Synthesis and Physical Properties of Reactive Amphiphilic Hydrogels Based on Poly(p-chloromethylstyrene) and Poly(ethylene glycol): Effects of Composition and Molecular Architecture

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.

Polymeric hydrogels-based materials for wastewater treatment

Low-cost and reliable wastewater treatment is a relevant issue worldwide to reduce the concentration of environmental pollutants. Industrial effluents containing dyes, heavy metals, and other inorganic and organic compounds can pollute water resources; therefore, novel technologies are required to mitigate and control their release into the environment. Adsorption is one of the simplest methods for treating contaminated water in which a wide spectrum of adsorbents can be used to remove emerging compounds. Hydrogels are interesting materials with high adsorption capacities that can be synthesized via green routes. These adsorbents are promising for large-scale industrial wastewater treatment applications; however, gaps still exist in achieving sustainable commercial implementation. This review focuses on the discussion and analysis of preparation, characterization, and adsorption properties of hydrogels for water purification. The advantages of these polymeric materials for water treatment were analyzed, including their performance in the removal of different organic and inorganic contaminants. Recent advances in the functionalization of hydrogels and the synthesis of novel composites have also been described. The adsorption capacities of hydrogel-based adsorbents are higher than 500 mg/g for different organic and inorganic pollutants, and can reach values of up to >2000 mg/g for organic compounds, significantly outperforming other materials reported for water cleaning. The main interactions involved in the adsorption of water pollutants using hydrogel-based adsorbents were described and explained to allow the interpretation of their removal mechanisms. The current challenges in the implementation of hydrogels for water purification in real-life operations are also highlighted. This review provides an updated picture of hydrogels as interesting materials to address water depollution worldwide.

Hydrogels with electrically conductive nanomaterials for biomedical applications

Hydrogels, soft 3D materials of cross-linked hydrophilic polymer chains with a high water content, have found numerous applications in biomedicine because of their similarity to native tissue, biocompatibility and tuneable properties. In general, hydrogels are poor conductors of electric current, due to the insulating nature of commonly-used hydrophilic polymer chains. A number of biomedical applications require or benefit from an increased electrical conductivity. These include hydrogels used as scaffolds for tissue engineering of electroactive cells, as strain-sensitive sensors and as platforms for controlled drug delivery. The incorporation of conductive nanomaterials in hydrogels results in nanocomposite materials which combine electrical conductivity with the soft nature, flexibility and high water content of hydrogels. Here, we review the state of the art of such materials, describing the theories of current conduction in nanocomposite hydrogels, outlining their limitations and highlighting methods for improving their electrical conductivity.

Frost Delay of a Water-Absorbing Surface with Engineered Wettability via Nonfreezing Water

Frost is common when a solid surface is subjected to a humid and cold environment. It can cause various inconveniences, complications, or fatal accidents. Water-repellent surfaces have demonstrated an antifreezing capability by enabling the water droplets to roll or bounce off before they freeze. However, these surfaces are often limited by their inability to shed the small water condensates, which can eventually grow and freeze. Recently, surfaces that can rapidly absorb and hydrogen bond with these water condensates have demonstrated significant delay in frost formation and growth. This is attributed to a lower freezing temperature of the absorbed water which makes it stay in a nonfreezing state. Herein, we report a surface with preferential wettability of water over oil (i.e., superhydrophilic and oleophobic wettability) that can significantly delay frost formation. The surface is fabricated by copolymerizing poly(ethylene glycol) diacrylate (PEGDA) and perfluorinated acrylate (1H,1H,2H,2H-heptadecafluorodecyl acrylate, HDF-acrylate) applied to a silane-grafted glass substrate (HDF-PEGDA). An HDF-PEGDA surface can quickly absorb condensed water which enables it to delay frost formation and growth for up to 20 min at a surface temperature of -35 °C. Also, the surface demonstrates that its frost-resistant capability remains almost unaffected even after being submerged in an oil bath due to its in-air oil repellency. Differential scanning calorimetry (DSC) measurements reveal that the significant quantity of absorbed water in an HDF-PEGDA surface remains in a nonfreezing state with a T_m value as low as -33 °C. A mathematical model that can predict the time at which the surface begins to be covered with frost is developed. Finally, an HDF-PEGDA is layered with a PEGDA copolymerized with sodium acrylate (Na-acrylate) that enables the continuous release of the absorbed water by posing forward osmotic pressure and regeneration of an HDF-PEGDA surface.

Multi-functional nanocellulose-chitosan dressing loaded with antibacterial lawsone for rapid hemostasis and cutaneous wound healing

Cutaneous wounds accompanied by massive bleeding, bacterial infections might be lethal and cause fundamental therapeutic impediments in clinical fields. As part of the push for a solution, biomaterial having hemostatic-antibacterial features is highly desirable. Inspired by this concept, freeze dried sponges were developed followed by combining tempo-oxidized nanocellulose (TOCN), chitosan using EDC/NHS cross-linker with antibacterial lawsone loading for controlled delivery of this compound during wound healing. The pore diameter decreased upon increasing chitosan (2.5, 3.5, 4.5, 5.5% w/v) while TOCN ensured scaffold's mechanical stability. The in vitro degradation, lawsone release from fibroblast cell-compatible sponge was faster in acidic pH 5.5 than physiologic pH 7.4 indicating adaptability to physiological skin milieu of wounds. The rat tail amputation model, 14 days rat full-thickness cutaneous-wound model ensured hemostasis, dramatic wound closure after TLC4.5 (optimized scaffold) treatment suggesting its potential as functional wound healing substitute showing obvious avenue for hemostatis and skin tissue reconstruction arena.

Elucidating the Molecular Mechanisms for the Interaction of Water with Polyethylene Glycol-Based Hydrogels: Influence of Ionic Strength and Gel Network Structure

The interaction of water within synthetic and natural hydrogel systems is of fundamental importance in biomaterial science. A systematic study is presented on the swelling behavior and states of water for a polyethylene glycol-diacrylate (PEGDA)-based model neutral hydrogel system that goes beyond previous studies reported in the literature. Hydrogels with different network structures are crosslinked and swollen in different combinations of water and phosphate-buffered saline (PBS). Network variables, polyethylene glycol (PEG) molecular weight (MW), and weight fraction are positively correlated with swelling ratio, while "non-freezable bound water" content decreases with PEG MW. The presence of ions has the greatest influence on equilibrium water and "freezable" and "non-freezable" water, with all hydrogel formulations showing a decreased swelling ratio and increased bound water as ionic strength increases. Similarly, the number of "non-freezable bound water" molecules, calculated from DSC data, is greatest-up to six molecules per PEG repeat unit-for gels swollen in PBS. Fundamentally, the balance of osmotic pressure and non-covalent bonding is a major factor within the molecular structure of the hydrogel system. The proposed model explains the dynamic interaction of water within hydrogels in an osmotic environment. This study will point toward a better understanding of the molecular nature of the water interface in hydrogels.

Thermal stimuli-responsive hyaluronic acid loaded cellulose based physical hydrogel for post-surgical de novo peritoneal adhesion prevention

Effective strategies for post-surgical adhesion prevention have increasingly focused on injectable adhesion barriers due to their minimal invasiveness and wider applicability. In this study, a thermo-reversible hydrogel was developed by combining high molecular weight hyaluronic acid (HA) at various concentrations (0.05, 0.25, and 0.45% w/v) with tempo-oxidized nanocellulose (TOCN), methyl cellulose (MC) and polyethylene glycol (PEG) for anti-adhesion application. The hydrogel preparation time was short and did not require any chemical modification. TOCN ensured the mechanical stability of the hydrogel. MC confirmed thermo-sensitive feature. Higher amounts of HA increased the rate of hydrogel degradation. The HA 0.25 hydrogel was free-flowing, injectable at ambient temperature, capable of faster (40 ± 2 s), and reversible sol-gel (4 °C-37 °C) transition. A rat side-wall cecum abrasion model was used to confirm the complete de novo adhesion prevention efficacy of optimized HA 0.25 hydrogel, where the scratched abdominal wall of animals treated with HA 0.25 hydrogel healed after 14 days. During in vivo experiment, PEG in the hydrogel played a crucial role in adhesion prevention by minimizing friction between the surgical site and nearby organs. In a nutshell, HA 0.25 hydrogel, fabricated without crosslinking agent, is a potential candidate for tissue adhesion prevention strategies.

Characterisation of hydrogels: Linking the nano to the microscale

Hydrogels are water enriched soft materials widely used for applications as varied as super absorbents, breast implants and contact lenses. Hydrogels have also been designed for smart functional devices including drug delivery, tissue engineering and diagnostics such as blood typing. The hydrogel properties and functionality depend on their crosslinking density, water holding capacity and fibre/polymer composition, strength and internal structure. Determining these parameters and properties are challenging. This review presents the main characterisation methods providing both qualitative and quantitative information of the structures and compositions of hydrogel. The length scale of interest ranges from the nano to the micro scale and the techniques and results are analysed in relationship to the hydrogel macroscopic applications. The characterisation methods examined aim at quantifying swelling, mechanical strength, mesh size, bound and free water content, pore structure, chemical composition, strength of chemical bonds and mechanical strength. These hydrogel parameters enable us to understand the fundamental mechanisms of hydrogel formation, to control their structure and functionality, and to optimize and tailor specific hydrogel properties to engineer particular applications.

Stereocomplex Poly(Lactic Acid) Amphiphilic Conetwork Gel with Temperature and pH Dual Sensitivity

A novel stereocomplex poly(lactic acid) amphiphilic conetwork gel with temperature and pH dual sensitivity was synthesized by ring-opening polymerization (ROP) and free radical copolymerization. The chemical structure and composition of hydrogel were characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H NMR) and X-ray diffraction (XRD). The temperature and pH sensitivity and good amphiphilicity of hydrogel were studied using digital photos, the swelling ratios and a scanning electron microscope (SEM). The thermal stability and mechanical properties of hydrogel were studied by differential scanning calorimeter (DSC) and dynamic viscoelastic spectrometer. The results indicated that the hydrogel has amphiphilicity, temperature and pH sensitivity, good thermal stability and mechanical strength.

Effective detection of biocatalysts with specified activity by using a hydrogel-based colourimetric assay - β-galactosidase case study

The main aim of this study was to prepare gelatine-based hydrogels containing entrapped substrate and to examine the applicability of these matrices for detection of enzymes with a specified catalytic activity. The general research concept assumed the use of a substrate that, in the presence of a particular enzyme, will quickly undergo conversion to a coloured product. ortho-Nitrophenyl-β-D-galactopyranoside (ONPG) was used as the immobilized substrate and β-galactosidase from Kluyveromyces lactis as the biocatalyst to be determined. Among other factors, the range of detectable concentrations of galactosidase, the operational pH range, the time necessary to achieve a visible response and the preferred storage conditions for the test were determined. As a result, an effective colourimetric test for β-galactosidase detection was obtained. Its main advantages include (i) the effective detection of the enzyme at concentrations greater than or equal to 0.6 mg.L-1, (ii) the ability to perform initial quantification of the enzyme on the basis of the intensity of the obtained colour (iii) applicability in a wide pH range (from 4.0 to 9.0), (iv) a relatively short response time (from 1 to a maximum of 30 minutes) and (v) stability in long-term storage at 4°C (90 days without loss of specific properties).

²H Solid-State NMR Analysis of the Dynamics and Organization of Water in Hydrated Chitosan

Understanding water–biopolymer interactions, which strongly affect the function and properties of biopolymer-based tissue engineering and drug delivery materials, remains a challenge. Chitosan, which is an important biopolymer for the construction of artificial tissue grafts and for drug delivery, has attracted extensive attention in recent decades, where neutralization with an alkali solution can substantially enhance the final properties of chitosan films cast from an acidic solution. In this work, to elucidate the effect of water on the properties of chitosan films, we investigated the dynamics and different states of water in non-neutralized (CTS-A) and neutralized (CTS-N) hydrated chitosan by mobility selective variable-temperature (VT) ²H solid-state NMR spectroscopy. Four distinct types of water exist in all of the samples with regards to dynamic behavior. First, non-freezable, rigid and strongly bound water was found in the crystalline domain at low temperatures. The second component consists of weakly bound water, which is highly mobile and exhibits isotropic motion, even below 260 K. Another type of water undergoes well-defined 180° flips around their bisector axis. Moreover, free water is also present in the films. For the CTS-A sample in particular, another special water species were bounded to acetic acid molecules via strong hydrogen bonding. In the case of CTS-N, the onset of motions of the weakly bound water molecules at 260 K was revealed by ²H-NMR spectroscopy. This water is not crystalline, even below 260 K, which is also the major contribution to the flexibility of chitosan chains and thus toughness of materials. By contrast, such motion was not observed in CTS-A. On the basis of the ²H solid-state NMR results, it is concluded that the unique toughness of CTS-N mainly originates from the weakly bound water as well as the interactions between water and the chitosan chains.

Zwitter-wettability and antifogging coatings with frost-resisting capabilities

Antifogging coatings with hydrophilic or even superhydrophilic wetting behavior have received significant attention due to their ability to reduce light scattering by film-like condensation. However, under aggressive fogging conditions, these surfaces may exhibit frost formation or excess and nonuniform water condensation, which results in poor optical performance of the coating. In this paper, we show that a zwitter-wettable surface, a surface that has the ability to rapidly absorb molecular water from the environment while simultaneously appearing hydrophobic when probed with water droplets, can be prepared by using hydrogen-bonding-assisted layer-by-layer (LbL) assembly of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA). An additional step of functionalizing the nano-blended PVA/PAA multilayer with poly(ethylene glycol methyl ether) (PEG) segments produced a significantly enhanced antifog and frost-resistant behavior. The addition of the PEG segments was needed to further increase the nonfreezing water capacity of the multilayer film. The desirable high-optical quality of these thin films arises from the nanoscale control of the macromolecular complexation process that is afforded by the LbL processing scheme. An experimental protocol that not only allows for the exploration of a variety of aggressive antifogging challenges but also enables quantitative analysis of the antifogging performance via real-time monitoring of transmission levels as well as image distortion is also described.