Functional properties of cell-seeded three-dimensionally woven poly(epsilon-caprolactone) scaffolds for cartilage tissue engineering.

Articular cartilage possesses complex mechanical properties that provide healthy joints the ability to bear repeated loads and maintain smooth articulating surfaces over an entire lifetime. In this study, we utilized a fiber-reinforced composite scaffold designed to mimic the anisotropic, nonlinear, and viscoelastic biomechanical characteristics of native cartilage as the basis for developing functional tissue-engineered constructs. Three-dimensionally woven poly(epsilon-caprolactone) (PCL) scaffolds were encapsulated with a fibrin hydrogel, seeded with human adipose-derived stem cells, and cultured for 28 days in chondrogenic culture conditions. Biomechanical testing showed that PCL-based constructs exhibited baseline compressive and shear properties similar to those of native cartilage and maintained these properties throughout the culture period, while supporting the synthesis of a collagen-rich extracellular matrix. Further, constructs displayed an equilibrium coefficient of friction similar to that of native articular cartilage (mu(eq) approximately 0.1-0.3) over the prescribed culture period. Our findings show that three-dimensionally woven PCL-fibrin composite scaffolds can be produced with cartilage-like mechanical properties, and that these engineered properties can be maintained in culture while seeded stem cells regenerate a new, functional tissue construct.

Measurement of the cross section and angular correlations for associated production of a Z boson with b hadrons in pp collisions at √s = 7 TeV

A study of proton-proton collisions in which two b hadrons are produced in association with a Z boson is reported. The collisions were recorded at a centre-of-mass energy of 7TeV with the CMS detector at the LHC, for an integrated luminosity of 5:2 fb-1. The b hadrons are identified by means of displaced secondary vertices, without the use of reconstructed jets, permitting the study of b-hadron pair production at small angular separation. Differential cross sections are presented as a function of the angular separation of the b hadrons and the Z boson. In addition, inclusive measurements are presented. For both the inclusive and differential studies, different ranges of Z boson momentum are considered, and each measurement is compared to the predictions from different event generators at leading-order and next-to-leading-order accuracy. Copyright CERN.

Modelling of jet-impingement cooling for power electronics

The use of an innovative jet impingement cooling system in a power electronics application is investigated using numerical analysis. The jet impingement system, outlined by Skuriat et al, consists of a series of cells each containing an array of holes. Cooling fluid is forced through the device, forming an array of impingement jets. The jets are arranged in a manner, which induces a high degree of mixing in the interface boundary layer. This increase in turbulent mixing is intended to induce higher Nusselt numbers and effective heat transfer coefficients. Enhanced cooling efficiency enables the power electronics module to operate at a lower temperature, greatly enhancing long-term reliability. The results obtained through numerical modelling deviates markedly from the experimentally derived data. The disparity is most likely due to the turbulence model selected and further analysis is required, involving evaluation of more advanced turbulence models.

Can Pickering emulsion formation aid the removal of creosote DNAPL from porous media?

The purpose of this investigation was to examine the proposition that creosote, emplaced in an initially water saturated porous system, can be removed from the system through Pickering emulsion formation. Pickering emulsions are dispersions of two immiscible fluids in which coalescence of the dispersed phase droplets is hindered by the presence of colloidal particles adsorbed at the interface between the two immiscible fluid phases. Particle trapping is strongly favoured when the wetting properties of the particles are intermediate between strong water wetting and strong oil wetting. In this investigation the necessary chemical conditions for the formation of physically stable creosote-in-water emulsions protected against coalescence by bentonite particles were examined. It was established that physically stable emulsions could be formed through the judicious addition of small amounts of sodium chloride and the surfactant cetyl-trimethylammonium bromide. The stability of the emulsions was initially established by visual inspection. However, experimental determinations of emulsion stability were also undertaken by use of oscillatory rheology. Measurements of the elastic and viscous responses to shear indicated that physically stable emulsions were obtained when the viscoelastic systems showed a predominantly elastic response to shearing. Once the conditions were established for the formation of physically stable emulsions a "proof-of-concept" chromatographic experiment was carried out which showed that creosote could be successfully removed from a saturated model porous system. (C) 2007 Elsevier Ltd. All rights reserved.

A methodology for characterising new lead-free solder paste formulations used for flip-chip assembly applications

The paper reports on the investigation of the rheological behaviour new lead-free solder pastes formulations for use in flip-chip assembly applications. The study is made up of three parts; namely the evaluation of the effect of plate geometry, the effect of temperature and processing environment and the effect of torsional frequencies on the rheological measurements. Different plate geometries and rheological tests were used to evaluate new formulations in terms of wall slip characteristics, linear viscoelastic region and shear thinning behaviour. A technique which combines the use of the creep-recovery and dynamic frequency sweep tests was used to further characterise the paste structure, rheological behaviour and the processing performance of the new paste formulations. The technique demonstrated in this study has wide utility for R & D personnel involved in new paste formulation, for implementing quality control procedures used in paste manufacture and packaging and for qualifying new flip-chip assembly lines

Development of an in-situ, non-destructive ultrasonic monitoring technique for solder pastes

This paper concerns the use of a non-destructive ultrasonic technique for characterising the rheological properties of solder paste and specifically, the use of through-mode microsecond ultrasonic pulses for evaluation of viscoelastic properties of paste materials at the molecular level. Ultrasonic techniques are a widely used and a reliable form of non-destructive testing of materials. This is because techniques such as ultrasounds while used for testing or monitoring material properties, has offered immense benefits in applications where access to the sample is restricted or when handling the sample for testing could interfere with the monitoring or analysis process. Very often, this would mean that the measurements taken are not a true representation of the behaviour of the material (due to externally incorporated changes into the material's physical state during the removal or testing process). Ultrasonic based techniques are being increasingly used for quality control and production monitoring functions which requires evaluation of the changes in material properties over wide range of industrial applications such as cement paste quality, plastic/polymer extrusion process, dough, and even sugar content in beverage drinks. In addition, ultrasound techniques are of great interest for their capacity to take rapid measurements in systems which are optically opaque. The viscometer and rheometer are two of the most widely used rheological instruments used in industry for monitoring the quality of solder pastes, during the production and packaging stage. One of the potential limitations of viscometer and rheometer based measurements is that the collection and preparation of the solder paste samples can irreversibly alter the structure and flow behaviour of the sample. Hence the measurement may not represent the actual quality of the whole production batch. Secondly, rheological measurements and the interpretation of rheological data is a very technical and time consuming process, which requires professionally trained R&D personnel. It is for these reasons that materials suppliers (who formulate and produce solder pastes) and solder paste consumers (especially, contract electronics manufacturers) are keen to see the development of simple, easy to use and accurate techniques for the theological characterisation of solder pastes. The results from the work show that the technique can be used by R&D personnel involved in paste formulation and manufacture to monitor the batch-to-batch quality and consistency.

In-situ non-destructive ultrasonic rheology technique for monitoring different lead-free solder pastes for surface mount applications

This paper investigates the application of a non-destructive ultrasonic technique for characterising the rheological properties of solder paste through the use of through-mode microsecond ultrasonic pulses for evaluation of viscoelastic properties of lead-free solder paste containing different types of flux. Ultrasonic techniques offer a robust and reliable form of non-destructive testing of materials where access to the sample is restricted or when sample handling can interfere with the monitoring or analysis process due to externally incorporated changes to the material’s physical state or accidental contamination during the removal or testing process. Ultrasonic based techniques are increasingly used for quality control and production monitoring functions which requires evaluation of changes in material properties for a wide range of industrial applications such as cement paste quality, plastic/polymer extrusion process, dough and even sugar content in beverage drinks. In addition, ultrasound techniques are of great interest for their capability to take rapid measurements in systems which are optically opaque. The conventional industry approach for characterising the rheological properties of suspensions during processing/packaging stage is mainly through the use of viscometer and some through the use of rheometer. One of the potential limitations of viscometer and rheometer based measurements is that the collection and preparation of the solder paste samples can irreversibly alter the structure and flow behaviour of the sample. Hence the measurement may not represent the actual quality of the whole production batch. Secondly, rheological measurements and the interpretation of rheological data is a very technical and time consuming process, which requires professionally trained R&D personnel. The ultrasound technique being proposed provides simple, yet accurate and easy to use solution for the in-situ rheological characterisation of solder pastes which will benefit the materials suppliers (who formulate and produce solder pastes) and solder paste consumers (especially, contract electronics manufacturers). The results from the work show that the technique can be used by R&D personnel involved in paste formulation and manufacture to monitor the batch-to-batch quality and consistency.

Numerical Method for Cost-Weight Optimisation of Stringer-Skin Panels

The need to integrate cost into the early product definition process as an engineering parameter is addressed. The application studied is a fuselage panel that is typical for commercial transport regional jets. Consequently, a semi-empirical numerical analysis using reference data was coupled to model the structural integrity of thin-walled structures with regard to material failure and buckling: skin, stringer, flexural, and interrivet. The optimization process focuses on direct operating cost (DOC) as a function of acquisition cost and fuel burn. It was found that the ratio of acquisition cost to fuel burn was typically 4:3 and that there was a 10% improvement in the DOC for the minimal DOC condition over the minimal weight condition because of the manufacturing cost saving from having a reduced number of larger-area stringers and a slightly thicker skin than that preferred by the minimal weight condition. Also note that the minimal manufacturing cost condition was slightly better than the minimal weight condition, which highlights the key finding: The traditional minimal weight condition is a dated and suboptimal approach to airframe structural design.

Formulation and characterisation of tetracycline-containing bioadhesive polymer networks designed for the treatment of periodontal disease.

This study described the drug release, rheological (dynamic and flow) and textural/mechanical properties of a series of formulations composed of 15% w/w polymethylvinylether-co-maleic anhydride (PMVE-MA), 0-9% w/w polyvinylpyrrolidone (PVP) and containing 1-5% w/w tetracycline hydrochloride, designed for the treatment of periodontal disease. All formulations exhibited pseudoplastic flow with minimal thixotropy. Increasing the concentration of PVP sequentially increased the zero-rate viscosity (derived from the Cross model) and the hardness and compressibility of the formulations (derived from texture profile analysis). These affects may be accredited to increased polymer entanglement and, in light of the observed synergy between the two polymers with respect to their textural and rheological properties, interaction between PVP and PMVE-MA. Increasing the concentration of PVP increased the storage and loss moduli yet decreased the loss tangent of all formulations, indicative of increased elastic behaviour. Synergy between the two polymers with respect to their viscoelastic properties was observed. Increased adhesiveness, associated with increased concentrations of PVP was ascribed to the increasing bioadhesion and tack of the formulations. The effect of increasing drug concentration on the rheological and textural properties was dependent on PVP concentration. At lower concentrations (0, 3% w/w) no effect was observed whereas, in the presence of 9% w/w PVP, increasing drug concentration increased formulation elasticity, zero rate viscosity, hardness and compressibility. These observations were ascribed to the greater mass of suspended drug in formulations containing the highest concentration of PVP. Drug release from formulations containing 6 and 9% PVP (and 5% w/w drug) was prolonged and swelling/diffusion controlled. Based on the drug release, rheological and textural properties, it is suggested that the formulation containing 15% w/w PMVE-MA, 6% w/w PVP and tetracycline hydrochloride (5% w/w) may be useful for the treatment of periodontal disease.

Poly(epsilon-caprolactone) and poly(epsilon-caprolactone)-polyvinylpyrrolidone-iodine blends as ureteral biomaterials: characterisation of mechanical and surface properties, degradation and resistance to encrustation in vitro.

This study describes the physicochemical properties and in vitro resistance to encrustation of solvent cast films composed of either poly(epsilon-caprolactone) (PCL), prepared using different ratios of high (50,000) to low (4000) (molecular weight) m.wt., or blends of PCL and the polymeric antimicrobial complex, poly(vinylpyrrolidone)-iodine (PVP-I). The incorporation of PVP-I offered antimicrobial activity to the biomaterials. Films were characterised in terms of mechanical (tensile analysis, dynamic mechanical thermal analysis) and surface properties (dynamic contact angle analysis, scanning electron microscopy), whereas degradation (at 37degreesC in PBS at pH 7.4) was determined gravimetrically. The resistance of the films to encrustation was evaluated using an in vitro encrustation model. Reductions in the ratio of high:low-m.wt. PCL significantly reduced the ultimate tensile strength, % elongation at break and the advancing contact angle of the films. These effects were attributed to alterations in the amorphous content and the more hydrophilic nature of the films. Conversely, there were no alterations in Young's modulus, the viscoelastic properties and glass-transition temperature. Incorporation of PVP-I did not affect the mechanical or rheological properties of the films, indicative of a limited interaction between the two polymers in the solid state. Manipulation of the high:low m.wt. ratio of PCL significantly altered the degradation of the films, most notably following longer immersion periods, and resistance to encrustation. Accordingly, maximum degradation and resistance to encrustation was observed with the biomaterial composed of 40:60 high:low m.wt. ratios of PCL; however, the mechanical properties of this system were considered inappropriate for clinical application. Films composed of either 50:50 or 60:40 ratio of high:low m.wt. PCL offered an appropriate compromise between physicochemical properties and resistance to encrustation. This study has highlighted the important usefulness of degradable polymer systems as ureteral biomaterials

Proof of polar ejection from the close-binary core of the planetary nebula Abell 63

We present the first detailed kinematical analysis of the planetary nebula Abell 63, which is known to contain the eclipsing close-binary nucleus UU Sge. Abell 63 provides an important test case in investigating the role of close-binary central stars on the evolution of planetary nebulae. Longslit observations were obtained using the Manchester echelle spectrometer combined with the 2.1-m San Pedro Martir Telescope. The spectra reveal that the central bright rim of Abell 63 has a tube-like structure. A deep image shows collimated lobes extending from the nebula, which are shown to be high-velocity outflows. The kinematic ages of the nebular rim and the extended lobes are calculated to be 8400 +/- 500 and 12900 +/- 2800 yr, respectively, which suggests that the lobes were formed at an earlier stage than the nebular rim. This is consistent with expectations that disc-generated jets form immediately after the common envelope phase. A morphological-kinematical model of the central nebula is presented and the best-fitting model is found to have the same inclination as the orbital plane of the central binary system; this is the first proof that a close-binary system directly affects the shaping of its nebula. A Hubble-type flow is well-established in the morphological-kinematical modelling of the observed line profiles and imagery. Two possible formation models for the elongated lobes of Abell 63 are considered, (i) a low-density, pressure-driven jet excavates a cavity in the remnant asymptotic giant branch (AGB) envelope; (ii) high-density bullets form the lobes in a single ballistic ejection event.

Physicochemical characterization of bioactive polyacrylic acid organogels as potential antimicrobial implants for the buccal cavity

This study describes the formulation and physicochemical characterization of poly(acrylic acid) (PAA) organogels, designed as bioactive implants for improved treatment of infectious diseases of the oral cavity. Organogels were formulated containing a range of concentrations of PAA (3-10% w/w) and metronidazole (2 or 5% w/w, representing a model antimicrobial agent) in different nonaqueous solvents, namely, glycerol (Gly), polyethylene glycol (PEG 400), or propylene glycol (PG). Characterization of the organogels was performed using flow rheometry, compressional analysis, oscillatory rheometry, in vitro mucoadhesion, moisture uptake, and drug release, methods that provide information pertaining to the nonclinical and clinical use of these systems. Increasing the concentration of PAA significantly increased the consistency, compressibility, storage modulus, loss modulus, dynamic viscosity, mucoadhesion, and the rate of drug release. These observations may be accredited to enhanced molecular polymer entanglement. In addition, the choice of solvent directly affected the physicochemical parameters of the organogels, with noticeable differences observed between the three solvents examined. These differences were accredited to the nature of the interaction of PAA with each solvent and, importantly, the density of the resultant physical cross-links. Good correlation was observed between the viscoelastic properties and drug release, with the exception of glycerol-based formulations containing 5 and 10% w/w PAA. This disparity was due to excessive swelling during the dissolution analysis. Ideally, formulations should exhibit controlled drug release, high viscoelasticity, and mucoadhesion, but should flow under minimal stresses. Based on these criteria, PEG 400-based organogels composed of 5% or 10% w/w PAA exhibited suitable physicochemical properties and are suggested to be a potentially interesting strategy for use as bioactive implants designed for use in the oral cavity. © 2008 American Chemical Society.

Rheological characterization of thermoresponsive semisolids for vaginal HIV vaccine delivery

Purpose. To manufacture and characterize, through oscillatory rheology, thermoresponsive rheologically structured vehicles
(RSV’s) capable of enhanced retention times within the vagina for the purposes of HIV vaccine delivery.
Methods. Pluronics F127, F108 and F68 were investigated and RSV’s were prepared by dissolving sorbic acid (0.1% w/w)
and mucoadhesive component (Gantrez SBF97 or Noveon AA1, 3% w/w) in the required amount of H2O and NaOH.
Pluronic (10% w/w) was added via mixing in an ice-bath followed by hydroxyethylcellulose (5%) and subsequently
poly(vinylpyrollidone) (4%w/w). Oscillatory temperature sweeps between 10-38°C were preformed within the linear
viscoelastic region of the formulations on an AR2000 rheometer (T.A. Instruments, Surrey, England) with a 2cm diameter
parallel plate geometry and a plate gap of 1000µm at 1Hz.

Spatially resolved diagnostics on a micro atmospheric pressure plasma jet

Despite enormous potential for technological applications, fundamentals of stable non-equilibrium micro-plasmas at ambient pressure are still only partly understood. Micro-plasma jets are one sub-group of these plasma sources. For an understanding it is particularly important to analyse transport phenomena of energy and particles within and between the core and effluent of the discharge. The complexity of the problem requires the combination and correlation of various highly sophisticated diagnostics yielding different information with an extremely high temporal and spatial resolution. A specially designed rf microscale atmospheric pressure plasma jet (µ-APPJ) provides excellent access for optical diagnostics to the discharge volume and the effluent region. This allows detailed investigations of the discharge dynamics and energy transport mechanisms from the discharge to the effluent. Here we present examples for diagnostics applicable to different regions and combine the results. The diagnostics applied are optical emission spectroscopy (OES) in the visible and ultraviolet and two-photon absorption laser-induced fluorescence spectroscopy. By the latter spatially resolved absolutely calibrated density maps of atomic oxygen have been determined for the effluent. OES yields an insight into energy transport mechanisms from the core into the effluent. The first results of spatially and phase-resolved OES measurements of the discharge dynamics of the core are presented.

Generation of Atomic Oxygen in the Effluent of an Atmospheric Pressure Plasma Jet

The planar 13.56MHz RF-excited low temperature atmospheric pressure plasma jet (APPJ) investigated in this study is operated with helium feed gas and a small molecular oxygen admixture. The effluent leaving the discharge through the jet’s nozzle contains very few charged particles and a high reactive oxygen species’ density. As its main reactive radical, essential for numerous applications, the ground state atomic oxygen density in the APPJ’s effluent is measured spatially resolved with two-photon absorption laser induced fluorescence spectroscopy. The atomic oxygen density at the nozzle reaches a value of ~1016 cm-3. Even at several centimetres distance still 1% of this initial atomic oxygen density can be detected. Optical emission spectroscopy (OES) reveals the presence of short living excited oxygen atoms up to 10 cm distance from the jet’s nozzle. The measured high ground state atomic oxygen density and the unaccounted for presence of excited atomic oxygen require further investigations on a possible energy transfer from the APPJ’s discharge region into the effluent: energetic vacuum ultraviolet radiation, measured by OES down to 110 nm, reaches far into the effluent where it is presumed to be responsible for the generation of atomic oxygen.