Organ Repair,Hemostasis, and In Vivo Bonding of Medical Devices by Aqueous Solutions of Nanoparticles

Sutures are traumatic to soft connective tissues, such as liver or lungs. Polymer tissue adhesives require complex in vivo control of polymerization or cross‐linking reactions and currently suffer from being toxic, weak, or inefficient within the wet conditions of the body. Herein, we demonstrate using Stöber silica or iron oxide nanoparticles that nanobridging, that is, adhesion by aqueous nanoparticle solutions, can be used in vivo in rats to achieve rapid and strong closure and healing of deep wounds in skin and liver. Nanoparticles were also used to fix polymer membranes to tissues even in the presence of blood flow, such as occurring after liver resection, yielding permanent hemostasis within a minute. Furthermore, medical devices and tissue engineering constructs were fixed to organs such as a beating heart. The simplicity, rapidity, and robustness of nanobridging bode well for clinical applications, surgery, and regenerative medicine.     

Rheological aging and rejuvenation in microgel pastes

We have studied experimentally the rheological behavior of concentrated suspensions of soft deformable microgels below the yield point. We have found history-dependent effects which are interpreted in terms of aging and rejuvenation phenomena, analogous to those existing in glassy systems. The stress amplitude controls the long-time memory and determines the slow evolution of the suspensions.     

Synthesis of self‐healing supramolecular rubbers from fatty acid derivatives,diethylene triamine,and urea

We describe the synthesis of supramolecular self‐healing elastomers from vegetable oil fatty acid derivatives, diethylene triamine, and urea. Our strategy to obtain materials that are self‐healing but do not flow relies on the use of a wide molecular distribution of randomly branched oligomers equipped with self‐complementary and complementary hydrogen bonding groups. We prepared such oligomers with a two steps procedure. In the first step, diethylene triamine was condensed with dimer acids. In the second step, the oligomers obtained were allowed to react with urea. The molecules were characterized by NMR and IR spectroscopies and Monte‐Carlo simulations were used to analyze the molecular size distribution. The sensitivity to small variations of the experimental conditions has been examined and the robustness of the synthetic procedure optimized. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7925–7936, 2008     

Ligand and base additive effects on the reversibility of nucleophilic addition in palladium-catalyzed allylic aminations monitored by nucleophile crossover

A nucleophile crossover experiment was used to monitor the reversibility of nucleophilic addition of benzylamine to π-allylpalladium complexes. Dppe, dppp, dppb, and PHOX showed more crossover than PPh₃ and dppm in both DMF and dichloromethane. Crossover was inhibited by the addition of DBU or Cs₂CO₃, but much less elimination to diene side products was observed with Cs₂CO₃. Analysis of percent crossover vs. percent reaction completion using the PHOX ligand revealed that with added DBU or Cs₂CO₃ crossover only began occurring after 100% completion had been reached.     

Permeation of a solvent mixture through an elastomeric membrane—The case of pervaporation

This article presents a model for the permeation of solvent mixtures through an elastomer in the particular case of pervaporation. An analytical expression for each solvent permeation rate is derived, in the limited case of a membrane that undergoes small swelling, without making any assumptions on the solvent diffusion coefficients and their dependence on solvent concentrations. Applying this analytical expression to different situations, we fitted most of the curves previously published on pervaporation experiments. In particular, we correlated the synergy developed by a mixture of two solvents in the permeation process with the sign of their Flory–Huggins interaction parameter χ_AB. This explains why, in most cases (χ_AB > 0), a molecule permeating easily through a membrane is mixed with a molecule permeating much less easily; the latter can see its permeation flux increase by a factor 10 or 100 because the swelling of the polymer induced by the more permeable molecule “opens the meshes of the network” allowing the less permeable molecule to pass through more easily. Within our analysis, the efficiency of the pervaporation process, expressed through the separation factor, is derived very simply as a function of the interaction coefficients and the viscosities of solvents and exhibits an exponential dependence on the volume fraction of either component as seen in most experiments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 183–193, 2003     

Films from soft‐core/hard‐shell hydrophobic latexes: Structure and thermomechanical properties

Structured latexes provide a promising route to hard coatings without the use of coalescing aids. We studied the thermomechanical properties of films from structured soft‐core/hard‐shell hydrophobic latexes. We found that the mechanical properties of these films were closely related to their very particular organization. When the rigid phase was continuous, whatever its volume fraction, the films exhibited a high elastic modulus. An analysis of the viscoelastic properties of the films provided a good method for obtaining information about the interphase between the hard shell and soft core of the latex particles. By varying the film structure through annealing or the particle composition (core/shell ratio, core crosslinking, etc.), we were able to tune the mechanical properties of the films. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2989–3000, 2000     

An analysis of the reaction–diffusion mechanism governing the chlorination process of poly(vinyl chloride)

Chlorinated poly(vinyl chloride) (CPVC) obtained through a dry chlorination of PVC films or grains can show a heterogeneous repartition of its chlorine atoms because the reaction process is limited by the mass transfer of the chlorine gas in the material. In order to describe the evolution of such a system, a set of coupled equations is derived where only two dimensionless constants have to be determined: K_S, which depends on the solubility of the chlorine gas in the PVC, and K_T, the ratio between the diffusion and the reaction characteristic times. The kinetics of chlorination obtained for the different regimes matches the available experimental data, and the corresponding concentration profiles for the chlorinated PVC chains are displayed to demonstrate how a heterogeneous chlorination can arise from this dual process. In particular, a sharp interface appears in the diffusion‐limited regime that separates the chlorinated region from an unchlorinated core and is shown to progress deeper into the film with the square root of time. To a larger extent, this analysis shows how heterogeneity of reaction and nonlinear effects can arise from a coupling between a diffusive phenomenon and a reactive phenomenon. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3201–3209, 2000