Triggerable tough hydrogels for gastric resident dosage forms

Development of Bioorthogonally Degradable Tough Hydrogels Using Enamine N-Oxide Based Crosslinkers

Inducibly degradable polymers present new opportunities to integrate tough hydrogels into a wide range of biomaterials. Rapid and inducible degradation enables fast transition in material properties without sacrificing material integrity prior to removal. In pursuit of bioorthogonal chemical modalities that will enable inducible polymer degradation in biologically relevant environments, enamine N-oxide crosslinkers are developed for double network acrylamide-based polymer/alginate hydrogels. Bioorthogonal dissociation initiated by the application of aqueous diboron solution through several delivery mechanisms effectively lead to polymer degradation. Their degradation by aqueous B2(OH)4 solution results in a fracture energy half-life of <10 min. The biocompatibility of the degradable hydrogels and B2(OH)4 reagent is assessed, and the removability of strongly adhered tough hydrogels on mice skin is evaluated. Thermoresponsive PNiPAAm/Alg hydrogels are fabricated and application of the hydrogels as a chemically inducible degradable intraoral wound dressing is demonstrated. It is demonstrated through in vivo maximum tolerated dose studies that diboron solution administered to mice by oral gavage is well tolerated. Successful integration of enamine N-oxides within the tough double network hydrogels as chemically degradable motifs demonstrates the applicability of enamine N-oxides in the realm of polymer chemistry and highlights the importance of chemically induced bioorthogonal dissociation reactions for materials science.

Advances in Electrically Conductive Hydrogels: Performance and Applications

Electrically conductive hydrogels are highly hydrated 3D networks consisting of a hydrophilic polymer skeleton and electrically conductive materials. Conductive hydrogels have excellent mechanical and electrical properties and have further extensive application prospects in biomedical treatment and other fields. Whereas numerous electrically conductive hydrogels have been fabricated, a set of general principles, that can rationally guide the synthesis of conductive hydrogels using different substances and fabrication methods for various application scenarios, remain a central demand of electrically conductive hydrogels. This paper systematically summarizes the processing, performances, and applications of conductive hydrogels, and discusses the challenges and opportunities in this field. In view of the shortcomings of conductive hydrogels in high electrical conductivity, matchable mechanical properties, as well as integrated devices and machines, it is proposed to synergistically design and process conductive hydrogels with applications in complex surroundings. It is believed that this will present a fresh perspective for the research and development of conductive hydrogels, and further expand the application of conductive hydrogels.

Research progress on the performance of expandable systems for long-term gastric retention

Gastroretentive systems have gained attention due to their prolonged retention time in the human body, and they have the potential to improve treatment effects, simplify treatment regimens, and improve patient compliance. Among these systems, expandable gastroretentive systems (EGRSs) have emerged as an important type of carrier that can reside in the stomach for a desired period through on-demand expansion for drug delivery, obesity intervention, and medical diagnosis. As the physiological environment significantly influences the performance of EGRSs, here, the physiological factors such as the stomach's physiological structure and activity pattern, and the character of gastric juice are summarized. Following this, the research progress of EGRSs from ingestion to removal for long-term gastric retention is discussed with respect to the influencing factors and reinforcement strategies in mechanics. Additionally, as the duration of gastric retention increases, safety concerns arise. As such, safety issues in terms of removal after retention or in an emergency are also analyzed. Finally, the biomedical application of EGRSs as diagnostic and therapeutic tools and the potential direction for further research are discussed. STATEMENT OF SIGNIFICANCE: Expandable gastroretentive systems (EGRSs) resist gastric emptying due to their size exceeding the pylorus diameter, offering promising advantages for obesity intervention, drug delivery, and carrying sensors. However, a long gastroretentive time only by such a size mismatch is hard to be achieved due to the uninterrupted stomach contraction and gastric juice erosion. Recent studies indicate that the retention time and stability of EGRSs can be regulated by adjusting their mechanical properties. Hence, this review summarizes the state-of-art progress of EGRSs for long-term gastric retention from a mechanical perspective for the first time, focuses on material components and synthesis methods, and the reinforcement strategies, and suggests the required mechanical property parameters of EGRSs.

Cell response to extracellular matrix viscous energy dissipation outweighs high-rigidity sensing

The mechanics of the extracellular matrix (ECM) determine cell activity and fate through mechanoresponsive proteins including Yes-associated protein 1 (YAP). Rigidity and viscous relaxation have emerged as the main mechanical properties of the ECM steering cell behavior. However, how cells integrate coexisting ECM rigidity and viscosity cues remains poorly understood, particularly in the high-stiffness regime. Here, we have exploited engineered stiff viscoelastic protein hydrogels to show that, contrary to current models of cell-ECM interaction, substrate viscous energy dissipation attenuates mechanosensing even when cells are exposed to higher effective rigidity. This unexpected behavior is however readily captured by a pull-and-hold model of molecular clutch-based cell mechanosensing, which also recapitulates opposite cellular response at low rigidities. Consistent with predictions of the pull-and-hold model, we find that myosin inhibition can boost mechanosensing on cells cultured on dissipative matrices. Together, our work provides general mechanistic understanding on how cells respond to the viscoelastic properties of the ECM.

Towards multifunctional robotic pills

Robotic pills leverage the advantages of oral pharmaceutical formulations-in particular, convenient encapsulation, high loading capacity, ease of manufacturing and high patient compliance-as well as the multifunctionality, increasing miniaturization and sophistication of microrobotic systems. In this Perspective, we provide an overview of major innovations in the development of robotic pills-specifically, oral pills embedded with robotic capabilities based on microneedles, microinjectors, microstirrers or microrockets-summarize current progress and applicational gaps of the technology, and discuss its prospects. We argue that the integration of multiple microrobotic functions within oral delivery systems alongside accurate control of the release characteristics of their payload provides a basis for realizing sophisticated multifunctional robotic pills that operate as closed-loop systems.

Multifaceted Hydrogel Scaffolds: Bridging the Gap between Biomedical Needs and Environmental Sustainability

Hydrogels are dynamically evolving 3D networks composed of hydrophilic polymer scaffolds with significant applications in the healthcare and environmental sectors. Notably, protein-based hydrogels mimic the extracellular matrix, promoting cell adhesion. Further enhancing cell proliferation within these scaffolds are matrix-metalloproteinase-triggered amino acid motifs. Integration of cell-friendly modules like peptides and proteins expands hydrogel functionality. These exceptional properties position hydrogels for diverse applications, including biomedicine, biosensors, environmental remediation, and the food industry. Despite significant progress, there is ongoing research to optimize hydrogels for biomedical and environmental applications further. Engineering novel hydrogels with favorable characteristics is crucial for regulating tissue architecture and facilitating ecological remediation. This review explores the synthesis, physicochemical properties, and biological implications of various hydrogel types and their extensive applications in biomedicine and environmental sectors. It elaborates on their potential applications, bridging the gap between advancements in the healthcare sector and solutions for environmental issues.

Mechanical Regulation of Polymer Gels

The mechanical properties of polymer gels devote to emerging devices and machines in fields such as biomedical engineering, flexible bioelectronics, biomimetic actuators, and energy harvesters. Coupling network architectures and interactions has been explored to regulate supportive mechanical characteristics of polymer gels; however, systematic reviews correlating mechanics to interaction forces at the molecular and structural levels remain absent in the field. This review highlights the molecular engineering and structural engineering of polymer gel mechanics and a comprehensive mechanistic understanding of mechanical regulation. Molecular engineering alters molecular architecture and manipulates functional groups/moieties at the molecular level, introducing various interactions and permanent or reversible dynamic bonds as the dissipative energy. Molecular engineering usually uses monomers, cross-linkers, chains, and other additives. Structural engineering utilizes casting methods, solvent phase regulation, mechanochemistry, macromolecule chemical reactions, and biomanufacturing technology to construct and tailor the topological network structures, or heterogeneous modulus compositions. We envision that the perfect combination of molecular and structural engineering may provide a fresh view to extend exciting new perspectives of this burgeoning field. This review also summarizes recent representative applications of polymer gels with excellent mechanical properties. Conclusions and perspectives are also provided from five aspects of concise summary, mechanical mechanism, biofabrication methods, upgraded applications, and synergistic methodology.

Drinkable in situ-forming tough hydrogels for gastrointestinal therapeutics

Pills are a cornerstone of medicine but can be challenging to swallow. While liquid formulations are easier to ingest, they lack the capacity to localize therapeutics with excipients nor act as controlled release devices. Here we describe drug formulations based on liquid in situ-forming tough (LIFT) hydrogels that bridge the advantages of solid and liquid dosage forms. LIFT hydrogels form directly in the stomach through sequential ingestion of a crosslinker solution of calcium and dithiol crosslinkers, followed by a drug-containing polymer solution of alginate and four-arm poly(ethylene glycol)-maleimide. We show that LIFT hydrogels robustly form in the stomachs of live rats and pigs, and are mechanically tough, biocompatible and safely cleared after 24 h. LIFT hydrogels deliver a total drug dose comparable to unencapsulated drug in a controlled manner, and protect encapsulated therapeutic enzymes and bacteria from gastric acid-mediated deactivation. Overall, LIFT hydrogels may expand access to advanced therapeutics for patients with difficulty swallowing.

In Situ Gelation Strategy for Efficient Drug Delivery in a Gastrointestinal System

Developing a microenvironment-responsive drug delivery system (DDS) for the gastrointestinal system is of great interest to enhance drug efficiency and minimize side effects. Unfortunately, the rapid-flowing digestive juice in the gastrointestinal tract and the continuous contraction and peristalsis of the gastrointestinal tract muscle accelerate the elimination of drug carriers. In this study, a boric hydroxyl-modified mesoporous Mg(OH)2 drug carrier is prepared to prolong the drug retention time. Results show that the newly designed DDS presents high biocompatibility and can immediately turn the free polyhydric alcohol molecules into a gelation form. The in situ-formed gelation network presents high viscosity and can prevent the drug carriers from being washed away by the digestive juice in the gastrointestinal tract.

Sutureless vascular anastomotic approaches and their potential impacts

Sutureless anastomotic devices present several advantages over traditional suture anastomosis, including expanded global access to microvascular surgery, shorter operation and ischemic times, and reduced costs. However, their adaptation for arterial use remains a challenge. This review aims to provide a comprehensive overview of sutureless anastomotic approaches that are either FDA-approved or under investigation. These approaches include extraluminal couplers, intraluminal devices, and methods assisted by lasers or vacuums, with a particular emphasis on tissue adhesives. We analyze these devices for artery compatibility, material composition, potential for intimal damage, risks of thrombosis and restenosis, and complications arising from their deployment and maintenance. Additionally, we discuss the challenges faced in the development and clinical application of sutureless anastomotic techniques. Ideally, a sutureless anastomotic device or technique should eliminate the need for vessel eversion, mitigate thrombosis through either biodegradation or the release of antithrombotic drugs, and be easily deployable for broad use. The transformative potential of sutureless anastomotic approaches in microvascular surgery highlights the necessity for ongoing innovation to expand their applications and maximize their benefits.

Multifunctional Composite Scaffold with Nanosilver, Graphene Oxide, and Macrophage Membrane Vesicles for Sequential Treatment of Infected Bone Defects

The management of infected bone defects poses a significant clinical challenge, and current treatment modalities exhibit various limitations. This study focuses on the development of a multifunctional composite scaffold comprising nanohydroxyapatite/polyethyleneglycol diacrylate matrix, silver nanoparticles, graphene oxide (GO), sodium alginate, and M2-type macrophage membrane vesicles (MVs) to enhance the healing of infected bone defects. The composite scaffold demonstrates several key features: first, it releases sufficient quantities of silver ions to effectively eliminate bacteria; second, the controlled release of MVs leads to a notable increase in M2-type macrophages, thereby significantly mitigating the inflammatory response. Additionally, GO acts synergistically with nanohydroxyapatite to enhance osteoinductive activity, thereby fostering bone regeneration. Through meticulous in vitro and in vivo investigations, the composite scaffold exhibits broad-spectrum antimicrobial effects, robust immunomodulatory capabilities, and enhanced osteoinductive activity. This multifaceted composite scaffold presents a promising approach for the sequential treatment of infected bone defects, addressing the antimicrobial, immunomodulatory, and osteogenic aspects. This study introduces innovative perspectives and offers new and effective treatment alternatives for managing infected bone defects.

Biofabrication of Living Actuators

The impact of tissue engineering has extended beyond a traditional focus in medicine to the rapidly growing realm of biohybrid robotics. Leveraging living actuators as functional components in machines has been a central focus of this field, generating a range of compelling demonstrations of robots capable of muscle-powered swimming, walking, pumping, gripping, and even computation. In this review, we highlight key advances in fabricating tissue-scale cardiac and skeletal muscle actuators for a range of functional applications. We discuss areas for future growth including scalable manufacturing, integrated feedback control, and predictive modeling and also propose methods for ensuring inclusive and bioethics-focused pedagogy in this emerging discipline. We hope this review motivates the next generation of biomedical engineers to advance rational design and practical use of living machines for applications ranging from telesurgery to manufacturing to on- and off-world exploration.

Growth of Double-Network Tough Hydrogel Coatings by Surface-Initiated Polymerization

Hydrogel coatings exhibit versatile applications in biomedicine, flexible electronics, and environmental science. However, current coating methods encounter challenges in simultaneously achieving strong interfacial bonding, robust hydrogel coatings, and the ability to coat substrates with controlled thickness. This paper introduces a novel approach to grow a double-network (DN) tough hydrogel coating on various substrates. The process involves initial substrate modification using a silane coupling agent, followed by the deposition of an initiator layer on its surface. Subsequently, the substrate is immersed in a DN hydrogel precursor, where the coating grows under ultraviolet (UV) illumination. Precise control over the coating thickness is achieved by adjusting the UV illumination duration and the initiator quantity. The experimental measurement of adhesion reveals strong bonding between the DN hydrogel coating and diverse substrates, reaching up to 1012.9 J/m2 between the DN hydrogel coating and a glass substrate. The lubricity performance of the DN hydrogel coating is experimentally characterized, which is dependent on the coating thickness, applied pressure, and sliding velocity. The incorporation of 3D printing technology into the current coating method enables the creation of intricate hydrogel coating patterns on a flat substrate. Moreover, the hydrogel coating's versatility is demonstrated through its effective applications in oil-water separation and antifogging glasses, underscoring its wide-ranging potential. The robust DN hydrogel coating method presented here holds promise for advancing hydrogel applications across diverse fields.

Construction methods and biomedical applications of PVA-based hydrogels

Polyvinyl alcohol (PVA) hydrogel is favored by researchers due to its good biocompatibility, high mechanical strength, low friction coefficient, and suitable water content. The widely distributed hydroxyl side chains on the PVA molecule allow the hydrogels to be branched with various functional groups. By improving the synthesis method and changing the hydrogel structure, PVA-based hydrogels can obtain excellent cytocompatibility, flexibility, electrical conductivity, viscoelasticity, and antimicrobial properties, representing a good candidate for articular cartilage restoration, electronic skin, wound dressing, and other fields. This review introduces various preparation methods of PVA-based hydrogels and their wide applications in the biomedical field.

Mussel-Inspired Calcium Alginate/Polyacrylamide Dual Network Hydrogel: A Physical Barrier to Prevent Postoperative Re-Adhesion

Intrauterine adhesions (IUA) has become one of the main causes of female infertility. How to effectively prevent postoperative re-adhesion has become a clinical challenge. In this study, a mussel-inspired dual-network hydrogel was proposed for the postoperative anti-adhesion of IUA. First, a calcium alginate/polyacrylamide (CA-PAM) hydrogel was prepared via covalent and Ca2+ cross-linking. Benefiting from abundant phenolic hydroxyl groups, polydopamine (PDA) was introduced to further enhance the adhesion ability and biocompatibility. This CA-PAM hydrogel immersed in 10 mg/mL dopamine solution possessed remarkable mechanical strength (elastic modulus > 5 kPa) and super stretchability (with a breaking elongation of 720%). At the same time, it showed excellent adhesion (more than 6 kPa). Surprisingly, the coagulation index of the hydrogel was 27.27 ± 4.91, demonstrating attractive coagulation performance in vitro and the potential for rapid hemostasis after surgery.

Activated Metals to Generate Heat for Biomedical Applications

Delivering heat in vivo could enhance a wide range of biomedical therapeutic and diagnostic technologies, including long-term drug delivery devices and cancer treatments. To date, providing thermal energy is highly power-intensive, rendering it oftentimes inaccessible outside of clinical settings. We developed an in vivo heating method based on the exothermic reaction between liquid-metal-activated aluminum and water. After establishing a method for consistent activation, we characterized the heat generation capabilities with thermal imaging and heat flux measurements. We then demonstrated one application of this reaction: to thermally actuate a gastric resident device made from a shape-memory alloy called Nitinol. Finally, we highlight the advantages and future directions for leveraging this novel in situ heat generation method beyond the showcased example.

Hydrogel Bioelectronics for Health Monitoring

Hydrogels are considered an ideal platform for personalized healthcare due to their unique characteristics, such as their outstanding softness, appealing biocompatibility, excellent mechanical properties, etc. Owing to the high similarity between hydrogels and biological tissues, hydrogels have emerged as a promising material candidate for next generation bioelectronic interfaces. In this review, we discuss (i) the introduction of hydrogel and its traditional applications, (ii) the work principles of hydrogel in bioelectronics, (iii) the recent advances in hydrogel bioelectronics for health monitoring, and (iv) the outlook for future hydrogel bioelectronics' development.

Supramolecular nanoarchitectonics of phenolic-based nanofiller for controlled diffusion of versatile drugs in hydrogels

Drug-dependent design of hydrogels is currently required for engineering the controlled release of therapeutics, which is a major contributor to the technical challenges relating to the clinical translation of hydrogel-drug systems. Herein, by integrating supramolecular phenolic-based nanofillers (SPFs) into hydrogel microstructures we developed a facile strategy to endow a range of clinically relevant hydrogels with controlled release properties for diverse therapeutic agents. The assembly of multiscale SPF aggregates leads to tunable mesh size and multiple dynamic interactions between SPF aggregates and drugs, which relaxes the available choices of drugs and hydrogels. This simple approach allowed for the controlled release of 12 representative drugs evaluated with 8 commonly used hydrogels. Moreover, the anesthetic drug lidocaine was loaded into SPF-integrated alginate hydrogel and demonstrated sustained release for 14 days in vivo, validating the potential for long-term anesthesia in patients.

Untethered shape-changing devices in the gastrointestinal tract

INTRODUCTION

Advances in microfabrication, automation, and computer engineering seek to revolutionize small-scale devices and machines. Emerging trends in medicine point to smart devices that emulate the motility, biosensing abilities, and intelligence of cells and pathogens that inhabit the human body. Two important characteristics of smart medical devices are the capability to be deployed in small conduits, which necessitates being untethered, and the capacity to perform mechanized functions, which requires autonomous shape-changing.

AREAS COVERED

We motivate the need for untethered shape-changing devices in the gastrointestinal tract for drug delivery, diagnosis, and targeted treatment. We survey existing structures and devices designed and utilized across length scales from the macro to the sub-millimeter. These devices range from triggerable pre-stressed thin film microgrippers and spring-loaded devices to shape-memory and differentially swelling structures.

EXPERT OPINION

Recent studies demonstrate that when fully enabled, tether-free and shape-changing devices, especially at sub-mm scales, could significantly advance the diagnosis and treatment of GI diseases ranging from cancer and inflammatory bowel disease (IBD) to irritable bowel syndrome (IBS) by improving treatment efficacy, reducing costs, and increasing medication compliance. We discuss the challenges and possibilities associated with ensuring safe, reliable, and autonomous operation of these smart devices.

Ethanol-free Cross-Linking of Alginate Nanofibers Enables Controlled Release into a Simulated Gastrointestinal Tract Model

The use of alginate nanofibers in certain biomedical applications, including targeted delivery to the gut, is limited because an ethanol-free, biocompatible cross-linking method has not been demonstrated. Here, we developed water-stable, alginate-based nanofibers by systematically exploring post-electrospinning cross-linking approaches that used calcium ions dissolved in (1) a glycerol/water cosolvent system and (2) acidic, neutral, or basic aqueous solutions. Scanning electron microscopy proved that the fibers cross-linked in a glycerol cosolvent or pH-optimized solutions had maintained the same morphology as the ethanol-based literature control. Notably, cross-linked fibers were generally smaller in diameter than the as-spun fibers due to both chemical interactions and mass loss during cross-linking, which was supported by mass measurements, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. During stability tests wherein the cross-linked fibers were exposed to three aqueous solutions, the cross-linked fibers were stable in water and acid buffer yet swelled in phosphate buffer saline, making them useful scaffolds for pH-controlled release applications. Proof-of-concept release experiments were conducted using a simulated gastrointestinal tract model. As desired, the cargo remained encapsulated within the cross-linked nanofibers when exposed to an acidic solution that modeled the stomach. Upon exposure to a solution that mimicked the intestines, the cargo was released. We suggest that these cross-linked, alginate-based nanofiber mats hold the potential to be broadly used in biomedical and environmental applications.

Hydrogels for Mucosal Drug Delivery

Mucosal tissues are often a desirable site of drug action to treat disease and engage the immune system. However, systemically administered drugs suffer from limited bioavailability in mucosal tissues where technologies to enable direct, local delivery to these sites would prove useful. In this Spotlight on Applications article, we discuss hydrogels as an attractive means for local delivery of therapeutics to address a range of conditions affecting the eye, nose, oral cavity, gastrointestinal, urinary bladder, and vaginal tracts. Considering the barriers to effective mucosal delivery, we provide an overview of the key parameters in the use of hydrogels for these applications. Finally, we highlight recent work demonstrating their use for inflammatory and infectious diseases affecting these tissues.

Fabrication of Polymeric Hydrogels Containing Esomeprazole for Oral Delivery: In Vitro and In Vivo Pharmacokinetic Characterization

Hydrogel is one of the most interesting and excellent candidates for oral drug delivery. The current study focuses on formulation development of hydrogels for controlled oral delivery of esomeprazole. The hydrogels were prepared by solution casting method by dissolving polymers in Polyvinyl alcohol (PVA) solution. Calcium alginate, Hydroxyl propyl methylcellulose (HPMC), acrylic acid and chondroitin sulfate were used in the preparation of hydrogels. Fourier transform infrared (FTIR) analysis showed no incompatibilities between drug and excipients used in the preparation of formulations. The hydrogels were characterized for size and surface morphology. Drug encapsulation efficiency was measured by Ultraviolet-visible (UV-VIS) spectroscopy. In vitro release studies were carried out using dissolution apparatus. The formulated hydrogels were then compared with the marketed product in vivo using rabbits. The result indicates that prepared hydrogels have a uniform size with a porous surface. The esomeprazole encapsulation efficiency of the prepared hydrogels was found to be 83.1 ± 2.16%. The esomeprazole-loaded hydrogel formulations showed optimum and Pharmacopeial acceptable range swelling behavior. The release of esomeprazole is controlled for 24 h (85.43 ± 0.32% in 24 h). The swelling and release of drug results make the prepared hydrogels a potential candidate for the controlled delivery of esomeprazole. The release of the drug from prepared hydrogel followed the super case transport-2 mechanism. The in vivo studies showed that prepared hydrogel formulations showed controlled and prolonged release of esomeprazole as compared to drug solution and marketed product. The formulations were kept for stability studies; there was no significant change observed in physical parameters, i.e., (appearance, color change and grittiness) at 40 °C ± 2/75% ± RH. There was a negligible difference in the drug content observed after the stability study suggested that all the formulations are stable under the given conditions for 60 days. The current study provides a valuable perspective on the controlled release profile of Hydroxyl propyl methylcellulose (HPMC) and calcium alginate-based esomeprazole hydrogels.

Utilizing 4D Printing to Design Smart Gastroretentive, Esophageal, and Intravesical Drug Delivery Systems

The breakthrough of 3D printing in biomedical research has paved the way for the next evolutionary step referred to as four dimensional (4D) printing. This new concept utilizes the time as the fourth dimension in addition to the x, y, and z axes with the idea to change the configuration of a printed construct with time usually in response to an external stimulus. This can be attained through the incorporation of smart materials or through a preset smart design. The 4D printed constructs may be designed to exhibit expandability, flexibility, self-folding, self-repair or deformability. This review focuses on 4D printed devices for gastroretentive, esophageal, and intravesical delivery. The currently unmet needs and challenges for these application sites are tried to be defined and reported on published solution concepts involving 4D printing. In addition, other promising application sites that may similarly benefit from 4D printing approaches such as tracheal and intrauterine drug delivery are proposed.

Magnetically Powered Chitosan Milliwheels for Rapid Translation, Barrier Function Rescue, and Delivery of Therapeutic Proteins to the Inflamed Gut Epithelium

Inflammatory bowel disease (IBD) is mediated by an overexpression of tumor necrosis factor-α (TNF) by mononuclear cells in the intestinal mucosa. Intravenous delivery of neutralizing anti-TNF antibodies can cause systemic immunosuppression, and up to one-third of people are non-responsive to treatment. Oral delivery of anti-TNF could reduce adverse effects; however, it is hampered by antibody degradation in the harsh gut environment during transit and poor bioavailability. To overcome these shortcomings, we demonstrate magnetically powered hydrogel particles that roll along mucosal surfaces, provide protection from degradation, and sustain the local release of anti-TNF. Iron oxide particles are embedded into a cross-linked chitosan hydrogel and sieved to produce 100-200 μm particles called milliwheels (m-wheels). Once loaded with anti-TNF, these m-wheels release 10 to 80% of their payload over 1 week at a rate that depends on the cross-linking density and pH. A rotating magnetic field induces a torque on the m-wheels that results in rolling velocities greater than 500 μm/s on glass and mucus-secreting cells. The permeability of the TNF-challenged gut epithelial cell monolayers was rescued in the presence of anti-TNF carrying m-wheels, which both neutralized the TNF and created an impermeable patch over leaky cell junctions. With the ability to translate over mucosal surfaces at high speed, provide sustained release directly to the inflamed epithelium, and provide barrier rescue, m-wheels demonstrate a potential strategy to deliver therapeutic proteins for the treatment of IBD.

Actively Triggerable Metals via Liquid Metal Embrittlement for Biomedical Applications

Actively triggerable materials, which break down upon introduction of an exogenous stimulus, enable precise control over the lifetime of biomedical technologies, as well as adaptation to unforeseen circumstances, such as changes to an established treatment plan. Yet, most actively triggerable materials are low-strength polymers and hydrogels with limited long-term durability. By contrast, metals possess advantageous functional properties, including high mechanical strength and conductivity, that are desirable across several applications within biomedicine. To realize actively triggerable metals, a mechanism called liquid metal embrittlement is leveraged, in which certain liquid metals penetrate the grain boundaries of certain solid metals and cause them to dramatically weaken or disintegrate. In this work, it is demonstrated that eutectic gallium indium (EGaIn), a biocompatible alloy of gallium, can be formulated to reproducibly trigger the breakdown of aluminum within different physiologically relevant environments. The breakdown behavior of aluminum after triggering can further be readily controlled by manipulating its grain structure. Finally, three possible use cases of biomedical devices constructed from actively triggerable metals are demonstrated.

Pirfenidone-loaded hyaluronic acid methacryloyl hydrogel for preventing epidural adhesions after laminectomy

It is inevitable that scar formation occurs between the spinal dura and surrounding tissues after laminectomy. While extensive epidural fibrosis, which results in limited nerve root activity and severe pain, is the main cause of postoperative failed-back surgery syndrome. Novel biomaterial loading effective drugs based on reasonable design are eagerly needed for the safe and effective prevention of epidural adhesions. We filtrated a suitable dose of pirfenidone (PFD) to load hyaluronic acid methacryloyl (HAMA) hydrogel in vitro. And then, we compare PFD-loaded HAMA hydrogel with only using PFD or HAMA hydrogels after laminectomy by in vivo studies in rats. We describe a safe and efficient anti-adhesive PFD-loaded HAMA hydrogel that prevents epidural fibrosis through the stable and sustained release of PFD. It was shown that the PFD-loaded HAMA hydrogel effectively inhibited cell penetration and suppressed collagen I/III expression. Thus, it effectively prevented the formation of adhesions through pharmacological and physical processes. The PFD-loaded HAMA hydrogel can effectively prevent adhesion formation in both pharmacological and physical barrier effects.

Soft robot-enabled controlled release of oral drug formulations

The creation of highly effective oral drug delivery systems (ODDSs) has long been the main objective of pharmaceutical research. Multidisciplinary efforts involving materials, electronics, control, and pharmaceutical sciences encourage the development of robot-enabled ODDSs. Compared with conventional rigid robots, soft robots potentially offer better mechanical compliance and biocompatibility with biological tissues, more versatile shape control and maneuverability, and multifunctionality. In this paper, we first describe and highlight the importance of manipulating drug release kinetics, i.e. pharmaceutical kinetics. We then introduce an overview of state-of-the-art soft robot-based ODDSs comprising resident, shape-programming, locomotive, and integrated soft robots. Finally, the challenges and outlook regarding future soft robot-based ODDS development are discussed.

Strong, Chemically Stable, and Enzymatically On-Demand Detachable Hydrogel Adhesion Using Protein Crosslink

Achieving strong adhesion between hydrogels and diverse materials is greatly significant for emerging technologies yet remains challenging. Existing methods using non-covalent bonds have limited pH and ion stability, while those using covalent bonds typically lack on-demand detachment capability, limiting their applications. In this study, a general strategy of covalent bond-based and detachable adhesion by incorporating amine-rich proteins in various hydrogels and inducing the interfacial crosslinking of the hydrogels using a protein-crosslinking agent is demonstrated. The protein crosslink offers topological adhesion and can reach a strong adhesion energy of ≈750 J m^-2 . The chemistry of the adhesion is characterized and that the inclusion of proteins inside the hydrogels does not alter the hydrogels' properties is shown. The adhesion remains intact after treating the adhered hydrogels with various pH solutions and ions, even at an elevated temperature. The detachment is triggered by treating proteinase solution at the bonding front, causing the digestion of proteins, thus breaking up the interfacial crosslink network. In addition, that this approach can be used to adhere hydrogels to diverse dry surfaces, including glass, elastomers and plastics, is shown. The stable chemistry of protein crosslinks opens the door for various applications in a wide range of chemical environments.

Silk Fibroin-Based Tough Hydrogels with Strong Underwater Adhesion for Fast Hemostasis and Wound Sealing

Rapid and strong adhesion of hydrogel adhesives is required for instant wound closure and hemostasis. However, in situ hydrogel formation and sufficient adhesion at target tissue sites in biological environments are severely compromised by the presence of blood and body fluids. In this work, an underwater adhesive hydrogel (named SHCa) is fabricated with rapid in situ gelation, enhanced mechanical toughness, and robust underwater adhesion. The SHCa can undergo rapid UV irradiation-induced gelation under water within 5 s and adhere firmly to underwater surfaces for 6 months. The synergistic effects of crystalline β-sheet structures and dynamic energy-dissipating mechanisms enhance the mechanical toughness and cohesion, supporting the balance between adhesion and cohesion in wet environments. Importantly, the SHCa can achieve rapid in situ gelation and robust underwater adhesion at various tissue surfaces in highly dynamic fluid environments, substantially outperforming the commercially available tissue adhesives. The lap shear adhesion strength and wound closure strength of SHCa on blood-covered substrates are 7.24 and 12.68 times higher than those of cyanoacrylate glue, respectively. Its fast hemostasis and wound sealing performance are further demonstrated in in vivo animal models. The proposed hydrogel with strong underwater adhesion provides an effective tool for fast wound closure and hemostasis.

Development of an Ingestible Expandable Capsule for Weight Loss

Obesity has grown to epidemic proportions with 2.1 billion people being overweight worldwide. A food-grade expandable capsule named EndoXpand for the treatment of overweight people was designed and developed in this study. EndoXpand consists of an inner expandable material (core), an embracing membrane, and a gelatin capsule shell. It is designed to occupy volume in the stomach and reduce hunger sensation. The occupied volume is changeable over time, dependent on the number of ingested capsules and their degradation time. This will avoid gastric accommodation to constant volume devices as seen in the use of intragastric balloons. Several materials were tested. Collagen casing was selected as the membrane and corn silk was used to tie the membrane. Dried black fungus (Auricularia auricula) was the biological material that expanded most. However, synthesized cellulose-based hydrogel expanded more and was chosen as the optimal expandable core material. The hydrogel-based EndoXpand expanded 72 times after soaking in an acidic environment for 80 min. The corn silk ligations weakened and broke after 3 h. This resulted in release of the expanded material that was designed to easily pass the pylorus and travel down the intestine for digestion or excretion. In conclusion, this study provides design and in vitro proof-of-technology data for a potential groundbreaking approach. Further studies are needed in animal models and human phase I studies.

Electronically powered drug delivery devices: considerations and challenges

INTRODUCTION

Electronically powered drug delivery devices enable a controlled drug release route for a more convenient and painless way with reduced side effects. The current advances in microfabrication and microelectronics have facilitated miniaturization and intelligence with the integration of sensors and wireless communication modules. These devices have become an essential component of commercialized on-demand drug delivery.

AREAS COVERED

This review aims to provide a concise overview of current progress in electronically powered drug devices, focusing on delivery strategies, manufacturing techniques, and control circuit design with specific examples.

EXPERT OPINION

The application of electronically powered drug delivery systems is now considered a feasible therapeutic approach with improved drug release efficiency and increased patient comfort. It is anticipated that these technologies will gradually fulfill clinical needs and resolve commercialization challenges in the future. This review discusses the current advances in electronic drug delivery devices, especially focusing on designing strategies to achieve an effective drug release, as well as the perspectives and challenges for future applications in clinical therapy.

Superior stretchable and tough P(AA‐co‐AAm)/silica hybrid hydrogels enabled by acid‐mediated radiation polymerization

The emerging stretchable and tough hydrogels find their extraordinary contributions in widespread use. However, the applicability of existing tough hydrogels in harsh environments like highly acidic stomachs has remained a challenge. Here, we develop superior stretchable and tough P(AA‐co‐AAm)/SiO2 hybrid hydrogels through radiation‐induced polymerization and crosslinking in the presence of acids. The performance of the nanocomposite gels was optimized by altering fabrication variables including acid concentration, monomer composition and absorbed dose. The mechanic tests show that the protonated hybrid hydrogels displayed a high elongation at break (1919%), fracture strength (117 kPa), and compressive strength at 50% strain (126 kPa). These values are superior to those of conventional polyelectrolyte hydrogels and expect to significantly broaden the application. The proposed strategy is quite general and offers an alternative strategy to develop tough hydrogels.

Hydrogels as promising carriers for the delivery of food bioactive ingredients

The burden of public health challenges associated with the western dietary and living style is growing. Nutraceuticals have been paid increasing attentions due to their effects in promotion of health. However, in the gastrointestinal (GI) tract, the nutraceuticals suffer from not only the harsh acidic environment of the stomach and a variety of digestive enzymes, but also the antibacterial activity of intestinal bile salts and the action of protease from the gut microbiota. The amount of the nutraceuticals arriving at the sites in GI tract for absorption or exerting the bioactivities is always unfortunately limited, which puts forward high requirements for protection of nutraceuticals in a certain high contents during oral consumption. Hydrogels are three-dimensional polymeric porous networks formed by the cross-linking of polymer chains, which can hold huge amounts of water. Compared with other carries with the size in microscopic scale such as nanoparticle and microcapsules, hydrogels could be considered to be more suitable delivery systems in food due to their macroscopic bulk properties, adjustable viscoelasticity and large spatial structure for embedding nutraceuticals. Regarding to the applications in food, natural polymer-based hydrogels are commonly safe and popular due to their source with the appealing characteristics of affordability, biodegradability and biocompatibility. Although chemical crosslinking has been widely utilized in preparation of hydrogels, it prefers the physical crosslinking in the researches in food. The reasonable design for the structure of natural polymeric hydrogels is essential for seeking the favorable functionalities to apply in the delivery system, and it could be possible to obtain the enhanced adhesive property, acid stability, resistant to bile salt, and the controlled release behavior. The hydrogels prepared with proteins, polysaccharides or the mix of them to deliver the functional ingredients, mainly the phenolic components, vitamins, probiotics are discussed to obtain inspiration for the wide applications in delivery systems. Further efforts might be made in the in situ formation of hydrogels in GI tract through the interaction among food polymers and small-molecular ingredients, elevation of the loading contents of nutraceuticals in hydrogels, development of stomach adhesive hydrogels as well as targeting modification of gut microbiota by the hydrogels.

Ionically cross-linked alginate-chitosan core-shell hydrogel beads for oral delivery of insulin

Here, core-shell hydrogel beads for oral insulin delivery at intestine was reported, which was a target site for insulin absorption. The core-shell hydrogel beads were prepared using naturally derived alginate and chitosan polysaccharides by simple dropping technique. In order to effectively control leakage of insulin from core-shell hydrogel beads, insulin was embedded into the layered double hydroxides (LDHs). LDH/insulin-loaded complexes were firstly coated with chitosan, and then coated with alginate to generate core-shell hydrogel beads. The biocompatibility and angiogenic response of core-shell hydrogel beads were evaluated by direct contact of the beads with chick embryo chorioallantoic membrane, which indicates safety of the core-shell beads. The beads successfully retained the insulin within the core-shell structure at pH 1.2, indicating that insulin had a good protective effect in harsh acidic environments. Interestingly, insulin release starts at the simulated intestinal fluid (pH 6.8) and continue to release for 24 h in a sustained manner.

Injectable Hybrid-Crosslinked Hydrogels as Fatigue-Resistant and Shape-Stable Skin Depots

Injectable hydrogels have gained considerable attention, but they are typically mechanically weak and subject to repeated physiological stresses in the body. Herein, we prepared polyurethane diacrylate (EPC-DA) hydrogels, which are injectable and can be photocrosslinked into fatigue-resistant implants. The mechanical properties can be tuned by changing photocrosslinking conditions, and the hybrid-crosslinked EPC-DA hydrogels exhibited high stability and sustained release properties. In contrast to common injectable hydrogels, EPC-DA hydrogels exhibited excellent antifatigue properties with >90% recovery during cyclic compression tests and showed shape stability after application of force and immersion in an aqueous buffer for 35 days. The EPC-DA hydrogel formed a shape-stable hydrogel depot in an ex vivo porcine skin model, with establishment of a temporary soft gel before in situ fixing by UV crosslinking. Hybrid crosslinking using injectable polymeric micelles or nanoparticles may be a general strategy for producing hydrogel implants resistant to physiological stresses.

Recent advances in multi-mechanism design of crack-resistant hydrogels

For conventional hydrogels, the phenomenon of crack generation and propagation caused by high-stress concentration is ubiquitous. However, this phenomenon is unfavorable in many applications, such as wearable electronics, tissue engineering, and tunable adhesion. Fortunately, many hydrogels that can suppress crack growth during deformation and maintain the original mechanical properties during deformation, called crack-resistant hydrogels, have been published. Herein, the state-of-the-art of crack-resistant hydrogels is comprehensively reviewed. Starting from the principle of designing a crack-resistant hydrogel, we first survey the relevant crack-resistant strategies. The latest crack-resistant hydrogels are then categorized according to their crack-resistant mechanisms (including energy dissipation at the molecular level, multiscale structure, crack pinning, crack deflection, and sliding of chain), and their crack-resistant processes are described in detail. Furthermore, we summarize the current challenges and make an outlook for crack-resistant hydrogels, which might lead to substantial progress in the future design and development of these high-performance materials.

Translating Therapeutic Microgels into Clinical Applications

Microgels are crosslinked, water-swollen networks with a 10 nm to 100 µm diameter and can be modified chemically or biologically to render them biocompatible for advanced clinical applications. Depending on their intended use, microgels require different mechanical and structural properties, which can be engineered on demand by altering the biochemical composition, crosslink density of the polymer network, and the fabrication method. Here, the fundamental aspects of microgel research and development, as well as their specific applications for theranostics and therapy in the clinic, are discussed. A detailed overview of microgel fabrication techniques with regards to their intended clinical application is presented, while focusing on how microgels can be employed as local drug delivery materials, scavengers, and contrast agents. Moreover, microgels can act as scaffolds for tissue engineering and regeneration application. Finally, an overview of microgels is given, which already made it into pre-clinical and clinical trials, while future challenges and chances are discussed. This review presents an instructive guideline for chemists, material scientists, and researchers in the biomedical field to introduce them to the fundamental physicochemical properties of microgels and guide them from fabrication methods via characterization techniques and functionalization of microgels toward specific applications in the clinic.

Controlled Nutrient Delivery through a pH-Responsive Wood Vehicle

To lower the risk of disease and improve health, many nutrients benefit from intestinal-targeted delivery. Here, we present a nutrient-delivery system based on a pH-responsive "wood scroll", in which nutrients are stored, protected, and controllably released through the rolled structure and natural microchannels of a flexible wood substrate, thus ensuring higher bioactivity as well as prolonged steady release of the nutrient load to the intestine. We loaded the wood's natural microchannels with probiotics as a proof-of-concept demonstration. The probiotic-loaded wood scrolls can survive the simulated conditions of the stomach with a high survival rate (95.40%) and exhibit prolonged release (8 h) of the probiotic load at a constant release rate (4.17 × 10⁸ CFUs/h) in the simulated conditions of the intestine. Moreover, by modifying the macroscopic geometry and microstructures of the wood scrolls, both the nutrient loading and release behaviors can be tuned over a wide range for customized or personalized nutrient management. The wood scrolls can also deliver other types of nutrients, as we demonstrate for tea polyphenols and rapeseed oil. This wood scroll design illustrates a promising structurally controlled strategy for the delivery of enteric nutrients using readily available, low-cost, and biocompatible biomass materials that have a naturally porous structure for nutrient storage, protection, and controlled release.

Dynamic omnidirectional adhesive microneedle system for oral macromolecular drug delivery

Oral drug administration remains the preferred route for patients and health care providers. Delivery of macromolecules through this route remains challenging because of limitations imposed by the transport across the gastrointestinal epithelium and the dynamic and degradative environment. Here, we present the development of a delivery system that combines physical (microneedle) and nonphysical (enhancer) modes of drug delivery enhancement for a macromolecule in a large animal model. Inspired by the thorny-headed intestinal worm, we report a dynamic omnidirectional mucoadhesive microneedle system capable of prolonged gastric mucosa fixation. Moreover, we incorporate sodium N-[8-(2-hydroxybenzoyl) amino] caprylate along with semaglutide and demonstrate enhanced absorption in swine resistant to physical displacement in the gastric cavity. Meanwhile, we developed a targeted capsule system capable of deploying intact microneedle-containing systems. These systems stand to enable the delivery of a range of drugs through the generation and maintenance of a privileged region in the gastrointestinal tract.

Hydrogels for modified-release drug delivery systems

Hydrogels for the modified-release drug delivery systems is a continuously growing area of interest for the pharmaceutical industry. According to the global market, the use of polymers in this area is projected to reach $31.4 million by 2027. This review discusses the recent advances and perspectives of hydrogel in drug delivery systems for oral, parenteral, nasal, topical, and ophthalmic. The search strategy did in January 2021, and it conducted an extensive database to identify studies published from January 2010 to December 2020.We described the main characteristic of the polymers to obtain an ideal hydrogel for a specific route of administration and the formulations that was a highlight in the literature. It concluded that the hydrogels are a set useful to decrease the number of doses, side effects, promote adhesion of patient and enhances the bioavailability of the drugs improving the safety and efficacy of the treatment.

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.

Clip Chemistry: Diverse (Bio)(macro)molecular and Material Function through Breaking Covalent Bonds

In the two decades since the introduction of the "click chemistry" concept, the toolbox of "click reactions" has continually expanded, enabling chemists, materials scientists, and biologists to rapidly and selectively build complexity for their applications of interest. Similarly, selective and efficient covalent bond breaking reactions have provided and will continue to provide transformative advances. Here, we review key examples and applications of efficient, selective covalent bond cleavage reactions, which we refer to herein as "clip reactions." The strategic application of clip reactions offers opportunities to tailor the compositions and structures of complex (bio)(macro)molecular systems with exquisite control. Working in concert, click chemistry and clip chemistry offer scientists and engineers powerful methods to address next-generation challenges across the chemical sciences.

Bioinspired tough gel sheath for robust and versatile surface functionalization

Sutures pervade surgeries, but their performance is limited by the mechanical mismatch with tissues and the lack of advanced functionality. Existing modification strategies result in either deterioration of suture's bulk properties or a weak coating susceptible to rupture or delamination. Inspired by tendon endotenon sheath, we report a versatile strategy to functionalize fiber-based devices such as sutures. This strategy seamlessly unites surgical sutures, tough gel sheath, and various functional materials. Robust modification is demonstrated with strong interfacial adhesion (>2000 J m-2). The surface stiffness, friction, and drag of the suture when interfacing with tissues can be markedly reduced, without compromising the tensile strength. Versatile functionalization of the suture for infection prevention, wound monitoring, drug delivery, and near-infrared imaging is then presented. This platform technology is applicable to other fiber-based devices and foreseen to affect broad technological areas ranging from wound management to smart textiles.

Fabrication of ulcer-adhesive oral keratin hydrogel for gastric ulcer healing in a rat

Hydrogel has been used for in suit gastric ulcer therapy by stopping bleeding, separating from ulcer from gastric fluids and providing extracellular matrix scaffold for tissue regeneration, however, this treatment guided with endoscopic catheter in most cases. Here, we developed an oral keratin hydrogel to accelerate the ulcer healing without endoscopic guidance, which can specially adhere to the ulcer because of the high-viscosity gel formation on the wound surface in vivo. Approximately 50% of the ulcer-adhesive keratin hydrogel can resident in ethanol-treated rat stomach within 12 h, while approximately 18% of them maintained in health rat stomach in the same amount of time. Furthermore, Keratin hydrogels accelerated the ethanol-induced gastric ulcer healing by stopping the bleeding, preventing the epithelium cells from gastric acid damage, suppressing inflammation and promoting re-epithelization. The oral administration of keratin hydrogel in gastric ulcer treatment can enhance the patient compliance and reduce the gastroscopy complications. Our research findings reveal a promising biomaterial-based approach for treating gastrointestinal ulcers.

Oral Drug Delivery: Conventional to Long Acting New-Age Designs

The Oral route of administration forms the heartwood of the ever-growing tree of drug delivery technology. It is one of the most preferred dosage forms among patients and controlled release community. Despite the high patient compliance, the deliveries of anti-cancerous drugs, vaccines, proteins, etc. via the oral route are limited and have recorded a very low bioavailability. The oral administration must overcome the physiological barriers (low solubility, permeation and early degradation) to achieve efficient and sustained delivery. This review aims at highlighting the conventional and modern-age strategies that address some of these physiological barriers. The modern age designs include the 3D printed devices and formulations. The superiority of 3D dosage forms over conventional cargos is summarized with a focus on long-acting designs. The innovations in Pharmaceutical organizations (Lyndra, Assertio and Intec) that have taken giant steps towards commercialization of long-acting vehicles are discussed. The recent advancements made in the arena of oral peptide delivery are also highlighted. The review represents a comprehensive journey from Nano-formulations to micro-fabricated oral implants aiming at specific patient-centric designs.

Rapidly Visible-Light-Mediated Photogelations for One-Step Engineering Multifunctional Tough Hydrogel Tubes

Hydrogel tubes as one kind of perfusable tubular materials, show promising applications in a wide spectrum of fields. However, there is still a great challenge to design a rapid, biocompatible, and straightforward strategy for one-step engineering tough hydrogel tubes, which have excellent mechanical properties, unique resilience, and multiple functions. Herein, we explore visible-light-mediated orthogonal photochemistry to achieve the fabrication of tough hydrogel tubes with double networks via a coaxial-nozzle spinning technique under short blue-light irradiation (∼20 s). The as-prepared tubes are tough (2.3 MJ m^-3) and have mechanical strength (∼300 kPa) with a critical strain of 16, good fatigue resistance, and resilience (>95% within 3 min). These perfusable tubular hydrogels not only can be knitted and assembled to complicated 2D/3D structures, but also are designed to fabricate functional tubes in one step with the applications in fields of smart materials, soft electronics, and sensors.

New insights into food hydrogels with reinforced mechanical properties: A review on innovative strategies

Enhancement on the mechanical properties of hydrogels leads to a wider range of their applications in various fields. Therefore, there has been a great interest recently for developing new strategies to reinforce hydrogels. Moreover, food gels must be edible in terms of both raw materials and production. This paper reviews innovative techniques such as particle/fiber-reinforced hydrogel, double network, dual crosslinking, freeze-thaw cycles, physical conditioning and soaking methods to improve the mechanical properties of hydrogels. Additionally, their fundamental mechanisms, advantages and disadvantages have been discussed. Important biopolymers that have been employed for these strategies and also their potentials in food applications have been summarized. The general mechanism of these strategies is based on increasing the degree of crosslinking between interacting polymers in hydrogels. These links can be formed by adding fillers (oil droplets or fibers in filled gels) or cross-linkers (regarding double network and soaking method) and also by condensation or alignment of the biopolymers (freeze-thaw cycle and physical conditioning) in the gel network. The properties of particle/fiber-reinforced hydrogels extremely depend on the filler, gel matrix and the interaction between them. In freeze-thaw cycles and physical conditioning methods, it is possible to form new links in the gel network without adding any cross-linkers or fillers. It is expected that the utilization of gels will get broader and more varied in food industries by using these strategies.