Chemical Cross-linking Process Research Articles

Metal sulfide-decorated lamellar porous carbon framework hybrids for fast lithium storage with high volumetric capacity

Porous carbon nanosheets have shown great potential in electrochemical energy storage devices, yet their intrinsic limited volumetric capacity and energy density remain a great concern. Herein, lamellar porous carbon framework hybrids (LPCFHs) have been facilely developed by thermal-induced bulk self-assembly of block copolymers with precisely controllable molecular structure, followed by stepwise chemical crosslinking and morphology-persistent carbonization processes. The as-obtained LPCFHs consist of densely covalent connected alternate layers (porous carbon nanosheets and porous carbon spacers) and homogenously dispersed metal sulfide nanoparticles. The ordered compact stacking structure of carbon nanosheets endows LPCFHs with a high tap density and fast electron transfer both in lateral and vertical dimension, while the porous carbon spacers enable fast channels for ion transfer. Moreover, the metal sulfide nanoparticles strongly interacted with carbon nanosheets are homogenously distributed in LPCFHs, resulting in sufficient active sites. As a result, when used as anode materials in lithium-ion batteries (LIBs), tin sulfide-decorated LPCFHs (LPCFHs-SnS) deliver a volumetric capacity of up to 1285 mAh cm−3; meanwhile, high-rate capability (488 mAh g−1 at 5 A g−1) and excellent cycling stability (capacity retention of 88.3 % after 500 cycles at 1 A g−1) are also achieved, demonstrating great potential for practical application in LIBs.

Reprocessable and self-healable boronic-ester based poly(styrene-b-isoprene-b-styrene) vitrimeric elastomer with improved thermo-mechanical property and adhesive performance

It is fascinating to develop vitrimeric elastomers with excellent processability and improved physical properties through incorporating reversible covalent bonds into traditional thermoplastic elastomers. In this work, a poly(styrene-b-isoprene-b-styrene) (SIS) thermoplastic elastomer was selected as the base elastomer and converted into vitrimer through peroxide-induced crosslinking reaction with di-vinyl-terminated boronic ester crosslinker. Kissinger model predicts that the activation energy of vitrimer crosslinking process is slightly higher than that of chemical crosslinking process. The peroxide content was adjusted to tune the composition of permanent chemical crosslinks and dynamic chemical crosslinks. In this way, SIS vitrimer elastomer with tailored multiple network structure was successfully prepared. The stress relaxation behavior of all SIS-BE samples shows Arrhenius-type temperature-dependency and the bond-exchange activation energy (Ea) of SIS-D0.5-B5 sample was estimated as 44.14 kJ/mol. SIS vitrimer elastomer shows improved creep-resistance, comparative mechanical strength and elastic recovery in relative to crosslinked SIS elastomer while maintaining good reprocessbility and self-healing efficiency. Additionally, SIS vitrimeric elastomer shows an increased lap-shear strength from 0.53 MPa to 1.02 MPa with the increase of DCP content. Therefore, we have demonstrated the potential for industrial-scale production of SIS vitrimer elastomer and its applications as reprocessable and healable adhesives.

Gelatin Methacryloyl (GelMA)-Based Biomaterial Inks: Process Science for 3D/4D Printing and Current Status.

Tissue engineering for injured tissue replacement and regeneration has been a subject of investigation over the last 30 years, and there has been considerable interest in using additive manufacturing to achieve these goals. Despite such efforts, many key questions remain unanswered, particularly in the area of biomaterial selection for these applications as well as quantitative understanding of the process science. The strategic utilization of biological macromolecules provides a versatile approach to meet diverse requirements in 3D printing, such as printability, buildability, and biocompatibility. These molecules play a pivotal role in both physical and chemical cross-linking processes throughout the biofabrication, contributing significantly to the overall success of the 3D printing process. Among the several bioprintable materials, gelatin methacryloyl (GelMA) has been widely utilized for diverse tissue engineering applications, with some degree of success. In this context, this review will discuss the key bioengineering approaches to identify the gelation and cross-linking strategies that are appropriate to control the rheology, printability, and buildability of biomaterial inks. This review will focus on the GelMA as the structural (scaffold) biomaterial for different tissues and as a potential carrier vehicle for the transport of living cells as well as their maintenance and viability in the physiological system. Recognizing the importance of printability toward shape fidelity and biophysical properties, a major focus in this review has been to discuss the qualitative and quantitative impact of the key factors, including microrheological, viscoelastic, gelation, shear thinning properties of biomaterial inks, and printing parameters, in particular, reference to 3D extrusion printing of GelMA-based biomaterial inks. Specifically, we emphasize the different possibilities to regulate mechanical, swelling, biodegradation, and cellular functionalities of GelMA-based bio(material) inks, by hybridization techniques, including different synthetic and natural biopolymers, inorganic nanofillers, and microcarriers. At the close, the potential possibility of the integration of experimental data sets and artificial intelligence/machine learning approaches is emphasized to predict the printability, shape fidelity, or biophysical properties of GelMA bio(material) inks for clinically relevant tissues.

Fabrication and characterization of a bioactive composite scaffold based on polymeric collagen/gelatin/nano β-TCP for alveolar bone regeneration

One strategy to correct alveolar bone defects is use of bioactive bone substitutes to maintain the structure of defect site and facilitate cells and vessels' ingrowth. This study aimed to fabricate and characterize the freeze-dried bone regeneration scaffolds composed of polymeric Type I collagen, nano Beta-tricalcium phosphate (β-TCP), and gelatin. The stable structures of scaffolds were obtained by thermal crosslinking and EDC/NHS ((1-ethyl-3-(3-dimethylaminopropyl) carbodiimide)/(N-hydroxysuccinimide)) chemical crosslinking processes. Subsequently, the physicochemical and biological properties of the scaffolds were characterized and assessed. The results indicated the bioactive composite scaffolds containing 10% and 20% (w/v) nano β-TCP exhibited suitable porosity (84.45 ± 25.43 nm, and 94.51 ± 14.69 nm respectively), a rapid swelling property (reaching the maximum swelling rate at 1 h), excellent degradation resistance (residual mass percentage of scaffolds higher than 80% on day 90 in PBS and Type I collagenase solution respectively), and sustained calcium release capabilities. Moreover, they displayed outstanding biological properties, including superior cell viability, cell adhesion, and cell proliferation. Additionally, the scaffolds containing 10% and 20% (w/v) nano β-TCP could promote the osteogenic differentiation of MC3T3-E1. Therefore, the bioactive composite scaffolds containing 10% and 20% (w/v) nano β-TCP could be further studied for being used to treat alveolar bone defects in vivo.

A dual-crosslinking electroactive hydrogel based on gelatin methacrylate and dibenzaldehyde-terminated telechelic polyethylene glycol for 3D bio-printing

Gelatin was widely used as scaffold materials in 3D bio-printing due to its excellent bioactivity and availability and especially that their arginine–glycine–aspartic acid (RGD) sequences could efficiently promote cell adhesion and proliferation. In this study, an electroactive and 3D bio-printable hydrogel was prepared through a two-step chemical cross-linking process. Specifically, residual free amino groups of methacrylated gelatin (GelMA) were cross-linked with the aldehyde groups of dibenzaldehyde-terminated telechelic polyethylene glycol (DF-PEG) via Schiff base bonds, forming a gel at 37 °C. During the subsequent 3D bio-printing process, GelMA underwent UV curing, forming a secondary cross-linked network to the mechanical strength and stability of the printed structure. The uniform dispersion of carbon nanotubes (CNTs) in the GelMA/DF-PEG composite hydrogel significantly increased its conductivity. The optimized GelMA/DF-PEG composite hydrogel, i.e., 30% GelMA and 25% DF-PEG (G30D25-CNTs), exhibited superior bio-printability. When the content of CNTs was above 4%, the conductivity of G30D25-CNTs hydrogel exceeded 10–2 S/m, which satisfied the needs of cells for micro-current stimulation. Furthermore, the pore microstructures, swelling behavior, degradation ability and cell toxicity of G30D25-CNTs electroactive hydrogels were thoroughly evaluated. Thus, the G30D25-CNTs hydrogel with 4% MWCNTs could be considered for further application in electrical stimulation of tissue regeneration such as muscle and cardiac nerve tissue repair.

Novel soy protein isolate/sodium alginate-based functional aerogel for efficient uptake of organic dye from effluents

In response to the increasing global concern regarding water pollution, there is a growing demand for the development of novel adsorbents capable of effectively eliminating hazardous organic pollutants from effluents. In this study, we present a functional soy protein isolate (SPI)/sodium alginate (ALG)/polyethyleneimine (PEI) aerogel prepared via a facile chemical crosslinking process as a novel adsorbent with excellent capabilities for removing toxic methyl blue (MB) dye from effluents. Thanks to the synergistic dense oxygen and nitrogen-containing functional groups in the networks, the ALG/SPI/PEI (ASP) aerogel displayed high adsorption capacity for MB (106.3 mg/g) complying the adsorption kinetics and isotherm with the pseudo-second-order and Langmuir models, respectively. Remarkably, the MB adsorption capability of the ASP aerogel surpasses that of its pristine counterpart and outperforms recently reported adsorbents. Moreover, the aerogel maintained >80% of initial adsorption capability in the fourth regenerative cycle, indicating excellent reusability. The superior MB adsorbability coupled with high-efficiency regenerability in this study reveal the significant potential of ASP aerogel in efficiently eliminating organic dye from wastewater.

Hollow glass microspheres embedded in porous network of chitosan aerogel used for thermal insulation and flame retardant materials

In recent years, biopolymer aerogels as thermal insulation materials have received widespread attention due to natural abundance, cost-efficiency, and environment-friendly. However, the flammability and low strength hinder its practical application. Hollow glass microspheres (HGMs) as an inorganic thermal insulation filler have been filled in biopolymer aerogels to improve flame retardancy. However, the structure formed by HGMs embedded porous network of biopolymer aerogel has rarely been investigated, which not only reduce thermal conductivity through high porosity, but also adjust the filling volume of HGMs and achieve uniform distribution through chemical cross-linking. Herein, a biopolymer aerogel composite was assembled by chitosan aerogel (CSA) and different volume of HGMs by chemical cross-linking, freeze-drying, and silylation modification processes. When the filling volume fraction of HGMs reached 40 %, a skeleton structure was initially formed. The composites with HGMs volume of 40 %–60 % exhibited low density, high porosity, low thermal conductivity, good mechanical property, and excellent flame retardancy. According to GB 8624-2012 standard for classification, the composite with 60 % HGMs achieved class A1 non-combustible.

Ion-imprinted nanocellulose aerogel with comprehensive optimized performance for uranium extraction from seawater

Significantly abundant uranium resources in seawater are considered promising alternatives to terrestrial uranium reserves. The adsorption capacity and speed, binding selectivity, mechanical properties, and antibiofouling ability are the most important features for practical uranium adsorbent applications. Herein, a new nanocellulose aerogel, which contains specific binding spatial structures for uranyl ions, designated as I-CNF aerogel, is fabricated by combining ion-imprinting and chemical cross-linking strategies. The ion-imprinted and chemically stabilized functional sites endow the I-CNF aerogel with robust binding affinity and selectivity for uranyl ions. The ordered lamellar structure, porosity, and high hydrophilicity together facilitate uranyl ion access to the functional sites in the adsorbent and endow the adsorbent with a high uranium adsorption capacity. Furthermore, owing to the chemical cross-linking process and the generated Schiff base groups, the adsorbent exhibits high mechanical strength, excellent reusability, and effective antibiofouling activity. Benefitting from these optimized properties, I-CNF aerogel demonstrates a high uranium extraction capacity of 9.46 mg g−1 with an ultrahigh selectivity of 19.01 to uranium against vanadium in natural seawater, making it a highly potential candidate for practical uranium extraction in natural seawater.

Polymer based dual drug delivery system for targeted treatment of fluoroquinolone resistant Staphylococcus aureus mediated infections

The present study attempts to treat S. aureus-induced soft skin infections using a combinatorial therapy with an antibiotic, Ciprofloxacin (CIP), and an efflux pump inhibitor 5-Nitro-2-(3-phenylpropoxy) pyridine (5-NPPP) through a smart hydrogel delivery system. The study aims to reduce the increasing rates of infections and antimicrobial resistance; therefore, an efflux pump inhibitor molecule is synthesized and delivered along with an antibiotic to re-sensitize the pathogen towards antibiotics and treat the infections. CIP-loaded polyvinyl alcohol (PVA) hydrogels at varying concentrations were fabricated and optimized by a chemical cross-linking process, which exhibited sustained drug release for 5 days. The compound 5-NPPP loaded hydrogels provided linear drug release for 2 days, necessitating the need for the development of polymeric nanoparticles to alter the release drug pattern. 5-NPPP loaded Eudragit RSPO nanoparticles were prepared by modified nanoprecipitation—solvent evaporation method, which showed optimum average particle size of 230–280 nm with > 90% drug entrapment efficiency. The 5-NPPP polymeric nanoparticles loaded PVA hydrogels were fabricated to provide a predetermined sustained release of the compound to provide a synergistic effect. The selected 7% PVA hydrogels loaded with the dual drugs were evaluated using Balb/c mice models induced with S. aureus soft skin infections. The results of in vivo studies were evidence that the dual drugs loaded hydrogels were non-toxic and reduced the bacterial load causing re-sensitization towards antibiotics, which could initiate re-epithelization. The research concluded that the PVA hydrogels loaded with CIP and 5-NPPP nanoparticles could be an ideal and promising drug delivery system for treating S. aureus-induced skin infections.

Fe3O4-polyvinyl alcohol sponge as photo-absorber in interfacial solar steam generation

Interfacial solar steam generation (ISSG) is a potential technology to relieve the freshwater shortage. However, developing a cost-effective method to design photo-absorbers with steady desalination performance remains a significant challenge. A Fe3O4-polyvinyl alcohol sponge photo-absorber (Fe-PAS) was made by employing sodium alginate and CaCl2 in a simple chemical crosslinking process. Because the porous structure of the polyvinyl alcohol sponge (which traps sunlight) and the narrow bandgap of the Fe3O4 (which captures sunlight) work together, the light absorption of wet Fe-PAS can reach 96.54 %, making water evaporate at a rate of 1.44 kg m−2 h−1. With the help of a sufficient water supply from the polyester fiber pillar (PFP), the Fe-PAS photo-absorber shows a steady evaporation rate of about 1.40 kg m−2 h−1 under 1-solar intensity during desalination. The 240 h (30 days, with 8 h of operation per day) of indoor desalination experiments prove that Fe-PAS is durable and has a steady evaporation performance. Outdoor desalination experiments demonstrate that Fe-PAS can extract freshwater from salt water. The Fe-PAS photo-absorber offers a substantial possibility in mitigating freshwater shortages.

Production of Cellulose Hydrogel from Nipa (Nypa fruticans Wurmb) Frond

Objectives: The study is aimed to assess the potential of nipa frond biomass to produce cellulose hydrogel by analyzing the elemental composition, morphology, solubility, and effectivity of the isolated nipa a-cellulose (iNaC). Methods: The iNaC was produced through physico-chemical treatments and examined using a scanning electron microscope. After dissolving the cellulose, it was mixed with various chemical cross-linkers to produce cellulose hydrogels. Findings: Results showed that the iNaC had well-distributed microfibrils of cellulose arranged in parallel orthogonal layers. Solubility (%) reveals treatment 2, involving 10% NaOH pre-treatment of iNaC, yielded the ideal cellulose for eco-friendly and cost-effective cellulose solution production with high solubility percentage. Moreover, cellulose-based hydrogels were more viscous and more turbid than water-based hydrogels, increasing the integrity of the produced hydrogels. Novelty: The study demonstrates that iNaC can be transformed into a cellulose-based hydrogel through a one-step chemical crosslinking process, which can streamline the production process and reduce toxic pollution. This has important environmental benefits and potential applications in medical, agricultural, and wastewater treatment. Keywords: Cellulose Hydrogel; Nipa Frond; Biomass; Chemical Crosslinking

Self-Healing Hydrogels: From Synthesis to Multiple Applications

Due to the good reliability and long-term stability, self-healing hydrogels have emerged as promising soft materials for tissue engineering, smart wearable sensors, bioelectronics, and energy storage devices. The self-healing mechanism depends on reversible chemical or physical cross-linking interactions. Self-healing hydrogels with fascinating features (including mechanical performances, biocompatibility, conductivity, antibacterial ability, responsiveness, etc.) are being designed and developed according to the practical application requirements. In this review, the recent progress on self-healing hydrogels in their synthesis strategies and multiple applications is summarized. Their synthesis strategies involve reversible chemical or physical cross-linking processes or a combination of the two. Their recent applications include flexible strain sensors, supercapacitors, actuators, adhesives, wound healing, drug delivery, tumor treatment, 3D printing, etc. Finally, the current challenges, future development, and opportunities for self-healing hydrogels are discussed.

Construction of a bioactive copper-based metal organic framework-embedded dual-crosslinked alginate hydrogel for antimicrobial applications

Metal-organic frameworks (MOFs) containing bioactive metals have the potential to exhibit antimicrobial activity by releasing metal ions or ligands through the cleavage of metal-ligand bonds. Recently, copper-based MOFs (Cu-MOFs) with sustained release capability, porosity, and structural flexibility have shown promising antimicrobial properties. However, for clinical use, the controlled release of Cu2+ over an extended time period is crucial to prevent toxicity. In this study, we developed an alginate-based antimicrobial scaffold and encapsulated MOFs within a dual-crosslinked alginate polymer network. We synthesized Cu-MOFs containing glutarate (Glu) and 4,4′-azopyridine (AZPY) (Cu(AZPY)-MOF) and encapsulated them in an alginate-based hydrogel through a combination of visible light-induced photo and calcium ion-induced chemical crosslinking processes. We confirmed Cu(AZPY)-MOF synthesis using scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, and thermogravimetric analysis. This antimicrobial hydrogel demonstrated excellent antibacterial and antifungal properties against two bacterial strains (MRSA and S. mutans, with >99.9 % antibacterial rate) and one fungal strain (C. albicans, with >78.7 % antifungal rate) as well as negligible cytotoxicity towards mouse embryonic fibroblasts, making it a promising candidate for various tissue engineering applications in biomedical fields.

Strong and Tough Cellulose Hydrogels via Solution Annealing and Dual Cross-Linking.

Strong and tough hydrogels are promising candidates for flexible electronics, biomedical devices, and so on. However, the conflict between improving the mechanical strength and toughness properties of polysaccharide-based hydrogels remains unsolved. Herein, a strategy is proposed to produce a hierarchically structured cellulose hydrogel that combines solution annealing and dual cross-linking treatment approaches. The solution annealing considerably increases the hydrophobic stacking and chemical cross-linking of the cellulose chains, thereby facilitating their subsequent self-assembly and recrystallization during the chemical and physical cross-linking processes. The cellulose hydrogels exhibit superposed chemically and physically cross-linked domains comprising homogeneous nanoporous network structures, which in turn are composed of interconnected cellulose nanofibers and cellulose II crystallite hydrates. These cellulose hydrogels exhibit a high water content of 76-84% and excellent mechanical properties that compare favorably to those of biomacromolecule-based hydrogels. The prepared hydrogels exhibit a mechanical strength and work of fracture of 21±3MPa and 2.6±0.4MJm-3 under compression, and 7.2±0.7MPa and 5.9±0.6MJm-3 under tension, respectively. It is anticipated that this strategy will be applicable to other biomacromolecules and crystalline polymers, and that it will enable the construction of other hydrogels exhibiting high mechanical performances.

Thermo‐Responsive Nanocomposite Bioink with Growth‐Factor Holding and its Application to Bone Regeneration (Small 9/2023)

Thermo-Responsive Nanocomposite Bioinks Poly(organophosphazene)-based thermo-responsive nanocomposite bioink, with tunable mechanical property under a moderate temperature range, exhibits good 3D printing outcomes without additional chemical crosslinking process. The bioink encapsulates growth factors through physical interaction, exhibiting biological activities and therapeutic potential for bone defect repair. More details can be found in article number 2203464 by Soo-Chang Song and co-workers.

A comparative study of the effects of chemical crosslinking agents on NBSK handsheet properties

Chemical crosslinking is an established method for improving the wet performance of paper. In the chemical crosslinking process, covalent bonds are formed between cellulosic surfaces. The formed intra- and inter-fiber bonds increase the paper’s wet strength and reduce its water absorptivity. The majority of published studies concern crosslinking treatments with glyoxal, citric acid (CA), or with 1,2,3,4-butanetetra-carboxylic acid (BTCA). The most severe disadvantage of the crosslinking treatments with glyoxal, CA, and BTCA is that the formed crosslinks make the fibers and the paper more brittle. This downside effect has largely impeded the utilization of crosslinking in paper and paperboard making. In the present study, handsheets made from Nordic bleached softwood kraft pulp (NBSK) were crosslinked with methylated 1,3-dimethylol-4,5-dihydroxyethylene urea (mDMDHEU), which is commonly used in cotton fabric finishing. Similar to using glyoxal and citric acid, crosslinking with mDMDHEU notably increased the handsheet wet strength and decreased the water absorption. Compared to the use of glyoxal or CA, the crosslinking with mDMDHEU did not make the handsheets that brittle. These results suggest that mDMDHEU could be a more viable crosslinking agent for improving the wet performance of paper products.

Recyclable and high-performance metal coordination bonds cross-linked polybenzimidazole aerogels for flame retardancy, thermal insulation and dyes adsorption applications

Aerogels made from high-performance polymers have attracted great interests in recent years. However, traditional chemical crosslinking process is complex, and makes it difficult to adjust the skeleton structure of aerogels and achieve polymer recovery. Herein, polybenzimidazole aerogels with good mechanical property, uniform porous structure, and specific surface area as high as 660.23 m2/g are facilely prepared through metal coordination. The excellent thermal stability, high flame resistance, and low thermal conductivity make the aerogels good candidates for flame-retarding and high-temperature thermal insulating materials. Notably, the reversible metal coordination crosslinking permits the recycling of aerogels, which has not been realized in previous high-performance polymer aerogels yet. Moreover, the aerogels can repeatedly adsorb dyes from wastewater because of their large specific surface area, good chemical resistance, and abundant polar imidazole groups. This work is expected to provide a simple approach to recyclable, high-performance, and multifunctional polymer aerogels.

Design, synthesis, and characterization of a novel dual cross-linked gelatin-based bioadhesive for hard and soft tissues adhesion capability

Many surgical treatments require a suitable tissue adhesive that maintains its performance in wet conditions and can be applied simultaneously for hard and soft tissues. In the present study, a dual cross-linked tissue adhesive was synthesized by mixing the gelatin methacryloyl (Gel-MA) and gelatin-dopamine conjugate (Gel-Dopa). The setting reaction was based on a photopolymerization process in the presence of a combination of riboflavin and triethanolamine and a chemical cross-linking process attributed to the genipin as a natural cross-linker. Modified gelatin macromolecules were characterized and the best wavelength for free radical generation in the presence of riboflavin was obtained. Tissue adhesives were prepared with 30% hydrogels of Gel-MA and Gel-Dopa with different ratios in distilled water. The gelation occurred in a short time after light irradiation. The chemical, mechanical, physical, and cytotoxicity properties of the tissue adhesives were evaluated. The results showed that despite photopolymerization, chemical crosslinking with genipin played a more critical role in the setting process. Water uptake, degradation behavior, cytotoxicity, and adhesion properties of the adhesives were correlated with the ratio of the components. The SEM images showed a porous structure that could ensure the entry of cells and nutrients into the surgical area. While acceptable properties in most experiments were observed, all features were improved as the Gel-Dopa ratio increased. Also, the obtained hydrogels revealed excellent adhesive properties, particularly with bone even after wet incubation, and it was attributed to the amount of gelatin-dopamine conjugate. From the obtained results, it was concluded that a dual adhesive hydrogel based on gelatin macromolecules could be a good candidate as a tissue adhesive in wet condition.

Double – network hydrogel based on exopolysaccharides as a biomimetic extracellular matrix to augment articular cartilage regeneration

Cartilage regeneration remains a current challenge with no satisfactory strategy in surgery. Hydrogels with structurally and biochemically biomimicking characteristics have been regarded as a promising approach for the success of cartilage regeneration. Naturally sourced hydrogels from exopolysaccharides are ideal candidates for the construction of biomimetic extracellular matrix (ECM) because of their biomimetic networks, high water content, cytocompatibility, and biodegradability. Here, an approach that integrates covalent and ionic bonds in a hydrogel system is shown to form a natural polymeric hydrogel double network (DN) for promoting the adhesion and proliferation of chondrocytes and supporting the formation of matured cartilage tissue. DN hydrogels comprised of chemically crosslinked hyaluronan (HA) and physically crosslinked gellan gum (GG) were developed for potential scaffold fabrication. Compared with HA single network (SN) hydrogel and GG SN hydrogel, the obtained HA/GG DN hydrogel with Young's modulus of 28.6 kPa exhibited adequate compressive strength (208.9 kPa) and high toughness (dissipated energy 2837 J/m3) and thus can be used as a biomimetic extracellular matrix for minimal invasively repairing cartilage. In vitro studies showed that HA/GG DN hydrogel-based ECM promoted the proliferation of chondrocytes. The HA/GG DN hydrogel significantly supported the deposition of cartilage ECM-specific sulfated glycosaminoglycan and type II collagen and facilitated the formation of cartilage tissues. In a rabbit osteochondral defect model, HA/GG DN hydrogel significantly improved cartilage regeneration. The HA/GG DN hydrogel as a biomimetic ECM is a promising candidate as a biomaterial scaffold for cartilage regeneration and repair. Statement of significanceThe fabrication of a biomaterial scaffold as an artificial extracellular matrix (ECM) for cartilage regeneration remains a big challenge. In this work, we fabricated a double-network (DN) hydrogel based on hyaluronan and gellan gum (HA/GG) through a sequential chemical and physical cross-linking process. The HA/GG DN hydrogel exhibited high compressive strength, high toughness, stiffness, and good self-recovery property. The HA/GG DN hydrogel can support chondrocyte proliferation and new ECM deposition correlated with the enhanced mechanical properties, good cytocompatibility, and biodegradability. In vivo animal experiments demonstrated that this HA/GG DN hydrogel facilitates hyaline-like cartilage regeneration. These findings imply that the developed HA/GG DN hydrogel as a biomimetic ECM offers a hopeful new platform for cartilage tissue engineering.

Hydrophilic Nonwoven Nanofiber Membranes as Nanostructured Supports for Enzyme Immobilization.

The high porosity, interconnected pore structure, and high surface area-to-volume ratio make the hydrophilic nonwoven nanofiber membranes (NV-NF-Ms) promising nanostructured supports for enzyme immobilization in different biotechnological applications. In this work, NV-NF-Ms with excellent mechanical and chemical properties were designed and fabricated by electrospinning in one step without using additives or complicated crosslinking processes after electrospinning. To do so, two types of ultrahigh-molecular-weight linear copolymers with very different mechanical properties were used. Methyl methacrylate-co-hydroxyethyl methacrylate (p(MMA)-co-p(HEMA)) and methyl acrylate-co-hydroxyethyl acrylate (p(MA)-co-p(HEA)) were designed and synthesized by reverse atom transfer radical polymerization (reverse-ATRP) and copper-mediated living radical polymerization (Cu0-MC-LRP), respectively. The copolymers were characterized by nuclear magnetic resonance (1H-NMR) spectroscopy and by triple detection gel permeation chromatography (GPC). The polarity, topology, and molecular weight of the copolymers were perfectly adjusted. The polymeric blend formed by (MMA)1002-co-(HEMA)1002 (Mw = 230,855 ± 7418 Da; Mn = 115,748 ± 35,567 Da; PDI = 2.00) and (MA)11709-co-(HEA)7806 (Mw = 1.972 × 106 ± 33,729 Da; Mn = 1.395 × 106 ± 35,019 Da; PDI = 1.41) was used to manufacture (without additives or chemical crosslinking processes) hydroxylated nonwoven nanofiber membranes (NV-NF-Ms-OH; 300 nm in fiber diameter) with excellent mechanical and chemical properties. The morphology of NV-NF-Ms-OH was studied by scanning electron microscopy (SEM). The suitability for enzyme binding was proven by designing a palette of different surface functionalization to enable both reversible and irreversible enzyme immobilization. NV-NF-Ms-OH were successfully functionalized with vinyl sulfone (281 ± 20 μmol/g), carboxyl (560 ± 50 μmol/g), and amine groups (281 ± 20 μmol/g) and applied for the immobilization of two enzymes of biotechnological interest. Galactose oxidase was immobilized on vinyl sulfone-activated materials and carboxyl-activated materials, while laccase was immobilized onto amine-activated materials. These preliminary results are a promising basis for the application of nonwoven membranes in enzyme technology.