Hydrogel Functionalized Janus Membrane for Skin Regeneration

Electrical Stimulating Redox Membrane Incorporated with PVA/Gelatin Nanofiber for Diabetic Wound Healing

Chronic wounds adversely affect the quality of life. Although electrical stimulation has been utilized to treat chronic wounds, there are still limitations to practicing it due to the complicated power system. Herein, an electrostimulating membrane incorporated with electrospun nanofiber (M-sheet) to treat diabetic wounds is developed. Through the screen printing method, the various alternate patterns of both Zn and AgCl on a polyurethane substrate, generating redox-mediated electrical fields are introduced. The antibacterial ability of the patterned membrane against both E. coli and S. aureus is confirmed. Furthermore, the poly(vinyl alcohol) (PVA)/gelatin electrospun fiber is incorporated into the patterned membrane to enhance biocompatibility and maintain the wet condition in the wound environment. The M-sheet can improve cell proliferation and migration in vitro and has an immune regulatory effect by inducing the polarization of macrophage to the M2 phenotype. Finally, when applied to a diabetic skin wound model, the M-sheet displays an accelerated wound healing rate and enhances re-epithelialization, collagen synthesis, and angiogenesis. It suggests that the M-sheet is a simple and portable system for the spontaneous generation of electrical stimulation and has great potential to be used in the practical wound and other tissue engineering applications.

A Highly Stable, Multifunctional Janus Dressing for Treating Infected Wounds

The limited and unstable absorption of excess exudate is a major challenge during the healing of infected wounds. In this study, a highly stable, multifunctional Janus dressing with unidirectional exudate transfer capacity is fabricated based on a single poly(lactide caprolactone) (PLCL). The success of this method relies on an acid hydrolysis reaction that transforms PLCL fibers from hydrophobic to hydrophilic in situ. The resulting interfacial affinity between the hydrophilic/phobic PLCL fibers endows the Janus structure with excellent unidirectional liquid transfer and high structural stability against repeated stretching, bending, and twisting. Various other functions, including wound status detection, antibacterial, antioxidant, and anti-inflammatory properties, are also integrated into the dressing by incorporating phenol red and epigallocatechin gallate. An in vivo methicillin-resistant Staphylococcus aureus-infected wound model confirms that the Janus dressing, with the capability to remove exudate from the infected site, not only facilitates epithelialization and collagen deposition, but also ensures low inflammation and high angiogenesis, thus reaching an ideal closure rate up to 98.4% on day 14. The simple structure, multiple functions, and easy fabrication of the dressing may offer a promising strategy for treating chronic wounds, rooted in the challenges of bacterial infection, excessive exudate, and persistent inflammation.

Janus hydrogels: merging boundaries in tissue engineering for enhanced biomaterials and regenerative therapies

In recent years, the design and synthesis of Janus hydrogels have witnessed a thriving development, overcoming the limitations of single-performance materials and expanding their potential applications in tissue engineering and regenerative medicine. Janus hydrogels, with their exceptional mechanical properties and excellent biocompatibility, have emerged as promising candidates for various biomedical applications, including tissue engineering and regenerative therapies. In this review, we present the latest progress in the synthesis of Janus hydrogels using commonly employed preparation methods. We elucidate the surface and interface interactions of these hydrogels and discuss the enhanced properties bestowed by the unique "Janus" structure in biomaterials. Additionally, we explore the applications of Janus hydrogels in facilitating regenerative therapies, such as drug delivery, wound healing, tissue engineering, and biosensing. Furthermore, we analyze the challenges and future trends associated with the utilization of Janus hydrogels in biomedical applications.

PAA-PU Janus Hydrogels Stabilized by Janus Particles and its Interfacial Performance During Hemostatic Processing

Hydrogel is a very promising dressing for hemostasis and wound healing due to its good adhesion and long-term moist environment. However, secondary injury caused by tissue adhesion due to homogeneous hydrogel cannot be ignored. The obvious interface existing in Janus hydrogel will weaken its asymmetric function. Here, a hierarchical adhesive polyacrylic acid-polyurushiol water-oil Janus hydrogel (JPs@PAA-PU) without adhesive layer is fabricated by one-pot method in the stabilization of polystyrene@silica-siliver Janus particles (JPs). The morphological structure, mechanical properties, anisotropic chemical composition, and adhesion performance, in vivo, and in vitro hemostatic properties of Janus hydrogel are investigated. Result shows that the obtained Janus hydrogel possesses obvious compartmentalization in microstructure, functional groups, and chemical elements. Janus hydrogel is provided with asymmetric interfacial toughness with top 52.45 ± 2.29 Kpa and bottom 7.04 ± 0.88 Kpa on porcine liver. The adhesion properties of PAA side to tissue, red blood cells and platelets, promoting effect of PU side on coagulation cascade reaction and its physical battier endow Janus hydrogel with shorter hemostatic time and less blood loss than control group. It also exhibits excellent antibacterial effects against Escherichia coli and Staphylococcus aureus (>90%). Janus hydrogel possesses biosafety, providing safety guarantee for clinical applications in the future.

A comprehensive review on the inherent and enhanced antifouling mechanisms of hydrogels and their applications

Biofouling remains a persistent challenge within the domains of biomedicine, tissue engineering, marine industry, and membrane separation processes. Multifunctional hydrogels have garnered substantial attention due to their complex three-dimensional architecture, hydrophilicity, biocompatibility, and flexibility. These hydrogels have shown notable advances across various engineering disciplines. The antifouling efficacy of hydrogels typically covers a range of strategies to mitigate or inhibit the adhesion of particulate matter, biological entities, or extraneous pollutants onto their external or internal surfaces. This review provides a comprehensive review of the antifouling properties and applications of hydrogels. We first focus on elucidating the fundamental principles for the inherent resistance of hydrogels to fouling. This is followed by a comprehensive investigation of the methods employed to enhance the antifouling properties enabled by the hydrogels' composition, network structure, conductivity, photothermal properties, release of reactive oxygen species (ROS), and incorporation of silicon and fluorine compounds. Additionally, we explore the emerging prospects of antifouling hydrogels to alleviate the severe challenges posed by surface contamination, membrane separation and wound dressings. The inclusion of detailed mechanistic insights and the judicious selection of antifouling hydrogels are geared toward identifying extant gaps that must be bridged to meet practical requisites while concurrently addressing long-term antifouling applications.

Hydrogel-Based Growth Factor Delivery Platforms: Strategies and Recent Advances

Growth factors play a crucial role in regulating a broad variety of biological processes and are regarded as powerful therapeutic agents in tissue engineering and regenerative medicine in the past decades. However, their application is limited by their short half-lives and potential side effects in physiological environments. Hydrogels are identified as having the promising potential to prolong the half-lives of growth factors and mitigate their adverse effects by restricting them within the matrix to reduce their rapid proteolysis, burst release, and unwanted diffusion. This review discusses recent progress in the development of growth factor-containing hydrogels for various biomedical applications, including wound healing, brain tissue repair, cartilage and bone regeneration, and spinal cord injury repair. In addition, the review introduces strategies for optimizing growth factor release including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cellular system-based delivery. Finally, the review presents current limitations and future research directions for growth factor-delivering hydrogels.

Fundamental properties of smart hydrogels for tissue engineering applications: A review

Tissue engineering is an advanced and potential biomedical approach to treat patients suffering from lost or failed an organ or tissue to repair and regenerate damaged tissues that increase life expectancy. The biopolymers have been used to fabricate smart hydrogels to repair damaged tissue as they imitate the extracellular matrix (ECM) with intricate structural and functional characteristics. These hydrogels offer desired and controllable qualities, such as tunable mechanical stiffness and strength, inherent adaptability and biocompatibility, swellability, and biodegradability, all crucial for tissue engineering. Smart hydrogels provide a superior cellular environment for tissue engineering, enabling the generation of cutting-edge synthetic tissues due to their special qualities, such as stimuli sensitivity and reactivity. Numerous review articles have presented the exceptional potential of hydrogels for various biomedical applications, including drug delivery, regenerative medicine, and tissue engineering. Still, it is essential to write a comprehensive review article on smart hydrogels that successfully addresses the essential challenging issues in tissue engineering. Hence, the recent development on smart hydrogel for state-of-the-art tissue engineering conferred progress, highlighting significant challenges and future perspectives. This review discusses recent advances in smart hydrogels fabricated from biological macromolecules and their use for advanced tissue engineering. It also provides critical insight, emphasizing future research directions and progress in tissue engineering.

Janus polyurethane sponge as an antibiofouling, antibacterial, and exudate-managing dressing for accelerated wound healing

The non-fouling condition, bacteria-free environment and suitable moisture at wound site are crucial for chronic wound healing. However, it remains highly meaningful yet challenging to develop wound dressings that can simultaneously achieve these desirable functions. In this work, a kind of multifunctional Janus polyurethane sponge (Janus-PU) was designed and fabricated by coating near-infrared (NIR)-responsive and superhydrophobic nanoparticles (F-ZnO@Ag NPs) on one surface of sponge. The nano-functionalized outer layer can endow Janus-PU with superhydrophobic antifouling property for preventing bacterial colonization and broad-spectrum antibacterial activity due to the presence of Ag NPs. Especially, the synergistic combination of asymmetric structure and strong NIR photothermal effect can impart Janus-PU with NIR-controlled unidirectional exudate removal, thus achieving an optimal wetting environment for wound healing. The mice full-thickness skin acute wounds treated with Janus-PU under NIR irradiation showed superior anti-infection and healing effect compared to the commercial dressings. Significantly, the treatment using Janus-PU with NIR irradiation can accelerate the recovery of methicillin-resistant Staphylococcus aureus (MRSA)-infected diabetic chronic wounds due to the synergistic effect of antibiofouling, antibacterial and exudate-managing. The Janus-PU as a promising multifunctional dressing can prevent bacterial invasion and create an appropriate environment for wound healing, providing an effective solution for intractable wounds and infections. STATEMENT OF SIGNIFICANCE: The development of advanced wound dressings to ensure non-fouling condition, bacteria-free environment and suitable moisture is crucial for chronic wound healing. However, it remains a considerable challenge to simultaneously integrate antibiofouling, antibacterial and exudate-managing properties into a single dressing. In this work, we developed a kind of multifunctional Janus polyurethane sponge (Janus-PU) by a single-sided superhydrophobic modification strategy, which can simultaneously achieve superhydrophobic antifouling property, effective broad-spectrum antibacterial and near-infrared controlled exudate removal. The Janus-PU designed herein can not only create an optimal environment for accelerated wound healing, but also avoid frequent dressing replacement, thus providing an ideal material system for intractable wounds and infections.

Recent progress of antibacterial hydrogels in wound dressings

Hydrogels are essential biomaterials due to their favorable biocompatibility, mechanical properties similar to human soft tissue extracellular matrix, and tissue repair properties. In skin wound repair, hydrogels with antibacterial functions are especially suitable for dressing applications, so novel antibacterial hydrogel wound dressings have attracted widespread attention, including the design of components, optimization of preparation methods, strategies to reduce bacterial resistance, etc. In this review, we discuss the fabrication of antibacterial hydrogel wound dressings and the challenges associated with the crosslinking methods and chemistry of the materials. We have investigated the advantages and limitations (antibacterial effects and antibacterial mechanisms) of different antibacterial components in the hydrogels to achieve good antibacterial properties, and the response of hydrogels to stimuli such as light, sound, and electricity to reduce bacterial resistance. Conclusively, we provide a systematic summary of antibacterial hydrogel wound dressings findings (crosslinking methods, antibacterial components, antibacterial methods) and an outlook on long-lasting antibacterial effects, a broader antibacterial spectrum, diversified hydrogel forms, and the future development prospects of the field.

Recent advancements in wound management: Tailoring superwettable bio-interfaces

Skin tissue suffering from severe damages fail in self-regeneration. Proper wound dressings are highly demanded to protect the wound region and accelerate the healing process. Although large efforts have been devoted, there still exist disturbing dilemmas for traditional dressings. The exquisite design of bio-interface upon superwettable materials opens new avenues and addresses the problems perfectly. However, the advancements in this area have rarely been combed. In light of this, this minireview attempts to summarize recent strategies of superwettable bio-interfaces for wound care. Concentrating on the management of biofluids (blood and exudate), we described superwettable hemostatic bio-interfaces first, and then introduced the management of exudates. Finally, the perspective of this area was given. This minireview gives a comprehensive outline for readers and is believed to provide references for the design of superwettable materials in biomedical area.

Advances in Asymmetric Wettable Janus Materials for Oil–Water Separation

The frequent occurrence of crude oil spills and the indiscriminate discharge of oily wastewater have caused serious environmental pollution. The existing separation methods have some defects and are not suitable for complex oil–water emulsions. Therefore, the efficient separation of complex oil–water emulsions has been of great interest to researchers. Asymmetric wettable Janus materials, which can efficiently separate complex oil–water emulsions, have attracted widespread attention. This comprehensive review systematically summarizes the research progress of asymmetric wettable Janus materials for oil–water separation in the last decade, and introduces, in detail, the preparation methods of them. Specifically, the latest research results of two-dimensional Janus materials, three-dimensional Janus materials, smart responsive Janus materials, and environmentally friendly Janus materials for oil–water separation are elaborated. Finally, ongoing challenges and outlook for the future research of asymmetric wettable Janus materials are presented.

Intelligent Paper-Free Sprayable Skin Mask Based on an In Situ Formed Janus Hydrogel of an Environmentally Friendly Polymer

Traditional skin care masks usually use a piece of paper to hold the aqueous essences, which are not environmentally friendly and not easy to use. While a paper-free mask is desired, it is faced with a dilemma of moisture holding and rapid release of encapsulated bioactive substances. Herein, a paper-free sprayable skin mask is designed from an intelligent material-a thermogel which undergoes sol-gel-suspension transitions upon heating-to solve this dilemma. A synthesized block copolymer of poly(ethylene glycol) and poly(lactide-co-glycolide) with appropriate ratios can be dissolved in water, and thus easily mixed with a biological substance. The mixture is sprayable. After spraying, a Janus film is formed in situ with a physical gel on the outside and a suspension on the inside facing skin. Thus, both moisture holding and rapid release are achieved. Such a thermogel composed of biodegradable amphiphilic block copolymers loaded with nicotinamide as a skin mask is verified to reduce pigmentation on a 3D pigmented reconstructed epidermis model and further in a clinical study. This work might be stimulating for investigations and applications of biodegradable and intelligent soft matter in the fields of drug delivery and regenerative medicine.

Engineering shape memory and morphing protein hydrogels based on protein unfolding and folding

Engineering shape memory/morphing materials have achieved considerable progress in polymer-based systems with broad potential applications. However, engineering protein-based shape memory/morphing materials remains challenging and under-explored. Here we report the design of a bilayer protein-based shape memory/morphing hydrogel based on protein folding-unfolding mechanism. We fabricate the protein-bilayer structure using two tandem modular elastomeric proteins (GB1)₈ and (FL)₈. Both protein layers display distinct denaturant-dependent swelling profiles and Young’s moduli. Due to such protein unfolding-folding induced changes in swelling, the bilayer hydrogels display highly tunable and reversible bidirectional bending deformation depending upon the denaturant concentration and layer geometry. Based on these programmable and reversible bending behaviors, we further utilize the protein-bilayer structure as hinge to realize one-dimensional to two-dimensional and two-dimensional to three-dimensional folding transformations of patterned hydrogels. The present work will offer new inspirations for the design and fabrication of novel shape morphing materials.

Engineering shape memory and morphing materials achieved considerable progress in polymer-based systems, but protein-based shape memory and morphing materials remain less investigated. Here, the authors report the engineering of protein-based shape memory and morphing hydrogels using protein folding-unfolding as a general mechanism to trigger shape morphing in protein-bilayer structures.

Versatile polymer-based strategies for antibacterial drug delivery systems and antibacterial coatings

Human health damage and economic losses due to bacterial infections are very serious worldwide. Excessive use of antibiotics has caused an increase in bacterial resistance. Fortunately, various non-antibiotic antibacterial materials...

Bioactivity and Antibacterial Behaviors of Nanostructured Lithium-Doped Hydroxyapatite for Bone Scaffold Application

The material for bone scaffold replacement should be biocompatible and antibacterial to prevent scaffold-associated infection. We biofunctionalized the hydroxyapatite (HA) properties by doping it with lithium (Li). The HA and 4 Li-doped HA (0.5, 1.0, 2.0, 4.0 wt.%) samples were investigated to find the most suitable Li content for both aspects. The synthesized nanoparticles, by the mechanical alloying method, were cold-pressed uniaxially and then sintered for 2 h at 1250 °C. Characterization using field-emission scanning electron microscopy (FE-SEM) revealed particle sizes in the range of 60 to 120 nm. The XRD analysis proved the formation of HA and Li-doped HA nanoparticles with crystal sizes ranging from 59 to 89 nm. The bioactivity of samples was investigated in simulated body fluid (SBF), and the growth of apatite formed on surfaces was evaluated using SEM and EDS. Cellular behavior was estimated by MG63 osteoblast-like cells. The results of apatite growth and cell analysis showed that 1.0 wt.% Li doping was optimal to maximize the bioactivity of HA. Antibacterial characteristics against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were performed by colony-forming unit (CFU) tests. The results showed that Li in the structure of HA increases its antibacterial properties. HA biofunctionalized by Li doping can be considered a suitable option for the fabrication of bone scaffolds due to its antibacterial and unique bioactivity properties.

High-Performance Ultrafine Bubble Aeration on Janus Aluminum Foil Prepared by Laser Microfabrication

Aeration is a mass transfer process, in which gas is dispersed into a liquid by utilizing air inflation or agitation. Typically, a microporous device is often used for aeration. Increasing the gas flow rate and decreasing the pore size reduce the bubble size, but the surface wettability of the gas/solid interface also has a significant impact on the bubble size, which is rarely studied. In this study, a superhydrophilic/superhydrophobic Janus aluminum foil (JAF) is fabricated by laser microstructuring and low surface energy modification. The gas-repelling superhydrophilic surface not only facilitates ultrafine bubble generation but also allows the bubbles to detach from the aerator surface quickly, while the superhydrophobic surface prevents water from infiltrating into the aeration chamber and reduces the mass transfer resistance. The micropores with different diameters are obtained by adjusting the laser processing parameters. The pore prepared by the laser is uniform, consequently leading to the uniform bubble size. When the pore diameter is set to 30 μm, the diameter of bubbles released from the superhydrophilic surface of the JAF is only 0.326 mm, and the gas dissolution rate is about six times that of the double-sided superhydrophobic aluminum foil. This simple, low-cost, and controllable method of the laser processing JAF has broad applications in wastewater treatment, energy production, and aquaculture.

A Versatile Surface Modification Method via Vapor-phase Deposited Functional Polymer Films for Biomedical Device Applications

For last two decades, the demand for precisely engineered three-dimensional structures has increased continuously for the developments of biomaterials. With the recent advances in micro- and nano-fabrication techniques, various devices with complex surface geometries have been devised and produced in the pharmaceutical and medical fields for various biomedical applications including drug delivery and biosensors. These advanced biomaterials have been designed to mimic the natural environments of tissues more closely and to enhance the performance for their corresponding biomedical applications. One of the important aspects in the rational design of biomaterials is how to configure the surface of the biomedical devices for better control of the chemical and physical properties of the bioactive surfaces without compromising their bulk characteristics. In this viewpoint, it of critical importance to secure a versatile method to modify the surface of various biomedical devices. Recently, a vapor phase method, termed initiated chemical vapor deposition (iCVD) has emerged as damage-free method highly beneficial for the conformal deposition of various functional polymer films onto many kinds of micro- and nano-structured surfaces without restrictions on the substrate material or geometry, which is not trivial to achieve by conventional solution-based surface functionalization methods. With proper structural design, the functional polymer thin film via iCVD can impart required functionality to the biomaterial surfaces while maintaining the fine structure thereon. We believe the iCVD technique can be not only a valuable approach towards fundamental cell-material studies, but also of great importance as a platform technology to extend to other prospective biomaterial designs and material interface modifications for biomedical applications.

Combination of lyophilized adipose-derived stem cell concentrated conditioned medium and polysaccharide hydrogel in the inhibition of hypertrophic scarring

BACKGROUND

Mesenchymal stem cell-based acellular therapies have been widely exploited in managing hypertrophic scars. However, low maintenance dose and transitory therapeutic effects during topical medication remain a thorny issue. Herein, this study aimed to optimize the curative effect of adipose-derived stem cell conditioned medium (ADSC-CM) in the prevention of hypertrophic scarring.

METHODS

In the present study, ADSC-CM was concentrated via the freeze-drying procedure. The efficacy of different dose groups (CM, CM5, CM10) was conducted on the proliferation, apoptosis, and α-smooth muscle actin (α-SMA) expression of human keloid fibroblasts (HKFs) in vitro. Incorporation of adipose-derived stem cell concentrated conditioned medium (ADSCC-CM) into polysaccharide hydrogel was investigated in rabbit ear, in vivo. Haematoxylin-eosin (H&E) and Masson's trichrome staining were performed for the evaluation of scar hyperplasia.

RESULTS

We noted that ADSCC-CM could downregulate the α-SMA expression of HKFs in a dose-dependent manner. In the rabbit ear model, the scar hyperplasia in the medium-dose group (CM5) and high-dose group (CM10) was inhibited with reduced scar elevation index (SEI) under 4 months of observation. It is noteworthy that the union of CM5 and polysaccharide hydrogel (CM5+H) yielded the best preventive effect on scar hyperplasia. Briefly, melanin, height, vascularity, and pliability in the CM5+H group were better than those of the control group. Collagen was evenly distributed, and skin appendages could be regenerated.

CONCLUSIONS

Altogether, ADSCC-CM can downregulate the expression of α-SMA due to its anti-fibrosis effect and promote the rearrangement of collagen fibres, which is integral to scar precaution. The in situ cross bonding of ADSCC-CM and polysaccharide hydrogel could remarkably enhance the therapeutic outcomes in inhibiting scar proliferation. Hence, the alliance of ADSCC-CM and hydrogel may become a potential alternative in hypertrophic scar prophylaxis.

Antibacterial Nanopillar Array for an Implantable Intraocular Lens

Postsurgical intraocular lens (IOL) infection caused by pathogenic bacteria can result in blindness and often requires a secondary operation to replace the contaminated lens. The incorporation of an antibacterial property onto the IOL surface can prevent bacterial infection and postoperative endophthalmitis. This study describes a polymeric nanopillar array (NPA) integrated onto an IOL, which captures and eradicates the bacteria by rupturing the bacterial membrane. This is accomplished by changing the behavior of the elastic nanopillars using bending, restoration, and antibacterial surface modification. The combination of the polymer coating and NPA dimensions can decrease the adhesivity of corneal endothelial cells and posterior capsule opacification without causing cytotoxicity. An ionic antibacterial polymer layer is introduced onto an NPA using an initiated chemical vapor deposition process. This improves bacterial membrane rupture efficiency by increasing the interactions between the bacteria and nanopillars and damages the bacterial membrane using quaternary ammonium compounds. The newly developed ionic polymer-coated NPA exceeds 99% antibacterial efficiency against Staphylococcus aureus, which is achieved through topological and physicochemical surface modification. Thus, this paper provides a novel, efficient strategy to prevent postoperative complications related to bacteria contamination of IOL after cataract surgery.

Facilitated Transdermal Drug Delivery Using Nanocarriers-Embedded Electroconductive Hydrogel Coupled with Reverse Electrodialysis-Driven Iontophoresis

We herein developed an iontophoretic transdermal drug delivery system for the effective delivery of electrically mobile drug nanocarriers (DNs). Our system consists of a portable and disposable reverse electrodialysis (RED) battery that generates electric power for iontophoresis through the ionic exchange. In addition, in order to provide a drug reservoir to the RED-driven iontophoretic system, an electroconductive hydrogel composed of polypyrrole-incorporated poly(vinyl alcohol) (PYP) was used. The PYP hydrogel facilitated electron transfer from the RED battery and accelerated the mobility of electrically mobile DNs released from the PYP hydrogel. In this study, we showed that fluconazole- or rosiglitazone-loaded DNs could be functionalized with charge-inducing agents, and DNs with charge modification resulted in facilitated transdermal transport via repulsive RED-driven iontophoresis. In addition, topical application and RED-driven iontophoresis of rosiglitazone-loaded DNs resulted in an effective antiobese condition displaying decreased bodyweight, reduced glucose level, and increased conversion of white adipose tissues to brown adipose tissues in vivo. Consequently, we highlight that this transdermal drug delivery platform would be extensively utilized for delivering diverse therapeutic agents in a noninvasive way.

Synthesis and Applications of Hydrogels in Cancer Therapy

Hydrogels are water-insoluble, hydrophilic, cross-linked, three-dimensional networks of polymer chains having the ability to swell and absorb water but do not dissolve in it, that comprise the major difference between gels and hydrogels. The mechanical strength, physical integrity and solubility are offered by the crosslinks. The different applications of hydrogels can be derived based on the methods of their synthesis, response to different stimuli, and their different kinds. Hydrogels are highly biocompatible and have properties similar to human tissues that make it suitable to be used in various biomedical applications, including drug delivery and tissue engineering. The role of hydrogels in cancer therapy is highly emerging in recent years. In the present review, we highlighted different methods of synthesis of hydrogels and their classification based on different parameters. Distinctive applications of hydrogels in the treatment of cancer are also discussed.

Gelatin-based micro-hydrogel carrying genetically engineered human endothelial cells for neovascularization

Cell delivery systems based on micro-hydrogels may facilitate the long-term survival of cells upon transplantation. Micro-hydrogels may effectively support cell proliferation, attachment, and migration in ischemic environments. In this study, we report the fabrication of a gelatin methacrylate (GelMA)-based micro-hydrogel for efficient in vivo delivery of genetically engineered endothelial cells. Micro-hydrogels were initially processed via electrospraying of GelMA and alginate (ALG) mixtures (at different ratios) on to calcium chloride (CaCl₂) solution. Electrospraying of the GelMA/ALG mixture resulted in the formation of a micro-hydrogel, owing to ALG crosslinking. Secondary crosslinking of GelMA with UV light and ALG hydrogel chelation using sodium citrate solution resulted in GelMA-based micro-hydrogel formation. We observed the angiogenic response of human umbilical vein endothelial cells (HUVECs) in GelMA concentration-dependent manner. The seeding of HUVECs engineered to express human vascular endothelial growth factor on to the GelMA micro-hydrogel and the subsequent transplantation of the micro-hydrogel into a hindlimb ischemia model effectively attenuated the ischemia condition. This facile and simple micro-hydrogel fabrication strategy may serve as a robust method to fabricate efficient cell carriers for various ischemic diseases. STATEMENT OF SIGNIFICANCE: For the therapeutic angiogenesis, it is important to provide the therapeutic cells with a carrier that could stabilize therapeutic cells and facilitate long-term survival of cells. Furthermore, it is also important to administer as many therapeutic cells as possible in a fixed volume. From these cues, we fabricated ECM-based micro-hydrogel produced by the high through-put system. And we intended to facilitate activation of therapeutic cells by coating the therapeutic cells onto the micro-hydrogel. In this manuscript, we fabricated methacrylate gelatin (GelMA) based micro-hydrogels using the electro-spraying method and coated HUVECs engineered to express hVEGF onto the micro-hydrogels. Then, we identified that GelMA concentration-dependent angiogenic response of HUVECs. Furthermore, we demonstrated that the VEGF secreting HUVEC-GelMA micro-hydrogels induced the restoration of blood flow and neovascularization in a hind-limb ischemia mouse model. These findings demonstrate that the high-throughput fabrication of ECM micro-hydrogels could be a novel platform to apply in neovascularization and tissue engineering.

Janus Membranes: Creating Asymmetry for Energy Efficiency

Membranes are recognized as a key component in many environment and energy-related applications, but conventional membranes are challenged to satisfy the growing demand for ever more energy-efficient processes. Janus membranes, a novel class with asymmetric properties on each side, have recently emerged and represent enticing opportunities to address this challenge. With an inner driving force arising from their asymmetric configuration, Janus membranes are appealing for enhancing energy efficiency in a variety of membrane processes by promoting the desired transport. Here, the fundamental principles to prepare Janus membranes with asymmetric surface wettability and charges are summarized, and how they work in conventional and unconventional membrane processes is demonstrated.

Multifunctional smart hydrogels: potential in tissue engineering and cancer therapy

In recent years, clinical applications have been proposed for various hydrogel products. Hydrogels can be derived from animal tissues, plant extracts and/or adipose tissue extracellular matrices; each type of hydrogel presents significantly different functional properties and may be used for many different applications, including medical therapies, environmental pollution treatments, and industrial materials. Due to complicated preparation techniques and the complexities associated with the selection of suitable materials, the applications of many host-guest supramolecular polymeric hydrogels are limited. Thus, improvements in the design and construction of smart materials are highly desirable in order to increase the lifetimes of functional materials. Here, we summarize different functional hydrogels and their varied preparation methods and source materials. The multifunctional properties of hydrogels, particularly their unique ability to adapt to certain environmental stimuli, are chiefly based on the incorporation of smart materials. Smart materials may be temperature sensitive, pH sensitive, pH/temperature dual sensitive, photoresponsive or salt responsive and may be used for hydrogel wound repair, hydrogel bone repair, hydrogel drug delivery, cancer therapy, and so on. This review focuses on the recent development of smart hydrogels for tissue engineering applications and describes some of the latest advances in using smart materials to create hydrogels for cancer therapy.

Dual Salt- and Thermoresponsive Programmable Bilayer Hydrogel Actuators with Pseudo-Interpenetrating Double-Network Structures

Development of smart soft actuators is highly important for fundamental research and industrial applications but has proved to be extremely challenging. In this work, we present a facile, one-pot, one-step method to prepare dual-responsive bilayer hydrogels, consisting of a thermoresponsive poly( N-isopropylacrylamide) (polyNIPAM) layer and a salt-responsive poly(3-(1-(4-vinylbenzyl)-1 H-imidazol-3-ium-3-yl)propane-1-sulfonate) (polyVBIPS) layer. Both polyNIPAM and polyVBIPS layers exhibit a completely opposite swelling/shrinking behavior, where polyNIPAM shrinks (swells) but polyVBIPS swells (shrinks) in salt solution (water) or at high (low) temperatures. By tuning NIPAM:VBIPS ratios, the resulting polyNIPAM/polyVBIPS bilayer hydrogels enable us to achieve fast and large-amplitude bidirectional bending in response to temperatures, salt concentrations, and salt types. Such bidirectional bending, bending orientation, and degree can be reversibly, repeatedly, and precisely controlled by salt- or temperature-induced cooperative swelling-shrinking properties from both layers. Based on their fast, reversible, and bidirectional bending behavior, we further design two conceptual hybrid hydrogel actuators, serving as a six-arm gripper to capture, transport, and release an object and an electrical circuit switch to turn on-and-off a lamp. Different from the conventional two- or multistep methods for preparation of bilayer hydrogels, our simple, one-pot, one-step method and a new bilayer hydrogel system provide an innovative concept to explore new hydrogel-based actuators through combining different responsive materials that allow us to program different stimuli for soft and intelligent materials applications.

pH-Responsive Janus Film Constructed with Hydrogen-Bonding Assembly and Dopamine Chemistry

Poly(acrylic acid) (PAA) was partially grafted with dopamine (PAA-dopa), and then layer-by-layer assembled with poly(vinylpyrrolidone) (PVPON) to prepare hydrogen-bonded (PVPON/PAA-dopa) _n film. Polydopamine (PDA) was deposited on (PVPON/PAA-dopa) _n film in the presence of oxidant, and hence the whole (PVPON/PAA-dopa) _nPDA film was cross-linked. (PVPON/PAA-dopa) _nPDA could be utilized as a platform to produce the free-standing Janus film because of the easy detaching process and various chemical reactivity of PDA layer. Ag nanoparticles were formed on (PVPON/PAA-dopa) _nPDA film by electroless metallization. 1 H,1 H,2 H,2 H-Perfluorodecanethiol (PFDT) was used to further modify the film through Michael addition. After detaching from the substrate, (PVPON/PAA-dopa)₂₀PDA/Ag/PFDT exhibits reversible swelling-shrinking behavior as the pH value changes. This free-standing film shows Janus character, one side is hydrophobic, whereas the other side is hydrophilic. In addition, the hydrophobic surface exhibits a surface-enhanced Raman scattering effect, whereas the hydrophilic side does not.