Robert L. Shambaugh

Flow Perfusion Improves Seeding of Tissue Engineering Scaffolds with Different Architectures

Engineered bone grafts have been generated in static and dynamic systems by seeding and culturing osteoblastic cells on 3-D scaffolds. Seeding determines initial cellularity and cell spatial distribution throughout the scaffold, and affects cell–matrix interactions. Static seeding often yields low seeding efficiencies and poor cell distributions; thus creating a need for techniques that can improve these parameters. We have evaluated the effect of oscillating flow perfusion on seeding efficiency and spatial distribution of MC3T3-E1 pre-osteoblastic cells in fibrous polystyrene matrices (20, 35 and 50-μm fibers) and foams prepared by salt leaching, using as controls statically seeded scaffolds. An additional control was investigated where static seeding was followed by unidirectional perfusion. Oscillating perfusion resulted in the most efficient technique by yielding higher seeding efficiencies, more homogeneous distribution and stronger cell–matrix interactions. Cell surface density increased with inoculation cell number and then reached a maximum, but significant detachment occurred at greater flow rates. Oxygen plasma treatment of the fibers greatly improved seeding efficiency. Having similar porosity and dimensions, fibrous matrices yielded higher cell surface densities than foams. Fluorescence microscopy and histological analyses in polystyrene and PLLA scaffolds demonstrated that perfusion seeding produced more homogeneous cell distribution, with fibrous matrices presenting greater uniformity than the foams.

DISCHARGE COEFFICIENTS FOR COMPRESSIBLE FLOW THROUGH SMALL-DIAMETER ORIFICES AND CONVERGENT NOZZLES

Abstract This paper presents a study of the compressible-flow behavior of light gases through small orifices and convergent nozzles with diameters ranging from 0.9 to 1.9 mm. The subsonic and critical-flow regions for 16 orifice and nozzle flow elements with the following geometries have been tested experimentally: sharp or knife-edge orifices, straight-bore orifices, rounded-entry nozzles, and elliptical-entry nozzles. Air flow was primarily studied, but data for carbon dioxide, argon, helium, and two distinct argon-helium mixtures were also collected. In addition, the upstream temperature was varied from 295 to 700 K. The data have been reduced for correlation purposes to a discharge coefficient defined as the fraction of the isentropic, adiabatic mass flow rate attained by real fluids in an actual orifice or nozzle. An error analysis shows that the reported discharge coefficients are accurate to ± 1.2% for air flow and ± 1.6% for the other gases studied. The discharge coefficient for knife-edge orifices correlates very well with a dimensionless pressure drop for the entire range of diameters, gases, pressures and temperatures studied. The discharge coefficient does not correlate with the throat Reynolds number for compressible flow through knife-edge orifices. Moreover, an analogous behavior of the discharge coefficient for larger diameters than those tested is expected for knife-edge and thin-plate orifices. Straight-bore orifices, with length-to-diameter ratios close to or slightly greater than unity, yield discharge coefficients which are approximately independent of flow rate, upstream temperature, and gas properties. These discharge coefficients are, however, highly sensitive to the length-to-diameter ratio of the straight bore. Finally, the discharge coefficients for both rounded- and elliptical-entry nozzles correlate well with a throat Reynolds number. The correlation shows that as the Reynolds number is decreased the discharge coefficient drops precipitously for Re Re > 20,000 the discharge coefficient increases slowly with increasing Reynolds number. This behavior is consistent with both previous data and fluid dynamics theory for rounded- and elliptical-entry nozzles.

Investigation of gravity-spun, melt-spun, and melt-blown polypropylene fibers using atomic force microscopy

The morphology exhibited in a polymer depends on the particular process and processing conditions used to shape and modify the polymer. This morphology has an important influence on the final polymer product (sheet, molded part, etc.). Ten years ago, atomic force microscopy (AFM) was applied for the first time on polymer materials. Since then, AFM has been used extensively on polypropylene (PP) surfaces, but still very little has been reported on the use of AFM for analyzing PP fibers. The purpose of our work was to show the modifications of (a) the morphology and (b) the microstiffness of PP fiber surfaces processed under different operating conditions. Three fiber production processes were used: gravity spinning, melt spinning, and melt blowing.

Image-based modeling: A novel tool for realistic simulations of artificial bone cultures

Computational modeling has been promulgated as a means of optimizing artificial bone tissue culturing ex vivo. In the present report, we show, as a proof-of-concept, that it is possible to model the exact microenvironment within the scaffolds while accounting for their architectural complexities and the presence of cells/tissues in their pores. Our results clearly indicate that image-based modeling has the potential to be a powerful tool for computer-assisted tissue engineering.

Use of CFD to Design a Melt Blowing Die

Computational Fluid Dynamics (CFD) can play an important role in understanding the flow field below two converging rectangular jets. Each rectangular nozzle has a large length to width ratio, and the nozzles are parallel and very close to each other. This design is used in practical applications to produce polymeric fibers in the process known as melt blowing. In this paper we use turbulence models available in the CFD software Fluent 5.0 to study the detailed flow field. We also use experimental measurements to compare with the simulation results, and we test altemative die designs with the goal of identifying those that perform better.Copyright