Small intestinal submucosa as a vascular graft: a review

Continuing investigations of vascular graft materials suggest that unacceptable graft complications continue and that the ideal graft material has not yet been found. We have developed and tested a biologic vascular graft material, small intestine submucosa (SIS), in normal dogs. This material, when used as an autograft, allograft, or xenograft has demonstrated biocompatibility and high patency rates in aorta, carotid and femoral arteries, and superior vena cava locations. The grafts are completely endothelialized at 28 days post-implantation. At 90 days, the grafts are histologically similar to normal arteries and veins and contain a smooth muscle media and a dense fibrous connective tissue adventitia. Follow-up periods of up to 5 years found no evidence of infection, intimal hyperplasia, or aneurysmal dilation. One infection-challenge study suggested that SIS may be infection resistant, possibly because of early capillary penetration of the SIS (2 to 4 days after implantation) and delivery of body defenses to the local site. We conclude that SIS is a suitable blood interface material and is worthy of continued investigation. It may serve as a structural framework for the application of tissue engineering technologies in the development of the elusive ideal vascular graft material.     

Time-Dependent Behavior of Ceramic (Zirconia)-Metal (NiCoCrAlY) Particulate Composites

The estimation of time-dependent properties for ceramic-metal mixturesis important for analyzing the effects of thermal loading oncompositionally graded thermal barrier coatings. A mean fieldmicromechanics approach is developed to compute effective time-dependentproperties of ceramic (zirconia)-metal (NiCoCrAlY) particulate compositematerials. These properties are then used to predict the transientthermal stresses in these composites when they are subjected to thermalshock. These thermal stresses include the effects of time-dependentmaterial response.     

On the use of the finite element method for the solution of a cracked strip under thermal shock

The finite element method is used to solve the problem of a strip containing a crack and subjected to a thermal shock on one edge. The solution of the edge crack problem is compared to the exact solution and it is shown that the FEM yields results with less than 1% error. The dependence of the accuracy of the solution on the time increment is examined. The problem of a strip containing an internal crack is then solved using the FEM. The effects of the Biot number, the length of the crack and the distance of the crack to the edge of the strip, on the transient stress intensity factors are analyzed.     

Transient thermoelastic fracture of interface cracks: Effect of bending restraints

The behavior of an interface crack at the center and at the edge of a restrained, bimaterial structure subjected to transient thermal loads is studied. A linear, elastic fracture analysis is used to determine the effects of material property and layer thickness ratio on the transient strain energy release rates. Quantitative comparisons for a range of moduli one order of magnitude either side of equality are tabulated for equal sized material on either side of the crack in terms of the near tip displacements and strain energy release rates.     

Phase Behavior of a Meat-Starch Extrudate Illustrated on a State Diagram

ABSTRACT: The phase behavior of a meat-starch extruded system was illustrated on a state diagram. A mixture of meat and potato granules (1.48:1) was extruded with a twin-screw extruder. The extrudates were equilibrated at relative humidities between 0 to 88% and their glass transitions were determined.
Starch and proteins were phase separated at macromolecular level and retained their own phase transitions. The state diagram of the system showed that proteins dictated the texture of the mixed system, with starch contributing to the high value of the mechanical properties. Water had a plasticizing effect on both biopolymers. At room temperature, the extrudates with aw < 0.32 were glassy, while those with aw > 0.57 were rubbery.     

In situ Raman cell for high pressure and temperature studies of metal and complex hydrides

A novel cell for in situ Raman studies at hydrogen pressures up to 200 bar and at temperatures as high as 400 °C is presented. This device permits in situ monitoring of the formation and decomposition of chemical structures under high pressure via Raman scattering. The performance of the cell under extreme conditions is stable as the design of this device compensates much of the thermal expansion during heating which avoids defocusing of the laser beam. Several complex and metal hydrides were analyzed to demonstrate the advantageous use of this in situ cell. Temperature calibration was performed by monitoring the structural phase transformation and melting point of LiBH(4). The feasibility of the cell in hydrogen atmosphere was confirmed by in situ studies of the decomposition of NaAlH(4) with added TiCl(3) at different hydrogen pressures and the decomposition and rehydrogenation of MgH(2) and LiNH(2).     

Design and scaling of wheat dough extrusion by numerical simulation of flow and heat transfer

This paper proposes a computational method to obtain simultaneous scale-up of mixing and heat transfer in single screw extruders by several parametric 3D non-isothermal numerical simulations. The numerical experiments of flow and heat transfer modeling studies are conducted using the Mackey and Ofoli [Cereal Chem. 67 (1990) 221] viscosity model for low to intermediate moisture wheat doughs in the metering section of a single screw extruder. The non-isothermal flow model includes viscous dissipation and the complete three-dimensional flow geometry including leakage flows without any simplifications such as unwinding the screw. Based on Rauwendaal [Polymer Extrusion, Hanser Publishers, New York, 1986] residence time distribution (RTD) and specific mechanical energy (SME) were chosen as the design parameters for the scale-up of mixing and heat transfer respectively. Parametric numerical simulations were conducted by varying screw geometric variables such as helix angle, channel depth, screw diameter to channel depth ratio, screw length to screw diameter ratio, and the clearance between the screw flights and barrel. SME and RTD curves vs. screw parameters were developed from the numerical simulations. From the design charts two differently sized extruders were obtained which had a scale-up of about 10 times based on throughput rates but had the same RTD and SME.