Polyurethanes as potential substrates for sub-retinal retinal pigment epithelial cell transplantation

Transplantation of cultured retinal pigment epithelial (RPE) cells under the failing macular is a potential treatment for age related macular degeneration. An important step in the development of this procedure is the identification of a suitable membrane on which to grow and transplant the cells. This paper evaluates the potential of using polyurethanes in this application since they possess several of the required properties, such as, flexibility, robustness, biostability and good biocompatiblilty although their hydrophobicity can limit cell adhesion. Three commercially available polyether urethanes (Pellethane, Tecoflex and Zytar) were evaluated in terms of their wettability using dynamic contact angle analysis and their ability to support a monolayer of functioning RPE cells (ARPE-19) . Furthermore Pellethane and Tecoflex were treated with a simple air plasma treatment and analysed as above. In the "as received condition" only a few RPE cells attached to the Pellethane and Tecoflex and remained clumped. RPE cells grew to confluence on the Zytar substrate by 7 days without further surface modification. Air gas plasma treatment of both Pellethane and Tecoflex increased the wettability of the surfaces and this resulted in the growth of a monolayer of well-spread RPE cells on both materials. Morphologically these cells grew with a normal 'cobblestone' phenotype. These results demonstrate the potential of these polyurethanes for this application.     

A note on the optimum design of four bar crank-rocker mechanismsNote sur le calcul optimum des mécanismes a quatre barres avec une manivelle

In this paper, the classical transmission angle problem is discussed from a general approximation point of view. It is shown that the least square and Chebyshev optimizations are two closely related approaches to this problem. A least square optimum solution to this problem is investigated by means of a parametric representation for the link lengths, and results are compared with those available in literature. It is found that the computations for the least square method can be easily performed by using a pocket calculator.     

Learning with a mutualistic teacher

The concept of a “mutualistic teacher” is introduced for unsupervised learning of the mean vectors of the components of a mixture of multivariate normal densities, when the number of classes is also unknown. The unsupervised learning problem is formulated here as a multi-stage quasi-supervised problem incorporating a cluster approach. The mutualistic teacher creates a quasi-supervised environment at each stage by picking out “mutual pairs” of samples and assigning identical (but unknown) labels to the individuals of each mutual pair. The number of classes, if not specified, can be determined at an intermediate stage. The risk in assigning identical labels to the individuals of mutual pairs is estimated. Results of some simulation studies are presented.     

Effect of mastication on molecular weight and molecular weight distribution of EPDM polymer and SBR

EPDM and SBR were masticated on an open mill. The temperature range of mastication for EPDM was 68–480°F. SBR was milled at 170–200°F. The gel-permeation chromatography analyses were made on the masticated samples. For EPDM at 68°F, molecular weight decreases and molecular weight distribution narrows with mastication time; the degradation process is nonrandom. At constant mastication time between 182 and 315°F, there is little change in molecular weight. Mastication for 18 min at 480°F broadens the molecular weight distribution; the degradation is random. For SBR at 170–200°F, molecular weight decreases and molecular weight distribution narrows with mastication time; the degradation process is also nonrandom. Nonrandom degradation for both EPDM and SBR results in a narrowing of the molecular weight distribution, without build-up of low molecular weight molecules, and without a shift in the peak molecular weight. This is contrary to nonrandom degradation of natural rubber where a shift in the peak molecular weight occurs with mastication time.     

Natural plant enzyme inhibitors. Isolation and characterisation of two α-amylase inhibitors from Colocasia antiquorum tubers

Two α-amylase inhibitors I-1 and I-2, were purified to homogeneity from Colocasia antiquorum tubers by extraction with 0.02m phosphate buffer pH 7.6, treatment with diethyl amino ethyl-cellulose, ammonium sulphate fractionation, chromatography on Sephadex G-50 and chromatography on phenyl sepharose CL-4B. Both the inhibitors were basic proteins. I-1 alone contained carbohydrates to the extent of 5.4%. The molecular weights of I-1 and I-2 were found to be about 14 300 and 12 500, respectively, by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The inhibitors inactivated human salivary, human pancreatic and hog pancreatic amylases but they had no action on Bacillus subtilis and Aspergillus oryzae amylases and resisted attack by pepsin, trypsin, chymotrypsin and pronase. Chemical modification of amino groups and guanidino groups of I-1 and I-2 resulted in loss of inhibitory activities. Formation of enzyme inhibitor complexes between hog pancreatic amylase, I-1 and I-2 were demonstrated by gel chromatography on Sephadex G-100. Total amylase inhibitory activity in Colocasia tubers decreased gradually during plant growth.     

An alternate form of the ramberg-osgood formula for matrix displacement analysis

A new stress-strain law, which is a three parameter representation of stress in terms of strain has been proposed for the matrix displacement analysis of structures made of non-hookean materials. This formula has been utilized to study three typical problems. These studies brought out the effectiveness and suitability of this law for matrix displacement analysis.     

Process Intensification of Biodiesel Production Using a Tubular Micro-Reactor (TMR): Experimental and Numerical Assessment

The aim of this paper is to present an alternative to conventional biodiesel production by taking advantage of the flow patterns formed in micro-reactors. Biodiesel production was carried out 15 times faster in a tubular micro-reactor (TMR) than a well-mixed batch reactor (BR), achieving conversions up to ～99% with 4?min of residence time. The experimental results were analyzed using dimensionless numbers and computational fluid dynamics (CFD) simulations. The CFD results showed that under the conditions used in the present study, the slug flow pattern can be expected, and this could explain the high conversion (>90%) reached in the TMR without using high methanol-oil molar ratios. The internal movement (auto-mixing) in the slug enhanced the mass transfer. Moreover, CFD simulations showed that at low conversion (<25%), the internal velocity of the oil slug will be the key factor related to the reactor performance.     

Preparation,Characterization and Assessment of the Novel Gelatin–tamarind Gum/Carboxymethyl Tamarind Gum-Based Phase-Separated Films for Skin Tissue Engineering Applications

The current study delineates the development of novel gelatin–tamarind gum/carboxymethyl tamarind gum-based phase-separated films for probable skin tissue engineering applications. Polyethylene glycol was used as plasticizer. The films were characterized thoroughly using mechanical tester and impedance analyzer. Cell proliferation ability and drug release properties of the films were investigated. Mechanical studies indicated composition-dependent stress relaxation properties. Polysaccharide containing films supported better proliferation of human keratinocytes as compared to control. Drug-loaded films showed good antimicrobial properties against Escherichia coli. Analysis of the results indicated that the prepared films may be tried as matrices for skin tissue engineering.