by adding starch by about a factor of 10⁴. Starch also alters the shape of hydroxyapatite to fibre-like.     

Topology optimization of plate/shell structures with respect to eigenfrequencies using a biologically inspired algorithm

In this article, a novel approach is presented to perform topology optimization in a simple and explicit way. The method capitalizes on the use of a bio-inspired algorithm to represent topology, leading to more flexible optimization solutions along with explicit structure representation. To avoid remeshing upon design changes, a special treatment called the enhanced stiffness transformation approach (ESTA) is introduced to transform the stiffness and mass matrices of the growing stiffener into a set of equivalent stiffness and mass matrices. In this way, stiffeners are separated from the finite element mesh and can grow in an arbitrary direction to form an optimized layout solution. Notably, this approach incorporates more geometric information into topology optimization, which improves the clarity of stiffener layouts. Finally, the effectiveness of the proposed method is illustrated with two examples of maximum eigenfrequency design of plate/shell structures.     

Crystallization process of cubic ZrO2 in calcium acetate solution

Ultrafine powders of cubic ZrO₂ were obtained at about 270° C by heating hydrated amorphous ZrO₂ in greater than 0.2 molal calcium acetate solutions. Ca²⁺ ions played a role as nucleii for crystallization and were introduced into distinct sites of the crystalline phases, that is, substituted for Zr⁴⁺ ions. Mn²⁺ ions produced almost the same effects on the crystallization of ZrO₂·EPR spectra for powder samples containing Mn²⁺ ions apparently showed two types as follows: for tetragonal ZrO₂ with a trace of monoclinic ZrO₂, the central fine structure transitions (M=+1/2–1/2) showed a well-resolved hyperfine structure. In addition to the m=0 transition, forbidden m=±1 transitions were observed. For cubic ZrO₂, the broad underlying response was observed as well as the hyperfine structure composed of six main peaks.     

Crystallization mechanisms of calcium phosphate cement for biological uses

Self-setting calcium phosphate cement for dental or surgical applications can be prepared by the addition of a liquid to a mixture of acidic and basic calcium phosphate. After hardening, the final compound becomes hydroxyapatite. Using an orthogonal central composite plan, the main factors which control the setting and the final hardness of the cement were defined and models are proposed. The mechanisms of crystallization, the role of free and linked water, and the nature of the final and intermediate compounds are described.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Three-dimensional matrices of calcium polyphosphates support bone growth in vitro and in vivo

Novel macroporous calcium polyphosphate (CPP) scaffolds, with three-dimensional interconnected structure, were fabricated using a polyurethane sponge method. They were then employed in both in vitro and in vivo assays to examine their suitability as bone tissue engineering scaffolds. In the former, subcultured rat marrow cells were seeded on the scaffolds at 7.0×105 cells/sample and cultured for 2 wk. Cell-free controls were employed to monitor changes in the scaffold itself. In the in vivo assay, CPP rods were implanted in rat distal femur and recovered after 2 wk. Samples were examined by scanning electron microscopy following freeze-fracturing. Both in vitro and in vivo assays demonstrated the growth of bone within the scaffolds. In vitro, the bone/CPP interface was occupied by a morphologically distinguishable cement line, while in vivo non-mineralized fibrous tissue was seen at the interface together with bone ingrowth into the scaffold microporosity. The morphology of the individual surface grains of the CPP scaffolds employed in vivo changed to a more rounded form, while no change in geometry was observed in the in vitro cell-free group. These preliminary studies indicate that three-dimensional CPPs can be successfully used as scaffolds for bone tissue engineering. © 1998 Kluwer Academic Publishers     

Chemical transformation of some biologically relevant calcium phosphates in aqueous media during a steam sterilization

The purpose of this study was to investigate the effect of steam sterilization on some biologically relevant calcium phosphates: CaHPO₄· 2H₂O (DCPD), calcium deficient apatite (CDA) and biphasic calcium phosphate (BCP). Suspensions of 0.2 g of each calcium phosphate compound with 5.0 ml of deionized water were prepared and steam sterilized in an autoclave (20 min at 121 °C). After sterilization the suspensions were filtered and the dried solids characterized with scanning electron microscopy, IR-spectroscopy and X-ray diffraction. The pH and calcium concentrations of the filtrates were determined with ion selective electrodes. Similar measurements were made with the same samples which were not sterilized. The sterilization procedure was found to result in the dehydration of DCPD and hydration of calcium oxide incorporated into the BCP. Solution pH was observed to change from 7.3 to 5.5 for the solutions in equilibrium with DCPD and from 8.5 to 10.6 for those in equilibrium with BCP. Minor changes both with the solid and liquid phases were found to occur during the steam sterilization of CDA. These results indicate that steam sterilization may have different effects on different calcium phosphate suspensions: it can result in dehydration of DCPD, fast hydration for CaO in BCP, but no significant effect on CDA.     

Crystallization rules of calcium oxalate crystals in lithogenic urine and in healthy urine in vitro

Crystallization of calcium oxalate (CaOxa) was comparatively studied in vitro in diluted lithogenic urine and in diluted healthy urine by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. In healthy urine, the crystallization was a growth-controlled process in the early stage of crystallization and a nucleation-controlled process in the middle and late stage. However, the crystallization of CaOxa was always a growth-controlled process in the lithogenic urine. That is, the size of CaOxa particles grow gradually and at last large size of CaOxa stones formed. Comparing the CaOxa crystals grown in lithogenic urine and in healthy urine, three differentiations were observed. First, the average particle size of CaOxa crystals precipitated in lithogenic urine is larger than that in healthy urine. Second, the morphology of calcium oxalate monohydrate (COM) crystals changes from sharp hexagonal in lithogenic urine to round and blunt in healthy urine. Third, calcium oxalate dihydrate (COD) crystals were induced in healthy urine. The results in this study may provide important clues to cure urinary stones.