A semi-analytic boundary element method for parabolic problems

A new semi-analytic solution method is proposed for solving linear parabolic problems using the boundary element method. This method constructs a solution as an eigenfunction expansion using separation of variables. The eigenfunctions are determined using the dual reciprocity boundary element method. This separation of variables-dual reciprocity method (SOV-DRM) allows a solution to be determined without requiring either time-stepping or domain discretisation. The accuracy and computational efficiency of the SOV-DRM is found to improve as time increases. These properties make the SOV-DRM an attractive technique for solving parabolic problems.     

Evaluation of in vitro stability of large unilamellar liposomes coated with a modified polysaccharide (O-palmitoylpullulan)

Aiming at encapsulation of a hydrosoluble drug, large unilamellar liposomes (LUV) of egg phosphatidylcholine (PC) were coated with a natural polysaccharide derivative, O-palmitoylpullulan (OPP), and its in vitro stability evaluated using fluorescent probes. This coating (in OPP/PC weight ratio of 3) improved significantly the in vitro stability of LUV by decreasing both the permeability and fluidity of the liposomal membrane.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Adhesion, growth and differentiation of human bone marrow stromal cells on non-porous calcium carbonate and plastic substrata: effects of dexamethasone and 1,25dihydroxyvitamin D3

Bone marrow contains stromal fibroblastic stem cells which have the potential to differentiate into bone-forming cells. Therefore addition of bone marrow to porous bone substitutes such as coral or coralline hydroxyapatite may be expected to enhance bone ingrowth into these implants. This study was designed to evaluate the possibility of growing human bone marrow stromal fibroblastic cells (HBMC) on a calcium carbonate substrate. For this purpose, HBMC were cultured for 20 days on plastic or calcium carbonate and cell adhesion, growth, and differentiation were studied. It was concluded that calcium carbonate is a highly compatible material for the growth of HBMC. Cells were capable of adhesion within 30 min and were spread within 24 h on this material. However, plating efficiency was decreased in comparison to plastic. Population doubling times (PDT) showed that they were similar when the cells were grown on plastic or calcium carbonate as substratum (PDT=4, 5.5 days). Early protein synthesis included collagen I, collagen III, osteopontin and bone sialoprotein. To induce differentiation of HBMC on plastic and calcium carbonate the influence of dexamethasone (Dex) and 1,25dihydroxyvitamin D3 (1,25(OH)₂D₃) on alkaline phosphatase (ALP) expression was studied. Basic ALP activity was similar when cells were grown on plastic or calcium carbonate. However, Dex and 1,25(OH)₂D₃ increased ALP activity of HBMC which could be driven best towards osteogenesis in the presence of Dex and 1,25(OH)₂D₃.     

Characterization of titanium alloy implant surfaces with improved dissolution resistance

The present work sets out to investigate the structure and chemistry of surface treated oxides (either aged in boiling water or air-heated) with improved dissolution resistance compared to conventionally passivated surfaces. X-ray photoelectron spectroscopy (XPS) has demonstrated a significant reduction in oxidized aluminium associated with an ageing-based surface treatment. Angle-dependent XPS has revealed an increase in amphoteric-OH surface sites for the thermal treatments. Atomic force microscopy (AFM) investigation suggests that these sites play a role in the improved proteinadsorption properties of these surfaces. These observations form the basis of a model which describes the influence of surface oxide on the kinetics of metal ion dissolution.     

Sterilization of heparinized Cuprophan hemodialysis membranes

The effects of sterilization of dry heparinized Cuprophan hemodialysis membranes by means of ethylene oxide (EtO) exposure, gamma irradiation, or steam on the anticoagulant activity and chemical characteristics of immobilized heparin and the permeability of the membrane were investigated. Sterilization did not result in a release of heparin or heparin fragments from heparinized Cuprophan. Sterilization of heparinized Cuprophan by means of EtO exposure and gamma irradiation induced a slight, insignificant decrease of the anticoagulant activity. In contrast, steam-sterilized heparinized Cuprophan showed a higher anticoagulant activity than unsterilized heparinized Cuprophan, which was most likely caused by cleavage of some of the covalent bonds between heparin and Cupropha. The effects of sterilization on the permeability of unmodified Cuprophan and heparinized Cuprophan were compared. The permeability of unmodified Cuprophan for vitamin B₁₂ (Vit B₁₂) and sulfobromophthalein (SBP) was reduced by 20–35% after EtO exposure and gamma irradiation and was reduced by 90–95% after steam sterilization. The water permeability of unmodified Cuprophan remained the same after EtO exposure and gamma irradiation but also dramatically reduced after steam sterilization. These reductions were ascribed to the collapse of pores of the membrane. The permeability of heparinized Cuprophan was not affected by EtO exposure and gamma irradiation but dramatically reduced after steam sterilization, although to a lesser extent than in the case of unmodified Cuprophan. Apparently, the presence of immobilized heparin (partially) prevented the collapse of pores during sterilization. Gamma irradiation was recommended as the preferred method of sterilization for heparinized Cuprophan.     

Improvement of Concrete Properties and Reinforcing Steel Inhibition Using a Natural Product Admixture

The use of a natural white juice, taken from magrabe banana stem, as concrete admixture to improve mechanical and physicrvchemical properties of concrete has been studied. The compressive strength, bulk density the free lime liberated during hydration and the combined water content were determined. The results indicate that the admixture acts as a retarder in most cases and as accelerator in some ones. Also, the admixture effect on the corrosion resistance of the reinforcing steel against surrounding aggressive media has been investigated using galvanostatic polarization technique. The addition of 0.2% admixture leads to the more inhibition of the steel     

INSTRUMENTATION FOR FLOW PROPERTIES OF GAS-SOLID SUSPENSIONS AND RECENT ADVANCES

Measurements of local velocity, density, and mass flow of phases of a gas-solid suspension are needed in determining transport properties, validating theoretical predictions, and formulating design procedures. Most of the available instruments are based on time averages or fluctuations with time. Primary standard for direct measurement of density of a phase such as solid particles is being developed. A laser phase Doppler device, within certain restrictions, may give local instantaneous density, while other optical methods and neutron beam remain secondary standards based on mass flow calibrations. An overall review including recent results has been made on both intrusive and non-intrusive instruments; their limitations and future possibilities are outlined and discussed. The limitations of the traditional approach utilizing the triangular relation between local averages of mass flow, velocity, and density of particles for the determination of flow properties, and higher order correlations are demonstrated.