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Because of the toxic glutaraldehyde, the chitosan-glutaraldehyde hydrogels are seriously limited in biomedical applications. In this study, exploiting bioactive compounds of Aloe barbadensis Miller, the chitosan/Aloe barbadensis Miller-glutaraldehyde (CS/AV-GDA) hydrogels were fabricated with 4-fold lower glutaraldehyde concentration without compromising hydrogel characteristics. The gelation time was controlled from a few seconds to several hours. The elastic modulus was varied from 483 to 99940 Pa. The CS/AV-GDA hydrogels could release the natural nitrite amount from 24.0 to 89.6 μ M within the first hour for antibacterial activity, then continuously deliver a few μ M every next hour for cell activities. The antibacterial test against Escherichia coli and Staphylococcus aureus revealed that the CS/AV-GDA hydrogels could kill the planktonic bacteria 5-fold more highly than control and prevent bacteria attachment on hydrogel surface effectively. Although the CS/AV-GDA hydrogels consumed only 0.25% glutaraldehyde concentration, their antibacterial capacities were comparable to chitosan-only hydrogels with 2% glutaraldehyde. For cytotoxicity tests, the CS/AV-GDA hydrogels using 0.25% glutaraldehyde concentration induce the human dermal fibroblasts proliferation significantly. All CS/AV-GDA hydrogels with glutaraldehyde crosslinker less than 1% showed non-cytotoxicity. As a result, the new CS/AV-GDA hydrogels might become an attractive candidate for medicine regeneration and tissue engineering.

The dual role of reactive oxygen and nitrogen species (RONS) in physiological and pathological processes in biological systems has been widely reported. It has been recently suggested that the regulation of RONS levels under physiological and pathological conditions is a potential therapy to promote health and treat diseases, respectively. Injectable hydrogels have been emerging as promising biomaterials for RONS-related biomedical applications owing to their excellent biocompatibility, three-dimensional and extracellular matrix-mimicking structures, tunable properties and easy functionalization. These hydrogels have been developed as advanced injectable platforms for locally generating or scavenging RONS, depending on the specific conditions of the target disease. In this review article, the design principles and mechanism by which RONS are generated/scavenged from hydrogels are outlined alongside a discussion of their in vitro and in vivo evaluations. Additionally, we highlight the advantages and recent developments of these injectable RONS-controlling hydrogels for regenerative medicines and tissue engineering applications.

Three-dimensional (3D) bioprinting has attracted considerable attention for producing 3D engineered cellular microenvironments that replicate complex and sophisticated native extracellular matrices (ECM) as well as the spatiotemporal gradients of numerous physicochemical and biological cues. Although various hydrogel-based bioinks have been reported, the development of advanced bioink materials that can reproduce the complexity of ECM accurately and mimic the intrinsic property of laden cells is still a challenge. This paper reports 3D printable bioinks composed of phenol-rich gelatin (GHPA) and graphene oxide (GO) as a component for a myogenesis-inducing material, which can form a hydrogel network in situ by a dual enzyme-mediated cross-linking reaction. The in situ curable GO/GHPA hydrogel can be utilized successfully as 3D-printable bioinks to provide suitable cellular microenvironments with facilitated myogenic differentiation of C2C12 skeletal myoblasts. Overall, we suggest that functional bioinks may be useful in muscle tissue engineering and regenerative medicine.

The impairment of regenerative processes induced by high blood-glucose level (hyperglycemia) and excessive reactive oxygen species (ROS) contributes to the diabetic complication progression and development. In this study, an injectable, in situ crosslinkable chitosan hydrogel with ROS-scavenging capability was developed by conjugating gallic acid onto the chitosan backbone (CGA). We hypothesized that gallic acid serves as both antioxidant and crosslinking moieties to form hydrogel in situ by means of enzymatic crosslinking with horseradish peroxidase (HRP). The rapid gelation (from 30 s) was observed by vial tilting. The mechanical properties and microstructures of CGA hydrogels can be well controlled by varying the concentrations of H2O2. The ROS-scavenging ability of these CGA hydrogels was demonstrated against DPPH radical, hydroxyl radical, and total reducing power. Notably, in an in vitro hyperglycemia environment, CGA hydrogels significantly improved the proliferation and migration of human dermal fibroblast cells, which are closely related to diabetic wound healing. These results suggest that CGA hydrogels have potential as advanced materials for the treatment of diabetes-related diseases via attenuating the excessive ROS production and improving cellular behaviors.

The need of tissue and organ for transplantation to repair or replace damaged tissues is significantly higher than the availability of donated organs. Tissue engineering that develops functional substitutes for damaged tissues and organs via employing a combination of 3D biomaterials, supportive bioactive molecules, and/or living cells followed by in vitro culture and/or in vivo implantation, therefore, has attracted much attention in engineering the substitutes. Among 3D biomaterials, hydrogel materials have been extensively explored as matrices for skeletal regeneration because of their biocompatibility, tailorable mechanical properties, flexibility in fabrication, and ability to encapsulate cells and bioactive factors for their sustained, localized and controlled presentation. This review focuses on polymeric hydrogels and theirs composites for both bone and cartilage regeneration, including required properties, design and fabrication, functioned as bared biomaterials or delivery vehicles of bioactive molecules and/or cells together with remaining challenges and future perspectives, emphasizing on the last few years.

The overexpression of reactive oxygen species (ROS) contributes to the pathogenesis of numerous diseases such as atherosclerosis, myocardial infarction, cancer, and chronic inflammation. Therefore, the development of materials that can locally control the adverse effects resulting from excessive ROS generation is of great significance. In this study, the antioxidant gallic acid-conjugated gelatin (GGA) was introduced into gelatin-hydroxyphenyl propionic (GH) hydrogels to create an injectable hydrogel with enhanced free radical scavenging properties compared to pure GH hydrogels. The modified hydrogels were rapidly formed by an HRP-catalyzed cross-linking reaction with high mechanical strength and biodegradability. The resulting GH/GGA hydrogels effectively scavenged the hydroxyl radicals and DPPH radicals, and the scavenging capacity could be modulated by varying GGA concentrations. Moreover, in an in vitro H2O2-induced ROS microenvironment, GH/GGA hydrogels significantly suppressed the oxidative damage of human dermal fibroblast (hDFBs) and preserved their viability by reducing intracellular ROS production. More importantly, the ROS scavenging hydrogel efficiently accelerated the wound healing process with unexpected regenerative healing characteristics, shown by hair follicle formation; promoted neovascularization; and highly ordered the alignment of collagen fiber in a full-thickness skin defect model. Therefore, we expect that injectable GH/GGA hydrogels can serve as promising biomaterials for tissue regeneration applications, including wound treatment and other tissue repair related to ROS overexpression. STATEMENT OF SIGNIFICANCE: Recently, many researchers have endeavored to develop injectable hydrogel matrices that can modulate the ROS level to normal physiological processes for the treatment of various diseases. Here, we designed an injectable gelatin hydrogel in which gallic acid, an antioxidant compound, was conjugated onto a gelatin polymer backbone. The hydrogels showed tunable properties and could scavenge the free radicals in a controllable manner. Because of the ROS scavenging properties, the hydrogels protected the cells from the oxidative damage of ROS microenvironment and effectively accelerated the wound healing process with high quality of healed skin. We believe that this injectable ROS scavenging hydrogel has great potential for wound treatment and tissue regeneration, where oxidative damage by ROS contributes to the pathogenesis.

Hydrogels that mimic the composition and properties of the extracellular matrix have attracted great attention as potential polymeric scaffolds for tissue engineering applications. In this study, an injectable hydrogel composed of hyaluronic acid and gelatin was developed via the oxidative coupling reaction using horseradish peroxidase (HRP). The hydrogel was prepared by mixing two phenol-conjugated polymer solutions, hyaluronic acid-tyramine (HA-TA) and gelatin-hydroxyphenyl propionic acid (GH), in the presence of HRP and hydrogen peroxide (H202). The gelation rate and mechanical properties of composite hydrogel were controlled by adjusting the HRP and H202 concentrations, respectively Compared to the pure HA-TA hydrogels, the stability and cellular behaviors of composite hydrogel improved significantly In addition, the injectable hydrogel system showed good performance in 3D printing with high cell viability after one day of printing. The results suggest that enzymatically crosslinked HA-TA and GH hybrid (HA-TA/GH) composite of HA-TA and GH hydrogel has the potential as a material for tissue engineering and 3D printing biofabrication.

Injectable hydrogels can serve as therapeutic vehicles and implants for the treatment of various diseases as well as for tissue repair/regeneration. In particular, the horseradish peroxidase (HRP) and hydrogen peroxide (H2O2)-catalyzed hydrogelation system has attracted much attention, due to its ease of handling and controllable gel properties. In this study, we introduce calcium peroxide (CaO2) as a H2O2-generating reagent to gradually supply a radical source for the HRP-catalyzed crosslinking reaction. This novel therapy can create stiff hydrogels without compromising the cytocompatibility of the hydrogels due to the use of initially high concentrations of H2O2. The physico-chemical properties of the hydrogels can be controlled by varying the concentrations of HRP and CaO2. In addition, the controlled and sustained release of bioactive molecules, including H2O2, O2, and Ca2+ ions, from the hydrogels could stimulate the cellular behaviors (attachment, migration, and differentiation) of human mesenchymal stem cells. Moreover, the hydrogels exhibited killing efficacy against both Gram-negative and Gram-positive bacteria, dependent on the H2O2 and Ca2+ release amounts. These positive results suggest that hydrogels formed by HRP/CaO2 can be used as potential matrices for a wide range of biomedical applications, such as bone regeneration and infection treatment.

Current stem cell-based therapy for cardiac repair and regeneration after myocardial infarction (MI) is not readily translatable into clinical scenarios due to the low retention and survival of the transplanted cells. Here, we evaluated a simple and feasible design of gelatin-hydroxyphenyl propionic acid (GH) hydrogel as an in situ cross-linkable and injectable cell delivery platform for cardiac tissue regeneration. The GH hydrogel exhibited improved cell retention and survival in vitro and in vivo when encapsulating mouse bone marrow-derived mesenchymal stem cells (MSCs) that were used as promising therapeutic candidates for stem cell therapy. Moreover, we demonstrated that MSC-encapsulating GH hydrogels led to a significant improvement in cardiac functional metrics, such as the fractional shortening (FS), ejection fraction (EF), and end-systolic volume (ESV). Similarly, MSC-encapsulating GH hydrogels induced favorable effects in the cardiac structures of the infarcted heart, producing less fibrosis and thicker infarcted walls. These results suggest that GH hydrogels can be used as an instructive cell delivery platform to provide a suitable microenvironment for transplanted cells; therefore, their in vivo applications combined with MSCs may provide great potential for repair and regeneration of injured cardiac tissues after MI.

Extracellular matrix (ECM) is playing a critical role which is component of mammalian tissue that provide structural support to cells. In addition, ECM act as a local depot for growth factors that control cell phenotype and differentiation. In this regard, scaffold that mimicking the ECM structure is important to growth or wound healing process. Gelatin is natural polymer and derived from collagen which is a major component of ECM. Using gelatin as an ECM mimicking structure has advantage of providing three-dimensional growth or supporting to regulate the cell behavior, proliferation, migration, cell survival, and differentiation. In this study, we developed enzyme-mediated crosslinking gelatin-based hydrogels with robust mechanical property to mimicking ECM and effectively attach to the surrounding tissue with high adhesive property. The effect of different concentration of graphene oxide (GO) on the physico-chemical properties of gelatin hydrogels were investigated, particularly tissue adhesion strength. In vitro proteolytic degradation behavior and human dermal fibroblast proliferation study confirmed the hydrogels were biodegradable and promote cell proliferation. Overall, we suggest that GO incorporated gelatin hydrogels with additional interfacial interactions, showing a promising potential as an injectable tissue adhesive.

Cordyline terminalis leaf extract (aqCT) possesses abundant polyphenols and other bioactive compounds, which are encapsulated in gelatin–polyethylene glycol–tyramine (GPT)/alpha-cyclodextrin (α-CD) gels to form the additional functional materials for biomedical applications. In this study, the gel compositions are optimized, and the GPT/α-CD ratios equal to or less than one half for solidification are found. The gelation time varies from 40.7 min to 5.0 h depending on the increase in GPT/α-CD ratios and aqCT amount. The aqCT extract disturbs the hydrogen bonding and host–guest inclusion of GPT/α-CD gel networks, postponing the gelation. Scanning electron microscope observation shows that all gels with or without aqCT possess a microarchitecture and porosity. GPT/α-CD/aqCT gels could release polyphenols from 110 to 350 nmol/mL at the first hour and sustainably from 5.5 to 20.2 nmol/mL for the following hours, which is controlled by feeding the aqCT amount and gel properties. GPT/α-CD/aqCT gels achieved significant antioxidant activity through a 100% scavenging DPPH radical. In addition, all gels are non-cytotoxic with a cell viability more than 85%. Especially, the GPT3.75α-CD10.5aqCT gels with aqCT amount of 3.1–12.5 mg/mL immensely enhanced the cell proliferation of GPT3.75α-CD10.5 gel without extract. These results suggest that the inherent bioactivities of aqCT endowed the resulting GPT/α-CD/aqCT gels with effective antioxidant and high biocompatibility, and natural polyphenols sustainably release a unique platform for a drug delivery system or other biomedical applications.

Cordyline terminalis leaf extract (aqCT) possesses abundant polyphenols and other bioactive compounds, which are encapsulated in gelatin–polyethylene glycol–tyramine (GPT)/alpha-cyclodextrin (α-CD) gels to form the additional functional materials for biomedical applications. In this study, the gel compositions are optimized, and the GPT/α-CD ratios equal to or less than one half for solidification are found. The gelation time varies from 40.7 min to 5.0 h depending on the increase in GPT/α-CD ratios and aqCT amount. The aqCT extract disturbs the hydrogen bonding and host–guest inclusion of GPT/α-CD gel networks, postponing the gelation. Scanning electron microscope observation shows that all gels with or without aqCT possess a microarchitecture and porosity. GPT/α-CD/aqCT gels could release polyphenols from 110 to 350 nmol/mL at the first hour and sustainably from 5.5 to 20.2 nmol/mL for the following hours, which is controlled by feeding the aqCT amount and gel properties. GPT/α-CD/aqCT gels achieved significant antioxidant activity through a 100% scavenging DPPH radical. In addition, all gels are non-cytotoxic with a cell viability more than 85%. Especially, the GPT3.75α-CD10.5aqCT gels with aqCT amount of 3.1–12.5 mg/mL immensely enhanced the cell proliferation of GPT3.75α-CD10.5 gel without extract. These results suggest that the inherent bioactivities of aqCT endowed the resulting GPT/α-CD/aqCT gels with effective antioxidant and high biocompatibility, and natural polyphenols sustainably release a unique platform for a drug delivery system or other biomedical applications.

Surface modification has emerged as a vital step to regulate the functionality of biomaterials to be bioactive or bioinert. Although various strategies have been reported, it is still challenging to develop advanced surface functionalization tools. Recently, mussel-derived catechol molecules and its derivatives have been extensively used as adhesive molecules for chemical functionalization because of their strong adhesiveness to various substrates through coordinate covalent bonds. However, they still exhibit limitations such as long reaction time owing to the lack of oxygen during the oxidative reaction. Herein, we report a facile strategy to functionalize surfaces using catechol moieties through calcium peroxide (CP)-mediated oxygen supply. We demonstrate that the oxygen supply increases the oxidation rate of catechol molecules, thus rapidly creating amine-rich substrates (within 30 min). Moreover, we prepare a poly(ethylene glycol)-modified cell culture plate to create a low-binding culture plate by a simple dipping procedure for three-dimensional cell spheroid formation. We demonstrate that our CP-mediated surface functionalization tool is a strong candidate for a wide range of biomedical applications.

Adhesive hydrogels offer considerable potential in biomedical applications because of the excellent integration between materials and tissues. Horseradish peroxidase (HRP)-catalyzed hydrogelation, with advantages that include ease of handling, simplicity in material design, high biocompatibility, and processability, is becoming a promising candidate to be engineered as an adhesive hydrogel. This review summarizes recent development of HRP-mediated hydrogelation towards the bioadhesive field, and other applications requiring the tissue adhesion of hydrogels. From the viewpoint of adhesive hydrogel designation, the basic chemistry of the adhesive mechanism, combinations of interactions, and currently commercial bioglues are summarized. The review recapitulated the adhesive hydrogel applications, the clinical translation ability, the controlling hydrogelation kinetics, the related physicochemical characteristics, cytotoxicity, and animal studies. Looking to the future, to make more substantial contributions to the bioadhesive field, or to various biomedical applications, higher adhesion should be continuously improved, and greater emphasis should be placed on clinical trials.

Preventing implant-associated infection, which can lead to implant failure and increased medical costs, is one of the biggest challenges in the orthopaedic surgeons. Therefore, the development of stable and highly effective surface modifications to increase the antimicrobial properties of implants is required. In this study, graphene oxide (GO-)-immobilized titanium dioxide (TiO₂) was developed to efficiently carry and release antimicrobial drugs. Firstly, tyramine-conjugated GO (GOTA) was synthesized and immobilized onto the surfaces of TiO₂ through tyrosinase (Tyr)-catalyzed oxidative reaction (GOTA/TiO₂). Doxycycline hyclate (Dox) was then loaded onto GOTA/TiO₂ via non-covalent interactions between GO and Dox (Dox/GOTA/TiO₂), including electrostatic interaction, π-π stacking, hydrophobic interaction, and hydrogen bonds. The amount of loaded drug was able to be controlled, reaching a maximum of 36 μg/cm2. in vitro experiments revealed that the sustained release of Dox from the TiO₂ surfaces continued for over 30 days. Compared with bare TiO₂ and GOTA/TiO2, Dox/GOTA/TiO₂ exhibited superior antibacterial activity against both gram-negative Escherichia coli and gram-positive Staphylococcus aureus bacteria, without affecting the viability of human dermal fibroblasts. The obtained results indicated that GO-immobilized TiO₂ is an effective carrier for antimicrobial drug delivery to reduce implant-associated infection through the synergistic antimicrobial effect of GO and the prescribed drugs.

The development of antibacterial wound dressing with easily removable characteristic and highly exudate absorption is becoming a major requirement in the treatment of chronic wounds. In this study, the in situ forming gelatin/oxidized alginate-tyramine hydrogels (GH/OATA) were designed to overcome the current limitations. These hybrid hydrogels were quickly and controllably formed from several seconds to a few minutes by horseradish peroxidase/H2O2. The hybrid hydrogels at the optimal composition of GH/OATA 50/50 v/v showed the unique feature including stiffness being similar to skin, high swelling ratio due to the hydrophilic property of oxidized alginate, low adhesive strength allowing for the easy dressing removal without pain. In addition, the hybrid hydrogels could release the H2O2 amount sustainably to kill bacteria. Furthermore, 3D culture of human dermal fibroblasts inside hybrid hydrogels achieved more than 80% cell proliferation which implies the cell-compatibility.

Recently, human hair-derived keratin protein has been recognized as biomaterial with high potential due to its excellent bioactivity and biocompatibility. Here, we designed human hair-derived keratin-based in situ cross-linkable hydrogels that can serve as a dynamic matrix for the enhanced wound healing. We demonstrated that our developed the keratin-based hydrogels accelerated re-epithelization and wound healing process in a full-thickness animal. Also, we investigated the molecular mechanism underlying the enhanced wound healing. In conclusion, our study proposes that human hair-derived keratin-based hydrogels with excellent bioactivity have great potential for use as a wound healing material, along with its other biomedical applications.

Injectable biomaterials have been widely utilized for biomedical applications because their implantation into the human body is minimally invasive and the therapeutic agents can be delivered locally. Shear-thinning hydrogels are notable because of their unique properties, whereby the viscosity decreases (solution) under shear stress and recovers (gel) after the removal of the shear stress. However, as most shear-thinning hydrogels are formed by physical crosslinking, their mechanical properties are often poor. To overcome this issue, additional secondary cross-linkages, via UV-crosslinking, thiol–ene reactions, and oxidative crosslinking, are usually applied. In this study, we developed a new shear-thinning hydrogel with improved mechanical strength, through host–guest interactions and thermo-gelling at 37 °C. Tetronic–adamantane (Tet–Ada) and β-cyclodextrin polymers (poly[β-CD]), which can dissolve in aqueous environments, were successfully synthesized. The chemical structures of the synthesized polymers were confirmed by proton nuclear magnetic resonance spectroscopy. The hydrogels rapidly started to form, via host–guest interactions between Ada and β-CD and self-assembly of the Tet micelles at 37 °C. The elastic modulus of the hydrogels was assessed by varying both the concentrations of the polymers and the temperature. Importantly, the Tet–Ada/poly(β-CD) hydrogels showed shear-thinning behaviors, rapid recovery properties, pH-responsive properties, and long-term release of the hydrophobic drug, doxorubicin (DOX). In addition, we demonstrated the biocompatibility of the hydrogels and the anticancer effect of DOX released from the hydrogels. In conclusion, we suggest the potential usage of the Tet–Ada/poly(β-CD) hydrogels as injectable materials for various biomedical applications, including drug delivery systems.

Although alginate-based hydrogels have been widely used as injectable matrices in a wide range of biomedical applications because of their biocompatibility and easy fabrication process, it is still challenging to improve their bioactivity. Growing evidence has demonstrated that hyperoxic oxygen facilitates wound healing processes via transient oxidative stress. Herein, we report an oxygen-generating alginate (OGA) hydrogel as a bioactive acellular matrix for enhanced wound healing. We fabricate OGA hydrogels through calcium peroxide (CaO2)-mediated ionotropic interactions. The oxygen-releasing behavior of the hydrogels can be accurately controlled. Moreover, we demonstrate that the OGA hydrogels accelerated wound healing in full-thickness wounds in mice.

Controlling the senescence of mesenchymal stem cells (MSCs) is essential for improving the efficacy of MSC-based therapies. Here, a model of MSC senescence was established by replicative subculture in tonsil-derived MSCs (TMSCs) using senescence-associated β-galactosidase, telomere-length related genes, stemness, and mitochondrial metabolism. Using transcriptomic and proteomic analyses, we identified glucose-regulated protein 78 (GRP78) as a unique MSC senescence marker. With increasing cell passage number, GRP78 gradually translocated from the cell surface and cytosol to the (peri)nuclear region of TMSCs. A gelatin-based hydrogel releasing a sustained, low level of reactive oxygen species (ROS-hydrogel) was used to improve TMSC quiescence and self-renewal. TMSCs expressing cell surface-specific GRP78 (csGRP78+), collected by magnetic sorting, showed better stem cell function and higher mitochondrial metabolism than unsorted cells. Implantation of csGRP78+ cells embedded in ROS-hydrogel in rats with calvarial defects resulted in increased bone regeneration. Thus, csGRP78 is a promising biomarker of senescent TMSCs, and the combined use of csGRP78+ cells and ROS-hydrogel improved the regenerative capacity of TMSCs by regulating GRP78 translocation.

To make up for the shortcomings of the suture-based approach and current coupler devices including long suturing time, exhaustive training, additional mechanical setting, and narrow working windows for size and type of diverse vessel types, a new, suture-free microneedle coupler was developed in this study. The needle shape for improved anastomosis performance and the condition for antithrombotic surface immobilization were determined. In particular, the polymer materials help to maintain healthy phenotypes of main vascular cell types. The performance in rabbit and porcine models of end-to-end vascular anastomosis indicate that this device can serve as a potent alternative to the current approaches.

Chronic wounds contribute a substantial social and economic burden on the healthcare system. The global cost of wound treatment was about $19.8 Billion USD in 2019. Healing of chronic wounds takes typically more than 3 months. Current treatments are ineffective and do not always promote wound closure, which requires the activation of multiple cell types. Extracellular vesicles (EVs) contain multiple biomolecules that influence surrounding cells and thus have large capacity to promote tissue repair. To harness the chemoattractant properties of EVs, we developed an extracellular vesicle-laden hydrogel (HydroGEV) with optimized stiffness to promote functional tissue repair, since both mechanical and biological factors influence cell growth and subsequent tissue repair. EVs were isolated and purified from placental stem cells, characterized and incorporated into a gelatin-based hydrogel (GHPA) with different relative stiff-nesses (low, medium and high) determined by crosslinking density. The EVs were found to increase the migration capability of cells in a migration assay, confirming their strong chemoattractant properties and supporting their application for cell recruitment in wound healing. When incorporated into GHPA hydrogels, the EVs effectively improved cell attachment regardless of the stiffness of the hydrogels. Importantly, we demonstrated that by optimizing hydrogel stiffness it was possible to achieve higher cell proliferation and more phenotypic morphology. These promising results support the potential of HydroGEV as a better therapeutic option for patients with acute or chronic wounds.

Injectable hydrogels can serve as therapeutic vehicles and implants for the treatment of various diseases as well as for tissue repair/regeneration. In particular, the horseradish peroxidase (HRP) and hydrogen peroxide (H2O2)-catalyzed hydrogelation system has attracted much attention, due to its ease of handling and controllable gel properties. In this study, we introduce calcium peroxide (CaO2) as a H2O2-generating reagent to gradually supply a radical source for the HRP-catalyzed crosslinking reaction. This novel therapy can create stiff hydrogels without compromising the cytocompatibility of the hydrogels due to the use of initially high concentrations of H2O2. The physico-chemical properties of the hydrogels can be controlled by varying the concentrations of HRP and CaO2. In addition, the controlled and sustained release of bioactive molecules, including H2O2, O2, and Ca2+ ions, from the hydrogels could stimulate the cellular behaviors (attachment, migration, and differentiation) of human mesenchymal stem cells. Moreover, the hydrogels exhibited killing efficacy against both Gram-negative and Gram-positive bacteria, dependent on the H2O2 and Ca2+ release amounts. These positive results suggest that hydrogels formed by HRP/CaO2 can be used as potential matrices for a wide range of biomedical applications, such as bone regeneration and infection treatment.

Thrombosis and inflammation after implantation remain unsolved problems associated with various medical devices with blood-contacting applications. In this study, we develop a multifunctional biomaterial with enhanced hemocompatibility and anti-inflammatory effects by combining the anticoagulant activity of heparin with the vasodilatory and anti-inflammatory properties of nitric oxide (NO). The co-immobilization of these two key molecules with distinct therapeutic effects is achieved by simultaneous conjugation of heparin (HT) and copper nanoparticles (Cu NPs), an NO-generating catalyst, via a simple tyrosinase (Tyr)-mediated reaction. The resulting immobilized surface showed long-term, stable and adjustable NO release for 14 days. Importantly, the makeup of the material endows the surface with the ability to promote endothelialization and to inhibit coagulation, platelet activation and smooth muscle cell proliferation. In addition, the HT/Cu NP co-immobilized surface enhanced macrophage polarization towards the M2 phenotype in vitro, which can reduce the inflammatory response and improve the adaptation of implants in vivo. This study demonstrated a simple but efficient method of developing a multifunctional surface for blood-contacting devices.

Phytoconstituents presenting in herbal plant broths are the biocompatible, regenerative, and cost-effective sources that can be utilized for green synthesis of silver nanoparticles. Different plant extracts can form nanoparticles with specific sizes, shapes, and properties. In the study, we prepared silver nanoparticles (P.uri.AgNPs, P.zey.AgNPs, and S.dul.AgNPs) based on three kinds of leaf extracts (Phyllanthus urinaria, Pouzolzia zeylanica, and Scoparia dulcis, respectively) and demonstrated the antifungal capacity. The silver nanoparticles were simply formed by adding silver nitrate to leaf extracts without using any reducing agents or stabilizers. Formation and physicochemical properties of these silver nanoparticles were characterized by UV-vis, Fourier transforms infrared spectroscopy, scanning electron microscope, transmission electron microscope, and energy dispersive X-ray spectroscopy. P.uri.AgNPs were 28.3 nm and spherical. P.zey.AgNPs were 26.7 nm with hexagon or triangle morphologies. Spherical S.dul.AgNPs were formed and they were relatively smaller than others. P.uri.AgNPs, P.zey.AgNPs and S.dul.AgNPs exhibited the antifungal ability effective against Aspergillus niger, Aspergillus flavus, and Fusarium oxysporum, demonstrating their potentials as fungicides in the biomedical and agricultural applications.

Exposure of aged mice to a young systemic milieu revealed remarkable rejuvenation effects on aged tissues, including skeletal muscle. Although some candidate factors have been identified, the exact identity and the underlying mechanisms of putative rejuvenating factors remain elusive, mainly due to the complexity ofin vivoparabiosis. Here, we present anin vitromuscle parabiosis system that integrates young- and old-muscle stem cell vascular niche on a three-dimensional microfluidic platform designed to recapitulate key features of native muscle stem cell microenvironment. This innovative system enables mechanistic studies of cellular dynamics and molecular interactions within the muscle stem cell niche, especially in response to conditional extrinsic stimuli of local and systemic factors. We demonstrate that vascular endothelial growth factor (VEGF) signaling from endothelial cells and myotubes synergistically contribute to the rejuvenation of the aged muscle stem cell function. Moreover, with the adjustable on-chip system, we can mimic both blood transfusion and parabiosis and detect the time-varying effects of anti-geronic and pro-geronic factors in a single organ or multi-organ systems. Our unique approach presents a complementaryin vitromodel to supplementin vivoparabiosis for identifying potential anti-geronic factors responsible for revitalizing aging organs.

Poly(ethylene glycol) (PEG) is widely used as a gold standard in bioconjugation and nanomedicine to prolong blood circulation time and improve drug efficacy. The conjugation of PEG to proteins, peptides, oligonucleotides (DNA, small interfering RNA (siRNA), microRNA (miRNA)) and nanoparticles is a well-established technique known as PEGylation, with PEGylated products have been using in clinics for the last few decades. However, it is increasingly recognized that treating patients with PEGylated drugs can lead to the formation of antibodies that specifically recognize and bind to PEG (i.e., anti-PEG antibodies). Anti-PEG antibodies are also found in patients who have never been treated with PEGylated drugs but have consumed products containing PEG. Consequently, treating patients who have acquired anti-PEG antibodies with PEGylated drugs results in accelerated blood clearance, low drug efficacy, hypersensitivity, and, in some cases, life-threatening side effects. In this succinct review, we collate recent literature to draw the attention of polymer chemists to the issue of PEG immunogenicity in drug delivery and bioconjugation, thereby highlighting the importance of developing alternative polymers to replace PEG. Several promising yet imperfect alternatives to PEG are also discussed. To achieve asatisfactory alternative, further joint efforts of polymer chemists and scientists in related fields are urgently needed to design, synthesize and evaluate new alternatives to PEG.

Horseradish peroxidase-catalyzed injectable gelatin hydrogels have attracted much attention in various biomedical fields because of their processability, biodegradability, and excellent biocompatib...

BACKGROUND: Polymeric hydrogels are extensively used as promising biomaterials in a broad range of biomedical applications, including tissue engineering, regenerative medicine, and drug delivery. These materials have advantages such as structural similarity to the native extracellular matrix (ECM), multi-tunable physicochemical and biological properties, and biocompatibility. METHODS: In situ forming hydrogels show a phase transition from a solution to a gel state through various physical and chemical cross-linking reactions. These advanced hydrogel materials have been widely used for tissue regenerative medicine because of the ease of encapsulating therapeutic agents, such as cells, drugs, proteins, and genes. RESULTS: With advances in biomaterials engineering, these hydrogel materials have been utilized as either artificial cellular microenvironments to create engineered tissue constructs or as bioactive acellular matrices to stimulate the native ECM for enhanced tissue regeneration and restoration. CONCLUSION: In this review, we discuss the use of in situ cross-linkable hydrogels in tissue engineering and regenerative medicine applications. In particular, we focus on emerging technologies as a powerful therapeutic tool for tissue regenerative medicine applications.

Gelatin hydrogel via Dopa-Fe3+ complexation and Fenton reaction was developed as a dual-crosslinked hydrogel fabrication method for biomedical application. In order to prepare these hydrogels, methacrylated gelatin dopamine (GMD) conjugates were synthesized. The hydrogels were formed rapidly by using hydrogen peroxide (H2O2) and iron(II) chloride (FeCl2), the acryl moieties at the gelatin conjugate react via Fenton reaction and created Fe3+ ions as a byproduct. These Fe3+ ions were used to form Dopa-Fe3+ complexes. The mechanical strength could be controlled by varying the H2O2 concentration and exhibited 2–3 times higher than that single-crosslinked hydrogels. Furthermore, the swelling ratio and degradation behavior of the hydrogels were controllable depending on the crosslinking density. It was also found that the GMD hydrogels have tissue adhesive ability because of the dopamine content. The developed GMD hydrogels without oxidizing agents under mild conditions can be used as injectable materials in tissue regenerative medicine and various biomedical applications.

Nitric oxide (NO) is an endogenous molecule with many critical biological functions that depend on its concentration. At high levels, NO provides broad-spectrum antibacterial effects through both its pathogen inhibition and killing abilities. However, its short half-life has been a great challenge to its clinical application in pharmaceutical forms. In this study, we incorporated the NO donor S-nitrosothiolated gelatin (GelSNO) into injectable gelatin-based hydrogels (GHs) to controllably release NO. Under catalysis by horseradish peroxidase, H2O2 oxidizes phenol moieties functionalized on gelatin to quickly form phenol-phenol crosslinks that encapsulate GelSNO. Through thermal, visible light, and oxidizing agent-driven mechanisms, NO is released from the GH/GelSNO hydrogels. By varying the GelSNO concentration, the release of NO was controllable in a wide range, 0.054–2.050 μmol/mL, for up to 14 days. In addition, NO release was fine-tunable as a function of H2O2 concentration. Notably, the in situ formation of peroxynitrite (ONOO−) that produces potent antibacterial effects originated from H2O2 residues and nitrous acid formed by NO and oxygen in aqueous solution. The Kirby-Bauer method indicated that there was an inhibition zone against both Escherichia coli and Staphylococcus aureus incubated with GH/GelSNO hydrogels. The AlarmaBlue assay showed that E. coli and S. aureus were completely killed at NO concentrations of 0.39 and 0.58 μmol/mL. Cytotoxicity tests of GH/GelSNO hydrogels on human dermal fibroblasts at the indicated bactericidal NO concentrations induced no cell toxicity. In summary, GH/GelSNO hydrogels may provide a new platform for topical delivery of NO in treating wound infections and for various biomedical applications. Statement of Significance NO is an effective antibacterial agent even in cases of antibiotic-resistant bacteria. Moreover, its intermediate, peroxynitrite, has been reported to have a much higher ability to kill bacteria. In this study, we utilized injectable GH/GelSNO hydrogels formed by HRP/H2O2 reaction not only to control NO release but also to generate peroxynitrite in situ from released NO and H2O2 residues. The GH/GelSNO hydrogels showed significant antibacterial ability on both gram-positive and negative bacteria, while no cytotoxicity was induced on human dermal fibroblasts. In addition, their tunable chemico-physical properties and controllable NO release within a wide range but narrow scale will make the hydrogels useful in various biomedical applications.

Introducing antifouling property to biomaterial surfaces has been considered an effective method for preventing the failure of implanted devices. In order to achieve this, the immobilization of zwitterions on biomaterial surfaces has been proven to be an excellent way of improving anti-adhesive potency. In this study, poly(sulfobetaine-co-tyramine), a tyramine-conjugated sulfobetaine polymer, was synthesized and simply grafted onto the surface of polyurethane via a tyrosinase-mediated reaction. Surface characterization by water contact angle measurements, X-ray photoelectron spectroscopy and atomic force microscopy demonstrated that the zwitterionic polymer was successfully introduced onto the surface of polyurethane and remained stable for 7 days. In vitro studies revealed that poly(sulfobetaine-co-tyramine)-coated surfaces dramatically reduced the adhesion of fibrinogen, platelets, fibroblasts, and S. aureus by over 90% in comparison with bare surfaces. These results proved that polyurethane surfaces grafted with poly(sulfobetaine-co-tyramine) via a tyrosinase-catalyzed reaction could be promising candidates for an implantable medical device with excellent bioinert abilities. Statement of Significance Antifouling surface modification is one of the key strategy to prevent the thrombus formation or infection which occurs on the surface of biomaterial after transplantation. Although there are many methods to modify the surface have been reported, necessity of simple modification technique still exists to apply for practical applications. The purpose of this study is to modify the biomaterial’s surface by simply immobilizing antifouling zwitterion polymer via enzyme tyrosinase-mediated reaction which could modify versatile substrates in mild aqueous condition within fast time period. After modification, pSBTA grafted surface becomes resistant to various biological factors including proteins, cells, and bacterias. This approach appears to be a promising method to impart antifouling property on biomaterial surfaces.