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Papers by audie thompson

Osmotically Driven Membrane Processes - Approach, Development and Current Status, 2018

Chemical engineering education, 2018

Historically Black Colleges and Universities (HBCUs) provide significant STEM degrees to African ... more Historically Black Colleges and Universities (HBCUs) provide significant STEM degrees to African Americans. Initiatives toward increasing diversity in STEM fields have been implemented by government and industry leaders. HBCUs annually award over 20% of all African American baccalaureate chemical engineering degrees. This speaks volume to the contribution HBCUs are making towards workforce diversity. This paper discusses the current statistics and impacts HBCUs have and could have in chemical engineering.

Hydrogels are a network of polymer chains with properties that absorb, store and transport soluti... more Hydrogels are a network of polymer chains with properties that absorb, store and transport solutions. A hydrogel membrane has a permeability that allows influx and excretion. Therefore, it is the ideal material for medicated membranes. This study investigates the crosslinking of poly(vinyl alcohol) (PVA) hydrogel membranes using different agents and explores the usability of the candidate membranes as drug delivery systems. The model protein, bovine albumin serum (BSA), was used to test the stability and controlled drug release rate characteristics of the candidate hydrogel membranes. This investigation also evaluated the stability different crosslinkers for hydrogel membranes. Glutaraldehyde (GA) and an alternative crosslinking method of ultraviolet irradiation with the sensitizer, sodium benzoate (SB), were used to crosslink PVA containing BSA. In GA crosslinked membranes, BSA release diffusion experiments showed 48%, 45%, and 63% recovery of protein at pH 6.5, 7.4 and 8.0, respec...

Biofouling is detrimental to water filtration processes and decreases the durability of membranes... more Biofouling is detrimental to water filtration processes and decreases the durability of membranes. Therefore, membranes, that are resistant to the accumulation of microorganisms, are a necessity for water filtration. In this study, Cellulose Acetate (CA) and Poly(vinyl alcohol) blend membranes were prepared by the phase inversion method. To increase the rejection of foulants through the membrane, silver (Ag +) was added then reduced (Ag 0) to decrease metal leaching. The casting solution consisted of 15% (w/v) polymer and 85% (w/v) N-Methyl 2-Pyrrolidone. Of the 15% (w/v) polymer concentration, different PVA concentrations were compared: 2% (w/v) 5% (w/v) and 10% (w/v). The membranes were analyzed for metal attachment, protein rejection, and water/foulant flux. Membranes were characterized with FTIR, XPS, SEM and Serial Dilution. FTIR confirmed the presence of the PVA's hydroxyl group and a decrease in the intensity of the CA's carbonyl group when blended. Additionally, membranes blended with PVA efficiently reduce adsorption of protein onto the membrane surface. Reduced silver membranes efficiently eradicate the growth of E.coli over a 5-hour time span pending E.coli colony concentration. SEM micrographs indicated differences in pore morphology with PVA while EDS confirms the presence of silver on membrane surface and sublayer. The water flux data displayed a great disparity when comparing CA membranes to PVA/CA membranes with a dramatic increase when blended with a surface modifier. Furthermore, a 28% increase in rejection was observed with the blended polymer.

This paper discusses the design of the Girls Accelerating and Learning STEM (G.A.L.S.) one-week r... more This paper discusses the design of the Girls Accelerating and Learning STEM (G.A.L.S.) one-week residential summer camp designed to encourage young girls to pursue engineering careers. Specifically, the camp exposed participants to the fields of computer science and engineering using experiential learning to develop participant interest and skills. At the end of the program, students participated in team competitions and presented their work. The end-of-program survey data showed that the G.A.L.S. camp had an impact on the enhancement of student interest in engineering as a potential career. The paper will provide details on the program components, and further discuss the impacts of the program and how it can be used as a model for future programs.

Forward osmosis (FO) is a technical term describing the natural phenomenon of osmosis: the transp... more Forward osmosis (FO) is a technical term describing the natural phenomenon of osmosis: the transport of water molecules across a semi-permeable membrane. The osmotic pressure difference is the driving force of water transport, as opposed to pressure-driven membrane processes. A concentrated draw solution (DS) with osmotic pressure draws water molecules from the feed solution (FS) through a semi-permeable membrane to the DS. The diluted DS is then reconcentrated to recycle the draw solutes as well as to produce purified water. As a major disadvantage, nature of FO membranes (asymmetrical structure) causes international concentration polarization (ICP) which promotes the decrease in water flux. Therefore, the number of studies related to improving both active and support layers of FO membranes is increasing in the applications. The purpose of the chapter is to bring an overview on the FO membrane manufacturing, characterizing and application area at laboratory or full scales. This chapter is published in two parts. In the first part, which appears here, the overview of membrane technologies and the definition of forward osmosis process are stated. The manufacturing methods of support and active layers forming FO membranes are described with common and/or new modification procedures.

Journal of Biomaterials and Nanobiotechnology, 2020

This study investigates poly(vinyl alcohol) (PVA) membranes as controlled release micro-matrices,... more This study investigates poly(vinyl alcohol) (PVA) membranes as controlled release micro-matrices, which can be useful in therapeutic applications for optimizing the administration of drugs. Currently, the use of hydrogels is limited by protein size. This study investigates the delivery of PspA, a large protein of approximately 38 kD. Pneumococcal surface protein A (PspA) has been shown to provide protective immunity against pneumococcal infection and is considered as a pneumococcal vaccine. The protein release experiments demonstrated that from an initial pH 7.4, approximately 60% of PspA diffuse into a neutral environment with an initial burst and a declining rate reaching equilibrium. The results indicate that the protein was successfully incorporated and released from the membrane over time. The hydrogel and protein interaction is temporary, and the membrane system is ideal for protein drug delivery. The data confirm that the protein did not aggregate and was active after release. The protein release is promising and a step forward to develop microneedles to facilitate high molecular weight protein delivery as well as vaccine delivery.

Journal of Applied Polymer Science, 2018

In this study, hydrovanilloin synthesized by electrochemical dimerization of vanillin has been us... more In this study, hydrovanilloin synthesized by electrochemical dimerization of vanillin has been used as a renewable substitute for bisphenol A for the preparation of epoxy resins. The reaction of the disodium salt of hydrovanilloin:epichlorohydrin 1:2 mol ratio at 80 C for 30 min in water gave a hydrovanilloindiglycidyl ether phenoxy resin. This hard thermoplastic resin showed T g of 135 C and stable up to 255 C in air. On the other hand, the disodium salt of hydrovanilloin:epichlorohydrin 1:4 mol ratio at 80 C for 30 min in water gives a curable oligomer of hydrovanilloindiglycidyl ether with 2.1 repeating units. This oligomer could be cured with aliphatic diamines: 1,2-diaminoethane, 1,4-diaminobutane, 1,6-diaminohexane, and isophorone diamine to give hard epoxy resins with T g values of 116, 118, 149 and 146 C, respectively.

BIOS, 2014

Host immune factors involved in bacterial ocular virulence were examined through the use of pneum... more Host immune factors involved in bacterial ocular virulence were examined through the use of pneumolysin, a cytoplasmic protein and pneumococcal strain D39 utilizing human corneal epithelial cells (HCEC). Recombinant pneumolysin activity was determined by a hemolysis assay using the following concentrations: 50-1000 ng/mL. HCEC were grown to confluency and exposed to 10 3 to 10 7 colony forming units (CFUs) of mid-log phase Streptococcus pneumoniae D39 for 2, 4, 6, and 24 h. HCEC were exposed to pneumolysin at various concentrations: 200-1000 ng/mL. ELISA and human cytokine array was performed on the supernatant. Fluorescence studies using cytotoxicity assay were performed on the HCEC cells following infection to determine live versus dead cells. The hemolysis assay showed that a minimum of 100 ng/mL PLY will lyse the red blood cells. Cytokine array on the HCEC exposed supernatants showed the presence of IL-6 and IL-8. Four hour exposure of HCEC cells to a range of 10 3 to 10 7 CFU of D39 resulted in monolayer disruption and decreased viability as compared to cells exposed to the media alone. HCEC cells exposed to any of the concentrations of bacteria exhibited signs of cellular damage and death. Following 24 h exposure, there was an increased expression of IL-8 (p < 0.001) compared to media alone. IL-6, IL-8 and IFN-gamma levels were elicited at a minimal of 200ng PLY. In addition to changes in viability and morphology of cultured cells, we detected specific cytokines in the culture supernatants of HCEC following exposure to S. pneumoniae D39.

GSTF International Journal on Education, Volume 1 Number 1, 2013

Hydrogel membranes continue to be investigated for potential use in a number of applications incl... more Hydrogel membranes continue to be investigated for potential use in a number of applications including bioseparations, water purification, controlled drug release, to name a few. The potential of hydrogels to overcome disadvantages typically associated with packed bed chromatography such as low protein loading, elution conditions and regeneration increase their potential applicability and use for biological separations. However, these materials typically provide limited selectivity between proteins of similar size, low protein loading and durability. To overcome these limitations, poly vinyl alcohol (PVA) hydrogels were functionalized with metal affinity ligand to provide a selective means to enhance protein loading and improve protein separation characteristics. Additionally, the crosslink ratio was varied from 1.25 % (v/v) to 5.0 % (v/v) to further enhance membrane selectivity while also increasing membrane durability. Characterization and comparison of membranes with varied degrees of crosslinking and examination of structural properties and behaviors of membranes were determined for this study. Atomic Absorption Spectroscopy (AAS), Fourier Transform Infrared spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) were used to characterize and to examine IMAH membranes after functionalization. Results demonstrate successful functionalization of the poly vinyl alcohol membrane with metal affinity ligands. The FTIR results showed different band frequencies for specific groups associated with PVA cross-linked with glutaraldehyde. The presence of the chelator did not impact the swelling properties of the membrane; however, the Bound Copper Content (BCC) was increased by 50% for the IDA-Me2+ membranes as the crosslinking ratio increased from 1.25% to 5% GA (v/v). Moreover, an increase in cross-linking ratio resulted in structural changes that enhanced copper attachment which increased protein solubility.

GSTF Journal of Engineering Technology, 2013

Previous studies have shown that functionalization of hydrogel membranes with metal affinity liga... more Previous studies have shown that functionalization of hydrogel membranes with metal affinity ligands increases the separation potential of the membranes for purification of biological systems. To achieve separation, histidines that are exposed on the proteins surface are attracted and attach to the metal ion within the IMA membrane matrix. The effectiveness of these membranes depends on several factors including, but not limited to, type of chelating group, the metal ion, and solution buffer. This paper is concerned with crosslinking of poly (vinyl) alcohol (PVA) with varied degrees of crosslinking that was subsequently functionalized with the immobilized metal affinity (IMA) group, that included a spacing element, (1, 4 Butanediol Diglycidyl ether (1,4 BDE)), chelator (NTA (Nitrilotriacetic acid)), and metal (Nickel (Ni2+). The impact of chelating ligand and glutaraldehyde concentration on the swelling and bound metal content was determined. Additionally, Fourier-transform infrared spectroscopy (FTIR) was used to examine the functional groups for the control (without metal attached) and affinity (with metal attached) membranes. Ultimately, this study suggests that crosslinking membranes with a higher glutaraldehyde percentage yielded a higher content of bound nickel.

Biophysical Journal, 2012

Biochemistry, 2010

The Cu(I) chaperone Cox11 is required for the insertion of Cu B into cytochrome c oxidase (CcO) o... more The Cu(I) chaperone Cox11 is required for the insertion of Cu B into cytochrome c oxidase (CcO) of mitochondria and many bacteria, including Rhodobacter sphaeroides. Exploration of the copper binding stoichiometry of R. sphaeroides Cox11 led to the finding that an apparent tetramer of both mitochondrial and bacterial Cox11 binds more copper than the sum of the dimers, providing another example of the flexibility of copper binding by Cu(I)-S clusters. Site-directed mutagenesis has been used to identify components of Cox11 that are not required for copper binding but are absolutely required for the assembly of Cu B , including conserved Cys-35 and Lys-123. In contrast to earlier proposals, Cys-35 is not required for dimerization of Cox11 or for copper binding. These findings, plus the location of Cys-35 at the C terminus of the predicted transmembrane helix and thereby close to the surface of the membrane, allows a proposal that Cys-35 is involved in the transfer of copper from the Cu(I) cluster of Cox11 to the Cu B ligands His-333/334 during the folding of CcO subunit I. Lys-123 is located near the Cu(I) cluster of Cox11, in an area otherwise devoid of charged residues. From the analysis of several Cox11 mutants, including K123E, L and R, we conclude that a previous proposal that Lys-123 provides charge balance for the stabilization of the Cu(I) cluster is unlikely to account for its absolute requirement for Cox11 function. Rather, consideration of the properties of Lys-123 and the apparent specificity of Cox11 suggests that Lys-123 plays a role in the interaction of Cox11 with its target.

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2012

3-type cytochrome c oxidase aa 3-type cytochrome c oxidase Copper chaperone Copper center assembl... more 3-type cytochrome c oxidase aa 3-type cytochrome c oxidase Copper chaperone Copper center assembly Cu A Sco protein The α proteobacter Rhodobacter sphaeroides accumulates two cytochrome c oxidases (CcO) in its cytoplasmic membrane during aerobic growth: a mitochondrial-like aa 3-type CcO containing a di-copper Cu A center and mono-copper Cu B , plus a cbb 3-type CcO that contains Cu B but lacks Cu A. Three copper chaperones are located in the periplasm of R. sphaeroides, PCu A C, PrrC (Sco) and Cox11. Cox11 is required to assemble Cu B of the aa 3type but not the cbb 3-type CcO. PrrC is homologous to mitochondrial Sco1; Sco proteins are implicated in Cu A assembly in mitochondria and bacteria, and with Cu B assembly of the cbb 3-type CcO. PCu A C is present in many bacteria, but not mitochondria. PCu A C of Thermus thermophilus metallates a Cu A center in vitro, but its in vivo function has not been explored. Here, the extent of copper center assembly in the aa 3-and cbb 3type CcOs of R. sphaeroides has been examined in strains lacking PCu A C, PrrC, or both. The absence of either chaperone strongly lowers the accumulation of both CcOs in the cells grown in low concentrations of Cu 2 +. The absence of PrrC has a greater effect than the absence of PCu A C and PCu A C appears to function upstream of PrrC. Analysis of purified aa 3-type CcO shows that PrrC has a greater effect on the assembly of its Cu A than does PCu A C, and both chaperones have a lesser but significant effect on the assembly of its Cu B even though Cox11 is present. Scenarios for the cellular roles of PCu A C and PrrC are considered. The results are most consistent with a role for PrrC in the capture and delivery of copper to Cu A of the aa 3-type CcO and to Cu B of the cbb 3-type CcO, while the predominant role of PCu A C may be to capture and deliver copper to PrrC and Cox11. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes.

Toxins, Mar 22, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY