The formation of smart emulsions or foams whose stability can be controlled on-demand by switching external parameters is of great interest for basic research and applications. An emerging group of ...smart stabilizers are microgels, which are nano- and micro-sized, three-dimensional polymer networks that are swollen by a good solvent. In the last decades, the influence of various external stimuli on the two-dimensional phase behavior of microgels at air- and oil-water interfaces has been studied. However, the impact of the top-phase itself has been barely considered. Here, we present data that directly address the influence of the top-phase on the microgel properties at interfaces. The dimensions of pNIPAM microgels are measured after deposition from two interfaces, i.e., air- and decane-water. While the total in-plane size of the microgel increases with increasing interfacial tension, the portions or fractions of the microgels situated in the aqueous phase are not affected. We correlate the area microgels occupy to the surface tensions of the interfaces, which allows to estimate an elastic modulus. In comparison to nanoindentation measurements, we observe a larger elastic modulus for the microgels. By combining compression, deposition, and visualization, we show that the two-dimensional phase behavior of the microgel monolayers is not altered, although the microgels have a larger total in-plane size at higher interfacial tension.
Abstract
The structural characterization of microgels at interfaces is fundamental to understand both their 2D phase behavior and their role as stabilizers that enable emulsions to be broken on ...demand. However, this characterization is usually limited by available experimental techniques, which do not allow a direct investigation at interfaces. To overcome this difficulty, here we employ neutron reflectometry, which allows us to probe the structure and responsiveness of the microgels in-situ at the air-water interface. We investigate two types of microgels with different cross-link density, thus having different softness and deformability, both below and above their volume phase transition temperature, by combining experiments with computer simulations of in silico synthesized microgels. We find that temperature only affects the portion of microgels in water, while the strongest effect of the microgels softness is observed in their ability to protrude into the air. In particular, standard microgels have an apparent contact angle of few degrees, while ultra-low cross-linked microgels form a flat polymeric layer with zero contact angle. Altogether, this study provides an in-depth microscopic description of how different microgel architectures affect their arrangements at interfaces, and will be the foundation for a better understanding of their phase behavior and assembly.
The volume occupied by colloids in a suspension - namely the volume fraction - is the thermodynamic variable that determines the phase behavior of these systems. While for hard incompressible spheres ...this quantity is well defined, for soft compressible colloids such as microgels - polymeric crosslinked networks swollen in a good solvent - the determination of the real volume occupied by these particles in solution is particularly challenging. This fact depends on two aspects: first the surface and, therefore, the volume of the microgels is hard to define properly given their external fuzziness; second, microgels can osmotically deswell, deform or interpenetrate their neighbors,
i.e.
change their shape and size depending on the solution concentration. Here, the form factors of few hydrogenated microgels embedded in a matrix of deuterated but otherwise identical microgels are measured using small-angle neutron scattering with contrast variation. From the analysis of the scattering data, the variation of the volume of the microgels as a function of concentration is obtained and used to calculate the real microgel volume fraction in solution. Soft neutral microgels are shown to facet already at low concentrations while in contrast, harder microgels maintain their shape and change their volume.
Small-angle neutron scattering with contrast variation is used to probe the real volume fraction of microgels in crowded solution. Soft microgels change their shape at constant volume while hard microgels maintain their spherical shape and deswell.
Ultra-low cross-linked (ULC) microgels are extremely soft polymers with advanced material properties exhibiting a colloid-to-polymer transition. Poly(
N
-isopropylacrylamide) (pNIPAM) microgels are ...commonly synthesized by radical precipitation polymerization of the fully protonated monomer
N
-isopropylacrylamide (NIPAM). Analogous deuterated monomers arouse interest regarding their varying scattering length densities in small-angle neutron scattering (SANS). An isotope substitution in the main monomer of a microgel changes its scattering length density, which enables the exploitation of the technique of contrast variation in SANS. Here, we demonstrate that the synthesis of the deuterated pNIPAM ULC microgels encounters challenges related to the self-cross-linking mechanism of the polymer chains. The location of the deuterium isotopes is crucial for the generation of deuterated pNIPAM ULC microgels: when the isopropyl group of NIPAM is deuterated, the cross-linking is strongly restrained and the formation of microgels is precluded. However, the deuteration of the vinyl group of NIPAM, ending as backbone in the pNIPAM chains, allows the self-cross-linking.
Ab initio
calculations of the bond dissociation enthalpies endorse that the cross-linking of the pNIPAM chains occurs
via
hydrogen atom abstraction at the tertiary carbon atom of the isopropyl group. Additionally, we show that the deuteration of the vinyl group barely shifts the transition temperature of the polymer compared to protonated pNIPAM, whereas deuteration of the isopropyl group results in a significant shift of the transition temperature toward higher temperatures. Finally, the deuterated ULC micro- and nanogels reveal a stronger cross-linked network with lower swelling ability compared to the protonated microgels.
Partial deuteration of the
N
-isopropylacrylamide monomer reveals new insights into the self-cross-linking of polymer chains in ultra-low cross-linked microgels.
Impurities in crystals generally cause point defects and can even suppress crystallization. This general rule, however, does not apply to colloidal crystals formed by soft microgel particles Iyer ...ASJ, Lyon LA (2009) Angew Chem Int Ed 48:4562–4566, as, in this case, the larger particles are able to shrink and join the crystal formed by a majority of smaller particles. Using small-angle X-ray scattering, we find the limit in large-particle concentration for this spontaneous deswelling to persist. We rationalize our data in the context of those counterions that are bound to the microgel particles as a result of the electrostatic attraction exerted by the fixed charges residing on the particle periphery. These bound counterions do not contribute to the suspension osmotic pressure in dilute conditions, as they can be seen as internal degrees of freedom associated with each microgel particle. In contrast, at sufficiently high particle concentrations, the counterion cloud of each particle overlaps with that of its neighbors, allowing these ions to freely explore the space outside the particles. We confirm this scenario by directly measuring the osmotic pressure of the suspension. Because these counterions are then no longer bound, they create an osmotic pressure difference between the inside and outside of the microgels, which, if larger than the microgel bulk modulus, can cause deswelling, explaining why large, soft microgel particles feel the squeeze when suspended with a majority of smaller particles. We perform small-angle neutron scattering measurements to further confirm this remarkable behavior.
Differences in terms of safety and efficacy of percutaneous edge-to-edge mitral repair between patients with functional and degenerative mitral regurgitation (MR) are not well established. We ...performed a systematic review and meta-analysis to clarify these differences.
PubMed, EMBASE, Google scholar database and international meeting abstracts were searched for all studies about MitraClip. Studies with <25 patients or where 1-year results were not delineated between MR aetiology were excluded. This study is registered with PROSPERO.
A total of nine studies investigating the mid-term outcome of percutaneous edge-to-edge repair in patients with functional versus degenerative MR were included in the meta-analysis (n=2615). At 1 year, there were not significant differences among groups in terms of patients with MR grade≤2 (719/1304 vs 295/504; 58% vs 54%; risk ratio (RR) 1.12; 95% CI: 0.86 to 1.47; p=0.40), while there was a significantly lower rate of mitral valve re-intervention in patients with functional MR compared with those with degenerative MR (77/1770 vs 80/818; 4% vs 10%; RR 0.60; 95% CI: 0.38 to 0.97; p=0.04). One-year mortality rate was 16% (408/2498) and similar among groups (RR 1.26; 95% CI: 0.90 to 1.77; p=0.18). Functional MR group showed significantly higher percentage of patients in New York Heart Association class III/IV (234/1480 vs 49/583; 16% vs 8%; p<0.01) and re-hospitalisation for heart failure (137/605 vs 31/220; 23% vs 14%; p=0.03). No differences were found in terms of single leaflet device attachment (25/969 vs 20/464; 3% vs 4%; p=0.81) and device embolisation (no events reported in both groups) at 1 year.
This meta-analysis suggests that percutaneous edge-to-edge repair is likely to be an efficacious and safe option in patients with both functional and degenerative MR. Large, randomised studies are ongoing and awaited to fully assess the clinical impact of the procedure in these two different MR aetiologies.
Background Transcatheter aortic valve replacement (TAVR)-in-TAVR is a possible treatment for transcatheter heart valve (THV) degeneration. However, the displaced leaflets of the first THV will create ...a risk plane (RP) under which the passage of a coronary catheter will be impossible. The aim of our study was to evaluate the potential risk of impaired coronary access (CA) after TAVR-in-TAVR. Methods and Results We prospectively performed coronary angiography after TAVR with different THVs in 137 consecutive patients, looking where the catheter crossed the valve frame. If coronary cannulation was achieved from below the RP, the distance between valve frame and aortic wall was measured by aortic angiography. CA after TAVR-in-TAVR was defined as feasible if the catheter passed above the RP, as theoretically feasible if passed under the RP with valve-to-aorta distance >2 mm, and as unfeasible if passed under the RP with valve-to-aorta distance ≤2 mm. Seventy-two patients (53%) received a Sapien 3 THV, 26 (19%) received an Evolut Pro/R THV, and 39 (28%) received an Acurate Neo THV. CA after TAVR-in-TAVR was considered feasible in 40.9% (68.1%, 19.2%, and 5.1%, respectively;
<0.001), theoretically feasible in 27.7% (8.3%, 42.3%, and 53.8%, respectively;
<0.001), and unfeasible in 31.4% (23.6%, 38.5%, and 41.1%, respectively;
=0.116). Independent predictors of impaired CA after TAVR-in-TAVR were female sex (odds ratio OR, 3.99; 95% CI, 1.07-14.86;
=0.040), sinotubular junction diameter (OR, 0.62; 95% CI, 0.48-0.80;
<0.001), and implantation of a supra-annular THV (OR, 6.61; 95% CI, 1.98-22.03;
=0.002). Conclusions CA after TAVR-in-TAVR might be unfeasible in >30% of patients currently treated with TAVR. Patients with a small sinotubular junction and those who received a supra-annular THV are at highest risk of potential CA impairment with TAVR-in-TAVR.
To realize carriers for drug delivery, cationic containers are required for anionic guests. Nevertheless, the toxicity of cationic carriers limits their practical use. In this study, we investigate a ...model system of polyampholyte N-isopropylacrylamide (NIPAM)-based microgels with a cationic core and an anionic shell to study whether the presence of a negative shell allows the cationic core to be shielded while still enabling the uptake and release of the anionic guest polyelectrolytes. These microgels are loaded with polystyrene sulfonate of different molecular weights to investigate the influence of their chain length on the uptake and release process. By means of small-angle neutron scattering, we evaluate the spatial distribution of polystyrene sulfonate within the microgels. The guest molecules are located in different parts of the core-shell microgels depending on their size. By combining these scattering results with UV-vis spectroscopy, electrophoretic mobility and potentiometric titrations we gain complementary results to investigate the uptake and release process of polyelectrolytes in polyampholyte core-shell microgels. Moreover, Brownian molecular dynamic simulations are performed to compare the experimental and theoretical results of this model. Our findings demonstrate that the presence of a shell still enables efficient uptake of guest molecules into the cationic core. These anionic guest molecules can be released through an anionic shell. Furthermore, the presence of a shell enhances the stability of the microgel-polyelectrolyte complexes with respect to the cationic precursor microgel alone.
Microgels composed of thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) are interfacial active. Their adsorption leads to deformation, causing conformational changes that have profound ...effects on the macroscopic properties of these films. Yet, methods to quantitatively probe the local density are lacking. We introduced scanning force microscopy (SFM) to quantitatively probe the internal structure of microgels physically adsorbed on a solid (SiO2)/water interface. Using a sharp SFM tip, we investigated the two types of microgels: (i) core–shell microgels featuring a hard silica core and a PNIPAM shell and (ii) hollow microgels obtained by dissolution of the silica core. Thus, both systems have the same polymer network as the peripheral structure but a distinctly different internal structure, that is, a rigid core versus a void. By evaluating the force–distance curves, the force profile during insertion of the tip into the polymer network enables to determine a depth-dependent contact resistance, which closely correlates with the density profiles determined in solution by small-angle neutron scattering. We found that the cavity of the swollen hollow microgels is still present when adsorbed to the solid substrate. Remarkably, while currently used techniques such as colloidal probe or reflectometry only provide an average of the z-profile, the methodology introduced herein actually probes the real three-dimensional density profile, which is ultimately important to understand the macroscopic behavior of microgel films. This will bridge the gap between the colloidal probe experiments that deform the microgel globally and the insertion in which the disturbance is located near the tip.
COAPT-trial entry criteria are useful to identify patients with better outcomes after transcatheter edge-to-edge repair (TEER). However, up to one-half of real-world patients with secondary mitral ...regurgitation (SMR) undergoing TEER do not meet these highly selective criteria and no study has formally investigated them. The aim of this study was to evaluate the predictors of good outcome after TEER in COAPT-ineligible patients.
All consecutive patients with SMR and heart failure (HF) treated with MitraClip at 3 European centres were retrospectively screened. The presence of at least 1 COAPT exclusion criterion was used to define a COAPT-ineligible profile, allowing the inclusion in the study population. Freedom from all-cause death or HF hospitalisation was evaluated at 2-year follow-up (primary end point).
A total of 305 patients (47%) had a COAPT-ineligible profile. An overall 58% rate of all-cause death or HF hospitalisation was detected at 2 years. Patients with a single COAPT exclusion criterion experienced fewer adverse events than those with multiple criteria (55% vs 69%). At multivariable Cox regression analysis, New York Heart Association functional class II, younger age (< 75 years), lower serum creatinine (< 2 mg/dL), lower left ventricular end-diastolic volume (< 240 mL), and the absence of hemodynamic instability, atrial fibrillation, and chronic obstructive pulmonary disease were independently associated with good outcome.
In this real-world series of patients with SMR undergoing TEER, a COAPT-ineligible profile was common. The presence of only 1 COAPT exclusion criterion or the absence of hemodynamic instability were associated with the most favourable outcomes.
Les critères d’admission à l’étude COAPT (CardiovascularOutcomesAssessment of the MitraClipPercutaneousTherapy for Heart Failure Patients With Functional Mitral Regurgitation) sont utiles pour identifier les patients susceptibles d’obtenir de meilleurs résultats après une réparation mitrale percutanée bord à bord (RMPBB). Cependant, en contexte réel, jusqu’à la moitié des patients atteints d'insuffisance mitrale secondaire (IMS) qui subissent une RMPBB ne répondent pas à ces critères hautement sélectifs et aucune étude formelle ne les a formellement étudiés. La présente étude visait à évaluer les prédicteurs d’une issue favorable à la suite d’une RMPBB chez les patients non admissibles selon les critères de l’étude COAPT.
Tous les patients consécutifs atteints d'IMS et d’insuffisance cardiaque (IC) traités au moyen d’un dispositif MitraClip dans trois centres européens ont été choisis de façon rétrospective. La présence d’au moins un critère d’exclusion de l’étude COAPT a été utilisée pour définir un profil non admissible selon les critères COAPT, et admettre les patients dans la population de la présente étude. L’absence de décès toutes causes confondues et d’hospitalisation pour IC a été évaluée après un suivi de deux ans (critère d’évaluation principal).
Au total, 305 patients (47 %) présentaient un profil non admissible selon les critères COAPT. Un taux global de 58 % de décès toutes causes confondues ou d’hospitalisation pour IC a été observé après un suivi de deux ans. Chez les patients présentant un seul critère d’exclusion de l’étude COAPT, la fréquence de manifestations indésirables a été plus faible que chez les patients présentant plus d’un critère d’exclusion (55 % vs 69 %). Dans une analyse de régression de Cox multivariée, la classe II de la classification de la NYHA, un âge moins avancé (< 75 ans), un taux sérique de créatinine faible (< 2 mg/dl), un volume télédiastolique faible dans le ventricule gauche (< 240 ml), et l’absence d’instabilité hémodynamique, de fibrillation auriculaire et de maladie pulmonaire obstructive chronique ont été des variables associées de façon indépendante à une issue favorable.
Chez cette série de patients traités en contexte réel qui étaient atteints d'IMS et qui ont été soumis à une RMPBB, un profil non admissible selon les critères de l’étude COAPT était une ca- ractéristique courante. La présence d’un seul critère d’exclusion de l’étude COAPT ou l’absence d’instabilité hémodynamique ont été associées aux issues les plus favorables.
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