Polymer Chemistry Blog

April M. Kloxin, Ph.D., is an Associate Professor in Chemical & Biomolecular Engineering and Materials Science & Engineering at the University of Delaware (UD) and a member of the Breast Cancer Research Program at the Helen F. Graham Cancer Center and Research Institute in the Christiana Care Health System.  She obtained her B.S. and M.S. in Chemical Engineering from North Carolina State University and Ph.D. in Chemical Engineering from the University of Colorado, Boulder, as a NASA Graduate Student Research Program Fellow.  She trained as a Howard Hughes Medical Institute postdoctoral research associate at the University of Colorado before joining the faculty at UD in 2011. Her group aims to create unique materials with multiscale property control for addressing outstanding problems in human health. Her research currently focuses on the design of responsive and hierarchically structured soft materials and development of controlled, dynamic models of disease and regeneration.  Her honors include the Biomaterials Science Lectureship 2019, ACS PMSE Arthur K. Doolittle Award 2018, a Susan G. Komen Foundation Career Catalyst Research award, a NSF CAREER award, and a Pew Scholars in Biomedical Sciences award.

What was your inspiration in working with polymers?

I have always enjoyed building things and had a desire to use those skills to help people.  I discovered my passion for using chemical approaches to build soft polymeric materials possessing unique and useful properties as an undergraduate and Master’s student at North Carolina State University (NCSU).  At NCSU, I had the opportunity to work in a collaborative environment with many extraordinary friends and colleagues having great polymer science and engineering expertise, including my MS thesis advisors Profs. Rich Spontak and Stuart Cooper.  This experience helped me understand the connection between molecular design and synthetic approaches for building polymeric materials with specific properties for a desired application.  I had the opportunity to fully realize and direct this passion working at the interface between polymeric materials and biological systems under the outstanding advisement and mentorship of Prof. Kristi Anseth at the University of Colorado, Boulder, for my Ph.D. and with the many remarkable researchers in her group and at the University.

What was the motivation behind your most recent Polymer Chemistry article?

From a biological perspective, my group has a focus on understanding how changes in the structure, mechanical properties, and compositions of tissues in the human body that occur upon injury influence the function and fate of key cells in healing and disease.  In this context, we have been interested in building synthetic mimics of these complex systems and processes, and we wanted to establish simple yet effective approaches for controlling the density and stiffness of soft materials when and where desired for hypothesis testing.  In the Polymer Chemistry manuscript, we were inspired by the work of Prof. Matt Becker (Duke University) amongst others demonstrating how the rate of formation of water-swollen polymer networks, hydrogels, could be used to control defect formation, network heterogeneity, and thereby the mechanical properties of the resulting materials.  We hypothesized that the rate-based control of properties that others observed with catalyzed step growth reactions was translatable to a photo-polymerized system, affording the implementation of a variety of photochemical controls (e.g., wavelength, intensity, time).  In particular, by selecting a wavelength of light that was not centered at the maximum absorption of the photoinitiator, we were better able to control the rate of photopolymerization with an accessible bench-top visible light LED system and thereby defect formation.  We then saw an opportunity to exploit dangling-end defects that were generated with this rate-based approach to increase crosslink density and ‘stiffen’ these materials with a secondary photopolymerization.  We are excited about the potential that this light-triggered rate-based approach for controlling mechanical properties of polymer networks has for a number of applications, including our on-going studies of cell response to matrix stiffening.

Which polymer or materials scientists are you most inspired by?

Oh, there are so many! I am especially inspired by the work and leadership of Prof. Paula Hammond (MIT) and Prof. Kristi Anseth, who continue to blaze trials at the interface between polymers, materials, and biology to solve complex problems, and Prof. Chris Bowman (University of Colorado, Boulder) and the late Prof. Charlie Hoyle (University of Southern Mississippi), who have pioneered the use of light-triggered step growth reactions for creating polymeric materials with diverse and robust properties.

Can you name some up and coming polymer chemists who you think will have a big impact on the field?

It is an exciting time in polymer chemistry with many excellent researchers working from different perspectives to advance not only the field of polymer chemistry, but also to make fundamental breakthroughs that have an impact in biology, medicine, and energy.  Selecting just a few is difficult in this context.  A few that come to mind at the moment whose work I find particularly inspiring are Prof. Aaron Esser Kahn (University of Chicago) in biomolecular design of polymeric materials for rewiring the immune system, Prof. Dominik Konkolewicz (Miami University Ohio) in bioconjugations and dynamic covalent chemistries with polymeric materials, Prof. Rachel A. Letteri (University of Virginia) in peptide-polymer conjugates for multi-scale and dynamic properties, and my own new colleague Prof. Laure Kayser (University of Delaware) in conducting and semiconducting polymers.

How do you spend your spare time?

I enjoy making things, from designing materials at work to preparing satisfying meals in the kitchen at home.  Breakfast foods are my favorite, and I have different recipes that I continue to hone on weekends for quick meals during the week.  I also love being outside walking, hiking, or running with my friends or my husband and our two sons, particularly in the beautiful early autumn weather we currently are having.

What profession would you choose if you weren’t a chemist?

My obsession with the complexity of biological systems and improving human health would keep me in science and engineering, whether in molecular biology or bioinformatics or more applied in medicine.

Read April’s recent Polymer Chemistry article now for FREE until 31st October!

Rate-based approach for controlling the mechanical properties of ‘thiol–ene’ hydrogels formed with visible light

The mechanical properties of synthetic hydrogels traditionally have been controlled with the concentration, molecular weight, or stoichiometry of the macromolecular building blocks used for hydrogel formation. Recently, the rate of formation has been recognized as an important and effective handle for controlling the mechanical properties of these water-swollen polymer networks, owing to differences in network heterogeneity (e.g., defects) that arise based on the rate of gelation. Building upon this, in this work, we investigate a rate-based approach for controlling mechanical properties of hydrogels both initially and temporally with light. Specifically, synthetic hydrogels are formed with visible light-initiated thiol–ene ‘click’ chemistry (PEG-8-norbornene, dithiol linker, LAP photoinitiator with LED lamp centered at 455 nm), using irradiation conditions to control the rate of formation and the mechanical properties of the resulting hydrogels. Further, defects within these hydrogels were subsequently exploited for temporal modulation of mechanical properties with a secondary cure using low doses of long wavelength UV light (365 nm). The elasticity of the hydrogel, as measured with Young’s and shear moduli, was observed to increase with increasing light intensity and concentration of photoinitiator used for hydrogel formation. In situ measurements of end group conversion during hydrogel formation with magic angle spinning (MAS ¹H NMR) correlated with these mechanical properties measurements, suggesting that both dangling end groups and looping contribute to the observed mechanical properties. Dangling end groups provide reactive handles for temporal stiffening of hydrogels with a secondary UV-initiated thiol–ene polymerization, where an increase in Young’s modulus by a factor of ∼2.5× was observed. These studies demonstrate how the rate of photopolymerization can be tuned with irradiation wavelength, intensity, and time to control the properties of synthetic hydrogels, which may prove useful in a variety of applications from coatings to biomaterials for controlled cell culture and regenerative medicine.

About the Webwriter

Simon Harrisson is a Chargé de Recherche at the Centre National de la Recherche Scientifique (CNRS), based in the Laboratoire des IMRCP in Toulouse. His research seeks to apply a fundamental understanding of polymerization kinetics and mechanisms to the development of new materials. He is an Advisory Board member for Polymer Chemistry. Follow him on Twitter @polyharrisson

Dr. Damien Quemener gained his Pd.D in 2005 in the “Laboratoire de Chimie des Polymères Organiques” at Bordeaux University (France), and was a postdoctoral fellow at the University of New South Wales (Center for Advanced Macromolecular Design) in Sydney, Australia until 2006. He joined Montpellier University in 2007 as an Associate Professor, working at the “Institut Europeen des Membranes” in Montpellier, France. He works at the interface between chemistry and physical chemistry of polymers and membranes with the goal of preparing new autonomous and dynamic porous materials.

What was your inspiration in becoming a chemist?

When I was at junior high school, I gained work experience in a medical laboratory, where I undertook simple and automatic analyses. I was fascinated by the fact that a simple colour change could give you very important results in the quest of a medical diagnostic. But right after I was also frustrated that I didn’t understand the theory beyond that so I decided to study chemistry not to change the world but to simply have a better understanding of it.

What was the motivation to write your Polymer Chemistry article?

Filtration membranes are now everywhere and are recognised as a key technology, for example in water purification. Classical membranes are designed to be highly stable towards mechanical and chemical stresses. We decided to take the opposite strategy in saying that a membrane should be unstable but controlled, in order to make it possible to adapt to any environmental changes. Therefore we have prepared a membrane from block copolymer micelles responsive to water pressure, pH or UV radiation.

Why did you choose Polymer Chemistry to publish your work?

Well, Polymer Chemistry is quite a new and very dynamic journal having a strong impact in the polymer community, and also because it’s a very quick way to publish hot results since the time to publication is short.

In which upcoming conferences may our readers meet you?

This year, I might attend Euromembrane 2015 on the 6-10. September 2015 in Germany but my plans are not yet finalised.

How do you spend your spare time?

Apart from my work, I love to spend my free time with my family since my two boys keep me connected to the day to day reality. I’m also a runner and I’m trying to run two marathons every year, my most recent one was Paris in April.

Which profession would you choose if you were not a scientist?

I would definitely be an architect and build modern style houses since I love to see how something drawn on a piece of paper can be transferred to life-size scale. That’s a common occurrence in the role of a researcher to.

Stimuli responsive nanostructured porous network from triblock copolymer self-assemblies

Zineb Mouline, Mona Semsarilar, Andre Deratani and Damien Quemener

An ABA triblock amphiphilic copolymer is synthesized using RAFT chemistry. The self-assembled micelles of this copolymer are then used to prepare nano-organized porous films that could be used as filtration membranes. In this work a novel strategy is developed to build the nanostructures and perform their self-assembly using reversible and non-covalent interactions to create free volume between the micelles, thus giving tuneable porosity to the film. The self-assembly of poly(styrene)-b-poly(phenylboronic acid)-b-poly(styrene) block copolymer, occurs at high concentration through solvent evaporation, which induces a progressive decrease of the inter-micellar distance, and results in the formation of an in situ network of micelles and the final porous film. Subsequent permeability tests were conducted under different stimuli (pH and UV), generating cross-linking and chemical exchange reactions, to ensure the best balance between permeability and mechanical strength. This work highlights an original strategy for pore size control, and provides new insights towards the design of stimuli-responsive materials.

Cyrille Boyer is a guest web-writer for Polymer Chemistry. He is currently an Associate Professor and an ARC-Future Fellow in the School of Chemical Engineering, University of New South Wales (Australia) and Deputy Director of the Australian Centre for NanoMedicine.

Dr. Andreas Walther graduated from Bayreuth University in Germany in 2008 with a PhD focusing on the self-assembly behaviour and applications of Janus particles and other soft, complex colloids. After a postdoctoral stay with a focus on biomimetic hybrid materials at Aalto University (Helsinki, Finland), he returned to Germany and established his independent research group at the DWI – Leibniz Institute for Interactive Materials in Aachen. His research interests concentrate on developing and understanding hierarchical self-assembly concepts inside and outside equilibrium, and on utilising and connecting such processes to soft materials research – often following bioinspired design principles. Andreas has published more than 90 papers and has recently been awarded the Bayer Early Excellence in Science Award (for Materials) and the Reimund Stadler Young Investigator Award of the German Chemical Society.

What was your inspiration in becoming a chemist?

I believe one of the big chemical companies is responsible for attracting me to chemistry by sending a “polymer science kit”, containing foams, resins and a toolkit to prepare Nylon fibres, to my senior class when I was still back in secondary school. Even nowadays, I still think that the classical experiment of pulling a polyamide fibre from the interface of oil/water monomer mixtures is one of the most intriguing and instructive experiments in a polymer class.

What was the motivation to write your Polymer Chemistry article?

Our main interest lies in developing self-assembly concepts to create new soft materials, for which we heavily rely on very well defined building blocks with tailored functionalities and interactions. Modern polymer chemistry provides us with the tools to make desirable building blocks with relative ease of synthesis. In this case we were interested in a straightforward way to modify the surfaces of colloidal particles to provide us with very specific biorecognition units, while at the same time rejecting all non-specific protein adhesion. Interestingly enough, despite all the common knowledge about the protein-repellent properties of polyethylene glycol (PEG) coatings, we could only find a very small amount of systematic studies discussing how for instance the architecture and composition of adsorbed PEG-based block copolymers influence protein repellency. So we went through a systematic study and optimised the building blocks to provide us with the required features for our future work. The underlying structure/property relationships at this point will be interesting for other researchers working on surface modification, biorecognition and protein-fouling.

Why did you choose Polymer Chemistry to publish your work?

Polymer Chemistry strives for high-level and interdisciplinary scientific contributions covering all modern aspects of polymer chemistry. We felt it to be the right place to achieve highest reach and recognition in the field.

In which upcoming conferences may our readers meet you?

European Polymer Federation Meeting, 21-26 June 2015, at Dresden, Germany.

How do you spend your spare time?

Keeping the work/life balance is probably one of the hardest challenges when working in science. I very much enjoy cooking to take my mind off stressful events, and I enjoy travelling to see new places and meet interesting people.

Which profession would you choose if you were not a scientist?

Indeed a very good question, I would probably follow another creative passion. Best-case scenario would then be running a restaurant in a picturesque place.

Combining the incompatible: Block copolymers consecutively displaying activated esters and amines and their use as protein-repellent surface modifiers with multivalent biorecognition

Daniel Hoenders,   Thomas Tigges and   Andreas Walther

We present the facile synthesis and orthogonal functionalization of diblock copolymers containing two mutually incompatible segments, i.e. primary amines and activated esters, that are displayed chronologically and synthesized by consecutive radical addition fragmentation transfer polymerization (RAFT) of suitably modified monomers. Post-polymerization modification of the active ester moieties with functionalized triethylene glycol derivatives (TEG-NH₂/BiotinTEG-NH₂) furnishes a protein-repellent block with specific biorecognition, and the activation of the amine groups via deprotection results in newly reactive primary amines. We subsequently use these amines as an anchoring layer for the coating of aldehyde-functionalized polystyrene (PS) colloids and demonstrate tight adhesion and enhanced protein-repellent characteristics combined with specific and multivalent biorecognition of avidin as a function of block ratios. Our strategy demonstrates a viable approach for orthogonal combination of widely needed, but mutually incompatible, functional groups into complex polymer architectures.

Cyrille Boyer is a guest web-writer for Polymer Chemistry. He is currently an associate professor and an ARC-Future Fellow in the School of Chemical Engineering, University of New South Wales (Australia), deputy director of the Australian Centre for NanoMedicine and member of Centre for Advanced Macromolecular Design.