2001 MRSEC REU Participants

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Calvin D. Birdinground Jr
Home Institution: United Tribes Technical College
Current year: Sophomore
MRSEC Faculty: Ward
Title of work: "Investigation into tube formation with systematically lengthened molecular building blocks"

The scope of our work is to investigate the host-guest interaction with monosulfonates. Our host molecules are compounds of Guanidinium monosulfonates; G[2-naphthlenesulfonate], G[4-biphenylsulfonate].

The Guanidinium monosulfonate compounds are saturated solutions in methanol. The guests o-xylene, 1,2-dichlorobenzene, and N,N-dimethylaniline are the added carefully to the saturated solutions. The crystals are then grown by methods of vapor diffusion and evaporation.

Matthew J. Horner has already prepared crystals of G[monosulfonates] with ; benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, ethylbenzene, anisole, 3,4-dimethylanisole, 3,5-dimethylanisole, N,N-dimethylanilene, 2-chlorotoluene, 1,2-dichlorobenzene, tertbutylbenzene, 1,2-dibromobenzene, 4-dimethylaminobenzonitrile, 4-dimethylaminobenzaldehyde, N,N-dimethyl-3-nitroaniline, N,N-dimethyl-p-nitroaniline, hexaflourobenzene, and guest free as well. These crystals were also grown by methods previously stated.

We have the melting points on the majority of the crystals already grown. The rest of the crystals have yet to grow so we can use NMR to determine if the guest were included and single crystal x-ray crystallography will also be used to determine the crystal structure.

Amy Geissler
Home Institution: College of St Benedict
Current year: Junior
MRSEC Faculty: Bates
Title of work: "Partial Hydrogenation of Polybutadiene"

Amphiphilic diblock copolymers that form bilayers in dilute solution can be modified to give them different physical properties. One process used to manipulate the polymer's properties is crosslinking. Through partial hydrogenation, the crosslinking density resulting can be controlled affecting physical abilities, such as stress and strain. Hydroxyl functional polybutadienes (PB-OH) were partially hydrogenated using decreasing amounts of a diimide produced by decomposing p-toluenesulfonylhydrazide (TSH). Tri-n-propylamine (TPA), an antioxidant, was used during hydrogenation to bind to the TDS fragments, hindering TDS from binding to the chain of the polymer. Using 1H NMR for analysis, the hydrogenated product contained excess TSH and its fragment, p-tolyl-p-toluenethiolsulfonate (TDS). The TSH and TDS finally were removed from the reaction solution by washing and extracting methods. The purified PB-OH can be used as a macroinitiator for the polymerization of polyethylene oxide (PEO) to form an amphiphilic diblock polymer. The diblock copolymers with varying amounts of saturation will be crosslinked in dilute aqueous solution and their properties analyzed using micromanipulation.

Sara Grabowski
Home Institution: Penn St
Current year: Sophomore
MRSEC Faculty: Ward
Title of work: "Isomer Separation with Guanidinium Disulfonate Apo-Crystals"

The project I'm doing is investigating isomer separation with apo-crystals of guanidinium disulfonates. The separation is from selective inclusion of isomers into free spaces of apo-crystals to form stable molecular inclusion crystals, the shape and size of the free space in the apo-crystal structure are determined by pillar molecules. The biphenyl disulfonate and naphthalene groups are going to be used as pillars for separation of the xylene isomers and ethyl benzene. The apo-crystal of guanidinium biphenyl disulfonate (G2BPDS) and guanidinium naphthalene disulfonate (G2NDS) is added into a binary mixture of xylene isomers and ethyl benzene. The samples of disulfonates in the mixture solution are intermittently taken to estimate the inclusion rate of guest molecules into the apo-crystals. The crystals are analyzed with TGA and GC to measure mass and composition of inclusion guests in the crystals. Also, crystallization of guanidinium disulfonate in methanol solution will be used to separate tetramethylbenzene isomers.

Kurt Koester
Home Institution: St Cloud State
Current year: Junior
MRSEC Faculty: Macosko
Title of work: "Characterization of the Co-continuity of Immiscible Polymer Blends"

Blending immiscible polymers is an important method for preparing new materials. These blended materials can have superior properties than either polymer in the blend. The mixing of two homopolymers can create several different morphologies. Co-continuous blends have both polymer phases interpenetrating throughout the blend. My research goal is to detect and characterize this co-continuity. The blends that we are working with are composed of polyethylene oxide (PEO) and polystyrene (PS). The samples are prepared in a twins screw batch mixer. After blending the samples are pressed into disks and cooled. The methods we will use to detect co-continuity are scanning electron microscopy (SEM) with image analysis, rheology, and solvent extraction. SEM images can be examined using a computer program that calculates the amount of interface between phases. This interfacial length can be indicative of co-continuity. Rheological data can show how the mechanical properties of the blend vary with morphology. Solvent extraction is an experiment that is used to find the range of compositions for which a blend is co-continuous by selectively removing one polymer phase. These methods will be used in future experiments that examine the formation of co-continuous blends.

Shawn Lim
Home Institution: U of M - Twin Cities
Current year: Junior
MRSEC Faculty: Hillmyer
Title of work: "Preparation of Novel Biodegradable Polymer Blends"

Despite its high modulus and tensile strength, polylactide (PLA), a biodegradable polymer, is intrinsically brittle. The strength of this interesting material can be improved by blending with tough polymers such as polyethylene (PE). However, as with most polymer blends, interfacial adhesion in PE/PLA binary blends is weak. Adding a small amount of polylactide-polyethylene block copolymer (PLA-b-PE) as a compatibilizer can reduce phase size and improve phase stability, adhesion and mechanical behavior of the composite material. Melt blending of binary and ternary blends will be conducted in the MiniMAX and Haake melt mixers to compare the effects of different blending conditions. The effect of high temperature annealing on particle size within the blends will be investigated using scanning electron microscopy (SEM) and laser scattering analysis techniques. The aim of this work is to determine the extent of homogeneity and phase stabilization of the blends upon addition of block copolymer. We expect that blends containing block copolymer should exhibit a greater degree of homogeneity of phases compared to binary blends, where a dispersion of fairly large PE particles within the PLA matrix is observed.

John McKeen
Home Institution: U of M - Twin Cities
Current year: Sophomore
MRSEC Faculty: Lodge
Title of work: Metal contacts to Polyacene Organic Semiconducting Thin Films

Pentacene, Tetracene, and other polyacenes have shown great promise as organic semiconductors, with the possibility of reducing processing and manufacturing costs over traditional semiconductors. Thin films of these materials are deposited under vacuum onto an oxidized single crystal Si wafer using vapor phase deposition, and the films are characterized by Atomic Force Microscopy (AFM). Using metal evaporation under vacuum, metal contacts are patterned onto the thin film through a shadow mask. Device performance is directly related to what metal the contacts are patterned from. If the work function of the metal does not properly match the HOMO or LUMO bands of the semiconductor, the contact will be rectifying rather than ohmic. Contact area versus current is also of interest. Once the contacts have been deposited, the I-V characteristics of the devices are measured. From this data we can determine the usefulness of the metal in forming an ohmic contact, as well as the current density through the device.

Elizabeth Nee
Home Institution: U Wis Madison
Current year: Junior
MRSEC Faculty: Hillmyer
Title of work: Effects of Glycation on Smooth Muscle Cells and Collagen Gels

The need for small diameter arterial grafts is increasing with the rise in heart disease. Several biologically engineered grafts have been produced, but many do not have the required mechanical strength to be used in the body. Recently, glycation has been used to increase the mechanical strength of media-equivalents. Glycation is induced by increasing the concentration of ribose in culture medium. As in diabetes, this causes the stiffening of soft tissues due to the nonenzymatic crosslinking of proteins. This study will further examine the effects incubation in ribose has upon the microstructure of collagen and smooth muscle cells, using histology and microstructure.

Joseph Ott
Home Institution: U Wis River Falls
Current year: Junior
MRSEC Faculty: Lodge
Title of work: Anomalous Micellization in Polystyrene-Polyisoprene Copolymer Solutions

The purpose of these experiments is to analyze the region of °8anomalous micellization°± in polystyrene-polyisoprene copolymer solutions. Dynamic light scattering (DLS) will be implemented to analyze the solutions as a function of temperature. During DLS the scattered light intensity is measured. Using the intensity autocorrelation function and ultimately the Stokes-Einstein equation, the hydrodynamic radius (Rh) of the micelles will be found. It is hypothesized that anomalous micellization is due to trace amounts of homopolymer, which alter the micellization process. These homopolymers correspond to the first block in anionic polymerization, polystyrene in this case. Therefore, anomalous micellization is expected to occur in solvents which are polyisoprene (PI) selective, or in polystyrene (PS) selective solvents which have been doped with PI homopolymer. Once a solution exhibits anomalous micellization, the stability of the anomalous micellization will also be analyzed.

Laura Owen
Home Institution: Gustavas Adolphus
Current year: Junior
MRSEC Faculty: Ward
Title of work: "Crystallization of organic polymorphs in polymer monoliths with adjustable porosity"

Certain molecules have the ability to crystallize with more than one solid-state packing arrangement. Each of these arrangements, or polymorphs, exhibits different chemical and physical properties (e.g., solubility, color, and bioavailability) that affect their behavior and utility in, for example, the pharmaceutical, agricultural, and specialty chemical disciplines. Control of polymorphism, which is crucial to the synthesis and processing of crystalline materials, is typically difficult owing to the overcoming the capricious nature of polymorphism. Though there are isolated examples of polymorph control during crystallization, there does not exist a universal strategy overcoming the unpredictability of polymorphism. Our project aims to examine the influence of polymeric media on the crystallization of organic compounds and polymorphism.

Dominique Seetapun
Home Institution: U of M - Twin Cities
Current year: Junior
MRSEC Faculty: Tranquillo
Title of work: The Effects of Intrinsic and Extrinsic Mechanical Stress on Upregulating Collagen Synthesis in tissue-Equivalents to Increase Mechanical Strength

Our lab group studies the production of tissue-equivalents (TE's) to replace diseased arteries, valves, etc. TE's are collagen constructs seeded with human cells. Their advantages are enhanced biocompatibility and the ability to grow, but currently have insufficient strength and stiffness to be used as a replacement tissue. One method to increase mechanical strength and stiffness is to upregulate collagen synthesis. To date, we have used fibrin gels to provide chemical cues to upregulate cell-mediated collagen synthesis (Neidert et. al. 2001). To further increase collagen production we plan on studying the application of intrinsic and extrinsic mechanical stresses. It is hypothesized that stiffer gels will cause intrinsic stresses on the cells and upregulate collagen synthesis. Intrinsic stresses will be increased by modulating the stiffness of the initial fibrin gel by cross-linking via Factor XIII or transglutaminase. Extrinsic stresses will be applied to fibrin gels at defined strains using a Flexcell Tissue Train system. The effectiveness of these protocols will be determined by assaying for total collagen content and by mechanical testing.

Andrew Seipel
Home Institution: Centre College
Current year: Junior
MRSEC Faculty: Tranquillo
Title of work: Prefailure and Failure Behavior of Inhomogeneous, Anisotropic Tissue Equivalents

The behavior of inhomogeneous, anisotropic tissue equivalents (TEs) under stress will be determined. The TEs are comprised of cells entrapped in a reconstituted type I collagen gel. Rat AT-1 and human dermal fibroblasts will be used independently to make the TEs. The alignment of the fibers in the TE will be manipulated by constraining the compaction of the fibers by the cells. The specific TEs to be studied will have inhomogeneous fiber alignment (i.e., the TE will have fiber orientations that differ from region to region). These tissues will be tested to determine their apparent stress versus strain relationship and fracture behavior when force is applied in varying directions. The data will be analyzed in connection with a computer simulation of TE micromechanics.

Sarah Setiawan
Home Institution: U of M - Twin Cities
Current year: Junior
MRSEC Faculty: Barocas
Title of work: Characterization of Micro-fluidic Systems

Microscale chemical technology is evolving very quickly - with many potential uses in sight. We are developing and evaluating a 100-um-scale separator analyzer flow (SAF) meter to measures flow rates of macromolecular suspensions in micro-chemical systems. The SAF meter has two parts - a separator and an analyzer. The separator splits the mixture into two streams using electrophoresis to create different concentrations in each stream. The analyzer measures the concentrations using a capacitive technique. In theory, the concentration difference measured by the analyzer is inversely proportional to the flow rate in the separator. To test the separator, we will pump solutions of bovine serum albumin (BSA) through the SAF meter and measure the concentrations collected from each output via UV-vis spectrophotometry. To test the analyzer, we will analyze streams of known BSA concentration. Upon completion of this project, we will have thus assessed both major components of the SAF meter.

Jonathan Tardos
Home Institution: Cooper Union
Current year: Junior
MRSEC Faculty: Tranquillo
Title of work: Substitution of Human Mesenchymal Stem Cellsin Place of Smooth Muscle Cells in an Artery Replacement

One focus of my graduate student mentor Jennifer Long and faculty advisor R.T. Tranquillo is on a tissue engineered artery replacement. Currently the components which make up the artificial artery are smooth muscle cells (SMC) grown in a compacted collagen or fibrin gel. The focus of this work involves the use of undifferentiated human mesenchymal stem cells (HMSC) derived from adult human bone marrow in collagen or fibrin gel hemispheres. One immediate benefit of HMSC over SMC is that stem cells can be harvested directly from the intended artery recipient; the recipient's immune system, therefore, will not reject the tissue. The goal of this study is to determine the feasibility of HMSC use in the tissue without loss of structural integrity and maintaining the immunological benefits.

HMSC were treated with platelet derived growth factor (PDGF) in order to promote cell differentiation to smooth muscle cells or without growth factor to maintain the undifferentiated state. Cross sections of the hemispheres were made and stained with antibodies to reveal smooth muscle phenotype by noting the presence of actin and myosin, two cytoskeletal proteins necessary for gel compaction. Time course measurements of the gel hemisphere height were made to monitor compaction under the various culture conditions: initial cell concentration, presence of growth factor, gel type (collagen or fibrin). The results will enable an informed decision about using HMSC substitution in our artificial artery.

Omar Zalatimo
Home Institution: Bucknell University
Current year: Sophomore
MRSEC Faculty: Tranquillo
Title of work: Oriented Chondroitin Sulfate Chains Influence On Proteoglycan Production In Chondrocytes

The hypothesis of the experiment is if chondroitin sulfate with correctly oriented CS chains will be more affective than randomly attached CS at stimulating PG production. Chondroitin sulfate on proteoglycans (PGs) increases the production of proteoglycans by chondrocytes. To construct artificial PGs, first chondroitin sulfate is isolated from bovine patella. The next part of the experiment is to use reductive amination to conjoin an amino group to the CS. With the amino group in place, the next step is to add a cross-linking molecule to the CS and BSA to form an artificial PG. Two cross-linkers are used, Sulfo-BSOCOES, which uses only the terminal amino to attach the ends of the CS to the BSA and carbodiimide, the control, which uses carboxyl groups at a number of different places on the CS to attach to the BSA. Finally, the artificial PGs are put in a chondrocyte culture that is deprived of extracellular matrix and tested how much the synthetic PGs will increase PG production.