The ability to generate a range of concentrations of various solutions rapidly and conveniently is an ongoing need in biotechnology. In this thesis we demonstrate how we took advantage of the full process control afforded by our recent custom high resolution 3D printer and resin advances to realize highly integrated and miniaturized microfluidic components for simultaneous on-chip serial dilution for dose-response assays. With judicious selection of mixed layer thicknesses and pixel-by-pixel dose control, we show that the diameter of 3D printed membrane valves can be reduced from 300 µm to 46 µm. We further introduce an entirely new kind of 3D printed valve, termed a squeeze valve, in which the active area is reduced still further to 15 µm x 15 µm. We demonstrate and characterize pumps based on each type of valve and introduce a short (<1 mm long) high aspect ratio channel that enables rapid diffusion-based mixing. We show that combining two pumps with this diffusion mixing channel results in a highly compact 1:1 mixer component. Connecting 10 of these components in series yields a miniature 10 stage 2-fold microfluidic serial dilution module that from two solution inputs simultaneously generates 10 output concentrations that cover three orders of magnitude. We show the efficacy of our serial dilution approach by demonstrating an assay for dose-dependent permeabilization of A549 cells in different concentrations of digitonin integrated into a single device. Our demonstration of component miniaturization in conjunction with a high degree of integration illustrates the promise of 3D printing to enable highly functional and compact microfluidic devices for a variety of biomolecular applications.

In recent years there has been an increased interest in inquiry-based learning, also known as experiential learning or problem-based learning, as a more appropriate model of teaching science. The purpose of this study was to incorporate inquiry-based learning in a college sophomore-level General Microbiology Laboratory. The goal of this laboratory course is to introduce students to basic techniques and procedures necessary for the study of microorganisms. Laboratory sections were randomly assigned to an experimental group or a control/reference group. The experimental group was taught the concept of serial dilutions using an inquiry-based learning approach whereas the control group was taught using traditional teaching methods. Analysis of the data generated from the students' involvement in the investigation during the fall semester indicated that the experimental group had a slightly greater improvement in their knowledge of serial dilution. The study continued in the spring semester and involved close to 300 students. During the spring semester both the experimental and the control groups had similar attitudes about their learning experience as evaluated by a Lickert Scale survey. However, a statistical analysis of the quiz scores of the students with values within the interquartiles indicated the experimental classes' quiz scores were significantly higher on quiz 2 taken at the midpoint in the study. Thus an inquiry-based learning approach was found to be beneficial to the middle 50% of the class. / Master of Science

Humanpatogena stammar av bakterien Yersinia enterocolitica kan orsaka akut gastroenterit. För identifiering av bakterien odlas fecesprover ut på CIN-agar. På senare år har en kromogen agarplatta framtagits som differentierar mellan patogena och apatogena stammar av Y. enterocolitica. Syftet med studien är att jämföra och utvärdera två CIN-agar, med agarbaser och supplement från två olika företag (Liofilchem och Oxoid), och CHROMagar Y. enterocolitica (CHROMagar). Odling av fecesprover samt seriespädning av sex Y. enterocolitica stammar och en Y. pseudotuberculosis utfördes. Vid utodlade fecesprover jämfördes växt och hämning av övriga bakterier. Vid seriespädning räknades antal kolonier på plattorna för respektive spädning, samt utseende av kolonier på plattor bedömdes. Resultatet tyder på att skillnad av hämningseffekt av Y. enterocolitica och utseende på kolonierna finns mellan de två CIN-agarplattorna. Oxoid’s CIN-agar erhöll större kolonier, lägre hämningseffekt av Y. enterocolitica och detektionsgräns än Liofilchem’s CIN-agar. På CHROMagar-plattan växte de patogena stammarna med bleklila kolonier och de apatogena stammarna med blåa kolonier. Hämningseffekt av Y. enterocolitica hos CHROMagar-plattan är densamma som Oxoid’s CIN-agar. Slutsatsen är således att Oxoid’s CIN-agar och CHROMagar har samma hämningseffekt av Y. enterocolitica men CHROMagar differentierar mellan patogena och apatogena stammar. Liofilchem’s CIN-agar har högre hämningseffekt än CHROMagar och Oxoid’s CIN-agar. / Pathogenic strains of Yersinia enterocolitica can cause acute gastroenteritis in humans. To identify the bacterium, cultivation of stool samples on CIN-agar are performed. A chromogenic medium has been developed that differentiate between pathogenic and nonpathogenic strains of Y. enterocolitica. The purpose is to compare and evaluate two CIN-agar, with agar bases and supplements from two companies (Liofilchem and Oxoid), and CHROMagar Y. enterocolitica (CHROMagar). Growth of stool samples and serial dilutions of six Y. enterocolitica strains and one strain of Y. pseudotuberculosis were performed. Comparisons of the growth and inhibition of other bacteria were done for the stool samples. Colonies for each dilution were counted and appearance of the colonies was evaluated. The result indicates that a difference in inhibitory effect on Y. enterocolitica and appearance of colonies exist between the two CIN-agar. All strains grew with larger colonies on Oxoid CIN-agar than on Liofilchem’s. Oxoid CIN-agar and CHROMagar have a lower inhibitory effect on Y. enterocolitica than Liofilchem’s. On CHROMagar, the pathogenic strains grew with mauve colonies, whilst the nonpathogenic strains grew with blue colonies. Thus, the conclusion is that CHROMagar and Oxoid CIN-agar have less inhibitory effect on Y. enterocolitica than Liofilchem’s. CHROMagar can differentiate between pathogenic and nonpathogenic strains.