Tailorable and Biocompatible Supramolecular-Based Hydrogels Featuring two Dynamic Covalent Chemistries

Engineering a Proximity Biosensor via Constitutional Dynamic Chemistry

Affinity binding-induced DNA assembly is a fundamental principle for designing proximity biosensors for sensitive and wash-free protein detection and imaging. However, current design strategies for these biosensors face an intrinsic trade-off between binding affinity and background signal. Here, we demonstrate that this intrinsic issue can be addressed by using constitutional dynamic chemistry (CDC) as a guiding principle in the rational design of proximity biosensors. As exists in a dynamic equilibrium, the constitutional dynamic network (CDN)-based proximity biosensors can be adjusted to maximize the affinity to the target protein while minimizing non-specific interactions that contribute to background signals. By further detecting the ratio of agonist to antagonist within the CDN, we also significantly improved assay robustness, enabling the sensitive detection of antibodies in complex matrices such as human serum. With the high affinity, low background, and high robustness, we anticipate that our CDN-based design strategy will find wide applications in biosensor development. Our study also opens the possibility to engineer protein-responsive synthetic systems with complex dynamic behaviors and functions.

Precise assembly/disassembly of homo-type and hetero-type macrocycles with photoresponsive and non-photoresponsive dynamic covalent bonds

Dynamic covalent macrocycles offer the advantage of tunable ring-opening/ring-closure and structural transformation, but their control with precision remains a daunting task due to the labile nature of reversible bonds. Herein we demonstrate the precise formation/scission of covalent macrocycles with varied sizes by contrasting the reactivity, stability, and degradability of light-active and light-inactive dynamic covalent bonds. The incorporation of photoswitchable and non-photoresponsive aldehyde sites into one single dialdehyde component afforded the creation of [1 + 1] type macrocycles with primary diamines of suitable lengths. The manipulation of light and acid/base stimuli allowed on-demand breaking/remaking of macrocycles, achieving the interconversion between macrocyclic and linear skeletons. Moreover, a combination of the dialdehyde, primary diamines, and secondary diamines enabled the construction of hetero-type [2 + 1 + 1'] macrocycles via enhanced discrimination and hierarchical assembly. Light-induced kinetic locking/unlocking of dynamic bonds further afforded macrocycle-to-macrocycle conversion when needed. Through leveraging controllable covalent connection/disconnection, switchable formation/disintegration of mechanically interlocked catenanes was further accomplished. The results described showcase the potential of photoinduced dynamic covalent chemistry for preparing complex architectures and should set the stage for molecular recognition, dynamic assemblies, synthetic motors, and responsive materials.

Design and Fabrication of Viscoelastic Hydrogels as Extracellular Matrix Mimicry for Cell Engineering

The extracellular matrix (ECM) performs both as a static scaffold and as a dynamic, viscoelastic milieu that actively participates in cell signaling and mechanical feedback loops. Recently, biomaterials with tunable viscoelastic properties have been utilized to mimic the native ECM in the fields of tissue engineering and regenerative medicines. These materials can be designed to support cell attachment, proliferation, and differentiation, facilitating the repair or replacement of damaged tissues. Moreover, viscoelasticity modulation of ECM mimicry helps to develop therapeutic strategies for diseases involving altered mechanical properties of tissues such as fibrosis or cancer. The study of biomaterial viscoelasticity thus intersects with a broad spectrum of biological and medical disciplines, offering insights into fundamental cell biology and practical solutions for improving human health. This review delves into the design and fabrication strategies of viscoelastic hydrogels, focusing particularly on two major viscoelastic parameters, mechanical strength and stress relaxation, and how the hydrogel mechanics influence the interactions between living cells and surrounding microenvironments. Meanwhile, this review discusses current bottlenecks in hydrogel-cell mechanics studies, highlighting the challenges in viscoelastic parameter decoupling, long-term stable maintenance of viscoelastic microenvironment, and the general applicability of testing standards and conversion protocols.

Multilevel Dynamic System as Molecular Morning-After Timer

Systems chemistry aims to develop molecular systems that display emerging properties arising from their network and absent in their individual constituents. Employing reversible chemistry under thermodynamic control represents a valuable tool for generating dynamic combinatorial libraries of interconverting molecules, which may exhibit intriguing collective behaviour. A simple dynamic combinatorial library was prepared using dithioacetal/thiol/disulfide exchanges. Because of the relative reactivities of these reversible reactions, the library constitutes a two-layer dynamic system with one layer active in an acid medium (thiol/dithioacetal exchange) and one layer active in a basic medium (thiol/disulfide exchange). This property enables the system to respond to momentary changes in acidity of the medium by activating different network regions, channeling some building blocks from one layer to another through shared thiol reagents (nodes). This momentaneous change in wiring affects the final steady state composition of the library, measured the next day, even though the event that caused it vanishes without leaving any residue. Therefore, the final composition of this dynamic system provides information about this transient past perturbation in the environment such as: when it occurred, how long it was, or how intense it was.

Carbohydrate-Based Reprocessable and Healable Covalent Adaptable Biofoams

Polymeric foams derived from bio-based resources and capable of self-healing and recycling ability are of great demand to fulfill various applications and address environmental concerns related to accumulation of plastic wastes. In this article, a set of polyester-based covalent adaptable biofoams (CABs) synthesized from carbohydrates and other bio-derived precursors under catalyst free conditions to offer a sustainable alternative to conventional toxic isocyanate-based polyurethane foams is reported. The dynamic β-keto carboxylate linkages present in these biofoams impart self-healing ability and recyclability to these samples. These CABs display adequate tensile properties especially compressive strength (≤123 MPa) and hysteresis behavior. The CABs swiftly stress relax at 150 °C and are reprocessable under similar temperature conditions. These biofoams have displayed potential for use as attachment on solar photovoltaics to augment the output efficiency. These CABs with limited swellability in polar protic solvents and adequate mechanical resilience are suitable for other commodity applications.

Kinetic Control of Complexity in Multiple Dynamic Libraries

Multiple dynamic libraries of compounds are generated when more than one reversible reaction comes into play. Commonly, two or more orthogonal reversible reactions are used, leading to non-communicating dynamic libraries which share no building blocks. Only a few examples of communicating libraries have been reported, and in all those cases, building blocks are reversibly exchanged from one library to the other, constituting an antiparallel dynamic covalent system. Herein we report that communication between two different dynamic libraries through an irreversible process is also possible. Indeed, alkyl amines cancel the dynamic regime on the nucleophilic substitution of tetrazines, generating kinetically inert compounds. Interestingly, such amine can be part of another dynamic library, an imine-amine exchange. Thus, both libraries are interconnected with each other by an irreversible process which leads to kinetically inert structures that contain parts from both libraries, causing a collapse of the complexity. Additionally, a latent irreversible intercommunication could be developed. In such a way, a stable molecular system with specific host-guest and fluorescence properties, could be irreversibly transformed when the right stimulus was applied, triggering the cancellation of the original supramolecular and luminescent properties and the emergence of new ones.

Switching between Nonisoenergetic Dynamic Covalent Reactions Using Host-Guest Chemistry

CO2 reacts with simple amines in the presence of water to generate dynamic combinatorial libraries of majority (i.e., ammonium carbamates) and minority (i.e., ammonium carbonates) nonisoenergetic covalent adducts. Over the past two decades, our laboratory has reported on a new class of cavitands, namely, dyn[n]arenes, from which a polyanionic macrocycle is a highly efficient receptor for linear polyammoniums that forms [2]pseudorotaxanes in water at neutral pH. Herein, we demonstrate that the formation of [2]pseudorotaxanes shifts the equilibrium of CO2 capture by polyamines in water toward the quasi-exclusive formation of carbonate adducts, providing the first example of a switch between two competitive and reversible covalent processes triggered by host-guest interactions. In addition, this supramolecular approach to CO2 capture exhibits enhanced capture efficiency by increasing the state of protonation of complexed vs uncomplexed polyamines. Altogether, we report here that a templating approach can divert the outcome of two reversible covalent chemistries involving nucleophilic additions and acid-base reactions, challenging therefore the common knowledge that noncovalent and covalent bonds operate in separate energy frames.

Biomedical Trends in Stimuli-Responsive Hydrogels with Emphasis on Chitosan-Based Formulations

Biomedicine is constantly evolving to ensure a significant and positive impact on healthcare, which has resulted in innovative and distinct requisites such as hydrogels. Chitosan-based formulations stand out for their versatile utilization in drug encapsulation, transport, and controlled release, which is complemented by their biocompatibility, biodegradability, and non-immunogenic nature. Stimuli-responsive hydrogels, also known as smart hydrogels, have strictly regulated release patterns since they respond and adapt based on various external stimuli. Moreover, they can imitate the intrinsic tissues' mechanical, biological, and physicochemical properties. These characteristics allow stimuli-responsive hydrogels to provide cutting-edge, effective, and safe treatment. Constant progress in the field necessitates an up-to-date summary of current trends and breakthroughs in the biomedical application of stimuli-responsive chitosan-based hydrogels, which was the aim of this review. General data about hydrogels sensitive to ions, pH, redox potential, light, electric field, temperature, and magnetic field are recapitulated. Additionally, formulations responsive to multiple stimuli are mentioned. Focusing on chitosan-based smart hydrogels, their multifaceted utilization was thoroughly described. The vast application spectrum encompasses neurological disorders, tumors, wound healing, and dermal infections. Available data on smart chitosan hydrogels strongly support the idea that current approaches and developing novel solutions are worth improving. The present paper constitutes a valuable resource for researchers and practitioners in the currently evolving field.

Thermoresponsive Injectable Hydrogel To Mimic the Heat- and Strain-Stiffening Behavior of Biopolymers toward Muscle Cell Proliferation

Injectable hydrogels with nonlinear mechanical attributes to emulate natural biopolymers hold paramount significance in tissue engineering, offering the potential to create scaffolds that seamlessly mimic the biomechanical intricacies of living tissues. Herein, we unveil a synthetic design strategy employing Schiff base chemistry to furnish a peptide-polymer hierarchical contractile injectable hydrogel network. This innovative design demonstrates cross-linking of supramolecular peptide nanostructures such as nanofibers, 1NF, and twisted bundles, 1TB, with a thermosensitive aldehyde-functionalized polymer, PCHO. These networks exhibit interesting nonlinear mechanical stiffening responses to temperature and external stress. Furthermore, the hydrogels transform into a gel state at physiological temperature to exhibit injectable behavior and demonstrate compression load-bearing capabilities. Finally, the hydrogel network exhibits excellent biocompatibility and cell proliferation toward fibroblast, L929, and myoblast, C2C12, to validate their use as potential extracellular matrix mimetic injectable scaffolds.

Dynamic covalent synthesis

Dynamic covalent synthesis aims to precisely control the assembly of simple building blocks linked by reversible covalent bonds to generate a single, structurally complex, product. In recent years, considerable progress in the programmability of dynamic covalent systems has enabled easy access to a broad range of assemblies, including macrocycles, shape-persistent cages, unconventional foldamers and mechanically-interlocked species (catenanes, knots, etc.). The reversibility of the covalent linkages can be either switched off to yield stable, isolable products or activated by specific physico-chemical stimuli, allowing the assemblies to adapt and respond to environmental changes in a controlled manner. This activatable dynamic property makes dynamic covalent assemblies particularly attractive for the design of complex matter, smart chemical systems, out-of-equilibrium systems, and molecular devices.

RGD peptide in cancer targeting: Benefits, challenges, solutions, and possible integrin-RGD interactions

RGD peptide can be found in cell adhesion and signaling proteins, such as fibronectin, vitronectin, and fibrinogen. RGD peptides' principal function is to facilitate cell adhesion by interacting with integrin receptors on the cell surface. They have been intensively researched for use in biotechnology and medicine, including incorporation into biomaterials, conjugation to medicinal molecules or nanoparticles, and labeling with imaging agents. RGD peptides can be utilized to specifically target cancer cells and the tumor vasculature by engaging with these integrins, improving drug delivery efficiency and minimizing adverse effects on healthy tissues. RGD-functionalized drug carriers are a viable option for cancer therapy as this focused approach has demonstrated promise in the future. Writing a review on the RGD peptide can significantly influence how drugs are developed in the future by improving our understanding of the peptide, finding knowledge gaps, fostering innovation, and making drug design easier.

Concentration- and Solvent-Induced Chiral Tuning by Manipulating Non-Proteinogenic Amino Acids in Glycoconjugate Supra-Scaffolds: Interaction with Protein, and Streptomycin Delivery

We showed solvent- and concentration-triggered chiral tuning of the fibrous assemblies of two novel glycoconjugates Z-P(Gly)-Glu and Z-F(4-N)-Glu made by chemical attachment of Cbz-protected [short as Z)] non-proteinogenic amino acids L-phenylglycine [short as P(Gly)] and 4-Nitro-L-phenylalanine [short as F(4-N)] with D-glucosamine [short as Glu]. Both biomimetic gelators can form self-healing and shape-persistent gels with a very low critical gelator concentration in water as well as in various organic solvents, indicating they are ambidextrous supergelators. Detailed spectroscopic studies suggested β-sheet secondary structure formation during anisotropic self-aggregation of the gelators which resulted in the formation of hierarchical left-handed helical fibers in acetone with an interlayer spacing of 2.4 nm. After the physical characterization of the gels, serum protein interaction with the gelators was assessed, indicating they may be ideal for biomedical applications. Further, both gelators are benign, non-immunogenic, non-allergenic, and non-toxic in nature, which was confirmed by performing the blood parameters and liver function tests on Wister rats. Streptomycin-loaded hydrogels showed efficacious antibacterial activity in vitro and in vivo as well. Finally, cell attachment and biocompatibility of the hydrogels were demonstrated which opens a newer avenue for promising biomedical and therapeutic applications.

Dual reactivity based dynamic covalent chemistry: mechanisms and applications

Dynamic covalent chemistry (DCC) focuses on the reversible formation, breakage, and exchange of covalent bonds and assemblies, setting a bridge between irreversible organic synthesis and supramolecular chemistry and finding wide utility. In order to enhance structural and functional diversity and complexity, different types of dynamic covalent reactions (DCRs) are placed in one vessel, encompassing orthogonal DCC without crosstalk and communicating DCC with a shared reactive functional group. As a means of adding tautomers, widespread in chemistry, to interconnected DCRs and combining the features of orthogonal and communicating DCRs, a concept of dual reactivity based DCC and underlying structural and mechanistic insights are summarized. The manipulation of the distinct reactivity of structurally diverse ring-chain tautomers allows selective activation and switching of reaction pathways and corresponding DCRs (C-N, C-O, and C-S) and assemblies. The coupling with photoswitches further enables light-mediated formation and scission of multiple types of reversible covalent bonds. To showcase the capability of dual reactivity based DCC, the versatile applications in dynamic polymers and luminescent materials are presented, paving the way for future functionalization studies.