Mechanical Properties Of Composite Hydrogels Research Articles

A Model of Mechanotransduction in Polyvinyl Alcohol‐Based Composite Hydrogels for Regulating Musculoskeletal Differentiation

AbstractIn regenerative medicine, extracellular matrix (ECM)‐inspired materials are currently being explored to imitate mechanotransduction pathways and control cell fate. In musculoskeletal tissue regeneration, enhancing mechano‐biological signals require biomaterials that are both biocompatible and viscoelastic and can retain water content. Herein, based on these requirements, various polyvinyl alcohol (PVA)‐based composite hydrogels, reinforced by polyhydroxy butyrate (PHB) nanofibers, are proposed to differentiate equine adipose‐derived stem cells for musculoskeletal regeneration. To study the role of fiber embedding in improving scaffold properties, different nanofiber assemblies, including chopped short ones with random orientation (PVAS), single‐layer (PVAL1), and double‐layer membranes (PVAL2) are positioned into the PVA matrix. PHB reinforcements negatively affect swelling and positively enhanced phase transition temperatures and crystallinity of PVA hydrogel. According to mechanical analysis results, compositing with PHB nanofibrous layers strengthen the PVA matrix due to some restrictions on PVA chain mobility. Gene expression investigations also reveal that higher matrix stiffness after layering with two PHB membranes (PVAL2) promotes osteogenesis, while the random addition of short‐chapped fibers (PVAS) facilitate tenogenic differentiation. As a consequence of the findings, fiber placement is crucial to the mechanical properties of composite hydrogels that ultimately control musculoskeletal differentiation signals through mechanosensing pathways.

Synthesis and Properties of Rosin-Based Composite Acrylamide Hydrogels

Hydrogels have been widely applied in agricultural drought-resistance, pollution regulation, drug delivery and so on. Acrylamide (AM) is usually used as raw material to synthesize acrylamide hydrogels. However, inherently low mechanical strength greatly limits their applications in some special areas. Therefore, it is necessary to choose suitable functional monomers to optimize acrylamide hydrogels and improve their mechanical performances. In this paper, a novel acrylamide monomer modified by rosin was synthesized, and then polyacrylamide/rosin-based acrylamide (RAM) composite hydrogels were prepared via free radical polymerization using potassium persulfate as initiator, N, N′-methylene-bisacrylamide (MBA) as a crosslinker. The influence of RAM monomer was investigated in detail. The chemical structure, pore structure, swelling properties, thermal performances and mechanical properties of composite hydrogels were characterized by Fourier Transform Infrared spectrometer (FT-IR), thermogravimetric analysis (TG), scanning electron microscope (SEM), and universal testing, respectively. The results showed that the thermal stability and mechanical property of RAM hydrogels were improved significantly. The compressive strength of RAM hydrogels was increased to 3.5 times than that of AM hydrogels, and the tensile strength was 5.1 times compared with AM hydrogels as well. Moreover, RAM hydrogels exhibited a faster initial swelling rate due to the new pore structure formed after introducing the RAM monomer.

Enhanced Mechanical Properties of Composite Hydrogels Containing Fractionated and Purified Lignin

Enhanced Mechanical Properties of Composite Hydrogels Containing Fractionated and Purified Lignin

Effect of Fiber Geometry on Fracture and Fatigue of Composite Hydrogels

Abstract Hydrogel-based biomedical applications are under rapid development. These applications usually demand hydrogels to have high toughness and high fatigue threshold. Recently, various fiber-reinforced composite hydrogels have been developed to meet this challenge. However, the effect of fiber geometry on the fracture and fatigue of composite hydrogels is still elusive. Here, we use a model composite hydrogel to study the influence of fiber width, fiber spacing, and fiber configuration on these properties. It is found that the toughness of the composite hydrogel does not increase monotonically with the fiber width or fiber spacing, but presents a peak. This is because the variation of fiber width and fiber spacing not only affects the volume of fiber in the fracture process zone but also influences the dissipated elastic energy density in that volume, which is affected by the stress concentration. The peak is a consequence of the trade-off between these two factors. Our study further shows that the shape of the fiber network affects the stress concentration in the fiber dramatically, thereby leading to a huge difference in the toughness and fatigue threshold of the composite hydrogels. This work highlights the importance of fiber size as well as the shape of fiber networks on the mechanical properties of composite hydrogels. It may help the design of tough and fatigue-resistant stretchable composite materials.

Magnetically driven pH-responsive composite hydrogel for controlled drug delivery

A multi-footed composite hydrogel with double responsiveness was prepared by the combination of sodium alginate (SA), gelatin and ferroferric oxide nanomaterials. Under magnetic field control, the multi-footed composite hydrogel could walk and move to the designated locations and release some drugs under the specific environment (pH 7.4) due to the pH sensitivity of SA. The gelatin addition effectively improved the mechanical properties of composite hydrogel, adjusting the drug release behavior of composite hydrogel by the decreased porous structure. Our results demonstrated that the proposed dual stimulus-responsive composite hydrogel could offer a promising choice for medical fixed-point drug release and disease treatment.

A green composite hydrogel based on xylan and lignin with adjustable mechanical properties, high swelling, excellent UV shielding, and antioxidation properties

AbstractThis study successfully prepared a novel green composite hydrogel based on carboxymethyl xylan and lignin with adjustable mechanical properties, high swelling, excellent UV shielding, and antioxidation performance. The structure and morphology of the hydrogel were characterized by Fourier transform infrared spectra, scanning electron microscopy, thermogravimetric analysis, rheological analysis, and swelling ratio. Results showed that lignin could significantly improve the mechanical properties of composite hydrogels. The compression stress and toughness of the composite hydrogel contained lignin increased by 39% and 60%, respectively, and the compressive deformation reached 90%. In addition, the addition of lignin increased the swelling ratio of the composite hydrogel reached 79.9 g/g. In addition, the composite hydrogel exhibited excellent UV shielding and antioxidation performance. The removal ratio of UV and free radicals is as high as 80% and 90%, respectively. The simple procedure and cost‐effective lignin as raw material for hydrogel with adjustable properties are favorable for medical‐biological applications.

The role of reduced graphene oxide as a “2D flexible crosslinking point” in composite hydrogels

AbstractThe composite hydrogels are widely used in various research directions. How to improve the mechanical properties is one of the concerns of researchers. In this work, the mechanical properties of composite hydrogels with reduced graphene oxide (rGO), kaolin (KL), montmorillonite (MMT), and attapulgite (APT) as additives were compared. The morphology of polyacrylamide (PAM) composite hydrogel was observed by electron microscope, and the hydrogen bonding between inorganic additives and PAM chain in the hydrated samples were detected by IR. The rheological data (G′, G", and tan δ) confirmed the beneficial effect of rGO as a two‐dimension (2D) material on the mechanical properties of hydrogels. In the tensile‐fracture experiments, the maximum tensile strain of PAM‐rGO was 568% and the maximum tensile force was 1.18 N, both of which were larger than that of the clay‐based composite hydrogel with the same mass concentration. Based on these experimental data, the response behavior of rGO in the process of hydrogel deformation was elucidated by the concept of “2D flexible crosslinking point,” and the reason why PAM‐rGO composite hydrogel had better mechanical strength was explained in detail.

Berberine carried gelatin/sodium alginate hydrogels with antibacterial and EDTA-induced detachment performances

Most existing hydrogel wound dressings lack gentle detachment property. In this work, novel hydrogels with anti-bacterial and induced detachment properties were prepared. Both gelatin (G) and sodium alginate (SA) are natural polymer materials. The G/SA hydrogels were prepared by dual cross-linking. The addition of SA significantly improves the mechanical properties of composite hydrogels. The tensile modulus and elongation at break of the G/SA hydrogels with 2.0% SA could reach 99.23 ± 2.18 kPa and 85.47 ± 5.01%, respectively. In addition, the interconnected porous network and high swelling ratio (over 9.99 ± 0.33) are beneficial to the transmission of oxygen and absorption of exudates to accelerate the healing of wound. Subsequently, berberine (BBR) was loaded into the G/SA hydrogels. The BBR/G/SA hydrogels show sustained drug release for 168 h and exhibit anti-bacterial effect against Staphylococcus aureus. The results of L929 cells cultured with the hydrogel extracts indicate good biocompatibility. Finally, results of EDTA-induced detachment performances demonstrate that the hydrogels could be removed from the wound as the internal structure destroyed. All illustrated results above demonstrated the BBR carried G/SA hydrogels have potential used as wound dressing materials in future.

Enzymatically Crosslinkable Hyaluronic Acid-Gelatin Hybrid Hydrogels as Potential Bioinks for Tissue Regeneration

Hydrogels that mimic the composition and properties of the extracellular matrix have attracted great attention as potential polymeric scaffolds for tissue engineering applications. In this study, an injectable hydrogel composed of hyaluronic acid and gelatin was developed via the oxidative coupling reaction using horseradish peroxidase (HRP). The hydrogel was prepared by mixing two phenol-conjugated polymer solutions, hyaluronic acid-tyramine (HA-TA) and gelatin-hydroxyphenyl propionic acid (GH), in the presence of HRP and hydrogen peroxide (H202). The gelation rate and mechanical properties of composite hydrogel were controlled by adjusting the HRP and H202 concentrations, respectively Compared to the pure HA-TA hydrogels, the stability and cellular behaviors of composite hydrogel improved significantly In addition, the injectable hydrogel system showed good performance in 3D printing with high cell viability after one day of printing. The results suggest that enzymatically crosslinked HA-TA and GH hybrid (HA-TA/GH) composite of HA-TA and GH hydrogel has the potential as a material for tissue engineering and 3D printing biofabrication.

Mechanical Properties of Composite Hydrogels for Tissue Engineering.

Tissue engineering provides solutions that require medicine to restore damaged tissues or even complete organs. This discipline combines biologically active scaffolds, cells and molecules; being the addition of nanoparticles into the scaffolds, one of the techniques that is attracting more interest these days. In this work, Hydroxyapatite Nanorods (HA) were added to the network of Gelatin hydrogel (GE), and the particular properties resulting from their interaction were studied. Specifically, viscoelastic properties were characterized as a function of gel and nanoparticle concentration, varying ratios and temperatures. Oscillatory Time Sweeps (OTS) provided the necessary information about how the timeresolved material property/structure alteration. A wide variety of Continuous Flow Tests and Frequency Sweeps were used to describe the mechanical properties of the material, proving that the presence of nanoparticles led to a reinforcement of the gel network, mechanical stiffness and strength. The thixotropic nature of the gels was also evaluated and the most common theoretical models were described and commented. The attributes inferred from the data, showed a material that can allow the natural growth of bone tissue whilst withstanding properly the mechanical efforts; resulting in a material with an outstanding suitability to be used in regenerative medicine.

Influence of fish collagen on viscoelastic properties and sol-gel phase transition of chitosan solutions

The thermosensitive hydrogels are widely used in tissue engineering due to their non-invasive application. Special interest of researchers, due to the specific characteristics of both materials, is aimed at composites of natural origin obtained from chitosan hydrogels combined with collagen. The mechanical properties of the thermosensitive chitosan-fish collagen hydrogels and the sol-gel phase transition parameters were determined by the rotational rheometry measurement techniques. Based on comparison of the obtained storage modulus G' curves, it was found that the addition of collagen negatively affects the mechanical properties of composite scaffolds. The addition of this protein substance decreases their elasticity. Only the smallest concentration (0.25g collagen/1 g chitosan) of collagen improves the mechanical properties of composite hydrogels, from 56 kPa to 61 kPa. Conducted non-isothermal studies allowed to conclude that the addition of collagen causes an increasing temperature of sol-gel phase transition. However, the observed changes are not a monotone function of the biopolymer concentration.

Mechanical Properties of Composite Hydrogels of Alginate and Cellulose Nanofibrils.

Alginate and cellulose nanofibrils (CNF) are attractive materials for tissue engineering and regenerative medicine. CNF gels are generally weaker and more brittle than alginate gels, while alginate gels are elastic and have high rupture strength. Alginate properties depend on their guluronan and mannuronan content and their sequence pattern and molecular weight. Likewise, CNF exists in various qualities with properties depending on, e.g., morphology and charge density. In this study combinations of three types of alginate with different composition and two types of CNF with different charge and degree of fibrillation have been studied. Assessments of the composite gels revealed that attractive properties like high rupture strength, high compressibility, high gel rigidity at small deformations (Young’s modulus), and low syneresis was obtained compared to the pure gels. The effects varied with relative amounts of CNF and alginate, alginate type, and CNF quality. The largest effects were obtained by combining oxidized CNF with the alginates. Hence, by combining the two biopolymers in composite gels, it is possible to tune the rupture strength, Young’s modulus, syneresis, as well as stability in physiological saline solution, which are all important properties for the use as scaffolds in tissue engineering.

Cellulose–halloysite nanotube composite hydrogels for curcumin delivery

Halloysite nanotubes (HNTs) were added to cellulose NaOH/urea solution to prepare composite hydrogels using epichlorhydrine crosslinking at an elevated temperature. The shear viscosity, mechanical properties, microstructure, swelling properties, cytocompatibility, and drug delivery behavior of the cellulose/HNT composite hydrogels were investigated. The viscosity of the composite solution increases with the addition of HNT. The compressive mechanical properties of composite hydrogels are significantly improved compared with pure cellulose hydrogel. The compressive strength of the composite hydrogels with 66.7% HNTs is 128 kPa, while that of pure cellulose hydrogel is only 29.8 kPa in compressive strength. Rheological measurement suggests the resistance to deformation is improved for composite hydrogels. X-ray diffraction and Fourier transform infrared spectroscopy show that the crystal structure and chemical structure of HNT are not changed in the composite hydrogels. Hydrogen bonding interactions between HNT and cellulose exist in the composites. A porous structure of the composite hydrogels with pore size of 200–400 μm was found by scanning electron microscopy. The addition of HNT leads to decreased swelling ratios in NaCl solution and pure water for the composite hydrogels. Cytotoxicity assays show that the cellulose/HNT composite hydrogels have a good biocompatibility with MC3T3-E1 cells and MCF-7 cells. Curcumin is further loaded into the composite hydrogel via physical adsorption. The curcumin-loaded composite hydrogels show a strong inhibition effect on the cancer cells. All the results illustrate that the cellulose/HNT composite hydrogels have promising applications such as anticancer drug delivery systems and anti-inflammatory wound dressings.

Effects of halloysite nanotubes on physical properties and cytocompatibility of alginate composite hydrogels

Sodium alginate (SA)/halloysite nanotubes (HNTs) composite hydrogels were successfully prepared by solution blending and cross-linking with calcium ions. HNTs can improve the physical properties and cytocompatibility of composite hydrogels. The static and shear viscosity of SA/HNTs solution increase by the addition of HNTs. FTIR suggests the presence of hydrogen bond interactions between HNTs and SA. The crystal structure of HNTs is retained in the composites as showed by the X-ray diffraction result. A porous structure with pore size of 100–250μm is found in the hydrogels, which can provide a space for cell growth and migration. The compressive mechanical properties of composite hydrogels significantly increase compared to the pure SA hydrogel. The SA/HNTs composite hydrogels with 80% HNTs loading exhibit the compressive stress at 80% strain of 2.99MPa, while the stress at 80% strain of pure SA hydrogel is only 0.8MPa. The dynamic storage modulus of composite hydrogels also markedly increases with HNTs concentration. The differential scanning calorimetry endothermic peak area and swelling ratios in NaCl solution of the composite hydrogels decrease by the addition of HNTs. Preosteoblast (MC3T3-E1) culture results reveal that the SA/HNTs composites especially at relatively low HNTs loading show a significant increase in cells adhesion and proliferation compared to the pure SA hydrogel. All the results demonstrate that the SA/HNTs composite hydrogels show a promising application in bone tissue engineering.

Fabrication and characterization of composite hydrogel particles with x-ray attenuating payloads

This paper reports the fabrication and characterization of composite hydrogel particles composed of poly(ethylene glycol) diacrylate (PEG-DA)-based hydrogels and x-ray attenuating payloads. The top–down fabrication method employed herein is demonstrated to yield composite hydrogel particles of varying size and shape for use as computed tomography (CT) imaging contrast agents. Characterization of the materials properties of the PEG-DA hydrogels was undertaken, demonstrating tunable mechanical properties of composite hydrogels based on hydrogel composition and UV cross-linking time. Analyses of the leakage rates of a conventional iodine-based small molecular contrast agent as well as a nanoparticulate x-ray attenuating material from the PEG-DA hydrogels were undertaken. In contradistinction to clinically available iodinated CT contrast agents, as well as recently developed nanoparticulate CT contrast agents, the approach presented herein yields an engineering flexibility to the design of CT contrast agents which may be leveraged to optimize this class of agents to a wide array of specific imaging and sensing applications.

Graphene oxide/poly(acrylic acid)/gelatin nanocomposite hydrogel: Experimental and numerical validation of hyperelastic model

Owing to excellent thermal and mechanical properties, graphene-based nanomaterials have recently attracted intensive attention for a wide range of applications, including biosensors, bioseparation, drug release vehicle, and tissue engineering. In this study, the effects of graphene oxide nanosheet (GONS) content on the linear (tensile strength and strain) and nonlinear (hyperelastic coefficients) mechanical properties of poly(acrylic acid) (PAA)/gelatin (Gel) hydrogels are evaluated. The GONS with different content (0.1, 0.3, and 0.5wt.%) is added into the prepared PAA/Gel hydrogels and composite hydrogels are subjected to a series of tensile and stress relaxation tests. Hyperelastic strain energy density functions (SEDFs) are calibrated using uniaxial experimental data. The potential ability of different hyperelastic constitutive equations (Neo-Hookean, Yeoh, and Mooney–Rivlin) to define the nonlinear mechanical behavior of hydrogels is verified by finite element (FE) simulations. The results show that the tensile strength (71%) and elongation at break (26%) of composite hydrogels are significantly increased by the addition of GONS (0.3wt.%). The experimental data is well fitted with those predicted by the FE models. The Yeoh material model accurately defines the nonlinear behavior of hydrogels which can be used for further biomechanical simulations of hydrogels. This finding might have implications not only for the improvement of the mechanical properties of composite hydrogels but also for the fabrication of polymeric substrate materials suitable for tissue engineering applications.

Structural and mechanical properties of composite hydrogels composed of clay and a polyelectrolyte prepared by mixing

We investigated the structural, mechanical, and swelling properties of composite hydrogels consisting of clay, a dispersing agent (tetrasodium diphosphate), and sodium polyacrylate (PAAS) prepared by mixing. Regardless of the simple preparation method, the gel exhibits excellent properties such as mechanical toughness and high swelling ability. For production of the tough gels, it is important to disperse clay particles using the dispersing agent and to use high molecular weight PAAS for formation of bridge connecting different clay particles in a dispersed state. Synchrotron small-angle X-ray scattering experiments reveal that PAAS was adsorbed on the positively charged edge of the clay particles.

Mechanical properties of temperature sensitive microgel/polyacrylamide composite hydrogels—from soft to hard fillers

In this study we investigated the mechanical properties of composite hydrogels based on a polyacrylamide (PAAm) matrix with embedded temperature sensitive poly(N-isopropylacrylamide) (PNiPAM) microgels. We analysed the mechanical properties of the composite material with tensile tests, shear and cavitation rheology. The results of the different experiments displayed an enhancement of mechanical stability with increasing concentration of incorporated microgels. The improved stability is related to an increase of physical cross-linking points due to the incorporation of the microgels. The incorporation of temperature responsive microgel particles introduces temperature sensitive mechanical behaviour of the composite hydrogels. The collapse of the microgels inside the polyacrylamide matrix leads to a change of the volume of the filler particles as well as to a change from a soft filler to a hard filler. The influence of the hard particles on the mechanical stability of the matrix is much stronger which leads to materials with enhanced mechanical properties at high temperatures.

Sustained release behavior of pH‐responsive poly(vinyl alcohol)/poly(acrylic acid) hydrogels containing activated carbon fibers

AbstractThe composites of pH‐responsive poly(vinyl alcohol)/poly(acrylic acid) hydrogel and activated carbon fibers (ACFs) were prepared as sustained drug release system with excellent mechanical properties. The mechanical properties of hydrogels were improved greatly by addition of ACFs. The thinner ACFs were more effective in increasing the mechanical properties of composite hydrogels. The cumulative amount of release and the release period were dependent on the surface area and the pore volume of ACFs. The drug release was maximized at basic condition due to the pH‐sensitive hydrogel matrices and the initial bust phenomenon was alleviated by incorporating ACFs in the hydrogels. The drug release was sustained about four times longer and the mechanical property was increased about 2.6 times higher because ACFs worked as drug reservoir and reinforcement. Cytotoxicity evaluation confirmed the biocompatible characteristics of the ACFs‐containing hydrogels. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011