In what was a fast-paced day of science and celebration, both Kim Clarke and Shalini Saxena defended their dissertations last Monday. Kim’s talk (The Fabrication and Study of Stimuli-Responsive Microgel-Based Modular Assemblies) focused on controlling the properties of responsive thin films composed of microgels by spatially separating the assembly-controlling functionalities from the responsive elements via core-shell synthesis. She also presented some nice stuff on the modular assembly of peptides onto microgels as a means to control microgel surface functionality via non-covalent approaches.
Shalini’s talk (Development and Characterization of Tunable Hydrogel Nanoparticle Assemblies) detailed her investigations into “raspberry-like particles” composed of dense (e.g. silica, polystyrene) cores with microgel shells. Through a series of clever approaches, she has been able to construct fairly complex 3-component aggregates, which form through a delicate interplay of microgel adhesion forces and mechanical properties. These heteroaggregates are of potential interest as drug delivery vehicles. The second part of her talk described new approaches for the rapid fabrication and patterning of microgel-based films with tunable mechanical properties. Preliminary studies suggest that such materials are of potential use as biointerfaces to direct cell proliferation.
Since I wasn’t able to get back into town for graduation, we stepped outside for some post-facto hooding (pix below), including an appearance by Emily, who you will recall defended earlier in the semester. Congrats to all three grads!
This is a little late, but it is still definitely worth a post! Last Tuesday, Mark Spears successfully defended his dissertation, entitled “Microgel-Based Coatings and their Use as Self-Healing, Dynamic Substrates for Bioapplications”. With a body of research spanning from non-fouling coatings to self-healing materials, Mark has done a ton of work in some very important areas. I expect big things from him in the future. As is tradition, I joined Mark and his family for a celebratory meal, this time at the Barrelhouse in Tech Square. Not a great photo, but they don’t hire the wait staff for their photography skills. Anyway, congratulations to Mark for delivering an outstanding defense summarizing 4 years worth of outstanding work.
Well, maybe that is overstating it. However, PLPs, as we call them, are pretty cool. This massive collaborative effort between Ashley Brown, Sarah Stabenfeldt, Tom Barker, Wilbur Lam, Nina Guzzetta, Alexander Alexeev, and yours truly was recently published online in Nature Materials. I won’t rehash the whole paper here – you should go read it for yourself. I will point out, however, that working on this stuff has been the most fun I have ever had in science. The team that Tom Barker, Ashley Brown, and I assembled in our goal to replicate key aspects of platelet behavior has been a blast to work with, and I sincerely hope that we can continue to push forward on what I think is an exciting intersection between biology, mechanical engineering, hematology, and polymer chemistry & physics.
Today we witnessed an outstanding presentation by Emily Herman on the topic of microgel/polyelectrolyte interactions as the final step in her path to a Ph.D. Of course, she defended her dissertation successfully, so we now get to call her Dr. Herman, which for some reason sounds like a ’70’s TV hospital drama to me. We celebrated the event with an awesome meal at the Cuban Diner with Emily and her family – well worth the trip back up to Marietta, to be sure. Thanks to Jose for his hospitality!
The next step for Emily is just across the biotech quad to some incubator space in the basement of the Environmental Science and Technology building. There she will be doing some top-secret research for a brand new company (she is employee #4, I think) that is sure to revolutionize our daily lives in a truly profound way. Stay tuned for more on that. In the meantime, Congratulations, Emily!
Updates have been challenging with all of the cross-country move activities. However, I finally found a few minutes to at least post on the newest papers from the group. First comes a collaboration with the Fernandez-Nieves group and Urs Gasser at PSI that we published in JCP entitled “Form factor of pNIPAM microgels in overpacked states“. Actually, those two groups did most (all?) of the heavy lifting there, performing some very nice neutron scattering studies on mixed phases of pNIPAm and deuterated-pNIPAm microgels. However, I don’t mean to diminish the importance of all the dirty work Emily did on the synthesis side, preparing low polydispersity samples of both types of microgels in the same size range – not an easy task, to be sure. The take home message from the work is that microgels don’t start deswelling until they are actually touching – that is there is no “osmotic deswelling” effect in packed phases and the particles maintain their dilute solution hydrodynamic sizes until they start getting mechanically squeezed for space.
The second new paper (published in Langmuir) comes from former group member Dr. Ling Zhang and current grad student Mark Spears entitled “Tunable Swelling and Rolling of Microgel Membranes“. Here they have shown that when microgel-based multilayers are prepared under specific conditions, a pH-induced swelling event can cause the film to delaminate as a single, continuous sheet (see figure). When bilayer films composed of two different types of microgels (even just different size microgels) are prepared, the delamination event is accompanied by differential swelling, which drives rolling into a tube or scroll. The rolled films are cool looking, but we also think this work tells us a great deal about the fundamental interactions and swelling properties of microgel thin films.
Shalini and Caroline recently collaborated to write an Accounts of Chemical Research article on “Microgel Mechanics in Biomaterial Design“. The work is a review of some of our efforts in at the microgel/bio interface, with the highlights being depicted in the artwork to the right (drawn by Prof. Lyon in ArtStudio on an iPad). In the leftmost depiction, we see that polyelectrolyte/microgel assemblies, when formed into a thin film, can mediate cell attachment and spreading in a manner that appears to relate to the viscoelasticity of the film, as opposed to being related to just the elasticity. We have also demonstrated that ultrasoft microgels can deform to a large degree when faced with transport through small pores (center image). This may be relevant for renal clearance of injectable drug delivery vehicles. Finally, on the right we see a cartoon representation of a core/shell microgel with a shell that can gate or tune the release of the interior microgel contents. Please feel free to share any thoughts on the article, which is just a small preamble to all the nano/micro/bio stuff churning in the group right now – stay tuned for some very cool stuff that should be coming out in the near future!
The group is staying but Dr. Lyon is going – this is the last week of Dr. Lyon’s (short) time as School Chair, and he will depart GT at the end of June for a new, very different position. Click here for details. This site will continue to share news and info regarding all things LyonGroup related for some time to come, with new research directions at GT being plotted jointly between Dr. Lyon (remotely) and Dr. Ashley Brown (research scientist at GT). Keep visiting – there are some cool results on the horizon!!
In what might be the final Lyon Group dinner ever (wow), we ventured out to Mellow Mushroom to wish Bob good luck in his next position. He is off to UNC-Chapel Hill to work with Sergei Sheiko on TBDA (To Be Determined Awesomeness). We are all sad to see Bob leave so soon after his return, but Prof. Lyon’s imminent departure from GT meant that it was time to seek greener pastures. We wish Bob the best of luck – there is no doubt he will continue to be a spectacular scholar, colleague, and friend.
from left to right: Anabel Liyen, Caroline, Haylee, Kim, Emily, Purva, Mark, Ashley, Nicole, Shalini, Dr. Lyon, Bob, and Keith (Kabir ditched us…)
Following up on the last post (December? Wow – sorry for the radio silence – things have been busy), I wanted to bring the special issue of Soft Matter on “Reconfigurable Soft Matter” to everyone’s attention. This issue was masterfully edited by Anna Balazs and Joanna Aizenberg to contain a rich array of approaches to soft materials. One thing I find wonderful about the issue is the span from the macroscopic (see: Bioinspired self-shaping materials) to the microscopic (see: Microstructured membranes) to the molecular (see: UV-burstable microcapsules based on azobenzene). Similarly, the issue spans what might be called “engineering approaches” to ones focused more on the fundamental physical sciences of such structures. If you have interest in the field, I encourage you to take a look – the issue should serve for some time as a nice entry point into the field for newcomers, and as a “2014 status report” for those already embedded in the field.
I guess I should have just waited a few days to include this in the last post. Anyway, the manuscript “Microgel Film Dynamics Modulate Cell Adhesion Behavior” was published on line this week in the journal Soft Matter. This is another collaboration between my group and the Garcia group, with Shalini, Mark, Jeff, and Hiro taking the lead on these studies. In this paper, we describe how the “self-healing” properties of microgel-based multilayer thin films appear to modulate cell attachment and spreading. The hypothesis is that the viscous behavior (as opposed to the elasticity) of the film is responsible for cells failing to adhere and spread on reconfigurable interfaces. This comes about through balancing the energy required to remodel the interface with the force exerted by cells when forming focal adhesions. In principle, this is is a relevant phenomenon for tissue engineering, since the film viscosity is related to the timescale of cell spreading and proliferation and could therefore be used to further control cell phenotype and tissue remodeling.
In the last few weeks we have seen three new papers show up online. First, we have “Host response to microgel coatings on neural electrodes implanted in the brain” published in Journal of Biomedical Materials Research Part A. Stacy Gutowski from the Garcia group did all the heavy lifting here, wherein she implanted neural electrodes in live rodents and subsequently analyzed the wound healing response to electrodes with and without microgel-based coatings. The coatings were made and analyzed largely by two former Lyon group members: Toni South and Jeff Gaulding. The take home message here is that the coatings did not result in dramatically improved wound healing – a disappointing result, but it is gratifying to see our materials used in such a complex biomedical application.
More recently, Kim Clarke published a paper entitled “Modulation of the Deswelling Temperature of Thermoresponsive Microgel Films” in Langmuir. Kim has demonstrated that simple copolymerization approaches can be used to tightly control microgel deswelling temperatures, and that constructing films of those particles permits tuning of film thermal responses. Importantly, films composed of mixed populations of different microgels result in composite thermal responses suggesting that individual microgels retain their individual deswelling properties and are not greatly influenced by the overall film structure. For example, mixing two microgels with distinct responses in a single film will produce two distinct deswelling transitions in the film. Kim is continuing this work to further understand the role of microgel structure and polyelectrolyte interactions in film volume phase transitions.
Finally, Langmuir Invited Feature Article entitled “Dynamic Materials from Microgel Multilayers” just showed up online. Mark, Emily, and Jeff worked together to summarize the group’s efforts over the last few years on self-healing and reconfigurable interfaces composed of microgel/polyelectrolyte complexes. With work continuing on this subject, we hope that this is just the tip of the iceberg in terms of our advances in self-healing materials.
This week Xiaobo (Bob) Hu returned to the group, this time as a postdoctoral scholar. Bob previously spent two years in the group as part of a Ph.D. exchange with his home institution (South China University of Technology). Now, after spending some time working in industry, he is back in the states to work on microgels. We are glad to have him back in the fold – time for karaoke…
Today we learned that Nicole Welsch has been awarded a 2-year fellowship from the German Research Foundation (DFG). Her proposed work, “Engineering of fibrin-specific biocompatible microgels for the use as hemostatic agents”, will help us to continue our growth in the area of extracellular-matrix derived materials. Congrats!