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.  

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.

Happy reading!

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!

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.

A new themed issue of Polymer Chemistry came out today, including an article from the group that I have already written about. Note that we also got a little artwork on the back cover, thanks to artist Jesse Larson. Check it out – the issue is well edited and covers a broad range of approaches to self-healing materials, with a focus (of course) on polymer chemistry. Enjoy…