Coordination with zirconium: A facile approach to improve the mechanical properties and thermostability of gelatin hydrogel

Mussel-Inspired Sonochemical Nanocomposite Coating on Catheters for Prevention of Urinary Infections

Catheter-associated urinary tract infections are the most common hospital-acquired infections and cause patient discomfort, increased morbidity, and prolonged stays, altogether posing a huge burden on healthcare services. Colonization occurs upon insertion, or later by ascending microbes from the rich periurethral flora, and is therefore virtually unavoidable by medical procedures. Importantly, the dwell time is a significant risk factor for bacteriuria because it gives biofilms time to develop and mature. This is why we engineer antibacterial and antibiofilm coating through ultrasound- and nanoparticle-assisted self-assembly on silicone surfaces and validate it thoroughly in vitro and in vivo. To this end, we combine bimetallic silver/gold nanoparticles, which exercise both biocidal and structural roles, with dopamine-modified gelatin in a facile and substrate-independent sonochemical coating process. The latter mussel-inspired bioadhesive potentiates the activity and durability of the coating while attenuating the intrinsic toxicity of silver. As a result, our approach effectively reduces biofilm formation in a hydrodynamic model of the human bladder and prevents bacteriuria in catheterized rabbits during a week of placement, outperforming conventional silicone catheters. These results substantiate the practical use of nanoparticle-biopolymer composites in combination with ultrasound for the antimicrobial functionalization of indwelling medical devices.

Zirconium ion mediated collagen nanofibrous hydrogels with high mechanical strength

Low mechanical strength is still the key question for collagen hydrogel consisting of nanofibrils as hard tissue repair scaffolds with no loss of biological function. In this work, novel collagen nanofibrous hydrogels with high mechanical strength were fabricated based on the pre-protection of trisodium citrate masked Zr(SO4)2 solution for collagen self-assembling nanofibrils and then further coordination with Zr(SO4)2 solution. The mature collagen nanofibrils with d-period were observed in Zr(IV) mediated collagen hydrogels by AFM when the Zr(IV) concentration was ≥ 10 mmol/L, and the distribution of zirconium element was uniform. Due to the coordination of Zr(IV) with ─COOH, ─NH2 and ─OH within collagen and the tighter entanglement of collagen nanofibrils, the elastic modulus and compressive strength of Zr(IV) mediated collagen nanofibrous hydrogel were 208.3 and 1103.0 kPa, which were approximate 77 and 12 times larger than those of pure collagen hydrogel, respectively. Moreover, the environmental stability such as thermostability, swelling ability and biodegradability got outstanding improvements and could be regulated by Zr(IV) concentration. Most importantly, the resultant hydrogel showed excellent biocompatibility and even accelerated cell proliferation.

Construction of gelatin/alginate hydrogels doped hemicyanine derivatives for photodynamic antibacterial application

Hydrogel systems based on natural polymer materials have provided alternative opportunities for preparing antimicrobial dressings. A composite antibacterial hydrogel system containing gelatin (Gel), alginate (Alg) and hemicyanine derivatives with different chain lengths (C3, C6 and C10) was constructed. The composite hydrogels have excellent swelling ability and low degradability due to the classical three-dimensional network structure. Because of the photosensitization ability of C3, C6 and C10, hydrogels containing these molecules can also effectively produce reactive oxygen species (ROS) under light. Importantly, the hydrogel containing C3 molecules that have higher spatial extension structure and shorter alkyl chain than C6 and C10 shows better photo-responsive antibacterial effect against drug-resistant Escherichia coli. The bacterial killing activity of the composite hydrogel system could be regulated by changing the alkyl chain length of the photosensitizers. This effective and photo-responsive composite hydrogel system is expected to be used for bacteria-infected wound repair and promoting wound healing.

New materials-based on gelatin coordinated with zirconium or aluminum for ecological retanning

Ecological retanning agent is an effective way to solve the pollution source of leather manufacturing industry. In this study, the gelatin from chrome-containing leather shavings in the leather industry was used to realize sustainable leather post-tanning. The gelatin hydrolysate (GH) coordinated with Zr4+ or Al3+ to prepare eco-friendly retanning agents GH-Zr and GH-Al. The successful coordination between GH and metal ions was characterized by FTIR and XPS. The retanning agents were characterized by FTIR curve-fitting and circular dichroism spectroscopy. The results showed that the conformation of the secondary structure of the polypeptide became ordered and stable after coordinating with the metal ions. The particle size and weight average molecular weight of the retanning agents were ~1700 nm and ~2100, respectively, measured by nanoparticle size analyzer and gel permeation chromatography (GPC). The retanning agents were applied to retanning of chrome tanned leather and glutaraldehyde tanned leather. The abundant free amino from retanning agents can consume the free formaldehyde. Meanwhile, retanning agents can effectively improve the multiple binding sites, resulting in favorable thickening rate (>110 %) and excellent dye and fatliquor absorption rate with ~99.91 % and ~93.18 %. Thus, this strategy can provide a viable choice for solid leather waste and sustainable development of the leather industry.

Hydrophobic association: A facile approach to prepare physical cross-linked gelatin hydrogel with desirable thermal stability, flexibility and self-healing ability

Methacrylic anhydride was added to 20 % gelatin solution to prepare gelatin methacryloyl (GelMA) but an unexpected gelation process was observed within several minutes. The experimental data revealed that the methacryloyl substitution can increase the hydrophobicity of gelatin and the micellar diameter in solution. Therefore, we speculated that the methacryloyl substitution caused the formation of micellar cross-links based on the hydrophobic residues of gelatin and the methacryloyl groups, thus obtaining the hydrophobic association hydrogels. The thixotropic and tensile experiments confirmed that GelMA hydrogel possessed the features of hydrophobic association hydrogels like self-healing and stretchable abilities. The rheological experiments revealed that the gelation rate and the mechanical strength of the GelMA hydrogels were in direct proportion to the concentration of GelMA and the degree of methacryloyl substitution. GelMA hydrogels possessed desirable thermal stability that it didn't melt after being heated to 90 °C. Furthermore, the MTT assays and calcein AM/PI staining revealed that GelMA hydrogel was biocompatible. These results collectively confirm that the hydrophobic association is a prospective and facile approach to prepare gelatin hydrogel with desirable properties for further application.

Neuroprotective α-pyrones from Nigrospora oryzae, an endophytic fungus residing in Taxus chinensis var. mairei

Endophytes coevolve with plant hosts and thus are more probable to acquire the character (in favor) of producing undescribed bioactive metabolites. Consequently, the topic has been intensely investigated for over two decades, but endophytic metabolites with neuroprotective effect remain scarce. The study presents the discovery of eight undescribed (named solanapyrones U-Z and prosolanapyrones A and B) and six known pyrones (solanapyrones A-C and E-G) from the culture of Nigrospora oryzae, an endophytic fungus associated with Taxus chinensis var. mairei. The structures and absolute configurations of undescribed pyrones were elucidated by extensive spectroscopic analysis, modified Mosher's method, and induced circular dichroism (ICD) spectrum. Solanapyrones A and B and an undescribed pyrone (solanapyrone U) were demonstrated to be more neuroprotective than clenbuterol in inducing bone marrow mesenchymal stem cells (bMSCs) to secret nerve growth factor (NGF). The work updates the pyrone chemodiversity in nature and extends the biofunction repertoire of solanapyrone-related polyketides.

Continuous Spinning of High-Tough Hydrogel Fibers for Flexible Electronics by Using Regional Heterogeneous Polymerization

Hydrogel fibers have attracted substantial interest for application in flexible electronics due to their ionic conductivity, high specific surface area, and ease of constructing multidimensional structures. However, universal continuous spinning methods for hydrogel fibers are yet lacking. Based on the hydrophobic mold induced regional heterogeneous polymerization, a universal self-lubricating spinning (SLS) strategy for the continuous fabrication of hydrogel fibers from monomers is developed. The universality of the SLS strategy is demonstrated by the successful spinning of 10 vinyl monomer-based hydrogel fibers. Benefiting from the universality of the SLS strategy, the SLS strategy can be combined with pre-gel design and post-treatment toughening to prepare highly entangled polyacrylamide (PAM) and ionic crosslinked poly(acrylamide-co-acrylic acid)/Fe3+ (W-PAMAA/Fe3+ ) hydrogel fibers, respectively. In particular, the W-PAMAA/Fe3+ hydrogel fiber exhibited excellent mechanical properties (tensile stress > 4 MPa, tensile strain > 400%) even after 120 days of swelling in the pH of 3-9. Furthermore, owing to the excellent multi-faceted performance and one-dimensionality of W-PAMAA/Fe3+ hydrogel fibers, flexible sensors with different dimensions and functions can be constructed bottom-up, including the one-dimensional (1D) strain sensor, two-dimensional (2D) direction sensor, three-dimensional (3D) pressure sensor, and underwater communication sensor to present the great potential of hydrogel fibers in flexible electronics.

Janus-type ionic conductive gels based on poly(N,N-dimethyl)acrylamide for strain/pressure sensors

Strain/pressure sensors with high sensitivity and a wide operation range have broad application prospects in wearable medical equipment, human-computer interactions, electronic skin, and so on. In this work, based on the different solubilities of Zr4+ in the aqueous phase and the hydrophobic ionic liquid [BMIM][Tf2N], we used N,N-dimethylacrylamide (DMA) as a vinyl monomer to prepare a Janus-type ionic conductive gel with one-sided adhesion through "one-step" UV irradiation polymerization. The Janus-type gel has satisfactory mechanical properties (tensile strength: 217.06 kPa, elongation at break: 1121.01%), electrical conductivity (conductivity: 0.10 S m-1), one-sided adhesion (adhesion strength to glass: 72.35 kPa) and antibacterial properties. The sensor based on the Janus gel can be used not only for real-time monitoring of strain changes caused by various movements of the human body (such as finger bending, muscle contraction, smiling, and swallowing) but also for real-time monitoring of pressure changes (such as pressing, water droplets, and writing movements). Therefore, based on the simplicity of this method for constructing Janus-type ionic conductive gels and the excellent electromechanical properties of the prepared gel, we believe that the method provided in this study has broad application prospects in the field of multifunctional wearable sensors.

Biomimetic Antibacterial Gelatin Hydrogels with Multifunctional Properties for Biomedical Applications

A facile novel approach of introducing dopamine and [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide via dopamine-triggered in situ synthesis into gelatin hydrogels in the presence of ZnSO4 is presented in this study. Remarkably, the resulting hydrogels showed 99.99 and 100% antibacterial efficiency against Gram-positive and Gram-negative bacteria, respectively, making them the highest performing surfaces in their class. Furthermore, the hydrogels showed adhesive properties, self-healing ability, antifreeze properties, electrical conductivity, fatigue resistance, and mechanical stability from -100 to 80 °C. The added multifunctional performance overcomes several disadvantages of gelatin-based hydrogels such as poor mechanical properties and limited thermostability. Overall, the newly developed hydrogels show significant potential for numerous biomedical applications, such as wearable monitoring sensors and antibacterial coatings.

Magnetic Hydrogel Beads as a Reusable Adsorbent for Highly Efficient and Rapid Removal of Aluminum: Characterization, Response Surface Methodology Optimization, and Evaluation of Isotherms, Kinetics, and Thermodynamic Studies

Biopolymers such as alginate and gelatin have attracted much attention because of their exceptional adsorption properties and biocompatibility. The magnetic hydrogel beads produced and used in this study had a core structure composed of magnetite nanoparticles and gelatin and a shell structure composed of alginate. The combination of the metal-ion binding ability of alginate and the mechanical strength of gelatin in magnetic hydrogel beads presents a new approach for the removal of metal from water sources. The beads were designed for aluminum removal and fully characterized using various methods, including Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, vibrating sample magnetometry, microcomputed tomography, and dynamic mechanical analysis. Statistical experimental designs were employed to optimize the parameters of the adsorption and recovery processes. Plackett-Burman Design, Box-Behnken Design, and Central Composite Design were used for identifying the significant factors and optimizing the parameters of the adsorption and recovery processes, respectively. The optimum parameters determined for adsorption are as follows: pH: 4, contact time: 30 min, adsorbent amount: 600 mg; recovery time: reagent 1 M HNO3; and contact time: 40 min. The adsorption process was described by using the Langmuir isotherm model. It reveals a homogeneous bead surface and monolayer adsorption with an adsorption capacity of 5.25 mg g-1. Limit of detection and limit of quantification values were calculated as 4.3 and 14 μg L-1, respectively. The adsorption process was described by a pseudo-second-order kinetic model, which assumes that chemisorption is the rate-controlling mechanism. Thermodynamic studies indicate that adsorption is spontaneous and endothermic. The adsorbent was reusable for 10 successive adsorption-desorption cycles with a quantitative adsorption of 98.2% ± 0.3% and a recovery of 99.4% ± 2.6%. The minimum adsorbent dose was determined as 30 g L-1 to achieve quantitative adsorption of aluminum. The effects of the inorganic ions were also investigated. The proposed method was applied to tap water and carboy water samples, and the results indicate that magnetic hydrogel beads can be an effective and reusable bioadsorbent for the detection and removal of aluminum in water samples. The recovery values obtained by using the developed method were quantitative and consistent with the results obtained from the inductively coupled plasma optical emission spectrometer.

Gelatin scaffold ameliorates proliferation & stem cell differentiation into the hepatic like cell and support liver regeneration in partial-hepatectomized mice model

Stem cell-based tissue engineering is an emerging tool for developing functional tissues of choice. To understand pluripotency and hepatic differentiation of mouse embryonic stem cells (mESCs) on a three-dimensional (3D) scaffold, we established an efficient approach for generating hepatocyte-like cells (HLCs) from hepatoblast cells. We developed porous and biodegradable scaffold, which was stimulated with exogenous growth factors and investigated stemness and differentiation capacity of mESCs into HLCs on the scaffoldin-vitro. In animal studies, we had cultured mESCs-derived hepatoblast-like cells on the scaffold and then, transplanted them into the partially hepatectomized C57BL/6 male mice model to evaluate the effect of gelatin scaffold on hepatic regeneration. The 3D culture system allowed maintenance of stemness properties in mESCs. The step-wise induction of mESCs with differentiation factors leads to the formation of HLCs and expressed liver-specific genes, including albumin, hepatocyte nucleic factor 4 alpha, and cytokeratin 18. In addition, cells also expressed Ki67, indicating cells are proliferating. The secretome showed expression of albumin, urea, creatinine, alanine transaminase, and aspartate aminotransferase. However, the volume of the excised liver which aids regeneration has not been studied. Our results indicate that hepatoblast cells on the scaffold implanted in PH mouse indicates that these cells efficiently differentiate into HLCs and cholangiocytes, forming hepatic lobules with central and portal veins, and bile duct-like structures with neovascularization. The gelatin scaffold provides an efficient microenvironment for liver differentiation and regeneration bothin-vitroandin-vivo. These hepatoblasts cells would be a valuable source for 3D liver tissue engineering/transplantation in liver diseases.

A Transparent, Tough and Self-Healable Biopolymeric Composites Hydrogel for Open Wound Management

Modern healthcare engineering requires a wound dressing solution supported by materials with outstanding features such as high biological compatibility, strong mechanical strength, and higher transparency with effective antibacterial properties. Here, we present a unique hydrogel technology consisting of two negatively charged biopolymers and a positively charged synthetic polymer. The interaction between charged polymers through hydrogen bonds has been created, which are revealed in the simulation by density functional theory and Fourier transform infrared spectra of individual polymers and the hydrogel film. The transparent hydrogel film dressings showed excellent stretchability, a higher water swelling ratio (60%), and strong mechanical strength (∼100 MPa) with self-healing abilities (85-90%). The fabricated hydrogel film showed stable blood clots (within 119 ± 15 s) with rapid hemostasis (<2%) properties and effective antibacterial studies against E. coli and S. aureus bacterial strains. In addition, the obtained hydrogel film also showed excellent cell viability on mouse fibroblast cells. With their enormous amenability to modification, these hydrogel films may serve as promising biomaterials for wound dressing applications.

Abundant tannic acid modified gelatin/sodium alginate biocomposite hydrogels with high toughness, antifreezing, antioxidant and antibacterial properties

The acidity of high tannic acid (TA) content solution can destroy the structure of protein, such as gelatin (G). This causes a big challenge to introduce abundant TA into the G-based hydrogels. Here, the G-based hydrogel system with abundant TA as hydrogen bonds provider was constructed by a "protective film" strategy. The protective film around the composite hydrogel was first formed by the chelation of sodium alginate (SA) and Ca2+. Subsequently, abundant TA and Ca2+ were successively introduced into the hydrogel system by immersing method. This strategy effectively protected the structure of the designed hydrogel. After treatment with 0.3 w/v TA and 0.06 w/v Ca2+ solutions, the tensile modulus, elongation at break and toughness of G/SA hydrogel increased about 4-, 2-, and 6-fold, respectively. Besides, G/SA-TA/Ca2+ hydrogels exhibited good water retention, anti-freezing, antioxidant, antibacterial properties and low hemolysis ratio. Cell experiments showed that G/SA-TA/Ca2+ hydrogels possessed good biocompatibility and could promote cell migration. Therefore, G/SA-TA/Ca2+ hydrogels are expected to be used in the field of biomedical engineering. The strategy proposed in this work also provides a new idea for improving the properties of other protein-based hydrogels.

Stretch-Induced Robust Intrinsic Antibacterial Thermoplastic Gelatin Organohydrogel for a Thermoenhanced Supercapacitor and Mono-gauge-factor Sensor

Sustainable organohydrogel electronics have shown promise in resolving the electronic waste (e-waste) evoked by traditional chemical cross-linking hydrogels. Herein, thermoplastic-recycled gelatin/oxidized starch (OST)/glycerol/ZnCl₂ organohydrogels (GOGZs) were fabricated by introducing the anionic polyelectrolyte OST and solvent exchange strategy to construct noncovalently cross-linking networks. Benefiting from the electrostatic interaction and hydrogen and coordination bonds, GOGZ possessed triple-supramolecular interactions and a continuous ion transport pathway, which resulted in excellent thermoplasticity and high ionic conductivities and mechanical and antibacterial properties. Because of the thermally induced phase transition of gelatin, GOGZ exhibited isotropic-ionic conductivity with a positive temperature coefficient and realized intrinsic affinity with the activated carbon electrode for fabricating a double-layer structure supercapacitor. These novel features significantly decreased the impedance (3.71 Ω) and facilitated the flexible supercapacitors to achieve thermoenhanced performance with 4.89 Wh kg^-1 energy density and 49.2 F g^-1 specific mass capacitance at 65 °C. Fantastically, the GOGZ-based stress sensor exhibited a monolinear gauge factor (R² = 0.999) at its full-range strain (0 to 350%), and its sensitivity increased with the thermoplastic-recycled times. Consequently, this sustainable and temperature-sensitive sensor (-40 to 60 °C) could serve as health monitoring wearable devices with excellent reliability (R² = 0.999) at tiny strain. Moreover, GOGZ could achieve efficient self-enhancement by stretch-induced alignment. The sustained weighted load, tensile strength, and elongation at break of the stretch-induced GOGZ were 6 kg/g, 2.37 MPa, and 300%, respectively. This self-enhanced feature indicated that GOGZ can be utilized as an artificial muscle. Eventually, GOGZ obtained high intrinsic antibiosis (D_{inhibition circle} > 25 mm) by a binding species (-COO^-NH₃⁺-) from COOH in OST and NH₂ in gelatin, freezing resistance, and water retention. In summary, this study provided an effective strategy to fabricate thermoplastic-recycled organohydrogels for multifunctional sustainable electronics with novel performance.

Nanoparticle-Reinforced Tough Hydrogel as a Versatile Platform for Pharmaceutical Drug Delivery: Preparation and in Vitro Characterization

Natural polymer-based hydrogels are excellent for encapsulating hydrophilic drugs, but they are mechanically weak and degrade easily. In this communication, we exploit the electrostatic interaction between nanosilicates (nSi) and gelatin methacrylate (GelMA) to form a mechanically tough nanocomposite hydrogel for pharmaceutical drug delivery. These hydrogels, prepared at subzero temperatures to form cryogels, displayed macroporous structures, which favors cell infiltration. The designed tough cryogel also showed a slower rate of degradation. Furthermore, we encapsulated the small molecule metformin and sustained the drug release under physiological conditions. Cryogel-loaded metformin reduced the effect of endothelial cell injury caused by nutrient deprivation in vitro. Finally, we hypothesize that this versatile nanocomposite material will find use in diverse biomedical applications.

Cooperation of Zr(IV)-N and Zr(IV)-O coordinate bonds of Zr(IV)-amide ensures the transparent and tough polyacrylamide hydrogels

Developing advanced soft machines and tissue engineering for load-bearing cartilage or tendons requires tough hydrogels. However, the construction of double or triple crosslinked networks for these tough hydrogels, i.e., a strong network crosslinked by covalent bonds and one or two sacrificial networks built by hydrogen bonds or coordinate bonds, generally asks for multiple steps. It remains a challenge to develop hydrogels with a combination of excellent toughness and a high content of water through the time-saving one-pot process. This study demonstrates that this puzzle could be solved through engineering zirconium(IV)-amide coordinate bonds. To be specific, the combination of strong Zr(IV)-O and moderate Zr(IV)-N coordinate bonds in Zr-polyacrylamide (Zr-PAAm) hydrogels has the advantage that they are usually generated through multiple cross-linked networks. Compared to chemical crosslinked PAAm hydrogels, the highly transparent Zr-PAAm hydrogels crosslinked by Zr(NO₃)₄ displayed a 26-times increase in fracture stress, 4-times in fracture strain, 6-times in elastic modulus, and over 250-times in toughness. Besides, the mechanical properties of Zr-PAAm hydrogels could be altered over a wide range via changing the anion species, showing a dependence on the Hofmeister effect. The co-existence of Zr(IV)-N and Zr(IV)-O has been confirmed through XPS and FTIR characterizations. In particular, the effect of Zr(IV)-N in Zr-PAAm hydrogels has been verified by comparing the property changes of Zr-PAAm hydrogels before and after swelling in water, in which the Zr(IV)-N in the as-prepared hydrogels was replaced by Zr(IV)-O in the swollen gels. With ultra-stretchability and high transparency, the colorless Zr-PAAm hydrogels displayed rich interference colors under stretching, which brought great potential in anti-counterfeiting materials.

Preparation, properties, and applications of gelatin-based hydrogels (GHs) in the environmental, technological, and biomedical sectors

Gelatin's versatile functionalization offers prospects of facile and effective crosslinking as well as combining with other materials (e.g., metal nanoparticles, carbonaceous, minerals, and polymeric materials exhibiting desired functional properties) to form hybrid materials of improved thermo-mechanical, physio-chemical and biological characteristics. Gelatin-based hydrogels (GHs) and (nano)composite hydrogels possess unique functional features that make them appropriate for a wide range of environmental, technical, and biomedical applications. The properties of GHs could be balanced by optimizing the hydrogel design. The current review explores the various crosslinking techniques of GHs, their properties, composite types, and ultimately their end-use applications. GH's ability to absorb a large volume of water within the gel network via hydrogen bonding is frequently used for water retention (e.g., agricultural additives), and absorbency towards targeted chemicals from the environment (e.g., as wound dressings for absorbing exudates and in water treatment for absorbing pollutants). GH's controllable porosity makes its way to be used to restrict access to chemicals entrapped within the gel phase (e.g., cell encapsulation), regulate the release of encapsulated cargoes within the GH (e.g., drug delivery, agrochemicals release). GH's soft mechanics closely resembling biological tissues, make its use in tissue engineering to deliver suitable mechanical signals to neighboring cells. This review discussed the GHs as potential materials for the creation of biosensors, drug delivery systems, antimicrobials, modified electrodes, water adsorbents, fertilizers and packaging systems, among many others. The future research outlooks are also highlighted.