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39 results on '"Hansen, Ryan R."'

2. Using Ongoing Laboratory Problems as Active Learning Research Projects in Transport Phenomena

Author

Hansen, Ryan R., Anderson, Audrey C., Barua, Niloy, and McGinley, Logan M.

Abstract

This report evaluates the use of active, open-ended research problems taken from the instructor's laboratory and assigned as mid-semester projects in Transport Phenomena. Projects are structured in a POGIL [process oriented guided inquiry learning] format and designed to engage students by providing them the opportunity to impact real research problems in their department. The impact of these assignments on student comprehension and engagement is evaluated by comparing exam performance of students with and without POGIL projects and through student surveys.

Published
2021
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21. Photodegradable Hydrogels for Rapid Screening, Isolation, and Genetic Characterization of Bacteria with Rare Phenotypes

Author

Fattahi, Niloufar, Nieves-Otero, Priscila A., Masigol, Mohammadali, van der Vlies, André J., Jensen, Reilly S., Hansen, Ryan R., and Platt, Thomas G.

Abstract

Screening mutant libraries (MLs) of bacteria for strains with specific phenotypes is often a slow and laborious process that requires assessment of tens of thousands of individual cell colonies after plating and culturing on solid media. In this report, we develop a three-dimensional, photodegradable hydrogel interface designed to dramatically improve the throughput of ML screening by combining high-density cell culture with precision extraction and the recovery of individual, microscale colonies for follow-up genetic and phenotypic characterization. ML populations are first added to a hydrogel precursor solution consisting of polyethylene glycol (PEG) o-nitrobenzyl diacrylate and PEG-tetrathiol macromers, where they become encapsulated into 13 μm thick hydrogel layers at a density of 90 cells/mm2, enabling parallel monitoring of 2.8 × 104mutants per hydrogel. Encapsulated cells remain confined within the elastic matrix during culture, allowing one to track individual cells that grow into small, stable microcolonies (45 ± 4 μm in diameter) over the course of 72 h. Colonies with rare growth profiles can then be identified, extracted, and recovered from the hydrogel in a sequential manner and with minimal damage using a high-resolution, 365 nm patterned light source. The light pattern can be varied to release motile cells, cellular aggregates, or microcolonies encapsulated in protective PEG coatings. To access the benefits of this approach for ML screening, an Agrobacterium tumefaciensC58 transposon ML was screened for rare, resistant mutants able to grow in the presence of cell free culture media from Rhizobium rhizogenesK84, a well-known inhibitor of C58 cell growth. Subsequent genomic analysis of rare cells (9/28,000) that developed into microcolonies identified that seven of the resistant strains had mutations in the acclocus of the Ti plasmid. These observations are consistent with past research demonstrating that the disruption of this locus confers resistance to agrocin 84, an inhibitory molecule produced by K84. The high-throughput nature of the screen allows the A. tumefaciensgenome (approximately 5.6 Mbps) to be screened to saturation in a single experimental trial, compared to hundreds of platings required by conventional plating approaches. As a miniaturized version of the gold-standard plating assay, this materials-based approach offers a simple, inexpensive, and highly translational screening technique that does not require microfluidic devices or complex liquid handling steps. The approach is readily adaptable to other applications that require isolation and study of rare or phenotypically pure cell populations.

Published
2024
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22. Controlling condensation and frost growth with chemical micropatterns

Author

Biomedical Engineering and Mechanics, Boreyko, Jonathan B., Hansen, Ryan R., Murphy, Kevin R., Nath, Saurabh, Retterer, Scott T., Collier, C. Patrick, Biomedical Engineering and Mechanics, Boreyko, Jonathan B., Hansen, Ryan R., Murphy, Kevin R., Nath, Saurabh, Retterer, Scott T., and Collier, C. Patrick

Abstract

In-plane frost growth on chilled hydrophobic surfaces is an inter-droplet phenomenon, where frozen droplets harvest water from neighboring supercooled liquid droplets to grow ice bridges that propagate across the surface in a chain reaction. To date, no surface has been able to passively prevent the in-plane growth of ice bridges across the population of supercooled condensate. Here, we demonstrate that when the separation between adjacent nucleation sites for supercooled condensate is properly controlled with chemical micropatterns prior to freezing, inter-droplet ice bridging can be slowed and even halted entirely. Since the edge-to-edge separation between adjacent supercooled droplets decreases with growth time, deliberately triggering an early freezing event to minimize the size of nascent condensation was also necessary. These findings reveal that inter-droplet frost growth can be passively suppressed by designing surfaces to spatially control nucleation sites and by temporally controlling the onset of freezing events.

Published
2016

36. Microstructured Block Copolymer Surfaces for Control of Microbe Adhesion and Aggregation.

Author

Hansen, Ryan R., Shubert, Katherine R., Morrell-Falvey, Jennifer L., Lokitz, Bradley S., Doktycz, Mitchel J., and Retterer, Scott T.

Subjects
BLOCK copolymers, MICROBIAL aggregation, MICROBIAL adhesion, BIOCHEMICAL substrates, SURFACE topography, LECTINS, BIOFILMS
Abstract

The attachment and arrangement of microbes onto a substrate is influenced by both the biochemical and physical surface properties. In this report, we develop lectin-functionalized substrates containing patterned, three-dimensional polymeric structures of varied shapes and densities and use these to investigate the effects of topology and spatial confinement on lectin-mediated microbe immobilization. Films of poly(glycidyl methacrylate)-block-4,4-dimethyl-2-vinylazlactone (PGMA-b-PVDMA) were patterned on silicon surfaces into line arrays or square grid patterns with 5 µm wide features and varied pitch. The patterned films had three-dimensional geometries with 900 nm film thickness. After surface functionalization with wheat germ agglutinin, the size of Pseudomonas fluorescens aggregates immobilized was dependent on the pattern dimensions. Films patterned as parallel lines or square grids with a pitch of 10 µm or less led to the immobilization of individual microbes with minimal formation of aggregates. Both geometries allowed for incremental increases in aggregate size distribution with each increase in pitch. These engineered surfaces combine spatial confinement with affinity-based capture to control the extent of microbe adhesion and aggregation, and can also be used as a platform to investigate intercellular interactions and biofilm formation in microbial populations of controlled sizes. [ABSTRACT FROM AUTHOR]

Published
2014
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37. Using polymeric materials to generate an amplified response to molecular recognition events.

Author

Sikes, Hadley D., Hansen, Ryan R., Johnson, Leah M., Jenison, Robert, Birks, John W., Rowlen, Kathy L., and Bowman, Christopher N.

Subjects
*MOLECULAR recognition, *POLYMERS, *MOLECULAR biology, *BIOMOLECULES, *MACROMOLECULES, *MOLECULES
Abstract

Clinical and field-portable diagnostic devices require the detection of atto- to zeptomoles of biological molecules rapidly, easily and at low cost, with stringent requirements in terms of robustness and reliability. Though a number of creative approaches to this difficult problem have been reported, numerous unmet needs remain in the marketplace, particularly in resource-poor settings. Using rational materials design, we investigated harnessing the amplification inherent in a radical chain polymerization reaction to detect molecular recognition. Polymerization-based amplification is shown to yield a macroscopically observable polymer, easily visible to the unaided eye, as a result of as few as ∼1,000 recognition events (10 zeptomoles). Design and synthesis of a dual-functional macromolecule that is capable both of selective recognition and of initiating a polymerization reaction was central to obtaining high sensitivity and eliminating the need for any detection equipment. Herein, we detail the design criteria that were used and compare our findings with those obtained using enzymatic amplification. Most excitingly, this new approach is general in that it is readily adaptable to facile detection at very low levels of specific biological interactions of any kind. [ABSTRACT FROM AUTHOR]

Published
2008
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39. Visual detection of labeled oligonucleotides using visible-light-polymerization-based amplification.

Author

Hansen RR, Sikes HD, and Bowman CN

Subjects
Base Sequence, DNA Primers, Sensitivity and Specificity, Light, Oligonucleotides analysis, Polymers chemistry
Abstract

DNA biochip technology holds potential for highly parallel, rapid, and sensitive genetic diagnostic screening of target pathogens and disease biomarkers. A primary limitation involves a simultaneous, sequence-specific identification of low copy number target polynucleotides using a clinically appropriate detection methodology that implements only inexpensive detection instrumentation. Here, a rapid (20 min), nonenzymatic method of signal amplification utilizing surface-initiated photopolymerization is presented in glass microarray format. Visible light photoinitiators covalently coupled to streptavidin were used to bind biotin-labeled capture sequences. Amplification was achieved through subsequent contact with a monomer solution and the appropriate light exposure to generate 20-240-nm-thick hydrogel layers exclusively from spots containing the biotin-labeled DNA. An amplification factor of 10(6) to 10(7) was observed as well as a detectable response generated from as low as approximately 10(4) labeled oligonucleotides using minimal instrumentation, such as an optical microscope or CCD camera.

Published
2008
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