Influence of Polymer Molecular Weight on the Parabolic and Linear Growth Regime of PDADMAC/PSS Multilayers

The buildup of polyelectrolyte multilayers is investigated in solution with multiple angle null-ellipsometry. Polyanion poly­(styrenesulfonate) (PSS) and polycation poly­(diallyldimethylammonium) (PDADMAC) are adsorbed sequentially from 0.1 M NaCl solution. First the films grow parabolically. After <i>N</i>_trans deposited PDADMAC/PSS layer pairs a transition from a parabolic to a linear growth occurs. For molecular weights above a threshold (<i>M</i>_w(PSS) > 25 kDa and <i>M</i>_w(PDADMAC) > 80 kDa), <i>N</i>_trans is 15, the thickness per layer pair in the linear growth regime is 12.3 nm. If either the PDADMAC or the PSS molecular weight is decreased below the threshold value, <i>N</i>_trans either falls (for PDADMAC, lowest value observed is 8) or rises (for PSS, highest value observed is 33), respectively. Simultaneously, in the linear growth regime, the thickness per layer pair decreases (down to 4.3 nm) or rises (up to 25 nm). Furthermore, for low molecular weight PSS, three growth regimes are observed: exponential, parabolic, and linear. The opposite effect of PDADMAC and PSS molecular weight reduction is discussed in terms of persistence lengths and linear charge density. The data suggest that molecular weight provides a way to control growth and internal structure of polyelectrolyte multilayers

Influence of Polycation (PDADMAC) Weight on Vertical Diffusion within Polyelectrolyte Multilayers during Film Formation and Postpreparation Treatment

The internal interfaces of polyelectrolyte multilayers are investigated with neutron reflectivity. The films are made from poly­(diallyldimethylammonium) (PDADMA), poly­(styrenesulfonate) (PSS), and deuterated PSS-d. Each film consists of a protonated and a deuterated block. The internal roughness is smallest next to the film/air interface and increases with the number of layer pairs away from the film/air interface until a metastable state is reached. Both the final internal roughness and the interdiffusion constant increase with the salt concentration in the deposition solution and with PDADMA polymer weight. The increased mobility found with high molecular weight PDADMA is attributed to residual stresses occurring during film formation. The experiments suggest that PSS and PDADMA move partly as a complex. Postpreparation immersion in 1 M NaCl salt solutions has little effect if the multilayer is prepared from low salt solution and with high molecular weight PDADMA. However, almost complete intermixing is observed for multilayers prepared from 0.1 M NaCl and with low molecular weight PDADMA (diffusion length exceeds 30 nm)

Lipid Monolayers and Adsorbed Polyelectrolytes with Different Degrees of Polymerization

Polystyrene sulfonate (PSS) of different molecular weight <i>M</i>_w is adsorbed to oppositely charged DODAB monolayers from dilute solutions (0.01 mmol/L). PSS adsorbs flatly in a lamellar manner, as is shown by X-ray reflectivity and grazing incidence diffraction (exception: PSS with <i>M</i>_w below 7 kDa adsorbs flatly disordered to the liquid expanded phase). The surface coverage and the separation of the PSS chains are independent of PSS <i>M</i>_w. On monolayer compression, the surface charge density increases by a factor of 2, and the separation of the PSS chains decreases by the same factor. Isotherms show that on increase of PSS <i>M</i>_w the transition pressure of the LE/LC (liquid expanded/liquid condensed) phase transition decreases. When the contour length exceeds the persistence length (21 nm), the transition pressure is low and constant. For low-<i>M</i>_w PSS (<7 kDa) the LE/LC transition of the lipids and the disordered/ordered transition of adsorbed PSS occur simultaneously, leading to a maximum in the contour length dependence of the transition enthalpy. These findings show that lipid monolayers at the air/water interface are a suitable model substrate with adjustable surface charge density to study the equilibrium conformation of adsorbed polyelectrolytes as well as their interactions with a model membrane

Reduced platelet forces underlie impaired hemostasis in mouse models of MYH9-related disease

MYH9-related disease patients with mutations in the contractile protein non-muscle myosin heavy chain IIA display, among others, macrothrombocytopenia and a mild to moderate bleeding tendency. In this study, we used three mouse lines, each with one point mutation in the Myh9 gene at positions 702, 1424, or 1841, to investigate mechanisms underlying the increased bleeding risk. Agonist-induced activation of Myh9 mutant platelets was comparable to controls. However, myosin light chain phosphorylation after activation was reduced in mutant platelets, which displayed altered biophysical characteristics and generated lower adhesion, interaction, and traction forces. Treatment with tranexamic acid restored clot retraction and reduced bleeding. We verified our findings from the mutant mice with platelets from patients with the respective mutation. These data suggest that reduced platelet forces lead to an increased bleeding tendency in MYH9 -related disease patients, and treatment with tranexamic acid can improve the hemostatic function. Teaser Impaired hemostasis in Myh9 mutant mice due to reduced platelet forces can be improved by tranexamic acid