Supramolecular polymeric biomaterials

Pyrogallol-rich supramolecular hydrogels with enzyme-sensitive microdomains for controlled topical delivery of hydrophobic drugs

Skin wound treatments require efficient and targeted delivery of therapeutic agents to promote fast tissue regeneration and prevent infections. Hydrogels are one of the most popular products in the wound care market, although their use as medicated wound dressings remains a massive challenge when hydrophobic drugs are needed due to the hydrophilic nature of these soft materials. In this study, we developed innovative, dynamic hydrogels based on polyvinyl alcohol (PVA), pyrogallol as a hydrogen bond crosslinker, and casein micelles as hydrophobic reservoirs of silver sulfadiazine (SSD) for enzyme-activated smart delivery at wound sites. The hydrogel formulation was optimized for mechanical strength, viscoelastic behavior, water absorption capacity, and drug-loading efficiency. In vitro drug delivery studies revealed a sustainable release profile of SSD for over 24 h from the micelles within the hydrogel network. Furthermore, biocompatibility evaluation using mouse fibroblast L929 cells demonstrated that the hydrogel did not inhibit cell viability, while in vivo experiments on Caenorhabditis elegans (C. elegans) proved its safety in complex organisms. This versatile hydrogel also has anti-inflammatory and antibacterial effects stemming from the therapeutic polyphenol, which could benefit the healing process. The combination of PVA, pyrogallol, and casein-based nanocarriers could offer an approach to wound healing, providing a new platform for hosting hydrophobic therapeutic substances. Overall, this hydrogel system shows great promise in wound care and could broaden the applications of this family of soft materials for treating various skin injuries.

DNA-Intercalating Supramolecular Hydrogels for Tunable Thermal and Viscoelastic Properties

Polymeric supramolecular hydrogels (PSHs) leverage the thermodynamic and kinetic properties of non-covalent interactions between polymer chains to govern their structural characteristics. As these materials are formed via endothermic or exothermic equilibria, their thermal response is challenging to control without drastically changing the nature of the chemistry used to join them. In this study, we introduce a novel class of PSHs utilizing the intercalation of double-stranded DNA (dsDNA) as the primary dynamic non-covalent interaction. The resulting dsDNA intercalating supramolecular hydrogels (DISHs) can be tuned to exhibit both endothermically or exothermically driven binding through strategic selection of intercalators. Bifunctional polyethylene glycol (MW~2000 Da) capped with intercalators of varying hydrophobicity, charge, and size (acridine, psoralen, thiazole orange, and phenanthridine) produced DISHs with comparable moduli (500-1000 Pa), but unique thermal viscoelastic responses. Notably, acridine-based cross-linkers displayed invariant and even increasing relaxation times with temperature, suggesting an endothermic binding mechanism. This methodology expands the set of structure-properties available to biomass-derived DNA biomaterials and promises a new material system where a broad set of thermal and viscoelastic responses can be obtained due to the sheer number and variety of intercalating molecules.

Effect of active carbonyl-carboxyl ratio on dynamic Schiff base crosslinking and its modulation of high-performance oxidized starch-chitosan hydrogel by hot extrusion 3D printing

The quest to develop 3D starch-based printing hydrogels for the controlled release of active substances with excellent mechanical and printing properties has gained significant attention. This work introduced a facile method based on crosslinking via Schiff base reaction for preparing bicomponent hydrogels. The method involved the utilization of customizable oxidized starch (OS) and chitosan (CS), enabling superior printing performance through the precise control of various active carbonyl-carboxyl ratios (ACR, 2:1, 1:1, and 2:3, respectively) of OS. OS-CS hydrogel (OSC) with an ACR level of 2:1 (OS-2-y%CS) underwent rearrangement during printing environment, fostering increased Schiff base reaction with a higher crosslinking degree and robust high structural recovery (>95 %). However, with decreasing ACR levels (from 2:1 to 2:3), the printing performance and mechanical strength of printed OSC (POSC) declined due to lower Schiff base bonds and increased phase separation. Compared with printed OS, POS-2-2%CS exhibited a remarkable 1250.52 % increase in tensile strength and a substantial 2424.71 % boost in compressive strength, enhanced shape fidelity and notable self-healing properties. Moreover, POS-2-2%CS exhibited stable diffusive drug release, showing potential application in the pH-responsive release of active substances. Overall, controlling the active carbonyl-carboxyl ratios provided an efficient and manageable approach for preparing high-performance 3D-printed hydrogels.

Water-Enhancing Gels Exhibiting Heat-Activated Formation of Silica Aerogels for Protection of Critical Infrastructure During Catastrophic Wildfire

A promising strategy to address the pressing challenges with wildfire, particularly in the wildland-urban interface (WUI), involves developing new approaches for preventing and controlling wildfire within wildlands. Among sprayable fire-retardant materials, water-enhancing gels have emerged as exceptionally effective for protecting civil infrastructure. They possess favorable wetting and viscoelastic properties that reduce the likelihood of ignition, maintaining strong adherence to a wide array of surfaces after application. Although current water-enhancing hydrogels effectively maintain surface wetness by creating a barricade, they rapidly desiccate and lose efficacy under high heat and wind typical of wildfire conditions. To address this limitation, unique biomimetic hydrogel materials from sustainable cellulosic polymers crosslinked by colloidal silica particles are developed that exhibit ideal viscoelastic properties and facile manufacturing. Under heat activation, the hydrogel transitions into a highly porous and thermally insulative silica aerogel coating in situ, providing a robust protective layer against ignition of substrates, even when the hydrogel fire suppressant becomes completely desiccated. By confirming the mechanical properties, substrate adherence, and enhanced substrate protection against fire, these heat-activatable biomimetic hydrogels emerge as promising candidates for next-generation water-enhancing fire suppressants. These advancements have the potential to dramatically improve the ability to protect homes and critical infrastructure during wildfire.

Thermoresponsive and Supramolecular Polymers: Interesting Biomaterials for Drug Delivery

How to use and deliver drugs to diseased and damaged areas has been one of the main concerns of pharmacologists and doctors for a long time. With the efforts of researchers, the advancement of technology, and the involvement of engineering in the health field, diverse and promising approaches have been studied and used to achieve this goal. A better understanding of biomaterials and the ability of production equipment led researchers to offer new drug delivery systems to the world. In recent decades, responsive polymers (exclusively to temperature and pH) and supramolecular polymers have received much attention due to their unique capabilities. Although this field of research still needs to be scrutinized and studied more, their recognition, examination, and use as drug delivery systems is a start for a promising future. This review study, focusing on temperature-responsive and supramolecular biomaterials and their application as drug delivery systems, deals with their structure, properties, and role in the noninvasive and effective delivery of medicinal agents.

Medical Applications and Cellular Mechanisms of Action of Carboxymethyl Chitosan Hydrogels

Carboxymethyl chitosan (CMCS) hydrogels have been investigated in biomedical research because of their versatile properties that make them suitable for various medical applications. Key properties that are especially valuable for biomedical use include biocompatibility, tailored solid-like mechanical characteristics, biodegradability, antibacterial activity, moisture retention, and pH stimuli-sensitive swelling. These features offer advantages such as enhanced healing, promotion of granulation tissue formation, and facilitation of neutrophil migration. As a result, CMCS hydrogels are favorable materials for applications in biopharmaceuticals, drug delivery systems, wound healing, tissue engineering, and more. Understanding the interactions between CMCS hydrogels and biological systems, with a focus on their influence on cellular behavior, is crucial for leveraging their versatility. Because of the constantly growing interest in chitosan and its derivative hydrogels in biomedical research and applications, the present review aims to provide updated insights into the potential medical applications of CMCS based on recent findings. Additionally, we comprehensively elucidated the cellular mechanisms underlying the actions of these hydrogels in medical settings. In summary, this paper recapitulates valuable data gathered from the current literature, offering perspectives for further development and utilization of carboxymethyl hydrogels in various medical contexts.

Hydrogen-Bonding-Regulated Morphology Control and the Impact on the Antibacterial Activity of Cationic π-Amphiphiles

This manuscript describes the synthesis, self-assembly, and antibacterial properties of naphthalene-diimide (NDI)-derived cationic π-amphiphiles. Three such asymmetric NDI derivatives with a nonionic hydrophilic wedge and a guanidine group in the two opposite sides of the NDI chromophore were considered. They differ by a single functional group (hydrazide, amide, and ester for NDI-1, NDI-2, and NDI-3, respectively), located in the linker between the NDI and the hydrophilic wedge. For NDI-1, the H-bonding among the hydrazides regulated unilateral stacking and a preferential direction of curvature of the resulting supramolecular polymer, producing an unsymmetric polymersome with the guanidinium groups displayed at the outer surface. NDI-3, lacking any H-bonding group, exhibits π-stacking without any preferential orientation and generates spherical particles with a relatively poor display of the guanidium groups. In sharp contrast to NDI-1, NDI-2 exhibits an entangled one-dimensional (1D) fibrillar morphology, indicating the prominent role of the H-bonding motif of the amide group and flexibility of the linker. The antibacterial activity of these assemblies was probed against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). NDI-1 showed the most promising antibacterial activity with a minimum inhibitory concentration (MIC) of ∼7.8 μg/mL against S. aureus and moderate activity (MIC ∼ 125 μg/mL) against E. coli. In sharp contrast, NDI-3 did not show any significant activity against the bacteria, suggesting a strong impact of the H-bonding-regulated directional assembly. NDI-2, forming a fibrillar network, showed moderate activity against S. aureus and negligible activity against E. coli, highlighting a significant impact of the morphology. All of these three molecules were found to be compatible with mammalian cells from the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) and hemolysis assay. The mechanistic investigation by membrane polarization assay, live/dead fluorescence assay, and microscopy studies confirmed the membrane disruption mechanism of cell killing for the lead candidate NDI-1.

Biomimetic Non-ergodic Aging by Dynamic-to-covalent Transitions in Physical Hydrogels

Hydrogels are soft materials engineered to suit a multitude of applications that exploit their tunable mechanochemical properties. Dynamic hydrogels employing noncovalent, physically cross-linked networks dominated by either enthalpic or entropic interactions enable unique rheological and stimuli-responsive characteristics. In contrast to enthalpy-driven interactions that soften with increasing temperature, entropic interactions result in largely temperature-independent mechanical properties. By engineering interfacial polymer-particle interactions, we can induce a dynamic-to-covalent transition in entropic hydrogels that leads to biomimetic non-ergodic aging in the microstructure without altering the network mesh size. This transition is tuned by varying temperature and formulation conditions such as pH, which allows for multivalent tunability in properties. These hydrogels can thus be designed to exhibit either temperature-independent metastable dynamic cross-linking or time-dependent stiffening based on formulation and storage conditions, all while maintaining structural features critical for controlling mass transport, akin to many biological tissues. Such robust materials with versatile and adaptable properties can be utilized in applications such as wildfire suppression, surgical adhesives, and depot-forming injectable drug delivery systems.

Improved biodistribution and enhanced immune response of subunit vaccine using a nanostructure formed by self-assembly of ascorbyl palmitate

New adjuvant strategies are needed to improve protein-based subunit vaccine immunogenicity. We examined the potential to use nanostructure of 6-O-ascorbyl palmitate to formulate ovalbumin (OVA) protein and an oligodeoxynucleotide (CpG-ODN) (OCC). In mice immunized with a single dose, OCC elicited an OVA-specific immune response superior to OVA/CpG-ODN solution (OC). Rheological studies demonstrated OCC's self-assembling viscoelastic properties. Biodistribution studies indicated that OCC prolonged OVA and CpG-ODN retention at injection site and lymph nodes, reducing systemic spread. Flow-cytometry assays demonstrated that OCC promoted OVA and CpG-ODN co-uptake by Ly6ChiCD11bhiCD11c+ monocytes. OCC and OC induced early IFN-γ in lymph nodes, but OCC led to higher concentration. Conversely, mice immunized with OC showed higher serum IFN-γ concentration compared to those immunized with OCC. In mice immunized with OCC, NK1.1+ cells were the IFN-γ major producers, and IFN-γ was essential for OVA-specific IgG2c switching. These findings illustrate how this nanostructure improves vaccine's response.

Biodegradable Zwitterionic Polymers as PEG Alternatives for Drug Delivery

Poly(ethylene glycol) (PEG) is a highly biocompatible and water-soluble polymer that is widely utilized for biomedical applications. Unfortunately, the immunogenicity and antigenicity of PEG severely restrict the biomedical efficacy of pegylated therapeutics. As emerging PEG alternatives, biodegradable zwitterionic polymers (ZPs) have attracted significant interest in recent years. Biodegradable ZPs generally are not only water-soluble and immunologically inert, but also possess a range of favorable biomedically relevant properties, without causing long-term side effects for in vivo biomedical applications. This review presents a systematic overview of recent studies on biodegradable ZPs. Their structural designs and synthetic strategies by integrating biodegradable base polymers with zwitterions are addressed. Their applications in the delivery of small molecule drugs (as mono-drugs or multi-drugs) and proteins are highlighted.

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.

Label-Free Composition Analysis of Supramolecular Polymer-Nanoparticle Hydrogels by Reversed-Phase Liquid Chromatography Coupled with a Charged Aerosol Detector

Supramolecular hydrogels formed through polymer-nanoparticle interactions are promising biocompatible materials for translational medicines. This class of hydrogels exhibits shear-thinning behavior and rapid recovery of mechanical properties, providing desirable attributes for formulating sprayable and injectable therapeutics. Characterization of hydrogel composition and loading of encapsulated drugs is critical to achieving the desired rheological behavior as well as tunable in vitro and in vivo payload release kinetics. However, quantitation of hydrogel composition is challenging due to material complexity, heterogeneity, high molecular weight, and the lack of chromophores. Here, we present a label-free approach to simultaneously determine hydrogel polymeric components and encapsulated payloads by coupling a reversed phase liquid chromatographic method with a charged aerosol detector (RPLC-CAD). The hydrogel studied consists of modified hydroxypropylmethylcellulose, self-assembled PEG-b-PLA nanoparticles, and a therapeutic compound, bimatoprost. The three components were resolved and quantitated using the RPLC-CAD method with a C4 stationary phase. The method demonstrated robust performance, applicability to alternative cargos (i.e., proteins) and was suitable for composition analysis as well as for evaluating in vitro release of cargos from the hydrogel. Moreover, this method can be used to monitor polymer degradation and material stability, which can be further elucidated by coupling the RPLC method with (1) a multi-angle light scattering detector (RPLC-MALS) or (2) high resolution mass spectrometry (RPLC-MS) and a Fourier-transform based deconvolution algorithm. We envision that this analytical strategy could be generalized to characterize critical quality attributes of other classes of supramolecular hydrogels, establish structure-property relationships, and provide rational design guidance in hydrogel drug product development.

Deliver on a Promise: Hydrogen-Bonded Polymer Nanomedicine with a Precise Ratio of Chemodrug and Photosensitizer for Intelligent Cancer Therapy

The outcomes of combined cancer therapy are largely related to loading content and contribution of each therapeutic agent; however, fine-tuning the ratio of two coloaded components toward precise cancer therapy is a great challenge and still remains in its infancy. We herein develop a supramolecular polymer scaffold to optimize the coloading ratio of chemotherapeutic agent and photosensitizer through hydrogen-bonding (H-bonding) interaction, for maximizing the efficacy of intelligent cancer chemo/photodynamic therapies (CT/PDT). To do so, we first synthesize a thymine (THY)-functionalized tetraphenylporphyrin photosensitizer (i.e., TTPP), featuring the same molecular configuration of H-bonding array with chemotherapeutic carmofur (e.g., 1-hexylcarbamoyl-5-fluorouracil, HCFU). Meanwhile, a six-arm star-shaped amphiphilic polymer vehicle P(DAPA-co-DPMA-co-OEGMA)6 (poly(diaminopyridine acrylamide-co-2-(diisopropylamino)ethyl methacrylate-co-oligo(ethylene glycol) monomethyl ether methacrylate)6) is prepared, bearing hydrophilic and biocompatible POEGMA segment, along with hydrophobic PDAPA and PDPMA segments, characterizing the randomly dispersed dual functionalities, i.e., heterocomplementary H-bonding DAP motifs and pH-responsive protonation DPMA content. Thanks to the identical DAP/HCFU and DAP/TTPP H-bonding association capability, the incorporation of both HCFU and TTPP to six-arm star-shaped P(DAPA-co-DPMA-co-OEGMA)6 vehicle, with an optimized coloading ratio, can be straightforwardly realized by adjusting the feeding concentrations, thus yielding the hydrogen-bonded supramolecular nanoparticles (i.e., HCFU-TTPP-SPNs), demonstrating the codelivery of two components with the promise to optimize the combined CT/PDT efficacy.

Rational Design of DNA Hydrogels Based on Molecular Dynamics of Polymers

In recent years, DNA has emerged as a fascinating building material to engineer hydrogel due to its excellent programmability, which has gained considerable attention in biomedical applications. Understanding the structure-property relationship and underlying molecular determinants of DNA hydrogel is essential to precisely tailor its macroscopic properties at molecular level. In this review, the rational design principles of DNA molecular networks based on molecular dynamics of polymers on the temporal scale, which can be engineered via the backbone rigidity and crosslinking kinetics, are highlighted. By elucidating the underlying molecular mechanisms and theories, it is aimed to provide a comprehensive overview of how the tunable DNA backbone rigidity and the crosslinking kinetics lead to desirable macroscopic properties of DNA hydrogels, including mechanical properties, diffusive permeability, swelling behaviors, and dynamic features. Furthermore, it is also discussed how the tunable macroscopic properties make DNA hydrogels promising candidates for biomedical applications, such as cell culture, tissue engineering, bio-sensing, and drug delivery.

Nanoparticle-Conjugated Toll-Like Receptor 9 Agonists Improve the Potency, Durability, and Breadth of COVID-19 Vaccines

Development of effective vaccines for infectious diseases has been one of the most successful global health interventions in history. Though, while ideal subunit vaccines strongly rely on antigen and adjuvant(s) selection, the mode and time scale of exposure to the immune system has often been overlooked. Unfortunately, poor control over the delivery of many adjuvants, which play a key role in enhancing the quality and potency of immune responses, can limit their efficacy and cause off-target toxicities. There is a critical need for improved adjuvant delivery technologies to enhance their efficacy and boost vaccine performance. Nanoparticles have been shown to be ideal carriers for improving antigen delivery due to their shape and size, which mimic viral structures but have been generally less explored for adjuvant delivery. Here, we describe the design of self-assembled poly(ethylene glycol)-b-poly(lactic acid) nanoparticles decorated with CpG, a potent TLR9 agonist, to increase adjuvanticity in COVID-19 vaccines. By controlling the surface density of CpG, we show that intermediate valency is a key factor for TLR9 activation of immune cells. When delivered with the SARS-CoV-2 spike protein, CpG nanoparticle (CpG-NP) adjuvant greatly improves the magnitude and duration of antibody responses when compared to soluble CpG, and results in overall greater breadth of immunity against variants of concern. Moreover, encapsulation of CpG-NP into injectable polymeric-nanoparticle (PNP) hydrogels enhances the spatiotemporal control over codelivery of CpG-NP adjuvant and spike protein antigen such that a single immunization of hydrogel-based vaccines generates humoral responses comparable to those of a typical prime-boost regimen of soluble vaccines. These delivery technologies can potentially reduce the costs and burden of clinical vaccination, both of which are key elements in fighting a pandemic.

Hydrogen-Bonded Polymer Nanomedicine with AIE Characteristic for Intelligent Cancer Therapy

One of the major goals of biomedical science is to pioneer advanced strategies toward precise and smart medicine. Hydrogen-bonding (H-bonding) assembly incorporated with an aggregation-induced emission (AIE) capability can serve as a powerful tool for developing supramolecular nanomedicine with clear tumor imaging and smart therapeutic performance. We here report a H-bonded polymeric nanoformulation with an AIE characteristic toward smart antitumor therapy. To do so, we first design a structurally novel tetraphenylethylene (TPE)-based H-bonding theranostic prodrug, TPE-(FUA)4, characterized by four chemotherapeutic fluorouracil-1-acetic acid (FUA) moieties arched to the TPE core. A six-arm star-shaped amphiphilic polymer vehicle, P(DAP-co-OEGEA)6, is prepared, bearing hydrophilic and biocompatible POEGEA (poly(oligo (ethylene glycol) ethyl acrylate) segments, along with a hydrophobic and H-bonding PDAP (poly(diaminopyridine acrylamide)) segment. Thanks to the establishment of the DAP/FUA H-bonding association, incorporating the TPE-(FUA)4 prodrug to the P(DAP-co-OEGEA)6 vehicle can yield H-bond cross-linked nanoparticles with interpenetrating networks. For the first time, AIE luminogens are interwoven into a six-arm star-shaped polymer via an intrinsic H-bonding array of the chemotherapeutic agent FUA, thus imposing an effective restriction of TPE molecular rotations. Concomitantly, encapsulated photothermal agent (IR780) via a hydrophobic interaction facilitates the formation of nanoassemblies, TPE-(FUA)4/IR780@P(DAP-co-OEGEA)6, featuring synergistic cancer chemo/photothermal therapy (CT/PTT). Our study can contribute a practical solution to fulfill biomedical requirements with a conductive advance in precision nanomedicine.

Effects of Cell-Adhesive Ligand Presentation on Pentapeptide Supramolecular Assembly and Gelation: Simulations and Experiments

The extracellular matrix (ECM) is a complex, hierarchical material containing structural and bioactive components. This complexity makes decoupling the effects of biomechanical properties and cell-matrix interactions difficult, especially when studying cellular processes in a 3D environment. Matrix mechanics and cell adhesion are both known regulators of specific cellular processes such as stem cell proliferation and differentiation. However, more information is required about how such variables impact various neural lineages that could, upon transplantation, therapeutically improve neural function after a central nervous system injury or disease. Rapidly Assembling Pentapeptides for Injectable Delivery (RAPID) hydrogels are one biomaterial approach to meet these goals, consisting of a family of peptide sequences that assemble into physical hydrogels in physiological media. In this study, we studied our previously reported supramolecularly-assembling RAPID hydrogels functionalized with the ECM-derived cell-adhesive peptide ligands RGD, IKVAV, and YIGSR. Using molecular dynamics simulations and experimental rheology, we demonstrated that these integrin-binding ligands at physiological concentrations (3-12 mm) did not impact the assembly of the KYFIL peptide system. In simulations, molecular measures of assembly such as hydrogen bonding and pi-pi interactions appeared unaffected by cell-adhesion sequence or concentration. Visualizations of clustering and analysis of solvent-accessible surface area indicated that the integrin-binding domains remained exposed. KYFIL or AYFIL hydrogels containing 3 mm of integrin-binding domains resulted in mechanical properties consistent with their non-functionalized equivalents. This strategy of doping RAPID gels with cell-adhesion sequences allows for the precise tuning of peptide ligand concentration, independent of the rheological properties. The controllability of the RAPID hydrogel system provides an opportunity to investigate the effect of integrin-binding interactions on encapsulated neural cells to discern how hydrogel microenvironment impacts growth, maturation, or differentiation.

Redox-Triggered Activation of Heavy-Atom-Free Photosensitizer and Implications in Targeted Photodynamic Therapy

A strategy for a redox-activatable heavy-atom-free photosensitizer (PS) based on thiolated naphthalimide has been demonstrated. The PS exhibits excellent reactive oxygen species (ROS) generation in the monomeric state. However, when encapsulated in a disulfide containing bioreducible amphiphilic triblock copolymer aggregate (polymersome), the PS exhibits aggregation in the confined hydrophobic environment, which results in a smaller exciton exchange rate between the singlet and triplet excited states (TDDFT studies), and consequently, the ROS generation ability of the PS was almost fully diminished. Such a PS (in the dormant state)-loaded redox-responsive polymersome showed excellent cellular uptake and intracellular release of the PS in its active form, which enabled cell killing upon light irradiation due to ROS generation. In a control experiment involving aggregates of a similar block copolymer, but lacking the bioreducible disulfide linkage, no intracellular reactivation of the PS was noticed, highlighting the importance of stimuli-responsive polymer assemblies in the area of targeted photodynamic therapy.

Advanced supramolecular design for direct ink writing of soft materials

The exciting advancements in 3D-printing of soft materials are changing the landscape of materials development and fabrication. Among various 3D-printers that are designed for soft materials fabrication, the direct ink writing (DIW) system is particularly attractive for chemists and materials scientists due to the mild fabrication conditions, compatibility with a wide range of organic and inorganic materials, and the ease of multi-materials 3D-printing. Inks for DIW need to possess suitable viscoelastic properties to allow for smooth extrusion and be self-supportive after printing, but molecularly facilitating 3D printability to functional materials remains nontrivial. While supramolecular binding motifs have been increasingly used for 3D-printing, these inks are largely optimized empirically for DIW. Hence, this review aims to establish a clear connection between the molecular understanding of the supramolecularly bound motifs and their viscoelastic properties at bulk. Herein, extrudable (but not self-supportive) and 3D-printable (self-supportive) polymeric materials that utilize noncovalent interactions, including hydrogen bonding, host-guest inclusion, metal-ligand coordination, micro-crystallization, and van der Waals interaction, have been discussed in detail. In particular, the rheological distinctions between extrudable and 3D-printable inks have been discussed from a supramolecular design perspective. Examples shown in this review also highlight the exciting macroscale functions amplified from the molecular design. Challenges associated with the hierarchical control and characterization of supramolecularly designed DIW inks are also outlined. The perspective of utilizing supramolecular binding motifs in soft materials DIW printing has been discussed. This review serves to connect researchers across disciplines to develop innovative solutions that connect top-down 3D-printing and bottom-up supramolecular design to accelerate the development of 3D-print soft materials for a sustainable future.

A win-win scenario for antibacterial activity and skin mildness of cationic surfactants based on the modulation of host-guest supramolecular conformation

The commercial cationic surfactants (CSAa) with quaternary ammonium (QA) groups have proved to be broad-spectrum bactericide against bacteria, fungi, and viruses. Nevertheless, they inevitably exhibit potent irritation on the skin. In this work, we systematically investigated the regulatory mechanism of the host-guest supramolecular conformation with β-cyclodextrin (β-CD) on the bactericidal performance and skin irritation of CSAa with different head groups and chain lengths. When the ratio of incorporated β-CD is not greater than 1:1, the bactericidal efficiency of CSAa@β-CD (n > 12) remained above 90 % due to the free QA groups and hydrophobic fraction that can act on negatively charged bacterial membranes. And once the ratio of β-CD exceeded 1:1, the β-CD attracted to the bacterial surface by hydrogen bonding might prevent CSAa@β-CD from acting on bacteria, resulting in a decrement in antibacterial performance. Even so, the antibacterial activity of CSAa with long alkyl chains (n = 16, 18) was independent from the complexation of β-CD. Accordingly, both the zein solubilization assay and the neutrophil migration assay on zebrafish skin evidenced that β-CD attenuated the interaction of surfactant with skin model proteins and the inflammatory effect on zebrafish, thereby enhancing skin mildness. In this way, we hope to create a simple but effective brainpower using the host-guest approach to guarantee both bactericidal efficiency and skin mildness without modifying the chemical structure of these commercial biocides.

Crosslinking konjac-glucomannan with kappa-carrageenan nanogels: A step toward the design of sacrificial materials

The challenge in designing sacrificial materials is to obtain materials that are both mechanically stable and easily dissolvable. This research aimed to meet this challenge by fabricating a new polymer-nanogel hydrogel based solely on hydrogen bonds between two polysaccharides. The study focused on hydrogels formed from soluble konjac-glucomannan and nanogels synthesized from kappa-carrageenan. This novel hydrogel exhibited self-healing and shear-thinning properties due to its weak physical interactions. The hydrogel dissolved simultaneously with its swelling. Changes in temperature or nanogel concentration, or the addition of potassium ions, altered the swelling and dissolution rates. Furthermore, adding KCl to the as-prepared hydrogel increased its compression and tensile moduli and its strength. The new formulation opens numerous possibilities as a potential sacrificial material for different applications since it is mechanically stable yet rapidly dissolves in physiological conditions without applying high temperatures or using chelating agents.

3D printed tissue models: From hydrogels to biomedical applications

The development of new advanced constructs resembling structural and functional properties of human organs and tissues requires a deep knowledge of the morphological and biochemical properties of the extracellular matrices (ECM), and the capacity to reproduce them. Manufacturing technologies like 3D printing and bioprinting represent valuable tools for this purpose. This review will describe how morphological and biochemical properties of ECM change in different tissues, organs, healthy and pathological states, and how ECM mimics with the required properties can be generated by 3D printing and bioprinting. The review describes and classifies the polymeric materials of natural and synthetic origin exploited to generate the hydrogels acting as "inks" in the 3D printing process, with particular emphasis on their functionalization allowing crosslinking and conjugation with signaling molecules to develop bio-responsive and bio-instructive ECM mimics.

Biocompatibility and Mechanical Properties of Carboxymethyl Chitosan Hydrogels

Hydrogels have the properties of solid substances and are useful for medicine, e.g., in systems for the controlled release of drugs or as wound dressings. They isolate the wound from the external environment and constitute a barrier to microorganisms while still being permeable to oxygen. In the current study, hydrogels were formed from concentrated aqueous solutions of carboxymethyl chitosan (CMCS) via electron beam irradiation, with the presence of a crosslinking agent: poly(ethylene glycol)diacrylate. The aim of the study was to compare the properties and action of biopolymer CMCS hydrogels with commercial ones and to select the best compositions for future research towards wound-dressing applications. The elasticity of the gel depended on the component concentrations and the irradiation dose employed to form the hydrogel. Young's modulus for the tested hydrogels was higher than for the control material. The Live/Dead test performed on human fibroblasts confirmed that the analyzed hydrogels are not cytotoxic, and for some concentrations, they cause a slight increase in the number of cells compared to the control. The biocompatibility studies carried out on laboratory rats showed no adverse effect of hydrogels on animal tissues, confirming their biocompatibility and suggesting that CMCS hydrogels could be considered as wound-healing dressings in the future. Ionizing radiation was proven to be a suitable tool for CMCS hydrogel synthesis and could be of use in wound-healing therapy, as it may simultaneously sterilize the product.

PEG-Infiltrated Polyoxometalate Frameworks with Flexible Form-Factors

We present the synthesis of metal oxide frameworks composed of the Preyssler anion, [NaP₅W₃₀O₁₁₀]^14-, bridged with transition-metal cations and infiltrated with polyethylene glycol. The frameworks can be dissolved in water to form freestanding rigid or flexible films or gels. Powder X-ray diffraction shows that all form-factors maintain the short-range order of the original crystals. Raman spectroscopy reveals that, similar to hydrogels, the macroscopic mechanical properties of these composites are dependent on the water content and the extent of hydrogen-bonding within the water network. The understanding gained from these studies facilitates solution-phase processing of polyoxometalate frameworks into flexible form factors.

Dynamic grafting of carboxylates onto poly(vinyl alcohol) polymers for supramolecularly-crosslinked hydrogel formation

Supramolecular hydrogels have attracted considerable interest due to their unique stimuli-responsive and self-healing properties. However, these hydrogel systems are usually achieved by covalent grafting of supramolecular units onto the polymer backbone, which in turn limits their reprocessability. Herein, we prepared a supramolecular hydrogel system by forming dynamic covalent crosslinks between 4-carboxyphenylboronic acid (CPBA) and polyvinyl alcohol (PVA). The system was then further crosslinked with either calcium ions or branched polyethylenimine (PEI) to generate hydrogels with distinctly different properties. Incorporation of calcium ions resulted in the formation of hydrogels with higher storage modulus of 7290 Pa but without self-healing properties. On the other hand, PEI-crosslinked hydrogel (PVA-CPBA-PEI) exhibited >2000% critical strain value, demonstrated high stability over 52 days and showed sustained antibacterial effect. A combination of supramolecular interactions and dynamic covalent crosslinks can be an alternate strategy to fabricate next generation hydrogel materials.

Injectable Liposome-based Supramolecular Hydrogels for the Programmable Release of Multiple Protein Drugs

Directing biological functions is at the heart of next-generation biomedical initiatives in tissue and immuno-engineering. However, the ambitious goal of engineering complex biological networks requires the ability to precisely perturb specific signaling pathways at distinct times and places. Using lipid nanotechnology and the principles of supramolecular self-assembly, we developed an injectable liposomal nanocomposite hydrogel platform to precisely control the release of multiple protein drugs. By integrating modular lipid nanotechnology into a hydrogel, we introduced multiple mechanisms of release based on liposome surface chemistry. To validate the utility of this system for multi-protein delivery, we demonstrated synchronized, sustained, and localized release of IgG antibody and IL-12 cytokine in vivo, despite the significant size differences between these two proteins. Overall, liposomal hydrogels are a highly modular platform technology with the ability the mediate orthogonal modes of protein release and the potential to precisely coordinate biological cues both in vitro and in vivo.

Hydrogen-Bonds Mediated Nanomedicine: Design, Synthesis and Applications

Among the various challenges in medicine, diagnosis, complete cure and healing of cancers remain difficult given the heterogeneity and complexity of such disease. Differing from conventional platforms with often unsatisfactory theranostic capabilities, the contribution of supramolecular interactions, such as hydrogen-bonds (H-bonds), to cancer nanotheranostics opens new perspectives for the design of biomedical materials, exhibiting remarkable properties and easier processability. Thanks to their dynamic characteristics, a feature generally observed for non-covalent interactions, H-bonding (macro)molecules can be used as supramolecular motifs for yielding drug- and diagnostic carriers that possess attractive features, arising from the combination of assembled nanoplatforms and the responsiveness of H-bonds. Thus H-bonded nanomedicine provides a rich toolbox that is useful to fulfill biomedical needs with unique advantages in early-stage diagnosis and therapy, demonstrating the promising potential in clinical translations and applications. We here summarize the design and synthetic routes towards H-bonded nanomedicines, focus on the growing understanding of the structure-function relationship for efficient cancer treatment. We propose a guidance for designing new H-bonded intelligent theranostic agents, to inspire more successful explorations of cancer nanotheranostics and finally to promote potential clinical translations. This article is protected by copyright. All rights reserved.

Low-intensity pulsed ultrasound promotes cell viability and inhibits apoptosis of H9C2 cardiomyocytes in 3D bioprinting scaffolds via PI3K-Akt and ERK1/2 pathways

The aim of this study was to investigate whether low-intensity pulsed ultrasound (LIPUS) promotes myocardial cell viability in three-dimensional (3D) cell-laden gelatin methacryloyl (GelMA) scaffolds. Cardiomyoblasts (H9C2s) were mixed in 6% (w/v) GelMA bio-inks and printed using an extrusion-based 3D bioprinter. These scaffolds were exposed to LIPUS with different parameters or sham-irradiated to optimize the LIPUS treatment. The viability of H9C2s was measured using Cell Counting Kit-8 (CCK8), cell cycle, and live and dead cell double-staining assays. Western blot analysis was performed to determine the protein expression levels. We successfully fabricated 3D bio-printed cell-laden GelMA scaffolds. CCK8 and live and dead cell double-staining assays indicated that the optimal conditions for LIPUS were a frequency of 0.5 MHz and an exposure time of 10 min. Cell cycle analysis showed that LIPUS promoted the entry of cells into the S and G2/M phases from the G0/G1 phase. Western blot analysis revealed that LIPUS promoted the phosphorylation and activation of ERK1/2 and PI3K-Akt. The ERK1/2 inhibitor (U0126) and PI3K inhibitor (LY294002) significantly reduced LIPUS-induced phosphorylation of ERK1/2 and PI3K-Akt, respectively, which in turn reduced the LIPUS-induced viability of H9C2s in 3D bio-printed cell-laden GelMA scaffolds. A frequency of 0.5 MHz and exposure time of 10 min for LIPUS exposure can be adapted to achieve optimized culture effects on myocardial cells in 3D bio-printed cell-laden GelMA scaffolds via the ERK1/2 and PI3K-Akt signaling pathways.

Acupoint nanocomposite hydrogel for simulation of acupuncture and targeted delivery of triptolide against rheumatoid arthritis

Background

Attenuating inflammatory response and relieving pain are two therapeutic therapeutical goals for rheumatoid arthritis (RA). Anti-inflammatory and analgesic drugs are often associated with many adverse effects due to nonspecific distribution. New drug delivery systems with practical targeting ability and other complementary strategies urgently need to be explored. To achieve this goal, an acupoint drug delivery system that can target deliver anti-inflammatory drugs and simulate acupuncture in relieving pain was constructed, which can co-deliver triptolide (TP) and 2-chloro-N (6)-cyclopentyl adenosine (CCPA).

Results

We have successfully demonstrated that acupoint nanocomposite hydrogel composed of TP-Human serum album nanoparticles (TP@HSA NPs) and CCPA could effectively treat RA. The result shows that CCPA-Gel can enhance analgesic effects specifically at the acupoint, while the mechanical and thermal pain threshold was 4.9 and 1.6 times compared with non-acupoint, respectively, and the nanocomposite gel further enhanced. Otherwise, the combination of acupoint and nanocomposite hydrogel exerted synergetic improvement of inflammation, bone erosion, and reduction of systemic toxicity. Furthermore, it could regulate inflammatory factors and restore the balance of Th17/Treg cells, which provided a novel and effective treatment strategy for RA. Interestingly, acupoint administration could improve the accumulation of the designed nanomedicine in arthritic paws (13.5% higher than those in non-acupoint at 48 h), which may explain the better therapeutic efficiency and low toxicity.

Conclusion

This novel therapeutic approach-acupoint nanocomposite hydrogel, builds a bridge between acupuncture and drugs which sheds light on the combination of traditional and modern medicine.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01157-z.

The role of biomaterials and scaffolds in immune responses in regenerative medicine: macrophage phenotype modulation by biomaterial properties and scaffold architectures

Scaffolds are an integral part of the regenerative medicine field. The contact of biomaterials with tissue, as was clearly observed over the years, induces immune reactions in a material and patient specific manner, where both surface and bulk properties of scaffolds, together with their 3D architecture, have a significant influence on the outcome. This review presents an overview of the reactions to the biomaterials with a specific focus on clinical complications with the implants in the context of immune reactions and an overview of the studies involving biomaterial properties and interactions with innate immune system cells. We emphasize the impact of these studies on scaffold selection and upscaling of microenvironments created by biomaterials from 2D to 3D using immune cell encapsulation, seeding in a 3D scaffold and co-culture with relevant tissue cells. 3D microenvironments are covered with a specific focus on innate cells since a large proportion of these studies used innate immune cells. Finally, the recent studies on the incorporation of adaptive immune cells in immunomodulatory systems are covered in this review. Biomaterial-immune cell interactions are a critical part of regenerative medicine applications. Current efforts in establishing the ground rules for such interactions following implantation can control immune response during all phases of inflammation. Thus, in the near future for complete functional recovery, tissue engineering and control over biomaterials must be considered at the first step of immune modulation and this review covers these interactions, which have remained elusive up to now.

Bioapplication of cyclodextrin-containing montmorillonite

Recent progresses in the integration of CDs and montmorillonite, as well as applications of CD-containing montmorillonite hybrid host systems are summarized in this review. Several efficient synthesis strategies, such as ion exchange, metal coordination, supramolecular strategies, polymerizations and organic synthesis methods, have been discussed during the preparation of CDs/montmorillonite hybrid composites. In particular, diverse instrumental techniques were highly recommended for characterizing the as-obtained hybrid systems, including their chemical composition and structures, crystallinity, surface/self-assembled morphologies, as well as other particular physiochemical properties, providing a direct guide for promoting the desired structures and exploring various applications. It should be noted that the introduction of functional groups, as well as the integration of CDs and montmorillonite granted the thus obtained CD-containing montmorillonite hybrid host systems a lot of unique features, providing great opportunities for expanding the practical applications to a series of biological and environmental areas, such as biosensors, sorption and decontamination of bio/environmental hazardous materials, biostudies about aqueous dispersity, stability and biocompatibility, drug loading and target delivery, controlled and sustained drug release, as well as antibacterial.

Deoxyribonucleic acid polymer nanoparticle hydrogels

Polymer nanoparticle hydrogels made of deoxyribonucleic acid and silica have been prepared and shown to display shear thinning and self-healing properties, sustained release of cargo and enzymatic degradation.

Self-assembly of amino acids toward functional biomaterials

Biomolecules, such as proteins and peptides, can be self-assembled. They are widely distributed, easy to obtain, and biocompatible. However, the self-assembly of proteins and peptides has disadvantages, such as difficulty in obtaining high quantities of materials, high cost, polydispersity, and purification limitations. The difficulties in using proteins and peptides as functional materials make it more complicate to arrange assembled nanostructures at both microscopic and macroscopic scales. Amino acids, as the smallest constituent of proteins and the smallest constituent in the bottom-up approach, are the smallest building blocks that can be self-assembled. The self-assembly of single amino acids has the advantages of low synthesis cost, simple modeling, excellent biocompatibility and biodegradability in vivo. In addition, amino acids can be assembled with other components to meet multiple scientific needs. However, using these simple building blocks to design attractive materials remains a challenge due to the simplicity of the amino acids. Most of the review articles about self-assembly focus on large molecules, such as peptides and proteins. The preparation of complicated materials by self-assembly of amino acids has not yet been evaluated. Therefore, it is of great significance to systematically summarize the literature of amino acid self-assembly. This article reviews the recent advances in amino acid self-assembly regarding amino acid self-assembly, functional amino acid self-assembly, amino acid coordination self-assembly, and amino acid regulatory functional molecule self-assembly.

Supramolecular Host-Guest Hydrogels for Corneal Regeneration

Over 6.2 million people worldwide suffer from moderate to severe vision loss due to corneal disease. While transplantation with allogenic donor tissue is sight-restoring for many patients with corneal blindness, this treatment modality is limited by long waiting lists and high rejection rates, particularly in patients with severe tissue damage and ocular surface pathologies. Hydrogel biomaterials represent a promising alternative to donor tissue for scalable, nonimmunogenic corneal reconstruction. However, implanted hydrogel materials require invasive surgeries and do not precisely conform to tissue defects, increasing the risk of patient discomfort, infection, and visual distortions. Moreover, most hydrogel crosslinking chemistries for the in situ formation of hydrogels exhibit off-target effects such as cross-reactivity with biological structures and/or result in extractable solutes that can have an impact on wound-healing and inflammation. To address the need for cytocompatible, minimally invasive, injectable tissue substitutes, host-guest interactions have emerged as an important crosslinking strategy. This review provides an overview of host-guest hydrogels as injectable therapeutics and highlights the potential application of host-guest interactions in the design of corneal stromal tissue substitutes.

A structure-supporting, self-healing, and high permeating hydrogel bioink for establishment of diverse homogeneous tissue-like constructs

The ready-to-use, structure-supporting hydrogel bioink can shorten the time for ink preparation, ensure cell dispersion, and maintain the preset shape/microstructure without additional assistance during printing. Meanwhile, ink with high permeability might facilitate uniform cell growth in biological constructs, which is beneficial to homogeneous tissue repair. Unfortunately, current bioinks are hard to meet these requirements simultaneously in a simple way. Here, based on the fast dynamic crosslinking of aldehyde hyaluronic acid (AHA)/N-carboxymethyl chitosan (CMC) and the slow stable crosslinking of gelatin (GEL)/4-arm poly(ethylene glycol) succinimidyl glutarate (PEG-SG), we present a time-sharing structure-supporting (TSHSP) hydrogel bioink with high permeability, containing 1% AHA, 0.75% CMC, 1% GEL and 0.5% PEG-SG. The TSHSP hydrogel can facilitate printing with proper viscoelastic property and self-healing behavior. By crosslinking with 4% PEG-SG for only 3 min, the integrity of the cell-laden construct can last for 21 days due to the stable internal and external GEL/PEG-SG networks, and cells manifested long-term viability and spreading morphology. Nerve-like, muscle-like, and cartilage-like in vitro constructs exhibited homogeneous cell growth and remarkable biological specificities. This work provides not only a convenient and practical bioink for tissue engineering, targeted cell therapy, but also a new direction for hydrogel bioink development.

Translational Applications of Hydrogels

Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

Thermodynamic Insights into Protein Adsorption on Supramolecular Assemblies of π-Amphiphiles

Nonspecific adsorption of proteins on the surface of nanocarriers plays a critical role in their cellular uptake and other biological functions. This article reports vesicular assemblies of two π-amphiphiles (NDI-1 and NDI-2) and thermodynamic aspects of their interaction with bovine serum albumin (BSA). Both contain a hydrophobic naphthalene-diimide (NDI) core and two oligo-oxyethylene (OE) wedges but differ by the presence of the hydrazide group in NDI-1. NDI-2 exhibits a constricted π-stacking and enthalpy-driven adsorption of BSA. In contrast, NDI-1 exhibits a stronger interaction due to enhanced entropy contribution. It is postulated that a tight packing of NDI chromophores in NDI-2 results in an inadequate space in the corona, leading to the dehydration of OE chains, which contributes to the observed enthalpy-driven binding. On the other hand, due to H-bonding along the direction of π-stacking in NDI-1, an enhanced interchromophoric distance provides more space in the shell, resulting in less dehydration of the OE chains, which results in an entropy gain from the BSA binding-induced release of water from the OE chains. Intercalation of an electron-rich pyrene in the electron-deficient NDI-1 stack further reduces the grafting density of the OE chains, resulting in negligible BSA adsorption, similar to a stealth polymer. A correlation can be seen between the thermodynamic landscape of the protein adsorption and the trend of their lower critical solution temperature (LCST), which follows the order NDI-1 + Py < NDI-1 < NDI-2.

Carbohydrate-Based Macromolecular Biomaterials

Carbohydrates are the most abundant and one of the most important biomacromolecules in Nature. Except for energy-related compounds, carbohydrates can be roughly divided into two categories: Carbohydrates as matter and carbohydrates as information. As matter, carbohydrates are abundantly present in the extracellular matrix of animals and cell walls of various plants, bacteria, fungi, etc., serving as scaffolds. Some commonly found polysaccharides are featured as biocompatible materials with controllable rigidity and functionality, forming polymeric biomaterials which are widely used in drug delivery, tissue engineering, etc. As information, carbohydrates are usually referred to the glycans from glycoproteins, glycolipids, and proteoglycans, which bind to proteins or other carbohydrates, thereby meditating the cell-cell and cell-matrix interactions. These glycans could be simplified as synthetic glycopolymers, glycolipids, and glycoproteins, which could be afforded through polymerization, multistep synthesis, or a semisynthetic strategy. The information role of carbohydrates can be demonstrated not only as targeting reagents but also as immune antigens and adjuvants. The latter are also included in this review as they are always in a macromolecular formulation. In this review, we intend to provide a relatively comprehensive summary of carbohydrate-based macromolecular biomaterials since 2010 while emphasizing the fundamental understanding to guide the rational design of biomaterials. Carbohydrate-based macromolecules on the basis of their resources and chemical structures will be discussed, including naturally occurring polysaccharides, naturally derived synthetic polysaccharides, glycopolymers/glycodendrimers, supramolecular glycopolymers, and synthetic glycolipids/glycoproteins. Multiscale structure-function relationships in several major application areas, including delivery systems, tissue engineering, and immunology, will be detailed. We hope this review will provide valuable information for the development of carbohydrate-based macromolecular biomaterials and build a bridge between the carbohydrates as matter and the carbohydrates as information to promote new biomaterial design in the near future.

User-defined, temporal presentation of bioactive molecules on hydrogel substrates using supramolecular coiled coil complexes

The ability to spatiotemporally control the presentation of relevant biomolecules in synthetic culture systems has gained significant attention as researchers strive to recapitulate the endogenous extracellular matrix (ECM) in vitro. With the biochemical composition of the ECM constantly in flux, the development of platforms that allow for user-defined control of bioactivity is desired. Here, we reversibly conjugate bioactive molecules to hydrogel-based substrates through supramolecular coiled coil complexes that form between complementary peptides. Our system employs a thiolated peptide for tethering to hydrogel surfaces (T-peptide) through a spatially-controlled photomediated click reaction. The complementary association peptide (A-peptide), containing the bioactive domain, forms a heterodimeric coiled coil complex with the T-peptide. Addition of a disruptor peptide (D-peptide) engineered specifically to target the A-peptide outcompetes the T-peptide for binding, and removes the A-peptide and the attached bioactive motif from the scaffold. We use this platform to demonstrate spatiotemporal control of biomolecule presentation within hydrogel systems in a repeatable process that can be extended to adhesive motifs for cell culture. NIH 3T3 fibroblasts seeded on hyaluronic acid hydrogels and polyethylene glycol-based fibrous substrates supramolecularly functionalized with an RGD motif demonstrated significant cell spreading over their nonfunctionalized counterparts. Upon displacement of the RGD motif, fibroblasts occupied less area and clustured on the substrates. Taken together, this platform enables facile user-defined incorporation and removal of biomolecules in a repeatable process for controlled presentation of bioactivity in engineered culture systems.

A facile, versatile hydrogel bioink for 3D bioprinting benefits long-term subaqueous fidelity, cell viability and proliferation

Both of the long-term fidelity and cell viability of three-dimensional (3D)-bioprinted constructs are essential to precise soft tissue repair. However, the shrinking/swelling behavior of hydrogels brings about inadequate long-term fidelity of constructs, and bioinks containing excessive polymer are detrimental to cell viability. Here, we obtained a facile hydrogel by introducing 1% aldehyde hyaluronic acid (AHA) and 0.375% N-carboxymethyl chitosan (CMC), two polysaccharides with strong water absorption and water retention capacity, into classic gelatin (GEL, 5%)-alginate (ALG, 1%) ink. This GEL-ALG/CMC/AHA bioink possesses weak temperature dependence due to the Schiff base linkage of CMC/AHA and electrostatic interaction of CMC/ALG. We fabricated integrated constructs through traditional printing at room temperature and in vivo simulation printing at 37°C. The printed cell-laden constructs can maintain subaqueous fidelity for 30 days after being reinforced by 3% calcium chloride for only 20 s. Flow cytometry results showed that the cell viability was 91.38 ± 1.55% on day 29, and the cells in the proliferation plateau at this time still maintained their dynamic renewal with a DNA replication rate of 6.06 ± 1.24%. This work provides a convenient and practical bioink option for 3D bioprinting in precise soft tissue repair.

Insights into the formation mechanisms and properties of pectin hydrogel physically cross-linked with chitosan nanogels

This study explores hydrogels based on the physical interaction between soluble pectin and chitosan nanogels. A simple technique for creating chitosan nanogels of controllable size was developed based on a two-step process: physical cross-linking with tripolyphosphate (TPP) and chemical cross-linking with genipin. The particles were stable at acidic pH, which allowed hydrogel formation. Thixotropy experiments demonstrated that the concentration but not the size of the nanogels strongly affected the gel shear modulus. The influence of the post-assembly conditions, including exposure to monovalent salts (NaCl, NaI, and NaF) and pH (2.5 or 5.5), on the gel swelling and mechanical properties was studied. Small angle x-ray scattering (SAXS) results provide evidence that these physical hydrogels are indeed a cross-linked network. These experiments provided insights into the influence of hydrogen bonds and electrostatic interactions on the gel network.

Thermo-Viscoelastic Response of Protein-Based Hydrogels

Because of the bioactivity and biocompatibility of protein-based gels and the reversible nature of bonds between associating coiled coils, these materials demonstrate a wide spectrum of potential applications in targeted drug delivery, tissue engineering, and regenerative medicine. The kinetics of rearrangement (association and dissociation) of the physical bonds between chains has been traditionally studied in shear relaxation tests and small-amplitude oscillatory tests. A characteristic feature of recombinant protein gels is that chains in the polymer network are connected by temporary bonds between the coiled coil complexes and permanent cross-links between functional groups of amino acids. A simple model is developed for the linear viscoelastic behavior of protein-based gels. Its advantage is that, on the one hand, the model only involves five material parameters with transparent physical meaning and, on the other, it correctly reproduces experimental data in shear relaxation and oscillatory tests. The model is applied to study the effects of temperature, the concentration of proteins, and their structure on the viscoelastic response of hydrogels.

Prolonged Codelivery of Hemagglutinin and a TLR7/8 Agonist in a Supramolecular Polymer-Nanoparticle Hydrogel Enhances Potency and Breadth of Influenza Vaccination

The sustained release of vaccine cargo has been shown to improve humoral immune responses to challenging pathogens such as influenza. Extended codelivery of antigen and adjuvant prolongs germinal center reactions, thus improving antibody affinity maturation and the ability to neutralize the target pathogen. Here, we develop an injectable, physically cross-linked polymer-nanoparticle (PNP) hydrogel system to prolong the local codelivery of hemagglutinin and a toll-like receptor 7/8 agonist (TLR7/8a) adjuvant. By tethering the TLR7/8a to a NP motif within the hydrogels (TLR7/8a-NP), the dynamic mesh of the PNP hydrogels enables codiffusion of the adjuvant and protein antigen (hemagglutinin), therefore enabling sustained codelivery of these two physicochemically distinct molecules. We show that subcutaneous delivery of PNP hydrogels carrying hemagglutinin and TLR7/8a-NP in mice improves the magnitude and duration of antibody titers in response to a single injection vaccination compared to clinically used adjuvants. Furthermore, the PNP gel-based slow delivery of influenza vaccines led to increased breadth of antibody responses against future influenza variants, including a future pandemic variant, compared to clinical adjuvants. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of influenza subunit vaccines.