Developing and physicochemical evaluation of cross-linked electrospun gelatin–glycerol nanofibrous membranes for medical applications

Cross-linking electrospinning

Although electrospinning (e-spinning) has witnessed rapid development in recent years, it has also been criticized by environmentalists due to the use of organic solvents. Therefore, aqueous e-spinning (green e-spinning) is considered a more attractive technique. However, considering the poor water resistance and mechanical properties of electrospun (e-spun) nanofibers, cross-linking is a perfect solution. In this review, we systematically discuss the cross-linking e-spinning system for the first time, including cross-linking strategies (in situ, liquid immersion, vapor, and spray cross-linking), cross-linking mechanism (physical and chemical cross-linking) of e-spun nanofibers, and the various applications (e.g., tissue engineering, drug delivery, water treatment, food packaging, and sensors) of cross-linked e-spun nanofibers. Among them, we highlight several cross-linking methods, including UV light cross-linking, electron beam cross-linking, glutaraldehyde (and other commonly used cross-linking agents) chemical cross-linking, thermal cross-linking, and enzymatic cross-linking. Finally, we confirm the significance of cross-linking e-spinning and reveal the problems in the construction of this system.

How to effectively and greenly prepare multi-scale structural starch nanoparticles for strengthening gelatin film (ultrasound-Fenton system)

Ultrasound (US) assisted with Fenton (US-Fenton) reaction was developed to efficiently and greenly prepare starch nanoparticles (SNPs) that were employed as nanofillers to enhance gelatin (G) film properties. Compared to Fenton reaction alone, US-Fenton reaction significantly improved preparation efficiency and dispersion of SNPs (p < 0.05). An optimal US-Fenton reaction parameter (300 mM H2O2, ascorbic acid 55 mM, US 45 min) was found to prepare SNPs with uniform sizes (50-90 nm) and low molecular weight (Mn 7.91 × 105 Da). The XRD, FT-IR, and SAXS analysis revealed that the US-Fenton reaction degraded the amorphous and crystalline zones of starch from top to down, leading to the collapse of the original layered structure starch and the progressive formation of SNPs. The different sizes of SNPs were selected to prepare the composite films. The G-SNP3 film (with 50-90 nm SNPs) showed the most outstanding UV blocking, tensile, and barrier properties. Especially, the tensile strength of G-5%SNP3 film (containing 5 % SNPs) increased by 156 % and 6 % over that of G film and G-5%SNP2 film (containing 5%SNPs with 100-180 nm), respectively. Therefore, the nanomaterial was promisingly prepared by the US-Fenton system and provided a strategy for designing and producing nanocomposite films.

Preparation and characterization of a novel intelligent starch/gelatin binary film containing purple sweet potato anthocyanins for Flammulina velutipes mushroom freshness monitoring

In this study, intelligent food package was developed and characterized by loading purple sweet potato polyphenolic extract (SPS) into starch/gelatin film. The application of this film in indicating the freshness of Flammulina velutipes was also determined. The color of SPS buffer changed from red to blue and final yellow when pH increasing from 3 to 10. The blending film with starch/gelatin ratio of 1:1 wt showed a minimum water vapor permeability of 6.26 × 10-11 gs-1 m-1 Pa-1. The value of elongation at break and tensile strength of the starch/gelatin film with starch/gelatin ratio of 1:1 wt increased to 78.89 % and 11.70 MPa. Upon its application to monitor of F. velutipes freshness level, SG11 film color changed from initially green to purplish gray and finally to yellow as F. velutipes deteriorated post storage. Our results suggested that SG11 films could be used as an intelligent packaging material in the future for other food products.

Influence of the Maillard Reaction on Properties of Air-Assisted Electrospun Gelatin/Zein/Glucose Nanofibers

To develop biodegradable, sustainable, and environment-friendly functional food-packaging materials, gelatin/zein/glucose nanofibers were fabricated through air-assisted electrospinning and then crosslinked by the Maillard reaction under mild conditions (60 °C and 50% relative humidity) in this study. Compared to traditional electrospinning, air-assisted electrospinning increased the yield of nanofibers by 10 times, and the average diameter from 263 nm to 664 nm, while the airflow facilitated uniform and smooth nanofiber formation. During the Maillard reaction in 0-5 days, the gelatin/zein/glucose showed no morphology change. Fourier transform infrared spectra analysis indicated that gelatin interacted with zein through hydrogen bonding and the occurrence of the Maillard reaction among the protein and glucose molecules. After four days of Maillard reaction, the nanofibers presented higher thermal stability, the most hydrophobic surface (water contact angle: 133.6°), and stiffer network structure (elastic modulus of 38.63 MPa, tensile strength of 0.85 MPa). Overall, Maillard-reaction-crosslinked gelatin/zein/glucose nanofibers showed favorable physical properties, which suggests their potential for application in food-active packaging.

Assessing the compressive elasticity and multi-responsive property of gelatin-containing weakly anionic copolymer gels via semi-IPN strategy

A series of semi-interpenetrating polymer network (semi-IPN) hydrogels based on acrylamide (AAm) and itaconic acid (ITA) was prepared in the presence of different amounts of the natural polymer gelatin (GLN). The semi-IPNs were synthesized by simultaneous polymerization using N,N'-methylene bisacrylamide as a crosslinking agent. A pH-sensitive system was obtained by adding 2 mol% ITA as an anionic comonomer. The effect of GLN content by changing the amine/carboxyl functional groups and incorporating carboxyl groups of ITA in semi-IPN on the swelling, elasticity and physical properties of the hydrogels was investigated. The presence of GLN improved the thermal stability, and the GLN-containing semi-IPNs exhibited a higher degradation temperature compared to the GLN-free copolymers. The addition of a small amount of GLN could effectively increase the swelling of the semi-IPNs in water. By employing the GLN-containing semi-IPN as a model system, the solvent/matrix interactions were demonstrated to reveal the effect of solvent structure on the swelling-shrinkage response. The addition of GLN improved the pH-sensitivity of the semi-IPN gels, resulting in a clear response to pH change by action of NH₃⁺ and COOH of GLN and additional COOH groups from ITA. The mechanical performance of the copolymer network was improved by entangling PAAm/ITA chains with GLN, which acted as a reinforcement node. In terms of the effect of Hofmeister anions on the swelling behavior, the anion effect became more pronounced with salt concentration. The affinity of semi-IPNs towards the cationic dyes methylene blue and malachite green was tested and the dependence of the adsorption process on the initial dye concentration, contact time and GLN content was determined. This method presents a simple and efficient approach for the design of chemically crosslinked protein-based gels for drug delivery applications.

In Situ Transformation of Electrospun Nanofibers into Nanofiber-Reinforced Hydrogels

Nanofiber-reinforced hydrogels have recently gained attention in biomedical engineering. Such three-dimensional scaffolds show the mechanical strength and toughness of fibers while benefiting from the cooling and absorbing properties of hydrogels as well as a large pore size, potentially aiding cell migration. While many of such systems are prepared by complicated processes where fibers are produced separately to later be embedded in a hydrogel, we here provide proof of concept for a one-step solution. In more detail, we produced core-shell nanofibers from the natural proteins zein and gelatin by coaxial electrospinning. Upon hydration, the nanofibers were capable of directly transforming into a nanofiber-reinforced hydrogel, where the nanofibrous structure was retained by the zein core, while the gelatin-based shell turned into a hydrogel matrix. Our nanofiber-hydrogel composite showed swelling to ~800% of its original volume and water uptake of up to ~2500% in weight. The physical integrity of the nanofiber-reinforced hydrogel was found to be significantly improved in comparison to a hydrogel system without nanofibers. Additionally, tetracycline hydrochloride was incorporated into the fibers as an antimicrobial agent, and antimicrobial activity against Staphylococcus aureus and Escherichia coli was confirmed.

Physicochemical characteristics of ginger essential oil nanoemulsion encapsulated by zein/NaCas and antimicrobial control on chilled chicken

An efficient antibacterial nanoemulsion was prepared using zein and NaCas to encapsulate ginger essential oil (GEO). Physical, optical, and mechanical properties as well as the antibacterial activities of GEO nanoemulsion were investigated. At 1:1 mass ratio of zein/NaCas, the GEO nanoemulsion possessed the highest solubility, entrapment efficiency and stability. The GEO/zein/NaCas complex was confirmed by ultraviolet and fluorescence spectroscopy. The addition of GEO led to more amorphous structure formation and the secondary structure changes of zein/NaCas improved the solubility and stability of GEO. GEO nanoemulsion inactivated two common foodborne bacteria, namely, Staphylococcus aureus and Pseudomonas aeruginosa, by destroying the cell membrane. Meanwhile, the GEO nanoemulsion exhibited better preservation effects on chilled chicken breasts than non-emulsified GEO and could effectively prolong the shelf life of chicken breasts for 6 days. This research provides a green and low-cost method for preparing GEO nanoemulsion to control the risk of foodborne pathogens.

Influence of substrate temperature parameter on electrospinning process: example of application to the formation of gelatin fibers

The substrate temperature was investigated to broaden the applicability of controlling the morphology of polymeric fibers produced during the electrospinning process. A laboratory electrospinning setup was designed using a substrate heated in a temperature range of 25 °C to 100 °C. A gelatin polymer was used as an example to obtain beads-free gelatin fibers by fixing the main electrospinning parameters. Based on XRD, FTIR, and DSC techniques, the electrospun gelatin fibers did not show any change in their chemical composition up to 100 °C. Heating the substrate at 50 °C may be the best selection factor to obtain gelatin fibers; the fiber diameters experienced a significant decrease from 680 ± 140 nm to 420 ± 120 nm with increasing substrate temperature from 25 to 50 °C, respectively. They showed stability of the diameter at 380 ± 130 nm and 390 ± 130 nm when increasing substrate temperatures from 75 to 100 °C, respectively, with a significant variation in their diameter distribution. Therefore, this ability to control the electrospinning process using a heated substrate makes it promising for fabricating electrospun beads-free fibers of biopolymers such as gelatin for tissue engineering and drug delivery carriers.

Encapsulation of sea buckthorn (Hippophae rhamnoides L.) leaf extract via an electrohydrodynamic method

Polyphenols from the leaves of sea buckthorn (Hippophae rhamnoides L.) are nutritious and bioactive substances that can be used as nutritional supplements. To improve their stability and bioaccessibility in vivo, chemical extracts of sea buckthorn leaves were, for the first time, encapsulated using electrohydrodynamic technology. The microcapsules were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The extract and microcapsules were evaluated for total phenols and flavonoids, total antioxidant activity, and their inhibitory effects on metabolic syndrome-related enzymes (α-glucosidase, α-amylase, and pancreatic lipase) under in vitro simulated digestion. The results indicated that the extract was successfully encapsulated; encapsulation protected polyphenols and flavonoids from degradation and increase their bioaccessibility in the intestine. The antioxidant activity and the inhibition of metabolic syndrome-related enzymes were better reserved after encapsulation. Our findings will help in promoting the potential of sea buckthorn as a nutritional supplement and expanding its commercial use.

Osteogenic Effect of a Biodegradable BMP-2 Hydrogel Injected into a Cannulated Mg Screw

Cannulated screws, containing an internal hole for inserting a guide pin, are commonly used in the management of bone fractures. Cannulated Mg screws can be biodegraded easily because their increased surface area including that of the inner hole rapidly reacts with body fluids. To delay biodegradation of cannulated Mg screws and improve bone regeneration, we developed a specific type of screw by injecting it with gelatin hydrogels [10 wt % gelatin_(gel) with 0.09 v/v % glutaraldehyde (cross-linker)] containing different concentrations (5, 10, or 25 μg/mL) of bone morphogenic proteins (BMPs). We analyzed the properties and biocompatibility of the screws with and without BMP-2 and found that the release rate of BMP-2 in the hydrogel changed proportionately with the degradation rate of the cross-linked hydrogel. Loading BMP-2 in the hydrogel resulted in sustained release of BMP-2 for 25 to 40 days or more. The degradation rate of BMP-2 hydrogels was inversely proportional to the concentration of BMP-2. The injection of the hydrogels in the cannulated screw delayed biodegradation inside of the screw by simulated body fluid. It also induced uniform corrosion and the precipitation of bioactive compounds onto the surface of the screw. In addition, osteoblast proliferation was very active near the BMP-2 hydrogels, depending on the BMP-2 concentration. The BMP-2 in the hydrogel improved cell differentiation. The cannulated screw injected with 10 μL/mL BMP-2 hydrogel prevented implant biodegradation and enhanced osteoconduction and osteointegration inside and outside the screw. In addition, the properties of BMP-2-loaded hydrogels can be changed by controlling the amount of the cross-linker and protein, which could be useful for tissue regeneration in other fields.

Effect of Regenerated Cellulose Fibers Derived from Black Oat on Functional Properties of PVA-Based Biocomposite Film

In this study, agricultural residue from black oat, a cover crop usually grown to improve soil nutrients between the periods of regular crop production, was used as a source of cellulose fibers. Concentrations of 1, 3, and 5 wt. % of regenerated cellulose (RC) fibers blended in poly(vinyl alcohol) (PVA) solution were used to prepare the reinforced composite films (CFs) by the solvent cast method. Compared to neat PVA film (control), the effects of RC addition on functional properties of CFs, such as water absorption, transparency, thermal stability, and mechanical property were investigated. All CFs with different RC concentrations exhibited improved mechanical property and thermal stability while the swelling property was decreased, and no significant changes were observed in the film transparency as compared with the control film. Among the CFs, films with 3% RC significantly decreased water vapor transmission rate, swelling, and soluble fraction (p < 0.05). In addition, Young’s modulus and tensile strength were increased by 40 MPa and 3 MPa, respectively, while elongation at break was decreased by 4%, compared to the control film. The results indicate that RC from black oat might be feasible as potential bio fillers to improve film properties in a bio-based composite matrix.

Assessment and Characterization of Some New Photosensitizers for Antimicrobial Photodynamic Therapy (aPDT)

The novelty of this study consists on the formulation and evaluation of five complex experimental natural photosensitizers (PS): gel with oregano essential oil (O), gel with methylene blue (AM), gel with a mixture of essential oils (Thieves-H), gel with arnica oil and curcuma extract (CU) and gel with frankincense essential oil (T), used as photosensitizing agents (PS) in antimicrobial photodynamic therapy (aPDT) in the control of microbial biofilm in oral cavity. The experimental PS were characterized by gas chromatography-mass spectrometry (GC-MS), Fourier-transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, cytotoxicity assay, antimicrobial effect and scanning electron microscopy (SEM). The IR spectra of the experimental PS with essential oils exhibit absorption bands due to the presence of water and glycerol in high quantities. The studied compounds had a reduced cytotoxic effect on cell cultures. The lowest cytotoxic effect was observed in experimental PS with oregano essential oil and methylene blue PS. Essential oils with proven antibacterial capabilities used in experimental PS confer antibacterial activity to the gels in which they are incorporated, an activity that may be more efficient use of a PDT therapy. Single bacteria were detected mainly by SEM after 12 h, while aggregate bacteria and micro colonies dominated the samples at 48 h.

A Novel Acetaminophen Soft-Chew Formulation Produced via Hot-Melt Extrusion with In-line Near-Infrared Monitoring as a Process Analytical Technology Tool

Patients who suffer from dysphagia have difficulty in swallowing hard tablets and capsules; hence, gelatin-based soft-chew dosages are used as an alternative and novel drug delivery approach to overcome this problem. However, the conventional method of producing gelatin-based soft-chew dosages has many potential issues. The objective of this study was to use glycerol and the hot-melt extrusion technique to address potential issues and optimize the formulation. Gelatin, acetaminophen, saccharin, xylitol, and sodium chloride and six different ratios of water and glycerol were used in the seven formulations. Extrusion process temperature of formulations 1-6 and formulation 7 were 90°C and 140°C, respectively. Near-infrared spectra were collected during extrusion to monitor quality consistency. Scanning electron microscopic images of the cross-section of the soft-chew dosages were recorded. Differential scanning calorimetry (DSC) was used to characterize the crystal states of each formulation. Texture profile analysis was used to evaluate the physical properties of the tablets. In vitro drug release characteristics were studied. A 45-day stability study was carried out to evaluate the stability of each formulation. Near-infrared spectra showed that formulations 1-6 were uniform while formulation 7 was not. From the DSC results, formulations 1 and 2 showed crystallinity of acetaminophen. Formulation 5 displayed the desired physical and chemical stability in texture profile analysis and in the in vitro drug release studies. By using glycerol and hot-melt extrusion, the potential issues of conventional methods were successfully addressed.

Characterization of gelatin/chitosan ploymer films integrated with docosahexaenoic acids fabricated by different methods

In this study, docosahexaenoic acid powder-enhanced gelatin-chitosan edible films were prepared by casting, electrospinning and coaxial electrospinning, respectively. The color (CR), transparency (UV), light transmission (UV), mechanical strength (TA-XT), thermal stability (DSC), crystalline structures (XRD), molecular interactions (FTIR), and microstructure (SEM) were assessed in the analytical research. The results of the research showed that the electrospinning process and the coaxial electrospinning process produced a smooth surface visible to by the naked eye and a uniform granular network structure in a unique film-forming manner, thereby exhibiting good water solubility and mechanical properties. In contrast, the casted film was smooth, transparent, and mechanically strong but poorly water soluble. It was also found that the addition of docosahexaenoic acid powder affected the optical, physical and mechanical properties of the film to varying degrees.

Action of ginger essential oil (Zingiber officinale) encapsulated in proteins ultrafine fibers on the antimicrobial control in situ

The ultrafine fibers were produced using a polymeric blend of soy protein isolate (SPI), polyethylene oxide (PEO), and zein at a ratio of 1:1:1 (v/v/v) by electrospinning. The ginger essential oil (GEO) was encapsulated in the ultrafine fibers and the morphology, Fourier-Transform Infrared Spectroscopy (FTIR) analysis, thermal properties and relative crystallinity were evaluated. The antimicrobial activity of ginger essential oil was evaluated against five bacteria (Listeria monocytogenes, Staphylococcus aureus, Escherichia coli 0157:H7, Salmonella typhimurium, and Pseudomonas aeruginosa). Based on the preliminary tests, the concentration of GEO selected to add in the polymer solution was 12% (v/v; GEO/polymer solution). The fiber produced with 12% (v/v) GEO was used for antimicrobial analysis and in situ application (in fresh Minas cheese) against L. monocytogenes by micro-atmosphere. The ultrafine fibers produced, regardless the concentration of the essential oil, presented homogeneous morphology with cylindrical shape without the presence of beads. The application of the active fibers containing 12% GEO showed high potential to be applied in food packaging to reduce microbial contamination.

Environmentally Friendly Gelatin/β-Cyclodextrin Composite Fiber Adsorbents for the Efficient Removal of Dyes from Wastewater

In this paper, environmentally friendly gelatin/β-cyclodextrin (β-CD) composite fiber adsorbents prepared by electrospinning were used for the removal of dyes from wastewater. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and a universal materials tester were employed to characterize the internal structures, surface morphologies and mechanical strength of the composite fiber adsorbents. Additionally, the fiber was evaluated as an adsorbent for the removal of methylene blue (MB) from aqueous solution. The effects of the raw material ratio, pH, temperature, concentration and adsorption time were studied. The results show that the gelatin/β-CD composite fiber adsorbents possess excellent mechanical strength and high adsorption efficiency for MB. The adsorption equilibrium and adsorption kinetics are well-described by the Langmuir isotherm model and the pseudo-second-order kinetic model, respectively. The theoretical maximum adsorption capacity is 47.4 mg·g-1. Additionally, after nine successive desorption-adsorption cycles, the removal rate is still over 70%. Moreover, the gelatin/β-CD composite fiber adsorbents exhibit excellent adsorption capability for basic fuchsin, gentian violet, brilliant blue R and malachite green dyes. Therefore, owing to the characteristics of degradability, low cost and high-efficiency, the gelatin/β-CD composite fiber can be used as an efficient adsorbent for the removal of dyes from wastewater.

Storage stability of electrospun pure gelatin stabilized with EDC/Sulfo-NHS

With the rapid development of biomimetic polymers for cell-based assays and tissue engineering, crosslinking electrospun nanofibrous biopolymer constructs is of great importance for achieving sustainable and efficient three-dimensional scaffold constructs. Uncrosslinked electrospun gelatin nanofibrous constructs immediately and completely dissolved in aqueous solutions due to their aqueous solubility and poor storage stability. Here, a novel and versatile approach for the fabrication and crosslinking of electrospun gelatin construct with tunable porosity and high aspect ratio nanofibers is presented. Uncrosslinked electrospun gelatin/genipin nanofibrous and pure gelatin nanofibrous constructs exhibited smooth surfaces that were well-defined, with a diameter in the range of 448 ± 364 nm and 257 ± 57 nm, respectively. Dehydrothermal, genipin-EDC/Sulfo-NHS, and EDC/Sulfo-NHS crosslinking approaches were examined to achieve insoluble gelatin nanofibrous constructs that were suitable for cell-based assays. Mechanical characterization demonstrated that the pure gelatin nanofibrous construct crosslinked via EDC/Sulfo-NHS exhibited an increased mechanical strength and stiffness and showed no dissolution in aqueous solutions and retained its fiber morphology. An excellent 1 month storage stability was demonstrated at 22, 4, -20, and -80°C (dehydrated) and at 4°C (hydrated). The as-crosslinked gelatin nanofibrous construct was highly biocompatible (90% cell viability), as demonstrated by the promoted proliferation of PC12 cells.