4 research outputs found
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><sub>trans</sub> deposited PDADMAC/PSS layer
pairs a transition from a parabolic to a linear growth occurs. For
molecular weights above a threshold (<i>M</i><sub>w</sub>(PSS) > 25 kDa and <i>M</i><sub>w</sub>(PDADMAC) >
80 kDa), <i>N</i><sub>trans</sub> 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><sub>trans</sub> 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><sub>w</sub> 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><sub>w</sub> 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><sub>w</sub>. 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><sub>w</sub> 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><sub>w</sub> 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