Surface behaviour of biomaterials: The theta surface for biocompatibility

“Biomaterials” are non-living substances selected to have predictable interactions with contacting biological phases, in applications ranging from medical/dental implants to food processing to control of biofouling in the sea. More than 30 years of empirical observations of the surface behaviours of various materials in biological settings, when correlated with the contact-angle-determined Critical Surface Tensions (CST) for these same materials, support the definition of the “theta surface”. The “theta surface” is that characteristic expression of outermost atomic features least retentive of depositing proteins, and identified by the bioengineering criterion of having measured CST between 20 and 30 mN/m. Biomaterials applications requiring strong bioadhesion must avoid this range, while those requiring easy release of accumulating biomass should have “theta surface” qualities. Selection of blood-compatible materials is a main example. It is forecast that future biomaterials will be safely and effectively translated directly to clinical use, without requiring animal testing, based on laboratory data for CST, protein denaturation, and cell spreading alone.     

Adhesive interactions between cells and biotinylated phospholipid vesicles in alginate: towards new responsive biomaterials

Creating tissue-mimetic biomaterials able to deliver bioactive compounds after receipt of a remote and non-invasive trigger has so far proved to be challenging. The possible applications of such “smart” biomaterials are vast, ranging from subcutaneous drug delivery to tissue engineering. Self-assembled phospholipid vesicles (liposomes) have the ability to deliver both hydrophilic and hydrophobic drugs, and controlling interactions between functionalized vesicles and cells within biomaterials is an important step for targeted drug delivery to cells. We report an investigation of the interactions between thermally-sensitive and biotin-coated dipalmitoyl phosphatidylcholine vesicles and 3T3 fibroblast cells. The stability of these vesicles under physiological conditions was assessed and their interaction with the cell membranes of fibroblasts in media and alginate/fibronectin mixtures was studied. Stable vesicle-cell aggregates were formed in fluid matrices, and could be a model system for improving the delivery of remotely released drugs within vesicle-containing biomaterials.     

Covalent attachment of poly (acrylic acid) onto multiwalled carbon nanotubes functionalized with formaldehyde via electrophilic substitution reaction

The functionalization with formaldehyde via an electrophilic substitution reaction and graft with poly (acrylic acid) (PAA) by “grafting from” technology have been carried out for multiwalled carbon nanotubes (MWNTs) and MWNTs-PAA composites have been formed. The IR and TEM results show presence of covalent band and so-called “core-shell” structures for MWNTs-PAA. The MWNTs-PAA exhibits excellent suspendability in water, which is significant to explore the potential application of carbon nanotube in biological and medical systems.     

Multivalent assembly of ultrasmall nanoparticles: One-, two-, and three-dimensional architectures of 2 nm gold nanoparticles

The assembly of nanoparticles (NPs) into complex structures is a fundamental topic in nanochemistry. Although progress has been made in this respect, the classical treatment of NPs as hard building blocks that lack the ability to anisotropically “bond” to each other limits the construction of more complex assemblies. More importantly, extension of methods of assembly of robust NPs to the assembly of ultrasmall ones with size below 2 nm is still challenging. Here we report the controlled self-assembly of ∼2 nm gold NPs into one-dimensional (1D) nanochain, two-dimensional (2D) nanobelt and three-dimensional (3D) nanocomet architectures by kinetically controlling the diffusion of ultrasmall gold NPs with anisotropic surfaces in solution. This process is presumed to allow selective ligand exchange with linkers at different binding sites on the NP surface, and results in “multivalent” interactions between NPs. Different from the assembly of “hard building blocks”, our results demonstrate the significance of surface effects for ultrasmall NPs (or clusters) in determining the structure of complex self-assemblies, and suggest the possibility of assembling these “molecule-like” ultrasmall nanocrystals into novel complex materials on a nanoscale approaching that of real atoms or molecules.      

Fibre reinforced concrete: new design perspectives

Although the use of Fibre Reinforced Concrete (FRC) for structural applications is continuously increasing, it is still limited with respect to its potentials, mainly due to the lack of International Building Codes for FRC structural elements. Within fib (Féderation Internationale du Béton), the Special Activity Group 5 is preparing a New fib Model Code that aims to update the previous CEB-FIP Model Code 90, published in 1993, that can be considered as the reference document for Eurocode 2. The New Model Code includes several innovations and addresses among other topics, new materials for structural design. In this respect, FRC will be introduced. The Technical Groups fib TG 8.3 “Fibre reinforced concrete” and fib TG 8.6 “Ultra high performance FRC” are preparing some sections of the New Model Code, including regular and high performance FRC. This paper aims to briefly explain the main concepts behind the structural rules for FRC structural design.     

Structural model of a microinhomogeneous cracked material

We develop a mathematical model of microscopically inhomogencous but macroscopically isotropic materials with statistically distributed components of tensors of stiffness and strength. In this model, the material is represented as the continuous set of “characteristic” (i.e., typical of a given material) disjoint microscopic domains (microvolumes). The microinhomogeneous material is identified with an “effectively homogeneous” material in such a way that, at the same points, the components of the displacement vector determined for these materials are equal. It is assumed that, for each “characteristic” microvolume the parameters of stiffness and strength of the material are constant and can be obtained as values of an arbitrary random variable distributed according to the Weibull law and averaged over a certain random interval of any length. The components of the tensor averaged as indicated above are also regarded as random variables distributed according to the normal law with the same probability of hitting any arbitrarily located “characteristic” microvolume. The model is based on the assumption that the material is isotropic both macroscopically and in any “characteristic” microvolume. The stress-strain state of the microinhomogeneous material is described by the “effective” (averaged over its volume) components of the stress tensor. The model takes into account cracks in the material if their length exceeds the size of the relevant “characteristic” volume. The model is justified for the case of an infinite microinhomogeneous cracked plane under uniaxial tension. It is shown that the parameters determining the stressed state of this plane are not independent in the vicinity of the crack tip. The relevant constraints are given by equations of the model. The choice of these parameters which ignores the indicated constraints leads to results contradicting well-known physical facts. By using the symmetry properties of the system under consideration and physical reasoning, we obtain equations for the determination of the size of “characteristic” domains and physically reasonable dependences of the maximal “effective” tensile stresses and their direction on the parameter of inhomogeneity of the material and average volume of defects. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, Lviv. Pidstryhach Institute of Applied Problems in Mechanics and Mathematics, Ukrainian Academy of Sciences, Lviv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 4, pp. 5–16, July–August, 1996.     

A Novel Technique for Experimental Thermophysical Characterization of Phase-Change Materials

The major objective of this project is to use phase-change materials (PCMs) as integrated components in passive solar heat recovery systems. The suggested approach involves experimental investigations and characterization of the global behavior of a parallelepiped “material wrap” filled with the PCM. The experimental apparatus permits simultaneous measurements of heat fluxes and temperatures. It also allows imposing and measuring temperatures variations with respect to selected time scales between the two predominant faces of the sample. The instantaneous heat flux measurements allow the determination of the “apparent” or overall heat storage capacities and thermal conductivities of the PCM—in the solid and liquid states—and that of the latent heat of melting. Results were found to be very satisfactory.     

A micromechanical model of collapsing quicksand

The discrete element method constitutes a general class of modeling techniques to simulate the microscopic behavior (i.e.  at the particle scale) of granular/soil materials. We present a contact dynamics method, accounting for the cohesive nature of fine powders and soils. A modification of the model adjusted to capture the essential physical processes underlying the dynamics of generation and collapse of loose systems is able to simulate “quicksand” behavior of a collapsing soil material, in particular of a specific type, which we call “living quicksand”. We investigate the penetration behavior of an object for varying density of the material. We also investigate the dynamics of the penetration process, by measuring the relation between the driving force and the resulting velocity of the intruder, leading to a “power law” behavior with exponent 1/2, i.e.  a quadratic velocity dependence of the drag force on the intruder.     

Multiple formation of microcracks during mechanical loading of polymers

General kinetic and thermodynamic reasoning is used to propose a new mechanism for multiple crack formation caused by a mechanical action on a polymer. It is shown that the role of information “carrier” to “ weak” (in terms of thermodynamic stability) spots localized in the polymer matrix is assigned to phonons as a unique class of quasiparticles which exist in nonconducting and nonmagnetic dielectrics. Pis’ma Zh. Tekh. Fiz. 23, 80–85 (December 26, 1997)     

Vibrating reed studies on high-T c superconductors

We present vibrating reed (VR) measurements on single crystal and ceramic “1-2-3” and melt-processed polycrystalline Bi-based compounds in a wide range of temperature (4·2–100 K) and magnetic field (B=0–4 T). The “depinning line” (DL) determined by the VR technique is equivalent to the “irreversibility line” determined by magnetization and susceptibility measurements. A comparison of the results on single crystal and polycrystalline 1-2-3 compounds indicates that the VR technique is sensitive to the intragranular properties of the polycrystalline reed. It is found that the DL for 1-2-3 compounds is much steeper than that for Bi-based compounds, reflecting an intrinsically different pinning in both the materials, in agreement with the measured elastic coupling (Labusch constant α(B, T)).     

Ten Years of Spin Hall Effect

In this short review I survey the theory of the spin Hall effect in doped semiconductors and metals in the light of recent experiments on both kinds of materials. After a brief introduction to different types of spin–orbit coupling in solids, I describe in detail the three conceptually distinct mechanisms that are known to contribute to the spin Hall effect, namely “skew-scattering”, “side-jump”, and “intrinsic mechanism”. The skew-scattering mechanism is shown to be dominant in certain clean two-dimensional semiconductors in which one component of the spin is conserved. In such systems the side-jump mechanism is sub-dominant, but universal in form, and can become dominant if the electron mobility is reduced by changing the temperature. Both skew-scattering and side-jump contributions are generally reduced by spin precession, and skew-scattering is completely suppressed in the linear Rashba model in the absence of magnetic field. Different models of spin–orbit coupling can, however, sustain an intrinsic spin Hall effect. A brief summary of the present experimental situation concludes the review.     

Micro-mechanics based derivation of the materials constitutive relations for carbon-nanotube reinforced poly-vinyl-ester-epoxy based composites

The atomic-level computational results of the mechanical properties of Multi-Walled Carbon Nanotube (MWCNT) reinforced poly-vinyl-ester-epoxy obtained in our recent work [Grujicic M, Sun Y-P, Koudela KL (2006) Appl Surf Sci (accepted for publication, March)], have been utilized in the present work within a continuum-based micro-mechanics formulation to determine the effective macroscopic mechanical properties of these materials. Since the MWCNT reinforcements and the polymer-matrix molecules are of comparable length scales, the reinforcement/matrix interactions which control the matrix-to-reinforcement load transfer in these materials are accounted for through direct atomic-level modeling of the “effective reinforcement” mechanical properties. The term an “effective reinforcement” is used to denote a MWCNT surrounded by a layer of the polymer matrix whose thickness is comparable to the MWCNT radius and whose conformation is changed as a result of its interactions with the MWCNT. The micro-mechanics procedure yielded the effective continuum mechanical properties for the MWCNT-reinforced poly-vinyl-ester-epoxy matrix composite mats with a random in-plane orientation of the MWCNTs as a function of the following composite microstructural parameters: the volume fraction of the MWCNTs, their aspect ratio, the extent of covalent functionalization of the MWCNT outer walls as well as a function of the mechanical properties of the matrix and the reinforcements.     

Dielectric relaxation with dipolar screening

The phenomenon of dipolar screening does not appear to have received sufficient attention in the past, in a manner comparable to charged particle screening, and yet it is shown that it is capable of explaining some forms of dielectric response to which no other evident explanation exists. While reorientations of mathematical dipoles of zero “length” do not entail any charge displacements, physical dipoles of finite length, l, do produce charge displacements and therefore screening. A theory of dipolar screening is presented and it is shown that relatively “dense” systems give complete screening so that neighbouring dipoles do not “see” one another, while in more dilute systems many dipoles fall within a screening radius, Rs, of any one dipole. Dipoles within Rs tend to adopt energetically favoured configuration and the entire system “seizes up” in a “domain”, thus reducing the number of dipoles which can be reoriented at finite frequencies. This revised version was published online in November 2006 with corrections to the Cover Date.     

Experimental studies on process-induced morphological characteristics of macro- and microstructures in laser consolidated alloys

Laser consolidation (LC) developed by National Research Council’s Industrial Materials Institute (NRC-IMI-London) since mid-1990s, is a laser cladding based rapid manufacturing and material additive process that could fabricate a “net-shape” functional metallic shape through a “layer-upon-layer” deposition directly from a computer aided design model without using molds or dies. In order to evaluate the LC processability of different materials, some representative nickel-based superalloys (IN-625, IN-718, IN-738, and Waspaloy), stainless steels (austenitic SS316L and martensitic SS420), and lightweight alloys (Ti–6Al–4V titanium alloy and Al-4047 aluminum alloy) have been investigated. Like other laser cladding based processes, due to process-induced rapid directional solidification, the LC alloys have demonstrated certain unique morphological characteristics. Moreover, the “as-consolidated” LC alloys, in nature, are in the “as-quenched” state, and some precipitation processes from their matrices, which are sometimes critical to the development of mechanical performance of the materials, could be effectively suppressed or retarded. Post-heat treatments, therefore, could necessarily facilitate the process of achieving their required operational microstructures. In this article, a comprehensive investigation was performed including metallurgical soundness and process-induced morphological characteristics of the LC materials, and microstructure development brought by post-LC heat treatments using optical microscope, scanning electron microscope, and X-ray diffraction. The implications on the mechanical performance of the LC materials were discussed as well in order to provide essential information for potential industrial applications of the LC materials.     

Der Stoff, aus dem das Leben ist

Between 1900 and 1930 colloid chemistry, a branch of physical chemistry, gained crucial importance for the understanding of vital phenomena. To many it seemed that the properties of colloids would differ from those of ordinary matter, paralleling the specific properties of protoplasm, the “living substance”. The application of theoretical concepts and experimental models of colloid chemistry to biological problems shaped “Biocolloidology” as a new research program, which appeared promising for the exploration of organic processes such as mitotic cell division, growth, muscle contraction and movement. “Biocolloidology” could simultaneously absorb the quest for a physical-chemical explanation of life and the (post)-romantic notion of organic nature as a container of creative and vital forces that was central to life-philosophy. At least until the late 1920s, it is argued, the merging of different scientific and philosophical metaphors made “Biocolloidology” and the concept of protoplasm highly appealing in a broad cultural context.      

Suppression of motion-induced residual longitudinal vibration of an elastic rod by input shaping

Various input-shaping schemes such as the “zero-vibration” (ZV), “zero-vibration-and-derivative” (ZVD), “negative ZV” (NZV), and “negative ZVD” (NZVD) schemes have previously been proposed to suppress motion-induced residual vibration of lightly damped structures. In such schemes, the input command of the dynamical system in question is properly administered (i.e., shaped), so that the dominant induced vibration modes are annihilated through destructive interference. Here we are concerned with the effects of system payload on the vibration reduction capabilities of the aforementioned input-shaping schemes, especially when they are applied to continuous systems. By use of the simple structure of a linearly elastic rod as a specific example, it is demonstrated that both the minimum achievable residual vibration amplitude and the tolerance of detuning parameter errors of the input-shaping schemes are sensitive to the amount of payload on the system. It is therefore imperative to take the factor of system payload into account in the design of practical input shapers.     

Functionalized materials for multistage platforms in the oral delivery of biopharmaceuticals

Recent developments in materials science and specific surface functionalization of materials are providing new tools for the rational design of precisely engineered drug delivery systems. Particular interest has been paid to the exploitation of functionalized materials in the administration of biopharmaceuticals by the oral route, traditionally challenging and frequently compromised when using conventional pharmaceutical approaches. Using such materials for producing particulate systems is a common approach to obtain advanced drug delivery systems capable of providing stable and biocompatible environments and allowing for a targeted delivery of the associated biopharmaceuticals. This work intends to provide a thorough, up-to-date and holistic discussion on specific engineering and surface functionalization strategies of multistage platforms towards the development of novel delivery platforms for oral drug administration, with particular focus on the different materials and their interactions at the biological-material-host interface. This review will also address the safety and toxicity concerns of the resulting drug delivery systems, as well as their regulatory status and pathway towards the market approval of novel biopharmaceutical products based on particulate delivery systems.     

Introducing the concept of “uncertainty in measurement” into domestic metrological practice

There are four options for introducing the uncertainty concept in Russia. Preference is given to the gradual replacement of “error characteristic,” “total mean-square error,” and “confidence limits of error” by the terms “uncertainty,” “combined standard uncertainty,” and “expanded uncertainty,” respectively. The incorrect and widespread perception that “uncertainty in measurement” is an alternative for “error” is pointed out. Translated from Izmeritel'naya Tekhnika, No. 5, pp. 27–28, May, 2000.     

Bosons in Disordered Optical Potentials

In this work we systematically investigate the properties of ultracold bosonic gases trapped in disordered optical potentials or “dirty” bosons. We solve the Bose-Hubbard Hamiltonian exactly, thus taking into account high order quantum correlations, for “dirty” Bose gases with different (a) types of disorder, (b) disorder strengths, and (c) interatomic interactions. We concentrate on lattices with three different types of disorder: quasiperiodic disorder, uniform random disorder and random speckle-type disorder.     

Practical interpretation of metrological traceability on gauge block as to VIM 3

In ISO/IEC Guide 99:2007, i.e. the International Vocabulary of Basic and General Terms in Metrology-3rd edition (VIM 3), the term “traceability” is replaced by “metrological traceability”, giving it a new definition as property of a measurement result which can be related to a reference. In essence, “metrological traceability” can offer an evidence of measurands tracing to the primary standards which can realize the SI units, and offer a documented unbroken chain of calibrations, thus considered as one of the most important terms in VIM 3. National Measurement Laboratory (NML, Chinese Taipei) has long operated its main mission of calibration implemented along with peer assessed traceability of its measurement systems, which demonstrate a calibration hierarchy conventionally in schematic approach. In dealing with definition of the new term “metrological traceability” in VIM 3, this paper elaborates in taking additionally a newly mathematical approach rather than schematic approach only to realize the practical interpretation of “metrological traceability” to show how the unbroken calibration chain is functioning seamless and robust on the gauge block measurement system in NML. Through such study activities, we well assure our strong confidence on technology inheritance of gauge block and the other measurement systems with sufficient metrological know-how in NML, which can continually pass to each entry level metrologist.