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.

Injectable On-Demand Pulsatile Drug Delivery Hydrogels Using Alternating Magnetic Field-Triggered Polymer Glass Transitions

Remote-controlled pulsatile or staged release has significant potential in a wide range of therapeutic treatments. However, most current approaches are hindered by the low resolution between the on- and off-states of drug release and the need for surgical implantation of larger controlled-release devices. Herein, we describe a method that addresses these limitations by combining injectable hydrogels, superparamagnetic iron oxide nanoparticles (SPIONs) that heat when exposed to an alternating magnetic field (AMF), and polymeric nanoparticles with a glass transition temperature (Tg) just above physiological temperature. Miniemulsion polymerization was used to fabricate poly(methyl methacrylate-co-butyl methacrylate) (p(MMA-co-BMA)) nanoparticles loaded with a model hydrophobic drug and tuned to have a Tg value just above physiological temperature (∼43 °C). Co-encapsulation of these drug-loaded nanoparticles with SPIONs inside a carbohydrate-based injectable hydrogel matrix (formed by rapid hydrazone cross-linking chemistry) enables injection and immobilization of the nanoparticles at the target site. Temperature cycling facilitated a 2.5:1 to 6:1 on/off rhodamine release ratio when the nanocomposites were switched between 37 and 45 °C; release was similarly enhanced by exposing the nanocomposite hydrogel to an AMF to drive heating, with enhanced release upon pulsing observed even 1 week after injection. Coupled with the apparent cytocompatibility of all of the nanocomposite components, these injectable nanocomposite hydrogels are promising as minimally invasive but remotely actuated release delivery vehicles capable of complex release kinetics with high on-off resolution.

Communication Protocols Integrating Wearables, Ingestibles, and Implantables for Closed-Loop Therapies

Body-conformal sensors and tissue interfacing robotic therapeutics enable the real-time monitoring and treatment of diabetes, wound healing, and other critical conditions. By integrating sensors and drug delivery devices, scientists and engineers have developed closed-loop drug delivery systems with on-demand therapeutic capabilities to provide just-in-time treatments that correspond to chemical, electrical, and physical signals of a target morbidity. To enable closed-loop functionality in vivo, engineers utilize various low-power means of communication that reduce the size of implants by orders of magnitude, increase device lifetime from hours to months, and ensure the secure high-speed transfer of data. In this review, we highlight how communication protocols used to integrate sensors and drug delivery devices, such as radio frequency communication (e.g., Bluetooth, near-field communication), in-body communication, and ultrasound, enable improved treatment outcomes.

Chemical modification of β-cyclodextrin towards hydrogel formation

β-CD is a cyclic oligosaccharide, which has trunked cone like structure. The unique structure makes it efficient for numerous applications. Though, the native β-CD has many issues like low solubility, absence of sufficient functionalities and lower complexation ability with guest molecules. One of the most effective paths to increase the efficiency of cyclodextrins is the generation of polycyclodextrins. In this perspective article, we have summarized the recent reports on the synthetic methods towards the modification of β-CD. Besides, this article reviews the current improvements of two types of β-CD centered supramolecular hydrogels: one is supramolecular hydrogels prepared from CD-based poly(pseudo)rotaxanes and the other is supramolecular hydrogels developed through the host-guest interaction between small guest molecules and CDs. The Polycyclodextrins have established noteworthy applications in several areas ranging from adsorbents for organic pollutants removal to effective carriers of bioactive agents.

Tofacitinib combined with melanocyte protector α-MSH to treat vitiligo through dextran based hydrogel microneedles

Vitiligo can cause serious damage to the appearance of patients and affect physical and mental health, but there is currently no simple and effective treatment. According to the theory of autoimmune disorder, the separable hydrogel microneedles delivering alpha-melanocyte-stimulating hormone (α-MSH) and tofacitinib were designed to treat vitiligo. This hydrogel microneedles were formed by dextran methacrylate (DexMA) and cyclodextrin-adamantane based host-guest supramolecules (HGSM) through CC double bond polymerization and host-guest assembly. The microneedle tips formed by the double cross-linked hydrogel can pierce the stratum corneum and deliver melanocyte protector α-MSH and JAK inhibitor tofacitinib directly to the epidermis and dermis. Under the treatment of α-MSH/tofacitinib microneedles, massive deposition of melanin in epidermis and hair follicles significantly accelerated skin and hair pigmentation.

Newly developed nano-biocomposite embedded hydrogel to enhance drug loading and modulated release of anti-inflammatory drug

A newly developed iron-based nano-biocomposite (nano Fe-CNB) impregnated alginate formulation (CA) is proposed to improve drug loading and exhibit pH-responsive behavior of model anti-inflammatory drug-ibuprofen for controlled release applications. The proposed formulation is investigated with conventional β-CD addition in CA. The nano Fe-CNB-based formulations with and without β-CD, (Fe-CNB β-CD CA and Fe-CNB CA) are compared with only CA and β-CD incorporated CA formulations. The results indicate the incorporation of nano-biocomposite or β-CD into CA enhances the drug loading (>40%). However, pH-responsive controlled release behavior is observed for nano Fe-CNB based formulations only. The release studies from Fe-CNB β-CD CA indicate ∼ 45% release in stomach pH (1.2) within 2 h. In contrast, Fe-CNB CA shows ∼20% release only in stomach pH and improved release (∼49%) at colon pH (7.4). The rheology and swelling studies indicate Fe-CNB CA remains intact in stomach pH with a minimal drug release, but it disintegrates at colon pH due to charge reversal behavior of nano-biocomposite and ionization of polymeric chains. Thus, Fe-CNB CA formulation is found to be a potential candidate for targeting colon delivery, inflammatory bowel disease, and post-operative conditions.

In situ forming gelatin: Cyclodextrin hydrogels prepared by “click chemistry” to improve the sustained release of hydrophobic drugs

Injectable hydrogels offer a wide range of attractive benefits in drug delivery applications, such as non-invasive administration, easy drug incorporation and locally controlled release at the target sites. Herein, we designed a simple and efficient method to prepare injectable hydrogels composed of gelatin and cyclodextrin (CD) for high loading capacity of hydrophobic drugs. The hydrogels were formed by thiol-functionalized gelatin (GSH) and βCD-vinyl sulfone (βCD-VS) as cross-linker, via thiol-ene “click” chemistry. Hydrogels comprising of different cross-linker feed amount were investigated in terms of their physico-chemical properties, such as gelation time, mechanical strength, swelling ratio, porosity and degradation rates. For the use as a drug delivery vehicle, dexamethasone (DEX), a commonly anti-inflammatory, immunosuppressive but poorly water soluble drug was chosen to show the high drug loading capacity and prolonged drug release of hydrogels. The drug release was found to be depended on the concentration of βCD-VS due to the drug-CD interaction. In vitro cytotoxicity experiment also showed the cell compatibility of these hydrogels against human dermal fibroblasts. In summary, we expect this gelatin-CD “click” hydrogel will be a promising candidate for localized and long-term delivery of hydrophobic drugs.

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

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

Fe3+-citric acid/sodium alginate hydrogel: A photo-responsive platform for rapid water purification

As water pollution in human society becomes more and more serious, the demand for materials that can be used for wastewater treatment is increasing. Here, we reported a sodium alginate-based hydrogel (Fe³⁺-CA/SA hydrogel) that can efficiently photocatalyze the degradation of malachite green. The Fe³⁺-CA/SA hydrogel is composed of sodium alginate, citric acid, and Fe³⁺. The hydrogel has multi-leveled pore structure and photochromic ability. Benefiting from the unique microstructure and positive feedback chemical reaction process, the hydrogel has high photocatalytic efficiency. Under 365 nm UV light irradiation, the hydrogel can degrade around 95% of malachite green (20 mg/L) in about 4 min, and there is no need to add H₂O₂ in the degradation process. The work helps to expand the application of sodium alginate-based hydrogels in the field of water treatment. It also has exploratory significance for the principle of photocatalytic degradation of malachite green.

Chemically Modified Biopolymers for the Formation of Biomedical Hydrogels

Biopolymers are natural polymers sourced from plants and animals, which include a variety of polysaccharides and polypeptides. The inclusion of biopolymers into biomedical hydrogels is of great interest because of their inherent biochemical and biophysical properties, such as cellular adhesion, degradation, and viscoelasticity. The objective of this Review is to provide a detailed overview of the design and development of biopolymer hydrogels for biomedical applications, with an emphasis on biopolymer chemical modifications and cross-linking methods. First, the fundamentals of biopolymers and chemical conjugation methods to introduce cross-linking groups are described. Cross-linking methods to form biopolymer networks are then discussed in detail, including (i) covalent cross-linking (e.g., free radical chain polymerization, click cross-linking, cross-linking due to oxidation of phenolic groups), (ii) dynamic covalent cross-linking (e.g., Schiff base formation, disulfide formation, reversible Diels-Alder reactions), and (iii) physical cross-linking (e.g., guest-host interactions, hydrogen bonding, metal-ligand coordination, grafted biopolymers). Finally, recent advances in the use of chemically modified biopolymer hydrogels for the biofabrication of tissue scaffolds, therapeutic delivery, tissue adhesives and sealants, as well as the formation of interpenetrating network biopolymer hydrogels, are highlighted.

Smart near infrared-responsive nanocomposite hydrogels for therapeutics and diagnostics

Nanocomposite (NC) hydrogels are emerging biomaterials that possess desirable and defined properties and functions for therapeutics and diagnostics. Particularly, nanoparticles (NPs) are employed as stimulus-transducers in NC hydrogels to facilitate the treatment process by providing controllable structural change and payload release under internal and external simulations. Among the various external stimuli, near-infrared (NIR) light has attracted considerable interest due to its minimal photo-damage, deep tissue penetration, low auto-fluorescence in living systems, facile on/off switch, easy remote and spatiotemporal control. In this study, we discuss four types of transducing nanomaterials used in NIR-responsive NC hydrogels, including metal-based nanoparticles, carbon-based nanomaterials, polydopamine nanoparticles (PDA NPs), and upconversion nanoparticles (UCNPs). This review provides an overview of the current progress in NIR-responsive NC hydrogels, focusing on their preparation, properties, applications, and future prospects.

Polymeric Hydrogel Scaffolds: Skin Tissue Engineering and Regeneration

Tissue engineering is a novel regenerative approach in the medicinal field that promises the regeneration of damaged tissues. Moreover, tissue engineering involves synthetic and natural biomaterials that facilitate tissue or organ growth outside the body. Not surprisingly, the demand for polymer-based therapeutical approaches in skin tissue defects has increased at an effective rate, despite the pressing clinical need. Among the 3D scaffolds for tissue engineering and regeneration approaches, hydrogel scaffolds have shown significant importance for their use as 3D cross-linked scaffolds in skin tissue regeneration due to their ideal moisture retention property and porosity biocompatibility, biodegradable, and biomimetic characteristics. In this review, we demonstrated the choice of ideal biomaterials to fabricate the novel hydrogel scaffolds for skin tissue engineering. After a short introduction to the bioactive and drug-loaded polymeric hydrogels, the discussion turns to fabrication and characterisation techniques of the polymeric hydrogel scaffolds. In conclusion, we discuss the excellent wound healing potential of stem cell-loaded hydrogels and Nano-based approaches to designing hydrogel scaffolds for skin tissue engineering.

Scaling Laws in the Diffusive Release of Neutral Cargo from Hollow Hydrogel Nanoparticles: Paclitaxel-Loaded Poly(4-vinylpyridine)

We study the nonequilibrium diffusive release of electroneutral molecular cargo encapsulated inside hollow hydrogel nanoparticles. We propose a theoretical model that includes osmotic, steric, and short-range polymer-cargo attractions to determine the effective cargo-hydrogel interaction, u_eff*, and the effective diffusion coefficient of the cargo inside the polymer network, D_eff*. Using dynamical density functional theory (DDFT), we investigate the scaling of the characteristic release time, τ_1/2, with the key parameters involved in the process, namely, u_eff*, D_eff*, and the swelling ratio. This effort represents a full study of the problem, covering a broad range of cargo sizes and providing predictions for repulsive and attractive polymer shells. Our calculations show that the release time through repulsive polymer networks scales with q²e^βu_eff*/D_eff* for βu_eff* ≫ 1. In this case, the cargo molecules are excluded from the shell of the hydrogel. For attractive shells, the polymer retains the cargo molecules on its internal surface and its interior, and the release time grows exponentially with the attraction strength. The DDFT calculations are compared to an analytical model for the mean first passage time, which provides an excellent quantitative description of the kinetics for both repulsive and attractive shells without fitting parameters. Finally, we apply the method to reproduce experimental results on the release of paclitaxel from hollow poly(4-vinylpyridine) nanoparticles and find that the slow release of the drug can be explained in terms of the strong binding attraction between the drug and the polymer.

Stimuli-responsive graphene-based hydrogel driven by disruption of triazine hydrophobic interactions

The study reported here concerns the preparation of a novel graphene-diaminotriazine (G-DAT) nanocomposite hydrogel for application in the drug delivery field. The hybrid nature of this material is founded on two key elements: the presence of the DAT backbone induced the formation of hydrophobic regions that allowed efficient loading of a series of drugs of increasing hydrophobicity (Metronidazole, Benzocaine, Ibuprofen, Naproxen and Imipramine), while simultaneously endowing swelling-induced pH-responsiveness to the hydrogel. Additionally, the incorporation of graphene was found to interfere with these hydrophobic domains through favourable non-covalent interactions, thus leading to the partial disruption of these aggregates. As a consequence, graphene facilitated and enhanced the release of model hydrophobic drug Imipramine in a synergistic manner with the pH trigger, and increased the swelling capacities and improved mechanical performance. This hybrid hydrogel can therefore be envisaged as a proof-of-concept system for the release of hydrophobic compounds in the field of drug delivery.

Targeted Drug Delivery via the Use of ECM-Mimetic Materials

The use of drug delivery vehicles to improve the efficacy of drugs and to target their action at effective concentrations over desired periods of time has been an active topic of research and clinical investigation for decades. Both synthetic and natural drug delivery materials have facilitated locally controlled as well as targeted drug delivery. Extracellular matrix (ECM) molecules have generated widespread interest as drug delivery materials owing to the various biological functions of ECM. Hydrogels created using ECM molecules can provide not only biochemical and structural support to cells, but also spatial and temporal control over the release of therapeutic agents, including small molecules, biomacromolecules, and cells. In addition, the modification of drug delivery carriers with ECM fragments used as cell-binding ligands has facilitated cell-targeted delivery and improved the therapeutic efficiency of drugs through interaction with highly expressed cellular receptors for ECM. The combination of ECM-derived hydrogels and ECM-derived ligand approaches shows synergistic effects, leading to a great promise for the delivery of intracellular drugs, which require specific endocytic pathways for maximal effectiveness. In this review, we provide an overview of cellular receptors that interact with ECM molecules and discuss examples of selected ECM components that have been applied for drug delivery in both local and systemic platforms. Finally, we highlight the potential impacts of utilizing the interaction between ECM components and cellular receptors for intracellular delivery, particularly in tissue regeneration applications.

Cyclodextrin embedded covalently crosslinked networks: synthesis and applications of hydrogels with nano-containers

Recent advancements in the synthesis of hydrogels containing cyclodextrin (CD) units within the gel network have been reviewed.

Peptide-/Drug-Directed Self-Assembly of Hybrid Polyurethane Hydrogels for Wound Healing

Drug-loading hydrogels are promising candidates in the bioengineering research field; nevertheless, hydrophobic drug loading into a hydrophilic carrier system remains unsolved and is full of challenges. In this work, following the potential dual interactions between peptides and aromatic drugs, we developed a potent hybrid hydrogel formation method, namely, "peptide-/drug-directed self-assembly". The hybrid hydrogels were synthesized using polyethylene glycol (PEG)-based Fmoc-FF peptide hybrid polyurethane, in which curcumin could be encapsulated through self-assembly with Fmoc-FF peptide via π-π stacking. On the basis of this, curcumin loading capacity could be improved to as high as 3.3 wt % with sustained release. In addition, the curcumin loading enhanced the hydrogel mechanical properties from 4 kPa to over 10 kPa, similar to that of natural soft tissues. Furthermore, the hydrogels were injectable with self-healing properties since the Fmoc-FF peptide/curcumin coassembly was noncovalent and reversible. Spectroscopy results confirmed the existence of the coassembly of Fmoc-FF peptide/curcumin. Further in vivo experiments effectively demonstrated that the hydrogels could improve the cutaneous wound healing in a full-thickness skin defected model. This peptide-/drug-directed self-assembly of hybrid polyurethane hydrogel could be used as a promising platform for tissue-engineering scaffold and biomedical application.

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).

Dual pH-/temperature-responsive and fluorescent hydrogel for controlled drug delivery

The purpose of this investigation is to develop a dual pH-/temperature-responsive and fluorescent hydrogel based on piperazine and Pluronic F127 (PF127). Firstly, polyurethane was synthesized using 1,6-hexamethylene diisocyanate, 1,4-bis(hydroxyethyl) piperazine, and PF127 by a step polymerization process. Erythrosine B (EB) is then incorporated into copolymers to offer a fluorescence property. The polyurethane-PF127-EB copolymer can spontaneously self-assemble into hydrogels with a great number of closely packed micelles, and the hydrogels also have the ability to undergo thermo-sensitive sol-gel phase transition above the critical gelation concentration. The gelation temperature can be adjusted near the physiological condition by modulating the concentration of the copolymer in an aqueous medium. The acid-titration curves indicate a good pH-responsive property, and the UV-vis and fluorescence spectra exhibit strong self-fluorescence signals for hydrogels. As a result, the hydrogels not only can serve as drug carriers but can also be utilized as fluorescence imaging probes in biomedical applications.

In situ forming injectable hydrogels for drug delivery and wound repair

Hydrogels have been utilized in regenerative applications for many decades because of their biocompatibility and similarity in structure to the native extracellular matrix. Initially, these materials were formed outside of the patient and implanted using invasive surgical techniques. However, advances in synthetic chemistry and materials science have now provided researchers with a library of techniques whereby hydrogel formation can occur in situ upon delivery through standard needles. This provides an avenue to minimally invasively deliver therapeutic payloads, fill complex tissue defects, and induce the regeneration of damaged portions of the body. In this review, we highlight these injectable therapeutic hydrogel biomaterials in the context of drug delivery and tissue regeneration for skin wound repair.

Injectable and body temperature sensitive hydrogels based on chitosan and hyaluronic acid for pH sensitive drug release

Hydrogels based on chitosan/hyaluronic acid/β-sodium glycerophosphate demonstrate injectability, body temperature sensitivity, pH sensitive drug release and adhesion to cancer cell. The drug (doxorubicin) loaded hydrogel precursor solutions are injectable and turn to hydrogels when the temperature is increased to body temperature. The acidic condition (pH 4.00) can trigger the release of drug and the cancer cell (Hela) can adhere to the surface of the hydrogels, which will be beneficial for tumor site-specific administration of drug. The mechanical strength, the gelation temperature, and the drug release behavior can be tuned by varying hyaluronic acid content. The mechanisms were characterized using dynamic mechanical analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and fluorescence microscopy. The carboxyl group in hyaluronic acid can form the hydrogen bondings with the protonated amine in chitosan, which promotes the increase of mechanical strength of the hydrogels and depresses the initial burst release of drug from the hydrogel.

Chemical Synthesis of Biomimetic Hydrogels for Tissue Engineering

Owing to the high water content, porous structure, biocompatibility and tissue-like viscoelasticity, hydrogels have become attractive and promising biomaterials for use in drug delivery, 3D cell culture and tissue engineering applications. Various chemical approaches have been developed for hydrogel synthesis using monomers or polymers carrying reactive functional groups. For in vivo tissue repair and in vitro cell culture purposes, it is desirable that the crosslinking reactions occur under mild conditions, do not interfere with biological processes and proceed at high yield with exceptional selectivity. Additionally, the cross-linking reaction should allow straightforward incorporation of bioactive motifs or signaling molecules, at the same time, providing tunability of the hydrogel microstructure, mechanical properties, and degradation rates. In this review, we discuss various chemical approaches applied to the synthesis of complex hydrogel networks, highlighting recent developments from our group. The discovery of new chemistries and novel materials fabrication methods will lead to the development of the next generation biomimetic hydrogels with complex structures and diverse functionalities. These materials will likely facilitate the construction of engineered tissue models that may bridge the gap between 2D experiments and animal studies, providing preliminary insight prior to in vivo assessments.

Oxidative Stress Regulation on Endothelial Cells by Hydrophilic Astaxanthin Complex: Chemical, Biological, and Molecular Antioxidant Activity Evaluation

An imbalance in the reactive oxygen species (ROS) homeostasis is involved in the pathogenesis of oxidative stress-related diseases. Astaxanthin, a xanthophyll carotenoid with high antioxidant capacities, has been shown to prevent the first stages of oxidative stress. Here, we evaluate the antioxidant capacities of astaxanthin included within hydroxypropyl-beta-cyclodextrin (CD-A) to directly and indirectly reduce the induced ROS production. First, chemical methods were used to corroborate the preservation of astaxanthin antioxidant abilities after inclusion. Next, antioxidant scavenging properties of CD-A to inhibit the cellular and mitochondrial ROS by reducing the disturbance in the redox state of the cell and the infiltration of lipid peroxidation radicals were evaluated. Finally, the activation of endogenous antioxidant PTEN/AKT, Nrf2/HO-1, and NQOI gene and protein expression supported the protective effect of CD-A complex on human endothelial cells under stress conditions. Moreover, a nontoxic effect on HUVEC was registered after CD-A complex supplementation. The results reported here illustrate the need to continue exploring the interesting properties of this hydrophilic antioxidant complex to assist endogenous systems to counteract the ROS impact on the induction of cellular oxidative stress state.

Designing hydrogels for controlled drug delivery

Hydrogel delivery systems can leverage therapeutically beneficial outcomes of drug delivery and have found clinical use. Hydrogels can provide spatial and temporal control over the release of various therapeutic agents, including small-molecule drugs, macromolecular drugs and cells. Owing to their tunable physical properties, controllable degradability and capability to protect labile drugs from degradation, hydrogels serve as a platform in which various physiochemical interactions with the encapsulated drugs control their release. In this Review, we cover multiscale mechanisms underlying the design of hydrogel drug delivery systems, focusing on physical and chemical properties of the hydrogel network and the hydrogel-drug interactions across the network, mesh, and molecular (or atomistic) scales. We discuss how different mechanisms interact and can be integrated to exert fine control in time and space over the drug presentation. We also collect experimental release data from the literature, review clinical translation to date of these systems, and present quantitative comparisons between different systems to provide guidelines for the rational design of hydrogel delivery systems.

Synthesis of adipic acid dihydrazide-decorated coco peat powder-based superabsorbent for controlled release of soil nutrients

We firstly employ adipic acid dihydrazide as an outstanding decoration substrate for the pretreatment of CP, and then synthesis a novel superabsorbent through grafting AA onto MA modified CP@ADH surface.

Sustained Small Molecule Delivery from Injectable Hyaluronic Acid Hydrogels through Host-Guest Mediated Retention

Self-assembled and injectable hydrogels have many beneficial properties for the local delivery of therapeutics; however, challenges still exist in the sustained release of small molecules from these highly hydrated networks. Host-guest chemistry between cyclodextrin and adamantane has been used to create supramolecular hydrogels from modified polymers. Beyond assembly, this chemistry may also provide increased drug retention and sustained release through the formation of inclusion complexes between drugs and cyclodextrin. Here, we engineered a two-component system from adamantane-modified and β-cyclodextrin (CD)-modified hyaluronic acid (HA), a natural component of the extracellular matrix, to produce hydrogels that are both injectable and able to sustain the release of small molecules. The conjugation of cyclodextrin to HA dramatically altered its affinity for hydrophobic small molecules, such as tryptophan. This interaction led to lower molecule diffusivity and the release of small molecules for up to 21 days with release profiles dependent on CD concentration and drug-CD affinity. There was significant attenuation of release from the supramolecular hydrogels (~20% release in 24h) when compared to hydrogels without CD (~90% release in 24h). The loading of small molecules also had no effect on hydrogel mechanics or self-assembly properties. Finally, to illustrate this controlled delivery approach with clinically used small molecule pharmaceuticals, we sustained the release of two widely used drugs (i.e., doxycycline and doxorubicin) from these hydrogels.

Supramolecular Guest-Host Interactions for the Preparation of Biomedical Materials

Supramolecular chemistry has emerged as an important technique for the formation of biomaterials, including nano- and microparticles and hydrogels. One specific class of supramolecular chemistry is the direct association of guest-host pairs, which involves host macrocycles such as cyclodextrins and cucurbit[n]urils and a wide range of guest molecules, where association is typically driven by molecule size and hydrophobicity. These systems are of particular interest in the biomedical field due to their dynamic nature, chemical diversity, relative ease of synthesis, and ability to interact with biological or synthetic molecules. In this review, we discuss aspects of polymeric material assembly mediated by guest-host interactions, including the fundamentals of assembly into functional biomedical materials. Additionally, applications of biomaterials that utilize guest-host interactions are discussed with a focus on injectable material formulations, the sequestration and delivery of encapsulated cargo (i.e., drugs, biomolecules), and the investigation of cell-material interactions (i.e., adhesion, differentiation, and delivery). While methodologies for guest-host mediated assembly and biological interaction have rapidly evolved in recent years, they remain far from realizing their full potential in the biomaterials field.

Injectable supramolecular hydrogels fabricated from PEGylated doxorubicin prodrug and α-cyclodextrin for pH-triggered drug delivery

Fabrication of in situ forming and acid-labile prodrug-based supramolecular hydrogels with adjustable gelation time for injectable drug delivery carriers.

One-step cross-linked injectable hydrogels with tunable properties for space-filling scaffolds in tissue engineering

One-step cross-linked injectable hydrogels are prepared through Schiff-based reaction with tunable properties for space-filling scaffolds.

Ultrasound accelerated sugar based gel for in situ construction of a Eu3+-based metallogel via energy transfer in a supramolecular scaffold

Phase control on the energy transfer process via an “off–on” approach between a 4-amino-naphthalimide derivative and Eu³⁺ ions was achieved in sugar-based organogel tissue.

Degradable/cytocompatible and pH responsive amphiphilic conetwork gels based on agarose-graft copolymers and polycaprolactone

Amphiphilic conetwork gels based on graft copolymers of agarose and polycaprolactone exhibited desirable cytocompatibility/blood compatibility and pH responsive release of hydrophilic and hydrophobic drugs, and may be suitable for biomedical applications.

In vitro and in vivo assessments of a 3-(3,4-dihydroxyphenyl)-2-propenoic acid bioconjugated gelatin-based injectable hydrogel for biomedical applications

Imparting functional properties on a biomaterial for high end applications is always a challenging task. In the present study, an attempt was made to construct an injectable hydrogel through bioconjugation of dihydroxy phenolic acids to a gelatin backbone. Bioconjugating caffeic acid with gelatin followed by oxidation with mild oxidation agents provided a hydrogel with all the requisite properties (biocompatibility, controlled biodegradability, and antioxidant, antimicrobial and wound healing ability). Bioconjugation was performed using EDC/NHS and the resultant gel named as caffeic acid bioconjugated gel (CBG gel). The physicochemical, rheological, swelling, in vitro (biocompatibility, biodegradability, antimicrobial properties, antioxidant properties and drug release properties) and in vivo (biocompatibility, biodegradability and wound healing properties) studies on the CBG gel were carried out using standard protocols. The bioconjugation was confirmed by ¹H NMR and UV-Vis analysis. Rheological analysis of the CBG gel revealed that the storage modulus was greater than the loss modulus at all the frequencies and suggested the elastic nature of the gel. About 50% weight gain within 12 hours during swelling studies and 50% weight loss within 12 hours during evaporation suggested the suitability of the CBG gel as a drug carrier. The drug release studies implied that there was an initial burst and later the release was sustained. The CBG gel promotes cell migration and demonstrates radical scavenging behavior. When subcutaneously injected into the animal, as in situ CBG gel, the gel was highly biocompatible and did not cause any necrosis. The crosstalk with adjacent tissue cells was smooth and the gel completely degraded within 24 days. The wound healing efficacy on full-thickness wounds suggested that the CBG gel accelerated healing and imparted high strength on the healed skin at an appreciable level. With all these additional functional properties, the CBG gel could be useful for biomedical applications.