In situ gelable interpenetrating double network hydrogel formulated from binary components: thiolated chitosan and oxidized dextran

Schiff base crosslinked hyaluronic acid hydrogels with tunable and cell instructive time-dependent mechanical properties

The dynamic interplay between cells and their native extracellular matrix (ECM) influences cellular behavior, imposing a challenge in biomaterial design. Dynamic covalent hydrogels are viscoelastic and show self-healing ability, making them a potential scaffold for recapitulating native ECM properties. We aimed to implement kinetically and thermodynamically distinct crosslinkers to prepare self-healing dynamic hydrogels to explore the arising properties and their effects on cellular behavior. To do so, aldehyde-substituted hyaluronic acid (HA) was synthesized to generate imine, hydrazone, and oxime crosslinked dynamic covalent hydrogels. Differences in equilibrium constants of these bonds yielded distinct properties including stiffness, stress relaxation, and self-healing ability. The effects of degree of substitution (DS), polymer concentration, crosslinker to aldehyde ratio, and crosslinker functionality on hydrogel properties were evaluated. The self-healing ability of hydrogels was investigated on samples of the same and different crosslinkers and DS to obtain hydrogels with gradient properties. Subsequently, human dermal fibroblasts were cultured in 2D and 3D to assess the cellular response considering the dynamic properties of the hydrogels. Moreover, assessing cell spreading and morphology on hydrogels having similar modulus but different stress relaxation rates showed the effects of matrix viscoelasticity with higher cell spreading in slower relaxing hydrogels.

Polysaccharide-Based Double-Network Hydrogels: Polysaccharide Effect, Strengthening Mechanisms, and Applications

Polysaccharides are carbohydrate polymers that are major components of plants, animals, and microorganisms, with unique properties. Biological hydrogels are polymeric networks that imbibe and retain large amounts of water and are the major components of living organisms. The mechanical properties of hydrogels are critical for their functionality and applications. Since synthetic polymeric double-network (DN) hydrogels possess unique network structures with high and tunable mechanical properties, many natural functional polysaccharides have attracted increased attention due to their rich and convenient sources, unique chemical structure and chain conformation, inherently desirable cytocompatibility, biodegradability and environmental friendliness, diverse bioactivities, and rheological properties, which rationally make them prominent constituents in designing various strong and tough polysaccharide-based DN hydrogels over the past ten years. This review focuses on the latest developments of polysaccharide-based DN hydrogels to comprehend the relationship among the polysaccharide properties, inner strengthening mechanisms, and applications. The aim of this review is to provide an insightful mechanical interpretation of the design strategy of novel polysaccharide-based DN hydrogels and their applications by introducing the correlation between performance and composition. The mechanical behavior of DN hydrogels and the roles of varieties of marine, microbial, plant, and animal polysaccharides are emphatically explained.

Advances in the Development of Nano-Engineered Mechanically Robust Hydrogels for Minimally Invasive Treatment of Bone Defects

Injectable hydrogels were discovered as attractive materials for bone tissue engineering applications given their outstanding biocompatibility, high water content, and versatile fabrication platforms into materials with different physiochemical properties. However, traditional hydrogels suffer from weak mechanical strength, limiting their use in heavy load-bearing areas. Thus, the fabrication of mechanically robust injectable hydrogels that are suitable for load-bearing environments is of great interest. Successful material design for bone tissue engineering requires an understanding of the composition and structure of the material chosen, as well as the appropriate selection of biomimetic natural or synthetic materials. This review focuses on recent advancements in materials-design considerations and approaches to prepare mechanically robust injectable hydrogels for bone tissue engineering applications. We outline the materials-design approaches through a selection of materials and fabrication methods. Finally, we discuss unmet needs and current challenges in the development of ideal materials for bone tissue regeneration and highlight emerging strategies in the field.

Thiolated Polymeric Hydrogels for Biomedical Applications: A Review

Hydrogels are a three-dimensional (3D) network of hydrophilic polymers. The physical and chemical crosslinking of polymeric chains maintains the structure of the hydrogels even when they are swollen in water. They can be modified with thiol by thiol epoxy, thiol-ene, thiol-disulfide, or thiol-one reactions. Their application as a matrix for protein and drug delivery, cellular immobilization, regenerative medicine, and scaffolds for tissue engineering was initiated in the early 21st century. This review focuses on the ingredients, classification techniques, and applications of hydrogels, types of thiolation by different thiol-reducing agents, along with their mechanisms. In this study, different applications for polymers used in thiolated hydrogels, including dextran, gelatin, polyethylene glycol (PEG), cyclodextrins, chitosan, hyaluronic acid, alginate, poloxamer, polygalacturonic acid, pectin, carrageenan gum, arabinoxylan, carboxymethyl cellulose (CMC), gellan gum, and polyvinyl alcohol (PVA) are reviewed.

Polymeric Gel Scaffolds and Biomimetic Environments for Wound Healing

Infected wounds that do not heal are a worldwide problem that is worsening, with more people dying and more money being spent on care. For any disease to be managed effectively, its root cause must be addressed. Effective wound care becomes a bigger problem when various traditional wound healing methods and products may not only fail to promote good healing. Still, it may also hinder the healing process, causing wounds to stay open longer. Progress in tissue regeneration has led to developing three-dimensional scaffolds (3D) or constructs that can be leveraged to facilitate cell growth and regeneration while preventing infection and accelerating wound healing. Tissue regeneration uses natural and fabricated biomaterials that encourage the growth of tissues or organs. Even though the clinical need is urgent, the demand for polymer-based therapeutic techniques for skin tissue abnormalities has grown quickly. Hydrogel scaffolds have become one of the most imperative 3D cross-linked scaffolds for tissue regeneration because they can hold water perfectly and are porous, biocompatible, biodegradable, and biomimetic. For damaged organs or tissues to heal well, the porosity topography of the natural extracellular matrix (ECM) should be imitated. This review details the scaffolds that heal wounds and helps skin tissue to develop. After a brief overview of the bioactive and drug-loaded polymeric hydrogels, the discussion moves on to how the scaffolds are made and what they are made of. It highlights the present uses of in vitro and in-vivo employed biomimetic scaffolds. The prospects of how well bioactiveloaded hydrogels heal wounds and how nanotechnology assists in healing and regeneration have been discussed.

In-situ forming hydrogel based on thiolated chitosan/carboxymethyl cellulose (CMC) containing borate bioactive glass for wound healing

Suitable wound dressings for accelerating wound healing are actively being designed and synthesised. In this study, thiolated chitosan (tCh)/oxidized carboxymethyl cellulose (OCMC) hydrogel containing Cu-doped borate bioglass (BG) was developed as a wound dressing to improve wound healing in a full-thickness skin defect of mouse animal model. Thiolation was used to incorporate thiol groups into chitosan (Ch) to enhance its water solubility and mucoadhesion characteristics. Here, the in situ forming hydrogel was successfully developed using the Schiff-based reaction, and its physio-chemical and antibacterial characteristics were examined. Borate BG was also incorporated in the generated hydrogel to promote angiogenesis and tissue regeneration at the wound site. Investigations of in vitro cytotoxicity assays demonstrated that the synthesised hydrogels showed good biocompatibility and promoted cell growth. These results inspired us to investigate the effectiveness of skin wound healing in a mouse model. On the backs of animals, two full-thickness wounds were created and treated utilising two different treatment conditions: (1) OCMC/tCh hydrogel, (2) OCMC/tCh/borate BG, and (3) control defect. The wound closure ratio, collagen deposition, and angiogenesis activity were measured after 14 days to determine the healing efficacy of the in situ hydrogels used as wound dressings. Overall, the hydrogel containing borate BG was maintained in the defect site, healing efficiency was replicable, and wound healing was apparent. In conclusion, we found consistent angiogenesis, remodelling, and accelerated wound healing, which we propose may have beneficial effects on the repair of skin defects.

Ultrafast in-situ forming halloysite nanotube-doped chitosan/oxidized dextran hydrogels for hemostasis and wound repair

A series of halloysite nanotube (HNT)-doped chitosan (CS)/oxidized dextran (ODEX) adhesive hydrogels were developed through a Schiff base reaction. The resultant CS/ODEX/HNT hydrogels could not only form in situ on wounds within only 1 s when injected, but could also adapt to wounds of different shapes and depths after injection. We established four rat and rabbit hemorrhage models and demonstrated that the hydrogels are better than the clinically used gelatin sponge for reducing hemostatic time and blood loss, particularly in arterial and deep noncompressible bleeding wounds. Moreover, the natural antibacterial features of CS and ODEX provided the hydrogels with strong bacteria-killing effects. Consequently, they significantly promoted methicillin-resistant Staphylococcus aureus -infected-wound repair compared to commercial gelatin sponge and silver-alginate antibacterial wound dressing. Hence, our multifunctional hydrogels with facile preparation process and utilization procedure could potentially be used as first-aid biomaterials for rapid hemostasis and infected-wound repair in emergency injury events.

Radiation-initiated high strength chitosan/lithium sulfonate double network hydrogel/aerogel with porosity and stability for efficient CO2 capture

Developing efficient and inexpensive CO₂ capture technologies is a significant way to reduce carbon emissions. In this work, a novel chitosan/lithium sulfonate double network high strength hydrogel is synthesized by electron beam radiation. Due to the electron beam having a wide radiation area and certain penetrating power, the free radical polymerization can be initiated more uniformly and quickly in the hydrogel. The network structure of the hydrogel prepared by radiation-initiated polymerization is more uniform than that prepared by conventional chemical initiator-initiated polymerization. Meanwhile, the introduction of the second network to construct the double network structure does not reduce the surface area of the aerogel, which is different from the conventional method of grafting or impregnation modified porous materials. Moreover, the synthesized aerogels have good physical and chemical stability. The freeze-dried aerogels possess a porous structure and CO₂ capture ability due to the CO₂-philic double network structure. Because of the inexpensive raw material and convenient radiation process, this work can reduce the cost of CO₂ adsorbents and has prospects of application in the field of CO₂ solid adsorbents.

Chitosan hydrogel is regenerated from alkali/urea aqueous solution and the lithium sulfonate second network is introduced by electron beam radiation-initiated in situ free radical polymerization. The freeze-dried aerogel has CO₂ capture capacity.

Designing Hydrogels for 3D Cell Culture Using Dynamic Covalent Crosslinking

Designing simple biomaterials to replicate the biochemical and mechanical properties of tissues is an ongoing challenge in tissue engineering. For several decades, new biomaterials have been engineered using cytocompatible chemical reactions and spontaneous ligations via click chemistries to generate scaffolds and water swollen polymer networks, known as hydrogels, with tunable properties. However, most of these materials are static in nature, providing only macroscopic tunability of the scaffold mechanics, and do not reflect the dynamic environment of natural extracellular microenvironment. For more complex applications such as organoids or co-culture systems, there remain opportunities to investigate cells that locally remodel and change the physicochemical properties within the matrices. In this review, advanced biomaterials where dynamic covalent chemistry is used to produce stable 3D cell culture models and high-resolution constructs for both in vitro and in vivo applications, are discussed. The implications of dynamic covalent chemistry on viscoelastic properties of in vitro models are summarized, case studies in 3D cell culture are critically analyzed, and opportunities to further improve the performance of biomaterials for 3D tissue engineering are discussed.

Recent Advances in Injectable Dual Crosslinking Hydrogels for Biomedical Applications

Injectable dual crosslinking hydrogels hold great promise to improve therapeutic efficacy in minimally invasive surgery. Compared with prefabricated hydrogels, injectable hydrogels can be implanted more accurately into deeply enclosed sites and repair irregularly shaped lesions, showing great applicable potential. Here, the current fabrication considerations of injectable dual crosslinking hydrogels are reviewed. Besides, the progress of the hydrogels used in corresponding applications and emerging challenges are discussed, with detailed emphasis in the fields of bone and cartilage regeneration, wound dressings, sensors and other less mentioned applications for their more hopeful employments in clinic. It is envisioned that the further development of the injectable dual crosslinking hydrogels will catalyze their innovation and transformation in the biomedical field.

Why chitosan could be apt candidate for glaucoma drug delivery - An overview

Most of the people in the world are affected by glaucoma, which leads to irreversible blindness. Several patient friendly treatments are available, nevertheless medications lack an easy and efficient way of sustained delivery. To make the delivery with enhanced bioavailability, biodegradable and non-biodegradable polymers-based drug carriers are explored. However, ocular drug delivery issues have not been resolved yet due to less adhesiveness, poor penetration ability, pH, and temperature dependent burst releases. Chitosan is found to be effective for ocular drug delivery due to excellent physio-chemical properties in terms of overcoming the existing issues. In this review, we aim to highlight why it has been chosen and the holy grail for ocular drug delivery. Besides, we have comprehensively reviewed recent patents on chitosan as a platform for ocular drug delivery and future perspectives on factors, lacunae and challenges that need to be addressed for better ocular delivery methods for glaucoma management.

Dual-Cross-Linked Network Hydrogels with Multiresponsive, Self-Healing, and Shear Strengthening Properties

Dual-cross-linked network (DCN) hydrogels with multiresponsive and self-healing properties are attracting intensive interests due to their enhanced mechanical strength for a wide range of applications. Herein, we developed a DCN hydrogel that combines a dynamic imine and a benzoxaboronic ester with a neutral pK_a value (∼7.2) as dual linkages and contains biocompatible zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] as the backbone. Oscillatory rheology result indicated shear strengthening mechanical properties compared to the single-cross-linked network (SCN) hydrogels, which use either imine bond or benzoxaboronic ester as the linkage alone. Due to the coexistence of stimuli-responsive imine and benzoxaboronic ester, the DCN hydrogels show sensitive multiple responsiveness to pH, sugar, and hydrogen peroxide. The dynamic nature of the dual linkages endows the DCN hydrogels with excellent self-healing ability after fracture. More importantly, the excellent biocompatibility and performance in three-dimensional (3D) cell encapsulation were established by a cytotoxicity Live/Dead assay, indicating DCN hydrogel's great potential as a cell culture scaffold. The biocompatible poly(MPC)-based backbone and the rapid formation of the cross-linking network make the DCN hydrogels promising candidates for future biomedical applications.

Injectable Functional Biomaterials for Minimally Invasive Surgery

Injectable materials represent very attractive ready-to-use biomaterials for application in minimally invasive surgical procedures. It is shown that this approach to treat, for example, vertebral fracture, craniofacial defects, or tumor resection has significant clinical potential in the biomedical field. In the last four decades, calcium phosphate cements have been widely used as injectable materials for orthopedic surgery due to their excellent properties in terms of biocompatibility and osteoconductivity. However, few clinical studies have demonstrated certain weaknesses of these cements, which include high viscosity, long degradation time, and difficulties being manipulated. To overcome these limitations, the use of sol-gel technology has been investigated, which has shown good results for synthesis of injectable calcium phosphate-based materials. In the last few decades, injectable hydrogels have gained increasing attention owing to their structural similarities with the extracellular matrix, easy process conditions, and potential applications in minimally invasive surgery. However, the need to protect cells during injection leads to the development of double network injectable hydrogels that are capable of being cross-linked in situ. This review will provide the current state of the art and recent advances in the field of injectable biomaterials for minimally invasive surgery.

Management of moderate-to-severe dry eye disease using chitosan-N-acetylcysteine (Lacrimera®) eye drops: a retrospective case series

PURPOSE

Dry eye disease is a highly prevalent condition that causes tear film instability, ocular discomfort, and visual disturbance. Lacrimera eye drops are approved for the short-term treatment of dry eye disease. We aimed to evaluate the clinical outcome of patients with moderate-to-severe dry eye disease treated with Lacrimera up to 1 month during routine clinical practice.

METHODS

We retrospectively collected data from 25 patients with dry eye disease from the start of Lacrimera treatment up to 1 month of follow-up period. We analyzed standard clinical parameters to follow the course of the patients' dry eye signs and symptoms.

RESULTS

Based on corneal staining data, we found that the percentage of patients with intact corneas raised from 12 to 64% after 1 month of Lacrimera treatment. During this period, we also observed an increase in both tear breakup time (p < 0.05) and Schirmer's score (p  < 0.001), with lower values indicating severer signs. Lacrimera eye drops were judged by 29% of the patients to be effective at relieving eye symptoms.

CONCLUSIONS

Lacrimera appears to be safe and effective in the treatment of dry eye disease, as assessed by corneal staining, tear breakup time, and Schirmer's analyses. Our data suggest that the regenerative effect of Lacrimera eye drops peaks at 2 weeks and is sustained for at least 1 month when administered for a longer period of time.

In situ forming oxidized salecan/gelatin injectable hydrogels for vancomycin delivery and 3D cell culture

Antibiotics are widely used in clinical medicine. As an important member, vancomycin often plays an irreplaceable role in some serious infections, but its use still lacks suitable carriers and effective formulations. In order to find a vancomycin carrier with potential for clinical application, a new class of oxidized salecan/gelatin based injectable hydrogels are constructed through dynamic covalent Schiff base reaction. The sodium periodate oxidized salecan (OS) precursor was synthesized, and then the gelatin/oxidized salecan (GS) hydrogels are formed by blending gelatin and OS buffer solutions without any additives under physiological condition. The chemical structure, as well as internal morphologies, mechanical properties, In vitro enzymatic degradation profile of hydrogels are investigated with proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), compression test and rheological experiments. The resulted hydrogels exhibit excellent antibacterial ability and variable characteristics. Moreover, the hydrogels display ideal drug release kinetics and mechanisms, and are applied successfully to the controlled release of vancomycin. Importantly, benefitting from the excellent biocompatibility and the reversibly crosslinked networks, GS hydrogels can function as suitable three dimensional (3D) extracellular matrix for HeLa cells, leading to the encapsulated cells maintaining a high viability and proliferative capacity. Therefore, the injectable GS hydrogels demonstrated attractive properties for future application in pharmaceutics and tissue engineering.

3D printing of high-strength chitosan hydrogel scaffolds without any organic solvents

Here, a novel direct ink printing method was developed to print high-strength chitosan hydrogel scaffolds without any organic solvents.

Dynamic crosslinked and injectable biohydrogels as extracellular matrix mimics for the delivery of antibiotics and 3D cell culture

Antibiotics are widely used in clinical medicine. As an important member, vancomycin often plays an irreplaceable role in some serious infections but for its use, there is still a lack of suitable carriers and effective formulations. To find a vancomycin carrier with potential for clinical applications, a new class of poly(γ-glutamic acid)/dextran-based injectable hydrogels have been constructed through dynamic covalent hydrazone linkages. Adipic dihydrazide (ADH)-grafted poly(γ-glutamic acid) (PGAADH) and sodium periodate-oxidized dextran (OD) precursors were synthesized; then, the hydrogels were formed by blending PGAADH and OD buffer solutions without any additives under physiological conditions. The newly formed precursor structures, mechanical properties, morphologies, hydrogel degradation profiles, and the interaction between the drug and precursors were investigated with FTIR spectroscopy, ¹H NMR spectroscopy, rheological experiments, compression tests, SEM, and isothermal titration calorimetric (ITC) measurements. The resulting hydrogels exhibited excellent antibacterial ability and ideal variable performances. Moreover, the hydrogels exhibited different drug release kinetics and mechanisms and were applied effectively towards the controlled release of vancomycin. Significantly, benefitting from the reversibly cross-linked systems and the excellent biocompatibility, the hydrogels can work as the ideal material for HeLa cell culture, leading to encapsulated cells with higher viability and capacity that is proliferative. Therefore, the injectable PGAADH/OD hydrogels demonstrated attractive properties for future applications in pharmaceutics and tissue engineering.

Polysaccharides-polypeptide derived biohydrogels were formed using hydrazone chemistry as crosslinking strategy, which have controllable drug release rate and many other potential applications, especially in sustained drug delivery and cell scaffold.

Adaptable to Mechanically Stable Hydrogels Based on the Dynamic Covalent Cross-Linking of Thiol-Aldehyde Addition

We exploit the thiol-aldehyde addition (TAA) reaction to build a dynamic covalent cross-linking (DCC) hydrogel in the physiological-pH environment. Due to the rapid and reversible TAA reaction, the resulting hydrogels are readily adapted for convenient manipulation, for example, free molding, easy injection, and self-healing. Meanwhile, the labile hemithioacetal bonds within the DCC hydrogel can convert to thermodynamically stable bonds via spontaneous thiol transfer reactions, thereby realizing poststabilization as needed. The successful application as a long-term scaffold for repair of barely self-healed bone defect indicated the hydrogels with both adaptability and mechanical stability based on thiol-aldehyde addition reaction is significant for biomedical areas.

An Antifouling Hydrogel Containing Silver Nanoparticles for Modulating the Therapeutic Immune Response in Chronic Wound Healing

Patients with diabetic wounds have deficient local and systemic cellular immunity. Herein, a new silver nanoparticle-containing hydrogel with antifouling properties was developed for enhancing the immune response in diabetic wound healing. The antifouling property was obtained by adjusting the composition of cationic chitosan and anionic dextran to approach zero charge. Furthermore, this hybrid hydrogel showed long-lasting and broad-spectrum antibacterial activity. Rapid wound contraction was observed after the treatment with the hydrogel, which suggested its superior healing activity to promote fibroblast migration, granulation tissue formation, and angiogenesis. The upregulation of CD68+ and CD3+ expression levels demonstrated that the hydrogel could trigger immune responses in the treatment of wound healing. These results show that this antifouling hybrid hydrogel as a wound dressing provided a promising strategy for the treatment of diabetic ulcers.

Double network hydrogel for tissue engineering

Double network (DN) hydrogels, a kind of promising soft and tough hydrogels, are produced by two unique contrasting networks with designed network entanglement burst into the field of materials science as versatile functional systems for a very broad range of applications. A part of the DN hydrogels is characterized by extraordinary mechanical properties providing efficient biocompatible and high strength for holding considerable promise in tissue engineering. Following DN hydrogels principles and consideration of biomedical applications, we provide an overall view of the present various DN hydrogels and look forward to the future of DN hydrogels for tissue engineering. In this review, the preparation methods, structure, properties, current situation, and challenges are mainly discussed for the purpose of tissue engineering. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

Biocompatible scaffolds based on natural polymers for regenerative medicine

The chitosan and gelatine are commonly used biopolymers for the tissue engineering applications. In the previous methods for the cryogels synthesis, multistep preparation methods using toxic cross-linking agents such as glutaraldehyde are reported. Here, we present a two-step preparation method of gelatin macroporous cryogels and one-step preparation method of chitosan or gelatin cryogels. The physico-chemical properties of obtained scaffolds were characterized using FTIR, zeta potential, SEM and laser confocal microscopy. Non-toxic and biodegradable cross-linking agents such as oxidized dextran and 1,1,3,3-tetramethoxypropane are utilized. The one-step chitosan cryogels had degradation degree ~2 times higher compared to the cryogels prepared with a two-step method i.e. reduced by borohydride. Scaffolds cross-linked by glutaraldehyde had about 40% viability, whereas nine various compositions of cryogels showed significantly higher viability (~80%) of fibroblast cells in vitro. The cryogels were obtained without using the harmful compounds and therefore can be used straightforward as biocompatible and biodegradable scaffolds for the cell culturing purposes and other biomedical applications.

The chitosan hydrogels: from structure to function

This review places an emphasis on chitosan intelligent hydrogels. The fabrication methods and mechanisms are introduced in this review and the interactions of the formation of hydrogels with both physical and chemical bonds are also introduced. The relationship between the structural characteristics and the corresponding functions of stimuli-responsive characteristics, self-healing functions and high mechanical strength properties of the chitosan hydrogels are discussed in detail.

Study of locust bean gum reinforced cyst-chitosan and oxidized dextran based semi-IPN cryogel dressing for hemostatic application

Severe blood loss due to traumatic injuries remains one of the leading causes of death in emergency settings. Chitosan continues to be the candidate material for hemostatic applications due to its inherent hemostatic properties. However, available chitosan-based dressings have been reported to have an acidic odor at the wound site due to the incorporation of acid based solvents for their fabrication and deformation under compression owing to low mechanical strength limiting its usability. In the present study semi-IPN cryogel was fabricated via Schiff's base cross-linking between the polyaldehyde groups of oxidized dextran and thiolated chitosan in presence of locust bean gum (LBG) known for its hydrophilicity. Polymerization at -12 °C yielded macroporous semi-IPN cryogels with an average pore size of 124.57 ± 20.31 μm and 85.46% porosity. The hydrophobicity index of LBG reinforced semi-IPN cryogel was reduced 2.42 times whereas the swelling ratio was increased by 156.08% compare to control cryogel. The increased hydrophilicity and swelling ratio inflated the compressive modulus from 28.1 kPa to 33.85 for LBG reinforced semi-IPN cryogel. The structural stability and constant degradation medium pH were also recorded over a period of 12 weeks. The cryogels demonstrated lower adsorption affinity towards BSA. The cytotoxicity assays (direct, indirect) with 3T3-L1 fibroblast cells confirmed the cytocompatibility of the cryogels. The hemolysis assay showed <5% hemolysis confirming blood compatibility of the fabricated cryogel, while whole blood clotting and platelet adhesion assays confirmed the hemostatic potential of semi-IPN cryogel.

Chemical Synthesis of Biomimetic Hydrogels for Tissue Engineering

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

Facile in situ formation of hybrid gels for direct-forming tissue engineering

Development of bioactive hydrogel as extracellular matrix (ECM) is a very important field for cell-based therapy. In this study, we provided a facile method based on sol-gel process for fabricating bioactive composite hydrogels. The composite hydrogels were composed of sol-gel derived silica and biopolymer. Different amounts of silica solution (20-80wt%) were mixed with 2% polymer sol (alginate) followed by aging and gelation to form a network so that the alginate-silica hybrid mixture could form a gel without any additional crosslinking process. The self-gelation time of the hybrid hydrogel measured by rheometer was reduced as the content of silica was increased. Such hydrogels had highly porous and interconnected structures. Their strut showed uniform surface texture. Under physiological conditions (PBS, 37°C), these hybrid hydrogels exhibited long-term stability compared to alginate hydrogels as control. The mechanical properties of these hydrogels such as compressive strength, compressive modulus, and work of fracture were significantly enhanced by hybridization with sol-gel derived silica. In vitro cell tests revealed that these hybrid hydrogels exhibited improved cell adhesion and proliferation behaviors compared to pure alginate hydrogel cross-linked by CaCl₂ solution. Furthermore, cell encapsulation within these hydrogels revealed that their alginate-silica composite provided suitable microenvironment for cell survival.

Effect of Topically Administered Chitosan-N-acetylcysteine on Corneal Wound Healing in a Rabbit Model

Purpose

The present study was performed to investigate the effect of topically administered chitosan-N-acetylcysteine (C-NAC) on corneal wound healing in a rabbit model.

Methods

A total of 20 New Zealand White rabbits were included in the randomized, masked, placebo-controlled experiment. A monocular epithelial debridement was induced by manual scraping under general anesthesia. Animals were randomized to receive either C-NAC two times daily or placebo. Monitoring of corneal wound healing was performed with ultra-high-resolution optical coherence tomography (OCT) and epithelial fluorescein staining. Measurements were done immediately after and up to 72 hours after wound induction.

Results

No difference in wound size was found immediately after surgical debridement between the C-NAC group and the placebo group. Wound healing was significantly faster in the C-NAC group compared to the placebo group (p < 0.01 for both methods). A good correlation was found between the OCT technique and the epithelial fluorescein staining in terms of wound size (r = 0.94).

Conclusions

Administration of C-NAC containing eye drops twice daily leads to a faster corneal wound healing in a rabbit model of corneal debridement as compared to placebo. Ultra-high-resolution OCT is considered a noninvasive, dye-free alternative to conventional fluorescein staining in assessing corneal wound healing also in humans.

Diabetic ulcer regeneration: stem cells, biomaterials, growth factors

The impairment of ulcer wound healing in diabetic patients is a vital clinical problem affecting millions of patients. Several clinical and basic science studies have demonstrated that stem cell therapy, to be effective in healing diabetic ulcer. Furthermore, these ulcer wounds may be healed from molecular maneuvering of growth factors to improve microcirculation within the ulcer wound. In addition, ulcer wound dressings may be employed as medicated systems, through the delivery of drugs, growth factors, peptides and stem cells. These dressing materials can include natural, modified and synthetic polymers, as well as their mixtures or combinations. This review paper will give a summary of some of the recent advances on the application of stem cells, biomaterials and growth factors in the treatment of diabetic ulcer wound.

Hydrogels for Biomedical Applications: Their Characteristics and the Mechanisms behind Them

Hydrogels are hydrophilic, three-dimensional networks that are able to absorb large quantities of water or biological fluids, and thus have the potential to be used as prime candidates for biosensors, drug delivery vectors, and carriers or matrices for cells in tissue engineering. In this critical review article, advantages of the hydrogels that overcome the limitations from other types of biomaterials will be discussed. Hydrogels, depending on their chemical composition, are responsive to various stimuli including heating, pH, light, and chemicals. Two swelling mechanisms will be discussed to give a detailed understanding of how the structure parameters affect swelling properties, followed by the gelation mechanism and mesh size calculation. Hydrogels prepared from natural materials such as polysaccharides and polypeptides, along with different types of synthetic hydrogels from the recent reported literature, will be discussed in detail. Finally, attention will be given to biomedical applications of different kinds of hydrogels including cell culture, self-healing, and drug delivery.

In situ forming interpenetrating hydrogels of hyaluronic acid hybridized with iron oxide nanoparticles

Four derivatives of hyaluronic acid (HA) bearing thiol (HA-SH), hydrazide (HA-hy), 2-dithiopyridyl (HA-SSPy), and aldehyde groups (HA-al) respectively were synthesized. Thiol and 2-dithiopyridyl as well as hydrazide and aldehyde make up two chemically orthogonal pairs of chemo-selective functionalities that allow in situ formation of interpenetrating (IPN) disulfide and hydrazone networks simultaneously upon the mixing of the above derivatives at once. The formation of IPN was demonstrated by comparing it with the formulations of the same total HA concentration but lacking one of the reactive components. The hydrogel composed of all four components was characterized by a larger elastic modulus than those of the control single networks (either disulfide or hydrazone) and the three component formulations gave the softest hydrogels. Moreover, a hydrazone cross-linkage was designed to contain a 1,2-diol fragment. This allowed us to partially disassemble one type of network in the IPN leaving another one unaffected. In particular, treatment of the IPN with either sodium periodate or dithiothreitol resulted in disassembly of the hydrazone and disulfide networks respectively and thus softening of the hydrogel. Contrarily, the single network hydrogels completely dissolved under the corresponding conditions. In corroboration with this, enzymatic degradation of the IPN by hyaluronidase was also substantially slower than the degradation of the single networks. In order to further improve the mechanical properties of the elaborated injectable IPN, it has been in situ hybridized with iron oxide nanoparticles (IONPs). The mesh size of the IPN was smaller than the size of the IONPs resulting in the retention of nanoparticles in the matrix under equilibrium swelling conditions. However, these nanoparticles were released upon enzymatic degradation suggesting their use as MRI tags for non-invasive tracking of the hydrogel material in vivo. Additionally, this injectable hybridized hydrogel with encapsulated IONPs can be used in hyperthermia cancer therapy.

Physiological pH-dependent gelation for 3D printing based on the phase separation of gelatin and oxidized dextran

An extrudable hydrogel with tunable gelation time under physiological pH ranges based on the phase separation of gelatin and oxidized dextran was demonstrated.

Injectable and 3D Bioprinted Polysaccharide Hydrogels: From Cartilage to Osteochondral Tissue Engineering

Biomechanical performance of functional cartilage is executed by the exclusive anisotropic composition and spatially varying intricate architecture in articulating ends of diarthrodial joint. Osteochondral tissue constituting the articulating ends comprise superfical soft cartilage over hard subchondral bone sandwiching interfacial soft-hard tissue. The shock-absorbent, lubricating property of cartilage and mechanical stability of subchondral bone regions are rendered by extended chemical structure of glycosaminoglycans and mineral deposition, respectively. Extracellular matrix glycosaminoglycans analogous polysaccharides are major class of hydrogels investigated for restoration of functional cartilage. Recently, injectable hydrogels have gained momentum as it offers patient compliance, tunable mechanical properties, cell deliverability, and facile administration at physiological condition with long-term functionality and hyaline cartilage construction. Interestingly, facile modifiable functional groups in carbohydrate polymers impart tailorability of desired physicochemical properties and versatile injectable chemistry for the development of highly potent biomimetic in situ forming scaffold. The scaffold design strategies have also evolved from single component to bi- or multilayered and graded constructs with osteogenic properties for deep subchondral regeneration. This review highlights the significance of polysaccharide structure-based functions in engineering cartilage tissue, injectable chemistries, strategies for combining analogous matrices with cells/stem cells and biomolecules and multicomponent approaches for osteochondral mimetic constructs. Further, the rheology and precise spatiotemporal positioning of cells in hydrogel bioink for rapid prototyping of complex three-dimensional anisotropic cartilage have also been discussed.

In situ formation of adhesive hydrogels based on PL with laterally grafted catechol groups and their bonding efficacy to wet organic substrates

Adhesives with catechol moieties have been widely investigated in recent years. However, actually how much catechol groups for these mussel bio-inspired adhesives, especially in their natural form under physiological condition, is appropriate to bond with organic substrates has not been studied intensively. This study blends ε-polylysine (PL), featuring laterally grafted catechols under physiological conditions (pH 7.4), with oxidized dextran to form a hydrogel in situ via the Schiff base without introducing small cytotoxic molecules as crosslinking agents. It finds that the amount of catechol groups imposes an obvious influence on gelation time, swelling behavior, and hydrogel morphology. Both the storage modulus and adhesion strength are found to increase first and decrease afterwards with an increase of pendent catechol content. Furthermore, catechol hydrogen interactions and the decrease in the crosslink density derived from the decrease of amino groups on PL are simultaneously found to affect the storage modulus. Meanwhile, multiple hydrogen-bonding interactions of catechol with amino, hydroxyl, and carboxyl groups, which are in abundance on the surface of tissue, are mainly found to provide an adhesive force. The study finds that with more catechol, there is a greater chance that the cohesive force will weaken, making the entire adhesion strength of the hydrogel decrease. Using a cytotoxicity test, the nontoxicity of the hydrogel towards the growth of L929 cells is proven, indicating that hydrogels have potential applications in soft tissue repair under natural physiological conditions.