Alginate Hydrogel Films Research Articles

Facile and Low‐Cost Electrochemical Synthesis of Zinc Alginate Hydrogel Films for Biomedical Applications

Facile and Low‐Cost Electrochemical Synthesis of Zinc Alginate Hydrogel Films for Biomedical Applications

Dual Functional Antibacterial-Antioxidant Core/Shell Alginate/Poly(ε-caprolactone) Nanofiber Membrane: A Potential Wound Dressing.

Core/shell nanofibers offer the advantage of encapsulating multiple drugs with different hydrophilicity in the core and shell, thus allowing for the controlled release of pharmaceutic agents. Specifically, the burst release of hydrophilic drugs from such fiber membranes causes an instantaneous high drug concentration, whereas a long and steady release is usually desired. Herein, we tackle the problem of the initial burst release by the generation of core/shell nanofibers with the hydrophilic antibiotic drug gentamycin loaded within a hydrophilic alginate core surrounded by a hydrophobic shell of poly(ε-caprolactone). Emulsion electrospinning was used as the nanofibrous mesh generation procedure. This process also allows for the loading of a hydrophobic compound, where we selected a natural antioxidant molecule, betulin (BTL), to detoxify the radicals. The resulting nanofibers exhibited a cylindrical shape with a core/shell structure. In vitro tests showed a controlled release of gentamicin from nanofibers via diffusion. The drug reached 93% release in an alginate hydrogel film but only 50% release in the nanofibers, suggesting its potential to minimize the initial burst release. Antibacterial tests revealed significant activity against both Gram-negative and Gram-positive bacteria. The antioxidant property of betulin was confirmed through the DPPH assay, where the incorporation of 20% BTL revealed 37.3% DPPH scavenging. The nanofibers also exhibited favorable biocompatibility in cell culture studies, and no harmful effects on cell viability were observed. Overall, this research offers a promising approach to producing core/shell nanofibrous mats with antibacterial and antioxidant properties, which could effectively address the requirements of wound dressings, including infection prevention and wound healing acceleration.

Photocatalytic Conversion of Methane to Ethanol at a Three-Phase Interface with Concentration-Matched Hydroxyl and Methyl Radicals.

The direct oxidation of CH4 to C2H5OH is attractive but challenging owing to the intricate processes involving carbon-chain growth and hydroxylation simultaneously. The inherent difficulty arises from the strong tendency of CH4 to overoxidize in the commonly used pressurized powder suspension systems rich in reactive oxygen radicals (ROR), which are specifically designed for CH4 concentration and activation. Meanwhile, the strong tendency of nucleophilic attack of potent ROR on the C-C bond of the resulting product C2H5OH ultimately leads to a higher selectivity for C1 oxygenates. This study addresses this multifaceted issue by designing a three-phase interface based on a hydrophilic floating Fe(III)-cross-linked macroporous alginate hydrogel film encapsulated with C3N4 [Fe(III)@ACN] to simultaneously enhance the accessibility of H2O and CH4 molecules to the active sites and species within the macroporous channel. The hydrophilic properties of Fe(III)@ACN allow the in situ production of H2O2 from C3N4 through the water oxidation reaction under irradiation. The concurrent photoinduced Fe(II) triggers Fenton reaction with H2O2 to produce •OH. The enhanced mass transfer of CH4 at the three-phase interface ensures the efficient formation of •CH3 by reacting with •OH, ultimately facilitating carbon-chain growth in the conversion pathway from CH4 to CH3OH and finally to C2H5OH with •CH3 and •OH present in comparable concentrations. Thus, the Fe(III)@ACN catalyst exhibits a remarkable 96% selectivity for alcohol, achieving a 90% selectivity for C2H5OH in the alcohol products. The C2H5OH production rate reaches 171.7 μmol g-1 h-1 without the need for precious-metal additive.

AgNPs-loaded chitosan/sodium alginate hydrogel film by in-situ green reduction with tannins for enhancing antibacterial activity

Bacterial infections pose a significant challenge to global public health, and the development of innovative antibacterial materials is becoming increasingly urgent. Currently, hydrogels are widely studied for the treatment of bacterial infection. However, it is still a great challenge to load antibacterial nanoparticles into the hydrogel matrix by using green synthesis method. Tannic acid (TA) is an eco-friendly reducing agent for the synthesis of metal nanoparticles, and it also has antibacterial activity. In this paper, an antibacterial chitosan/sodium alginate (HCS/SA) hydrogel film embedded with AgNPs was fabricated through in-situ green reduction with TA to utilize the synergistic antibacterial effect of TA and silver nanoparticles (AgNPs). The chemical composition and morphology of the antibacterial hydrogel were characterized by using FTIR, XRD, SEM, and EDS. The results demonstrated that TA solution under alkaline conditions could convert AgNO3 to AgNPs, and AgNPs were embedded uniformly on the surface of the HCS/SA hydrogel film. In addition, the pH of the TA solution significantly influenced the swelling behavior of the antibacterial hydrogel films. When the pH of the TA solution increased from 7 to 10, the swelling ratio of the antibacterial hydrogel film increased from 388.89% to 648.69%. In addition, the hemolysis rates of our prepared hydrogel films were below 5%, meeting the safety requirements. In vitro antibacterial experiments revealed that the fabricated hydrogel films showed excellent antibacterial effects against E. coli, S. aureus, and P. aeruginosa with inhibition zones up to 25.8 ± 0.24 mm, 32.2 ± 0.62 mm, and 22.6 ± 0.49 mm, respectively. Therefore, the antibacterial hydrogel films developed in this study hold potential for treating bacteria-infected wounds.

Fabrication and characterization of microwave-assisted synthesis of carbon dots crosslinked sodium alginate hydrogel films

In this study, potassium-incorporated carbon dots (K-CDs) and nitrogen-incorporated carbon dots (N-CDs) were composted using the microwave-assisted method, in which the carbon source is citric acid. Subsequently, the prepared CDs were added into sodium alginate (NaAlg)/CaCO3 to form a hydrogel film. The Ca2+ in the system is tend to be released in the presence of acidic CDs to promote the cross-linking of NaAlg. This study presents a NaAlg hydrogel film preparation process that requires no additional acid and is natural and environmentally friendly. Moreover, it gives the NaAlg hydrogel film excellent antioxidant and antimicrobial properties and also improves its mechanical properties and gel strength. The release behaviors of the CDs in the hydrogel films were also explored. The prepared CD-incorporated NaAlg hydrogel films have potential applications in medical, biological engineering, food preservation, and other fields owing to their functional properties.

Biocompatible Alginate Film Crosslinked with Ca2+ and Zn2+ Possesses Antibacterial, Antiviral, and Anticancer Activities.

Alginate is a highly promising biopolymer due to its non-toxic and biodegradable properties. Alginate hydrogels are often fabricated by cross-linking sodium alginate with calcium cations and can be engineered with highly desirable enhanced physical and biological properties for biomedical applications. This study reports on the anticancer, antiviral, antibacterial, in vitro, and in vivo toxicity, water absorption, and compound release properties of an alginate hydrogel crosslinked with calcium and different amounts of zinc cations. The results showed that the calcium alginate hydrogel film crosslinked with the highest amount of zinc showed similar water sorption properties to those of calcium alginate and released a suitable amount of zinc to provide anticancer activity against melanoma and colon cancer cells and has antibacterial properties against methicillin-resistant Staphylococcus epidermidis and antiviral activity against enveloped and non-enveloped viruses. This film is non-toxic in both in vitro in keratinocyte HaCaT cells and in vivo in the Caenorhabditis elegans model, which renders it especially promising for biomedical applications.

Carboxymethyl chitosan/sodium alginate hydrogel films with good biocompatibility and reproducibility by in situ ultra-fast crosslinking for efficient preservation of strawberry

Strawberry is a seasonal and regional fruit. Thus, strawberry waste caused by spoilage and decay is an urgent problem that must be solved. Developing hydrogel films (HGF) for multifunctional food packaging can effectively slow down strawberry. Based on the carboxymethyl chitosan/sodium alginate/citric acid with excellent biocompatibility, preservation effect, and ultrafast (10 s) coating on the strawberry surface, HGF specimens were designed and prepared through the electrostatic interaction of opposite charges between polysaccharides. The prepared HGF specimen exhibited excellent low moisture permeability and antibacterial properties. Its lethality rates against both Escherichia coli and Staphylococcus aureus were more than >99 %. The HGF could keep strawberries fresh for up to 8, 19, and 48 days at 25.0, 5.0, and 0 °C, respectively, by delaying the fruits' ripening, dehydration, microbial invasion, and respiration rate. The HGF dissolved and regenerated five times still exhibited good performance. The water vapor transmission rate of the regenerative HGF could reach 98 % of that of the original HGF. The regenerative HGF could maintain the freshness of strawberries for up to 8 days at 25.0 °C. This study provides new insight into an alternative film design for convenient, green, and renewable alternative films to delay perishable fruit spoilage.

Stimulation–Inhibition of Protein Release from Alginate Hydrogels Using Electrochemically Generated Local pH Changes

The electrochemically controlled release of proteins was studied in a Ca2+-cross-linked alginate hydrogel deposited on an electrode surface. The electrochemical oxidation of ascorbate or reduction of O2 was achieved upon applying electrical potentials +0.6 or -0.8 V (vs Ag/AgCl/KCl 3 M), respectively, resulting in decreasing or increasing pH locally near an electrode surface. The obtained local acidic solution resulted in the protonation of carboxylic groups in the alginate hydrogel and, as a result, the formation of a hydrophobic shrunken hydrogel film. Conversely, the produced alkaline local environment resulted in a hydrophilic swollen hydrogel film. The release of the proteins was effectively inhibited from the shrunk hydrogel and activated from the swollen hydrogel film. Overall, the electrochemically produced local pH changes allowed control over the biomolecule release process. While the release inhibition by applying +0.6 V was always effective and could be maintained as long as the positive potential was applied, the release activation was different depending on the protein molecular size, being more effective for smaller species, and molecule charge, being more effective for negatively charged species. The repetitive change from the inhibited to stimulated state of the biomolecule release process was obtained upon cyclic application of oxidative and reductive potentials (+0.6 V ↔ -0.8 V). The alginate hydrogel film shrinking-swelling as well as the protein release process were studied and visualized using a confocal fluorescent microscope. In order to be observed, an external surface of the alginate film and the loaded protein molecules were labeled with different fluorescent dyes, which then produced colored fluorescent images under a confocal microscope.

Fabrication, characterisation, and application of green crosslinked sodium alginate hydrogel films by natural crab-shell powders to achieve drug sustained release

In this study, natural crab-shell particles (CSP) and deacetylated crab-shell particles (dCSP) were used as crosslinking agents at the present of glucolactone to obtain high strength mono-crosslinked and bi-crosslinked sodium alginate (NaAlg) hydrogel films, respectively. The results indicated that the CSP in the system could occur Ca2+ crosslinking, and the addition of dCSP could help to form both Ca2+ crosslinking and polyelectrolytes interactions with NaAlg. The remaining unreacted CaCO3 could enhance the thermal stability of the films due to the high thermally stable CaCO3. The surface hydrophobicity, gel properties, mechanical strength and thermal stabilities of those bi-crosslinked NaAlg hydrogel films were better than those of neat NaAlg film and mono-crosslinked NaAlg hydrogel films, which overcome the inferior thermo-mechanical properties for traditional hydrogel films. In addition, the releasing time of those prepared hydrogel films for diclofenac sodium was higher than 36 h, which illustrated sustained drug releasing activity. The CSP modified NaAlg hydrogel film with 0.5% GDL content exhibited the highest cumulative release amount. The proposed approach is a promising green crosslinking technique to develop high performance NaAlg hydrogel films that can realize active ingredients and drugs sustained release in food packaging and medical wound dressing areas.

Engineering alginate hydrogel films with poly(3-hydroxybutyrate-co-3-valerate) and graphene nanoplatelets: Enhancement of antiviral activity, cell adhesion and electroactive properties

A new biodegradable semi-interpenetrated polymer network (semi-IPN) of two US Food and Drug Administration approved materials, poly(3-hydroxybutyrate-co-3-valerate) (PHBV) and calcium alginate (CA) was engineered to provide an alternative strategy to enhance the poor adhesion properties of CA. The synthesis procedure allows the additional incorporation of 10 % w/w of graphene nanoplatelets (GNPs), which have no cytotoxic effect on human keratinocytes. This quantity of multilayer graphene provides superior antiviral activity to the novel semi-IPN against a surrogate virus of SARS-CoV-2. Adding GNPs hardly affects the water absorption or electrical conductivity of the pure components of CA and PHBV. However, the semi-IPN's electrical conductivity increases dramatically after adding GNP due to molecular rearrangements of the intertwined polymer chains that continuously distribute the GNP nanosheets, This new hydrophilic composite biomaterial film shows great promise for skin biomedical applications, especially those that require antiviral and/or biodegradable electroconductive materials.

Investigating Pore-Opening of Hydrogel Foams at the Scale of Freestanding Thin Films.

Controlling the pore connectivity of polymer foams is key for most of their applications, ranging from liquid uptake, mechanics, and acoustic/thermal insulation to tissue engineering. Despite their importance, the scientific phenomena governing the pore-opening processes remain poorly understood, requiring tedious trial-and-error procedures for property optimization. This lack of understanding is partly explained by the high complexity of the different interrelated, multiscale processes which take place as the foam transforms from an initially fluid foam into a solid foam. To progress in this field, this work takes inspiration from long-standing research on liquid foams and thin films to develop model experiments in a microfluidic "Thin Film Pressure Balance." These experiments allow the investigation of isolated thin films under well-controlled environmental conditions reproducing those arising within a foam undergoing cross-linking and drying. Using the example of alginate hydrogel films, the evolution of isolated thin films undergoing gelation and drying is correlated with the evolution of the rheological properties of the same alginate solution in bulk. The overall approach is introduced and a first set of results is presented to propose a starting point for the phenomenological description of the different types of pore-opening processes and the classification of the resulting pore-opening types.

Preparation and application of sodium alginate hydrogel film loaded with nano-silver/graphene composite

Sodium alginate (SA) is a natural polymer material that has been widely studied and used in the biomedical field. Nano-silver (Ag) has been proven to present good antibacterial properties, but its application is limited due to its easy agglomeration. In this paper, a series of Ag-graphene composites (Ag-GO) were prepared and characterized by loading Ag nanoparticles on the surface of graphene oxide (GO) sheets. Ag-GO was then added into SA, and a double-layered SA hydrogel film (Ag-GO/SA) carrying Ag-GO was prepared by sol-gel process. FTIR, XRD and SEM characterizations were used to determine the chemical structure and micromorphology of Ag-GO/SA. In addition, swelling ability, mechanical and antibacterial properties, as well as in-vitro cytotoxicity and in-vivo wound healing ability of Ag-GO/SA samples were also evaluated. The results show that the prepared Ag-GO/SA has good swelling property, sufficient mechanical strength, excellent wound healing and antibacterial properties. Specially, the optimum hydrogel of Ag-GO/SA can promote wound healing in SD rats, with a wound healing rate of up to 98%, presenting great application potential as a new type of wound dressing.

Silver loaded hydroxyethylacryl chitosan/sodium alginate hydrogel films for controlled drug release wound dressings

Wound dressings composed of hydroxyethylacryl chitosan (HC) and sodium alginate (SA) were developed with antibacterial activity by loading Ag particles. The formation of Ag particle in the HC/SA films was achieved by an immersion method through in situ chemical reduction of AgNO3 solution and confirmed by FTIR, SEM-EDS, XRD and XRF techniques. The effect of Ag loading in the Ca-crosslinked HC/SA films with different crosslinking density was studied on swelling behavior, mechanical properties, cytotoxicity, antibacterial activity and drug release behavior. The results showed that Ag loading increased swelling degree in phosphate buffer and enhanced mechanical properties. The HC/SA films with Ag loading exhibited antibacterial activity against E. coli and S. aureus as well as no toxicity on Vero cell. In vitro drug release profiles of the films were examined using para-acetylaminophenol, as a soluble model drug. The increase in crosslinking density and Ag loading prolonged drug releasing rate and almost the films showed linearity profiles. It can be concluded that the HC/SA films with Ag loading have a promising potential in modern wound dressings with antibacterial property and controlled drug release.

Nanozyme-Triggered DNA Release from Alginate Films

Alginate hydrogel thin films of different compositions were electrochemically produced at an electrode surface, and their interfacial reactions were studied for biomolecule release. Nanozyme catalytic species represented by Au nanoparticles were used to trigger biomolecule release from an Fe3+-cross-linked alginate hydrogel film upon receiving a glucose signal. The oxidase-mimicking reaction catalyzed by Au nanoparticles resulted in the production of H2O2, which yielded free radicals through a Fenton-type reaction in the presence of iron cations. The generated free radicals resulted in degradation/dissolution of the alginate matrix and stimulated the release of entrapped DNA molecules. The systematic study addressed the issues of the uncontrolled leakage of the DNA molecules from alginate hydrogel and demonstrated the signal-triggered DNA release in systems with various configurations, ranging from a simple addition of H2O2 to the bulk solution to the in situ production of H2O2 by the nanozyme coentrapped in the alginate film. The present study adds an additional feature to the multioperational functions of nanozymes, representing their use in signal-controlled biomolecule-releasing systems.

The effect of chelation of sodium alginate with osteogenic ions, calcium, zinc, and strontium.

Alginates are attractive in tissue regeneration due to their similarity to the extracellular matrix, biocompatibility, biodegradability, non-antigenicity, and the ability to undergo ionotropic gelation. Alginate hydrogels are formed by ionic crosslinking mainly using calcium ions with some reports on the use of strontium and zinc ions. Strontium and zinc ions in trace amounts are known to accelerate bone healing due to their role in regulating osteoblasts and osteoclasts in addition to their antibacterial properties. This study reports the effect of forming alginate hydrogel films using three different ionic species, Ca2+, Zn2+ and Sr2+ with different M/G ratios on their physical properties as a method of introducing these ions in alginate composites for bone tissue engineering. The results reveal that mechanical and thermal properties of alginate films along with their water sorption behaviour are affected by the type of ions that crosslink them and the relative amounts of M and G length of the different block structures influence the gel forming ability. Since calcium, zinc and strontium are ions of interest due to their osteogenic properties, the results of this study can be used to tailor the properties of alginates for the development of composite scaffolds for bone tissue regeneration.

Influence of Manuka Honey on Mechanical Performance and Swelling Behaviour of Alginate Hydrogel Film

In this study, sodium alginate (SA) hydrogel film incorporated with Manuka honey was successfully developed. Swelling properties and gel fraction of hydrogel films decreased upon addition of Manuka honey in SA film. SA hydrogel film has the highest swelling percentage at 512 ± 21% and decreased to 197 ± 9% in SA hydrogel film containing 10% (v/v) of Manuka honey (SA-H10). In contrast, the SA-H10 hydrogel film has the lowest gel fraction at 12 ± 1% compared to SA hydrogel film at 45 ± 3%. The Young’s Modulus of SA hydrogel films with Manuka honey were increased as the concentrations of Manuka honey increased. The hydrogel films with higher concentration of Manuka honey (SA-H10) were soft with tensile strength, tensile strain and Young’s Modulus at 1.06 ± 3 MPa, 15 ±1% and 34 ± 3 MPa, respectively. The water vapour transmission rates (WVTRs) of SA-H hydrogel films were in the range of 1051 ± 48 – 1428 ± 84 g m−2 d−1, which comparable to WVTRs values with the commercial wound dressing products. The SA-H hydrogel films can be a potential material to be used as a wound dressing product.

Relative Humidity and Temperature Sensing Characteristics of an Optical Fiber Probe Based on Hollow-Core Fiber and Calcium Alginate Hydrogel Film

Hydrogel is a kind of functional cross-linked polymer material with 3-D network structure. When hydrogel is exposed to water environment, a mass of hydrophobic groups and hydrophilic residues existing in the cross linked netlike nano-structure is willing to combine with water molecules and expand, respectively. In this paper, a novel optical fiber probe based on hollow-core fiber and calcium alginate (CaAlg) hydrogel film is proposed and experimentally demonstrated. The experimental results of relative humidity (RH) and temperature sensing characteristics show that the proposed probe has a binomial response to RH in the range of 20%~90% RH and a linear response to temperature with the sensitivity of 121pm/°C. CaAlg is considered as an effective and potential as the humidity-sensitive material to optical fiber RH sensors.

Physical and mechanical properties of alginate-based hydrogel film as carrier for release of acetylthiocholine

The effects of different cross-linkers on mechanical and physical properties of alginate hydrogel films were determined to use prepared films as potential carrier structure for rapid detection system. Xylitol and d-mannitol cross-linked hydrogel films improved mechanical properties and generated more rigid, tough and stretchable film than uncross-linked film. Results exhibited increased tensile strength by 2.3 folds (58.3±5.8 MPa) and 1.8 folds (47.4±4.9MPa) when compared to uncross-linked film (25.8±7.3 MPa) respectively. Young’s modulus of d-mannitol cross-linked film was slightly greater (16.8±2.1 MPa) than that of xylitol (15.7±2.7 MPa) whereas the elongation at break (E%) value of xylitol cross-linking (5.46±1.2%) was greater than d-mannitol (2.72±0.8%) cross-linking. Altered mechanical properties were investigated in terms of different amount of % cumulative release of AchI and DTNB that were immobilized in film matrix. Results showed different release amount depending on types of cross-linkers as following: xylitolcrosslinked (71.5%) > d-mannitol (64.9%) > uncross-linked (58.3%) at 10 min of release period. The exponent value n which determined based on power-law expression was ranged between 0.56 and 0.98, and indicates the release was mediated by anomalous Non-Fickian diffusion.

Crosslinker Effects on Properties of Hydroxyethylacryl Chitosan/Sodium Alginate Hydrogel Films

SummaryThe aim of this research is to investigate the effects of Ca2+ and Zn2+ ions on the swelling behavior, mechanical property and antibacterial activity of hydroxyethylacryl chitosan (HC)/ sodium alginate (SA) hydrogel films. The hydrogel films composed of HC and SA in different proportions (75:25, 50:50 and 25:75 w/w) were prepared by dipping method using calcium chloride as a single crosslinking agent and both calcium chloride and zinc sulfate as a couple crosslinking agent. The structures of the films were characterized by infrared spectroscopy (FT‐IR). It was found that Ca2+ ions could only crosslink with SA through the formation of ionic bonds while Zn2+ ions could crosslink both HC through the formation of coordinate bonds and SA through the formation of partially ionic or coordinate bonds. The swelling behaviors of the films in phosphate buffered saline (PBS) were investigated. The results showed relatively high stability for the crosslinked films with the couple crosslinking agent. The mechanical properties of the hydrogel films were also tested. It was found that the mechanical properties of the calcium‐zinc crosslinked films were greater than calcium crosslinked films. The values of tensile strength and elongation at break of the calcium‐zinc crosslinked films in the fully hydrated state were up to 12.9 MPa and 67%, respectively. Additionally, the calcium‐zinc crosslinked films evidenced better antibacterial activity to Staphylococcus aureus than calcium crosslinked films. Moreover, all of prepared hydrogel films exhibited no cytotoxicity for Vero cells. The comprehensive results suggest their potential as a wound dressing.

Preparation and characterization of protein molecular imprinted calcium alginate hydrogel film with controllable thickness

Bovine serum albumin (BSA) imprinted calcium alginate (CaAlg MIP) hydrogel film was prepared using BSA as template molecule, sodium alginate (NaAlg) as the functional monomer, and CaCl2 as the ionic cross-linker. The thickness of the film was controlled by a glass rod enlaced with brass wires. The relationship between copper wire diameter and the thickness of CaAlg MIP was investigated. SEM, laser scanning confocal microscope and 3D ultra-depth three-dimensional microscope were used to characterize the CaAlg MIP. The mechanical properties of the wet CaAlg MIP prepared with different concentrations of NaAlg were investigated. Circular dichroism (CD) was used to characterize the conformation of the eluted BSA. The influence of different thickness and different eluants on the adsorption capacity of CaAlg MIP was discussed. The results showed that CaAlg MIP adsorbed more BSA than CaAlg NIP. There was no change of the conformation of protein during the preparing and eluting process. The CaAlg MIP can be prepared by a fast, low-cost and environmental friendly method in aqueous solution in the absence of any toxic surfactant or organic solvent, which would find its potential applications in the fields of cell culture and tissue engineering.