Hierarchical formation of supramolecular transient networks in water: a modular injectable delivery system

Dynamic Hydrogels with Tunable Mechanics for 3D Organoid Derivation

The mechanical properties of the hydrogel play a pivotal role in governing the formation and development of 3D organoids in vitro. However, commonly employed natural hydrogels, such as Matrigel and other extracellular matrix (ECM)-derived products, are characterized by ill-defined and complex compositions, resulting in non-tunable mechanical properties. This limitation poses challenges in controlling organoids' developmental trajectory and 3D morphology. Although numerous synthetic hydrogels with well-defined chemical structures have recently been adopted to study organoids by modulating stiffness, advanced research emphasizes the importance of dynamic mechanical cues, such as dynamic stiffness softening and dynamic viscoelasticity, for optimal organoid derivation. These cues are essential for mimicking the dynamic physiological states of organoids during their growth. Despite their potential, the concept of dynamic hydrogels is often used interchangeably, and a systematic review is lacking to clarify this ambiguity. Furthermore, the mechanisms through which dynamic mechanical cues regulate organoid formation have not been thoroughly reported. This review endeavors to summarize and categorize dynamic hydrogels and reveal the effects of dynamic mechanics on organoid derivation. Additionally, the prospects of dynamic hydrogels in organoid derivation are deliberated to promote a more rational design of synthetic hydrogels, guiding organoid derivation and propelling organoid technology in biomedicine.

Photoactuating artificial muscle from supramolecular assembly of an overcrowded alkene-derived molecular switch

The amplification of molecular motion along length scales for macroscopic muscle-like functions, based on supramolecular polymers, provides attractive opportunities ranging from soft actuators to responsive biomedical materials. Taking the challenge to reveal dynamic assembly parameters governing muscle functions, we present the design of a photoswitch amphiphile based on an overcrowded alkene-derived core, and developed supramolecular artificial muscles. Going from molecular motor amphiphile (MA) to switch amphiphile (SA), taking advantage of high thermal stability of the switch core, a self-recovering of bent SA artificial muscle is observed in post-photoactuation without external intervention. Eliminating molecular motions in SA artificial muscle during the post-photoactuation and aging process enables us to identify correlations between dynamic assembly transformations and macroscopic actuating functions. These findings provide insights into photoactuation and subsequent self-recovery mechanisms from the aspect of dynamic assembly process, which offers new opportunities for developing amphiphile-based supramolecular artificial muscles.

Bioelectronics hydrogels for implantable cardiac and brain disease medical treatment application

Hydrogel-based bioelectronic systems offer significant benefits for point-of-care diagnosis, treatment of cardiac and cerebral disease, surgical procedures, and other medical applications, ushering in a new era of advancements in medical technology. Progress in hydrogel-based bioelectronics has advanced from basic instrument and sensing capabilities to sophisticated multimodal perceptions and feedback systems. Addressing challenges related to immune responses and inflammation regulation after implantation, physiological dynamic mechanism, biological toxicology as well as device size, power consumption, stability, and signal conversion is crucial for the practical implementation of hydrogel-based bioelectronics in medical implants. Therefore, further exploration of hydrogel-based bioelectronics is imperative, and a comprehensive review is necessary to steer the development of these technologies for use in implantable therapies for cardiac and brain/neural conditions. In this review, a concise overview is provided on the fundamental principles underlying ionic electronic and ionic bioelectronic mechanisms. Additionally, a comprehensive examination is conducted on various bioelectronic materials integrated within hydrogels for applications in implantable medical treatments. The analysis encompasses a detailed discussion on the representative structures and physical attributes of hydrogels. This includes an exploration of their intrinsic properties such as mechanical strength, dynamic capabilities, shape-memory features, stability, stretchability, and water retention characteristics. Moreover, the discussion extends to properties related to interactions with tissues or the environment, such as adhesiveness, responsiveness, and degradability. The intricate relationships between the structure and properties of hydrogels are thoroughly examined, along with an elucidation of how these properties influence their applications in implantable medical treatments. The review also delves into the processing techniques and characterization methods employed for hydrogels. Furthermore, recent breakthroughs in the applications of hydrogels are logically explored, covering aspects such as materials, structure, properties, functions, fabrication procedures, and hybridization with other materials. Finally, the review concludes by outlining the future prospects and challenges associated with hydrogels-based bioelectronics systems.

Injectable biocompatible hydrogels with tunable strength based on crosslinked supramolecular polymer nanofibers

Hydrogels based on supramolecular assemblies offer attractive features for biomedical applications including injectability or versatile combinations of various building blocks. We here investigate a system combining benzenetrispeptides (BTP), which forms supramolecular fibers, with polymer polyethylene oxide (PEO) forming a dense hydrophilic shell around the fibers. Hydrogels are created through the addition of a bifunctional crosslinker (CL). Rheological studies revealed that shorter hydrophobic n-hexyl spacers (BTP-C6) lead to stronger hydrogels than BTP-C12 comprising n-dodecyl chains. All hydrogels recovered rapidly (<5 s) after deformation in step-strain-measurements. We varied the crosslinker content between 0.1, 1 and 10 mol% and the overall concentration of the gelator. While the shear storage modulus of all BTP-C12 hydrogels remains below 1 kPa independent of the variations, the shear storage modulus of BTP-C6 hydrogels can be tuned from around 0.2 kPa up to almost 8 kPa. Shear rate dependent viscosity measurements further revealed similar shear thinning behavior of all hydrogels, and the calculation of extrusion parameters confirmed that the hydrogels can be easily injected even through thin cannulae. Accordingly, we injected a fluorescein-containing BTP-C6 sample into chicken breast demonstrating the potential for application as an injectable drug depot. Furthermore, BTP-C6 hydrogels prevent the adherence of L929 mouse fibroblasts but preserve their relative metabolic activity (>87%) during incubation on the gel when compared to cells growing on adherent surfaces. Our investigations overall reveal that the BTP-C6 system in particular has attractive features for applications in tissue engineering or as an injectable and biocompatible drug depot.

From natural to synthetic hydrogels: how much biochemical complexity is required for mechanotransduction?

The biochemical complexity of a material determines the biological response of cells triggered by a cell-material interaction. The degree in which this complexity influences basic cell-material interactions such as cell adhesion, spreading, and mechanotransduction is not entirely clear. To this end, we compared three different hydrogel systems, ranging from completely natural to synthetic, in their ability to induce mechanotransduction in kidney epithelial cells (HK-2). A natural hydrogel system was developed based on a decellularized kidney extracellular matrix (dECM). Supramolecular ureido-pyrimidinone (UPy)-glycinamide molecules, with self-associative behavior, were used for a hybrid and complete synthetic system. A hybrid system was engineered by co-assembling this monovalent UPy molecule with a hyaluronic acid, functionalized with ∼7 UPy-groups (UPy-HA), into a transient network. A similar approach was used for the synthetic hydrogel system, in which the multivalent UPy-HA was replaced with a bivalent UPy-PEG molecule with bioinert properties. Both hybrid and synthetic hydrogel systems were more mechanically tunable compared to the dECM hydrogel. The higher bulk stiffness in combination with the introduction of collagen type I mimicking UPy-additives allowed these materials to induce more nuclear yes-associated protein translocation in HK-2 cells compared to the biochemically complex dECM hydrogel. This demonstrated that minimal biochemical complexity is sufficient for inducing mechanotransduction.

The Importance of Effective Ligand Concentration to Direct Epithelial Cell Polarity in Dynamic Hydrogels

Epithelial cysts and organoids are multicellular hollow structures formed by correctly polarized epithelial cells. Important in steering these cysts from single cells is the dynamic regulation of extracellular matrix presented ligands, and matrix dynamics. Here, control over the effective ligand concentration is introduced, decoupled from bulk and local mechanical properties, in synthetic dynamic supramolecular hydrogels formed through noncovalent crosslinking of supramolecular fibers. Control over the effective ligand concentration is realized by 1) keeping the ligand concentration constant, but changing the concentration of nonfunctionalized molecules or by 2) varying the ligand concentration, while keeping the concentration of non-functionalized molecules constant. The results show that in 2D, the effective ligand concentration within the supramolecular fibers rather than gel stiffness (from 0.1 to 8 kPa) regulates epithelial polarity. In 3D, increasing the effective ligand concentration from 0.5 × 10-3 to 2 × 10-3 m strengthens the effect of increased gel stiffness from 0.1 to 2 kPa, to synergistically yield more correctly polarized cysts. Through integrin manipulation, it is shown that epithelial polarity is regulated by tension-based homeostasis between cells and matrix. The results reveal the effective ligand concentration as influential factor in regulating epithelial polarity and provide insights on engineering of synthetic biomaterials for cell and organoid culture.

Investigating the self-assembly of 2NapFF and ureido-pyrimidinone multicomponent systems for cell culture

Low molecular weight gels are formed via the self-assembly of small molecules into fibrous structures. In the case of hydrogels, these networks entrap large volumes of water, yielding soft materials. Such gels tend to have weak mechanical properties and a high permeability for cells, making them particularly appealing for regenerative medicine applications. Ureido-pyrimidinone (UPy) supramolecular gelators are self-assembling systems that have demonstrated excellent capabilities as biomaterials. Here, we combine UPy-gelators with another low molecular weight gelator, the functionalized dipeptide 2NapFF. We have successfully characterized these multicomponent systems on a molecular and bulk scale. The addition of 2NapFF to a crosslinked UPy hydrogel significantly increased hydrogel stiffness from 30 Pa to 1300 Pa. Small-angle X-ray scattering was used to probe the underlying structures of the systems and showed that the mixed UPy and 2NapFF systems resemble the scattering data produced by the pristine UPy systems. However, when a bifunctional UPy-crosslinker was added, the scattering was close to that of the 2NapFF only samples. The results suggest that the crosslinker significantly influences the assembly of the low molecular weight gelators. Finally, we analysed the biocompatibility of the systems using fibroblast cells and found that the cells tended to spread more effectively when the crosslinking species was incorporated. Our results emphasise the need for thorough characterisation at multiple length scales to finely control material properties, which is particularly important for developing novel biomaterials.

Optical Monitoring of Supramolecular Interactions in Polymers

Many stimuli-responsive materials harness the reversible association of supramolecular binding motifs to enable advanced functionalities such as self-healing, switchable adhesion, or mechanical adaptation. Despite extensive research into the structure-property relationships of these materials, direct correlations between molecular-level changes in supramolecular binding and macroscopic material behaviors have mostly remained elusive. Here, we show that this challenge can be overcome with supramolecular binding motifs featuring integrated binding indicators. We demonstrate this using a novel motif that combines a hydrogen-bonding ureido-4-pyrimidinone (UPy) with two strategically placed pyrene fluorophores. Dimerization of this motif promotes pyrene excimer formation, facilitating the straightforward optical quantification of supramolecular assembly under various conditions. We exploit the new motif as a supramolecular cross-linker in poly(methyl acrylate)s to probe the extent of (dis)assembly as a function of cross-linker content, processing history, and applied stimuli. We demonstrate that the stimuli-induced dissociation of hydrogen-bonding linkages strongly depends on the initial cross-link density, which also dictates whether the force-induced dissociation in polymer films correlates with the applied stress or strain. Thus, beyond introducing a robust tool for the in situ study of dynamic (dis)assembly mechanisms in supramolecular systems, our findings provide new insights into the mechanoresponsive behavior of such materials.

Multibiofunctional Self-healing Adhesive Injectable Nanocomposite Polysaccharide Hydrogel

Injectable hydrogels with good antimicrobial and antioxidant properties, self-healing characteristics, suitable mechanical properties, and therapeutic effects have great practical significance for developing treatments for pressing healthcare challenges. Herein, we have designed a novel, self-healing injectable hydrogel composite incorporating cross-linked biofunctional nanomaterials by mixing alginate aldehyde (Ox-Alg), quaternized chitosan (QCS), adipic acid dihydrazide (ADH), and copper oxide nanosheets surface functionalized with folic acid as the bioligand (F-CuO). Gelation was achieved under physiological conditions via the dynamic Schiff base cross-linking mechanism. The developed nanocomposite injectable hydrogel demonstrated the fast self-healing ability essential to bear deformation and outstanding antibacterial properties along with ROS scavenging ability. Furthermore, the optimized formulation of our F-CuO-embedded injectable hydrogel exhibited excellent cytocompatibility, blood compatibility, and in vitro wound healing performance. Taken together, the F-CuO nanosheet cross-linked injectable hydrogel composite presented herein offers a promising candidate biomaterial with multifunctional properties to develop solutions for addressing clinical challenges.

Tuning Structural Organization via Molecular Design and Hierarchical Assembly to Develop Supramolecular Thermoresponsive Hydrogels

The cellular microenvironment is composed of a dynamic hierarchical fibrillar architecture providing a variety of physical and bioactive signals to the surrounding cells. This dynamicity, although common in biology, is a challenge to control in synthetic matrices. Here, responsive synthetic supramolecular monomers were designed that are able to assemble into hierarchical fibrous structures, combining supramolecular fiber formation via hydrogen bonding interactions, with a temperature-responsive hydrophobic collapse, resulting in cross-linking and hydrogel formation. Therefore, amphiphilic molecules were synthesized, composed of a hydrogen bonding ureido-pyrimidinone (UPy) unit, a hydrophobic alkyl spacer, and a hydrophilic oligo(ethylene glycol) tail. The temperature responsive behavior was introduced by functionalizing these supramolecular amphiphiles with a relatively short poly(N-isopropylacrylamide) (PNIPAM) chain (M n ∼ 2.5 or 5.5 kg/mol). To precisely control the assembly of these monomers, the length of the alkyl spacer between the UPy moiety and PNIPAM was varied in length. A robust sol-gel transition, with the dodecyl UPy-PNIPAM molecule, was obtained, with a network elasticity enhancing over 2000 times upon heating above room temperature. The UPy-PNIPAM compounds with shorter alkyl spacers were already hydrogels at room temperature. The sol-gel transition of the dodecyl UPy-PNIPAM hydrogelator could be tuned by the incorporation of different UPy-functionalized monomers. Furthermore, we demonstrated the suitability of this system for microfluidic cell encapsulation through a convenient temperature sol-gel transition. Our results indicate that this novel thermoresponsive supramolecular system offers a modular platform to study and guide single-cell behavior.

Using Chemistry To Recreate the Complexity of the Extracellular Matrix: Guidelines for Supramolecular Hydrogel-Cell Interactions

Hydrogels have emerged as a promising class of extracellular matrix (ECM)-mimicking materials in regenerative medicine. Here, we briefly describe current state-of-the-art of ECM-mimicking hydrogels, ranging from natural to hybrid to completely synthetic versions, giving the prelude to the importance of supramolecular interactions to make true ECM mimics. The potential of supramolecular interactions to create ECM mimics for cell culture is illustrated through a focus on two different supramolecular hydrogel systems, both developed in our laboratories. We use some recent, significant findings to present important design principles underlying the cell-material interaction. To achieve cell spreading, we propose that slow molecular dynamics (monomer exchange within fibers) is crucial to ensure the robust incorporation of cell adhesion ligands within supramolecular fibers. Slow bulk dynamics (stress-relaxation─fiber rearrangements, τ1/2 ≈ 1000 s) is required to achieve cell spreading in soft gels (<1 kPa), while gel stiffness overrules dynamics in stiffer gels. Importantly, this resonates with the findings of others which specialize in different material types: cell spreading is impaired in case substrate relaxation occurs faster than clutch binding and focal adhesion lifetime. We conclude with discussing considerations and limitations of the supramolecular approach as well as provide a forward thinking perspective to further understand supramolecular hydrogel-cell interactions. Future work may utilize the presented guidelines underlying cell-material interactions to not only arrive at the next generation of ECM-mimicking hydrogels but also advance other fields, such as bioelectronics, opening up new opportunities for innovative applications.

Intrinsic Self-Healable, Corrosion-Resistant Silicone Coating Based on Quadruple Hydrogen-Bonded Supramolecular Polymer

Corrosion-resistant coatings with self-healing capabilities are still a great challenge for metal protection. In this study, a corrosion-resistant coating with intrinsic self-healing capabilities was developed by compounding hydroxy-terminated silicone oil (HTSO) with 2-ureido-4[1H]-pyrimidone (UPy) derivatives. The smooth surface of the coating was shown by scanning electron microscopy (SEM), and good smoothness was also exhibited in the cross-section, which indicated that the coating is very homogeneous from the top to the bottom. Thermogravimetric analysis (TG) was employed to illustrate the temperature-resistant characteristics of the coating, revealing its significant chemical stability up to 360 °C. The corrosion resistance of the coating is assessed through electrochemical impedance spectroscopy (EIS), the typical impedance at 0.01 Hz is 1.70 × 109 and 2.44 × 108 Ω·cm2 before and after exposure to a 3.5 wt % NaCl solution for 70 days. There was no significant change in the water contact angle of the coatings before and after immersion; however, the adhesion strength was reduced. Notably, the coating demonstrates immediate and multiple self-healing properties. The tensile stress of the associated healing sample experiences an augmentation within the temperature range of 30-120 °C, with the critical fracture strain of the healed sample reaching 235% at 120 °C. The self-healing mechanism of the coating is systematically investigated using in situ Raman spectroscopy.

3D Printable Active Hydrogels with Supramolecular Additive-Driven Adaptiveness

Smart hydrogels are a promising candidate for the development of next-generation soft materials due to their stimuli-responsiveness, deformability, and biocompatibility. However, it remains challenging to enable hydrogels to actively adapt to various environmental conditions like living organisms. In this work, supramolecular additives are introduced to the hydrogel matrix to confer environmental adaptiveness. Specifically, their microstructures, swelling behaviors, mechanical properties, and transparency can adapt to external environmental conditions. Moreover, the presence of hydrogen bonding provides the hydrogel with applicable rheological properties for 3D extrusion printing, thus allowing for the facile preparation of thickness-dependent camouflage and multistimuli responsive complex. The environmentally adaptive hydrogel developed in this study offers new approaches for manipulating supramolecular interactions and broadens the capability of smart hydrogels in information security and multifunctional integrated actuation.

In-situ noncovalent interaction of ammonium ion enabled C-H bond functionalization of polyethylene glycols

The noncovalent interactions of ammonium ion with multidentate oxygen-based host has never been reported as a reacting center in catalytic reactions. In this work, we report a reactivity enhancement process enabled by non-covalent interaction of ammonium ion, achieving the C-H functionalization of polyethylene glycols with acrylates by utilizing photoinduced co-catalysis of iridium and quinuclidine. A broad scope of alkenes can be tolerated without observing significant degradation. Moreover, this cyano-free condition respectively allows the incorporation of bioactive molecules and the PEGylation of dithiothreitol-treated bovine serum albumin, showing great potentials in drug delivery and protein modification. DFT calculations disclose that the formed α-carbon radical adjacent to oxygen-atom is reduced directly by iridium before acrylate addition. And preliminary mechanistic experiments reveal that the noncovalent interaction of PEG chain with the formed quinuclidinium species plays a unique role as a catalytic site by facilitating the proton transfer and ultimately enabling the transformation efficiently.

The effect of charge and albumin on cellular uptake of supramolecular polymer nanostructures

Intracellular delivery of functional biomolecules by using supramolecular polymer nanostructures has gained significant interest. Here, various charged supramolecular ureido-pyrimidinone (UPy)-aggregates were designed and formulated via a simple "mix-and-match" method. The cellular internalization of these UPy-aggregates in the presence or absence of serum proteins by phagocytic and non-phagocytic cells, i.e., THP-1 derived macrophages and immortalized human kidney cells (HK-2 cells), was systematically investigated. In the presence of serum proteins the UPy-aggregates were taken up by both types of cells irrespective of the charge properties of the UPy-aggregates, and the UPy-aggregates co-localized with mitochondria of the cells. In the absence of serum proteins only cationic UPy-aggregates could be effectively internalized by THP-1 derived macrophages, and the internalized UPy-aggregates either co-localized with mitochondria or displayed as vesicular structures. While the cationic UPy-aggregates were hardly internalized by HK-2 cells and could only bind to the membrane of HK-2 cells. With adding and increasing the amount of serum albumin in the cell culture medium, the cationic UPy-aggregates were gradually taken up by HK-2 cells without anchoring on the cell membranes. It is proposed that the serum albumin regulates the cellular internalization of UPy-aggregates. These results provide fundamental insights for the fabrication of supramolecular polymer nanostructures for intracellular delivery of therapeutics.

Artificial cells with viscoadaptive behavior based on hydrogel-loaded giant unilamellar vesicles

Viscoadaptation is an essential process in natural cells, where supramolecular interactions between cytosolic components drive adaptation of the cellular mechanical features to regulate metabolic function. This important relationship between mechanical properties and function has until now been underexplored in artificial cell research. Here, we have created an artificial cell platform that exploits internal supramolecular interactions to display viscoadaptive behavior. As supramolecular material to mimic the cytosolic component of these artificial cells, we employed a pH-switchable hydrogelator based on poly(ethylene glycol) coupled to ureido-pyrimidinone units. The hydrogelator was membranized in its sol state in giant unilamellar lipid vesicles to include a cell-membrane mimetic component. The resulting hydrogelator-loaded giant unilamellar vesicles (designated as HL-GUVs) displayed reversible pH-switchable sol-gel behavior through multiple cycles. Furthermore, incorporation of the regulatory enzyme urease enabled us to increase the cytosolic pH upon conversion of its substrate urea. The system was able to switch between a high viscosity (at neutral pH) and a low viscosity (at basic pH) state upon addition of substrate. Finally, viscoadaptation was achieved via the incorporation of a second enzyme of which the activity was governed by the viscosity of the artificial cell. This work represents a new approach to install functional self-regulation in artificial cells, and opens new possibilities for the creation of complex artificial cells that mimic the structural and functional interplay found in biological systems.

Hydrogels for Gasotransmitter Delivery: Nitric Oxide, Carbon Monoxide, and Hydrogen Sulfide

Gasotransmitters, gaseous signaling molecules including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2 S), maintain myriad physiological processes. Low levels of gasotransmitters are often associated with specific problems or diseases, so NO, CO, and H2 S hold potential in treating bacterial infections, chronic wounds, myocardial infarction, ischemia, and various other diseases. However, their clinical applications as therapeutic agents are limited due to their gaseous nature, short half-life, and broad physiological roles. One route toward the greater application of gasotransmitters in medicine is through localized delivery. Hydrogels are attractive biomedical materials for the controlled release of embedded therapeutics as they are typically biocompatible, possess high water content, have tunable mechanical properties, and are injectable in certain cases. Hydrogel-based gasotransmitter delivery systems began with NO, and hydrogels for CO and H2 S have appeared more recently. In this review, the biological importance of gasotransmitters is highlighted, and the fabrication of hydrogel materials is discussed, distinguishing between methods used to physically encapsulate small molecule gasotransmitter donor compounds or chemically tether them to a hydrogel scaffold. The release behavior and potential therapeutic applications of gasotransmitter-releasing hydrogels are also detailed. Finally, the authors envision the future of this field and describe challenges moving forward.

Therapeutic Supramolecular Polymers: Designs and Applications

The self-assembly of low-molecular-weight building motifs into supramolecular polymers has unlocked a new realm of materials with distinct properties and tremendous potential for advancing medical practices. Leveraging the reversible and dynamic nature of non-covalent interactions, these supramolecular polymers exhibit inherent responsiveness to their microenvironment, physiological cues, and biomolecular signals, making them uniquely suited for diverse biomedical applications. In this review, we intend to explore the principles of design, synthesis methodologies, and strategic developments that underlie the creation of supramolecular polymers as carriers for therapeutics, contributing to the treatment and prevention of a spectrum of human diseases. We delve into the principles underlying monomer design, emphasizing the pivotal role of non-covalent interactions, directionality, and reversibility. Moreover, we explore the intricate balance between thermodynamics and kinetics in supramolecular polymerization, illuminating strategies for achieving controlled sizes and distributions. Categorically, we examine their exciting biomedical applications: individual polymers as discrete carriers for therapeutics, delving into their interactions with cells, and in vivo dynamics; and supramolecular polymeric hydrogels as injectable depots, with a focus on their roles in cancer immunotherapy, sustained drug release, and regenerative medicine. As the field continues to burgeon, harnessing the unique attributes of therapeutic supramolecular polymers holds the promise of transformative impacts across the biomedical landscape.

A Programmable Oxygenation Device Facilitates Oxygen Generation and Replenishment to Promote Wound Healing

Inadequate oxygenation is one of the chief culprits for delayed wound healing. However, current oxygen therapies, such as hyperbaric oxygen therapy and topical oxygen therapy, face hurdles in providing sustained and long-term oxygenation to reverse wound hypoxia. Furthermore, their efficacy in rejuvenating wound injury is restricted by limited penetration of oxygen in the wound bed. Herein, this study proposes a programmable and portable oxygenation device (named GUFO oxydevice) by ingeniously integrating i) a controllable oxygen generation and unidirectional transmission system (COGT-UTS), and ii) a supramolecular assembled perfluorinated hyperbranched polymer/gelatin (GUF) hydrogel in which the perfluorinated hyperbranched polymer (FHBP) acts as an oxygen reservoir to ensure sustained and convenient oxygen replenishment and thus directly regulate the hypoxic wound microenvironment. Accelerating the wound healing process by GUFO oxydevice is achieved in both a diabetic rat and an acute porcine wound model without any secondary tissue damages. The present study demonstrates that the GUFO oxydevice holds promise as a practically feasible candidate for wound treatment.

CO2-Driven Nebulization of pH-Sensitive Supramolecular Polymers for Intraperitoneal Hydrogel Formation and the Treatment of Peritoneal Metastasis

Because peritoneal metastasis (PM) from ovarian cancer is characterized by non-specific symptoms, it is often diagnosed at advanced stages. Pressurized intraperitoneal aerosol chemotherapy (PIPAC) can be considered a promising drug delivery method for unresectable PM. Currently, the efficacy of intraperitoneal (IP) drug delivery is limited by the off-label use of IV chemotherapeutic solutions, which are rapidly cleared from the IP cavity. Hence, this research aimed to improve PM treatment by evaluating a nanoparticle-loaded, pH-switchable supramolecular polymer hydrogel as a controlled release drug delivery system that can be IP nebulized. Moreover, a multidirectional nozzle was developed to allow nebulization of viscous materials such as hydrogels and to reach an even IP gel deposition. We demonstrated that acidification of the nebulized hydrogelator solution by carbon dioxide, used to inflate the IP cavity during laparoscopic surgery, stimulated the in situ gelation, which prolonged the IP hydrogel retention. In vitro experiments indicated that paclitaxel nanocrystals were gradually released from the hydrogel depot formed, which sustained the cytotoxicity of the formulation for 10 days. Finally, after aerosolization of this material in a xenograft model of PM, tumor progression could successfully be delayed, while the overall survival time was significantly increased compared to non-treated animals.

Smart hydrogels delivered by high pressure aerosolization can prevent peritoneal adhesions

Postoperative peritoneal adhesions occur in the majority of patients undergoing intra-abdominal surgery and are one of the leading causes of hospital re-admission. There is an unmet clinical need for effective anti-adhesive biomaterials, which can be applied evenly across the damaged tissues. We examined three different responsive hydrogel types, i.e. a thermosensitive PLGA-PEG-PLGA, a pH responsive UPy-PEG and a shear-thinning hexapeptide for this purpose. More specifically, their potential to be homogeneously distributed in the peritoneal cavity by high pressure nebulization and prevent peritoneal adhesions was evaluated. Solutions of each polymer type could be successfully nebulized while retaining their responsive gelation behavior in vitro and in vivo. Furthermore, none of the polymers caused in vitro toxicity on SKOV3-IP2 cells. Following intraperitoneal administration, both the PLGA-PEG-PLGA and the hexapeptide hydrogels resulted in local inflammation and fibrosis and failed in preventing peritoneal adhesions 7 days after adhesion induction. In contrast, the pH sensitive UPy-PEG formulation was well tolerated and could significantly reduce the formation of peritoneal adhesions, even outperforming the commercially available Hyalobarrier® as positive control. To conclude, local nebulization of the bioresponsive UPy-PEG hydrogel can be considered as a promising approach to prevent postsurgical peritoneal adhesions.

Iron Oxide Nanoparticles with Supramolecular Ureido-Pyrimidinone Coating for Antimicrobial Peptide Delivery

Antimicrobial peptides (AMPs) can kill bacteria by disrupting their cytoplasmic membrane, which reduces the tendency of antibacterial resistance compared to conventional antibiotics. Their possible toxicity to human cells, however, limits their applicability. The combination of magnetically controlled drug delivery and supramolecular engineering can help to reduce the dosage of AMPs, control the delivery, and improve their cytocompatibility. Lasioglossin III (LL) is a natural AMP form bee venom that is highly antimicrobial. Here, superparamagnetic iron oxide nanoparticles (IONs) with a supramolecular ureido-pyrimidinone (UPy) coating were investigated as a drug carrier for LL for a controlled delivery to a specific target. Binding to IONs can improve the antimicrobial activity of the peptide. Different transmission electron microscopy (TEM) techniques showed that the particles have a crystalline iron oxide core with a UPy shell and UPy fibers. Cytocompatibility and internalization experiments were carried out with two different cell types, phagocytic and nonphagocytic cells. The drug carrier system showed good cytocompatibility (>70%) with human kidney cells (HK-2) and concentration-dependent toxicity to macrophagic cells (THP-1). The particles were internalized by both cell types, giving them the potential for effective delivery of AMPs into mammalian cells. By self-assembly, the UPy-coated nanoparticles can bind UPy-functionalized LL (UPy-LL) highly efficiently (99%), leading to a drug loading of 0.68 g g-1. The binding of UPy-LL on the supramolecular nanoparticle system increased its antimicrobial activity against E. coli (MIC 3.53 µM to 1.77 µM) and improved its cytocompatible dosage for HK-2 cells from 5.40 µM to 10.6 µM. The system showed higher cytotoxicity (5.4 µM) to the macrophages. The high drug loading, efficient binding, enhanced antimicrobial behavior, and reduced cytotoxicity makes ION@UPy-NH2 an interesting drug carrier for AMPs. The combination with superparamagnetic IONs allows potential magnetically controlled drug delivery and reduced drug amount of the system to address intracellular infections or improve cancer treatment.

Molecular Tuning of a Benzene-1,3,5-Tricarboxamide Supramolecular Fibrous Hydrogel Enables Control over Viscoelasticity and Creates Tunable ECM-Mimetic Hydrogels and Bioinks

Traditional synthetic covalent hydrogels lack the native tissue dynamics and hierarchical fibrous structure found in the extracellular matrix (ECM). These dynamics and fibrous nanostructures are imperative in obtaining the correct cell/material interactions. Consequently, the challenge to engineer functional dynamics in a fibrous hydrogel and recapitulate native ECM properties remains a bottle-neck to biomimetic hydrogel environments. Here, the molecular tuning of a supramolecular benzene-1,3,5-tricarboxamide (BTA) hydrogelator via simple modulation of hydrophobic substituents is reported. This tuning results in fibrous hydrogels with accessible viscoelasticity over 5 orders of magnitude, while maintaining a constant equilibrium storage modulus. BTA hydrogelators are created with systematic variations in the number of hydrophobic carbon atoms, and this is observed to control the viscoelasticity and stress-relaxation timescales in a logarithmic fashion. Some of these BTA hydrogels are shear-thinning, self-healing, extrudable, and injectable, and can be 3D printed into multiple layers. These hydrogels show high cell viability for chondrocytes and human mesenchymal stem cells, establishing their use in tissue engineering applications. This simple molecular tuning by changing hydrophobicity (with just a few carbon atoms) provides precise control over the viscoelasticity and 3D printability in fibrillar hydrogels and can be ported onto other 1D self-assembling structures. The molecular control and design of hydrogel network dynamics can push the field of supramolecular chemistry toward the design of new ECM-mimicking hydrogelators for numerous cell-culture and tissue-engineering applications and give access toward highly biomimetic bioinks for bioprinting.

Exploration of molecular machines in supramolecular soft robotic systems

Soft robotic system, a new era of material science, is rapidly developing with advanced processing technology in soft matters, featured with biomimetic nature. An important bottom-up approach is through the implementation of molecular machines into polymeric materials, however, the synchronized molecular motions, acumination of strain across multiple length-scales, and amplification into macroscopic actuations remained highly challenging. This review presents the significances, key design strategies, and outlook of the hierarchical supramolecular systems of molecular machines to develop novel types of supramolecular-based soft robotic systems.

Controllable C-H Alkylation of Polyethers via Iron Photocatalysis

The efficient conversion of a C-H bond in the polyether chain to other functional groups provides great opportunities for development of novel applications in many research fields. However, this field is quite underdeveloped due to the key challenge on controlling the selectivity of the C-H bond functionalization over the chain cleavage. In this work, we report a controllable C-H bond alkylation of polyethers under mild conditions via photoinduced iron catalysis. The level of functionalization could be controlled by using different amounts of alkenes and various reaction times, while the molecular weight distributions were maintained narrow. A broad scope of electron-deficient alkenes containing nitrile, ester, epoxide, terminal alkynyl, 2,5-dioxotetrafuranyl, and 2,5-dioxopyrrolidinyl groups could be utilized to functionalize the different polyethers with great efficiencies. The potential applications of the modified polyethylene glycols and polyethylene oxides were explored by the preparation of novel hydrogels and solid-state electrolytes with enhancement of lithium ion conductivities. Moreover, the density functional theory calculation disclosed the plausible mechanism and explained the high selectivity for the C-H alkylation.

Decoupling between Translational Diffusion and Viscoelasticity in Transient Networks with Controlled Network Connectivity

The mobility of sustained molecules is influenced by viscoelasticity, which is strongly correlated with the diffusional property in polymeric liquid. However, the study of transient networks formed by a reversible crosslink, which is the viscoelastic liquid, was insufficient due to the absence of a model system. We compare the viscoelastic and diffusional properties of the transient networks, using the model system with controlled network connectivity (Tetra-PEG slime). According to independent measurements of viscoelasticity and diffusion, the root-mean-square distance the polymer diffuses during the viscoelastic relaxation time shows a large deviation from the self-size of the polymer, which is contrary to the conventional understanding. This decoupling between viscoelasticity and diffusion is unique for transient networks, suggesting that the viscoelastic relaxation is not induced by the diffusion of one prepolymer, particularly in the network with low connectivity. These findings will provide a definite basis for discussion to understand the viscoelasticity in transient networks.

Engineered hydrogels for mechanobiology

Cells' local mechanical environment can be as important in guiding cellular responses as many well-characterized biochemical cues. Hydrogels that mimic the native extracellular matrix can provide these mechanical cues to encapsulated cells, allowing for the study of their impact on cellular behaviours. Moreover, by harnessing cellular responses to mechanical cues, hydrogels can be used to create tissues in vitro for regenerative medicine applications and for disease modelling. This Primer outlines the importance and challenges of creating hydrogels that mimic the mechanical and biological properties of the native extracellular matrix. The design of hydrogels for mechanobiology studies is discussed, including appropriate choice of cross-linking chemistry and strategies to tailor hydrogel mechanical cues. Techniques for characterizing hydrogels are explained, highlighting methods used to analyze cell behaviour. Example applications for studying fundamental mechanobiological processes and regenerative therapies are provided, along with a discussion of the limitations of hydrogels as mimetics of the native extracellular matrix. The article ends with an outlook for the field, focusing on emerging technologies that will enable new insights into mechanobiology and its role in tissue homeostasis and disease.

Dynamic Bonds: Adaptable Timescales for Responsive Materials

Dynamic bonds introduce unique properties such as self-healing, recyclability, shape memory, and malleability to polymers. Significant efforts have been made to synthesize a variety of dynamic linkers, creating a diverse library of materials. In addition to the development of new dynamic chemistries, fine-tuning of dynamic bonds has emerged as a technique to modulate dynamic properties. This Review highlights approaches for controlling the timescales of dynamic bonds in polymers. Particularly, eight dynamic bonds are considered, including urea/urethanes, boronic esters, Thiol-Michael exchange, Diels-Alder adducts, transesterification, imine bonds, coordination bonds, and hydrogen bonding. This Review emphasizes how structural modifications and external factors have been used as tools to tune the dynamic character of materials. Finally, this Review proposes strategies for tailoring the timescales of dynamic bonds in polymer materials through both kinetic effects and modulating bond thermodynamics.

Self-Healing Hydrogels: Development, Biomedical Applications, and Challenges

Polymeric hydrogels have drawn considerable attention as a biomedical material for their unique mechanical and chemical properties, which are very similar to natural tissues. Among the conventional hydrogel materials, self-healing hydrogels (SHH) are showing their promise in biomedical applications in tissue engineering, wound healing, and drug delivery. Additionally, their responses can be controlled via external stimuli (e.g., pH, temperature, pressure, or radiation). Identifying a suitable combination of viscous and elastic materials, lipophilicity and biocompatibility are crucial challenges in the development of SHH. Furthermore, the trade-off relation between the healing performance and the mechanical toughness also limits their real-time applications. Additionally, short-term and long-term effects of many SHH in the in vivo model are yet to be reported. This review will discuss the mechanism of various SHH, their recent advancements, and their challenges in tissue engineering, wound healing, and drug delivery.

Chemical strategies to engineer hydrogels for cell culture

Two-dimensional and three-dimensional cell culture systems are widely used for biological studies, and are the basis of the organoid, tissue engineering and organ-on-chip research fields in applications such as disease modelling and drug screening. The natural extracellular matrix of tissues, a complex scaffold with varying chemical and mechanical properties, has a critical role in regulating important cellular functions such as spreading, migration, proliferation and differentiation, as well as tissue morphogenesis. Hydrogels are biomaterials that are used in cell culture systems to imitate critical features of a natural extracellular matrix. Chemical strategies to synthesize and tailor the properties of these hydrogels in a controlled manner, and manipulate their biological functions in situ, have been developed. In this Review, we provide the rational design criteria for predictably engineering hydrogels to mimic the properties of the natural extracellular matrix. We highlight the advances in using biocompatible strategies to engineer hydrogels for cell culture along with recent developments to dynamically control the cellular environment by exploiting stimuli-responsive chemistries. Finally, future opportunities to engineer hydrogels are discussed, in which the development of novel chemical methods will probably have an important role.

Modular mixing of benzene-1,3,5-tricarboxamide supramolecular hydrogelators allows tunable biomimetic hydrogels for control of cell aggregation in 3D

Few synthetic hydrogels can mimic both the viscoelasticity and supramolecular fibrous structure found in the naturally occurring extracellular matrix (ECM). Furthermore, the ability to control the viscoelasticity of fibrous supramolecular hydrogel networks to influence cell culture remains a challenge. Here, we show that modular mixing of supramolecular architectures with slow and fast exchange dynamics can provide a suitable environment for multiple cell types and influence cellular aggregation. We employed modular mixing of two synthetic benzene-1,3,5-tricarboxamide (BTA) architectures: a small molecule water-soluble BTA with slow exchange dynamics and a telechelic polymeric BTA-PEG-BTA with fast exchange dynamics. Copolymerisation of these two supramolecular architectures was observed, and all tested formulations formed stable hydrogels in water and cell culture media. We found that rational tuning of mechanical and viscoelastic properties is possible by mixing BTA with BTA-PEG-BTA. These hydrogels showed high viability for both chondrocyte (ATDC5) and human dermal fibroblast (HDF) encapsulation (>80%) and supported neuronal outgrowth (PC12 and dorsal root ganglion, DRG). Furthermore, ATDC5s and human mesenchymal stem cells (hMSCs) were able to form spheroids within these viscoelastic hydrogels, with control over cell aggregation modulated by the dynamic properties of the material. Overall, this study shows that modular mixing of supramolecular architectures enables tunable fibrous hydrogels, creating a biomimetic environment for cell encapsulation. These materials are suitable for the formation and culture of spheroids in 3D, critical for upscaling tissue engineering approaches towards cell densities relevant for physiological tissues.

Functional Thermoresponsive Hydrogel Molecule to Material Design for Biomedical Applications

Temperature-induced, rapid changes in the viscosity and reproducible 3-D structure formation makes thermos-sensitive hydrogels an ideal delivery system to act as a cell scaffold or a drug reservoir. Moreover, the hydrogels’ minimum invasiveness, high biocompatibility, and facile elimination from the body have gathered a lot of attention from researchers. This review article attempts to present a complete picture of the exhaustive arena, including the synthesis, mechanism, and biomedical applications of thermosensitive hydrogels. A special section on intellectual property and marketed products tries to shed some light on the commercial potential of thermosensitive hydrogels.

Tuning the affinity of amphiphilic guest molecules in a supramolecular polymer transient network

Dynamicity plays a central role in biological systems such as in the cellular microenvironment. Here, the affinity and dynamics of different guest molecules in a transient supramolecular polymer hydrogel system, i.e. the host network, are investigated. The hydrogel system consists of bifunctional ureido-pyrimidinone (UPy) poly(ethylene glycol) polymers. A monofunctional complementary UPy guest is introduced, designed to interact with the host network based on UPy–UPy interactions. Furthermore, two other guest molecules are synthesized, being cholesterol and dodecyl (c12) guests; both designed to interact with the host network via hydrophobic interactions. At the nanoscale in solution, differences in morphology of the guest molecules were observed. The UPy–guest molecule formed fibers, and the cholesterol and c12 guests formed aggregates. Furthermore, cellular internalization of fluorescent guest molecules was studied. No cellular uptake of the UPy–cy5 guest was observed, whereas the cholesterol–cy5 guest showed membrane binding and cellular uptake. Also the c12–cy5 guest showed cellular uptake. Formulation of the guest molecules into the UPy hydrogel system was done to study the guest–host affinity. No changes in mechanical properties as measured with rheology were found upon guest–hydrogel formulation. Fluorescence recovery after photobleaching showed the diffusive properties of the cy5-functionalized guests throughout the host network. The c12 guest displayed a relatively fast mobility, the UPy guest displayed a decrease in mobility, and the cholesterol–guest remained relatively stable in the host network with little mobility. This demonstrates the tunable dynamic differences of affinity-based interaction between guest molecules and the host network. Interestingly, the cholesterol guest is internalized in cells and is robustly incorporated in the hydrogel network, while the UPy guest is not taken up by cells but shows an affinity to the hydrogel network. These results show the importance of guest–hydrogel affinity for future drug release. However, if modified with cholesterol these guests, or future drugs, will be taken up by cells; if modified with a UPy unit this does not occur. In this way both the drug–hydrogel interaction and the cell internalization behavior can be tuned. Regulating the host–guest dynamics in transient hydrogels opens the door to various drug delivery purposes and tissue engineering.

Dynamicity plays a central role in biological systems, which can be mimicked by tuning dynamicity in hydrogel networks.

Synthetic dynamic hydrogels promote degradation-independent in vitro organogenesis

Epithelial organoids are most efficiently grown from mouse-tumour-derived, reconstituted extracellular matrix hydrogels, whose poorly defined composition, batch-to-batch variability and immunogenicity limit clinical applications. Efforts to replace such ill-defined matrices for organoid culture have largely focused on non-adaptable hydrogels composed of covalently crosslinked hydrophilic macromolecules. However, the excessive forces caused by tissue expansion in such elastic gels severely restrict organoid growth and morphogenesis. Chemical or enzymatic degradation schemes can partially alleviate this problem, but due to their irreversibility, long-term applicability is limited. Here we report a family of synthetic hydrogels that promote extensive organoid morphogenesis through dynamic rearrangements mediated by reversible hydrogen bonding. These tunable matrices are stress relaxing and thus promote efficient crypt budding in intestinal stem-cell epithelia through increased symmetry breaking and Paneth cell formation dependent on yes-associated protein 1. As such, these well-defined gels provide promising versatile matrices for fostering elaborate in vitro morphogenesis.

Supramolecular Biomaterials in the Netherlands

Synthetically designed biomaterials strive to recapitulate and mimic the complex environment of natural systems. Using natural materials as a guide, the ability to create high performance biomaterials that control cell fate, and support the next generation of cell and tissue-based therapeutics, is starting to emerge. Supramolecular chemistry takes inspiration from the wealth of non-covalent interactions found in natural materials that are inherently complex, and using the skills of synthetic and polymer chemistry, recreates simple systems to imitate their features. Within the past decade, supramolecular biomaterials have shown utility in tissue engineering and the progress predicts a bright future. On this 30th anniversary of the Netherlands Biomaterials and Tissue Engineering society, we will briefly recount the state of supramolecular biomaterials in the Dutch academic and industrial research and development context. This review will provide the background, recent advances, industrial successes and challenges, as well as future directions of the field, as we see it. Throughout this work, we notice the intricate interplay between simplicity and complexity in creating more advanced solutions. We hope that the interplay and juxtaposition between these two forces can propel the field forward.

Functional Chirality: From Small Molecules to Supramolecular Assemblies

Many structures in nature look symmetric, but this is not completely accurate, because absolute symmetry is close to death. Chirality (handedness) is one form of living asymmetry. Chirality has been extensively investigated at different levels. Many rules were coined in attempts made for many decades to have control over the selection of handedness that seems to easily occur in nature. It is certain that if good control is realized on chirality, the roads will be ultimately open towards numerous developments in pharmaceutical, technological, and industrial applications. This tutorial review presents a report on chirality from single molecules to supramolecular assemblies. The realized functions are still in their infancy and have been scarcely converted into actual applications. This review provides an overview for starters in the chirality field of research on concepts, common methodologies, and outstanding accomplishments. It starts with an introductory section on the definitions and classifications of chirality at the different levels of molecular complexity, followed by highlighting the importance of chirality in biological systems and the different means of realizing chirality and its inversion in solid and solution-based systems at molecular and supramolecular levels. Chirality-relevant important findings and (bio-)technological applications are also reported accordingly.

Bioinspired tunable hydrogels: An update on methods of preparation, classification, and biomedical and therapeutic applications

Hydrogels exhibit water-insoluble three-dimensional polymeric networks capable of absorbing large amounts of biological fluids. Both natural and synthetic polymers are used for the preparation of hydrogel networks. Such polymeric networks are fabricated through chemical or physical mechanisms of crosslinking. Chemical crosslinking is accomplished mainly through covalent bonding, while physical crosslinking involves self-healing secondary forces like H-bonding, host-guest interactions, and antigen-antibody interactions. The building blocks of the hydrogels play an important role in determining the mechanical, biological, and physicochemical properties. Hydrogels are used in a variety of biomedical applications like diagnostics (biodetection and bioimaging), delivery of therapeutics (drugs, immunotherapeutics, and vaccines), wound dressing and skin materials, cardiac complications, contact lenses, tissue engineering, and cell culture because of the inherent characteristics like enhanced water uptake and structural similarity with the extracellular matrix (ECM). This review highlights the recent trends and advances in the roles of hydrogels in biomedical and therapeutic applications. We also discuss the classification and methods of hydrogels preparation. A brief outlook on the future directions of hydrogels is also presented.

Intermolecular interactions of an isoindigo-based organic semiconductor with various crosslinkers through hydrogen bonding

The effects of crosslinkers, functioning via hydrogen bonding, on controlling the arrangement of molecules were investigated. The hole mobility of hydrogen-bonded organic materials displaying long-range order was significantly enhanced.

Highly compressible glass-like supramolecular polymer networks

Supramolecular polymer networks are non-covalently crosslinked soft materials that exhibit unique mechanical features such as self-healing, high toughness and stretchability. Previous studies have focused on optimizing such properties using fast-dissociative crosslinks (that is, for an aqueous system, dissociation rate constant k_d > 10 s^-1). Herein, we describe non-covalent crosslinkers with slow, tuneable dissociation kinetics (k_d < 1 s^-1) that enable high compressibility to supramolecular polymer networks. The resultant glass-like supramolecular networks have compressive strengths up to 100 MPa with no fracture, even when compressed at 93% strain over 12 cycles of compression and relaxation. Notably, these networks show a fast, room-temperature self-recovery (< 120 s), which may be useful for the design of high-performance soft materials. Retarding the dissociation kinetics of non-covalent crosslinks through structural control enables access of such glass-like supramolecular materials, holding substantial promise in applications including soft robotics, tissue engineering and wearable bioelectronics.

Smart/stimuli-responsive hydrogels: Cutting-edge platforms for tissue engineering and other biomedical applications

Recently, biomedicine and tissue regeneration have emerged as great advances that impacted the spectrum of healthcare. This left the door open for further improvement of their applications to revitalize the impaired tissues. Hence, restoring their functions. The implementation of therapeutic protocols that merge biomimetic scaffolds, bioactive molecules, and cells plays a pivotal role in this track. Smart/stimuli-responsive hydrogels are remarkable three-dimensional (3D) bioscaffolds intended for tissue engineering and other biomedical purposes. They can simulate the physicochemical, mechanical, and biological characters of the innate tissues. Also, they provide the aqueous conditions for cell growth, support 3D conformation, provide mechanical stability for the cells, and serve as potent delivery matrices for bioactive molecules. Many natural and artificial polymers were broadly utilized to design these intelligent platforms with novel advanced characteristics and tailored functionalities that fit such applications. In the present review, we highlighted the different types of smart/stimuli-responsive hydrogels with emphasis on their synthesis scheme. Besides, the mechanisms of their responsiveness to different stimuli were elaborated. Their potential for tissue engineering applications was discussed. Furthermore, their exploitation in other biomedical applications as targeted drug delivery, smart biosensors, actuators, 3D and 4D printing, and 3D cell culture were outlined. In addition, we threw light on smart self-healing hydrogels and their applications in biomedicine. Eventually, we presented their future perceptions in biomedical and tissue regeneration applications. Conclusively, current progress in the design of smart/stimuli-responsive hydrogels enhances their prospective to function as intelligent, and sophisticated systems in different biomedical applications.

Construction of a pillararene-based supramolecular polymer network and its application in efficient removal of dyes from water

An AB-type monomer based on a pillar[5]arene host and an imidazolium salt guest was successfully synthesized through a facile way. This monomer can self-assemble into linear supramolecular polymers in chloroform. After the addition of silver ions, the imidazolium salt group coordinated with silver ions to crosslink the linear supramolecular polymers at their ends, resulting in the formation of supramolecular polymer networks. Meanwhile, after further adding iodide ions, the supramolecular polymer network changed back to the linear supramolecular polymer. As a result, the topological structure of the system can be reversibly tuned. Furthermore, this supramolecular polymer network can be applied to remove organic dyes in water, suggesting its great potential in the treatment of waste water.

Review of Recent Advances and Their Improvement in the Effectiveness of Hydrogel-Based Targeted Drug Delivery: A Hope for Treating Cancer

Using hydrogels for delivering cancer therapeutics is advantageous in pharmaceutical usage as they have an edge over traditional delivery, which is tainted due to the risk of toxicity that it imbues. Hydrogel usage leads to the development of a more controlled drug release system owing to its amenability for structural metamorphosis, its higher porosity to seat the drug molecules, and its ability to shield the drug from denaturation. The thing that makes its utility even more enhanced is that they make themselves more recognizable to the body tissues and hence can stay inside the body for a longer time, enhancing the efficiency of the delivery, which otherwise is negatively affected since the drug is identified by the human immunity as a foreign substance, and thus, an attack of the immunity begins on the drug injected. A variety of hydrogels such as thermosensitive, pH-sensitive, and magnetism-responsive hydrogels have been included and their potential usage in drug delivery has been discussed in this review that aims to present recent studies on hydrogels that respond to alterations under a variety of circumstances in "reducing" situations that mimic the microenvironment of cancerous cells.

Choline-Functionalized Supramolecular Copolymers: Toward Antimicrobial Activity against Streptococcus pneumoniae

Dynamic binding events are key to arrive at functionality in nature, and these events are often governed by electrostatic or hydrophobic interactions. Synthetic supramolecular polymers are promising candidates to obtain biomaterials that mimic this dynamicity. Here, we created four new functional monomers based on the benzene-1,3,5-tricarboxamide (BTA) motif. Choline or atropine groups were introduced to obtain functional monomers capable of competing with the cell wall of Streptococcus pneumoniae for binding of essential choline-binding proteins (CBPs). Atropine-functionalized monomers BTA-Atr and BTA-Atr₃ were too hydrophobic to form homogeneous assemblies, while choline-functionalized monomers BTA-Chol and BTA-Chol₃ were unable to form fibers due to charge repulsion. However, copolymerization of BTA-Chol₃ with non-functionalized BTA-(OH)₃ yielded dynamic fibers, similar to BTA-(OH)₃. These copolymers showed an increased affinity toward CBPs compared to free choline due to multivalent effects. BTA-based supramolecular copolymers are therefore a versatile platform to design bioactive and dynamic supramolecular polymers with novel biotechnological properties.

Self-Healing of Hyaluronic Acid to Improve In Vivo Retention and Function

Convergent advances in the field of soft matter, macromolecular chemistry, and engineering have led to the development of biomaterials that possess autonomous, adaptive, and self-healing characteristics similar to living systems. These rationally designed biomaterials can surpass the capabilities of their parent material. Herein, the modification of hyaluronic acid (HA) to exhibit self-healing properties is described, and its physical and biological function both in vitro and in vivo is studied. The in vitro findings showed that self-healing HA designed to undergo self-repair improves lubrication, enhances free radical scavenging, and attenuates enzymatic degradation compared to unmodified HA. Longitudinal imaging following intraarticular injection of self-healing HA shows improved in vivo retention despite its low molecular weight. Concomitant with these functions, intraarticular injection of self-healing HA mitigates anterior cruciate ligament injury-mediated cartilage degeneration in rodents. This proof-of-concept study shows how incorporation of functional properties such as self-healing can be used to surpass the existing capabilities of biolubricants.

Dendrimer-Based Polyion Complex Vesicles: Loops Make Loose

Associations of amphiphiles assume their various morphologies according to the so-called packing parameter under thermodynamic control. However, one may raise the question of whether polymers can always relax fast enough to obey thermodynamic control, and how this may be checked. Here, a case of polyion complex (PIC) assemblies where the morphology appears to be subject to kinetic control is discussed. Poly (ethylene oxide)-b-(styrene sulfonate) block copolymers are combined with cationic PAMAM dendrimers of various generations (2-7). The PEO-PSS diblocks, and the corresponding PSS-PEO-PSS triblocks should have nearly identical packing parameters, but surprisingly creat different assemblies, namely core-shell micelles and vesicles, respectively. Moreover, the micelles are very stable against added salt, whereas the vesicles are not only much more sensitive to added salt, but also appear to exchange matter on relevant time scales. The small and largely quenched early-stage precursor complexes are responsible for the morphological and dynamic differences, implying that kinetic control may also be a way to obtain particles with well-defined and useful properties. The exciting new finding that triblocks produce more "active" vesicles will hopefully trigger the exploration of more pathways, and so learn how to tune PICsomes toward specific applications.