A photo-degradable injectable self-healing hydrogel based on star poly(ethylene glycol)-b-polypeptide as a potential pharmaceuticals delivery carrier

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.

Introductory Review of Soft Implantable Bioelectronics Using Conductive and Functional Hydrogels and Hydrogel Nanocomposites

Interfaces between implantable bioelectrodes and tissues provide critical insights into the biological and pathological conditions of targeted organs, aiding diagnosis and treatment. While conventional bioelectronics, made from rigid materials like metals and silicon, have been essential for recording signals and delivering electric stimulation, they face limitations due to the mechanical mismatch between rigid devices and soft tissues. Recently, focus has shifted toward soft conductive materials, such as conductive hydrogels and hydrogel nanocomposites, known for their tissue-like softness, biocompatibility, and potential for functionalization. This review introduces these materials and provides an overview of recent advances in soft hydrogel nanocomposites for implantable electronics. It covers material strategies for conductive hydrogels, including both intrinsically conductive hydrogels and hydrogel nanocomposites, and explores key functionalization techniques like biodegradation, bioadhesiveness, injectability, and self-healing. Practical applications of these materials in implantable electronics are also highlighted, showcasing their effectiveness in real-world scenarios. Finally, we discuss emerging technologies and future needs for chronically implantable bioelectronics, offering insights into the evolving landscape of this field.

Injectable Hydrogels: A Paradigm Tailored with Design, Characterization, and Multifaceted Approaches

Biomaterials denoting self-healing and versatile structural integrity are highly curious in the biomedicine segment. The injectable and/or printable 3D printing technology is explored in a few decades back, which can alter their dimensions temporarily under shear stress, showing potential healing/recovery tendency with patient-specific intervention toward the development of personalized medicine. Thus, self-healing injectable hydrogels (IHs) are stunning toward developing a paradigm for tissue regeneration. This review comprises the designing of IHs, rheological characterization and stability, several benchmark consequences for self-healing IHs, their translation into tissue regeneration of specific types, applications of IHs in biomedical such as anticancer and immunomodulation, wound healing and tissue/bone regeneration, antimicrobial potentials, drugs, gene and vaccine delivery, ocular delivery, 3D printing, cosmeceuticals, and photothermal therapy as well as in other allied avenues like agriculture, aerospace, electronic/electrical industries, coating approaches, patents associated with therapeutic/nontherapeutic avenues, and numerous futuristic challenges and solutions.

Synthesis and Properties of Injectable Hydrogel for Tissue Filling

Hydrogels with injectability have emerged as the focal point in tissue filling, owing to their unique properties, such as minimal adverse effects, faster recovery, good results, and negligible disruption to daily activities. These hydrogels could attain their injectability through chemical covalent crosslinking, physical crosslinking, or biological crosslinking. These reactions allow for the formation of reversible bonds or delayed gelatinization, ensuring a minimally invasive approach for tissue filling. Injectable hydrogels facilitate tissue augmentation and tissue regeneration by offering slow degradation, mechanical support, and the modulation of biological functions in host cells. This review summarizes the recent advancements in synthetic strategies for injectable hydrogels and introduces their application in tissue filling. Ultimately, we discuss the prospects and prevailing challenges in developing optimal injectable hydrogels for tissue augmentation, aiming to chart a course for future investigations.

Implantation of In Situ Gelling Systems for the Delivery of Chemotherapeutic Agents

Implantation is a modern method of administering chemotherapeutic agents, with a highly targeted effect and better patient tolerance due to the low frequency of administration. Implants are capable of controlled release, which makes them a viable alternative to infusional chemotherapy, allowing patients to enjoy a better quality of life without the need for prolonged hospitalization. Compared to subcutaneous implantation, intratumoral implantation has a number of significant advantages in terms of targeting and side effects, but this area of chemotherapy is still poorly understood in terms of clinical trials. At the same time, there are more known developments of drugs in the form of implants and injections for intratumoral administration. The disadvantages of classical intratumoral implants are the need for surgical intervention to install the system and the increased risk of tumor rupture noted by some specialists. The new generation of implants are in situ implants-systems formed in the tumor due to a phase transition (sol-gel transition) under the influence of various stimuli. Among this systems some are highly selective for a certain type of malignant neoplasm. Such systems are injected and have all the advantages of intratumoral injections, but due to the phase transition occurring in situ, they form depot forms that allow the long-term release of chemotherapeutic agents.

Supramolecular hydrogels for wound repair and hemostasis

The unique network characteristics and stimuli responsiveness of supramolecular hydrogels have rendered them highly advantageous in the field of wound dressings, showcasing unprecedented potential. However, there are few reports on a comprehensive review of supramolecular hydrogel dressings for wound repair and hemostasis. This review first introduces the major cross-linking methods for supramolecular hydrogels, which includes hydrogen bonding, electrostatic interactions, hydrophobic interactions, host-guest interactions, metal ligand coordination and some other interactions. Then, we review the advanced materials reported in recent years and then summarize the basic principles of each cross-linking method. Next, we classify the network structures of supramolecular hydrogels before outlining their forming process and propose their potential future directions. Furthermore, we also discuss the raw materials, structural design principles, and material characteristics used to achieve the advanced functions of supramolecular hydrogels, such as antibacterial function, tissue adhesion, substance delivery, anti-inflammatory and antioxidant functions, cell behavior regulation, angiogenesis promotion, hemostasis and other innovative functions in recent years. Finally, the existing problems as well as future development directions of the cross-linking strategy, network design, and functions in wound repair and hemostasis of supramolecular hydrogels are discussed. This review is proposed to stimulate further exploration of supramolecular hydrogels on wound repair and hemostasis by researchers in the future.

Photo-Controllable Smart Hydrogels for Biomedical Application: A Review

Nowadays, smart hydrogels are being widely studied by researchers because of their advantages such as simple preparation, stable performance, response to external stimuli, and easy control of response behavior. Photo-controllable smart hydrogels (PCHs) are a class of responsive hydrogels whose physical and chemical properties can be changed when stimulated by light at specific wavelengths. Since the light source is safe, clean, simple to operate, and easy to control, PCHs have broad application prospects in the biomedical field. Therefore, this review timely summarizes the latest progress in the PCHs field, with an emphasis on the design principles of typical PCHs and their multiple biomedical applications in tissue regeneration, tumor therapy, antibacterial therapy, diseases diagnosis and monitoring, etc. Meanwhile, the challenges and perspectives of widespread practical implementation of PCHs are presented in biomedical applications. This study hopes that PCHs will flourish in the biomedical field and this review will provide useful information for interested researchers.

Polypeptide-Based Systems: From Synthesis to Application in Drug Delivery

Synthetic polypeptides are biocompatible and biodegradable macromolecules whose composition and architecture can vary over a wide range. Their unique ability to form secondary structures, as well as different pathways of modification and biofunctionalization due to the diversity of amino acids, provide variation in the physicochemical and biological properties of polypeptide-containing materials. In this review article, we summarize the advances in the synthesis of polypeptides and their copolymers and the application of these systems for drug delivery in the form of (nano)particles or hydrogels. The issues, such as the diversity of polypeptide-containing (nano)particle types, the methods for their preparation and drug loading, as well as the influence of physicochemical characteristics on stability, degradability, cellular uptake, cytotoxicity, hemolysis, and immunogenicity of polypeptide-containing nanoparticles and their drug formulations, are comprehensively discussed. Finally, recent advances in the development of certain drug nanoformulations for peptides, proteins, gene delivery, cancer therapy, and antimicrobial and anti-inflammatory systems are summarized.

Thermo-induced physically crosslinked polypeptide-based block copolymer hydrogels for biomedical applications

Stimuli-responsive synthetic polypeptide-containing block copolymers have received considerable attention in recent years. Especially, unique thermo-induced sol-gel phase transitions were observed for elaborately-designed amphiphilic diblock copolypeptides and a range of poly(ethylene glycol) (PEG)-polypeptide block copolymers. The thermo-induced gelation mechanisms involve the evolution of secondary conformation, enhanced intramolecular interactions, as well as reduced hydration and increased chain entanglement of PEG blocks. The physical parameters, including polymer concentrations, sol-gel transition temperatures and storage moduli, were investigated. The polypeptide hydrogels exhibited good biocompatibility in vitro and in vivo, and displayed biodegradation periods ranging from 1 to 5 weeks. The unique thermo-induced sol-gel phase transitions offer the feasibility of minimal-invasive injection of the precursor aqueous solutions into body, followed by in situ hydrogel formation driven by physiological temperature. These advantages make polypeptide hydrogels interesting candidates for diverse biomedical applications, especially as injectable scaffolds for 3D cell culture and tissue regeneration as well as depots for local drug delivery. This review focuses on recent advances in the design and preparation of injectable, thermo-induced physically crosslinked polypeptide hydrogels. The influence of composition, secondary structure and chirality of polypeptide segments on the physical properties and biodegradation of the hydrogels are emphasized. Moreover, the studies on biomedical applications of the hydrogels are intensively discussed. Finally, the major challenges in the further development of polypeptide hydrogels for practical applications are proposed.

Self-Healing Injectable Hydrogels for Tissue Regeneration

Biomaterials with the ability to self-heal and recover their structural integrity offer many advantages for applications in biomedicine. The past decade has witnessed the rapid emergence of a new class of self-healing biomaterials commonly termed injectable, or printable in the context of 3D printing. These self-healing injectable biomaterials, mostly hydrogels and other soft condensed matter based on reversible chemistry, are able to temporarily fluidize under shear stress and subsequently recover their original mechanical properties. Self-healing injectable hydrogels offer distinct advantages compared to traditional biomaterials. Most notably, they can be administered in a locally targeted and minimally invasive manner through a narrow syringe without the need for invasive surgery. Their moldability allows for a patient-specific intervention and shows great prospects for personalized medicine. Injected hydrogels can facilitate tissue regeneration in multiple ways owing to their viscoelastic and diffusive nature, ranging from simple mechanical support, spatiotemporally controlled delivery of cells or therapeutics, to local recruitment and modulation of host cells to promote tissue regeneration. Consequently, self-healing injectable hydrogels have been at the forefront of many cutting-edge tissue regeneration strategies. This study provides a critical review of the current state of self-healing injectable hydrogels for tissue regeneration. As key challenges toward further maturation of this exciting research field, we identify (i) the trade-off between the self-healing and injectability of hydrogels vs their physical stability, (ii) the lack of consensus on rheological characterization and quantitative benchmarks for self-healing injectable hydrogels, particularly regarding the capillary flow in syringes, and (iii) practical limitations regarding translation toward therapeutically effective formulations for regeneration of specific tissues. Hence, here we (i) review chemical and physical design strategies for self-healing injectable hydrogels, (ii) provide a practical guide for their rheological analysis, and (iii) showcase their applicability for regeneration of various tissues and 3D printing of complex tissues and organoids.

Self-Healing Hydrogels: Preparation, Mechanism and Advancement in Biomedical Applications

Polymeric hydrogels are widely explored materials for biomedical applications. However, they have inherent limitations like poor resistance to stimuli and low mechanical strength. This drawback of hydrogels gave rise to ''smart self-healing hydrogels'' which autonomously repair themselves when ruptured or traumatized. It is superior in terms of durability and stability due to its capacity to reform its shape, injectability, and stretchability thereby regaining back the original mechanical property. This review focuses on various self-healing mechanisms (covalent and non-covalent interactions) of these hydrogels, methods used to evaluate their self-healing properties, and their applications in wound healing, drug delivery, cell encapsulation, and tissue engineering systems. Furthermore, composite materials are used to enhance the hydrogel's mechanical properties. Hence, findings of research with various composite materials are briefly discussed in order to emphasize the healing capacity of such hydrogels. Additionally, various methods to evaluate the self-healing properties of hydrogels and their recent advancements towards 3D bioprinting are also reviewed. The review is concluded by proposing several pertinent challenges encountered at present as well as some prominent future perspectives.

Multiresponsive hydrogels and organogels based on photocaged cysteine

Here we present the readily accessible amino acid 4,5-dimethoxy-2-nitrobenzyl-l-cysteine (DNC), as an ultra-low molecular weight gelator (MW = 316 g mol-1). Sonication of DNC in water or organic solvents as well as pH adjustment in water trigger gelation. A diverse set of stimuli (UV irradiation, oxidation, heat or pH change) induce a gel-sol transition. Moreover, the photo-triggered gel-sol transition was used to obtain a controlled cysteine release from the hydrogel.

Hydrogel, a novel therapeutic and delivery strategy, in the treatment of intrauterine adhesions

Intrauterine adhesions (IUAs) are caused by damage to the underlying lining of the endometrium. They' re related to disorder of endometrial repair. In recent years, hydrogels with controllable biological activity have been widely used for treating IUAs. They encapsulate estrogen, cytokines, cells, or exosomes, forming a delivery system to release therapeutic components for the treatment of IUAs. In addition, the hydrogel acting as a barrier can be degraded in the body automatically, reducing the risk of infection caused by secondary surgeries. In this review, we summarize the recent progress of hydrogels and their application in IUAs as both a novel alternative therapeutic and an artificial delivery strategy.

Stimuli-responsive hydrogels for intratumoral drug delivery

The ability of some hydrogels to exhibit a phase transition or change their structure in response to stimuli has been extensively explored for drug depot formation and controlled drug release. Taking advantage of the unique features of the tumor microenvironment (TME) or externally applied triggers, several injectable stimuli-responsive hydrogels have been described as promising candidates for intratumoral drug delivery. In this review, we provide a brief overview of the TME and highlight the advantages of intratumoral administration, followed by a summary of the reported strategies to endow hydrogels with responsiveness to physical (temperature and light), chemical (pH and redox potential), or biological (enzyme) stimuli.

Development of Hydrogels with Self-Healing Properties for Delivery of Bioactive Agents

Hydrogels are an important class of soft materials that find use in bioactive agent delivery. Because of their high water content, hydrogels generally show poor mechanical strength. Long-term wear and tear in physiological conditions may lead to damage in the hydrogel structure during the delivery of bioactive agents. This results in burst and uncontrolled agent release. One strategy to solve this problem is to incorporate self-healing properties into a hydrogel so that the hydrogel can heal fractures automatically to restore original mechanical properties. The objectives of this article are to revisit the latest advances in the design of self-healing hydrogel-based carriers and to offer insights into further research to translate these carriers from the laboratory to real applications.

Preparation and characterization of enzymatically cross-linked gelatin/cellulose nanocrystal composite hydrogels

Gelatin is an attractive hydrogel material because of its excellent biocompatibility and non-cytotoxicity, but poor mechanical properties of gelatin-based hydrogels become a big obstacle that limits their wide-spread application. To solve it, in this work, gelatin/cellulose nanocrystal composite hydrogels (Gel-TG-CNCs) were prepared using microbial transglutaminase (mTG) as the crosslinking catalyst and cellulose nanocrystals (CNCs) as reinforcements. The physicochemical properties of the composite hydrogels were investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The dynamic rheological measurement and uniaxial compression test were performed to study the effects of mTG and CNC contents on the storage modulus and breaking strength of the as-prepared Gel-TG-CNCs. Results showed that the addition of CNCs and mTG could significantly increase the storage modulus and breaking strength of gelatin-based hydrogels, especially when added simultaneously. The breaking strength of Gel-TG-CNCs (2%) at 25 °C can reach 1000 g which is 30 times greater than pure gelatin hydrogels. The biocompatibility of the composite hydrogels was also investigated by the MTT method with Hela cells, and the results demonstrated that the composite hydrogels maintained excellent biocompatibility. With a combination of good biocompatibility and mechanical properties, the as-prepared Gel-TG-CNCs showed potential application value in the biomedical field.

Injectable Self-Healing Adhesive pH-Responsive Hydrogels Accelerate Gastric Hemostasis and Wound Healing

Endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD) are well-established therapeutics for gastrointestinal neoplasias, but complications after EMR/ESD, including bleeding and perforation, result in additional treatment morbidity and even threaten the lives of patients. Thus, designing biomaterials to treat gastric bleeding and wound healing after endoscopic treatment is highly desired and remains a challenge. Herein, a series of injectable pH-responsive self-healing adhesive hydrogels based on acryloyl-6-aminocaproic acid (AA) and AA-g-N-hydroxysuccinimide (AA-NHS) were developed, and their great potential as endoscopic sprayable bioadhesive materials to efficiently stop hemorrhage and promote the wound healing process was further demonstrated in a swine gastric hemorrhage/wound model. The hydrogels showed a suitable gelation time, an autonomous and efficient self-healing capacity, hemostatic properties, and good biocompatibility. With the introduction of AA-NHS as a micro-cross-linker, the hydrogels exhibited enhanced adhesive strength. A swine gastric hemorrhage in vivo model demonstrated that the hydrogels showed good hemostatic performance by stopping acute arterial bleeding and preventing delayed bleeding. A gastric wound model indicated that the hydrogels showed excellent treatment effects with significantly enhanced wound healing with type I collagen deposition, α-SMA expression, and blood vessel formation. These injectable self-healing adhesive hydrogels exhibited great potential to treat gastric wounds after endoscopic treatment.

Evolution of drug-eluting biomedical implants for sustained drug delivery

In the field of drug delivery, the most commonly used treatments have traditionally been systemically delivered using oral or intravenous administration. The problems associated with this type of delivery is that the drug concentration is controlled by first pass metabolism, and therefore may not always remain within the therapeutic window. Implantable drug delivery systems (IDDSs) are an excellent alternative to traditional delivery because they offer the ability to precisely control the drug release, deliver drugs locally to the target tissue, and avoid the toxic side effects often experienced with systemic administration. Since the creation of the first FDA-approved IDDS in 1990, there has been a surge in research devoted to fabricating and testing novel IDDS formulations. The versatility of these systems is evident when looking at the various biomedical applications that utilize IDDSs. This review provides an overview of the history of IDDSs, with examples of the different types of IDDS formulations, as well as looking at current and future biomedical applications for such systems. Though there are still obstacles that need to be overcome, ever-emerging new technologies are making the manufacturing of IDDSs a rewarding therapeutic endeavor with potential for further improvements.

Hydrogel Properties and Their Impact on Regenerative Medicine and Tissue Engineering

Hydrogels (HGs), as three-dimensional structures, are widely used in modern medicine, including regenerative medicine. The use of HGs in wound treatment and tissue engineering is a rapidly developing sector of medicine. The unique properties of HGs allow researchers to easily modify them to maximize their potential. Herein, we describe the physicochemical properties of HGs, which determine their subsequent applications in regenerative medicine and tissue engineering. Examples of chemical modifications of HGs and their applications are described based on the latest scientific reports.

Polypeptide-based self-healing hydrogels: Design and biomedical applications

Self-healing hydrogels can heal themselves on the damaged sites, which opens up a fascinating way for enhancing lifetimes of materials. Polypeptide/poly(amino acid) is a class of polymers in which natural amino acid monomers or derivatives are linked by amide bonds with a stable and similar secondary structure as natural proteins (α-helix or β-fold). They have the advantages of nontoxicity, biodegradability, and low immunogenicity as well as easy modification. All these properties make polypeptides extremely suitable for the preparation of self-healing hydrogels for biomedical applications. In this review, we mainly focus on the progress in the fabrication strategies of polypeptide-based self-healing hydrogels and their biomedical applications in the recent 5 years. Various crosslinking methods for the preparation of polypeptide-based self-healing hydrogels are first introduced, including host-guest interactions, hydrogen bonding, electrostatic interactions, supramolecular self-assembly of β-sheets, and reversible covalent bonds of imine and hydrazone as well as molecular multi-interactions. Some representative biomedical applications of these self-healing hydrogels such as delivery system, tissue engineering, 3D-bioprinting, antibacterial and wound healing as well as bioadhesion and hemostasis are also summarized. Current challenges and perspectives in future for these "smart" hydrogels are proposed at the end . STATEMENT OF SIGNIFICANCE: Polypeptides with the advantages of nontoxicity, biodegradability, hydrophilicity and low immunogenicity, are extremely suitable for the preparation of self-healing hydrogels in biomedical applications. Recently, the researches of polypeptide-based self-healing hydrogel have drawn the great attentions for scientists and engineers. A review to summarize the recent progress in design and biomedical applications of these polypeptide-based self-healing hydrogels is highly needed. In this review, we mainly focus on the progress in fabrication strategies of polypeptide-based self-healing hydrogels and biomedical applications in recent five years and aim to draw the increased attention to the importance of these "smart" hydrogels, facilitating the advances in biomedical applications. We believe this work would draw interest from readers of Acta Biomaterialia.

Spatiotemporally Controlled Photoresponsive Hydrogels: Design and Predictive Modeling from Processing through Application

Photoresponsive hydrogels (PRHs) are soft materials whose mechanical and chemical properties can be tuned spatially and temporally with relative ease. Both photo-crosslinkable and photodegradable hydrogels find utility in a range of biomedical applications that require tissue-like properties or programmable responses. Progress in engineering with PRHs is facilitated by the development of theoretical tools that enable optimization of their photochemistry, polymer matrices, nanofillers, and architecture. This review brings together models and design principles that enable key applications of PRHs in tissue engineering, drug delivery, and soft robotics, and highlights ongoing challenges in both modeling and application.

A self-healing, robust adhesion, multiple stimuli-response hydrogel for flexible sensors

Ionic hydrogels have great application potential in human index monitoring and wound treatment, such as in wearable sensors, wound dressings, and ionic skin. However, the design of a hydrogel achieving the synergistic characteristics of excellent mechanical properties, robust adhesion, and multiple stimuli-responses remains a critical challenge. Herein, by introducing negatively charged clay nanosheets, we report a smart ionic Gelatin/PAAm/Clay hydrogel (GPNs gel) with a high conductivity of 10.87 mS cm-1. The as-prepared gel exhibits excellent self-healing properties, robust adhesion (interfacial toughness of up to 485 J m-2 with pigskin), and multiple stimuli-responses driven by salt ions, pH, and stress. Based on this hydrogel, a capacitive sensor has also been designed, which provides linear responses over a wide range (applied pressure up to 2 kPa) and sensitively monitors human motion. In addition, the gel also displays good biocompatibility with human lung embryonic (MRC-5) cells. These characteristics demonstrate that the GPNs gel is an ideal candidate for developing flexible sensor devices.

A review on recent advances in polymer and peptide hydrogels

In this review, we focus on the very recent developments on the use of the stimuli responsive properties of polymer hydrogels for targeted drug delivery, tissue engineering, and biosensing utilizing their different optoelectronic properties. Besides, the stimuli-responsive hydrogels, the conducting polymer hydrogels are discussed, with specific attention to the energy generation and storage behavior of the xerogel derived from the hydrogel. The electronic and ionic conducting gels have been discussed that have applications in various electronic devices, e.g., organic field effect transistors, soft robotics, ionic skins, and sensors. The properties of polymer hybrid gels containing carbon nanomaterials have been exemplified here giving attention to applications in supercapacitors, dye sensitized solar cells, photocurrent switching, etc. Recent trends in the properties and applications of some natural polymer gels to produce thermal and acoustic insulating materials, drug delivery vehicles, self-healing material, tissue engineering, etc., are discussed. Besides the polymer gels, peptide gels of different dipeptides, tripeptides, oligopeptides, polypeptides, cyclic peptides, etc., are discussed, giving attention mainly to biosensing, bioimaging, and drug delivery applications. The properties of peptide-based hybrid hydrogels with polymers, nanoparticles, nucleotides, fullerene, etc., are discussed, giving specific attention to drug delivery, cell culture, bio-sensing, and bioimaging properties. Thus, the present review delineates, in short, the preparation, properties, and applications of different polymer and peptide hydrogels prepared in the past few years.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.

Light-degradable hydrogels as dynamic triggers for gastrointestinal applications

Triggerable materials capable of being degraded by selective stimuli stand to transform our capacity to precisely control biomedical device activity and performance while reducing the need for invasive interventions. Here, we describe the development of a modular and tunable light-triggerable hydrogel system capable of interfacing with implantable devices. We apply these materials to two applications in the gastrointestinal (GI) tract: a bariatric balloon and an esophageal stent. We demonstrate biocompatibility and on-demand triggering of the material in vitro, ex vivo, and in vivo. Moreover, we characterize performance of the system in a porcine large animal model with an accompanying ingestible LED. Light-triggerable hydrogels have the potential to be applied broadly throughout the GI tract and other anatomic areas. By demonstrating the first use of light-degradable hydrogels in vivo, we provide biomedical engineers and clinicians with a previously unavailable, safe, dynamically deliverable, and precise tool to design dynamically actuated implantable devices.

Light-inducible activation of cell cycle progression in Xenopus egg extracts under microfluidic confinement

Cell-free Xenopus egg extract is a widely used and biochemically tractable model system that allows recapitulation and elucidation of fundamental cellular processes. Recently, the introduction of microfluidic extract manipulation has enabled compartmentalization of bulk extract and a newfound ability to study organelles on length scales that recapitulate key features of cellular morphology. While the microfluidic confinement of extracts has produced a compelling platform for the in vitro study of cell processes at physiologically-relevant length scales, it also imposes experimental limitations by restricting dynamic control over extract properties. Here, we introduce photodegradable polyethylene glycol (PEG) hydrogels as a vehicle to passively and selectively manipulate extract composition through the release of proteins encapsulated within the hydrogel matrix. Photopatterned PEG hydrogels, passive to both extract and encapsulated proteins, serve as protein depots within microfluidic channels, which are subsequently flooded with extract. Illumination by ultraviolet light (UV) degrades the hydrogel structures and releases encapsulated protein. We show that an engineered fluorescent protein with a nuclear localization signal (GST-GFP-NLS) retains its ability to localize within nearby nuclei following UV-induced release from hydrogel structures. When diffusion is considered, the kinetics of nuclear accumulation are similar to those in experiments utilizing conventional, bulk fluid handling. Similarly, the release of recombinant cyclin B Δ90, a mutant form of the master cell cycle regulator cyclin B which lacks the canonical destruction box, was able to induce the expected cell cycle transition from interphase to mitosis. This transition was confirmed by the observation of nuclear envelope breakdown (NEBD), a phenomenological hallmark of mitosis, and the induction of mitosis-specific biochemical markers. This approach to extract manipulation presents a versatile and customizable route to regulating the spatial and temporal dynamics of cellular events in microfluidically confined cell-free extracts.

Self-Healing Hydrogels with both LCST and UCST through Cross-Linking Induced Thermo-Response

Self-healing hydrogels have drawngreat attention in the past decade since the self-healing property is one of the characteristics of living creatures. In this study, poly(acrylamide-stat-diacetone acrylamide) P(AM-stat-DAA) with a pendant ketone group was synthesized from easy accessible monomers, and thermo-responsive self-healing hydrogels were prepared through a series of diacylhydrazide compounds cross-linking without any additional stimulus. Although the copolymers do not show thermo-response, the hydrogels became thermo-responsive andboth the lower critical solution temperature (LCST) and upper critical solution temperature (UCST) varied with the composition of the copolymer and structure of cross-linkers. With a dynamic covalent bond connection, the hydrogel showed gel-sol-gel transition triggered by acidity, redox, and ketone to acylhydrazide group ratios. This is another interesting cross-linking induced thermo-responsive (CIT) hydrogel with different properties compared to PNIPAM-based thermo-responsive hydrogels. The self-healing hydrogel with CIT properties could have great potential for application in areas related to bioscience, life simulation, and temperature switching.

A pH-responsive self-healing hydrogel based on multivalent coordination of Ni2+ with polyhistidine-terminated PEG and IDA-modified oligochitosan

A multivalent Ni²⁺ coordination hydrogel based on polyhistidine-terminated PEG and IDA-modified oligochitosan with enhanced neutral stability and mild-acid responsiveness is reported herein.