Viscoelastic Response in Hydrous Polymers: The Role of Hydrogen Bonds and Microstructure.

Water responsive polymers represent a remarkable group of soft materials, acting as a laboratory for diverse water responsive physical phenomena and cutting-edge biology-electronics interfaces. We report on peculiarly distinctive viscoelastic behaviors of the biobased water responsive polymer cellulose 10-undecenoyl ester, while biobased regenerated cellulose displays stronger hydroplastic behaviors. We discovered a novel hydrous deformation mechanism involving the stretching of hydrogen bonds mediated by hydroxyl groups and water molecules, serving as a crucial factor in accommodating deformations. In parallel, the microstructure of cellulose 10-undecenoyl ester with unique coexisting nanoparticles and a continuous phase of entangled chains is mechanically resilient in the anhydrous state but enhances structural stiffness in the hydrous state. This variation arises from a different hydration level within the hydrous microstructure. Such a fundamental discovery offers valuable insights into the connection between the microscopic physical properties that can be influenced by water and the corresponding viscoelastic responses, extending its applicability to a wide range of hygroscopic materials.

Scale-Spanning Strong Adhesion Using Cellulose-Based Microgels.

Adhesive gels derived from biobased sustainable materials have extremely broad application prospects, such as in flexible smart materials and biomedicine fields. Combining high toughness and strong, persisting repeatable adhesion has always been a daunting challenge for adhesive gels. However, bulk gels based on polysaccharides as the most abundant bio-based compounds usually possess a high toughness but weak interfacial adhesion due to the strong hydration potential. Herein, a novel kind of highly tough microgel membranes with rough surfaces is fabricated using loosely chemically cross-linked dihydroxypropyl cellulose (cDHPC) microgels (average size = 1.25 ± 0.03 µm). Such microgel membranes exhibit strong, instant, and persisting adhesion to various substrates with different surface roughness. Slight chemical cross-linking and multiple physical interactions within microgels and resulting microgel membranes lead to high tensile strength and toughness of 0.23 ± 0.03 MPa and 73.8 ± 9.3 KJ m-3 , respectively. The maximum adhesive strength and debonding work exceed 320 ± 0.50 KPa and 160.97 ± 0.20 J m-2 , respectively. After five cycles (re-lap after detaching), the adhesive strength still remains above 200 KPa. Their adhesive properties outperform most bio-based adhesive gels and even petroleum-based gels, which are based on synergistic molecular and microscaled topological interactions.

Block Copolymers Featuring Highly Photostable Photoacids Based on Vinylnaphthol: Synthesis and Self-Assembly.

The synthesis of a photoresponsive amphiphilic diblock quarterpolymer containing 5-vinyl-1-naphthol (VN) as a photostable photoacidic comonomer is presented. The preparation is realized via a sequential reversible addition fragmentation chain transfer (RAFT) polymerization starting from a nona(ethylene glycol) methyl ether methacrylate (MEO9 MA/"O") hydrophilic block, which is then used as a macro-RAFT agent in the terpolymerization of styrene (S), 2-vinylpyridine (2VP), and TBS-protected VN (tVN). The terpolymerization proceeds in a controlled fashion and two diblock quarterpolymers, P(Om )-b-P(Sx -co-2VPy -co-VNz ), with varying functional comonomer compositions are prepared. These diblock quarterpolymers form spherical core-corona micelles in aqueous media according to dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo-TEM). Upon irradiation, the photoacids within the micellar core experience a drastic increase in acidity causing a proton transfer from the photoacid to neighboring 2VP units. As a result, the hydrophilic/hydrophobic balance of the entire assembly is shifted, and the encapsulated cargo is released.

pH-Responsive Side Chains as a Tool to Control Aqueous Self-Assembly Mechanisms.

pH-Tunable nanoscale morphology and self-assembly mechanism of a series of oligo(p-phenyleneethynylene) (OPE)-based bolaamphiphiles featuring poly(ethylene imine) (PEI) side chains of different length and degree of hydrolysis are described. Protonation and deprotonation of the PEI chains by changing the pH alters the hydrophilic/hydrophobic balance of the systems and, in turn, the strength of intermolecular interactions between the hydrophobic OPE moieties. Low pH values (3) lead to weak interaction between the OPEs and result in spherical nanoparticles, in which aggregation follows an isodesmic mechanism. In contrast, higher pH values (11) induce deprotonation of the polymer chains and lead to a stronger, cooperative aggregation into anisotropic nanostructures. Our results demonstrate that pH-responsive chains can be exploited as a tool to tune self-assembly mechanisms, which opens exciting possibilities to develop new stimuli-responsive materials.

Tackling the Limitations of Copolymeric Small Interfering RNA Delivery Agents by a Combined Experimental-Computational Approach.

Despite the first successful applications of nonviral delivery vectors for small interfering RNA in the treatment of illnesses, such as the respiratory syncytial virus infection, the preparation of a clinically suitable, safe, and efficient delivery system still remains a challenge. In this study, we tackle the drawbacks of the existing systems by a combined experimental-computational in-depth investigation of the influence of the polymer architecture over the binding and transfection efficiency. For that purpose, a library of diblock copolymers with a molar mass of 30 kDa and a narrow dispersity (D < 1.12) was synthesized. We studied in detail the impact of an altered block size and/or composition of cationic diblock copolymers on the viability of each respective structure as a delivery agent for polynucleotides. The experimental investigation was further complemented by a computational study employing molecular simulations as well as an analytical description of systemic properties. This is the first report in which molecular dynamics simulations of RNA/cationic polymer complexes have been performed. Specifically, we developed and employed a coarse-grained model of the system at the molecular level to study the interactions between polymer chains and small interfering RNA. We were further able to confirm a threshold lengthbinding block/lengthnonbinding block ratio, which is required for efficient complexation of siRNA, and it was possible to find a correlation between the length of the cationic block and the size of the resulting polyplex. Hence, the combined insights from the experiments and the theoretical investigation resulted in a wealth of information about the properties of cationic diblock copolymers employed as RNA delivery agents, in particular regarding the molecular and mechanistic details of the interaction between the two components of a polyplex.

Different Routes to Ampholytic Polydehydroalanine: Orthogonal versus Simultaneous Deprotection.

Polydehydroalanine (PDha) is a polyampholyte featuring both a -NH2 and a -COOH in every repeat unit and with that presents a rather high charge density. The synthesis and polymerization of two monomers, benzyl 2-tert-butoxycarbonylaminoacrylate and methyl 2-benzyloxycarbonylaminoacrylate is herein reported, which feature different protective groups and, after polymerization, the resulting PtBABA and PBOMA can be transformed into PDha using polymer-analogous modification reactions. More important, the current choice of protective groups allows either simultaneous deprotection in one step in both cases, but also the orthogonal deprotection of either -NH2 or -COOH moiety for PtBABA, given that appropriate conditions are chosen. The polymers are prepared using free radical polymerization and all (intermediate) polymeric materials are investigated using a combination of NMR spectroscopy and size exclusion chromatography.

Controlling the Miscibility of X-Shaped Bolapolyphiles in Lipid Membranes by Varying the Chemical Structure and Size of the Polyphile Polar Headgroup.

Bolaamphiphiles are well-known naturally occurring structures that can increase the thermal and mechanical stability of the phospholipid membrane by incorporation in a transmembrane manner. Modifications of bolaamphiphiles to introduce particular structural elements such as a conjugated aromatic backbone and lateral side chains in the hydrophobic region lead to bolapolyphiles (BPs). We investigated the ability of BPs to form lyotropic phases in water. The BPs had an identical backbone and side chains, but different headgroup structures, leading to different abilities to act as hydrogen bond donors and acceptors. BPs with hydrophilic headgroups capable of acting as hydrogen bond donors as well as acceptors did not form lyotropic phases and were insoluble in water, independent of whether the polar groups were small or large. The extended lipophilic core structure and the multiple intermolecular hydrogen bonds between the headgroups prevented the formation of well-hydrated lyotropic aggregates. A BP with two large hydrophilic headgroups of several ethylene oxide moieties terminated by methyl groups formed sheet- and vesicle-like aggregates in water. These headgroups act only as hydrogen bond acceptors and cannot form hydrogen bonds in the absence of water. The miscibility of BPs with vesicles of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) in water and the resulting aggregate structures were also investigated. For BPs with headgroups acting as donors and acceptors of hydrogen bonds, macroscopic phase separation occurred in the mixed membranes, and two different membrane domains, a DPPC-rich one containing only little polyphile and a BP-rich one containing varying amounts of lipid, were formed. For headgroups without the ability to act as hydrogen bond donors, small BP aggregates were formed that were homogeneously distributed over the membrane. The lateral organization of BPs in lipid membranes can thus be controlled by the nature of the BP headgroup.

Reversible Adsorption of Methylene Blue as Cationic Model Cargo onto Polyzwitterionic Magnetic Nanoparticles.

The reversible electrostatic adsorption of the cationic dye methylene blue (MB) as a model compound to polydehydroalanine (PDha)-coated magnetic multicore nanoparticles (MCNP) is presented. The pH responsiveness of the zwitterionic coating material enables reversible switching of the net surface charge of the PDha@MCNP hybrid particles by changes in pH and thus allows reversible adsorption of MB at neutral pH and desorption at low pH values. The resulting hybrid materials can be very interesting systems in the context of water purification, and the reversible adsorption is studied using UV-vis spectroscopy under varying surrounding conditions. The particles are characterized using dynamic light scattering, zeta potential measurements, transmission electron microscopy, and thermogravimetric analysis.

Synthesis, Characterization, and Applications of Magnetic Nanoparticles Featuring Polyzwitterionic Coatings.

Throughout the last decades, magnetic nanoparticles (MNP) have gained tremendous interest in different fields of applications like biomedicine (e.g., magnetic resonance imaging (MRI), drug delivery, hyperthermia), but also more technical applications (e.g., catalysis, waste water treatment) have been pursued. Different surfactants and polymers are extensively used for surface coating of MNP to passivate the surface and avoid or decrease agglomeration, decrease or modulate biomolecule absorption, and in most cases increase dispersion stability. For this purpose, electrostatic or steric repulsion can be exploited and, in that regard, surface charge is the most important (hybrid) particle property. Therefore, polyelectrolytes are of great interest for nanoparticle coating, as they are able to stabilize the particles in dispersion by electrostatic repulsion due to their high charge densities. In this review article, we focus on polyzwitterions as a subclass of polyelectrolytes and their use as coating materials for MNP. In the context of biomedical applications, polyzwitterions are widely used as they exhibit antifouling properties and thus can lead to minimized protein adsorption and also long circulation times.

Zwitterionic Iron Oxide (γ-Fe2 O3 ) Nanoparticles Based on P(2VP-grad-AA) Copolymers.

This study presents the synthesis and characterization of zwitterionic core-shell hybrid nanoparticles consisting of a core of iron oxide multicore nanoparticles (MCNPs, γ-Fe2 O3 ) and a shell of sultonated poly(2-vinylpyridine-grad-acrylic acid) copolymers. The gradient copolymers are prepared by reversible addition fragmentation chain transfer polymerization of 2-vinylpyridine (2VP), followed by the addition of tert-butyl acrylate and subsequent hydrolysis. Grafting of P(2VP-grad-AA) onto MCNP results in P(2VP-grad-AA)@MCNP, followed by quaternization using 1,3-propanesultone-leading to P(2VPS -grad-AA)@MCNP with a zwitterionic shell. The resulting particles are characterized by transmission electron microscopy, dynamic light scattering, and thermogravimetric analysis measurements, showing particle diameters of ≈70-90 nm and an overall content of the copolymer shell of ≈10%. Turbidity measurements indicate increased stability toward secondary aggregation after coating if compared to the pristine MCNP and additional cytotoxicity tests do not reveal any significant influence on cell viability.