Hydrophobic Hydrogels Research Articles

A Protein-Adsorbent Hydrogel with Tunable Stiffness for Tissue Culture Demonstrates Matrix-Dependent Stiffness Responses.

Although tissue culture plastic has been widely employed for cell culture, the rigidity of plastic is not physiologic. Softer hydrogels used to culture cells have not been widely adopted in part because coupling chemistries are required to covalently capture extracellular matrix (ECM) proteins and support cell adhesion. To create an in vitro system with tunable stiffnesses that readily adsorbs ECM proteins for cell culture, we present a novel hydrophobic hydrogel system via chemically converting hydroxyl residues on the dextran backbone to methacrylate groups, thereby transforming non-protein adhesive, hydrophilic dextran to highly protein adsorbent substrates. Increasing methacrylate functionality increases the hydrophobicity in the resulting hydrogels and enhances ECM protein adsorption without additional chemical reactions. These hydrophobic hydrogels permit facile and tunable modulation of substrate stiffness independent of hydrophobicity or ECM coatings. Using this approach, we show that substrate stiffness and ECM adsorption work together to affect cell morphology and proliferation, but the strengths of these effects vary in different cell types. Furthermore, we reveal that stiffness mediated differentiation of dermal fibroblasts into myofibroblasts is modulated by the substrate ECM. Our material system demonstrates remarkable simplicity and flexibility to tune ECM coatings and substrate stiffness and study their effects on cell function.

Tuning network structures of hydrophobic hydrogels by controlling polymerization solvent

Hydrophobic hydrogels with various copolymer sequences and network structures are prepared by tuning the solvent condition of the reaction solution, which exhibit different appearance and properties under the same monomer composition.

Tough Hydrophobic Hydrogels for Monitoring Human Moderate Motions in Both Air and Underwater Environments

Tough Hydrophobic Hydrogels for Monitoring Human Moderate Motions in Both Air and Underwater Environments

Robust and smart underwater adhesion of hydrophobic hydrogel by phase change

Water-durable adhesives are widely explored in various fields like wearable electronics, tissue engineering and sea refloatation. However, in harsh underwater environment, adhesives with sound and comprehensive performance on various surfaces remain highly challenging. Herein, we report a hydrophobic hydrogel adhesive composed of crystalline octadecyl (C18) chains with versatile, robust and thermally switchable underwater adhesion. The inherent hydrophobicity and the amorphous state of C18 chains allow the hydrogel adhesive to conformally adapt to underwater surfaces, independent of surface energy, curvature, charge and roughness as well as the salinity and pH of the water environment. The crystallization of C18 chains greatly increases the modulus of the hydrogel, interlocking the adhesive to the contacting surfaces and resulting in the underwater adhesion up to 275 kPa. The phase change of hydrogel regulates the stress distribution at the contact interface and the adhesion capacity, resulting in a switchable underwater adhesion. The phase change of C18 chains also endows the hydrogel self-healing property, ensuring durability and reusability. Moreover, the temperature of phase change is around ∼ 40 ℃, endowing adhesive with bio-applications in dynamic watery environments. Therefore, the adhesive is highly potential in emerging areas of wearable electronics, tissue engineering and so on.

Guar gum reinforced conductive hydrogel for strain sensing and electronic devices

Hydrophobically associated conductive hydrogels got great attention due to their excellent properties like stretchability, energy dissipation mechanism, and strain sensor. But hydrophobically associated hydrogels have poor mechanical properties and time response to external stimuli. To enhance the mechanical properties and response to stimuli, Acrylamide- co-Butyl acrylate/Gum based conductive hydrogels were prepared. SDS works as a cross-linker and micelle-forming agent while NaCl makes hydrogel as conductive. The results show that our % strain sensing reached up to 400 %, and fracture stress and fracture strain reached to 0.5 MPa and 401 % respectively. Besides this, it's having an excellent response to continuous stretching and unstretching multiple cycles without any fracture up to 180 s and an excellent time response of 190 s. The conductivity of the hydrogel was 0.20 Sm−1. The hydrophobic hydrogels showed a clear and quick response to human motions like finger, wresting, writing, speaking, etc. Interestingly, our prepared hydrogels can detect the mood of the human face. Similarly, the hydrogels were found efficient in bridging the surface of electronic devices with human skin. This indicates that our prepared hydrogels can monitor human body motion and will replace the existing materials used in strain sensors in the near future.

Influence of crosslink on the formation of hydrophobic hydrogels

Recently invented hydrophobic hydrogel is a specific type of soft matter, which is composed of purely hydrophobic networks while maintaining ultra-high water content. Owing to their unique structures, hydrophobic hydrogels manifest various particularities for versatile applications. Therefore, it is essential to reveal the factors that determine the gels’ formation. Until now, the role played by the chemical crosslinks (e.g. crosslink ratio, structure) stays unclear. To figure out the mystery, herein we prepare a series of polyacrylate gels with different crosslinks at diverse crosslinker concentrations. Upon being soaked in water, the gels behave divergently in terms of dynamic swelling behavior. Unlike conventional gels, the maximum swelling degrees of three different hydrophobic hydrogels initially increase and then decrease with raising in crosslink ratio. Similarly, the swelling kinetics significantly vary with the crosslink ratio. From the data, a moderate crosslink ratio is required for the formation of hydrophobic hydrogels as it endows the polymer chain with high mobility and density. In addition, the chemical structure of crosslinks plays a less significant role in the formation of hydrophobic hydrogels but an important role in determining their swelling equilibrium states in water, which ultimately affects their mechanical performance. All these results may help us to uncover the formation mechanism of the hydrophobic hydrogels and establish a general standard for the preparation of such soft matter.

Underwater instant adhesion mechanism of self-assembled amphiphilic hemostatic granular hydrogel from Andrias davidianus skin secretion

SummaryThe widespread use of biological tissue adhesives for tissue repair is limited by their weak adhesion in a wet environment. Herein, we report the wet adhesion mechanism of a dry granular natural bioadhesive from Andrias davidianus skin secretion (ADS). Once contacting water, ADS granules self-assemble to form a hydrophobic hydrogel strongly bonding to wet substrates in seconds. ADS showed higher shear adhesion than current commercial tissue adhesives and an impressive 72-h underwater adhesion strength of ∼47kPa on porcine skin tissue. The assembled hydrogel in water maintained a dissipation energy of ∼8 kJ/m3, comparable to the work density of muscle, exhibiting its robustness. Unlike catechol adhesion mechanism, ADS wet adhesion mechanism is attributed to water absorption by granules, and the unique equilibrium of protein hydrophobicity, hydrogen bonding, and ionic complexation. The in vivo adhesion study demonstrated its excellent wet adhesion and hemostasis performance in a rat hepatic and cardiac hemorrhage model.

Anti-Fouling Performance of Hydrophobic Hydrogels with Unique Surface Hydrophobicity and Nanoarchitectonics.

Hydrogel is a kind of soft and wet matter, which demonstrates favorable fouling resistance owing to the hydration anti-adhesive surfaces. Different from conventional hydrogels constructed by hydrophilic or amphiphilic polymers, the recently invented “hydrophobic hydrogels” composed of hydrophobic polymers exhibit many unique properties, e.g., surface hydrophobicity and high water content, suggesting promising applications in anti-fouling. In this paper, a series of hydrophobic hydrogels were prepared with different chemical structures and water content for anti-fouling investigations. The hydrophobic hydrogels showed high static water contact angles (WCAs > 90°), indicating remarkable surface hydrophobicity, which is abnormal for conventional hydrogels. Compared with the conventional hydrogels, all the hydrophobic hydrogels exhibited less than 4% E. coli biofilm coverage, showing a contrary trend of anti-fouling ability to the water content inside the polymer. Typically, the poly(2-(2-ethoxyethoxy)ethyl acrylate) (PCBA) and poly(tetrahydrofurfuryl acrylate) (PTHFA) hydrogels with relatively high surface hydrophobicity showed as low as 5.1% and 2.4% E. coli biofilm coverage even after incubation for 7 days in bacteria suspension, which are about 0.32 and 0.15 times of that on the hydrophilic poly(N,N-dimethylacrylamide) (PDMA) hydrogels, respectively. Moreover, the hydrophobic hydrogels exhibited a similar anti-adhesion ability and trend to algae S. platensis. Based on the results, the surface hydrophobicity mainly contributes to the excellent anti-fouling ability of hydrophobic hydrogels. In the meantime, the too-high water content may be somehow detrimental to anti-fouling performance.

Hydrophobic hydrogels as internal curing agent for concrete: The double benefit of super high water content and excellent anti-ion permeability

Owing to their high water content, conventional superabsorbent polymer (SAP) hydrogels can serve as internal curing agents for concrete fabrication. However, the hydrophilic network in such hydrogels permits ion diffusion, which induces severe steel corrosion inside concrete in the marine environment. Herein, we introduce a brand-new hydrogel, termed “hydrophobic hydrogels”, for concrete curing. On one hand, these hydrogels possess super high water content (up to 99.6 wt%), which is even higher than that in normal SAP hydrogels; on the other hand, the anhydrous inhomogeneous hydrophobic structures can significantly retard or stop the ion permeation, which is significantly superior to SAP hydrogels. With ion diffusion measurement, the hydrophobic hydrogels achieve much better ion resistance than SAP hydrogels, with 2–5 orders' decrease in ion permeation rate. Among diverse hydrophobic hydrogels, the polymer's hydrophobicity and glass transition directly determine the permeation performance. Hydrogels with a more hydrophobic network and higher polymer Tg possess better anti-ion diffusion properties. At the optimal state, the poly(phenyl acrylate) hydrophobic hydrogels can completely stop the permeation process. Owing to the double benefit, the hydrophobic hydrogel cured concretes demonstrate a notable decrease in ion permeation compared to SAP hydrogel cured concrete, with only 1/20 of ion permeation to that in SAP groups with an electric flux test upon coated on the surface layers. Owing to the double benefit from super high water content and excellent anti-ion permeability, these hydrophobic hydrogels may serve as ideal candidates as concrete curing agents in the future.

Bioinspired Janus particles for hydrophobic modification of hydrogels with photothermal antibacterial capability

Hydrogels have received considerable attention due to their biocompatibility and desirable physical characteristics. Nonetheless, due to their open structure, hydrogels are prone to dehydration in air, resulting in a loss in their elasticity and function. Herein, we report a facile yet effective method for the modification of hydrophobic hydrogel surfaces by using bioinspired amphiphilic Janus silica particles, which are obtained by modifying hydrophilic polydopamine and hydrophobic 1H,1H,2H,2H-perfluorodecanthiol on their two sides via a templating method. With the coating of amphiphilic Janus silica particles, the water contact angles of poly(ethylene imine)-polyacrylamide and polydopamine-polyacrylamide hydrogels significantly increase to 96° and 97°, respectively. Furthermore, we demonstrate that the hydrophobic modification of the hydrogels by Janus silica particles improves the water retention capability, and the overall mechanical properties of bulk hydrogels are not compromised. In addition, we show that hydrogels coated with Janus silica particles not only exhibit hydrophobic surfaces but also have photothermal antibacterial capabilities. Consequently, this study provides a facile method for the fabrication of hydrogels with hydrophobic surfaces, which could potentially be applied to biomedical materials.

Modification of Hydrophobic Hydrogels into a Strongly Adhesive and Tough Hydrogel by Electrostatic Interaction

Modification of Hydrophobic Hydrogels into a Strongly Adhesive and Tough Hydrogel by Electrostatic Interaction

Dynamic swelling performance of hydrophobic hydrogels

Conventional gels manifest monotonous swelling or shrinking performance upon immersing in solvents until reaching an equilibrium state. Recently, we discovered that the “hydrophobic hydrogels” prepared from hydrophobic polymer networks demonstrated dynamic swelling performance without equilibrium states. Upon water immersion, the gels expanded tremendously at the first stage until reaching a swelling peak; subsequently, the gels shrunk at an extremely slow rate. While this phenomenon endows the material with an unusual feature, more efforts are highly demanding for the full understanding of this performance. Herein, we systematically investigate the hydrophobic hydrogels’ swelling kinetics by screening the organic solvent dependence, polymer effect, and temperature impact. It is revealed that the chemical structure of gels greatly influences the swelling kinetics. The higher the networks’ hydrophobicity, the slower the swelling kinetics. Meanwhile, organic solvents demonstrate a limited effect on the dynamic swelling performance. Moreover, higher temperature significantly accelerates the whole volume change process. Based on the swelling performance, we further develop hydrogel-based soft devices with time-programmable two-dimensional and three-dimensional shape-shifting performances.

Photoinduced post-modification of graphitic carbon nitride-embedded hydrogels: synthesis of 'hydrophobic hydrogels' and pore substructuring.

Hydrogels are a special class of crosslinked hydrophilic polymers with a high water content through their porous structures. Post-modifications of hydrogels propose an attractive platform so that a variety of fresh functions, which are not arising from initial monomers, could be accessible on a parental network. Photoinduced post-modification of hydrogels by embedding semiconductor nanosheets would be of high interest and novelty. Here, a metal-free semiconductor graphitic carbon nitride (g-CN)-embedded hydrogel as an initial network was synthesized via redox-couple initiation under dark conditions. Post-photomodification of so-formed hydrogel, thanks to the photoactivity of the embedded g-CN nanosheets, was exemplified in two scenarios. The synthesis of ‘hydrophobic hydrogel’ is reported and its application in delayed cation delivery was investigated. Furthermore, pores of the initial hydrogel were modified by the formation of a secondary polymer network. Such a facile and straightforward synthetic protocol to manufacture functional soft materials will be of high interest in near future by the means of catalysis and agricultural delivery.

Alter macrophage adhesion and modulate their response on hydrophobically modified hydrogels

• Facile modification of naturally derived polymers to increase hydrophobicity. • Hydrogels were crosslinked via in situ thiol-ene chemistry. • Protein adsorption and macrophage proliferation increased on hydrophobic hydrogels. • Macrophages pro-inflammatory response was suppressed on hydrophobic hydrogels. Adhesion of macrophages to material substrates plays an essential role in many biological behaviors and biomedical procedures, including wound healing, cancer treatment and biomaterial implantation. Therefore, altering the adhesion of macrophages using biomaterial design may help control their biological function. In this work, we developed a straightforward method to render the hydrogel surface more hydrophobic and demonstrated that the adhesion of macrophages on hydrogels was enhanced on these more hydrophobic surfaces. Compared to the unmodified methacrylated gellan gum (MGG) hydrogel, the water contact angle increased and the swelling ratio decreased for modified MGG hydrogels. The degree of hydrophobicity was controlled by attaching hydrophobic branches of different lengths to the MGG, while the modification did not change the hydrogel compressive modulus. This ensured that the observed different cell responses were mainly due to hydrophobicity change and not the mechanical property difference among the hydrogels. Cell (RAW 264.7 macrophages) proliferation and spreading increased with increasing surface hydrophobicity. Protein adsorption on hydrogel surfaces showed the same trend. Quantification of adhesion to hydrogel surfaces using a hydrophobic probe showed that adhesion was enhanced as substrate hydrophobicity increased. This suggests that cell adhesion may be promoted due to the increase in hydrophobic adhesion that could enhance protein adsorption. In addition, tumor necrosis factor-α (TNF-α) secretion by lipopolysaccharide (LPS) activated M1 and interleukin-4 (IL-4) activated M2 macrophages was also altered by substrate hydrophobicity. TNF-α production, a marker of pro-inflammatory macrophages, decreased with substrate hydrophobicity. These results suggest that substrate hydrophobic can be used to modulate macrophage responses.

Hydrophobic Hydrogels: Hydrophobic Hydrogels with Fruit‐Like Structure and Functions (Adv. Mater. 25/2019)

Hydrophobic Hydrogels: Hydrophobic Hydrogels with Fruit‐Like Structure and Functions (Adv. Mater. 25/2019)

Hydrophobic Hydrogels with Fruit-Like Structure and Functions.

Normally, a polymer network swells in a good solvent to form a gel but the gel shrinks in a poor solvent. Here, an abnormal phenomenon is reported: some hydrophobic gels significantly swell in water, reaching water content as high as 99.6 wt%. Such abnormal swelling behaviors in the nonsolvent water are observed universally for various hydrophobic organogels containing omniphilic organic solvents that have a higher affinity to water than to the hydrophobic polymers. The formation of a semipermeable skin layer due to rapid phase separation, and the asymmetric diffusion of water molecules into the gel driven by the high osmotic pressure of the organic solvent-water mixing, are found to be the reasons. As a result, the hydrophobic hydrogels have a fruit-like structure, consisting of hydrophobic skin and water-trapped micropores, to display various unique properties, such as significantly enhanced strength, surface hydrophobicity, and antidrying, despite their extremely high water content. Furthermore, the hydrophobic hydrogels exhibit selective water absorption from concentrated saline solutions and rapid water release at a small pressure like squeezing juices from fruits. These novel functions of hydrophobic hydrogels will find promising applications, e.g., as materials that can automatically take the fresh water from seawater.

Amphiphilic microblock tough cationic hydrogels with reduced permeability of the fluid channels: synthesis and properties

The high permeability channels would reduce the ultimate oil production resulting from excess water flooding. The objective of this paper is to prepare and evaluate a novel tough gel that can be used to significantly reduce the permeability of the fluid channels. We synthesized the hydrophobic associated hydrogel composed of poly(acrylamide-co-diacryl quaternary ammonium salts) (G(AM/DiAC)) by simple aqueous solution copolymerization method. Here, three diacryl quaternary ammonium salts are cation surfmer with different alkyl lengths (DiAC, carbon chain length = 6, 8, 10, respectively). The gel properties, including the mechanical performance and swelling property, as well as its influencing factors were investigated. The results showed that G(AM/DiAC) hydrogel has excellent mechanical properties. It was found that its mechanical properties were dependent on the alkyl length and dosage of surfmer. When carbon chain of DiAC was C8 and the dosage of DiAC8 reached 0.5 mol%, G(AM/DiAC8) hydrogel showed the most excellent mechanical performance (tensile strengths = 58.97 kPa, elongation-at-break = 3712% and compressive strengths = 100.01 kPa). The toughness mechanism derived from the increase in the sequence length and number of hydrophobic micro-blocks in the molecular chains of hydrogels. Furthermore, the hydrogels exhibited slow swelling property, in favor of deep migration and plugging high permeable layer. The swelling equilibrium time of hydrogels was prolonged by 10 days when the dosage of DiAC10 reached 0.9 mol%, by reason of the intermolecular dissociation between hydrophobic micro-blocks.

Structure and Properties of Hydrophobic Aggregation Hydrogel with Chemical Sensitive Switch

Hydrogels with chemical sensitive switch have control release properties in special environments. A series of polyacrylamide-octadecyl methacrylate hydrogels crosslinked by N,N′-bis (acryloyl) cystamine were synthesized as potential chemical sensitive system. When this hydrogel encounters dithiothreitol it can change its quality. The properties of the hydrogels were characterized by infrared spectroscopy, contact angle, and scanning electron microscopy. The water absorption of the hydrogel has the maximum value of 475%, when the content of octadecyl methacrylate is 5 wt%. The amount of weight loss was changed from 34.6% to 17.2%, as the content of octadecyl methacrylate increased from 3 wt% to 9.4 wt%. At the same time, the stress of the hydrogel decreased from 67.01% to 47.61%; the strength of the hydrogel reaches to the maximum 0.367 Mpa at 7 wt% octadecyl methacrylate. The increasing content of octadecyl methacrylate from 3 wt% to 9.4 wt% can enhance the hydrophobicity of the hydrogel; the contact angle of water to hydrogel changed from 14.10° to 19.62°. This hydrogel has the porous structure which permits loading of oils into the gel matrix. The functionalities of the hydrogel make it have more widely potential applications in chemical sensitive response materials.

Acellular mineral deposition within injectable, dual‐gelling hydrogels for bone tissue engineering

This study sought to characterize the composition and morphology of acellular mineralization occurring in thermally and chemically gelable hydrogels comprising copolymers of hydrophobic N-isopropylacrylamide as a function of hydrogel hydrophobicity and culture medium formulation. The deposition of calcium phosphate (CaP) mineral was hypothesized to occur with increasing hydrogel hydrophobicity and presence of serum proteins in the culture medium. Two hydrogel compositions with a solid content of 15 and 20 wt % were examined in serum-containing and nonserum-containing media for 0, 14, 28, and 56 days. Using biochemical assays, calcium, but not phosphate content, was found to significantly increase over time in hydrophobic hydrogels soaked in cell culture medium with fetal bovine serum. Significant increases in the calcium to phosphate ratio were observed within these hydrogels from day 0 to 56, with mineralization indicated by von Kossa histological staining. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) were used to analyze CaP mineral characteristics. No crystalline apatitic reflection peaks were observed using XRD, which was supported by the lack of observable mineral deposits as observed using SEM/EDX. However, FTIR showed the presence of new absorption peaks in the serum-containing samples at 28 and 56 days which suggested the formation of an immature apatitic-like mineral. The ability to undergo hydrophobicity-dependent and protein-mediated mineralization demonstrates the potential of these dual-gelling hydrogels as acellular self-mineralizing materials for bone tissue engineering. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 110-117, 2017.

Hydrophobic Hydrogels: Toward Construction of Floating (Bio)microdevices

Hydrogels, formed through cross-linking of hydrophilic polymer chains, represent a class of materials that are capable of holding large volumes of water. Here we report a novel class of hydrophobic hydrogels that can free-float on the surface of different aqueous media by coating conventional hydrogels with a layer of hydrophobic microparticles. We further demonstrate that these floating hydrogel-based devices can be used for sensing applications on liquid surfaces such as the construction of floating pH meters. Moreover, we demonstrate that the floating hydrogels present high mobility with excellent self-assembling property on the surface of water. Importantly, the floating systems reserved the intrinsic biocompatibility of the core hydrogels, enabling microengineering of floating tissue constructs. It is expected that these floating hydrophobic hydrogel-based devices will likely find widespread applications including but not limited to sensing, tissue engineering, and biomedicine.