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In cases of aortic stenosis, bioprosthetic heart valves (BHVs), with glutaraldehyde-fixed bovine pericardium leaflets (GLBP), are often implanted to replace the native diseased valve. Widespread use of BHVs, however, is restricted due to inadequate long-term durability, owing specifically to premature leaflet failure. Mechanical fatigue damage and calcification remain the primary leaflet failure modes, where glutaraldehyde treatment is known to accelerate calcification. The literature in this area is limited, with some studies suggesting mechanical damage increases calcification and others that they are independent degenerative mechanisms. In this study, specimens which were non-destructively pre-sorted according to collagen fibre architecture and uniaxially cyclically loaded until failure or 1 million cycles, were placed in an in vitro calcification solution. The weakest specimen group (those with fibres aligned perpendicular to the load) had statistically significantly higher volumes of calcification when compared to those with a high fatigue life. Moreover, SEM imaging revealed that ruptured and damaged fibres presented calcium binding sites; resulting in 4 times more calcification in fractured samples in comparison to those which did not fail by fatigue. To the authors’ knowledge, this study quantifies for the first time, that mechanical damage drives calcification in commercial-grade GLBP and that calcification varies spatially according to localised damage levels. These findings illustrate that not only is calcification of GLBP exacerbated by fatigue damage, but that both failure phenomena are underpinned by the collagen fibre organisation. Consequently, controlling for GLBP collagen fibre architecture in leaflets could minimise the progression of these primary failure modes in patient BHVs. Statement of significance Mechanical damage and calcification are the primary premature failure modes of glutaraldehyde-fixed bovine pericardial (GLBP) leaflets in bioprosthetic heart valves. In this study, commercial-grade GLBP specimens which were uniaxially cyclically loaded to failure or 1 million cycles, were placed in an in vitro calcification solution. MicroCT and SEM analysis showed that localised calcification levels varied spatially according to damage, where ruptured fibres offered additional calcium binding sites. Furthermore, specimens with a statistically significant lower fatigue life were associated with statistically significant higher calcification. This study revealed that mechanical damage drives calcification of GLBP. Non-destructive pre-screening of collagen fibres demonstrated that both the fatigue life and calcification potential of commercial-grade GLBP, are underpinned by the collagen fibre architecture.

Bioprosthetic heart valves (BHVs) are implanted in aortic valve stenosis patients to replace the native, dysfunctional valve. Yet, the long-term performance of the glutaraldehyde-fixed bovine pericardium (GLBP) leaflets is known to reduce device durability. The aim of this study was to investigate a type of commercial-grade GLBP which has been over-looked in the literature to date; that of high collagen fibre dispersion (HD). Under uniaxial cyclic loading conditions, it was observed that the fatigue behaviour of HD GLBP was substantially equivalent to GLBP in which the fibres are highly aligned along the loading direction. It was also found that HD GLBP had a statistically significant 9.5% higher collagen content when compared to GLBP with highly aligned collagen fibres. The variability in diseased BHV delivery sites results in unpredictable and complex loading patterns across leaflets in vivo. This study presents the possibility of a shift from the traditional choice of circumferentially aligned GLBP leaflets, to that of high fibre dispersion arrangements. Characterised by its high fatigue life and increased collagen content, in addition to multiple fibre orientations, GLBP of high fibre dispersion may provide better patient outcomes under the multi-directional loading to which BHV leaflets are subjected in vivo.

In cases of aortic stenosis, bioprosthetic heart valves (BHVs), with leaflets made from glutaraldehyde fixed bovine pericardium (GLBP), are often implanted to replace the native diseased valve. Widespread use of these devices, however, is restricted due to inadequate long-term durability owing specifically to premature leaflet failure. Mechanical fatigue damage and calcification remain the primary leaflet failure modes, where glutaraldehyde treatment is known to accelerate calcification. The literature in this area is limited, with some studies suggesting mechanical damage increases calcification and others that they are independent degenerative mechanisms. In this study, specimens which were non-destructively pre-sorted according to collagen fibre architecture and then uniaxially cyclically loaded until failure or 1 million cycles, were placed in anin-vitrocalcification solution. Measurements of percentage volume calcification demonstrated that the weakest specimen group (those with fibres aligned perpendicular to the load) had statistically significantly higher volumes of calcification when compared to those with a high fatigue life. Moreover, SEM imaging revealed that ruptured and damaged fibres presented binding sites for calcium to attach; resulting in more than 4 times the volume of calcification in fractured samples when compared to those which did not fail by fatigue. To the authors’ knowledge, this study quantifies for the first time, that mechanical damage drives calcification in commercial-grade GLBP and that this calcification varies spatially according to localised levels of damage. These findings illustrate that not only is calcification potential in GLBP exacerbated by fatigue damage, but that both failure phenomena are underpinned by the unloaded collagen fibre organisation. Consequently, controlling for GLBP collagen fibre architecture in leaflets could minimise the progression of these prevalent primary failure modes in patient BHVs.

It has been proposed that inappropriate positioning of transcatheter aortic valves (TAVs) is associated with procedural complications and decreased device durability. Second-generation TAVs allow for repositioning giving greater control over the final deployment position. However, the impact of positioning on the tissue surrounding these devices needs to be better understood, in particular for the interleaflet triangle in which the conductance system (bundle of His) resides. In this study, we investigate the impact of implantation depth on the frame-tissue interaction for a next-generation repositionable Lotus™ valve. For this purpose, a computational model simulating deployment of the Lotus valve frame into a calcified patient-specific aortic root geometry was generated to predict aortic root stress and frame eccentricity at three different deployment depths. The results of this study predicted that positioning of the Lotus valve had an influence on the stresses in the aortic sinus and frame eccentricity. An analysis of levels of stress arising in the vicinity of the bundle of His, as a function of implantation depth, was conducted, and it was found that, for the specific patient anatomy studied, although the sub-annular position showed reduced peak stress in the aortic sinus, this implantation position showed the highest stress in the area of greatest risks of conductance interference. In contrast, while a supra-annular position increased the peak arterial stress, this implantation position resulted in lower stress in the interleaflet triangle and thus might reduce the risk of conductance interference. These results provide pre-operative information that can inform clinical decision-making regarding TAVI positioning.

Bioprosthetic heart valves (BHVs) are implanted in aortic valve stenosis patients to replace the native, dysfunctional valve. Yet, the long-term performance of the glutaraldehyde-fixed bovine pericardium (GLBP) leaflets is known to reduce device durability. The aim of this study was to investigate a type of commercial-grade GLBP which has been over-looked in the literature to date; that of high collagen fibre dispersion (HD). Under uniaxial cyclic loading conditions, it was observed that the fatigue behaviour of HD GLBP was substantially equivalent to GLBP in which the fibres are highly aligned along the loading direction. It was also found that HD GLBP had a statistically significant 9.5% higher collagen content when compared to GLBP with highly aligned collagen fibres. The variability in diseased BHV delivery sites results in unpredictable and complex loading patterns across leaflets in vivo. This study presents the possibility of a shift from the traditional choice of circumferentially aligned GLBP leaflets, to that of high fibre dispersion arrangements. Characterised by its high fatigue life and increased collagen content, in addition to multiple fibre orientations, GLBP of high fibre dispersion may provide better patient outcomes under the multi-directional loading to which BHV leaflets are subjected in vivo.

Connacht was the only Irish province outside the penumbral aura of a Victorian-era Irish Football Association (IFA) division. Throughout the Gaelic Renaissance, this western province quintessentially represented the primitivistic and joyful aesthetic trope of Hy Brasil. It informed the transmundane thinking of those Celtophiles who classified soccer as a ‘garrison game'. Though the historiography of soccer in this isolated outpost is an impoverished habitus, within key urban sportive oubliettes resided sequestered soccer pioneers. This paper considers themes to include the introduction, agency, lucid diffusion and participation of the ‘socker code' in Connacht. Its inherently bottom-up organization, responses to top-down oppositional nativist fusillades, local mythos (often amid complex class and regional sporting allegiances) are expressed through multi-vocal identities and ethno-religious mentalities. The belated fin-de-siecle fizzle of rural soccer and veracity of perpetuated contentions regarding the ...

The durability of bovine pericardium leaflets employed in bioprosthetic heart valves (BHVs) can significantly limit the longevity of heart valve prostheses. Collagen fibres are the dominant load bearing component of bovine pericardium, however fibre architecture within leaflet geometries is not explicitly controlled in the manufacture of commercial devices. Thus, the purpose of this study was to ascertain the influence of pre-determined collagen fibre orientation and dispersion on the mechanical performance of bovine pericardium. Three tissue groups were tested in uniaxial tension: cross-fibre tissue (XD); highly dispersed fibre-orientations (HD); or preferred-fibre tissue (PD). Both the XD and PD tissue were tested under cyclic loading at 1.5 Hz and a stress range of 2.7 MPa. The results of the static tensile experiments illustrated that collagen fibre orientation and degree of alignment significantly influenced the material's response, whereby, there was a statistically significant decrease in material properties between the XD groups and both the PD and HD groups for ultimate tensile strength and stiffness (p 0.01). Furthermore, HD tissue had a stiffness of approximately 58% of the PD group, and XD tissue had a stiffness of approximately 18% of the PD group. The dynamic behaviour of the XD and PD groups was extremely distinct; for example a Weibull analysis indicated that the 50% probability of failure in specimens with fibres orientated perpendicular (XD) to the loading direction occurred at 375 cycles. Due to this failure, XD specimens survived on average less than 20% of the cycles completed by those in which fibres were aligned along the loading direction (PD). The results from this study indicate that fibre architecture is a significant factor in determining static strength and fatigue life in bovine pericardium, and thus must be incorporated in the design process to improve future device durability.

This article advances a synoptic monograph of the principal representations that particularise Ireland's wrestling arena from modern times to the twentieth century. Providing a delineated critique ...

Transcatheter aortic valve replacements (TAVRs) are a percutaneous alternative to surgical aortic valve replacements and are used to treat patients with aortic valve stenosis. This minimally invasive procedure relies on expansion of the TAVR stent to radially displace calcified aortic valve leaflets against the aortic root wall. However, these calcium deposits can impede the expansion of the device causing distortion of the valve stent and pericardial tissue leaflets. The objective of this study was to elucidate the impact of eccentric TAVR stent distortion on the dynamic deformation of the tissue leaflets of the prosthesis in vitro . Dual-camera stereophotogrammetry was used to measure the regional variation in strain in a leaflet of a TAVR deployed in nominal circular and eccentric (eccentricity index = 28%) orifices, representative of deployed TAVRs in vivo . It was observed that (i) eccentric stent distortion caused incorrect coaptation of the leaflets at peak diastole resulting in a ‘peel-back’ leaflet geometry that was not present in the circular valve and (ii) adverse bending of the leaflet, arising in the eccentric valve at peak diastole, caused significantly higher commissure strains compared with the circular valve in both normotensive and hypertensive pressure conditions (normotension: eccentric = 13.76 ± 2.04% versus circular = 11.77 ± 1.61%, p = 0.0014, hypertension: eccentric = 15.07 ± 1.13% versus circular = 13.56 ± 0.87%, p = 0.0042). This study reveals that eccentric distortion of a TAVR stent can have a considerable impact on dynamic leaflet deformation, inducing deleterious bending of the leaflet and increasing commissures strains, which might expedite leaflet structural failure compared to leaflets in a circular deployed valve.

Methane is the primary component of natural gas and a greenhouse gas, meaning that its presence in the atmosphere affects the earth's temperature and climate system. A new US-supported international partnership seeks to advance the recovery and use of methane as a clean energy source. The Methane to Markets Partnership is a public-private undertaking that involves sixteen national governments and more than 150 organizations committed to achieving economic, environmental and energy benefits. This paper provides an overview of the benefits of methane reduction and the goals and objectives of the Methane to Markets Partnership. In addition, it includes a discussion of the available opportunities and technologies for methane recovery and use in the coal, oil and gas, and landfill sectors. The paper concludes with some insights into the US government's involvement in the initiative and the methane emission reduction potential of the Partnership.

Although the route of sensitization to food allergens is still the subject of debate, it is generally accepted the gut immune system plays a pivotal role. However, hitherto the transport of allergens across the normal, pre-sensitized gut epithelium remained largely unknown. Our aim was to identify the route through which protein bodies and soluble proteins from digested peanuts penetrated the pre-sensitized gut epithelium in vivo and the specific cell types involved in the transport. Digestion of peanuts released a large number of protein bodies that are exclusively transported across the epithelium by specialized antigen-sampling M cells and delivered to the lymphoid tissue of Peyer's patch. Intracellular transport of soluble protein also occurred almost exclusively via M cells and it was negligible across absorptive enterocytes. We hypothesize that these conditions which are known to favour strongly the induction of immune responses rather than oral tolerance may play a significant role in the genesis of allergic reactions.

Previous mechanical studies using algae have concentrated on cell extension and growth using creep-type experiments, but there appears to be no published study of their failure properties. The mechanical strength of single large internode cell walls (up to 2 mm diameter and 100 mm in length) of the charophyte (giant alga) Chara corallina was determined by dissecting cells to give sheets of cell wall, which were then notched and fractured under tension. Tensile tests, using a range of notch sizes, were conducted on cell walls of varying age and maturity to establish their notch sensitivity and to investigate the propagation of cracks in plant cell walls. The thickness and stiffness of the walls increased with age whereas their strength was little affected. The strength of unnotched walls was estimated as 47+/-13 MPa, comparable to that of some grasses but an order of magnitude higher than that published for model bacterial cellulose composite walls. The strength was notch-sensitive and the critical stress intensity factor K1c was estimated to be 0.63+/-0.19 MNm(-3/2), comparable to published values for grasses.

Oligogalacturonates were produced by the limited enzymic hydrolysis of polygalacturonic acid and purified by ion-exchange chromatography. The fractions obtained were of limited polydispersity, determined by analytical ion-exchange chromatography. Oligomers with an average degree of polymerization of 10–15 were readily crystallized from aqueous salt solutions at neutral pH as single crystals. Crystal morphology of the salts examined, Na + , K + and Ca 2+ were characteristic of the salt. The wide-angle X-ray diffraction patterns obtained for the sodium salt were consistent with published fibre diffraction data of this salt form.

Poly(d,l)-lactide (PDLLA) homopolymer, with an average molecular weight of 20,000 daltons, was produced by the ring-opening polymerization of d,l-lactide in the presence of SnCl(2).2H(2)O as the catalyst. The PDLLA sponges loaded with chloramphenicol were prepared by a solvent evaporation technique. The drug loadings achieved were 14.84 and 25.23 mg for the PDLLA sponges with 35 and 70 mg total weights, respectively. These sponges were implanted in Wistar rats, and in vivo degradation, drug release, and tissue reactions were followed. The PDLLA sponges carrying no drug degraded with time linearly. Almost 80% of the sponges were degraded in about 180 days. While the drug-loaded PDLLA sponges were degraded much faster in 4 weeks (about 35% of the matrix was degraded), then the degradation slowed down significantly. Drug release from the sponges was parallel to the degradation. Almost 60% of the loaded drug released in 4 weeks. There were no acute inflammatory reactions in the initial period, either for the plain or for the drug-loaded PDLLA sponges. Macrophages and multinuclear giant cells start to appear after 7 days of implantation. The fibroblastic activity also started after the same period. After that, there were decreases in the number of some cells (neutrophils, lymphocytes, and macrophages), while multinuclear giant cells and fibroblastic activities gradually increased. Granulation tissue started at about 1 month, and new connective tissue was gradually formed until 180 days of implantation. There were significant numbers of inflammatory cells after 60 days, which were replaced by fibroblasts after 180 days. There was almost no significant neovascularization after 180 days, but implant fragmentation gradually increased (which slows the degradation) with time. It was concluded that this novel drug release sponge may be safely and effectively used as an active soft tissue-filling material.

The effect of an oil-soluble emulsifier upon adsorption properties of β-casein and β-lactoglobulin at the oil-water interface was studied. Addition of emulsifier improved the emulsification properties, but lowered emulsion stability. Higher concentrations decreased emulsification capacity, due to an increase in oil phase viscosity, and interfered with several protein assays, except the o-phthaldialdehyde (OPA) assay. Depletion measurements revealed that the emulsifier displaced β-casein more readily than β-lactoglobulin from the surface of droplets, which correlated with emulsification and stability measurements. Displacement of proteins was not complete due to emulsifier-induced formation of a multiple w-o-w emulsion, which accounted for the missing protein in the continuous phase.

Self expanding Transcatheter Aortic Valve Replacements (TAVR) can conform to the geometry of the aortic annulus and the calcified leaflet complex, which may result in leaflet distortion and altered leaflet kinematics, but such changes have not yet been characterized. In this study we developed a computational model to investigate the deployment of a self expanding TAVR in a realistic aortic root model derived from multi-slice computed tomography (MSCT) images. We simulated TAVR crimping/deployment in realistic and idealized aortic root models, followed by diastolic loading of the TAVR leaflets in its final deployed configuration. The TAVR deployed in a realistic aortic root had increased peak loading in the commissural region of the leaflets compared to TAVRs under idealized circular deployment conditions (2.97 vs. 1.52 MPa). Furthermore, orientation of the TAVR in the asymmetric aortic annulus such that the commissures of the TAVR are aligned with the native valve commissures minimized the effect of TAVR stent distortion on peak stresses in the TAVR leaflets (2.97 vs. 2.35 MPa). We propose that preoperative planning of the orientation of the TAVR in the aortic root annulus might minimize the impact of potential stent distortion on leaflet function and may in turn increase long term leaflet durability.

Patients with aortic stenosis present with calcium deposits on the native aortic valve, which can result in non-concentric expansion of Transcatheter Aortic Valve Replacement (TAVR) stents. The objective of this study is to evaluate whether eccentric deployment of TAVRs lead to turbulent blood flow and blood cell damage. Particle Image Velocimetry was used to quantitatively characterize fluid velocity fields, shear stress and turbulent kinetic energy downstream of TAVRs deployed in circular and eccentric orifices representative of deployed TAVRs in vivo. Effective orifice area (EOA) and mean transvalvular pressure gradient (TVG) values did not differ substantially in circular and eccentric deployed valves, with only a minor decrease in EOA observed in the eccentric valve (2.0 cm(2) for circular, 1.9 cm(2) for eccentric). Eccentric deployed TAVR lead to asymmetric systolic jet formation, with increased shear stresses (circular = 97 N/m(2) vs. eccentric = 119 N/m(2)) and regions of turbulence intensity (circular = 180 N/m(2) vs. eccentric = 230 N/m(2)) downstream that was not present in the circular deployed TAVR. The results of this study indicate that eccentric deployment of TAVRs can lead to altered flow characteristics and may potentially increase the hemolytic potential of the valve, which were not captured through hemodynamic evaluation alone.

This paper describes three different versions of left heart simulators that have been developed at the Cardiovascular Fluid Mechanics Laboratory at Georgia Institute of Technology, specifically designed to provide high fidelity experimental datasets necessary for rigorous validation of computational tools. These systems are capable of simulating physiological and pathological flow, pressure and geometric conditions, and can be investigated using a variety of experimental tools to measure relevant biomechanical quantities. The development of such robust simulators is a critical step in ensuring applicability of patient specific computational tools.Copyright © 2013 by ASME

Aortic stenosis is an age related degenerative disease of the aortic valve that causes narrowing of the valve and aortic regurgitation [1]. Transcatheter Aortic Valve (TAV) implantation is a percutaneous alternative to open heart surgery, which allows for the treatment of a cohort of patients for whom conventional surgery is deemed excessively risky due to high postoperative mortality rates or pre-existing illness [2].Copyright © 2013 by ASME

Patient specific computational analyses can aid in preoperative planning and long term evaluation of asymmetric deployed Transcatheter Aortic Valves (TAV) in calcified aortic annuli. In this study we developed and validated a preclinical computational tool to predict the performance of TAVs in vivo

The creaming behaviour of model pourable salad dressings has been studied over a wide range of xanthan and oil phase concentrations. They were produced by mixing a colloidally stable emulsion with xanthan solutions. The model dressings were completely flocculated by depletion at all xanthan concentrations >0.1 g/l. Creaming behaviour was in three phases: an initial delay phase, followed by more or less linear creaming and finally cream compression. Delayed creaming has not been reported previously. It is of great practical interest, because a complete absence of creaming is the aim of successful dressing formulation. The length of the delay phase was proportional to the emulsion concentration, inversely proportional to the oil/aqueous phase density difference and scaled over more than four orders of magnitude with the xanthan concentration to powers between 3 and 4. Traditionally, the stabilisation of salad dressing by xanthan is explained by the yield stress of its solutions. It is shown that they do not have one, and we offer an alternative explanation. It is suggested that the depletion flocculation of the emulsion droplets, induced by the addition of xanthan, leads to the formation of a particle network and that it is the time-dependent yield stress of this network which stabilises the dressing.

The aortic valve is responsible for controlling the unidirectional flow of blood within the heart during the cardiac cycle [1]. Aortic stenosis reduces the opening area of the valve, impeding blood flow and can lead to increased strain on the heart muscle, onset of early fatigue and heart failure. The disease is prevalent in the elderly population and is predicted to affect 88.5 million people by 2050 [2]. Open heart surgery to replace stenotic valves with either bioprosthetic or mechanical surgical valves is the current gold standard of care. However 30% of patients presenting with stenosis are refused this highly invasive surgery because of high postoperative mortality rates in elderly patients or those with pre-existing illnesses [2]. Transcatheter Aortic Valves (TAV) are an alternative to conventional heart valve surgery [2, 3–4], which use minimally invasive techniques to replace stenotic valves. TAV’s consist of tissue leaflets on a self or balloon expandable percutaneous valve stent which is deployed via a transfemoral or transapical based approach. Owing to the fact that the first CE certification of a TAV (Edwards SAPIEN) was only in 2010 and received FDA approval for clinical trials in 2011, the long term performance of implanted TAV’s is as of yet unknown.Copyright © 2012 by ASME

We report a study of the creaming behavior of an alkane-in-water emulsion at varying oil volume fractions in the presence of the nonadsorbing polymer, hydroxyethylcellulose (HEC). Pairwise interaction potentials predict a shallow secondary minimum for this system arising from the attractive potential produced by the so-called depletion effect. Use of an ultrasonic creaming monitor has allowed us to verify the predicted flocculation and quantify the separation of the system into colloidrich and colloid-poor phases. The phase diagram for 20.2% v/v oil and varying polymer concentrations has been determined. At 0.02% w/w HEC we have investigated the effect of oil volume fraction on the phase composition of the system. The observed behavior has been compared with that predicted from the available theoretical treatments for phase separation but with due regard to the possible effects of polydispersity.

International audience; Low density lipoproteins (LDL) from egg yolk have a classical structure of lipoprotein with a core of neutral lipids surrounded by a monolayer of apoproteins and phospholipids. This structure collapses during adsorption and all constituents spread at the interface. To understand better the nature of the interactions between apoproteins and lipids at the interface, we have deposited LDL at an air-water interface and analysed the isotherms during their compression on a Langmuir trough. Then, these LDL films were studied by atomic force microscopy (AFM) imaging. To identify the protein and lipid structures, we imaged films before and after lipid solubilisation by butanol. To study the interactions in the LDL films, we have varied the pH, ionic strength and used simplified model systems. We also studied the correlation between observed structures and interfacial rheology of the film. The isotherms of interfacial LDL films were similar for pH 3 and 7, but their structures observed in AFM were different. At surface pressures below the transition corresponding to the demixion of apoprotein-neutral lipid complexes, the LDL film structure was not governed by electrostatic interactions. However, above this surface pressure transition (45mN/m), there was an effect of charge on this structure. Around the transition zone, the rheological properties of LDL films at pH 3 were different as a function of pH (viscous at pH 3 and visco-elastic at pH 7). So, the rheological properties of LDL films could be linked to the structures formed by apoproteins and observed in AFM.

The displacement of the proteins (beta-lactoglobulin and beta-casein) from an air-water interface by the nonionic (Tween 20 and Tween 60) and ionic (sodium dodecyl sulfate, cetyltrimethylammonium bromide, and lyso-phosphatidylcholine-lauroyl) surfactants has been visualized by atomic force microscopy (AFM). The surface structure has been sampled by the use of Langmuir-Blodgett deposition onto mica substrates to allow imaging in the AFM. In all cases, the displacement process was found to occur through the recently proposed orogenic mechanism (Mackie et al. J. Colloid Interface Sci. 1999, 210, 157-166). In the case of the nonionic surfactants, the displacement involved nucleation and growth of surfactant domains leading to failure of the protein network and subsequent loss of protein into the bulk phase. The surface pressure dependence of the growth of surfactant domains and the failure of the network were found to be the same for both Tween 20 and Tween 60, demonstrating that the breakdown of the protein film was dominated by the mechanical properties of the network. The displacement of protein by ionic surfactants was found to be characterized by nucleation of surfactant domains with little domain growth prior to failure of the network. The size of the domains formed by ionic surfactants was found to be limited by the strong intersurfactant repulsive forces between the charged headgroups. Screening of these charges led to an increase in the size of the domains. The surface pressure at which the network continuity was lost was found to be dependent on the type of surfactant and, in all cases, to occur at higher surface pressures than that required for nonionic surfactants. This has been attributed to surfactant-protein binding that initially strengthens the protein network at low surfactant concentrations. Evidence obtained from surface shear rheology supports this assertion.

Atomic force microscopy (AFM) has been used to investigate the displacement of a commercial whey protein system and the behavior as compared to that of beta-lactoglobulin (Mackie, A. R.; Gunning, A. P.; Wilde, P. J.; Morris, V. J. Orogenic displacement of protein from the air-water interface by competitive adsorption. J. Colloid Interface Sci. 1999, 210, 157-166). The whey protein isolate (WPI) was displaced from an air-water interface by the surfactants Tween 20 and Tween 60. Displacement data obtained were compared with data obtained for pure beta-lactoglobulin and have shown that WPI was more resistant to displacement from the air-water interface than native beta-lactoglobulin. This was related to the greater surface elasticity of WPI at higher surface stresses. In the presence of Tween 20, WPI was observed to remain on the interface at surface pressures up to 8 mN/m greater than the surface pressure at which complete displacement of beta-lactoglobulin was observed. Displacement of WPI and beta-lactoglobulin films by the surfactant Tween 60 showed similar results. However, because of the lower surface activity of Tween 60, it was not possible to reach surface tension values similar to those obtained for Tween 20. Despite the lower surface activity of Tween 60, WPI was still observed to be present at the interface at surface pressure values greater than those by which beta-lactoglobulin had been completely displaced.

The effects of water content and temperature variation on the release of flavor components into the headspace over flavors, encapsulated by an extrusion process, in low water content carbohydrate matrixes is studied. The largest amounts of release occurred when the matrix was above its glass transition temperature, whether this was due to increased water content or elevated temperature. Under these conditions up to 70% of the sucrose in the matrix crystallized over a period of 10 days, as quantified using Fourier transform Raman spectroscopy. Smaller amounts of headspace release occurred when the water content of the encapsulated flavor system was decreased from 3. 5 to 3.1% w/w. Small amounts of release occurred from the "as prepared" materials, which were associated with the presence of small amounts of unencapsulated flavor oil with direct access to the headspace. It was concluded that release due to matrix permeability was relatively slow as compared with the above mechanisms.

Atomic force microscopy (AFM) has been used to image interfacial films of bovine serum albumen and beta-casein produced at hexadecane/water and air/water interfaces, respectively. Planar oil/water and air/water interfaces have been used to model protein films such as may form in emulsions and foams. The protein films were picked up onto mica sheets and imaged under butanol. Both systems studied yielded homogeneous flat networks which could be imaged at molecular resolution and which demonstrate the potential for using AFM to probe interfacial networks.

The growth rates and yields of Listeria monocytogenes and Yersinia enterocolitica were determined in liquid culture media, and in model oil-in-water emulsions that contained 30, 70 or 83% (v/v) hexadecane. In emulsions with a mean droplet size of 2 microns containing 83% (v/v) hexadecane, the growth of both organisms resulted in decreased yields. Additionally, in these emulsions adjusted to pH 5.0 or 4.4 the growth rate of L. monocytogenes was significantly less than in other model systems which had an aqueous phase of equivalent chemical composition. Microscopic examination of the 83% (v/v) emulsion showed that its microstructure immobilized the bacteria, which were constrained to grow as colonies. Bacteria behaved similarly in model emulsions of either hexadecane or sunflower oil. Manipulation of the droplet size distribution of the emulsions changed the form and rate of growth of bacteria within them.

Methods are presented for investigating the site and form of growth of bacteria in model oil-in-water emulsions and in dairy cream. Following growth of the bacteria, the continuous aqueous phase is gelled using agarose and the oil phase removed using a mixture of chloroform and methanol. Using this method, the authors have found that Listeria monocytogenes, Salmonella typhimurium and Yersinia enterocolitica grow in the form of colonies in concentrated oil-in-water emulsions. Colonies of L. monocytogenes and Y. enterocolitica also form in artificially-inoculated fresh and tinned dairy cream. If information about the precise site of growth is not required, the authors have discovered that intact colonies can be liberated from the model emulsions by dissolving away the oil phase with chloroform: methanol.

PEG based hyperbranched copolymers have been synthesised using a high concentration of ethylene glycol dimethacrylate (EGDMA) as the branching agent (up to 10% molar ratio of total feed monomers) via a new in situ deactivation enhanced atom transfer radical polymerisation (DE-ATRP). These hyperbranched copolymers exhibited a lower critical solution temperature (LCST) close to body temperature and photo-crosslinkable behavior.

Publisher Summary Many foods are emulsions during or after manufacture. In oil-in-water emulsions, the dispersed oil droplets generally possess a lower density than the continuous aqueous phase. Unless the droplets are very small or the emulsion is very concentrated, the density difference leads to the gradual accumulation of the droplets at the top of the container (creaming) with consequent loss of perceived quality. Polysaccharide stabilizers are frequently used to reduce the rate of creaming as well as to impart the required mouth-feel properties to a food product. This chapter presents a paper that presents creaming results for n-alkane-in-water emulsions containing the polysaccharide hydroxyethylcellulose. The analysis of the data in the paper draws heavily on the work of A. S. Michaels and J. C. Boiger, who investigated the sedimentation behavior of flocculated kaolin suspensions. Their treatment includes general descriptions of flocculated systems and it has been found to be a useful starting point for the preliminary analysis of the results presented in the paper.

The creaming of concentrated alkane-in-water emulsions stabilised by a non-ionic surfactant has been measured in the presence of hydroxyethylcellulose polysaccharide. Creaming rates under gravity were determined by visual observation. In the emulsions containing polysaccharide the creaming was much more rapid than expected from consideration of the oil droplet size, density difference, the rheological properties of the continuous phase and the current oil concentration. Flocculation effects would appear to be the primary mechanism for the anomalous behaviour, although other effects cannot be entirely ruled out at this stage. The final oil concentrations in the creamed emulsion phases have also been measured, and an interpretation is given in terms of the pressure in the cream, the droplet size and the interfacial tension.

The anionic polysaccharide xanthan, widely used as a stabilizer in food dispersions, induces flocculation by a depletion mechanism. The effect of flocculation, induced by the presence of xanthan, on the gravitational destabilization (creaming and compaction) of 20% oil-in-water emulsions is presented. The detailed gravitational destabilization processes are studied by following changes in the concentration profile with time. In the absence of flocculant the polydisperse droplets rise as a diffuse meniscus and form a cream of ~70% oil at the top of the sample. Such behaviour is consistent with creaming in a dispersion of non-interacting polydisperse particles. In contrast the flocculated droplets form a sharp meniscus and cream rapidly. At the top of the sample the floes form a less concentrated cream which undergoes compaction under gravity. The compaction is characterized by a concentration-dependent bulk modulus.

La mesure de la vitesse de passage des ultrasons permet l'evaluation de la sedimentation/cremage dans les dispersions. L'etude, en fonction de la concentration de l'emulsion, permet d'analyser le mecanisme de separation et, dans certains cas, les proprietes de la couche sediment/creme. Application aux produits laitiers