290 research outputs found
On the benefits of rubbing salt in the cut: self-healing of saloplastic PAA/PAH compact polyelectrolyte complexes.
The inherent room temperature mending and self-healing properties of saloplastic PAA/PAH CoPECs are studied. After ultracentrifugation of PAA/PAH polyelectrolyte complexes, tough, elastic materials are obtained that undergo self-healing facilitated by salt. At intermediate salt concentrations the CoPECs remain elastic enough to recover their original shape while the chains are mobile enough to repair the cut, thus leading to actual self-healing behavior.journal articleresearch support, non-u.s. gov'tresearch support, u.s. gov't, non-p.h.s.2014 Apr 232014 01 29importe
Freely Suspended Cellular āBackpacksā Lead to Cell Aggregate Self-Assembly
Cellular ābackpacksā are a new type of anisotropic, nanoscale thickness microparticle that may be attached to the surface of living cells creating a ābio-hybridā material. Previous work has shown that these backpacks do not impair cell viability or native functions such as migration in a B and T cell line, respectively. In the current work, we show that backpacks, when added to a cell suspension, assemble cells into aggregates of reproducible size. We investigate the efficiency of backpackācell binding using flow cytometry and laser diffraction, examine the influence of backpack diameter on aggregate size, and show that even when cellābackpack complexes are forced through small pores, backpacks are not removed from the surfaces of cells.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-08-19762)National Science Foundation (U.S.) (Graduate Research Fellowship)United States. Dept. of DefenseUnited States. Air Force Office of Scientific ResearchHoward Hughes Medical Institute (Investigator)United States. Dept. of Defense (National Defense Science and Engineering Graduate Fellowship 32 CFR 168a
Compact Polyelectrolyte Complexes: āSaloplasticā Candidates for Biomaterials
Precipitates of polyelectrolyte complexes were transformed into rugged shapes suitable for bioimplants by ultracentrifugation in the presence of high salt concentration. Salt ions dope the complex, creating a softer material with viscous fluid-like properties. Complexes that were compacted under the centrifugal field (CoPECs) were made from poly(diallyldimethyl ammonium), PDADMA, as polycation, and poly(styrene sulfonate), PSS, or poly(methacrylic acid), PMAA, as polyanion. Dynamic mechanical testing revealed a rubbery plateau at lower frequencies for PSS/PDADMA with moduli that decreased with increasing salt concentration, as internal ion pair cross-links were broken. CoPECs had significantly lower modulii compared to similar polyelectrolyte complexes prepared by the āmultilayering ā method. The difference in mechanical properties was ascribed to higher water content (located in micropores) for the former and, more importantly, to their nonstoichiometric polymer composition. The modulus of PMAA/PDADMA CoPECs, under physiological conditions, demonstrated dynamic mechanical properties that were close to those of the nucleus pulposus in an intervertebral disk
Free-standing polyelectrolyte membranes made of chitosan and alginate
Free-standing films have increasing applications in the biomedical field as drug delivery systems for wound healing and tissue engineering. Here, we prepared free-standing membranes by the layer-by-layer assembly of chitosan and alginate, two widely used biomaterials. Our aim was to produce a thick membrane and to study the permeation of model drugs and the adhesion of muscle cells. We first defined the optimal growth conditions in terms of pH and alginate concentration. The membranes could be easily detached from polystyrene or polypropylene substrate without any postprocessing step. The dry thickness was varied over a large range from 4 to 35 Ī¼m. A 2-fold swelling was observed by confocal microscopy when they were immersed in PBS. In addition, we quantified the permeation of model drugs (fluorescent dextrans) through the free-standing membrane, which depended on the dextran molecular weight. Finally, we showed that myoblast cells exhibited a preferential adhesion on the alginate-ending membrane as compared to the chitosan-ending membrane or to the substrate side.This work was financially supported by Foundation for Science and Technology (FCT) through the Scholarship SFRH/BD/64601/2009 granted to S.G.C. C.M. is indebted to Grenoble INP for financial support via a postdoctoral fellowship. This work was supported by the European Commission (FP7 Program) via a European Research Council starting grant (BIOMIM, GA 259370 to C.P.). C.P. is also grateful to Institut Universitaire de France and to Grenoble Institute of Technology for financial support. We thank Isabelle Paintrand for her technical help with the confocal apparatus and Patrick Chaudouet for his help with SEM imaging
Electrochemical/electrospray mass spectrometric studies of electrochemically stimulated ATP release from PP/ATP films
Plasmonic detection and visualization of directed adsorption of charged single nanoparticles to patterned surfaces
Exchange Reactions between Alkanethiolates and Alkaneselenols on Au{111}
When alkanethiolate self-assembled monolayers on Au{111} are exchanged with alkaneselenols from solution, replacement of thiolates by selenols is rapid and complete, and is well described by perimeter-dependent island growth kinetics. The monolayer structures change as selenolate coverage increases, from being epitaxial and consistent with the initial thiolate structure to being characteristic of selenolate monolayer structures. At room temperature and at positive sample bias in scanning tunneling microscopy, the selenolate-gold attachment is labile, and molecules exchange positions with neighboring thiolates. The scanning tunneling microscope probe can be used to induce these place-exchange reactions
Stressful Surfaces: Cell Metabolism on a Poorly Adhesive Substrate
The adhesion and proliferation of
cells are exquisitely sensitive
to the nature of the surface to which they attach. Aside from cell
counting, cell āhealthā on surfaces is typically established
by measuring the metabolic rate with dyes that participate in the
metabolic pathway or using ālive/deadā assays with combinations
of membrane permeable/impermeable dyes. The binary information gleaned
from these testsīøwhether cells are attached or not, and whether
they are living or deadīøprovides an incomplete picture of cell
health. In the present work, proliferation rates and net metabolism
of 3T3 fibroblasts seeded on ābiocompatibleā ultrathin
polyelectrolyte multilayer films and on control tissue culture plastic
were compared. Cells adhered to, and proliferated on, both surfaces,
which were shown to be nontoxic according to live/dead assays. However,
adhesion was poorer on the multilayer surface, illustrated by diffuse
organization of the actin cytoskeleton and less-developed focal adhesions.
Proliferation was also slower on the multilayer. When normalized for
the total number of cells, it was shown that cells on multilayers
experienced a five-day burst of metabolic stress, after which the
metabolic rate approached that of the control surface. This initial
state of high stress has not been reported or appreciated in studies
of cell growth on multilayers, although the observation period for
this system is usually a few days
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