Evolution of hierarchical porous structures in supramolecular guest-host hydrogels

Homogeneous films from amphiphilic hyaluronan and their characterization by confocal microscopy and nanoindentation

Self-supporting films from amphiphilic hyaluronan are suitable for medical applications like wound dressings or resorbable implants. These films are typically cast from water/alcohol solutions. However, when the mixed solvent evaporates in ambient air, convection flows develop in the solution and become imprinted in the film, potentially compromising its properties. Consequently, we developed a novel film manufacturing method: drying in a closed box under saturated vapour conditions. Using this approach, we prepared a series of optically clear lauroyl-hyaluronan (LHA) films with uniform thickness and compared them to their air-dried counterparts. We first evaluated swelling ratios and elastic moduli for LHA films with varying degrees of substitution. The box-dried films swelled significantly less and were 1-2 orders of magnitude stiffer than air-dried films from the same LHA sample. Confocal microscopy revealed that box-dried films exhibited a regular microstructure, while air-dried films displayed a pore-size gradient and strong microstructure modulation due to convection flows. Local elastic modulus variations arising from these microstructures were assessed using nanoindentation mapping. Importantly, achieving the desired film stiffness requires much lower polymer modification when box-drying is used, enhancing the biological response to the material. These findings have implications for all polysaccharide formulations that utilize mixed solvents.

Recent advances and progress in biotemplate catalysts for electrochemical energy storage and conversion

Complex structures and morphologies in nature endow materials with unexpected properties and extraordinary functions. Biotemplating is an emerging strategy for replicating nature structures to obtain materials with unique morphologies and improved properties. Recently, efforts have been made to use bio-inspired species as a template for producing morphology-controllable catalysts. Fundamental information, along with recent advances in biotemplate metal-based catalysts are presented in this review through discussions of various structures and biotemplates employed for catalyst preparation. This review also outlines the recent progress on preparation routes of biotemplate catalysts and discusses how the properties and structures of these templates play a crucial role in the final performance of metal-based catalysts. Additionally, the application of bio-based metal and metal oxide catalysts is highlighted for various key energy and environmental technologies, including photocatalysis, fuel cells, and lithium batteries. Biotemplate metal-based catalysts display high efficiency in several energy and environmental systems. Note that this review provides guidance for further research in this direction.

Macrocyclic Supramolecular Assemblies Based on Hyaluronic Acid and Their Biological Applications

Hyaluronic acid (HA), which contains multiple carboxyl, hydroxyl, and acetylamino groups and is an agent that targets tumors, has drawn great attention in supramolecular diagnosis and treatment research. It can not only assemble directly with macrocyclic host-guest complexes through hydrogen bonding and electrostatic interactions but also can be modified with macrocyclic compounds or functional guest molecules by an amidation reaction and used for further assembly. Macrocycles play a main role in the construction of supramolecular drug carriers, targeted imaging agents, and hydrogels, such as cyclodextrins and cucurbit[n]urils, which can encapsulate photosensitizers, drugs, or other functional guest molecules via host-guest interactions. Therefore, the formed supramolecular assemblies can respond to various stimuli, such as enzymes, light, electricity, and magnetism for controlled drug delivery, enhance the luminescence intensity of the assembly, and improve drug loading capacity. In addition, the nanosupramolecular assembly formed with HA can also improve the biocompatibility of drugs, reduce drug toxicity and side effects, and enhance cell permeability; thus, the assembly has extensive application value in biomedical research. This Account mainly focuses on macrocyclic supramolecular assemblies based on HA, especially their biological applications and progress in the field, and these assemblies include (i) guest-modified HA, such as pyridinium-, adamantane-, peptide-, and other functional-group-modified HA, along with their cyclodextrin and cucurbit[n]uril assemblies; (ii) macrocycle-modified HA, such as HA modified with cyclodextrins and cucurbit[n]uril derivatives and their assembly with various guests; (iii) direct assembly between unmodified HA and cyclodextrin- or cucurbit[n]uril-based host-guest complexes. Particularly, we discussed the important role of macrocyclic host-guest complexes in HA-based supramolecular assembly, and the roles included improving the water solubility and efficacy of hydrophobic drugs, enhancing the luminescent intensity of assemblies, inducing room temperature phosphorescence and providing energy transfer systems, constructing multi-stimulus-responsive supramolecular assemblies, and in situ formation of hydrogels. Additionally, we believe that obtaining in-depth knowledge of these HA-based macrocyclic supramolecular assemblies and their biological applications encompasses many challenges regarding drug carriers, targeted imaging agents, wound healing, and biomedical soft materials and would certainly contribute to the rapid development of supramolecular diagnosis and treatment.

Macromolecular Solute Transport in Supramolecular Hydrogels Spanning Dynamic to Quasi-Static States

Hydrogels prepared from supramolecular cross-linking motifs are appealing for use as biomaterials and drug delivery technologies. The inclusion of macromolecules (e.g., protein therapeutics) in these materials is relevant to many of their intended uses. However, the impact of dynamic network cross-linking on macromolecule diffusion must be better understood. Here, hydrogel networks with identical topology but disparate cross-link dynamics are explored. These materials are prepared from cross-linking with host-guest complexes of the cucurbit[7]uril (CB[7]) macrocycle and two guests of different affinity. Rheology confirms differences in bulk material dynamics arising from differences in cross-link thermodynamics. Fluorescence recovery after photobleaching (FRAP) provides insight into macromolecule diffusion as a function of probe molecular weight and hydrogel network dynamics. Together, both rheology and FRAP enable the estimation of the mean network mesh size, which is then related to the solute hydrodynamic diameters to further understand macromolecule diffusion. Interestingly, the thermodynamics of host-guest cross-linking are correlated with a marked deviation from classical diffusion behavior for higher molecular weight probes, yielding solute aggregation in high-affinity networks. These studies offer insights into fundamental macromolecular transport phenomena as they relate to the association dynamics of supramolecular networks. Translation of these materials from in vitro to in vivo is also assessed by bulk release of an encapsulated macromolecule. Contradictory in vitro to in vivo results with inverse relationships in release between the two hydrogels underscores the caution demanded when translating supramolecular biomaterials into application.

Multicharged cyclodextrin supramolecular assemblies

Multicharged cyclodextrin (CD) supramolecular assemblies, including those based on positively/negatively charged modified mono-6-deoxy-CDs, per-6-deoxy-CDs, and random 2,3,6-deoxy-CDs, as well as parent CDs binding positively/negatively charged guests, have been extensively applied in chemistry, materials science, medicine, biological science, catalysis, and other fields. In this review, we primarily focus on summarizing the recent advances in positively/negatively charged CDs and parent CDs encapsulating positively/negatively charged guests, especially the construction process of supramolecular assemblies and their applications. Compared with uncharged CDs, multicharged CDs display remarkably high antiviral and antibacterial activity as well as efficient protein fibrosis inhibition. Meanwhile, charged CDs can interact with oppositely charged dyes, drugs, polymers, and biomacromolecules to achieve effective encapsulation and aggregation. Consequently, multicharged CD supramolecular assemblies show great advantages in improving drug-delivery efficiency, the luminescence properties of materials, molecular recognition and imaging, and the toughness of supramolecular hydrogels, in addition to enabling the construction of multistimuli-responsive assemblies. These features are anticipated to not only promote the development of CD-based supramolecular chemistry but also contribute to the rapid exploitation of these assemblies in diverse interdisciplinary applications.

Bioprinting of Complex Multicellular Organs with Advanced Functionality-Recent Progress and Challenges Ahead

Bioprinting has emerged as one of the most promising strategies for fabrication of functional organs in the lab as an alternative to transplant organs. While progress in the field has mostly been restricted to a few miniaturized tissues with minimal biological functionality until a few years ago, recent progress has advanced the concept of building three-dimensional multicellular organ complexity remarkably. This review discusses a series of milestones that have paved the way for bioprinting of tissue constructs that have advanced levels of biological and architectural functionality. Critical materials, engineering and biological challenges that are key to addressing the desirable function of engineered organs are presented. These are discussed in light of the many difficulties to replicate the heterotypic organization of multicellular solid organs, the nanoscale precision of the extracellular microenvironment in hierarchical tissues, as well as the advantages and limitations of existing bioprinting methods to adequately overcome these barriers. In summary, the advances of the field toward realistic manufacturing of functional organs have never been so extensive, and this manuscript serves as a road map for some of the recent progress and the challenges ahead.

A Biocompatible Therapeutic Catheter-Deliverable Hydrogel for In Situ Tissue Engineering

Hydrogels have emerged as a diverse class of biomaterials offering a broad range of biomedical applications. Specifically, injectable hydrogels are advantageous for minimally invasive delivery of various therapeutics and have great potential to treat a number of diseases. However, most current injectable hydrogels are limited by difficult and time-consuming fabrication techniques and are unable to be delivered through long, narrow catheters, preventing extensive clinical translation. Here, the development of an easily-scaled, catheter-injectable hydrogel utilizing a polymer-nanoparticle crosslinking mechanism is reported, which exhibits notable shear-thinning and self-healing behavior. Gelation of the hydrogel occurs immediately upon mixing the biochemically modified hyaluronic acid polymer with biodegradable nanoparticles and can be easily injected through a high-gauge syringe due to the dynamic nature of the strong, yet reversible crosslinks. Furthermore, the ability to deliver this novel hydrogel through a long, narrow, physiologically-relevant catheter affixed with a 28-G needle is highlighted, with hydrogel mechanics unchanged after delivery. Due to the composition of the gel, it is demonstrated that therapeutics can be differentially released with distinct elution profiles, allowing precise control over drug delivery. Finally, the cell-signaling and biocompatibility properties of this innovative hydrogel are demonstrated, revealing its wide range of therapeutic applications.

Jammed Microgel Inks for 3D Printing Applications

3D printing involves the development of inks that exhibit the requisite properties for both printing and the intended application. In bioprinting, these inks are often hydrogels with controlled rheological properties that can be stabilized after deposition. Here, an alternate approach is developed where the ink is composed exclusively of jammed microgels, which are designed to incorporate a range of properties through microgel design (e.g., composition, size) and through the mixing of microgels. The jammed microgel inks are shear-thinning to permit flow and rapidly recover upon deposition, including on surfaces or when deposited in 3D within hydrogel supports, and can be further stabilized with secondary cross-linking. This platform allows the use of microgels engineered from various materials (e.g., thiol-ene cross-linked hyaluronic acid (HA), photo-cross-linked poly(ethylene glycol), thermo-sensitive agarose) and that incorporate cells, where the jamming process and printing do not decrease cell viability. The versatility of this particle-based approach opens up numerous potential biomedical applications through the printing of a more diverse set of inks.

Supramolecular and dynamic covalent hydrogel scaffolds: from gelation chemistry to enhanced cell retention and cartilage regeneration

This review highlights the most recent progress in gelation strategies of biomedical supramolecular and dynamic covalent crosslinking hydrogels and their applications for enhancing cell retention and cartilage regeneration.

Sustained delivery of anti-VEGFs from thermogel depots inhibits angiogenesis without the need for multiple injections

Polyurethane thermogels show sustained delivery of bioactive anti-VEGFs therapeutics to the eye.

Functional Hydrogels With Tunable Structures and Properties for Tissue Engineering Applications

Tissue engineering (TE) has been used as an attractive and efficient process to restore the original tissue structures and functions through the combination of biodegradable scaffolds, seeded cells, and biological factors. As a unique type of scaffolds, hydrogels have been frequently used for TE because of their similar 3D structures to the native extracellular matrix (ECM), as well as their tunable biochemical and biophysical properties to control cell functions such as cell adhesion, migration, proliferation, and differentiation. Various types of hydrogels have been prepared from naturally derived biomaterials, synthetic polymers, or their combination, showing their promise in TE. This review summarizes the very recent progress of hydrogels used for TE applications. The strategies for tuning biophysical and biochemical properties, and structures of hydrogels are first introduced. Their influences on cell functions and promotive effects on tissue regeneration are then highlighted.

Supramolecular polymeric biomaterials

Polymeric chains crosslinked through supramolecular interactions-directional and reversible non-covalent interactions-compose an emerging class of modular and tunable biomaterials. The choice of chemical moiety utilized in the crosslink affords different thermodynamic and kinetic parameters of association, which in turn illustrate the connectivity and dynamics of the system. These parameters, coupled with the choice of polymeric architecture, can then be engineered to control environmental responsiveness, viscoelasticity, and cargo diffusion profiles, yielding advanced biomaterials which demonstrate rapid shear-thinning, self-healing, and extended release. In this review we examine the relationship between supramolecular crosslink chemistry and biomedically relevant macroscopic properties. We then describe how these properties are currently leveraged in the development of materials for drug delivery, immunology, regenerative medicine, and 3D-bioprinting (253 references).

Incorporating β-cyclodextrin into collagen scaffolds to sequester growth factors and modulate mesenchymal stem cell activity

The development of biomaterials for a range of tissue engineering applications increasingly requires control over the bioavailability of biomolecular cues such as growth factors in order to promote desired cell responses. While efforts have predominantly concentrated on covalently-bound or freely-diffusible incorporation of biomolecules in porous, three-dimensional biomaterials, opportunities exist to exploit transient interactions to concentrate growth factor activity over desired time frames. Here, we report the incorporation of β-cyclodextrin into a model collagen-GAG scaffold as a means to exploit the passive sequestration and release of growth factors via guest-host interactions to control mesenchymal stem cell differentiation. Collagen-GAG scaffolds that incorporate β-cyclodextrin show improved sequestration as well as extended retention and release of TGF-β1. We further show extended retention and release of TGF-β1 and BMP-2 from β-cyclodextrin modified scaffolds was sufficient to influence the metabolic activity and proliferation of mesenchymal stem cells as well as differential activation of Smad 2/3 and Smad 1/5/8 pathways associated with differential osteo-chondral differentiation. Further, gene expression analysis showed TGF-β1 release from β-cyclodextrin CG scaffolds promoted early chondrogenic-specific differentiation. Ultimately, this work establishes a novel method for the incorporation and display of growth factors within CG scaffolds via supramolecular interactions. Such a design framework offers opportunities to selectively alter the bioavailability of multiple biomolecules within a three-dimensional collagen-GAG scaffold to enhance cell activity for a range of musculoskeletal regenerative medicine applications.

STATEMENT OF SIGNIFICANCE

We describe the incorporation of β-cyclodextrin into a model CG-scaffold under development for musculoskeletal tissue engineering applications. We show β-cyclodextrin modified scaffolds promote the sequestration of soluble TGF-β1 and BMP-2 via guest-host interactions, leading to extended retention and release. Further, β-cyclodextrin modified CG scaffolds promote TGF-β1 or BMP-2 specific Smad signaling pathway activation associated with divergent osseous versus chondrogenic differentiation pathways in mesenchymal stem cells.

Injectable, Guest-Host Assembled Polyethylenimine Hydrogel for siRNA Delivery

While siRNA has tremendous potential for therapeutic applications, advancement is limited by poor delivery systems. Systemically, siRNAs are rapidly degraded, may have off-target silencing, and necessitate high working concentrations. To overcome this, we developed an injectable, guest-host assembled hydrogel between polyethylenimine (PEI) and polyethylene glycol (PEG) for local siRNA delivery. Guest-host modified polymers assembled with siRNAs to form polyplexes that had improved transfection and viability compared to PEI. At higher concentrations, these polymers assembled into shear-thinning hydrogels that rapidly self-healed. With siRNA encapsulation, the assemblies eroded as polyplexes which were active and transfected cells, observed by Cy3-siRNA uptake or GFP silencing in vitro. When injected into rat myocardium, the hydrogels localized polyplex release, observed by uptake of Cy5.5-siRNA and silencing of GFP for 1 week in a GFP-expressing rat. These results illustrate the potential for this system to be applied for therapeutic siRNA delivery, such as in cardiac pathologies.

A supramolecular self-assembly host–guest system from cyclodextrin as an absolute water-soluble fluorescence sensor for aluminium ions: synthesis, characterization and sensing activity

In the study, an organic molecule derived from paeonol and anthraniloyl hydrazine (L) was synthesized via a Schiff-base reaction.