“Dumb” pH-Independent and Biocompatible Hydrogels Formed by Copolymers of Long-Chain Alkyl Glycidyl Ethers and Ethylene Oxide

The formation and rheological properties of hydrogels based on amphiphilic ABA triblock polyether copolymers are described, relying solely on the hydrophobic interaction of long-chain alkyl glycidyl ether (AlkGE)- based A-blocks that are combined with a hydrophilic poly(ethylene glycol) (PEG) midblock. Via anionic ring-opening copolymerization (AROP), ethylene oxide (EO) and long-chain alkyl glycidyl ethers (AlkGEs) were copolymerized, using deprotonated poly(ethylene glycol) (PEG) macroinitiators (Mn of 10, 20 kg mol-1). The polymerization afforded amphiphilic ABA triblock copolymers with molar masses in the range of 21-32 kg mol-1 and dispersities (Đ) of Đ = 1.07-1.17. Kinetic studies rev…

Bone Scaffolds Based on Degradable Vaterite/PEG‐Composite Microgels

Vaterite, a metastable modification of calcium carbonate, embedded in a flexible microgel packaging with adjustable mechanical properties, functionality, and biocompatibility, provides a powerful scaffolding for bone tissue regeneration, as it is easily convertible to bone-like hydroxyapatite (HA). In this study, the synthesis and physical analysis of a packaging material to encapsulate vaterite particles and osteoblast cells into monodisperse, sub-millimeter-sized microgels, is described whereby a systematic approach is used to tailor the microgel properties. The size and shape of the microgels is controlled via droplet-based microfluidics. Key requirements for the polymer system, such as …

Direct Evidence of Heteroleptic Complexation in the Macroscopic Dynamics of Metallo-supramolecular Polymer Networks

Secondary Structure-Driven Hydrogelation Using Foldable Telechelic Polymer-Peptide Conjugates.

The synthesis of ABA and ABA' triblock polyethylene glycol-and polysarcosine-peptide conjugates is reported. The A/A' peptides are based on phenylalanine(F)-histidine(H) pentapeptide sequences FHFHF, which promote pH-switchable β-sheet self-assembly into nanorods in water. Only parallel β-sheet-driven folding and intermolecular assembly using ABA triblock polymer-peptide conjugates leads to interstrand cross-linking and hydrogelation, highlighting the impact of supramolecular interactions-directed structure formation at the nano- and mesoscopic level.

Inverse Thermogelation of Aqueous Triblock Copolymer Solutions into Macroporous Shear-Thinning 3D Printable Inks

Amphiphilic block copolymers that undergo (reversible) physical gelation in aqueous media are of great interest in ditIerent areas including drug delivery, tissue engineering, regenerative medicine, and biofabrication. We investigated a small library of ABA-type triblock copolymers comprising poly(2-methyl-2-oxazoline) as the hydrophilic shell A and different aromatic poly(2-oxazoline)s and poly(2-oxazine)s cores B in an aqueous solution at different concentrations and temperatures. Interestingly, aqueous solutions of poly(2-methyl-2-oxazoline)-block-poly(2-phenyl-2-oxazine)-block-poly(2-methyl-2-oxazoline) (PMeOx-b-PPheOzi-b-PMeOx) undergo inverse thermogelation below a critical temperatur…

Self-Diffusion of Associating Star-Shaped Polymers

The dynamics of associating bonds in transient polymer networks exerts a paramount influence on their relaxation and time-dependent mechanical properties. In particular, diffusive motion of polymers mediated by the dissociation and association equilibrium of reversible junctions can affect the materials’ structural stability, dynamic mechanical properties, and a broad spectrum of functionality that arises from the constant motion of polymer chains. In this work, forced Rayleigh scattering is used to measure the diffusion of terpyridine end-functionalized four-arm poly(ethylene glycol) polymers transiently interlinked by zinc ions in organic solvent across a wide range of length and time sca…

Connectivity Defects and Collective Assemblies in Model Metallo‐Supramolecular Dual‐Network Hydrogels

Concentration-dependent switch between chain association and dissociation of oppositely charged weak polyelectrolytes in solution

Abstract Joint solutions of oppositely charged weak polyelectrolytes are considerably less studied than their strong counterparts; as a result, their thermodynamic understanding is still unsatisfactory. This shortcoming hampers the development of a general picture about the physical properties of these mixtures, which further hampers their use to design new materials. To close this gap, we investigate the ternary system ethanol/polyacid/polybase (polyacid: methacrylic acid containing copolymer; polybase: N,N-dimethylaminoethyl methacrylate containing terpolymer) with respect to its demixing and viscometric behavior. Complete homogeneity can only be reached if the total polymer concentration…

Origin of the low-frequency plateau and the light-scattering slow mode in semidilute poly(ethylene glycol) solutions

A low-frequency plateau is often found in the rheological spectra of various kinds of semidilute solutions of polymers and other colloids; also, many such solutions have been reported to show slow-modes in their dynamic light scattering autocorrelation functions. Both these observations may lead to the hypothesis of weak associative network structures built by the dissolved polymer chains or colloidal building blocks. To challenge this hypothesis, we conduct a series of comparative studies on semidilute solutions of poly(ethylene glycol) by using classical rheology as well as passive microrheology based on dynamic light scattering, along with structural studies using static light scattering…

Microfluidics and Macromolecules: Top-Down Analytics and Bottom-Up Engineering of Soft Matter at Small Scales

Microfluidics is the art of creating and manipulating small portions of fluids. A typical variant of this art is fluid transport within small channels, either in form of laminar co-flow of miscible streams or in form of segmented-flow dripping and jetting of immiscible streams. Either method provides means to expose components of interest to defined local conditions such as spatially controlled concentration profiles that could not be established without the microfluidic auxiliaries. This ability renders microfluidics uniquely useful as both a method for advanced analytics and synthesis. This article sheds a spotlight on the use and utility of this method in macromolecular chemistry and phy…

Enhancement of metallo-supramolecular dissociation kinetics in telechelic terpyridine-capped poly(ethylene glycol) assemblies in the semi-dilute regime.

The dynamics of supramolecular polymer assemblies is governed by that of their polymeric building blocks and that of the transient bonds between them. Entrapment of such bonds by topological crowding often causes renormalization of the bond lifetimes towards prolonging. In the present study, by contrast, we show that this effect can also be inverse in the case of telechelic metallo-supramolecular polymers in semi-dilute solution. We focus on linear poly(ethylene glycols) capped by terpyridine binding motifs at both ends that can form metal–ligand coordinative bonds with various transition metal ions, thereby creating transient metallo-supramolecular assemblies of varying length and binding …

Bridging rigidity and flexibility : modulation of supramolecular hydrogels by metal complexation

The combination of complementary, noncovalent interactions is a key principle for the design of multistimuli responsive hydrogels. In this work, an amphiphilic peptide, supramacromolecular hydrogelator which combines metal-ligand coordination induced gelation and thermoresponsive toughening is reported. Following a modular approach, the incorporation of the triphenylalanine sequence FFF into a structural (C3EG ) and a terpyridine-functionalized (C3Tpy ) C3 -symmetric monomer enables their statistical copolymerization into self-assembled, 1D nanorods in water, as investigated by circular dichroism (CD) spectroscopy and transmission electron microscopy (TEM). In the presence of a terpyridine …

Sticker Multivalency in Metallo-supramolecular Polymer Networks

Local dynamics in supramolecular polymer networks probed by magnetic particle nanorheology

Transient supramolecular polymer networks are promising candidates as soft self-healing or stimuli-sensitive materials. In this paper, we employ a novel nanorheological approach, magnetic particle nanorheology (MPN), in order to better understand the local dynamic properties of model supramolecular networks from a molecular point of view. Hence, the bond strength between four-arm star-shaped polyethylene glycol (PEG) functionalized at the four extremities with terpyridine ligands is tuned by implementing different metal ions with variable complexation affinities for the ligand. We show that MNP allows for the evaluation of the strength and connectivity of the polymer networks by the estimat…

Cell adhesion on UV-crosslinked polyurethane gels with adjustable mechanical strength and thermoresponsiveness

Temperature-responsive polyurethane (PU) hydrogels represent a versatile material platform for modern tissue engineering and biomedical applications. However, besides intrinsic advantages such as high mechanical strength and a hydrolysable backbone composition, plain PU materials are generally lacking bio-adhesive properties. To overcome this shortcoming, the authors focus on the synthesis of thermoresponsive PU hydrogels with variable mechanical and cell adhesive properties obtained from linear precursor PUs based on poly(ethylene glycol)s (pEG) with different molar masses, isophorone diisocyanate, and a dimerizable dimethylmaleimide (DMMI)-diol. The cloud point temperatures of the dilute,…

Dynamic Model Metallo‐Supramolecular Dual‐Network Hydrogels with Independently Tunable Network Crosslinks

Amphiphilic poly(ether urethanes) carrying associative terpyridine side groups with controlled spacing

The rational design of transiently crosslinked polymer gels requires a profound understanding of how molecular and topological factors determine the mechanical and dynamic material properties. To refine so-far established structure–property relations, complementary and versatile model sytems are still a crucial prerequisiste. In this study, the synthesis of a metallo-supramolecular associating terpyridine-diol (referred to as sticker) and its incorporation into poly(ethylene glycol) (pEG) based polyurethanes (PU) with strictly alternating vs. random sequences and variable sticker spacings is described. Synergetic effects resulting from the proximity of multiple neighboring urethane and stic…

Dynamics of supramolecular associative polymer networks at the interplay of chain entanglement, transient chain association, and chain‐sticker clustering

The dynamic mechanical properties of supramolecular associative polymer networks depend on the average number of entanglements along the network‐forming chains, Nₑ, and on their content of associative groups, f. In addition, there may be further influence by aggregation of the associative groups into clusters, which, in turn, is influenced by the chemical structure of these groups, and again by Nₑ and f of the polymer. Therefore, the effects of these parameters are interdependent. To conceptually understand this interdependency, we study model networks in which (a) Nₑ, (b) f, and (c) the chemical structure of the associative groups are varied systematically. Each network is probed by rheolo…

Energy Consumption for the Desalination of Salt Water Using Polyelectrolyte Hydrogels as the Separation Agent

The energy consumption for a novel desalination approach using charged hydrogels under externally applied pressure is experimentally measured and calculated. The salt separation is based on a partial rejection of mobile salt ions caused by the fixed charges inside the polyelectrolyte network. Self-synthesized and commercial poly(acrylic acid) hydrogels are used to study the desalination performance in reference to sodium chloride solutions within the concentration range of 0.1–35 g L−1. The influence of various synthetic parameters, such as the degree of crosslinking (DC) and the size and shape of the particles, is investigated. Furthermore, the effect of process parameters including the am…

Salt partitioning in ionized, thermo-responsive hydrogels: perspective to water desalination

Charged hydrogels are capable of swelling in aqueous salt solutions, whereby part of the salt ions is repelled due to the presence of fixed charged groups inside the hydrogel. This effect creates a concentration gradient between the absorbed solution and the surrounding fluid known as salt partitioning, offering a potential for these materials to be employed to desalinate saltwater. If the charged hydrogels are thermo-sensitive as well, then the purer, absorbed solution can be recovered by shrinking the hydrogels upon temperature change. To tailor that potential in water-purification and desalination applications, the main parameters influencing the salt partitioning, the deswelling of the …

Scattering perspectives on nanostructural inhomogeneity in polymer network gels

Abstract Scattering methods based on spatial and temporal contrast fluctuations in polymer-network gels, which originate from polymer-segmental density fluctuations, reveal rich insight into different types and levels of nanostructural inhomogeneity in these soft materials. Complementary contrasting as provided by light, neutron, and X-ray scattering allows such information to be obtained on nano- to micrometer length scales. On top of that, complementary use of static and dynamic scattering methods allows the interplay and effect of these inhomogeneities to be unraveled. This article interrelates a multitude of studies on the application of scattering techniques for analytical assessment o…

Dynamics-based assessment of nanoscopic polymer-network mesh structures and their defects.

Polymer-network gels often exhibit complex nanoscopic architectures. First, the polymer-network mesh topology on scales of 1–10 nm is usually not uniform and regular, but disordered and irregular. Second, on top of that, many swollen polymer networks display spatial inhomogeneity of their polymer segmental density and crosslinking density on scales of 10–100 nm. This multi-scale structural complexity affects the permeability, mechanical strength, and optical clarity of the polymer gels, which is of central relevance for their performance in popular applications. As a result, there is a need to characterize the polymer network structures on multiple scales. On the scale of the spatial inhomo…

Structural and Gelation Characteristics of Metallo-Supramolecular Polymer Model-Network Hydrogels Probed by Static and Dynamic Light Scattering

Supramolecular polymer gels are a promising class of materials whose polymer components are connected by transient bonds such as metal–ligand interactions, thereby spanning a dynamic network throug...

Macromol. Chem. Phys. 2/2017

Macromolecules in Microfluidics: A Synergy for Systems Engineering

Reversible Hydrogels with Switchable Diffusive Permeability

Hydrogels are polymer networks swollen in water that are characterized by soft mechanics and high permeability. This makes them good candidates for separation and membrane technologies. The diffusion is controlled by the mesh size of the network, and this can be made tunable through the introduction of thermoresponsive polymers. However, this is still a developing field. To contribute to this development, a dual dynamic network is formed composed of four-arm polyethylene glycol precursors in which each arm is functionalized with both a terpyridine moiety capable of forming reversible metal–ligand complexes along with branches of poly(N-isopropylacrylamide) (pNIPAAm), which can be swit…

Connectivity defects enhance chain dynamics in supramolecular polymer model-network gels

Supramolecular polymer networks exhibit twofold dynamics: that of their polymer chains and that of the transient bonds between them, which is further complexed when irregular network structures lead to local variation of both. A typical irregularity is imperfect network-chain connectivity. To assess the impact of that, we study the diffusion of three different types of tracer polymers in supramolecular model networks of four-arm star-shaped poly(ethylene glycol). First, we focus on tracers that carry three stickers and one fluorescent label at their four arms, thereby creating an inherent network connectivity defect in their vicinity. Second, we embed tracers that carry four stickers and fo…

Deconvolution of the Effects of Binary Associations and Collective Assemblies on the Rheological Properties of Entangled Side-Chain Supramolecular Polymer Networks

The properties and function of supramolecular polymer networks are determined not only by pairwise interchain transient associations but also by chain entanglement and nanoscopic phase separation of the associative groups. To unravel the impact and interplay of these different factors, we devise a set of model supramolecular polymer networks in which the number of entanglements and the density of associative groups are systematically varied. Rheological data show that by increasing the density of associative groups, the plateau modulus grows to a steady level and extends over a distinct frequency range. This is credited to the presence of binary associations with unique partner exchange tim…

Metallo-Polymer Chain Extension Controls the Morphology and Release Kinetics of Microparticles Composed of Terpyridine-Capped Polylactides and their Stereocomplexes.

Control over morphology and porosity of supramolecular complexed polylactide (PLA) microparticles can be achieved by manipulation of the supramolecular interactions between their constituent polymeric building blocks. It is expected that such modular systems are ideal candidates to serve as degradable delivery carriers. In view of this goal, this study reports about a modular fabrication of biodegradable microparticles from terpyridine (TPy) and bisterpyridine (bisTPy) end-functionalized PLAs that can be transiently extended by chain association through differently strong complexation to three metal cations: Ni2+ , Co2+ , or Fe2+ . Further influence on the morphology of the particles can be…

The Next 100 Years of Polymer Science

International audience; The year 2020 marks the 100th anniversary of the first article on poly merization, published by Hermann Staudinger. It is Staudinger who realized that polymers consist of long chains of covalently linked building blocks. Polymers have had a tremendous impact on the society ever since this initial publication. People live in a world that is almost impossible to imagine without synthetic polymers. But what does the future hold for polymer science? In this article, the editors and advisory board of Macromolecular Chemistry and Physics reflect on this question.

Coordination Geometry Preference Regulates the Structure and Dynamics of Metallo-Supramolecular Polymer Networks

Metal–ligand interactions are extensively used for the development of biomimetic polymers. Macroscopic properties of such systems are closely tied to the microscopic structure and dynamics of not o...

Core-Shell Microgels with Switchable Elasticity at Constant Interfacial Interaction.

Hydrogels based on poly(N-isopropylacrylamide) (pNIPAAm) exhibit a thermo-reversible volume phase transition from swollen to deswollen states. This change of the hydrogel volume is accompanied by changes of the hydrogel elastic and Young's moduli and of the hydrogel interfacial interactions. To decouple these parameters from one another, we present a class of submillimeter sized hydrogel particles that consist of a thermosensitive pNIPAAm core wrapped by a nonthermosensitive polyacrylamide (pAAm) shell, each templated by droplet-based microfluidics. When the microgel core deswells upon increase of the temperature to above 34 °C, the shell is stretched and dragged to follow this deswelling i…

Rational Design of Thermoresponsive Microgel Templates with Polydopamine Surface Coating for Microtissue Applications.

Functional microgels provide a versatile basis for synthetic in vitro platforms as alternatives to animal experiments. The tuning of the physical, chemical, and biological properties of synthetic microgels can be achieved by blending suitable polymers and formulating them such to reflect the heterogenous and complex nature of biological tissues. Based on this premise, this paper introduces the development of volume-switchable core-shell microgels as 3D templates to enable cell growth for microtissue applications, using a systematic approach to tune the microgel properties based on a deep conceptual and practical understanding. Microscopic microgel design, such as the tailoring of the microg…

Efficiency range of the Belousov-Zhabotinsky reaction to induce the self-organization of transient bonds in metallo-supramolecular polymeric systems.

The periodic change of the oxidation state of the metal catalyst in the oscillating Belousov-Zhabotinsky (BZ) reaction has been reported to establish a periodic organization of metallo-supramolecular bonds in polymeric systems, which results in autonomous viscosity oscillations. To appraise the possible extent of quantitative control on the viscosity oscillation features, we assess how the kinetics of the BZ reaction affects the periodic self-organization of the metal-ligand coordination, and vice versa. Our model system includes mono-, bis-, and tetra-functional polyethyleneglycol (PEG) precursors end grafted with terpyridine ligands that are complexed with ruthenium ions, which oscillate …

Defects and defect engineering in Soft Matter.

Soft matter covers a wide range of materials based on linear or branched polymers, gels and rubbers, amphiphilic (macro)molecules, colloids, and self-assembled structures. These materials have applications in various industries, all highly important for our daily life, and they control all biological functions; therefore, controlling and tailoring their properties is crucial. One way to approach this target is defect engineering, which aims to control defects in the material's structure, and/or to purposely add defects into it to trigger specific functions. While this approach has been a striking success story in crystalline inorganic hard matter, both for mechanical and electronic properti…

Active and Passive Motion in Complex pH‐Fields

An Inverse Thermogelling Bioink Based on an ABA-Type Poly(2-oxazoline) Amphiphile

Hydrogels are key components in several biomedical research areas such as drug delivery, tissue engineering, and biofabrication. Here, a novel ABA-type triblock copolymer comprising poly(2-methyl-2-oxazoline) as the hydrophilic A blocks and poly(2-phenethyl-2-oxazoline) as the aromatic and hydrophobic B block is introduced. Above the critical micelle concentration, the polymer self-assembles into small spherical polymer micelles with a hydrodynamic radius of approx 8-8.5 nm. Interestingly, this specific combination of hydrophilic and hydrophobic aromatic moieties leads to rapid thermoresponsive inverse gelation at polymer concentrations above a critical gelation concentration (20 wt %) into…

Origin of nanostructural inhomogeneity in polymer-network gels

Polymer-network gels often display nano- to microstructural spatial inhomogeneity of their polymer-segmental and crosslinking densities, especially if they are formed by uncontrolled free-radical crosslinking copolymerization of mono- and multifunctional monomers and crosslinkers. This structural complexity markedly affects their optical clarity, mechanical strength, and permeability, which is of central relevance for their performance in everyday-life and high-tech products. This review summarizes and inter-relates a rich amount of existing studies on the origin of this inhomogeneity. It arcs from early fundamental work in the 1990s, development and assessment of highly ideal and super tou…

Emergence, evidence, and effect of junction clustering in supramolecular polymer materials

A significant fraction of biomaterials consists of supramolecular polymers and networks formed by non-covalent interactions between associative motifs. They typically contain complex structures in which on top of binary associations, phase-separation and aggregation of associative junctions occur. Such hierarchical assemblies have significant influences on the dynamics as well as the physical and mechanical properties of the materials. Similar to supramolecular biomaterials, aggregation of associative junctions has also been frequently reported to occur in synthetic supramolecular polymers and networks. Engineering of such secondary structures in a sense to create and control the extent of …

Dominance of Chain Entanglement over Transient Sticking on Chain Dynamics in Hydrogen-Bonded Supramolecular Polymer Networks in the Melt

The chain dynamics in supramolecular polymer networks is determined by the interplay of the kinetics of transient interchain association and relaxation of the network chains themselves. This interplay can be addressed by studying model supramolecular polymer networks in which the number of associative side groups and the molar mass of the covalently jointed backbone polymers are both varied systematically. To realize this idea, we use precursor chains with three different molar masses, which comes along with different extents of entanglement in the melt state. For each molar mass, the precursor polymers are functionalized with three different relative contents of associative side groups, gi…

Light-Fueled, Spatiotemporal Modulation of Mechanical Properties and Rapid Self-Healing of Graphene-Doped Supramolecular Elastomers

Gaining spatially resolved control over the mechanical properties of materials in a remote, programmable, and fast-responding way is a great challenge toward the design of adaptive structural and functional materials. Reversible, temperature-sensitive systems, such as polymers equipped with supramolecular units, are a good model system to gain detailed information and target large-scale property changes by exploiting reversible crosslinking scenarios. Here, it is demonstrated that coassembled elastomers based on polyglycidols functionalized with complementary cyanuric acid and diaminotriazine hydrogen bonding couples can be remotely modulated in their mechanical properties by spatially conf…

Tuning the life-time of supramolecular hydrogels using ROS-responsive telechelic peptide-polymer conjugates

Abstract The synthesis of multi-stimuli responsive peptide-poly(ethylene glycol) ABA-type conjugates is reported. The β-sheet encoded intramolecular folding and intermolecular self-assembly into 1D nanorods is based on a phenylalanine(F)-methionine(M)-histidine(H) FMHMHF hexapeptide sequence, and the supramolecular nanorods are stabilised by a shielding corona of hydrophilic PEG polymers. Interstrand crosslinking leads to the formation of physical networks and hydrogels at physiological pH and at room temperature. The thioether functional groups integrate oxidation responsive properties in the supramolecular polymer assemblies. We show that the glucose fuelled and glucose oxidase catalysed …

Physics of agarose fluid gels: Rheological properties and microstructure

Agarose, a strongly gelling polysaccharide, is a common ingredient used to optimize the viscoelastic properties of a multitude of food products. Through aggregation of double helices via hydrogen bonds while cooling under quiescent conditions it forms firm and brittle gels. However, this behavior can be altered by manipulating the processing conditions viz shear. For example, gelation under shear leads to microgel particles with large surface area, which in turn leads to completely different rheological properties and texture. Such fluid gels are shown to play an important role in texture modification of foods and beverages for dysphagia patients. In this study, different concentration of a…

Thermodynamic control over energy dissipation modes in dual-network hydrogels based on metal-ligand coordination.

Modern polymeric hydrogels use reversible bonds to mimic biological functionalities. However, true biological materials benefit from several supramolecular elements and deliver multiple functions at the same time. To approach similar creation and control of multiple different functional elements in a synthetic soft material, we develop a model dual-network hydrogel in which multiple energy dissipating modes are formed by metal–ligand coordination and regulated by their association thermodynamics. This idea is realized by using linear and tetra-arm poly(ethylene glycol) (PEG) precursors with complementary reactive end groups. The former also carries terpyridine ligands on both ends, which fo…