Open Access. Powered by Scholars. Published by Universities.®
- Keyword
- Publication Year
Articles 1 - 22 of 22
Full-Text Articles in Engineering
Sans Study Of Highly Resilient Poly(Ethylene Glycol) Hydrogels, Erika M. Saffer, Melissa A. Lackey, David M. Griffin, Suhasini Kishore, Gregory N. Tew, Surita R. Bhatia
Sans Study Of Highly Resilient Poly(Ethylene Glycol) Hydrogels, Erika M. Saffer, Melissa A. Lackey, David M. Griffin, Suhasini Kishore, Gregory N. Tew, Surita R. Bhatia
Gregory N. Tew
Polymer networks are critically important for numerous applications including soft biomaterials, adhesives, coatings, elastomers, and gel-based materials for energy storage. One long-standing challenge these materials present lies in understanding the role of network defects, such as dangling ends and loops, developed during cross-linking. These defects can negatively impact the physical, mechanical, and transport properties of the gel. Here we report chemically cross-linked poly(ethylene glycol) (PEG) gels formed through a unique cross-linking scheme designed to minimize defects in the network. The highly resilient mechanical properties of these systems (discussed in a previous publication) [J. Cui, M. A. Lackey, A. E. Madkour, …
Identification Of Synthetic Host Defense Peptide Mimics That Exert Dual Antimicrobial And Anti-Inflammatory Activities, Nicolás Navasa, Abhigyan Som, Avital Percher, Richard W. Scott, Gregory N. Tew, Juan Anguita
Identification Of Synthetic Host Defense Peptide Mimics That Exert Dual Antimicrobial And Anti-Inflammatory Activities, Nicolás Navasa, Abhigyan Som, Avital Percher, Richard W. Scott, Gregory N. Tew, Juan Anguita
Gregory N. Tew
A group of synthetic antimicrobial oligomers, inspired by naturally occurring antimicrobial peptides, were analyzed for the ability to modulate innate immune responses to Toll-like receptor (TLR) ligands. These synthetic mimics of antimicrobial peptides (SMAMPs) specifically reduced cytokine production in response to Staphylococcus aureus and the S. aureus component lipoteichoic acid (LTA), a TLR2 agonist. Anti-inflammatory SMAMPs prevented the induction of tumor necrosis factor (TNF), interleukin 6 (IL-6), and IL-10 in response to S. aureus or LTA, but no other TLR2 ligands. We show that these SMAMPs bind specifically to LTA in vitro and prevent its interaction with TLR2. Importantly, the …
Anion Mediated Activation Of Guanidine Rich Small Molecules, Abhigyan Som, Yongjiang Xu, Richard W. Scott, Gregory N. Tew
Anion Mediated Activation Of Guanidine Rich Small Molecules, Abhigyan Som, Yongjiang Xu, Richard W. Scott, Gregory N. Tew
Gregory N. Tew
No abstract provided.
Room Temperature Magnetic Materials From Nanostructured Diblock Copolymers, Zoha M. Al-Badri, Raghavendra R. Maddikeri, Yongping Zha, Hitesh D. Thaker, Priyanka Dobriyal, Raja Shunmugam, Thomas P. Russell, Gregory N. Tew
Room Temperature Magnetic Materials From Nanostructured Diblock Copolymers, Zoha M. Al-Badri, Raghavendra R. Maddikeri, Yongping Zha, Hitesh D. Thaker, Priyanka Dobriyal, Raja Shunmugam, Thomas P. Russell, Gregory N. Tew
Gregory N. Tew
Nanostructured magnetic materials are important for many advanced applications. Consequently, new methods for their fabrication are critical. However, coupling self-assembly to the generation of magnetic materials in a simple, straight-forward manner has remained elusive. Although several approaches have been considered, most have multiple processing steps, thus diminishing their use of self-assembly to influence magnetic properties. Here we develop novel block copolymers that are preprogrammed with the necessary chemical information to microphase separate and deliver room temperature ferromagnetic properties following a simple heat treatment. The importance of the nanostructured confinement is demonstrated by comparison with the parent homopolymer, which provides only …
Depletion Versus Deflection: How Membrane Bending Can Influence Adhesion, Jin Nam, Maria Santore
Depletion Versus Deflection: How Membrane Bending Can Influence Adhesion, Jin Nam, Maria Santore
Maria Santore
During depletion-driven vesicle adhesion, a stiff membrane’s resistance to bending at fixed tension prevents contact angle equilibrium and vesicle spreading over an opposing vesicle, while more flexible vesicles partially engulf opposing vesicles. Estimates of the bending cost associated with the spreading contact line, relative to the adhesion energy, were consistent with the observed spreading or lack of spreading for the flexible and stiff membranes, respectively, and predicted a lag time sometimes preceding spreading.
Synthesis Of Hydrogels Via Ring-Opening Metathesis Polymerization: Factors Affecting Gelation, Gregory N. Tew, Ahmad E. Madkour, Joshua M. Grolman
Synthesis Of Hydrogels Via Ring-Opening Metathesis Polymerization: Factors Affecting Gelation, Gregory N. Tew, Ahmad E. Madkour, Joshua M. Grolman
Gregory N. Tew
Ring-opening metathesis polymerization (ROMP) was used to synthesize hydrogels via copolymerization of a diamine monomer 3 and a novel cross-linker 5 using Grubbs' third generation catalyst as initiator. Reactions were performed at two different monomer concentrations and at various initial molar ratios of cross-linker to initiator. At low monomer concentration, gelation occurred at initial cross-linker to initiator ratios of 1.5 and greater, which decreased to values of 1.05 and greater when increasing the monomer concentration. This result is in agreement with the Flory–Stockmayer theory. The gel yield and swelling properties were also found to be dependent on the cross-linker to …
Contact Angle Hysteresis: A Different View And A Trivial Recipe For Low Hysteresis Hydrophobic Surfaces, Joseph W. Krumpfer, Thomas J. Mccarthy
Contact Angle Hysteresis: A Different View And A Trivial Recipe For Low Hysteresis Hydrophobic Surfaces, Joseph W. Krumpfer, Thomas J. Mccarthy
Thomas J. McCarthy
Contact angle hysteresis is addressed from two perspectives. The first is an analysis of the events that occur during motion of droplets on superhydrophobic surfaces. Hysteresis is discussed in terms of receding contact line pinning and the tensile failure of capillary bridges. The sign of the curvature of the solid surface is implicated as playing a key role. The second is the report of a new method to prepare smooth low hysteresis surfaces. The thermal treatment of oxygen plasma-cleaned silicon wafers with trimethylsilyl-terminated linear poly(dimethylsiloxane) (PDMS - commercial silicone oils) in disposable glass vessels is described. This treatment renders silicon/silica …
Apolar Ortho-Phenylene Ethynylene Oligomers: Conformational Ordering Without Intermolecular Aggregation, Jing Jiang, Morris M. Slutsky, Ticora V. Jones, Gregory N. Tew
Apolar Ortho-Phenylene Ethynylene Oligomers: Conformational Ordering Without Intermolecular Aggregation, Jing Jiang, Morris M. Slutsky, Ticora V. Jones, Gregory N. Tew
Gregory N. Tew
This paper describes the characterization of solvent induced folding behavior for non-polar (NP) alkoxy substituted ortho-phenylene ethynylene (o-PE) oligomers. Oligomers of lengths up to nine units have been shown to adopt helical conformations in heptane by NMR and CD spectroscopy, while chloroform promotes extended conformations. Surprisingly, the molar ellipticity values found in heptane for these oligomers are very small compared to other literature values of meta-phenylene ethynylene (m-PE) folded systems; however, comparable molar ellipticity values were found for a closed macrocyclic o-PE suggesting the weak ellipticity is a molecular-feature rather than a quality of folding indicator.
Biopolymerization-Driven Self-Assembly Of Nanofiber Air-Bridges, Santosh Pabba, Mehdi M. Yazdanpanah, Brigitte H. Fasciotto Totten, Vladimir V. Dobrokhotov, Jeremy M. Rathfon, Gregory N. Tew, Robert W. Cohn
Biopolymerization-Driven Self-Assembly Of Nanofiber Air-Bridges, Santosh Pabba, Mehdi M. Yazdanpanah, Brigitte H. Fasciotto Totten, Vladimir V. Dobrokhotov, Jeremy M. Rathfon, Gregory N. Tew, Robert W. Cohn
Gregory N. Tew
Several proteins, including actin and fibrin, polymerize in vivo to form nanometre diameter fibers. These processes can be duplicated in vitro using only the essential enzyme and protein precursors. These same protein solutions are directed to self-assemble into oriented arrays of air-bridges using only the crude operation of hand brushing them over textured micron-scale surfaces. The creation of these suspended structures could be used as nanomechanical elements in various sensors and actuators, and their fabrication by this rapid directed self-assembly method would be useful, especially during the early phases of prototype device development. The fabrication method extends earlier studies (Harfenist …
Fast Disinfecting Antimicrobial Surfaces, Ahmad E. Madkour, Jeffery M. Dabkowski, Klaus Nüsslein, Gregory N. Tew
Fast Disinfecting Antimicrobial Surfaces, Ahmad E. Madkour, Jeffery M. Dabkowski, Klaus Nüsslein, Gregory N. Tew
Gregory N. Tew
Silicon wafers and glass surfaces were functionalized with facially amphiphilic antimicrobial copolymers using the "grafting from" technique. Surface-initiated atom transfer radical polymerization (ATRP) was used to grow poly(butylmethacrylate)-co-poly(Boc-aminoethyl methacrylate) from the surfaces. Upon Boc-deprotection, these surfaces became highly antimicrobial and killed S. aureus and E. coli 100% in less than 5 min. The molecular weight and grafting density of the polymer were controlled by varying the polymerization time and initiator surface density. Antimicrobial studies showed that the killing efficiency of these surfaces was independent of polymer layer thickness or grafting density within the range of surfaces studied.
Cationic Nanoparticles Induce Nanoscale Disruption In Living Cell Plasma Membranes, Jiumei Jiumei, Jessica A. Hessler, Krishna Putchakayala, Brian K. Panama, Damian P. Khan, Seungpyo Hong, Douglas G. Mullen, Stassi C. Dimaggio, Abhigyan Som, Gregory N. Tew, Anatoli N. Lopatin, James R. Baker Jr., Mark M. Banaszak Holl, Bradford G. Orr
Cationic Nanoparticles Induce Nanoscale Disruption In Living Cell Plasma Membranes, Jiumei Jiumei, Jessica A. Hessler, Krishna Putchakayala, Brian K. Panama, Damian P. Khan, Seungpyo Hong, Douglas G. Mullen, Stassi C. Dimaggio, Abhigyan Som, Gregory N. Tew, Anatoli N. Lopatin, James R. Baker Jr., Mark M. Banaszak Holl, Bradford G. Orr
Gregory N. Tew
It has long been recognized that cationic nanoparticles induce cell membrane permeability. Recently, it has been found that cationic nanoparticles induce the formation and/or growth of nanoscale holes in supported lipid bilayers. In this paper, we show that noncytotoxic concentrations of cationic nanoparticles induce 30−2000 pA currents in 293A (human embryonic kidney) and KB (human epidermoid carcinoma) cells, consistent with a nanoscale defect such as a single hole or group of holes in the cell membrane ranging from 1 to 350 nm2 in total area. Other forms of nanoscale defects, including the nanoparticle porating agents adsorbing onto or intercalating into …
Synthesis And Characterization Of Amphiphilic O-Phenylene Ethynylene Oligomers, Morris M. Slutsky, Jason S. Phillip, Gregory N. Tew
Synthesis And Characterization Of Amphiphilic O-Phenylene Ethynylene Oligomers, Morris M. Slutsky, Jason S. Phillip, Gregory N. Tew
Gregory N. Tew
We have previously reported the synthesis of short o-phenylene ethynylene oligomers with polar triethylene glycol side chains which adopt a helical conformation in solution with three residues per turn. Two new oligomers have been synthesized, a hexamer and a nonamer, incorporating a repeated triad motif of polar–nonpolar–polar sidechains in order to create a hydrophobic stripe in the folded conformation which we report here for the first time. Helical folding in solution was observed and, unlike the previously-reported oligomers, these new oligomers are ordered solids at room temperature. Although these oligomers were designed to assemble into helical bundle-like structures, no evidence …
Extending Helicity—Capturing The Helical Character Of Longer Ortho-Phenylene Ethynylene Oligomers, Ticora V. Jones, Morris M. Slutsky, Gregory N. Tew
Extending Helicity—Capturing The Helical Character Of Longer Ortho-Phenylene Ethynylene Oligomers, Ticora V. Jones, Morris M. Slutsky, Gregory N. Tew
Gregory N. Tew
Antimicrobial peptides are small cationic amphiphiles that play an important role in the innate immune system. Given their broad specificity, they appear to be ideal therapeutic agents. As a result, over the last decade, there has been considerable interest in developing them as intravenously administered antibiotics. However, it has proven difficult to accomplish this goal with peptide-based structures. Although it has been possible to solve some relatively simple problems such as susceptibility to proteolysis, more severe problems have included the expense of the materials, toxicity, limited efficacy, and limited tissue distribution. In an effort to overcome these problems, we developed …
Mechanism Of A Prototypical Synthetic Membraneactive Antimicrobial: Efficient Hole-Punching Via Interaction With Negative Intrinsic Curvature Lipids, Lihua Yanga, Vernita D. Gordon, Dallas R. Trinkle, Nathan W. Schmidt, Matthew A. Davis, Clarabelle Devries, Abhigyan Som, John E. Cronan Jr., Gregory N. Tew, Gerard C. L. Wong
Mechanism Of A Prototypical Synthetic Membraneactive Antimicrobial: Efficient Hole-Punching Via Interaction With Negative Intrinsic Curvature Lipids, Lihua Yanga, Vernita D. Gordon, Dallas R. Trinkle, Nathan W. Schmidt, Matthew A. Davis, Clarabelle Devries, Abhigyan Som, John E. Cronan Jr., Gregory N. Tew, Gerard C. L. Wong
Gregory N. Tew
Phenylene ethynylenes comprise a prototypical class of synthetic antimicrobial compounds that mimic antimicrobial peptides produced by eukaryotes and have broad-spectrum antimicrobial activity. We show unambiguously that bacterial membrane permeation by these antimicrobials depends on the presence of negative intrinsic curvature lipids, such as phosphatidylethanolamine (PE) lipids, found in high concentrations within bacterial membranes. Plate-killing assays indicate that a PE-knockout mutant strain of Escherichia coli drastically out-survives the wild type against the membrane-active phenylene ethynylene antimicrobials, whereas the opposite is true when challenged with traditional metabolic antibiotics. That the PE deletion is a lethal mutation in normative environments suggests that resistant …
Conformationally Rigid Proteomimetics: A Case Study In Designing Antimicrobial Aryl Oligomers, G. J. Gabriel, Gregory N. Tew
Conformationally Rigid Proteomimetics: A Case Study In Designing Antimicrobial Aryl Oligomers, G. J. Gabriel, Gregory N. Tew
Gregory N. Tew
The promise of proteomics to provide a vast library of protein structural data is exciting to scientists desiring an unprecedented understanding of the relationship between protein structure and function. This powerful knowledge will provide insight into the design rules for proteomimetics which are oligomers and polymers that can be more stable and inexpensive to produce than natural proteins, but still emulate the main biological function of the natural molecule. This Emerging Area article is intended to stimulate discussion on innovative strategies to design the next generation of proteomimetics. Specifically we will examine the design evolution of facially amphiphilic aryl oligomers, …
Antimicrobial Polymers Prepared By Romp With Unprecedented Selectivity: A Molecular Construction Kit Approach, Karen Lienkamp, Ahmad E. Madkour, Ashlan Musante, Christopher F. Nelson, Klaus Nüsslein, Gregory N. Tew
Antimicrobial Polymers Prepared By Romp With Unprecedented Selectivity: A Molecular Construction Kit Approach, Karen Lienkamp, Ahmad E. Madkour, Ashlan Musante, Christopher F. Nelson, Klaus Nüsslein, Gregory N. Tew
Gregory N. Tew
Synthetic Mimics of Antimicrobial Peptides (SMAMPs) imitate natural host-defense peptides, a vital component of the body’s immune system. This work presents a molecular construction kit that allows the easy and versatile synthesis of a broad variety of facially amphiphilic oxanorbornene-derived monomers. Their ring-opening metathesis polymerization (ROMP) and deprotection provide several series of SMAMPs. Using amphiphilicity, monomer feed ratio, and molecular weight as parameters, polymers with 533 times higher selectivitiy (selecitviy = hemolytic concentration/minimum inhibitory concentration) for bacteria over mammalian cells were discovered. Some of these polymers were 50 times more selective for Gram-positive over Gram-negative bacteria while other polymers surprisingly …
Cavitation Rheology For Soft Materials, Jessica A. Zimberlin, Naomi Sanabria-Delong, Gregory N. Tewmassachusetts - Amherst, Alfred J. Crosby
Cavitation Rheology For Soft Materials, Jessica A. Zimberlin, Naomi Sanabria-Delong, Gregory N. Tewmassachusetts - Amherst, Alfred J. Crosby
Gregory N. Tew
To guide the development of tissue scaffolds and the characterization of naturally heterogeneous biological tissues, we have developed a method to determine the local modulus at an arbitrary point within a soft material. The method involves growing a cavity at the tip of a syringe needle and monitoring the pressure of the cavity at the onset of a mechanical instability. This critical pressure is directly related to the local modulus of the material. The results focus on the network development of poly(lactide)–poly(ethylene oxide)–poly(lactide) triblock copolymer and poly(vinyl alcohol) hydrogels. These materials serve as model materials for tissue scaffolds and soft …
Activity Of An Antimicrobial Peptide Mimetic Against Planktonic And Biofilm Cultures Of Oral Pathogens, Nicholas Beckloff, Danielle Laube, Tammy Castro, David Furgang, Steven Park, David Perlin, Dylan Clements, Haizhong Tang, Richard W. Scott, Gregory N. Tew, Gill Diamond
Activity Of An Antimicrobial Peptide Mimetic Against Planktonic And Biofilm Cultures Of Oral Pathogens, Nicholas Beckloff, Danielle Laube, Tammy Castro, David Furgang, Steven Park, David Perlin, Dylan Clements, Haizhong Tang, Richard W. Scott, Gregory N. Tew, Gill Diamond
Gregory N. Tew
Antimicrobial peptides (AMPs) are naturally occurring, broad-spectrum antimicrobial agents that have recently been examined for their utility as therapeutic antibiotics. Unfortunately, they are expensive to produce and are often sensitive to protease digestion. To address this problem, we have examined the activity of a peptide mimetic whose design was based on the structure of magainin, exhibiting its amphiphilic structure. We demonstrate that this compound, meta-phenylene ethynylene (mPE), exhibits antimicrobial activity at nanomolar concentrations against a variety of bacterial and Candida species found in oral infections. Since Streptococcus mutans, an etiological agent of dental caries, colonizes the tooth surface and forms …
Lyotropic Columnar Liquid Crystals Based On Polycatenar 1h-Imidazole Amphiphiles And Their Assembly Into Bundles At The Surface Of Silicon, Sang Hyuk Seo, Gregory N. Tew, Ji Young Chang
Lyotropic Columnar Liquid Crystals Based On Polycatenar 1h-Imidazole Amphiphiles And Their Assembly Into Bundles At The Surface Of Silicon, Sang Hyuk Seo, Gregory N. Tew, Ji Young Chang
Gregory N. Tew
Polycatenar 1H-imidazole amphiphiles, consisting of a 1H-imidazole head connected through a benzene ring to a trialkyloxyphenyl tail, were synthesized and their self-assembling properties investigated. The 1H NMR and fluorescence spectroscopy studies showed that in nonpolar solvents, the amphiphiles formed reverse micelles in which the hydrophilic imidazole heads aggregated inside the micelles through intermolecular hydrogen bonding and the nonpolar alkyl chains were located at the periphery of the micelles. In concentrated solutions, they formed lyotropic liquid crystals having columnar hexagonal structures. The molecules were arranged in a disk via hydrogen bonding between successive imidazole moieties. When dilute solutions of the amphiphiles …
New Properties From Pla–Peo–Pla Hydrogels, Gregory N. Tew, Naomi Sanabria-Delong, Sarvesh K. Agrawal, Surita R. Bhatia
New Properties From Pla–Peo–Pla Hydrogels, Gregory N. Tew, Naomi Sanabria-Delong, Sarvesh K. Agrawal, Surita R. Bhatia
Gregory N. Tew
Polymeric materials are important in many medical applications. Regenerative medicine offers the potential to repair or replace damaged tissue and polymers are an essential component of many tissue engineering approaches. Hydrogels have many advantageous properties but, generally, lack robust mechanical properties. At the same time, mounting evidence points to the importance of the matrix modulus when constructing devices. In this context, triblock copolymers made from poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) have been prepared and formulated into hydrogels. Investigations into their mechanical properties found the elastic modulus to be greater than 10 kPa which is at least one order of magnitude stiffer than previously …
Synthesis Of Urea Oligomers And Their Antibacterial Activity, Haizhong Tang, Robert J. Doerksen, Gregory N. Tew
Synthesis Of Urea Oligomers And Their Antibacterial Activity, Haizhong Tang, Robert J. Doerksen, Gregory N. Tew
Gregory N. Tew
Facially amphiphilic urea oligomers were successfully prepared in a one-pot reaction by carbonyl diimidazole (CDI) coupling and showed greater antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Bacillus subtilis than MSI-78.
De Novo Design Of Biomimetic Antimicrobial Polymers, Gregory N. Tew, Dahui Liu, Bin Chen, Robert J. Doerksen, Justin Kaplan, Patrick J. Carroll, Michael L. Klein, William F. Degrado
De Novo Design Of Biomimetic Antimicrobial Polymers, Gregory N. Tew, Dahui Liu, Bin Chen, Robert J. Doerksen, Justin Kaplan, Patrick J. Carroll, Michael L. Klein, William F. Degrado
Gregory N. Tew
The design of polymers and oligomers that mimic the complex structures and remarkable biological properties of proteins is an important endeavor with both fundamental and practical implications. Recently, a number of nonnatural peptides with designed sequences have been elaborated to provide biologically active structures; in particular, facially amphiphilic peptides built from β-amino acids have been shown to mimic both the structures as well as the biological function of natural antimicrobial peptides such as magainins and cecropins. However, these natural peptides as well as their β-peptide analogues are expensive to prepare and difficult to produce on a large scale, limiting their …