PAAm Hydrogel Research Articles

A coating with hydrogel@nanostructure on Ti surfaces via controllable Nano-mechanical interlocking

The elasticity mismatch between Ti and tissue limits the performance of Ti medical devices. How to create a coating with mimicking natural soft tissue stiffness and possessing strong mechanical bond is a challenge in implant manufacturing. Here, we developed a combined coating, that is, an anodized Ti surface (ATS) with nanostructures coated with a layer of PAAm hydrogel with tunable elasticity. Due to the nano-mechanical interlocking and hydrogen bonding synergy, the PAAm hydrogel layer was tightly anchored in nanostructures on the ATS. By regulating the oxidation voltage, nanostructures including nanopores, nanotubes, and punch-through nanotubes were fabricated on the ATS, and these three kinds of anodized nanostructures increase the porosity of the ATS sequentially. The lap shear test has shown that the shear strength increases linearly with increasing the porosity, and the shear strength of the punch-through nanotube structures with the PAAm hydrogel coating reaches 59.28 kPa. The adhesion mechanism between the anodized Ti nanostructures and the PAAm hydrogel coating is mainly due to the nano-mechanical interlocking and hydrogen bonding synergy, which was proven by morphology analysis, XRD, and ATR-FTIR characterization of the samples subjected to lap shear load. The hydrogel-nanostructures coating has demonstrated the potential to be applied in Ti medical devices.

Adhesion Mechanics and Detachment Dynamics of Vanishing Surface Layers on Hydrogels.

Cross-linked hydrogel surfaces exhibit reduced stiffness when polymerized against polymeric hydrophobic surfaces. As such, these layers play a critical role in contact mechanics, particularly exhibiting strong relative adhesion with colloidal probes when the contact area is small. This prevents the use of continuum models of adhesive soft contact. To connect mechanisms of stretch to the force response, depth-controlled nanoindentation experiments were conducted on polyacrylamide (pAAM) hydrogel samples using colloidal probe atomic force microscopy (AFM). The pAAM sample had a high water content of >90% and was molded against polyoxymethylene (POM) to create a more dilute surface layer with thickness ∼0.5 μm. Indentations to multiple depths between 50 nm and 1.25 μm were repeated 10 times each. First, the force drops during the unloading, and separation segments of each indentation were characterized. This described the detachment progression for increasing areas of contact, revealing that the pull-off force for a single chain was in the single-pN range. Second, the stretched polymer network was modeled as an array of parallel, linear springs. Assuming a constant areal chain density of α = 100 chains/μm2, the maximum force of adhesion was plotted versus the volume of chains stretched upward, and the average chain stiffness was calculated from a linear fit to be 22.8 × 10-6 N/m. A Weibull distribution analysis of detachment events revealed a dependence of chain stiffness on maximum indentation depth (dmax), with higher stiffness at shallower depths approaching kchain ≈ 20 × 10-6 N/m. These findings on adhesion mechanics between a vanishing hydrogel surface and probe can guide the development of multifunctional hydrogels for various biomedical applications.

A photo-chemo-mechanical coupling constitutive model for photopolymerization-based 3D printing hydrogels

Photopolymerization-based 3D printing has emerged as a key technology in hydrogel manufacturing, broadening the attributes of hydrogels and extending their applications into diverse engineering fields. However, the mechanical properties of hydrogels dramatically impact the functionality and quality in practice. It is necessary to develop an appropriate theoretical model to predict the evolution of the mechanical properties of hydrogels during the photopolymerization process. In this work, systematical experiments were performed to investigate mechanical properties of PAAm hydrogel under different photopolymerization condition. The results reveal a noticeable increasement in both elastic and viscous behavior of hydrogel with the advancement of polymerization. To fully capture the experimental observations, we developed a coupled photo-chemo-mechanical theoretical framework that integrates reaction kinetics with a physically-based viscoelastic constitutive model. Within this model, the degree of conversion serves as an internal variable, which related to microscopic structures such as correlation length, and tube diameter. The developed model exhibits remarkable prediction ability for hydrogels with various degree of polymerization. The current work paves a potentially new avenue for understanding the evolution of mechanical properties in photopolymerized hydrogels, providing theoretical guidance for the manufacturing of hydrogels through photopolymerization-based 3D printing.

Self-activated hydrogel cascade reactor integrated with glucose oxidase and silver nanoparticle for enhanced treatment of bacterial infection

The recognition of silver nanoparticles (AgNPs) as a nanozyme with peroxidase-like activity has offered a promising solution to address the challenges of bacterial resistance and argyria risk. However, the catalytic efficacy of AgNPs is limited by the need for a strong acidic environment and high concentrations of hydrogen peroxide (H2O2). In this work, we developed a self-activated hydrogel cascade reactor (AUGP) for enhanced treatment of bacterial infection. The AUGP integrates the properties of glucose oxidase (GOx) and polyacrylamide (pAAm) hydrogel microsphere. The confinement effect of pAAm hydrogel microsphere enables glucose oxidation to occur in a confined space, which creates an acidic environment to activate AgNPs activity, initiating the cascade reaction between GOx and AgNPs. Meanwhile, the confinement effect facilitates the accumulation of a high local concentration of H2O2, allowing AUGP to generate hydroxyl radicals (•OH) without the need for external H2O2. Additionally, the release of Ag+ from AUGP is achieved upon the generation of •OH. The synergistic action of Ag+ and •OH confers exceptional antibacterial efficacy to AUGP. Importantly, the etching effect of H2O2 ensures the absence of any residual AgNPs, reducing the risk of argyria. In vivo studies validated the efficacy of AUGP in wound disinfection with minimal toxicity.

Impact of surface biofunctionalization strategies on key effector cells response in polyacrylamide hydrogels for bone regeneration

Despite the clinical prevalence of various bone defect repair materials, a full understanding of their influence on bone repair and regeneration remains elusive. This study focuses on poly(acrylamide) (PAAm) hydrogels, popular 2D model substrates, which have regulable mechanical properties within physiological. However, their bio-inert nature requires surface biofunctionalization to enhance cell-material interactions and facilitate the study of bone repair mechanisms. We utilized PAAm hydrogels of varying stiffness (18, 76 and 295 kPa), employed sulfosuccinimidyl-6-(4′-azido-2′-nitropheny-lamino) hexanoate (sulfo-SANPAH) and N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride/N-hydroxysuccinimidyl acrylate (EDC/NHS) as crosslinkers, and cultured macrophages, endothelial cells, and bone mesenchymal stem cells on these hydrogels. Our findings indicated that sulfo-SANPAH's crosslinking efficiency surpassed that of EDC/NHS, irrespective of pore size and stiffness. Importantly, we observed that the stiffness and surface biofunctionalization method of hydrogels significantly impacted cell adhesion and proliferation. The collagen-modified hydrogels by EDC/NHS strategy failed to support the normal biological behavior of bone mesenchymal stem cells and hindered endothelial cell spreading. In contrast, these modified hydrogels by the sulfo-SANPAH method showed good cytocompatibility with the three types of cells. This study underscores the critical role of appropriate conjugation strategies for PAAm hydrogels, providing valuable insights for hydrogel surface modification in bone repair and regeneration research.

Superior Induced Pluripotent Stem Cell Generation through Phactr3-Driven Mechanomodulation of Both Early and Late Phases of Cell Reprogramming

Human cell reprogramming traditionally involves time-intensive, multistage, costly tissue culture polystyrene-based cell culture practices that ultimately produce low numbers of reprogrammed cells of variable quality. Previous studies have shown that very soft 2- and 3-dimensional hydrogel substrates/matrices (of stiffnesses ≤ 1 kPa) can drive ~2× improvements in human cell reprogramming outcomes. Unfortunately, these similarly complex multistage protocols lack intrinsic scalability, and, furthermore, the associated underlying molecular mechanisms remain to be fully elucidated, limiting the potential to further maximize reprogramming outcomes. In screening the largest range of polyacrylamide (pAAm) hydrogels of varying stiffness to date (1 kPa to 1.3 MPa), we have found that a medium stiffness gel (~100 kPa) increased the overall number of reprogrammed cells by up to 10-fold (10×), accelerated reprogramming kinetics, improved both early and late phases of reprogramming, and produced induced pluripotent stem cells (iPSCs) having more naïve characteristics and lower remnant transgene expression, compared to the gold standard tissue culture polystyrene practice. Functionalization of these pAAm hydrogels with poly- l -dopamine enabled, for the first-time, continuous, single-step reprogramming of fibroblasts to iPSCs on hydrogel substrates (noting that even the tissue culture polystyrene practice is a 2-stage process). Comparative RNA sequencing analyses coupled with experimental validation revealed that a novel reprogramming regulator, protein phosphatase and actin regulator 3, up-regulated under the gel condition at a very early time point, was responsible for the observed enhanced reprogramming outcomes. This study provides a novel culture protocol and substrate for continuous hydrogel-based cell reprogramming and previously unattained clarity of the underlying mechanisms via which substrate stiffness modulates reprogramming kinetics and iPSC quality outcomes.

Stiffness‐Switchable, Biocatalytic pH‐Responsive DNA‐Functionalized Polyacrylamide Cryogels and their Mechanical Applications

AbstractThe large‐pore interconnected channels in cryogels, allow convectional flow and rapid mass‐transport of solute constituents between the solution and cryogel polymer framework, as compared to slower, diffusionally‐controlled mass‐transport in small‐pore hydrogels. These features are applied to develop enzyme‐loaded polyacrylamide (pAAm) cryogels, and glucose oxidase (GOx)‐loaded pH‐responsive DNA‐based pAAm cryogels, revealing enhanced biocatalytic transformations, enhanced temporal stiffness changes, and mechanical bending functions, as compared to analog hydrogels. DNA‐based pAAm cryogel/hydrogel matrices, revealing pH‐switchable stiffness properties through reversible reconfiguration of DNA‐bridging units into i‐motif structures, are introduced. Enhanced switchable stiffness changes of DNA‐based pAAm cryogels, as compared to analog hydrogels, are demonstrated upon subjecting the cryogel/hydrogel matrices to auxiliary pH‐changes, or by integration of GOx into the frameworks, and driving pH‐changes through GOx‐catalyzed aerobic oxidation of glucose to gluconic acid. Enhanced stiffness changes of pAAm cryogels represent a major advance to control the mechanical properties of cryogels and are attributed to the convectionally‐controlled mass‐transport in the cryogel matrices. Moreover, bilayer constructs consisting of poly‐N‐isopropylacrylamide (pNIPAM) cryogels and pH‐responsive DNA‐based pAAm cryogel or hydrogel structures are constructed. Enhanced pH/glucose triggered mechanical bending rates of the pNIPAM cryogel/pAAm cryogel or pNIPAM cryogel/GOx‐loaded pAAm cryogel, as compared to analog pNIPAM cryogel/pAAm hydrogel frameworks are demonstrated.

Poly(acrylamide) Spheroids with Tunable Elasticity for Scalable Cell Culture Applications

Microfluidics In article 2200246, Annette M. Schmidt's and her co-workers' approach toward spherical, mm-scaled PAAm hydrogel beads with adjustable, soft elastic properties as a matrix for scalable cell culture is described. The beads are produced by a continuous microfluidic approach, and after surface modification with biomarkers, their suitability as a matrix for scalable cell cultivation is successfully demonstrated with three different cell types in model experiments and in a tidal bioreactor system.

Poly(acrylamide) Spheroids with Tunable Elasticity for Scalable Cell Culture Applications

AbstractMany biological tissues resemble hydrogels and display Young's moduli below 50 kPa, corresponding to most cell types for the natural environmental conditions to grow. Contrastingly, conventional cell culture usually involves rigid substrates resulting in stiff priming effects, which are of increasing concern when it comes to scalable culturing of adhesive cells for regenerative purposes. As a solution to this problem, the employment of synthetic poly(acryl amide) (PAAm)‐based hydrogel beads with tissue‐matched mechanical properties are proposed as soft matrix for culture modes suitable for tidal bioreactor culture. Herein, technology is described to generate spherical, mm‐scaled PAAm hydrogel beads with adjustable, soft elastic properties that are produced by a continuous microfluidic approach. A simple and robust method is demonstrated to functionalize the spheroids with protein ligands, and the suitability of the matrix for cell cultivation is successfully demonstrated with three different cell types (murine mesenchymal stem cells, renal carcinoma cells, and human induced pluripotent stem cells) in model experiments and in a tidal bioreactor system. This versatile approach will pave the way toward novel cell culture systems based on bioreactors that allow scalable, soft carrier‐based expansion of cells on matrices with tissue‐matched elasticity.

Tailoring Physical Properties of Dual-Network Acrylamide Hydrogel Composites by Engineering Molecular Structures of the Cross-linked Network.

We demonstrate the impact of engineering molecular structures of poly(acrylamide) (PAAm) and poly(N-isopropylacrylamide) (PNIPAm) hydrogel composites on several physical properties. The network structure was systematically varied by (i) the type and the concentration of difunctional cross-linkers and (ii) the type of native or chemically modified natural polymers, including sodium alginate, methacrylate/dopamine-incorporated porcine skin gelatin and fish skin gelatin, and thiol-incorporated lignosulfonate, which are attractive biopolymers generated in pulp and food industries because of their abundance, rich chemical functionalities, and environmental friendliness. First, we added cross-linking agents of varying lengths at different concentrations to assess how the cross-linking agent modulates the mechanical properties of acrylamide-based composites with alginate. After chemically modifying gelatins from fish or porcine skin with methacrylate and/or dopamine, the acrylamide-based composites were fabricated with the chemically modified gelatins and thiolated lignosulfonate to assess the stress–strain behavior. Furthermore, swelling ratios were measured with respect to temperature change. The mechanical properties were systematically modulated by the changes in the molecular structure, that is, the length of the chemical unit between two end alkene groups in the difunctional cross-linker and the types of the additive natural polymers. Overall, PAAm hydrogel composites exhibit a significant, negative correlation between toughness and the volume fraction of the swollen state and between strain at fracture and the volume fraction of the swollen state. In contrast, PNIPAm hydrogel composites showed positive, but only moderate correlations, which is attributed to the difference in the network polymer structure.

Superabsorbent graphene oxide/carbon nanotube hybrid Poly(acrylic acid-co-acrylamide) hydrogels for efficient salinity gradient energy harvest

Hydrogels can be employed to recover salinity gradient (SG) energy as they can exhibit reversible swelling and shrinking behaviors in alternate freshwater and sea water. The swelling ratio and mechanic property of hydrogels are essential for the SG energy harvest. Herein, different amounts of graphene oxide (GO) or carbon nanotube (CNT) were successfully introduced to the matrix of poly(acrylic acid-co-acrylamide) (PAAM) hydrogels. Compared to the original PAAM hydrogels, both the swelling property and mechanic strength of the GO/CNT hybrid PAAM hydrogels were significantly enhanced. Although the CNT/PAAM hydrogels exhibited relatively higher swelling ratio (1578 g g−1) than that of GO/PAAM (1423 g g−1), the highest SG energy recovery was obtained by using GO/PAAM hydrogels (7.07 J g−1). The reason was due to the better mechanical strength of GO/PAAM hydrogels, which resulted from the covalent bonds between the extensive oxygenated functional groups in GO and the polymeric chains. Moreover, excellent reproducibility was observed with GO/PAAM hydrogels over 10 cycles because of their highly structure integrity. These results demonstrated that GO/CNT hybrid hydrogels are efficient for SG energy recovery attributed to the high swelling ability as well as the strong mechanical property.

Nanocage Ferritin Reinforced Polyacrylamide Hydrogel for Wearable Flexible Strain Sensors.

Biocomposite hydrogels are promising for applications in wearable flexible strain sensors. Nevertheless, the existing biocomposite hydrogels are still hard to meet all requirements, which limits the practical application. Here, inspired by the structure and composition of natural ferritin, we design a PAAm-Ferritin hybrid hydrogel through a facile method. Ferritin is uniformly distributed in the cross-linking networks and acts as a nanocage spring model, leading to the enhanced tensile strength of the hydrogel. The fracture stress is 99 kPa at 1400% maximum elongation. As fabricated PAAm-Ferritin hybrid hydrogels exhibit high toughness and low elastic modulus (21 kPa). The PAAm-Ferritin hybrid hydrogels present excellent biocompatibility and increased conductivity compared with PAAm hydrogel. Impressively, as a wearable flexible strain sensor, the PAAm-Ferritin hybrid hydrogels have high sensitivity (gauge factor = 2.06), excellent reliability, and cycling stability. This study indicates the feasibility of utilizing ferritin to synthesize functional materials, which is conducive to expanding the use of protein synthesis of materials technology and application fields.

Polyacrylamide hydrogel lubricates cartilage after biochemical degradation and mechanical injury.

Intra-articular injections of hyaluronic acid have been a mainstay of osteoarthritis treatment for decades. However, controversy surrounds the mechanism of action and efficacy of this therapy. As such, there has been recent interest in developing synthetic lubricants that lubricate cartilage. Recently, a synthetic 4 wt% polyacrylamide (pAAm) hydrogel was shown to effectively decrease lameness in horses. However, its mechanism of action and ability to lubricate cartilage is unknown. The goal of this study was to characterize the lubricating ability of this hydrogel and determine its efficacy for healthy and degraded cartilage. The study utilized previously established IL-1β-induced biochemical degradation and mechanical impact injury models to degrade cartilage. The lubricating ability of the hydrogel was then characterized using a custom-built tribometer using a glass counterface and friction was evaluated using the Stribeck framework for articular cartilage. pAAm hydrogel was shown to significantly lower the friction coefficient of cartilage explants from both degradation models (30%-40% reduction in friction relative to controls). A striking finding from this study was the aggregation of the pAAm hydrogel at the articulating surface. The surface aggregation was observed in the histological sections of explants from all treatment groups after tribological evaluation. Using the Stribeck framework, the hydrogel was mapped to higher Sommerfeld numbers and was characterized as a viscous lubricant predominantly in the minimum friction mode. In summary, this study revealed that pAAm hydrogel lubricates native and degraded cartilage explants effectively and may have an affinity for the articulating surface of the cartilage.

Hydrogel microreactor integrated double cascade reactions for synergistic bacterial inactivation and wound disinfection

Catalytic bacterial inactivation mediated by peroxidase nanomimics, which converts hydrogen peroxide (H2O2) to hydroxyl radical (•OH) with high toxicity, has been emerged as a promising solution to combat bacterial infections and antibiotic resistance. However, the bacterial inactivation efficacy was often restricted by the low catalytic activity of peroxidase nanomimics and the short half-life and limited diffusion distance of •OH. Here, we developed a hydrogel microreactor (GHAP) integrated double cascade reactions to sequentially generate •OH and nitric oxide (NO) for synergistic bacterial inactivation, where NO offers a complementary effect to compensate •OH for incomplete bacterial inactivation. The GHAP was fabricated by the coencapsulation of glucose oxidase (GOx), hemoglobin (Hb) and zeolitic imidazolate framework-8 loaded with arginine (Arg) in polyacrylamide (pAAm) hydrogel microsphere. The presence of glucose can trigger GHAP to sequentially generate •OH and NO though the successive coupling of GOx with Hb and Arg. The pAAm microsphere was demonstrated to enhance cascade catalytic efficiencies and shield GHAP against harsh conditions due to its confinement effect. Importantly, compared with single •OH/NO-generated cascade systems, the superiority of GHAP was highlighted by the synergistic antibacterial effects of •OH and NO, which thereby endows GHAP with a greatly enhanced antibacterial performance and an exceptional broad-spectrum antibacterial ability. In vivo experiments in a mouse model demonstrated that GHAP could be used for wound disinfection with minimal side effects. This work opens a new avenue for the rational design of biomimetic reactors for biomedical applications.

3D Printing of Conductive Hydrogel-Elastomer Hybrids for Stretchable Electronics.

Electronically conductive hydrogels integrated with dielectric elastomers show great promise in a wide range of applications, such as biomedical devices, soft robotics, and stretchable electronics. However, one big conundrum that impedes the functionality and performance of hydrogel-elastomer-based devices lies in the strict demands of device integration and the requirements for devices with satisfactory mechanical and electrical properties. Herein, the digital light processing three-dimensional (3D) printing method is used to fabricate 3D functional devices that bridge submillimeter-scale device resolution to centimeter-scale object size and simultaneously realize complex hybrid structures with strong adhesion interfaces and desired functionalities. The interconnected poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) network endows the PAAm hydrogel with high conductivity and superior electrical stability and poly(2-hydroxyethyl acrylate) functions as an insulating medium. The strong interfacial bonding between the hydrogel and elastomer is achieved by incomplete photopolymerization that ensures the stability of the hybrid structure. Lastly, applications of stretchable electronics illustrated as 3D-printed electroluminescent devices and 3D-printed capacitive sensors are conceptually demonstrated. This strategy will open up avenues to fabricate conductive hydrogel-elastomer hybrids in next-generation multifunctional stretchable electronics.

Photo-Dissociable Fe3+-Carboxylate Coordination: A General Approach toward Hydrogels with Shape Programming and Active Morphing Functionalities.

An extendable double network design for hydrogels with programmable external geometries and actuating trajectories is presented. Chemically cross-linked polyacrylamide as the first network penetrated with linear alginate chains is prepared for demonstration. The coordination of Fe3+ ions with carboxylate groups in alginate chains acts as the second network, and its dissociation through photoreduction is utilized to realize the photoresponsive shape memory property; the shape fixity ratio and shape recovery ratio both exceed 90%. The gradient dissociation of Fe3+-carboxylate coordination under UV facilitates 3D programming of hydrogel geometry. On another aspect, the resulted cross-linking gradient differentiates the extent and rate of solvent-induced volume change of the PAAm network, endowing the hydrogel with photo-programmable solvent-driven actuating behavior. Furthermore, by inducing the formation of Fe3+-carboxylate coordination within the entire network for shape programming and cross-linking gradients in specific regions as active joints, hydrogels with designed actuating behaviors based on specific 3D shapes are realized. The shape memory and active morphing functionalities enabled by photo-dissociable Fe3+-carboxylate coordination in PAAm hydrogel can be generally extended to other hydrogels.

Effects of network structures on the fracture of hydrogel

The polymer network structures and topologies in hydrogels can significantly affect their mechanical properties. The network structures can vary dramatically with different synthetic conditions of hydrogels. Herein, we study the effects of the polymer network structures on mechanical properties of poly(acrylamide) (PAAm) hydrogels synthesized through free radical polymerizations. We focus on investigating how the initial monomer concentration ϕ0 during the synthesis influences the network structures and thus their mechanical properties. Specifically, we measure the swelling capability of the polymer network, the elasticity and fracture of swollen hydrogels with a fixed volume fraction of polymer. Our results have revealed that for PAAm hydrogels with the same volume fraction of polymer, their elasticity, stretchability, work of rupture and fracture toughness can vary significantly if ϕ0 during the synthesis is different. Our study may provide important guideline for synthesizing hydrogels with tailorable mechanical properties without changing the chemistry and synthesis procedure.

Multifunctional double network hydrogel film for skin wound healing

Skin wound management is an important issue in the medical community. Herein, we report a multifunctional film with many advanced features as a dressing for the healing of wounds. The dressing was made using chitosan and poly(acrylamide) (pAAm) hydrogel in order to form a double network (DN) hydrogel film. Compared to the pure chitosan hydrogel, which is fragile, the added pAAm network conferred excellent mechanical capability to the composite film, making it flexible and easy to treat. By further doping the hydrogel with carbon nanotubes and drugs, the film could promote wound healing. Animal experiments demonstrated that the DN hydrogel film could reduce inflammation and promote tissue regeneration. Thus, this film is promising as a treatment for wound healing.

Ferrocene-functionalized hybrid hydrogel dressing with high-adhesion for combating biofilm

Bacterial infection is a common phenomenon in the process of postoperative wound healing. In severe cases, it may even lead to life-threatening, which brings a heavy burden to the clinical treatment and causes huge losses to the society and economy. As one of the most commonly applied medical materials for wound treatment, hydrogel dressings are mainly used to cover and protect wounds and provide a favorable environment to facilitate wound healing. In this work, we developed an antibacterial hydrogel dressing (Fc-PAAM) with high adhesion, which is consisted of polyacrylamide (PAM) hydrogel framework and polyacrylic acid-functionalized (PAA) with ferrocene (Fc). Morphology, adhesion and pressure resistance of PAAM hydrogel were confirmed by using scanning electron microscope (SEM) and universal testing machine, and Fc decoration in the hydrogel network was well demonstrated by using Fourier transform infrared spectroscopy (FT-IR). Ultraviolet-visible spectroscopy (UV–vis) displayed that the Fc-PAAM hydrogel had excellent peroxidase-like activity as well. It not only exhibited prominent antimicrobial activity against Gram (+/−) bacteria, but also performed high efficiency in preventing the formation of biofilms. In addition, in vivo experiments indicated that this adhesive dressing could significantly prevent bacterial infections. Compared with other clinical treatment methods, this kind of hydrogel is not easy to cause bacterial resistance, and the used raw materials are easy to obtain and low in price, which can amplify the antibacterial properties of H2O2 and provide a new opportunity for the treatment of clinical bacterial infections.

Absorption and adsorption studies of polyacrylamide/sodium alginate hydrogels

The aim of this study is to investigate the use of hydrogels as adsorbent in the removal of methylene blue (MB), a cationic dyestuff commonly used in industry, by adsorption from waste water. Therefore, sodium alginate-modified polyacrylamide-sodium alginate (PAAm/SA) hydrogels with the different concentration of sodium alginate were synthesized by free radical solution polymerization under normal atmospheric conditions. The absorbents were characterized using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The absorption and adsorption experiments were performed and the effects of several experimental parameters including pH and contact time upon the adsorption process were evaluated. As a result of swelling tests, PAAm/SA hydrogels swelled in the range of 12.72–25.52 gwater gdry gel−1 in water, while PAAm hydrogel swelled to 8.5 gwater gdry gel−1. Methylene blue adsorption, which showed a rapid increase with increasing pH in the range of pH 2.0–6.0, reached the highest value at pH 7.0. Adsorption equilibrium was investigated by using Langmuir, Freundlich, and Temkin isotherm models. Two kinetic models, (i) pseudo-first-order and (ii) pseudo-second-order kinetic models, were applied to test the experimental data. Pseudo-second-order kinetic model well fitted the kinetic results, suggesting chemisorption as the most probable adsorption mechanism. Adsorption of methylene blue with hydrogels was well fitted with the Freundlich isotherm model, indicating the multilayer adsorption process on heterogeneous surfaces. The prepared hydrogels can be potential candidates for use as absorbents to treat wastewater.