Thixotropic composite hydrogels based on agarose and inorganic hybrid gellants

Water can be used as oxidant in conjunction with metal particles to form metal-water propellant to increase the energy of propellant.For this application,water needs to be stored in form of solid and capable of becoming liquid when use.Stable and thixotropic hydrogel has good potential as water-retaining material and oxidant of metal-based propellant.In this study,we prepared organic/inorganic composite hydrogels by combining inorganic gellants hectorite and fumed silica with organic gellant agarose,respectively.The total content of the gellants can be reduced to less than 2%by adding agarose.The influence of agarose on water content,phase transition temperature,centrifugal stability and other basic physical properties of composite hydrogels were discussed.The results show that the composite hydrogels have better thixotropy and stability than pure inorganic hydrogels,and the gel-sol transformation can be realized by applying shear force or heating to the phase transition temperature.The composite hydrogels have good shear thinning ability and improved mechanical stability.Fumed silica/agarose hydrogels have better physical stability,while the thixotropy and shear thinning ability of hectorite/agarose hydrogels are better.

Engineering Smart Composite Hydrogels for Wearable Health Monitoring

Growing health awareness triggers the public's concern about health problems. People want a timely and comprehensive picture of their condition without frequent trips to the hospital for costly and cumbersome general check-ups. The wearable technique provides a continuous measurement method for health monitoring by tracking a person's physiological data and analyzing it locally or remotely.During the health monitoring process,different kinds of sensors convert physiological signals into electrical or optical signals that can be recorded and transmitted, consequently playing a crucial role in wearable techniques. Wearable application scenarios usually require sensors to possess excellent flexibility and stretchability. Thus, designing flexible and stretchable sensors with reliable performance is the key to wearable technology. Smart composite hydrogels, which have tunable electrical properties, mechanical properties, biocompatibility, and multi-stimulus sensitivity, are one of the best sensitive materials for wearable health monitoring. This review summarizes the common synthetic and performance optimization strategies of smart composite hydrogels and focuses on the current application of smart composite hydrogels in the field of wearable health monitoring.

Cell-homing and immunomodulatory composite hydrogels for effective wound healing with neovascularization

Wound healing in cases of excessive inflammation poses a significant challenge due to compromised neovascularization.Here,we propose a multi-functional composite hydrogel engineered to overcome such conditions through recruitment and activation of macrophages with adapted degradation of the hydrogel.The composite hydrogel(G-TSrP)is created by combining gelatin methacryloyl(GelMA)and nanoparticles(TSrP)composed of tannic acid(TA)and Sr^(2+).These nanoparticles are prepared using a one-step mineralization process assisted by metal-phenolic network formation.G-TSrP exhibits the ability to eliminate reactive oxygen species and direct polarization of macrophages toward M2 phenotype.It has been observed that the liberation of TA and Sr^(2+)from G-TSrP actively facilitate the recruitment and up-regulation of the expression of extracellular matrix remodeling genes of macrophages,and thereby,coordinate in vivo adapted degradation of the G-TSrP.Most significantly,G-TSrP accelerates angiogenesis despite the TA’s inhibitory properties,which are counteracted by the released Sr^(2+).Moreover,G-TSrP enhances wound closure under inflammation and promotes normal tissue formation with strong vessel growth.Genetic analysis confirms macrophage-mediated wound healing by the composite hydrogel.Collectively,these findings pave the way for the development of biomaterials that promote wound healing by creating regenerative environment.

Nanocellulose/nitrogen and fluorine co-doped graphene composite hydrogels for high-performance supercapacitors

Three-dimensional graphene materials have been studied as typical supercapacitors electrode materials by virtue of their ultrahigh specific surface area and good ion transport capacity.However,improvement of the poor volumetric electrochemical performance of these graphene materials has been required although they have high gravimetric energy density.In this work,nanocellulose/nitrogen and fluorine co-doped graphene composite hydrogels(NC-NFGHs)were prepared through a convenient hydrothermal approach utilizing ammonium fluoride as the heteroatom source.Nanocellulose(NC)and high concentration of graphene oxide(GO)were utilized to adjust the structure of NC-NFGHs and increase their packing density.Subsequently,the aqueous symmetric supercapacitor based on NC-NFGH-80 exhibits remarkable gravimetric(286.6 F·g^(-1))and volumetric(421.3 F·cm^(-3))specific capacitance at 0.3 A·g^(-1),good rate performance,and remarkable cycle stability up to 10,000 cycles.Besides,the all-solid-state flexible symmetric supercapacitors(ASSC)fabricated by NC-NFGH-80 also delivered a large specific capacitance of 117.1 F·g^(-1)at 0.3 A·g^(-1)and long service life over 10,000 cycles at 10 A·g^(-1).This compact porous structure and heteroatom co-doped graphene material supply a favorable strategy for high-performance supercapacitors.

Promotion of microvasculature formation in alginate composite hydrogels by an immobilized peptide GYIGSRG

The ability to create artificial thick tissues is a major tissue engineering problem, requiring the formation of a suitable vascular supply. In this work we examined the ability of inducing angiogenesis in a bioactive hydrogel. GYIGSRG （NH2-Gly-Tyr-Ile- Gly-Ser-Arg-Gly-COOH, GG） has been conjugated to sodium alginate （ALG） to synthesize a biological active biomaterial ALG-GG. The product was characterized by IH NMR, FT-IR and elemental analysis. A series of CaCO3/ALG-GG composite hydrogels were prepared by crosslinking ALG-GG with D-glucono-8-1actone/calcium carbonate （GDL/CaCO3） in different molar ratios. The mechanical strength and swelling ratio of the composite hydrogels were studied. The results revealed that both of them can be regulated under different preparation conditions. Then, CaCO3/ALG-GG composite hydrogel was im- planted in vivo to study the ability to induce angiogenesis. The results demonstrated that ALG-GG composited hydrogel can induce angiogenesis significantly compared with non-modified ALG group, and it may be valuable in the development of thick tissue engineering scaffold.

Fabrication and Characterization of Chitosan Based Injectable Thermosensitive Hydrogels Containing Silica/Calcium Phosphate Nanocomposite Particles

In this study, the effect of silica/calcium phosphate (SiCaP) nanocomposite particles on the properties of a novel chitosan-based thermosensitive hydrogel system was examined. SiCaP nanocomposite powder was fabricated using a sol-gel method and then used to fabricate nanocomposite hydrogels (Ch- β/7.5SiCaP and Ch-β/15SiCaP) including chitosan and β-glycerophosphate (Ch-β) as a matrix. Results revealed that compared to the Ch-β hydrogel without SiCaP, the presence of SiCaP particles in nanocomposite hydrogels maintained pH stability during the sol-gel transition, accelerated the gelation and improved the stiffness of nanocomposite hydrogels. Gelation time at 37℃ was reduced approximately 75% and stiffness was increased approximately 115%. Both of these changes are attributed to chemical and physical interactions of the SiCaP bioactive particles with chitosan. Furthermore, compared to the Ch-β hydrogel, the presence of SiCaP in the Ch-β/7.5SiCaP nanocomposite hydrogel did not affect biocompatibility negatively, but improved osteoblastic cell differentiation. Our studies suggest that these nanocomposite hydrogels may offer an innovative approach to bone regeneration strategies.

3D-printable Boron Nitride/Polyacrylic Hydrogel Composites with High Thermal Conductivities

Polyacrylic acid(PAA)hydrogel composites with different hexagonal boron nitride(h-BN)fillers were synthesized and successfully 3D-printed while their thermal conductivity was systematically studied.With the content of h-BN increasing from 0.1 wt%to 0.3 wt%,the thermal conductivity of the 3D-printed composites has been improved.Moreover,through the shear force given by the 3D printer,a complete thermal conductivity path is obtained inside the hydrogel,which significantly improves the thermal conductivity of the h-BN hydrogel composites.The maximum thermal conductivity is 0.8808 W/(m·K),leading to a thermal conductive enhancement of 1000%,compared with the thermal conductivity of pure PAA hydrogels.This study shows that using h-BN fillers can effectively and significantly improve the thermal conductivity of hydrogelbased materials while its 3D-printable ability has been maintained.

Enhanced adsorption of Methylene Blue from aqueous solution by chitosan-g-poly(acrylic acid)/vermiculite hydrogel composites

A series of chitosan-g-poly （acrylic acid）/vermiculite hydrogel composites were synthesized and used as adsorbents for the investigation of the effect of process parameters such as vermiculite content, pH of dye solution, contact time, initial concentration of dye solution, temperature, ionic strength and concentration of surfactant sodium dodecyl sulfate on the removal of Methylene Blue （MB） from aqueous solution. The results showed that the adsorption capacity for dye increased with increasing pH, contact time and initial dye concentration, but decreased with increasing temperature, ionic strength and sodium dodecyl sulfate concentration in the present of the surfactant. The adsorption kinetics of MB onto the hydrogel composite followed pseudo second-order kinetics and the adsorption equilibrium data obeyed Langmuir isotherm. By introducing 10 wt.% vermiculite into chitosan-g-poly （acrylic acid） polymeric network, the obtaining hydrogel composite showed the highest adsorption capacity for MB, and then could be regarded as a potential adsorbent for cationic dye removal in a wastewater treatment process.

Effect of Preparation Methods on Mechanical Properties of PVA/HA Composite Hydrogel

Poly(vinyl alcohol) (PVA)/hydroxyapatite (HA) composite hydrogel specimens were prepared with 15% PVA and 1%,2%, 3%, 4% and 5% HA by repeated freezing-thawing. The tests of static and dynamic mechanical properties were carried out todiscuss the influence of different contents of HA and freezing-thawing cycles on the mechanical properties of PVA/HA compositehydrogel. The results of static mechanical tests showed that the PVA/HA composite hydrogel with 3% HA and ninefreezing-thawing cycles had excellent stress relaxation properties, higher relaxation ratio, lower stress equilibrium value andpresented better properties of creep and recovery. The results of dynamic mechanical test showed that the PVA/HA compositehydrogel with nine freezing-thawing cycles had higher storage modulus and loss modulus, so was the PVA/HA compositehydrogel with 3% HA.

Halloysite Nanotube Composited Thermo-responsive Hydrogel System for Controlled-release

Halloysite nanotube-composited thermo-responsive hydrogel system has been successfully developed for controlled drug release by copolymerization of N-isopropylacrylamide （NIPAM） with silane-modified halloysite nanotubes （HNT） through thermally initiated free-radical polymerization. With methylene blue as a model drug, thermo-responsive drug release results demonstrate that the drug release from the nanotubes in the composited hy-drogel can^be well controlled by manipulating the environmental temperature. When the hydrogel network is swol- len at temperature below the lower critical solution temperature （LCST）, drug releases steadily from lumens of the embedded nanotubes, whereas the drug release stops when hydrogel shrinks at temperature above the LCST. The release of model drug from the HNT-composited hydrogel matches well with its thermo-responsive volume phasetransition, and shows characteristics of well controlled release. The design strategy and release results of the pro- posed novel HNT-composited thermo-responsive hydrogel system provide valuable guidance for designing respon- s_i_ve nanocomposites for controlled-release of active agents.

Evaluation of different crosslinking methods in altering the properties of extrusion-printed chitosan-basedmulti-material hydrogel composites

Three-dimensional printing technologies exhibit tremendous potential in the advancing fields of tissue engineering and regenerative medicine due to the precise spatial control over depositing the biomaterial.Despite their widespread utilization and numerous advantages,the development of suitable novel biomaterials for extrusion-based 3D printing of scaffolds that support cell attachment,proliferation,and vascularization remains a challenge.Multi-material composite hydrogels present incredible potential in this field.Thus,in this work,a multi-material composite hydrogel with a promising formulation of chitosan/gelatin functionalized with egg white was developed,which provides good printability and shape fidelity.In addition,a series of comparative analyses of different crosslinking agents and processes based on tripolyphosphate(TPP),genipin(GP),and glutaraldehyde(GTA)were investigated and compared to select the ideal crosslinking strategy to enhance the physicochemical and biological properties of the fabricated scaffolds.All of the results indicate that the composite hydrogel and the resulting scaffolds utilizing TPP crosslinking have great potential in tissue engineering,especially for supporting neo-vessel growth into the scaffold and promoting angiogenesis within engineered tissues.

Alginate Composite Hydrogel Bead with Multilayer Flake Structure for Dye Adsorptions

With the rapid development of textile industry,a large amount of dye-contaminated effluents was produced and caused serious environmental problem.To remove the dye from effluents,adsorption materials have been applied because of their relatively cheap,high efficiency,and easy handling.In this study,a novel composite hydrogel bead with unique multilayer flake structure was fabricated by alginate,acrylamide and attapulgite for dye adsorption.Acrylamide was grafted polymerization onto alginate to obtain alginate-g-poly(acrylamide).Then alginate-g-poly(acrylamide)was cross-linked by Ca2+ions in present of attapulgite to form composite hydrogel bead.Scanning electron microscopy(SEM)results show that the freeze dried composite hydrogel bead has multilayer flake structure incorporating attapulgite.Fourier transform infrared spectroscopy(FTIR)and Thermo-gravimetric analysis(TGA)results indicate that acrylamide has been successfully grafted polymerization on sodium alginate.Grafting polymerization of acrylamide onto sodium alginate obviously enhances the swelling of hydrogel bead.Incorporating of attapulgite into hydrogel bead effectively enhances the adsorption capacity to methylene blue and the maximum adsorption capacity is 155.7 mg g-1.Multilayer flake structure increases the adsorption area for methylene blue,but hinders the diffusion of methylene blue into the inner of composite hydrogel bead.High pH solution is beneficial to the adsorption.Pseudo-second order model and Fraundlinch model best describe the adsorption kinetic and isotherm,respectively.These results indicate that composite hydrogel bead is a promising adsorption material for dye-contaminated water treatment.

Droplet-based bioprinting enables the fabrication of cell–hydrogel–microfibre composite tissue precursors

Composites offer the option of coupling the individual benefits of their constituents to achieve unique material properties,which can be of extra value in many tissue engineering applications.Strategies combining hydrogelswith fibre-based scaffolds can create tissue constructs with enhanced biological and structural functionality.However,developing efficient and scalable approaches to manufacture such composites is challenging.Here,we use a droplet-based bioprinting system called reactive jet impingement(ReJI)to integrate a cell-laden hydrogel with a microfibrous mesh.This system uses microvalves connected to different bioink reservoirs and directed to continuously jet bioink droplets at one another in mid-air,where the droplets react and form a hydrogel that lands on a microfibrous mesh.Cell–hydrogel–fibre composites are produced by embedding human dermal fibroblasts at two different concentrations(5×10^(6) and 30×10^(6) cells/mL)in a collagen–alginate–fibrin hydrogel matrix and bioprinted onto a fibre-based substrate.Our results show that both types of cell–hydrogel–microfibre composite maintain high cell viability and promote cell–cell and cell–biomaterial interactions.The lower fibroblast density triggers cell proliferation,whereas the higher fibroblast density facilitates faster cellular organisation and infiltration into the microfibres.Additionally,the fibrous component of the composite is characterised by high swelling properties and the quick release of calcium ions.The data indicate that the created composite constructs offer an efficient way to create highly functional tissue precursors for laminar tissue engineering,particularly for wound healing and skin tissue engineering applications.

Research on the Long Time Swelling Properties of Poly (vinyl alcohol)/Hydroxylapatite Composite Hydrogel

Poly(vinyl alcohol)/hydroxylapatite(PVA/HA)composite hydrogel was prepared by repeated freezing and thawing.The water loss properties of the resultant hydrogel were investigated by using optical microscope.Long time immersion tests of PVA/HA composite hydrogel were carried out in the diluted calf serum solution to study the change laws of swelling properties with the freezing-thawing cycles and HA content.The micro-morphologies of PVA/HA composite hydrogel after long time immersion were observed by means of the high-accuracy 3D profiler.The results show that the swelling process of PVA/HA composite hydrogel is the converse process of its water loss.Long time swelling ratio curves of PVA/HA composite hydrogel in the calf serum solution are manifested as four stages of quick increase,decrease,slow decrease and stable balance,and its equilibrium swelling ratio decreases with the increase of freezing-thawing cycles and HA content.It is revealed that the network structure of the composite hydrogel immersed for a long period is significantly improved with the increase of HA content. Perfect network structures of PVA/HA composite hydrogel as well as full and equilibrium tissues after swelling equilibrium are obtained when the HA content is 3% and the number of freezing-thawing cycles is 7.

Preparation and Properties of Guiqi Polysaccharides/Chitosan/Alginate Composite Hydrogel Microspheres

A series of the Guiqi polysaccharides/chitosan/alginate composite hydrogel microspheres(GPcM)with different particle sizes were prepared with Guiqi polysaccharides(GP),chitosan(CS)and sodium alginate(Alg).The optimum preparation process was also determined by single factor and orthogonal experiment analysis.The GPcM were characterized by fourier transform infrared spectroscopy(FT-IR),scanning electron microscope(SEM),drug loading efficiency test(LE),encapsulation efficiency test(EE)and in vitro release study.The results showed that the Guiqi polysaccharides chitosan hydrogel(GPCH)and sodium alginate hydrogel(SAH)formed a crossover system in GPcM.The GPcM have a uniform particle size ranging from 395.1μm to 841.5μm.The drug loading efficiency and encapsulation efficiency of the GPcM were 56.3%and 72.6%,respectively.The bovine serum albumin(BSA)loaded in the GPcM released slowly within 180 h.The results suggested that the GPcM may have potential application value in drug sustained and controlled release system.

Preparation and Properties of Nanocellulose/Sodium Alginate Composite Hydrogel

Cellulose nanofiber(CNF)was isolated from Okara using deep eutectic solvent(DES)with high-speed stirring.The composite hydrogels obtained by using different proportions of CNF and sodium alginate(SA)had different properties.The CNF/SA composite hydrogels were analyzed using Fourier transform infrared spectroscopy and scanning electron microscopy and tested for compression properties,rheological properties,water content,and swelling degree.Physical crosslinking between SA and Ca^(2+),and different degrees of hydrogen bond formation between SA and CNF were observed.The CNF/SA composite hydrogel have great potential as reinforcements in eco-friendly composite hydrogels for diverse applications.

Production of a novel non-toxicγ-PGA/casein composite hydrogel using MTG and optimization by response surface methodology

Theγ-PGA-based food hydrogel exhibits good biodegradability and biocompatibility,and is non-toxic to humans.In this study,a novel hydrogel(γ-PGA/casein composite hydrogel)was prepared by combining casein with y-PGA separated from natto using microbial transglutaminase(MTG)as the crosslinker.The effects of the MTG mass concentration,gelation time,crosslinking temperature,pH,and the mass ratio of y-PGA to casein on the crosslinking ratio of y-PGA and swelling ratio of theγ-PGA/casein hydrogel were investigated.Furthermore,the synthesis conditions were optimized by response surface methodology to optimize three important factors,i.e.crosslinking temperature,pH and the mass ratio of y-PGA to casein.The results of single factor experiments showed that the MTG mass concentration and crosslinking time had little impacts on the crosslinking ratio of y-PGA and the swelling ratio;the preferred MTG mass concentration,crosslinking time,temperature and pH were selected as 0.3%,7 h,40℃and 7.5;and the preferred mass ratio ofγ-PGA to casein was 0.1 for the crosslinking ratio ofγ-PGA and 0.2 for the swelling ratio.The response surface experiment results showed that the optimum crosslinking temperature,pH and the mass ratio of y-PGA to casein ratio were 42.4℃,7.33,and 0.18,respectively.Under these optimum conditions,the predicted crosslinking ratio of y-PGA and swelling ratio reached 90.35%and 112.07%,which were highly consistent with the experimental values(88.00%and 115.87%).Theγ-PGA/casein composite hydrogel developed in this study shows promising application potential in food industry,biomedical field,and cosmetic industry.

Photocrosslinkable human amniotic membrane hydrogel for recovery from spinal cord injury

The recovery and reconstruction of central nervous system function after spinal cord injury(SCI)is a worldwide problem.The difficulty lies in the feasibility issue of new axons passing through the injured area and the negative effect of scarring after injury.As a biological material,the human amniotic membrane(HAM)has the advantages of protecting nerve growth,inhibiting scar formation,and promoting neovascularization,but its weak physical properties are difficult to apply in treating SCI.In this study,HAMs were first decellularized and then chemically grafted with methacrylic anhydride.Next,the composite was photocrosslinked with gelatin methacrylate to prepare a cross-network biological complex.The final complexes prepared by appeal were used for in vitro and in vivo studies of SCI in rats,separately.In the in vitro experiment,the composite scaffold inherited abundant biological factors from the amniotic membrane and had the physical properties of a hydrogel,thus providing a favorable environment for the growth and development of neurons and blood vessels.In the in vivo experiment,the composite reduced scarring and promoted the growth of new nerves.Overall,the composite scaffolds can stably simulate the extracellular microenvironment in SCI defects,regulate pathological changes,and promote the generation of new neurons.Therefore,decellularized HAM hydrogels are promising biocomposite materials for central nerve repair after SCI.

ECM-mimicking composite hydrogel for accelerated vascularized bone regeneration

Bioactive hydrogel materials have great potential for applications in bone tissue engineering.However,fabrication of functional hydrogels that mimic the natural bone extracellular matrix(ECM)remains a challenge,because they need to provide mechanical support and embody physiological cues for angiogenesis and osteogenesis.Inspired by the features of ECM,we constructed a dual-component composite hydrogel comprising interpenetrating polymer networks of gelatin methacryloyl(GelMA)and deoxyribonucleic acid(DNA).Within the composite hydrogel,the GelMA network serves as the backbone for mechanical and biological stability,whereas the DNA network realizes dynamic capabilities(e.g.,stress relaxation),thereby promoting cell proliferation and osteogenic differentiation.Furthermore,functional aptamers(Apt19S and AptV)are readily attached to the DNA network to recruit bone marrow mesenchymal stem cells(BMSCs)and achieve sustained release of loaded vascular endothelial growth factor towards angiogenesis.Our results showed that the composite hydrogel could facilitate the adhesion of BMSCs,promote osteogenic differentiation by activating focal adhesion kinase(FAK)/phosphatidylinositol 3-kinase(PI3K)/protein kinase B(Akt)/β-Catenin signaling pathway,and eventually enhance vascularized bone regeneration.This study shows that the multifunctional composite hydrogel of GelMA and DNA can successfully simulate the biological functions of natural bone ECM and has great potential for repairing bone defects.