Structure-property relationship of a model network containing solvent

Synthesis of optically active star polymers consisting of helical poly(phenylacetylene) chains by the living polymerization of phenylacetylenes and their chiroptical properties

Star polymers consisting of three helical poly(phenylacetylene) chains with a precisely controlled molecular weight (molar mass dispersity < 1.03) were successfully synthesized by the living polymerization of phenylacetylene derivatives with a Rh-based multicomponent catalyst system comprising trifunctional initiators, which have three phenylboronates centered on a benzene ring, the Rh complex [Rh(nbd)Cl]2, diphenylacetylene, triphenylphosphine, and a base. The analysis of chiroptical properties of the optically active star polymers obtained by the living polymerization of optically active phenylacetylene derivatives revealed that the star polymers exhibited chiral amplification properties owing to their unique topology compared with the corresponding linear polymers.

Peptide-dendrimer-reinforced bioinks for 3D bioprinting of heterogeneous and biomimetic in vitro models

Despite 3D bioprinting having emerged as an advanced method for fabricating complex in vitro models, developing suitable bioinks that fulfill the opposing requirements for the biofabrication window still remains challenging. Although naturally derived hydrogels can better mimic the extracellular matrix (ECM) of numerous tissues, their weak mechanical properties usually result in architecturally simple shapes and patchy functions of in vitro models. Here, this limitation is addressed by a peptide-dendrimer-reinforced bioink (HC-PDN) which contained the peptide-dendrimer branched PEG with end-grafted norbornene (PDN) and the cysteamine-modified HA (HC). The extensive introduction of ethylene end-groups facilitates the grafting of sufficient moieties and enhances thiol-ene-induced crosslinking, making HC-PDN exhibits improved mechanical and rheological properties, as well as a significant reduction in reactive oxygen species (ROS) accumulation than that of methacrylated hyaluronic acid (HAMA). In addition, HC-PDN can be applied for the bioprinting of numerous complex structures with superior shape fidelity and soft matrix microenvironment. A heterogeneous and biomimetic hepatic tissue is concretely constructed in this work. The HepG2-C3As, LX-2s, and EA.hy.926s utilized with HC-PDN and assisted GelMA bioinks closely resemble the parenchymal and non-parenchymal counterparts of the native liver. The bioprinted models show the endothelium barrier function, hepatic functions, as well as increased activity of drug-metabolizing enzymes, which are essential functions of liver tissue in vivo. All these properties make HC-PDN a promising bioink to open numerous opportunities for in vitro model biofabrication. STATEMENT OF SIGNIFICANCE: In this manuscript, we introduced a peptide dendrimer system, which belongs to the family of hyperbranched 3D nanosized macromolecules that exhibit high molecular structure regularity and various biological advantages. Specifically, norbornene-modified peptide dendrimer was grafted onto PEG, and hyaluronic acid (HA) was selected as a base material for bioink formulation because it is a component of the ECM. Peptide dendrimers confer the following advantages to bioinks: (a) Geometric symmetry can facilitate construction of bioinks with homogeneous networks; (b) abundant surface functional groups allow for abundant crosslinking points; (c) the biological origin can promote biocompatibility. This study shows conceptualization to application of a peptide-dendrimer bioink to extend the Biofabrication Window of natural bioinks and will expand use of 3D bioprinting of in vitro models.

Structurally decoupled stiffness and solute transport in multi-arm poly(ethylene glycol) hydrogels

Synthetic hydrogels are widely used as artificial 3D environments for cell culture, facilitating the controlled study of cell-environment interactions. However, most hydrogels are limited in their ability to represent the physical properties of biological tissues because stiffness and solute transport properties in hydrogels are closely correlated. Resultingly, experimental investigations of cell-environment interactions in hydrogels are confounded by simultaneous changes in multiple physical properties. Here, we overcame this limitation by simultaneously manipulating four structural parameters to synthesize a library of multi-arm poly (ethylene glycol) (PEG) hydrogel formulations with robustly decoupled stiffness and solute transport. This structural design approach avoids chemical alterations or additions to the network that might have unanticipated effects on encapsulated cells. An algorithm created to statistically evaluate stiffness-transport decoupling within the dataset identified 46 of the 73 synthesized formulations as robustly decoupled. We show that the swollen polymer network model accurately predicts 11 out of 12 structure-property relationships, suggesting that this approach to decoupling stiffness and solute transport in hydrogels is fundamentally validated and potentially broadly applicable. Furthermore, the unprecedented control of hydrogel network structure provided by multi-arm PEG hydrogels confirmed several fundamental modeling assumptions. This study enables nuanced hydrogel design for uncompromised investigation of cell-environment interactions.

The Impact of Polymerization Chemistry on the Mechanical Properties of Poly(dimethylsiloxane) Bottlebrush Elastomers

We compare the low-strain mechanical properties of bottlebrush elastomers (BBEs) synthesized using ring-opening metathesis and free radical polymerization. Through comparison of experimentally measured elastic moduli and those predicted by an ideal, affine model, we evaluate the efficiency of our networks in forming stress-supporting strands. This comparison allowed us to develop a structural efficiency ratio that facilitates the prediction of mechanical properties relative to polymerization chemistry (e.g., softer BBEs when polymerizing under dilute conditions). This work highlights the impact that polymerization chemistry has on the structural efficiency ratio and the resultant mechanical properties of BBEs with identical side chains, providing another "knob" by which to control polymer network properties.

Recent Advances in Mechanical Reinforcement of Zwitterionic Hydrogels

As a nonspecific protein adsorption material, a strong hydration layer provides zwitterionic hydrogels with excellent application potential while weakening the interaction between zwitterionic units, leading to poor mechanical properties. The unique anti-polyelectrolyte effect in ionic solution further restricts the application value due to the worsening mechanical strength. To overcome the limitations of zwitterionic hydrogels that can only be used in scenarios that do not require mechanical properties, several methods for strengthening mechanical properties based on enhancing intermolecular interaction forces and polymer network structure design have been extensively studied. Here, we review the works on preparing tough zwitterionic hydrogel. Based on the spatial and molecular structure design, tough zwitterionic hydrogels have been considered as an important candidate for advanced biomedical and soft ionotronic devices.

Experimental Comparison of Bond Lifetime and Viscoelastic Relaxation in Transient Networks with Well-Controlled Structures

We demonstrate an experimental comparison of the bond lifetime, estimated using surface plasmon resonance (SPR), and the viscoelastic relaxation time of transient networks with well-controlled structures (dynamically cross-linked Tetra-PEG gel). SPR and viscoelastic measurements revealed that the temperature dependences of the two characteristic times are in agreement, while the viscoelastic response is delayed with respect to the lifetime by a factor of 2-3, dependent on the network strand length. Polymers cross-linked by temporary interactions form transient networks, which show fascinating viscoelasticity with a single relaxation mode. However, the molecular understanding of such simple viscoelasticity has remained incomplete because of the difficulty of experimentally evaluating bond lifetimes and heterogeneous structures in conventional transient networks. Our results suggest that bond dissociation and recombination both contribute to the macromechanical response. This report on direct bond-lifetime-viscoelastic-relaxation time comparison provides important information for the molecular design of transient network materials.

Recent Advances in Design Strategies of Tough Hydrogels

Hydrogels are a fascinating class of materials popular in numerous fields, including tissue engineering, drug delivery, soft robotics, and sensors, attributed to their 3D network porous structure containing a significant amount of water. However, traditional hydrogels exhibit poor mechanical strength, limiting their practical applications. Thus, many researchers have focused on the development of mechanically enhanced hydrogels. This review describes the design considerations for constructing tough hydrogels and some of the latest strategies in recent years. These tough hydrogels have an up-and-coming prospect and bring great hope to the fields of biomedicine and others. Nonetheless, it is still no small challenge to realize hydrogel materials that are tough, multifunctional, intelligent, and zero-defect. This article is protected by copyright. All rights reserved.

Peter L, Chan C, Mikhailova T, Bexheti V, Kapadia A, Carbery WP, Ng K, Maity P. Microfluidic-Supported Synthesis of Anisotropic Polyvinyl Methacrylate Nanoparticles via Interfacial Agents

For polymer particles, recent studies emphasized that the particle shape—not size—plays the dominant role in novel applications in fields ranging from nanotechnology, biomedicine, to photonics, which has intensified the quest...

Solute Transport Dependence on 3D Geometry of Hydrogel Networks

Hydrogels are used in drug delivery applications, chromatography, and tissue engineering to control the rate of solute transport based on solute size and hydrogel-solute affinity. Ongoing modeling efforts to quantify the relationship between hydrogel properties, solute properties, and solute transport contribute toward an increasingly efficient hydrogel design process and provide fundamental insight into the mechanisms relating hydrogel structure and function. However, here we clarify previous conclusions regarding the use of mesh size in hydrogel transport models. We use 3D geometry and hydrogel network visualizations to show that mesh size and junction functionality both contribute to the mesh radius, which determines whether a solute can diffuse within a hydrogel. Using mesh radius instead of mesh size to model solute transport in hydrogels will correct junction functionality-dependent modeling errors, improving hydrogel design predictions and clarifying mechanisms of solute transport in hydrogels.

Synthesis and Physicochemical Evaluation of Bees' Chitosan-Based Hydrogels Modified with Yellow Tea Extract

The novelty of the research involves designing the measurement methodology aimed at determining the structure-property relationships in the chitosan-based hydrogels containing yellow tea extract. Performed investigations allowed us to determine the swelling properties of hydrogels in selected time intervals, evaluate the mutual interactions between the hydrogels and simulated physiological liquids via pH measurements and directly assess the impact of such interactions on the chemical structure of hydrogels using Fourier transform infrared (FT-IR) spectroscopy and their wettability by the measurements of the flatness of the drop on the surface of the tested samples via the static drop method. Next, the surface morphology of hydrogels was characterized by the Scanning Electron Miscorcopy (SEM) and their elasticity under the tension applied was also verified. It was proved that incubation in simulated physiological liquids resulted in a decrease in contact angles of hydrogels, even by 60%. This also caused their certain degradation which was reflected in lower intensities of bands on FT-IR spectra. Further, 23% v/v yellow tea extract in hydrogel matrices caused the decrease of their tensile strength. An increase in the amount of the crosslinker resulted in a decrease in the sorption capacity of hydrogels wherein their modification caused greater swelling ability. In general, the investigations performed provided much information on the tested materials which may be meaningful considering their application, e.g., as dressing materials.

Effect of Nonlinear Elasticity on the Swelling Behaviors of Highly Swollen Polyelectrolyte Gels

Polyelectrolyte gels exhibit swelling behaviors that are dependent on the external environment. The swelling behaviors of highly charged polyelectrolyte gels can be well explained using the Flory-Rehner model combined with the Gibbs-Donnan effect and Manning's counterion condensation effect (the FRGDM model). This study investigated the swelling properties of a series of model polyelectrolyte gels, namely tetra-polyacrylic acid-polyethylene glycol gels (Tetra-PAA-PEG gels), and determined the applicability of the FRGDM model. The swelling ratio (V_s/V₀) was well reproduced by the FRGDM model in the moderate swelling regime (V_s/V₀ < 10). However, in the high swelling regime (V_s/V₀ > 10), the FRGDM model is approx. 1.6 times larger than the experimental results. When we introduced the finite extensibility to the elastic free energy in the FRGDM model, the swelling behavior was successfully reproduced even in the high swelling regime. Our results reveal that finite extensibility is one of the factors determining the swelling equilibrium of highly charged polyelectrolyte gels. The modified FRGDM model reproduces well the swelling behavior of a wide range of polyelectrolyte gels.

Comparative Study on Enzyme Immobilization Using Natural Hydrogel Matrices—Experimental Studies Supported by Molecular Models Analysis

Currently, great attention is focused on conducting manufacture processes using clean and eco-friendly technologies. This research trend also relates to the production of immobilized biocatalysts of industrial importance using matrices and methods that fulfill specified operational and environmental requirements. For that reason, hydrogels of natural origin and the entrapment method become increasingly popular in terms of enzyme immobilization. The presented work is the comparative research on invertase immobilization using two natural hydrogel matrices—alginate and gelatin. During the study, we provided the molecular insight into the structural characteristics of both materials regarding their applicability as effective enzyme carriers. In order to confirm our predictions of using these hydrogels for invertase immobilization, we performed the typical experimental studies. In this case, the appropriate conditions of enzyme entrapment were selected for both types of carrier. Next, the characterization of received invertase preparations was made. As a final experimental result, the gelatin-based hydrogel was selected as an effective carrier for invertase immobilization. Hereby, using mild conditions and a pro-ecological, biodegradable matrix, it was possible to obtain very stable and reactive biocatalyst. The choice of gelatin-immobilized invertase preparation was compatible with our predictions based on the molecular models of hydrogel matrices and enzyme used.

Recent Developments and Future Challenges of Hydrogels as Draw Solutes in Forward Osmosis Process

Forward osmosis (FO) has been recently regarded as a promising water treatment technology due to its lower energy consumption and lower membrane fouling propensity compared to the reverse osmosis (RO). The absence of suitable draw solute constraints the wide-range application of the FO. Hydrogels are three-dimensional hydrophilic polymer networks that can absorb a huge amount of water. Particularly, stimuli-responsive polymer hydrogels can undergo a reversible volume change or solution-gel phase transition in response to external environmental stimuli, including temperature, light, pressure, solvent composition, and pH. These intrinsic properties indicate the lowest regeneration cost of draw solutes compared to the thermal method and other membrane processes. This review aims to introduce the research progress on hydrogels as draw solutes, clarify the existing problems and point out the further research direction.

Hydrogels as Potential Nano-, Micro- and Macro-Scale Systems for Controlled Drug Delivery

This review is an extensive evaluation and essential analysis of the design and formation of hydrogels (HGs) for drug delivery. We review the fundamental principles of HGs (their chemical structures, physicochemical properties, synthesis routes, different types, etc.) that influence their biological properties and medical and pharmaceutical applications. Strategies for fabricating HGs with different diameters (macro, micro, and nano) are also presented. The size of biocompatible HG materials determines their potential uses in medicine as drug carriers. Additionally, novel drug delivery methods for enhancing treatment are discussed. A critical review is performed based on the latest literature reports.