Micelle Crosslinked Polyacrylic Acid Hydrogels with Resilience and Self-Recovery Properties

Micelle crosslinking method is one of the several techniques to fabricate hydrogels with good mechanical performance. Micelle crosslinked hydrogels reported so far are fabricated using a multistep preparation process due to the functionalization of block copolymers or surfactants with acrylate, aldehyde, azo, or reversible addition-fragmentation chain transfer groups to create a polymer network. Herein, a simple one-step approach is introduced to produce resilient hydrogels prepared by bulk polymerization of acrylic acid and esterification with Triton X-100 (TX-100) in the presence of catalyst sulfuric acid (H₂SO₄). The advantage of this study is that TX-100 surfactants self-assembling into micelles are directly bonded onto polymer chains through an ester bond without any further modification. The obtained hydrogels exhibit tensile strengths up to 135 ± 8 kPa and compressive strengths up to 16 ± 1 MPa over 94% strains as well as complete self-recovery and high resilience abilities (≈86% at strains up to 400%) originating from hydrophobic associations in the core of micelles acting as dynamic cross-linkers along with hydrogen bonds and entanglements between polymer chains acting as additional crosslink points. The overall results show that the hydrogels can be good candidate as elastic materials in many fields.     

Development of a poly(N‐vinyl‐2‐pyrrolidone)/poly (ethylene glycol) hydrogel membrane reinforced with methyl methacrylate‐grafted polypropylene fibers for possible use as wound dressing

A hydrogel is a polymeric material that exhibits the ability to swell in water and retains a significant fraction of water within its structure, but does not dissolve in water. One of the major problems in the application of these materials is their relatively poor mechanical strength, attributed to the high degree of hydration of the gel. This work was directed to the study of the interactions between hydrophobic and hydrophilized fibers, with the objective of optimization of the mechanical properties of poly(N‐vinyl‐2‐pyrrolidone) membranes. The membranes were prepared by electron‐beam irradiation of an aqueous polymer solution. A nonwoven cloth made of polypropylene matted fiber, grafted with methyl methacrylate, was employed as a reinforcement. The changes in the main properties of the membranes, such as the gel content, swelling characteristics, cytotoxicity, and mechanical behavior, were investigated. The results showed an increase of 800% in tensile strength, without changes in the swelling and cytotoxicity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 662–666, 2002     

The mechanical properties of β‐Si3N4 whiskers‐reinforced dental resin composites

The surface‐modified β‐Si₃N₄ whiskers were used as inorganic fillers to reinforce dental resin (Bis‐GMA/TEGDMA) matrix with filler level ranging from 0 to 60 wt %. The experimental results indicated that the fracture strength of the composites increased from 79.85 to 139.8 MPa with increasing the whiskers loading. The compressive strength, elastic modulus, and rockwell hardness all increased monotonously with increasing filler level. Furthermore, thermal cycling did not decrease the fracture strength of the composites. Moreover, the composites showed good biocompatibility to support MG63 cells adhesion and proliferation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40692.     

Poly(L‐lactic acid) nanocomposites with layered double hydroxides functionalized with ibuprofen

The detrimental effect of cell adhesion on polymer surfaces has been a limiting factor in the medical deployment of many implants. We examined the potential to decrease cell proliferation while simultaneously increasing mechanical performance through Zn–Al layered double hydroxide (LDH) organically modified with ibuprofen dispersed in poly(L ‐lactic acid) (PLLA). These composites are commonly referred to as nanocomposites. The thermophysical and mechanical properties of the hybrids were studied with wide‐angle X‐ray diffraction (WAXD), transmission electron microscopy (TEM), differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and tensile testing. The WAXD and TEM results indicated that intercalated and exfoliated nanocomposites were obtained. The storage modulus, tensile modulus, and ultimate tensile strength were improved. The LDH affected the cold crystallization and reduced the thermal stability of the neat PLLA. Smooth muscle cells were used for in vitro studies of the nanocomposites. It was found that the hybrids reduced cell proliferation, and the amount of cell reduction was related to ibuprofen release. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Highly flame‐retardant polyurethane foam based on reactive phosphorus polyol and limonene‐based polyol

Polyurethane foams are in general flammable and their flammability can be controlled by adding flame‐retardant (FR) materials. Reactive FR have the advantage of making strong bond within the polyurethane chains to provide excellent FR over time without compromising physico‐mechanical properties. Here, phenyl phosphonic acid and propylene oxide‐based reactive FR polyol was synthesized and used along with limonene based polyol for preparation of FR polyurethanes. All the obtained foams showed higher closed cell content (above 96%). By the addition of FR–polyol, the compressive strength of the foams showed 160% increment which could be due to reactive nature of FR–polyol. Moreover, 1.5 wt % of phosphorus (P) content reduced the self‐extinguishing time of the foam from 81 (28% weight loss) to 11.2 s (weight loss of 9.8%). Cone test showed 68.6% reduction in peak heat release rate along with 23.4% reduction in thermal heat release. The change in char structure of carbon after burning was analyzed using Raman spectra which, suggests increment in the graphitic phase of the carbon over increased concentration of phosphorus. It can be concluded from this study that phosphorous based polyol could be blended with bio‐based polyols to prepare highly FR and superior physico‐mechanical rigid polyurethane foams. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46224.     

Organic–inorganic hybrid linseed oil‐based urethane oil wood coatings

To prepare alkoxysilane‐functionalized urethane oil (AFUO) using linseed oil, 3‐aminopropyltriethoxysilane (APTES) was first reacted with diisocyanate to obtain an NCO‐terminating oligomer. The reaction was continued by adding linseed oil glyceride to form an AFUO prepolymer. The auto‐oxidative drying coating was obtained after adding a metal dryer to the AFUO prepolymer. Urethane oil (UO) coating, as a control, was obtained by the same procedure as that for AFUO, but without containing alkoxysilane‐functional groups in the formation. Siloxane hybrid urethane oil (SHUO) wood coatings were prepared by mixing tetraethyl orthosilicate (TEOS) solutions, as an external crosslinking agent by sol–gel process, with the AFUO and UO coatings. We found that introducing of APTES into the molecular chains of the UO coating resulted in a film with superior impact and abrasion resistance, and it is the most efficient process to enhance the UO films. The addition of TEOS into AFUO coatings shortened the curing time and further improved the crosslinking density of the AFUO films; however, the physical properties like impact resistance, bending resistance, and gloss were even worse than AFUO films. Mixing of TEOS and UO coating also shorten the curing time and improved the heat resistance, lightfastness, and hardness of the UO coating. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44562.     

Tunable transport of glucose through ionically‐crosslinked alginate gels: Effect of alginate and calcium concentration

Alginate beads have numerous biomedical applications, ranging from cell encapsulation to drug release. The present study focuses on the controlled release of glucose from calcium‐alginate beads. The effects of alginate concentrations (1–6 wt %) and calcium chloride concentrations (0.1–1.0M) on glucose release from beads were examined. It was found that the time required for complete glucose release from beads could be tuned from 15 min to over 2 h, simply by varying alginate and calcium chloride concentrations in beads. For calcium‐alginate beads with sodium alginate concentrations of 1–4 wt %, higher sodium alginate concentrations lead to more prolonged release of glucose and thus a smaller value of a rate constant k, a parameter shown to be proportional to the diffusion coefficient of glucose in the alginate gel. For beads with sodium alginate concentrations of 4–6 wt %, there was no statistically significant difference in k values, indicating a lower limit for glucose release from calcium‐alginate beads. Similarly, higher calcium chloride concentrations appear to extend glucose release, however, no conclusive trend can be drawn from the data. In a 50 : 50 mixture of calcium‐alginate beads of two different alginate concentrations (1 and 4 wt %), glucose release showed a two‐step profile over the time range of 20–50 min, indicating that the pattern and time of glucose release from beads can be tuned by making combinations of beads with varying alginate and/or calcium chloride concentrations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Designing Starch‐Based Nanospheres to Make Hydrogels with High Mechanical Strength

A robust method to prepare hydrogels with high mechanical strength is presented. Core/shell nanospheres with derivatizable allyl groups in the shell were first prepared. Starch‐based nanospheres were used as crosslinker to prepare polyacrylamide hydrogels. The starch‐based nanospheres were bridged by acrylamide to form crosslink points in the hydrogel network. They possess an extremely high mechanical strength. The results show that starch‐based nanosphere hydrogels can sustain strengths of 10.34 MPa, which is 60 times greater than for a normal hydrogel. The mechanical properties of SNH can be tailored by varying the content of SN. This approach offered a new way of making functional hydrogel with biodegradable component as a substitute for tissue.

     

Tuning the Mechanical Properties of BIEE‐Crosslinked Semi‐Interpenetrating,Double‐Hydrophilic Hydrogels

Double‐hydrophilic, semi‐interpenetrating (semi‐IPN) hydrogels are synthesized by encapsulating hydrophilic polyvinylpyrrolidone (PVP) linear chains in structure‐defined 1,2‐bis‐(2‐iodoethoxy)ethane (BIEE)‐crosslinked (poly(2‐(dimethylamino)ethyl methacrylate) (pDMAEMA) hydrogels. A series of semi‐IPN double‐hydrophilic hydrogels are prepared in which the pDMAEMA/BIEE content is kept the same and only the PVP content is varied, from 0 up to 33 wt%. The mechanical properties of the water‐swollen hydrogels are experimentally evaluated under unconfined compressive loading conditions, while a nonlinear hyperelastic constitutive equation is used to predict their mechanical response. No significant difference is found in the mechanical response of the semi‐IPN PVP/pDMAEMA/BIEE hydrogel containing 5 wt% PVP compared to the pDMAEMA/BIEE analog, however, for greater loading percentages (15 and 33 wt% of PVP), the semi‐IPN hydrogels exhibit less stiffness/higher ductility. Furthermore, in vitro biocompatibility studies are carried out for the pDMAEMA/BIEE and the semi‐IPN PVP/pDMAEMA/BIEE, indicating that both the formulations exhibit no toxicity in cultured cells.     

Hydrogels from scleroglucan and ionic crosslinkers: Characterization and drug delivery

The polysaccharide scleroglucan (Sclg), exploited as a matrix suitable for modified drug delivery, was crosslinked in the presence of three ions: borate, aluminum, and iron. A rheological investigation indicated the main differences between the hydrogels in their viscoelastic linear response: the Sclg/borax system showed the highest strength when deformed by elongation, whereas the strength of the other systems broke down, in terms of viscosity, at much lower values of the imposed strain. Tablets prepared from the gels showed remarkable differences in their water uptake and dimensional swelling. On the other hand, the tablets, loaded with drugs of different steric hindrances, showed similar release behavior, regardless of the crosslinking agent. Scanning electron microscopy analysis was related to the delivery and rheological profiles. Texture analysis, carried out on tablets swollen for 5 h, showed different values of cohesion. Furthermore, when the generalized Maxwell model was applied to the relaxation data, the obtained mechanical spectra showed a more pronounced solidlike character of the Sclg/iron network in comparison with the prevailing viscous behavior of the other matrices. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Poplar wood–methylol urea composites prepared by in situ polymerization. II. Characterization of the mechanism of wood modification by methylol urea

A prepolymer was used to prepare wood/prepolymer composites by a pulse‐dipping machine. The mechanical properties and dimensional stability were evaluated. The characterization of natural and modified woods was performed by Fourier transform infrared spectroscopy, ¹³C‐NMR spectroscopy, X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) with energy‐dispersive X‐ray analysis (EDXA). Cross‐polarization/magic‐angle spinning ¹³C‐NMR analysis revealed that the in situ polymerization between the prepolymer and the hydroxyls in the wood structure took place with the reduction of hydroxyl groups. XPS analysis indicated that the content of carbon decreased, whereas the content of oxygen increased. SEM–EDXA indicated a good dispersion of the modifier in the wood fiber and other vertical cells. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42406.     

Rheological behavior of alginate solutions for biomanufacturing

The rheological behavior of alginate solutions were investigated for the optimal design of a biomanufacturing system to produce alginate structures for tissue engineering. Its rheological properties were determined by a rheometer through rotational and oscillatory tests. Experimental results were used to model the alginate solutions characteristics. The findings suggest that alginate solutions undergo shear‐thinning effects with increasing shear rates. It is also possible to observe that its loss modulus is higher than the storage modulus ones being both modulus dependent upon the frequency, which is a typical characteristic of dilute solutions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Some Mechanical Properties of Poly[(acrylic acid)‐co‐(itaconic acid)] Hydrogels

Two series of hydrogels of poly[(acrylic acid)‐co‐(itaconic acid)] have been prepared by copolymerization in solution using tetrafunctional N,N′‐methylenebisacrylamide (NMBA) as cross‐linker. The resulting polymer was swollen in water at 298 K to yield homogenous transparent hydrogels. These hydrogels were characterized in terms of swelling and compression‐strain measurements. The influence of the comonomer composition and concentration of cross‐linking agent on volumetric swelling and the mechanical properties of these hydrogels were investigated. Inefficient cross‐linking is indicated by the small values of ν_e relative to the theoretical cross‐linking densities.

Dependence of measured affective cross‐linking density (ν_e) on the theoretical cross‐linking density (ν_t) for acrylic acid/itaconic acid hydrogels prepared at a fixed composition of AA80/AI20 wt.‐%, but at different concentrations of NMBA.     

Zinc ion‐induced formation of hierarchical N‐succinyl chitosan film

A series of N‐succinyl Chitosan (NSCS) hydrogel derived from different substitution degree of NSCS were fabricated through the zinc ions crosslinking. Subsequently, a light‐weight, transparent, and hierarchical NSCS‐Zn(II) film was obtained by drying the hydrogel. The hierarchical structure of NSCS‐Zn(II) film was confirmed by scanning electron microscopy. The NSCS‐Zn(II) film exhibited excellent mechanical strength because of the preferential formation of the alignment structure. The tensile strength and Young's modulus reaches 119.3 MPa and 2.67 GPa when the NSCS substitution degree was 91.95%. Furthermore, a remarkable and enhanced broad‐spectrum bactericidal properties of the NSCS‐Zn(II) film was revealed through E. coli and S. aureus exposure, respectively. These features indicated that NSCS‐Zn(II) film is a promising material that can be used in biomedical engineering. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44664.     

Improvement of the mechanical properties of chitosan‐alginate wound dressings containing silver through the addition of a biocompatible silicone rubber

The benefits of associating chitosan with alginate for the production of wound dressings are well documented. However, the mechanical resistance of these devices is limited. This work aimed to improve the mechanical properties of chitosan‐alginate membranes both with and without the microbicide agent AlphaSan^® RC2000 (silver sodium hydrogen zirconium phosphate) by incorporating the liquid silicone rubber Silpuran^® 2130 A/B. Membranes containing AlphaSan^® RC2000 but without Silpuran^® 2130 A/B have increased opacity, thickness, and water absorption, but low stability in water and tensile strength. The silicone gel remained in the structure of the formulations even after successive washing steps and its inclusion in the membranes reduced their thickness and swelling in aqueous media, improving their homogeneity, adhesiveness, stability, tensile strength, and flexibility. Thus, the addition of Silpuran^® 2130 A/B proved to contribute positively to many relevant, particularly mechanical, properties of chitosan‐alginate wound dressings whether or not they contained AlphaSan^® RC2000. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41686.     

Properties of soy protein isolate/poly(ethylene‐co‐ethyl acrylate‐co‐maleic anhydride) blends

Blends of soy protein isolate (SPI) with 10, 20, 30, 40, and 50% poly(ethylene‐co‐ethyl acrylate‐co‐maleic anhydride) (PEEAMA), with or without addition of 2.0 wt % methylene diphenyl diisocyanate (MDI), were prepared by mixing with an intensive mixer at 150°C for 5 min, and then milling through a 1‐mm sieve. Blends were then compression‐molded into a tensile bar at 140°C. Thermal and mechanical properties and water absorption of the blends were studied by differential scanning calorimetry (DSC), dynamical mechanic analysis (DMA), a test of modulus and tensile strength (with an Instron tensile tester), a water absorption test, and scanning electron microscopy (SEM). The blends showed two composition‐dependent glass transition temperatures. Furthermore, as the SPI content increased, the melting temperature of PEEAMA remained constant but the heat of fusion decreased. These results indicate that SPI and PEEAMA were partially miscible. Morphology observations support these results. Increasing the PEEAMA content resulted in decreases in the modulus and tensile strengths and increases in the elongation and toughness of the blends. Water absorption of the blends also decreased with increased PEEAMA content. Incorporating MDI further decreased the water absorption of the blends. The mechanism of water sorption of SPI was relaxation controlled, and that of the blends was diffusion controlled. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 407–413, 2003     

Fragrance‐Containing Microcapsules Based on Interfacial Thiol‐Ene Polymerization

In this study, microcapsules containing fragrance oils as active agent were synthesized by interfacial thiol‐ene polymerization in oil‐in‐water emulsion. One water‐soluble dithiol and four oil‐soluble acrylates were used as “click”able monomers. The polymerization kinetics was studied by HPLC and ¹H‐NMR. The size and morphology of the microcapsules were characterized by means of light scattering, optical microscope, and scanning electron microscope, and their thermal property was examined by TGA. The encapsulation efficiency and stability of the microcapsules were monitored at room temperature and 45 °C for 1 month. In general, this interfacial thiol‐ene polymerization was demonstrated to be a facile and efficient approach for fragrance microencapsulation with new and stable shell materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43905.     

Near‐Infrared Light‐Triggered Dual Drug Release Using Gold Nanorod‐Embedded Thermosensitive Nanogel‐Crosslinked Hydrogels

Gold nanorod (AuNR)‐embedded poly(N‐isopropylacrylamide) (PNIPAM) hydrogels offer the possibility of achieving near‐infrared (NIR) light‐triggered drug release. In addition, using nanoparticles as a crosslinker can enhance the mechanical properties of PNIPAM hydrogels, and nanoparticle‐crosslinked hydrogels provide an important approach for dual drug release. Here, NIR light‐triggered dual drug release using AuNR‐embedded thermosensitive nanogel‐crosslinked hydrogels is reported for the first time. Two kinds of drugs are encapsulated, one in the nanogel and the other in the hydrogel. The volume phase transition of the PNIPAM hydrogels is induced by NIR light by utilizing the photothermal effect of AuNRs. By changing the number of embedded AuNRs and the intensity of NIR light, the release rate and drug quantity can be adjusted for on‐demand release. Because of its NIR light‐triggering and nanoparticle‐crosslinking capabilities, AuNR‐embedded thermosensitive nanogel‐crosslinked hydrogels may expand the application scope of hydrogels and provide enhanced properties in their applications.