David DiBiasio

Comparison of Chondrogensis in Static and Perfused Bioreactor Culture

As a result of the low yield of cartilage from primary patient harvests and a high demand for autologous cartilage for reconstructive surgery and structural repair, primary explant cartilage must be augmented by tissue engineering techniques. In this study, chondrocytes seeded on PLLA/PGA scaffolds in static culture and a direct perfusion bioreactor were biochemically and histologically analyzed to determine the effects of fluid flow and media pH on matrix assembly. A gradual media pH change was maintained in the bioreactor within 7.4−6.96 over 2 weeks compared to a more rapid decrease from 7.4 to 6.58 in static culture over 3 days. Seeded scaffolds subjected to 1 μm/s flow demonstrated a 118% increase (p < 0.05) in DNA content, a 184% increase (p < 0.05) in GAG content, and a 155% (p< 0.05) increase in hydroxyproline content compared to static culture. Distinct differences were noted in tissue morphology, including more intense staining for proteoglycans by safranin‐O and alignment of cells in the direction of media flow. Culture of chondrocyte seeded matrices thus offers the possibility of rapid in vitro expansion of donor cartilage for the repair of structural defects, tracheal injury, and vascularized tissue damage.

Evaluation of a spiral curriculum for engineering

This paper discusses results of the first two offerings of an experimental and innovative first-year chemical engineering curriculum. The curriculum is project-based in that it emphasizes learning through engagement in open-ended projects from early in the curriculum. It is spiral in that it revisits concepts periodically with increasing sophistication throughout the curriculum. The curriculum is intended to increase technical proficiency, communication and teamwork skills, and identification with chemical engineering as a major and profession. This paper reports results attained through comparison of students from experimental and traditional course sequences with regard to these objectives.

Stability of continuous culture with recombinant organisms

It was found that both poor selection pressure and a variable rate of plasmid loss were present in the system studied and that both have significant effects on continuous reactor operation. At least some of these effects were analyzed by a simple model. At this point, experimental analysis for extracellular levels of tryptophan sufficient to support X- growth (1-4 mg/l) has given contradictory results. This has at least partially indicated the effect may be an intracellular one, and thus the culture history would be critical in such experiments. Since the system studied is not atypical of recombinant cultures, it leads one to speculate on the generality of the phenomena and its extent in other cultures. If important, the use of double auxotrophs or auxotrophs that are mutant in a metabolite for which the cell has a greater growth requirement should be used. Additionally, the presence of higher copy numbers in yeast at lower growth rates also leads one to speculate on how these apparently contradictory phenomena are related.

Use of Magnetic Resonance Imaging to Analyze the Performance of Hollow-Fiber Bioreactors

Preliminary experiments were described that demonstrate that MRI is an effective tool for the noninvasive study of hollow-fiber bioreactors. Flow-compensated velocity-encoding pulse sequences were successively applied to analyze the velocity patterns in a module operated without cells, with an artificially induced flow field perturbation. Diffusion damping pulse sequences were also used to spatially resolve regions of cell growth in a bioreactor. These experiments provide the necessary basis from which future flow and spectroscopic studies can be conducted.

Effects of immobilization on growth, substrate consumption, β-galactosidase induction, and byproduct formation inEscherichia coli

SummarySome metabolic properties of both suspended and immobilized aerobically and anaerobically growingEscherichia coli cells were investigated. Metabolic activity was found to be substantially different whenE. coli cells were immobilized in alginate. Cells grown immobilized in alginate, and then released from the gel, synthesized 1.6 (aerobic growth) and 4.9 (anaerobic growth) times as much β-galactosidase per cell in response to induction as did suspended cells. Under both aerobic and anaerobic conditions, the cell yield from glycerol for immobilized cells was half that for suspended cells. At specific growth rates that were not significantly different from those of suspended cells, immobilized cells consumed glycerol at twice the rate of suspended cells. Immobilized cells produced elevated quantities of acetate, pyruvate, and lactate. Interpretation of these findings is discussed in terms of the kinetics of energy metabolism and the regulation of inducible protein synthesis inE. coli.

Predator-prey interactions: egg-eating predators

Abstract This manuscript is intended to provide further insight into the dynamics of predator-prey interactions in which the predator population feeds on the eggs of the prey population. Reasons are provided for the results shown in a previous article. It is further shown that, by making a slight change in the predator harvesting function of the previous model, a more realistic model is developed which has the advantages of a stable steady state point and an unstable extinction point. Comments are also made regarding the special case of this model for which the predator population is constant with respect to the harvest of the preys eggs. Lastly, a proposition is set forth by which the results of this work could be tested.

An integrated, project-based, spiral curriculum for the first year of chemical engineering

Summary form only given. The authors developed a project-based, spiral curriculum for chemical engineering, beginning with the sophomore year. The curriculum addresses problems in the current state of engineering education, such as lack of student motivation, poor retention, segmented learning, lack of integration and the need to deliver cost effective technical education to a student audience of diverse backgrounds and learning styles. The spiral curriculum was well received by students in the initial offering during the 1997-98 academic year.

Effect of oxygen supply on metabolism of immobilized and suspended Escherichia coli.

The effect of reduced oxygen supply on the production of a recombinant protein (plasmid-encoded beta-galactosidase) was investigated in Escherichia coli. A novel modified bubble tank reactor was used to provide a direct comparison between immobilized and suspended cells in identical environments except for the immobilization matrix. Decreased oxygen supply led to increased beta-galactosidase synthesis by both immobilized and suspended cells. Immobilized cells produced similar amounts of beta-galactosidase as the suspended cells. Lactose consumption and acetate production, on a per cell basis, were significantly higher in immobilized cells, suggesting that immobilized cells utilized fermentative metabolism. However, a transport analysis of the immobilized cell system showed that immobilized cells were not subject to either external or internal mass transfer gradients.

Design and operating criteria for hollow fiber bioreactors

We have analyzed the design and operation of hollow fiber bioreactors for cell culture on the basis of cell growth efficiency and non-uniform fiber spacing. Operating diagrams are presented that describe reactor performance as a function of important operating variables like oxygen concentration and the fiber packing density. The diagrams allow one to find the best set of operating conditions for a fixed reactor design, or to rationally adjust the design parameters for fixed operating conditions.

Active and cooperative learning in an introductory chemical engineering course

A sophomore level chemical engineering course was redesigned to emphasize active and cooperative learning. The structure used was a peer-assisted cooperative learning model developed at WPI. The experimental course was compared to a control course taught by the passive lecture method. The control and test courses were compared using student performance, attitudes, evaluations of the course and instructor and faculty time. We found that student performance was better and content coverage was increased in the test class. Faculty time was reduced by 24% using the peer assisted cooperative learning model. Composite student evaluations of the course and instructor increased slightly from the control to the test course. Student attitudes about the profession increased during the test course, but were mixed regarding working in teams.