Ronald G. Larson - US grants

DESCRIPTION (Applicant's abstract): We propose to develop a portable, self-contained, microfabricated device for extraction of genomic information from RNA or DNA viruses. Initially, we choose as a model system and as an important target the hemagglutinin HA1 of influenza A virus. Influenza is a prevalent human pathogen with an RNA genome. Mutations in the hemagglutinin (HA1) domains of influenza regularly produce new virulent forms that are responsible for 6 percent of annual mortalities in the U.S.A. Seasonal changes in influenza HA1 have a major impact on influenza epidemics and public health, and pose an on-going threat of world-wide pandemic. From analyses of influenza virus evolution, 18 of the most dangerous mutation sites have been identified. A present need is a reliable means to rapidly survey domestic and foreign populations for the emergence of new mutations. A self-contained, inexpensive, microfabricated device that can rapidly detect viral mutations using a small amount of sample would address this need. To expedite development of such a device we will perform research to achieve the following specific aims: Aim 1 - Determine the Influenza-A RNA purity requirements for Aims 2-4 by preparing samples of three levels: (a) cultured viral-infected cells, (b) purified whole viral particles, and (c) purified viral RNA. Aim 2 - On a microfabricated device, reverse transcribe and amplify the HA1 hemagglutinin domain of Influenza A using reverse-transcription PCR to produce double-stranded complementary DNA. Aim 3 - On a microfabricated device, perform fluorescent primer extension reactions on double-stranded DNA produced in Aim 2 to detect variations in bases in codons from the HA1 domain of hemagglutinin that have been involved in past viral mutations. Aim 4 - On a microfabricated device, separate primer-extended DNA products by gel electrophoresis and identify the locations of the base variations. Aim 5 - Integrate RNA separation, RT-PCR, primer extension reactions, electrophoretic separation, and (if necessary) RNA purification on a single microfabricated device. Aim 6 - Develop a silica gel RNA-adsorption column for purification of RNA on a microfabricated device.

OIA-0116331
PI: Solomon
Abstract

The PI and six colleagues in the Departments of Chemical engineering, Materials Science and Engineering, Biomedical Engineering, and Electrical and Computer Engineering at the University of Michigan are requesting funds to purchase a confocal laser scanning microscope. This will enhance their research and research training in nanoscale engineering of complex fluids and biomaterials. Specifics proposed applications of the instrument are: to quantify defect dynamics during annealing of colloidal crystals, to detect self-assembled proteins, to observe microfluidic flows on cellular development, and to facilitate the efficient design of microfabricated devices.

0304316
Larson
This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 02-148, category NIRT. The objective of this proposal is to design and build a microfabricated platform for study of DNA/protein interactions at the nano-scale. These interactions are at the heart of the cellular machinery for maintaining and transcribing DNA, and include transcription factors, as well as histones and other chromatin proteins. These DNA/protein interactions are under active study at the cellular level, but the next steps towards a detailed understanding of them require their study at smaller length scales, including the nanoscale. Therefore, a microfabricated devise will be built, which contains a main channel of length 20 to 30 microns and of width ranging from 20 nm to 2 microns. Individual DNA molecules will be stretched in the channel and positioned using high frequency electric fields, and anchored at gold electrodes using thiol groups chemically attached to the ends of the DNA molecules. This long, very thin, channel will be joined to thin side channels for addition of DNA-interacting proteins locally to specific regions of the DNA molecule. The proteins will be further localized by use of capture electrodes as well as hydrodynamic focusing using flow through other side streams, and other confinement methods. The channels will be etched in silicon, and bonded to a thin glass substrate, to permit examination by optical microscopy. The broader impacts of the proposal include the integration of the proposed research with the introduction of a new Nanoscale Science and Engineering (NSE) curriculum for graduate students. The new course will focus on nano- fabrication issues related to integration of electronic function with microfluidics and transport issues related to the processing of biological samples.

DESCRIPTION (provided by applicant): The constant threats posed by Influenza and other RNA viruses of pandemic due to antigenic shift or transfer from an animal host, and of season-to-season variation due to antigenic drift can be most effectively countered by pervasive monitoring. Viral monitoring in the clinic and field would be assisted greatly by the availability of microfabricated devices capable of rapid, inexpensive genotyping. To accelerate the emergence of such devices we propose research to engineer and build two prototype microfabricated devices, one to detect influenza A sub-types, and the other to perform single nucleotide polymorphism (SNP) detection to monitor antigenic drift. We will also develop and integrate a purification system to prepare sufficient quantity and purity of RNA material from virus-containing clinical samples for the microfabricated device to perform reverse transcription-PCR (RT-PCR) and genotyping reactions. Specifically, we aim to Aim 1 - Develop a microfabricated device capable of producing viral RNA from biological samples with the levels of purity and concentration required to perform on-chip RT-PCR reactions. Aim 2 - On a microfabricated device, perform an RT-PCR reaction on HA 1 hemagglutinin domain of influenza A, producing double-stranded complementary DNA. Aim 3 - On a microfabricated device, perform restriction digestion reactions that can distinguish H1, H3, and H5 types of influenza A. Perform a multiplex reaction that can simultaneously detect RNA from influenza A and another RNA virus, such as influenza B or SARS. Aim 4 - On a microfabricated device, perform single-nucleotide polymorphisms that can distinguish antigenic drift in the HA1 domain of influenza A. Aim 5 - Integrate RT-PCR, restriction digestion, and electrophoretic separation onto a single microfabricated device, and integrate this with a system for RNA extraction from clinical, throat-culture, samples.

DESCRIPTION (provided by applicant): The constant threats posed by Influenza and other RNA viruses of pandemic due to antigenic shift or transfer from an animal host, and of season-to-season variation due to antigenic drift can be most effectively countered by pervasive monitoring. Viral monitoring in the clinic and field would be assisted greatly by the availability of microfabricated devices capable of rapid, inexpensive genotyping. To accelerate the emergence of such devices we propose research to engineer and build two prototype microfabricated devices, one to detect influenza A sub-types, and the other to perform single nucleotide polymorphism (SNP) detection to monitor antigenic drift. We will also develop and integrate a purification system to prepare sufficient quantity and purity of RNA material from virus-containing clinical samples for the microfabricated device to perform reverse transcription-PCR (RT-PCR) and genotyping reactions. Specifically, we aim to Aim 1 - Develop a microfabricated device capable of producing viral RNA from biological samples with the levels of purity and concentration required to perform on-chip RT-PCR reactions. Aim 2 - On a microfabricated device, perform an RT-PCR reaction on HA 1 hemagglutinin domain of influenza A, producing double-stranded complementary DNA. Aim 3 - On a microfabricated device, perform restriction digestion reactions that can distinguish H1, H3, and H5 types of influenza A. Perform a multiplex reaction that can simultaneously detect RNA from influenza A and another RNA virus, such as influenza B or SARS. Aim 4 - On a microfabricated device, perform single-nucleotide polymorphisms that can distinguish antigenic drift in the HA1 domain of influenza A. Aim 5 - Integrate RT-PCR, restriction digestion, and electrophoretic separation onto a single microfabricated device, and integrate this with a system for RNA extraction from clinical, throat-culture, samples.

TECHNICAL SUMMARY

Rheology is more sensitive to polymer architecture, including molecular weight distribution and long-chain branching distribution, than is any other measurable property. Thus there is great motivation to carry out rheological measurements on well-chosen polymer melts and solutions that will lead to improved ability to link rheology to polymer molecular weight and branching distributions. Three new projects are proposed. First, the effects of polydispersity in arm and backbone length on the linear viscoelasticity of well defined entangled H polymers, which have two branch points and four arms, will be studied. Recent models show that H-branched polymers should have rheology that is very sensitive to polydispersity, so that these studies, along with corresponding theoretical work, will allow strong tests of these theories to be carried out, and help in the development of a more accurate theory of branch point motion. Second, using model materials from Dow Chemical Co., linear viscoelastic data will be obtained that will be sensitive to higher order effects of branch point motion and used to test the ability of an existing algorithm, the hierarchical model, to predict accurately these data. The third problem will be to test the principle of universal scaling of linear and nonlinear rheological properties in polymer solutions, which holds that all such properties, when measured at a fixed value of the ratio of c/ce, the concentration to the entanglement concentration superpose, when plotted in dimensionless form. This concept will be tested thoroughly by measuring sets of linear and nonlinear data for different molecular weights, at several fixed values of c/ce and by extending these tests to binary blends of linear polymers.

NON-TECHNICAL SUMMARY

Over 200 billion pounds of polymers are produced commercially worldwide, and shaped into a wide variety of products. The shaping processes depend on their flow properties, or rheology, which, in turn, depends on molecular characteristics, such as molecular weight distribution and branching distribution. Thus, there is a huge industrial interest in better defining the relationship between polymer molecular structure and rheology. The proposed work will increase knowledge of this relationship, leading to polymers that are designed better at the molecular level. Insights from this grant, and past grants from the same NSF program, will assist in collaborations the proposer has with Dow Chemical Co. and Procter and Gamble. A new book, co-authored by the proposer, Molecular Structure and Rheology of Molten Polymers, published this year, contains work from the previous NSF grants, and the work to be carried out under the new grant will similarly be well publicized, both to U.S. industry and overseas, through international collaborations. The work data will also lead to improvements in a commercial software package IRIS, for predicting rheological properties of polymer melts, that is used widely in industry.

TECHNICAL SUMMARY

Understanding remains incomplete regarding the relaxation of complex branching structures in entangled polymer melts with multiple branch points, such as H- or comb-branched polymers, or for polymers with branches of differing lengths, such as asymmetric stars and asymmetric H polymers, or for hyperbranched polymers (i.e., with branch-on-branch topology). To address these issues, which are important both scientifically and for applications to commercial polymer manufacture, we are performing a combination of the following tasks: 1. Synthesis of high-quality model branched polymers with branches of the same or different length that are carefully designed to test physical theories. 2. Careful characterization of the molecular weight and branching properties of these polymers. 3. Measurement of the linear rheological properties over a wide frequency range. 4. Comparison of the measured viscoelastic properties with predictions derived from the various alternative proposed theories. We plan to accomplish these tasks through a collaborative framework, involving a collaborator, Jimmy Mays, who will use a novel route to synthesize 1) asymmetric H polymers; 2) asymmetric star-on-star polymers, based on a core star polymer, each branch of which terminates in two unequal length branches; and 3) combs with tetrafunctional branch points. These polymers will be carefully characterized by gel permeation chromatography and TGIC, and studied through rheological measurements, including careful long-time creep rheometry with the help of instrumentations and methods available in the laboratory of Prof. John Dealy, a collaborator at McGill University. Existing computational models for predicting the measured rheology will be employed in collaboration with Chinmay Das in the McLeish group at Leeds University.

NON-TECHNICAL SUMMARY:

To form advanced plastic fibers or thin plastic sheets used for packaging, molten plastic is pulled or stretched at extremely high speeds. The performance of this process depends on how the polymer molecules in the plastic are entangled with each other, and how they escape those entanglements. Polymers that branch into multiple long strands are exceptionally useful for industry, since they serve as netting that strengthens the plastic so that it does not rip or bursting when blown into shape. Larson?s team has found that changes to as few one branch in a million branch points can significantly impact the properties of the melt relevant to its strength as a melt. The reason for this is that branched polymers entangle extremely well with other branched polymers. To escape these entanglements, they must reconfigure by reeling branches towards the branch point, like Houdini dislocating his shoulder to escape a straight jacket. Therefore, the entanglements are long-lived and make the plastic easier to shape. Larson?s team is chemically synthesizing special branched polymers that are exceptionally useful in determining how branched polymers manage to perform their ?Houdini? acts and how to optimize this for advanced performance. Their measurements of the rates at which polymers escape entanglements is providing knowledge that is of great interest to collaborators at Dow Chemical Company and other plastics manufacturing companies. The research has been highly interdisciplinary and international with collaborators at the University of Tennessee, McGill University, the University of Leeds, and Dow Chemical Company.

0853662
Larson

Despite substantial progress achieved in understanding the microstructural basis of transport and rheology in many classes of complex fluids, including polymers, colloids, glasses, liquidcrystals and others, the flow behavior of one of the most important classes of complex fluids, surfactant solutions, remains mysterious. In particular, it has been known for at least two decades that translucent solutions of thread/rod like surfactant micelles undergo a phase transition to form viscoelastic gels under sufficiently strong shear or extensional flows. Lacking an understanding even of what these structures are, they are simply given the name Flow-Induced Structures, or FIS. While progress has been made towards simulating thread/rod like(nanoscale) micelles at the molecular level, and towards simulating the macroscopic consequences of the presence of FIS, such as banded structures in the shear flow, there is an almost complete lack of theoretical connection between molecular structures and the possibility and conditions under which such nano structures might manifest.

Intellectual Merit. This is a collaborative investigation between two universities to help close gaps in understanding through both experiments and a multi scale set of simulations encompassing length and time scales ranging from atomic (and nano) to continuum. A set of experiments exploring the regimes of transient and novel permanent flow-induced structures, induced by extensional deformation in micro channels, will be carried out. In parallel, the project proposes four different simulation methods. 1) Atomistic Molecular Dynamic Simulations. These can capture the structure and interactions of one or two thread like micelle fragments in a periodic box roughly 10 nm on a side, at the atomic level on timescales of 10 nanoseconds. This is long enough and big enough to determine ionic effects on micellar structure and intermicellar interactions. 2) Coarse Grained (CG) Molecular Dynamics Simulations. Using the Marrink MARTINI model that lumps around four heavy atoms into each bead, a 1000 fold speed up relative to atomistic simulations is attained, reaching nearly to the millisecond time scale, while preserving molecular scale properties through suitably chosen CG potentials. The CG model will allow for the determination of micelle persistence lengths and the stability of thread like micelles as a function of salt concentration. 3) Brownian Dynamics Simulations using pearl necklace micelle model. This model, pioneered by Ryckaert and coworkers, treats the wormlike micelle as a string of beads that can break and fuse end-to-end, and is fast enough to allow for the equilibration of micelle length distributions, with and without flow. We will incorporate into this model the potential for micelle junctions or cross links, and bundling, thereby allowing for the first time a molecular scale simulation of flow induced gel formation. 4) Kinetic Model and Constitutive Equation. We will attempt to draw from the simulations the ingredients necessary to build a kinetic model and, if possible, a full nonlinear constitutive equation for flow of thread like micelles. Through this set of interlocking simulations, each aimed at different length and time scales, complemented by experiments, the investigators have developed a roadmap to bridge between molecular properties and macroscopic flow effects such as flow induced gelation and shear banding.

Broader impacts include a collaboration with scientists at Proctor and Gamble, whose nterest is in understanding, modeling, and controlling the properties of thread like micellar solutions. They plan annual meetings between P&G scientists and our team of graduate and undergraduate students and faculty as well as month long student interships at P&G. This will lead to fruitful exchange of ideas, bringing practical commercial concerns to the attention of students, and carrying novel fundamental ideas and new modeling methods into the corporate world. They plan to also recruit UG (REU) as well as school students including minority students (through STARS program at Washington University) and involve them in developing modules driven by fast GROMACS and MARTINI engines with coarse grained potentials to help learn self assembly in surfactant solutions.

ABSTRACT:
EFRI-BSBA: Engineering Synthetic Mimics of DNA- Protein Recognition Systems

Proposal # 0938019
PI: Larson, Ronald G.

The research objective of this collaborative project is to create artificial "DNA" consisting of charged lines or nanowires deposited on a silicon substrate, with charged synthetic nanoparticles functioning as synthetic "proteins." Proteins transcribe DNA into RNA, regulate genes, and replicate DNA, all with remarkable efficiency and precision. To do so, in each cell, thousands of proteins scan continuously millions of bases of DNA, and bind firmly only when encountering precise sequences of six to twenty base pairs. This superb sequence discrimination is achieved through a combination of simple physical forces - primarily electrostatic, hydrophobic, hydrogen bonding, and van der Waals. These forces result in the diffusion of positively charged proteins along negatively charged DNA, binding firmly only when a precise pattern of charged, polar, and hydrophobic regions on the protein complements sites on DNA having the appropriate base sequence. If this mechanism could be harnessed within synthetic systems, it would represent a transformative breakthrough that would open the door to wide-ranging applications in the areas of nanoscale sensing, actuation and programmed assembly. Examined in this project will be both charged organic PAMAM dendrimers and surfactant-coated inorganic CdSe and CdTe nanoparticles, and engineer their charge distributions, as well as hydrogen bonding and van der Waals interactions to produce weak binding to generic DNA sequences or line charge distributions and strong binding to specific ones, using molecular dynamics simulations to guide the design. The research will aim to engineer both the one-dimensional search and the binding at specific sites by patterned nanoparticles to complementarily patterned lines on silicon. This research also intends to drive reactions upon firm binding, including photoemission, thus taking the first steps towards precise nano-actuation. Broader impacts include responding to a "grand challenge" by laying a foundation for the diagnosis, repair, and ultimately self-fabrication of nanomaterials and nanocircuitry. The PIs will also develop an outreach and minority recruiting program using a miniaturized "Biological Mimics Roadshow" for use in the classroom in collaboration with U-of-M's IDEA Institute. This program will be supplemented by running residential summer science camps for Detroit minority high school students, which will introduce high school minority students to some of the most exciting science and engineering, and encourage their pursuit of these fields.

Planning Grant for an I/UCRC for Macromolecular Topology

1134832 University of Cincinnati; Gregory Beaucage
1134788 University of Michigan; Ronald Larson

The University of Cincinnati and the University of Michigan are collaborating to establish the proposed center, with the University of Cincinnati as the lead institution.

This is a planning grant request from the University of Cincinnati and the University of Michigan to explore a potential I/UCRC in macromolecular topology. Funds are requested for a two-day planning meeting with potential industrial sponsors in Cincinnati. The proposed Center for Macromolecular Topology (CMT) will address a need in the polymer industry to synthetically control, characterize, model and simulate complex macromolecular architectures to manipulate mechanical and rheological properties.

The CMT will develop human capacity in the chemical industry. The center will significantly enhance the nations research infrastructure base, and plans to coordinate internet based video courses on rheology, scattering, synthesis and modeling of complex macromolecular systems that will be available to industrial as well as academic participants and the general public on arrangement with the Universities. CMT will actively recruit women and minority graduate and undergraduate students. The center has as a main goal enhancement of the intellectual capacity of the engineering workforce and capabilities in controlling molecular topology. Improvement in the control of molecular topology will lead directly to improvements in a wide range of consumer and industrial products from gels to tires; from plastic packaging to viscosity enhancement in oils.

TECHNICAL SUMMARY:

Mixtures of a monodisperse linear polymer with a monodisperse "star"-branched polymer represent the simplest polymers that expose the greatest deficiencies in current understanding of "constraint release" -- the effect that motion of one polymer chain has on its entanglements with other chains. This problem will be attacked by (1) obtaining a series of carefully synthesized star 1,4-polybutadiene polymers, which are then thoroughly characterized by the most advanced method available, namely temperature gradient interaction chromatraphy, or TGIC, (2) formulating and measuring the rheology of a set of some 40 mixtures of "star"-branched and linear polymers covering a range of constraint-release conditions, (3) applying the most advanced "tube" theories to predict the rheology of these mixtures and other such mixtures already available in the literature, and (4) collaborating through an international network, thereby accessing new polymer materials, dielectric relaxation data on cis-polyisoprene star/linear mixtures, and accessing results from "slip-link" and molecular dynamics polymer simulations for the prediction of the rheology and dielectric relaxation of these star/linear blends.


NON-TECHNICAL SUMMARY:

Polymers are among the most widely used synthetic materials; over 300 million tons are produced annually, for use in automobiles, medical supplies and equipment, wrappings for food preservation, and many other applications. The manufacture of such polymers in the United States is now increasingly attractive, due to cheap and abundant sources of natural gas, from which the starting chemicals for common polymers, such as polyolefins, are obtained. To economize on the quantity needed and to speed and cost-reduce the shaping of polymers into products, the flow properties of polymers must be optimized. This often involves the strategic addition of controlled amounts of long-chain branching to the polymer molecules. However, design of branching strategies depends on a thorough knowledge of polymer dynamics, which is currently inhibited by lack of understanding of a phenomenon called "constraint release" -- the effect that motion of one polymer chain has on its entanglements with other chains. This proposal represents a direct attack on this unsolved problem, using advanced tools of polymer synthesis and newly discovered methods of characterization of branching at unprecedented levels of accuracy. Understanding will be greatly enhanced by collaborating with an international team, which includes the most knowledgeable scientists in the world on various aspects of the problem, including synthesis (in Saudi Arabia, Korea, and the U.S.), characterization (in Korea and Japan), and computational modeling (in the U.S. and United Kingdom). The research will create the most complete body of experimental work on "constraint release" in branched polymers, and the data and theories will be made available to industrial researchers through publication, web-based access, and direct interaction with industrial researchers. Ph.D., Undergraduate, and High School students will be trained in the course of the research.

CBET - 1500377
PI: Larson, Ronald

Surfactants are used in many household, medical, and industrial products. Surfactant molecules in solution can spontaneously assemble into structures, which can strongly influence the properties of the liquid. This project will develop a theory to predict the properties of solutions of thread-like micelles, which are long flexible surfactant structures. The particular focus of the proposed work is to explore the role of micelle branching in the behavior of these interesting solutions. The results of the work will be incorporated into an open source software package that will be made freely available for use in the industrial formulation of surfactant solutions. Students involved in the research will have the opportunity to gain experience in industrially-related research through internships at collaborating companies.

A detailed, quantitative theory will be developed to predict the linear rheology of solutions of branched threadlike micelles, including effects of reptation (or sliding) of the micelles through the entanglement network, as well as fluctuations in the "primitive path" of the micelles, micelle breakage and rejoining, formation and breakage of network junctions, and other relaxation phenomena. These phenomena will be modeled using a "Pointer Algorithm" developed by the PI that accounts for micelle relaxation phenomena, but not for micellar branching. The incorporation of branch formation will represent a major advance in understanding the dynamics and rheology of surfactant solutions. This methodology will provide accurate estimates of micelle lengths, breakage rates, and rates of formation and breakage of branch points, and the number of branches per micelle, extracted from rheology data by fits of this data to predictions of the Pointer Algorithm.

PI: Larson, Ronald
Proposal Number: 1602183

The goal of the proposed research is to develop predictive methods for coating material properties and to even prescribe these properties by designing materials from the molecular level up. The results of this research would find many applications in engineering and in the industry, since the utility of coating materials in everyday life is unequivocal. Most of the objects around us are coated with a material that either enhances their usefulness or their life time (computer and tablet screens, furniture, metallic objects and tools, walls etc.).


While there has been great interest and effort in the area of multi-scale modeling, there have been few, if any, successful predictions of colloidal scale transport properties based on multi-scale modeling starting with atomistic inputs for materials of large-scale commercial interest. Here, it is proposed to integrate a set of methods developed in recent years to allow prediction of the impact of surfactant, polymer, and colloidal composition on the rheological properties of latex coatings. Latex coatings contain surfactant molecules, polymer molecules with hydrophobic "sticker" end groups, and colloidal particles that are bridged by the polymer molecules to form a transient network. The simulation tools to be implemented and integrated are molecular dynamics simulations at the atomistic, coarse-grained (CG) and implicit-solvent CG levels, Brownian dynamics simulations using coarse-grained polymer chains using finitely extensible (FENE) spring models, population balance methods for tracking numbers of bridging polymer chains between pairs of colloidal particles, and Stokesian dynamics methods for computing the hydrodynamic interactions of colloidal particles undergoing shear flow. Also to be exploited are methods of computing free energies of microscopic transitions, such as free energy of transition of a bridging to a looping chain, and free energy of compression of polymer chains bound to colloidal particles. While all of these tools have been developed or exploited in the Larson group over the past decade, and integration of many of the methods has been carried out at the level of thermodynamics, the proposed new research is to map the transport properties of these methods onto each other, so that transport rates determined at the finest levels allow input parameters and time-scales of coarser-grained methods to be specified. The mapping will also be validated and improved upon, through comparison with experimental data. Accomplishment of this project will lead to a set of inter-locking modeling tools that will not only allow prediction of the rheological properties of latex coatings, but will establish a paradigm to be followed for modeling many other complex materials and multi-scale transport processes. Broader impacts include interactions with industry. An outreach to minority students will be undertaken and a Ph.D. student will be recruited and trained both through the work at Michigan and through summer internships at Dow Chemical Company. An open source software package for prediction of the rheological properties of polymer/colloid materials will be developed and international collaborations with Edinburgh University and Durham University at the UK will be established.

NON-TECHNICAL SUMMARY:

Electrically charged polymers, called polyelectrolytes, are common in biology and include DNA, RNA, proteins, and mucous layers. They are increasingly used for applications ranging from drug delivery to membranes for sensing or batteries. Membranes of polyelectrolytes for these applications can be built up, layer by layer, by sequentially dipping a surface into a negatively charged polyelectrolyte followed by dipping into a positively charged one. Additionally, gels swollen with water, known as "coacervates", can be made by mixing two oppositely charged polyelectrolytes. Despite the importance of these materials in biology and advanced applications, their behavior is poorly known, and neither the properties of coacervates nor the rate of growth of layer-by-layer membranes is understood at present. While promising theories for such polyelectrolyte materials have recently been developed, there is little systematic experimental data to test and confirm these theories so as to help design advanced materials. To provide such tests, this project will use both simple and advanced experimental methods to measure the composition of coacervates, and the growth rate and thickness of layer-by-layer films. These measurements will be carried out systematically with varying salt concentration and pH to establish quantitative trends needed to test and confirm newly developed theory and provide a firm base for design of advanced materials made from polyelectrolytes. Such knowledge is also relevant in biological systems, including the interactions of positively charged proteins with negatively charged DNA, which controls the structure and function of chromosomes. Beyond the research, broader impacts of this project will include the education of graduate and undergraduate students, outreach, and development of specialized computational codes relevant to this topic.


TECHNICAL SUMMARY:

To understand and test theories for the equilibrium and dynamics of assemblies of oppositely charged polyelectrolytes, several phases of study will be performed. First, the phase behavior including compositions of individual polyions in both coacervate and supernatant phases for four common polyelectrolyte mixtures will be measured by high pressure liquid chromatography, proton NMR, and other methods. The results will be compared to the predictions of new theories, and used to test and improve these theories. Titrations with acid and base will be used to determine ion pairing equilibrium constants, ionization equilibrium, and thermodynamic "chi" parameters. In addition, Layer-by-Layer (LbL) growth rates for these polyelectrolytes will be measured and the thermodynamic information determined by theory and phase behavior will be used to predict these growth rates. The diffusivities of polyions through the polyelectrolyte multilayer needed for predictions of LbL growth will be inferred from strengths of ion pairing obtained from atomistic molecular dynamics (MD) simulations of a polyanion and polycation in water and salt.

On a dollar per mass basis, active pharmaceutical ingredients (APIs) are perhaps the most valuable chemicals in the world, and yet much of the mass of APIs in drugs taken is not absorbed in the body, entering the water supply and potentially harming human health and the environment. At the same time, despite rapid advances in the science of personalized medicine, and digital, additive manufacturing, the trillion-dollar-per-year pharmaceutical industry retains its century-old manufacturing processes and uses supply chain and distribution models that are potentially prone to tampering, contamination, and disruption. To address this problem, researchers and drug manufacturers have begun developing 3D printing approaches, as well as techniques borrowed from other industries (e.g. thin-film coatings) for drug formulation, dose customization, and release profile engineering. However, fundamental challenges remain with material compatibilities, ingredient dispersion in solvents or matrix materials, process control, and scalability. This fundamental research project aims to address these challenges by converging several new breakthroughs in additive manufacturing, molecular and crystallization modeling, surface science and engineering, and patient-specific in vitro disease models. This project will train students of diverse backgrounds, including women and minorities, and those concerned with patient care and safety, public health, drug costs, regulatory law and practices.

This fundamental research project will introduce a radically new approach to drug formulation and distributed manufacturing, offering new means of controlling crystalline structure, cocrystallization, and adaptation to different delivery vehicles. Currently, predictive model-based process design for organic crystallization processes is still in relative infancy. Likewise, processes for cocrystallization require further work to systematize coformer selection and prediction of conditions for cocrystal formation. The novel, solvent-free process used here offers possibilities for developing novel pharmaceutical cocrystallization research tools, as well as a path to scalable cocrystal manufacturing. The technology platform of controlled surface wettability patterns to enable low-cost dissolution assays, combined with the organoid assays will create new paradigms for on-site validation and control of product quality, which will be particularly beneficial in a distributed manufacturing setting. The organoid assays used could enable rapid testing of new medications in more realistic cellular microenvironments prior to human trials. This research will facilitate the path to accelerating the time from drug development to manufacturing and distribution, and help prevent potentially dangerous by-products or contaminants from reaching patients.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

PART 1: NON-TECHNICAL SUMMARY

Polyelectrolyte complexes are a mixture of two kinds of electrically charged, long polymer molecules, of opposite charge. Their opposite charge causes the two kinds of polyelectrolytes, which can be very different from each other, to nevertheless attract each other and form an intimate mixture, or complex. An important example of a polyelectrolyte complex is the chromosome, which contains DNA, which is a negatively charged polymer and hence repels itself. Nature therefore uses positively charged proteins to bind to the DNA and bundle it into the compact shape of the chromosome. Among the many other examples of polyelectrolyte complexes are biological membranes, underwater adhesives, drug delivery vehicles, and food processing agents. Despite their importance and the growing interest in them for advanced applications, basic understanding of how to control their structure and mechanical properties remains undeveloped. The proposed work focuses on measurements of the mechanical properties of these complexes, such as their viscosity and stiffness, and computer simulations to determine how these properties are controlled by the composition, including the polyelectrolytes, salts, and pH. Understanding the relationship between the composition and mechanical properties will provide deep insight into why complexes have the properties they do, and how to design these properties for future applications. There may also be connections to biological function, which are affected by the micro-mechanical properties of these complexes. The research will be integrated with education of graduate and undergraduate students, outreach, and creation of software.


PART 2: TECHNICAL SUMMARY

The PI and his group will measure the linear rheology of polyelectrolyte coacervates of widely varying composition and containing different salts, and seek to test time-temperature, time-salt, time-hydration, and time-pH superpositions that allow data to be collapsed onto approximate “master curves.” Specifically, they will measure the linear rheological properties of polycations poly(N,N-dimethylaminoethyl methacrylate) and poly(diallyldimethylammonium) with polyanions poly(acrylic acid) and poly(styrene sulfonate), and with salt ions Na+ or K+, and Cl- or Br-. They will explore the surprising differences and anomalies among coacervates, depending on the polyelectrolytes, salts, and the chain lengths used, including an asymmetry in relaxation time produced by changing the molecular weight of polyanion vs. polycation, anomalous dependence of viscosity on degree of polymerization, and a low-frequency plateau modulus for some, but not all, coacervates. The systematic approach will provide a comprehensive understanding of the key determinants of rheological behaviour and overcome the limitations of existing data sets. They will also carry out molecular dynamics simulations to determine the nature of the local interactions among polyelectrolytes and salt ions that determine the rates of relaxation. This will be done in part through development of novel time correlation functions to determine whether local monomer diffusion is governed by ion-pairing dynamics, or by collective “glassy” dynamics, or some mixture of the two.
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This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

This award will provide partial support for the 2022 Gordon Research Conference (GRC) on Colloidal, Macromolecular, and Polyelectrolyte Solutions: Connecting Theory and Simulations to Experiments and Applications, which will be held February 6-11, 2022 in Ventura, CA. The conference will be preceded by a Gordon Research Seminar (GRS) for graduate students. Together, the two events will provide opportunities for researchers, especially young investigators and students, to present results of their research, meet senior experts in the field, and discuss emerging research trends in colloidal and polymeric solutions. These materials are important in a variety of technology areas including coatings, paints, personal-care products and cosmetics, and food processing. The goal of the GRC and GRS is to bring promote discussions that will enable comparisons between experiments, numerical simulations, and theory for these important materials.

Colloidal and polymer science, including polyelectrolytes, is growing in importance in a wide range of applications, especially those involving biotechnology. The development of RNA vaccines was enabled in part by creating nanoparticle complexes of DNA, a polyelectrolyte, with oppositely charged surfactants. Synthetic structures that mimic cells, such as membraneless organelles, are formed by segregating charged proteins that exhibit polyelectrolyte phase behavior. Increasing computing power, new computational methods, and high resolution experiments now allow comparisons between experiment and simulation at length and time scales that are accessible to both. This is the theme of the GRC/GRS. Session topics will include polyelectrolytes and ionic liquids, confined colloids, directed assembly, propelled colloids, interfacial systems, polymers and biology, polymer glasses, and driven elastomers. The GRS for graduate students will include technical sessions as well as career development sessions for students and young investigators.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.