Polyacrylamide Network Research Articles

Chemical polymerization of pyrrole in the presence of l‐serine or l‐glutamic acid: Electrically controlled amoxicillin release from composite hydrogel

ABSTRACTPolypyrrole (PPy) was chemically prepared from aqueous solutions individually containing l‐serine or l‐glutamic acid, with the addition of ammonium persulfate as the oxidant. The electrical, XPS and FTIR characterizations indicated that the amino acids co‐doped the PPy backbone. TEM revealed that PPy presented a quasi‐spherical morphology with diameters in nanometric scale. The nanostructures of PPy‐glutamic acid efficiently adsorbed therapeutic doses of amoxicillin. Composite hydrogels were obtained by the entrapment of amoxicillin‐loaded PPy in polyacrylamide network. The antibiotic molecules can be subsequently released (or sustained) from composite hydrogel in response to application (or removal) of electrical stimulation. This tuning release profile can lead to promising drug delivery applications such as implantable devices and iontophoretic systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41804.

Reactive macromolecular micelle crosslinked highly elastic hydrogel with water-triggered shape-memory behaviour

Highly stretchable hydrogels based on the micellar copolymerization technique often dissolve in water; they may also become fragile or not exhibit their initially good mechanical performance when submerged in large amounts of water. In addition, the shape-deformation and shape-recovery processes of most reported shape-memory hydrogels need to be carried out at high temperatures. As yet, there have been no published reports on hydrogels which are both highly resilient and have water-responsive shape-memory properties. In this work, a novel, highly elastic polyacrylamide-based hydrogel was developed based on the micellar copolymerization technique using a polymerizable macromolecular micelle with hydrophobic cores locked by hydrogen bonds as a multifunctional crosslinker. The equilibrium water-swelling micelle crosslinked hydrogels still showed highly stretchable behaviour (elongation at break >700%) and even better resilience (almost no hysteresis and residual strains) than the as-prepared hydrogels. Together with the advantages of the highly elastic properties of the hydrogels and the dehydration-induced glass transition of the polyacrylamide network, the hydrogels also have a water-responsive shape-memory behaviour, which can be realized under mild and “green” conditions, i.e., in air and water at room temperature.

Robust and selective nano cavities for protein separation: An interpenetrating polymer network modified hierarchically protein imprinted hydrogel

In the present work, we report a novel method for the reinforcement of hierarchically structured molecularly imprinted polymer (MIP) for the separation of human serum albumin (HSA) and immunoglobulin G (IgG) proteins under pressure driven flow conditions. The template proteins (HSA or IgG) were first physically adsorbed at their isoelectric point on the surface of wide pore silica particles. Thereafter, the pore system was filled with a monomer solution and polymerized to form a lightly crosslinked polyacrylamide network covering the protein template. In order to enhance the rigidity of the hydrogels, different type of crosslinkers such as ethylene glycol dimethacrylate (EGDMA), 3,4-dihydroxyphenethylamine (DA) and methylene-bis-acrylamide (MBA), at least partially interpenetrated into the initially made acrylamide base hydrogel leading to formation of an interpenetrating polymer network (IPN). Then the silica matrix was removed to leave highly porous and reinforced MIP. TGA together with FT-IR and TEM analysis supported the interpenetration of the secondary crosslinkers in the initially formed polymer matrix. The compression property of the modified hydrogels as a function of degree of swelling was in the following order: DA>EGDMA>MBA-IPN-modified hydrogel. Batch binding assay verified the capability of the IPN modified MIPs to capture the target proteins. Moreover, solid phase extraction, HPLC and SDS-PAGE revealed that the EGDMA modified MIP could selectively capture and separate the proteins from human serum or fermentation broth.

Fracture of the Physically Cross-Linked First Network in Hybrid Double Network Hydrogels

Fundamental understanding of the fracture process and toughening mechanisms of double network (DN) hydrogels is critical for rational design of the next generation of tough DN gels with desirable mechanical properties. However, current knowledge of DN gels from synthesis methods to toughening mechanisms mainly comes from chemically cross-linked DN gels. Little is known about hybrid physically chemically cross-linked DN gels. Herein, we synthesize tough DN hydrogels by combining two types of cross-linked polymer networks: a physically cross-linked first network of agar and a covalently cross-linked second network of polyacrylamide (PAM). The resulting Agar/PAM DN gels achieved high toughness of 500–1000 J/m2. More importantly, we reveal several differences and similarities between hybrid Agar/PAM DN gels and chemically linked PAMPS/PAM DN gels. First, different from the nearly velocity-independent mechanical properties in chemically linked DN gels, hybrid Agar/PAM DN gels show velocity-dependent fracture behaviors and toughness. Second, successive cyclic loading–unloading tests indicate the continuous fracture of the first agar network, instead of a phase transition from continuous to discontinuous in chemically linked DN gels. Third, Agar/PAM DN gels exhibit different yielding and necking behaviors from chemically linked DN gels, including much lower yielding stress/strain, no stable necking platform, and simultaneous necking. We thus propose a chain pulling-out model to interpret the continuous fracture process of the first agar network and associated energy dissipation mechanism for hybrid Agar/PAM DN gels. This work strives to provide a better fundamental understanding of structure–property relationship of DN gels, which help to develop new DN gels with desirable properties.

PAM/graphene/Ag ternary hydrogel: synthesis, characterization and catalytic application

Development of a 3D monolithic ternary composite architecture consisting of polyacrylamide network, functionalized graphene and silver nanoparticles using a facile, fast, and inexpensive water-based approach for highly efficient catalytic applications.

Tissue Engineering: Composite Three‐Dimensional Woven Scaffolds with Interpenetrating Network Hydrogels to Create Functional Synthetic Articular Cartilage (Adv. Funct. Mater. 47/2013)

A 3D woven fiber scaffold infiltrated with an interpenetrating network hydrogel mimics the load-bearing and tribological properties of native cartilage. The woven fiber scaffold, created by X. Zhao, F. Guilak, and co-workers on page 5833, provides controlled tensile and compressive mechanical properties in three dimensions, while the infused hydrogel, consisting of an interpenetrating network of alginate and polyacrylamide, provides high toughness and a low coeffecient of friction. This biomimetic, fiber-reinforced composite structure has potential as an acellular or cell-based replacement for cartilage.

A Simple Preparation of a Stable CdS-Polyacrylamide Nanocomposite: Structure, Thermal and Optical Properties

A facile approach was employed for the preparation of stable luminescent nanocomposites of CdS quantum dots (QDs) and polyacrylamide (PAM) through the cross coupling chemistry. Initially, CdS QDs were synthesized in a well controlled manner using 3-mercaptopropionic acid as a capping agent. Then, carboxylic acid groups on CdS QDs were chemically incorporated into PAM matrices with the assistance of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride and N-hydroxysulfosuccinimide coupling agents. FT-IR analysis was used to investigate the chemical incorporation of CdS QDs in PAM matrices via the covalent protocol. The XPS elemental mapping studies further suggested the formation of CdS-PAM nanocomposites. FE-SEM and TEM images were engaged to study the morphologies, and distribution of CdS QDs in the PAM networks. The physical structure of the CdS-PAM nanocomposites was investigated by XRD analysis. Thermal stability of the nanocomposites was observed to be enhanced in compare to PAM as evidenced from TGA data. The UV-vis and photoluminescence studies of the CdS-PAM nanocomposites suggested their promising optical applications.

VOCs abatement using thick eggshell Pt/SBA-15 pellets with hierarchical porosity

Mechanically stable 3-D pellets made of mesoporous SBA-15 silica fibers containing highly dispersed platinum nanoparticles have been successfully synthesized with the aid of a sacrificial polyacrylamide network using a gel-casting deposition technique. The pellets exhibit a hierarchical porosity, with spaces of 3 microns among the silica fibers, and a core–shell distribution of Pt, with an outer Pt-rich layer of 450 microns accounting for over 73% of the Pt. Both factors (hierarchical structure and concentration of the catalyst on the outer pellet surface) facilitated reactant access to the catalyst centers, and as a consequence an excellent catalytic activity toward the total oxidation of n-hexane, used as a VOC model. There was no measurable loss of activity after 70h on stream and the subsequent examination of the catalyst revealed that interparticle coalescence of Pt nanoparticles was largely prevented due to the encapsulation of the noble-metal particles within the silica mesochannels.

Highly Elastic and Superstretchable Graphene Oxide/Polyacrylamide Hydrogels

Graphene oxide (GO)/polyacrylamide (PAM) hydrogels with highly elastic and superstretchable mechanical behavior is fabricated by the synergistic effects of a Ca2+-induced GO crosslinking network, chemically crosslinked PAM network, and entanglements between these networks via hydrogen-bonding interactions. This new nanocomposite material may broaden the applications of hydrogels in the biomedical field and take us closer to artificial biotissues. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Performance and biocompatibility of extremely tough alginate/polyacrylamide hydrogels

Although hydrogels now see widespread use in a host of applications, low fracture toughness and brittleness have limited their more broad use. As a recently described interpenetrating network (IPN) of alginate and polyacrylamide demonstrated a fracture toughness of ∼9000 J/m2, we sought to explore the biocompatibility and maintenance of mechanical properties of these hydrogels in cell culture and in vivo conditions. These hydrogels can sustain a compressive strain of over 90% with minimal loss of Young's Modulus as well as minimal swelling for up to 50 days of soaking in culture conditions. Mouse mesenchymal stem cells exposed to the IPN gel-conditioned media maintain high viability, and although cells exposed to conditioned media demonstrate slight reductions in proliferation and metabolic activity (WST assay), these effects are abrogated in a dose-dependent manner. Implantation of these IPN hydrogels into subcutaneous tissue of rats for 8 weeks led to mild fibrotic encapsulation and minimal inflammatory response. These results suggest the further exploration of extremely tough alginate/PAAM IPN hydrogels as biomaterials.

PH-dependent structure and photochromic properties of phosphomolybdic acid/polyacrylamide composite films

A series of nanocomposite films with different pH were constructed by entrapped phosphomolybdic acid (PMoA) into polyacrylamide (PAM) networks. The structure, photochromic properties and mechanism of composite films were studied with transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet–visible spectra (UV–vis) and X-ray photoelectron spectroscopy (XPS). The results indicated that pH had a significant effect on the microstructure and photochromic properties of composite films. The TEM image showed that PMoA particles changed from well dispersed sphere-shape to irregular similar ball-shape with the increase of pH. XRD pattern showed that PMoA changed from crystal phase to amorphous phase with pH increased. The FT-IR results revealed that the octahedral structure of PMoA was destroyed with the increase of pH. PMoA/PAM films with pH 2 had higher photochromic efficiency than those films with other pH value. According to XPS, the different photochromic properties were caused by the microstructure change of the heteropoly compound with different pH value.

Tuning Mechanical Properties of Chondroitin Sulfate‐Based Double‐Network Hydrogels

SummaryHigh strength double‐network (DN) biopolymer‐based hydrogels were created using copolymers of methacrylated chondroitin sulfate (MCS) and poly(ethylene glycol) diacrylate (PEGDA) as the first network and polyacrylamide (PAAm) as the second network. The concentration and cross‐linking of the networks were adjusted to control the mechanical properties including the failure stress, failure strain, Young's modulus, and yielding behavior. First, we increased the cross‐linking of the first network both by increasing the MCS concentration from 13 to 20 wt% and by copolymerizing MCS with 2 to 6 wt% PEGDA. The additional cross‐linking increased the Young's modulus as much as five times, reaching 3.3 MPa, and the failure stress up as much as four times, reaching 2.9 MPa. However, this also reduced failure strain from a high of 2.9 mm/mm to a low of 0.12 mm/mm and diminished the yielding region. Changes in the concentrations of acrylamide or its cross‐linking with N,N′‐methylenebisacrylamide (BIS) in the second network had a lesser effect on the DN properties. We hypothesized that to obtain a yielding region which results in high toughness, we need to alter the cross‐linking of the first network such that the yield stress of the MCS‐PEGDA/PAAm DN does not exceed the failure stress of PAAm network. Because of the wide range of mechanical properties achieved in these DNs with limited changes in the swelling degrees, unlike conventional single‐network gels, the DN approach allows attainment of a much greater range of mechanical behavior than is possible with single networks.

Synthesis of multiple-shell porous CeO2 hollow spheres by a hydrogel template method

CeO2 hollow spheres with porous multiple-shell were synthesized via a simple electric-current assisted template method. Dense polyacrylamide network, as the template, plays an important role in the formation of the porous and hollow CeO2 spheres, such as providing favorable nucleation sites for the formation of Ce(OH)3 nanocrystals, controlling the size of the aqueous domains, and limiting crystal arrangement in the domains. Furthermore, the interaction between Ce3+ ions and amide groups of the polyacrylamide was the driving force for the self-assembly of the crystals, resulting in the porous Ce(OH)3 hollow spheres. The effects of the reaction parameters on the morphology, size and number of the shells of the porous hollow structures were investigated, and the formation mechanism of the hierarchical porous CeO2 hollow spheres was proposed.

Strain-induced reversible isotropic–anisotropic structural transition of imogolite hydrogels

Robust hydrogels have been developed by addition of imogolite, a perfect rigid polyelectrolyte with a nanotube shape, into polyacrylamide networks. It was revealed that the obtained gel exhibited the distinct isotropic–anisotropic structural transition in response to small tensile strain. The birefringence as large as about 7 × 10−5 due to the anisotropic diffraction appeared/disappeared reversibly upon stretching and releasing the gels in-between of 3 and 0 mm/mm strain.

Double-Network Strategy Improves Fracture Properties of Chondroitin Sulfate Networks.

A tough and ductile, ultrathin film, double-network (DN), biopolymer-based hydrogel displaying the yielding phenomenon was synthesized from methacrylated chondroitin sulfate (MCS) and polyacrylamide (PAAm). The DN of MCS/PAAm exhibited a failure stress more than 20 times greater than the single network (SN) of either MCS or PAAm and exhibited yielding stresses over 1500 kPa. In addition, the stress-strain behavior with a yielding region was also seen in a hydrogel of MCS and poly(N,N-dimethyl acrylamide) (PDMAAm). By replacing PAAm with PDMAAm, interactions known to toughen networks are removed. This demonstration supports the idea that the brittle/ductile combination is key to the DN effect over specific interactions between the networks. The MCS/PAAm and MCS/PDMAAm DN hydrogels had comparable mechanical properties to the archtypal DN hydrogels of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS)/PAAm. In addition, these tough and ductile, biopolymer-based, double-network hydrogels demonstrated a substantial yielding region.

Lamellar–micelle transition in a hydrogel induced by polyethylene glycol grafting

We demonstrate, for the first time, a distinct change of the bulk properties of a hydrogel based on the lamellar–micelle transition. The hydrogel consists of thousands of periodical stacks of bilayer membranes, poly(dodecyl glyceryl itaconate) (PDGI), inside a dilute polyacrylamide network. Along with a bright structure color, the hydrogel exhibits a strong anisotropy in its bulk properties. By grafting a short chain polymer lipid, poly(ethylene glycol) dodecyl ether (C12EO23), to the bilayer membrane, sharp changes in the structure color, swelling and modulus of the hydrogel are observed in a narrow C12EO23 concentration range. These changes are ascribed to the structure transition of the single domain lamellar phase to the multi-domain micelle phase of PDGI, induced by the excluded volume effect of two dimensionally grafted poly(ethylene glycols) (PEG). By controlling the water permeable nano-channels formed during the structure transition, a specific molecular diffusion and recognition are demonstrated. This lamellar bilayer hydrogel could be a new insight into the lipid bilayer system to investigate the nature of biological membranes by the bulk behaviors of hydrogels.

Polyacrylamide gels with ionized functional groups in their selective recognition of trimeric molecular form of human growth hormone

Networks of polyacrylamide with ionized functional groups were studied for the possibility of imprinting of oligomeric form of human growth hormone (hGH). Trimeric molecular form of hGH was molecularly imprinted for the first time. The results show that approximately 35–40 % (w/w) of the templates (depending on polymerization conditions) could be extracted from the molecularly imprinted acrylamide polymers. Artificial gel antibodies against trimeric hGH in the form of granules of hydrogel were compared with granules of non-imprinted polymer. Investigation of the binding to imprinted polymer of the template hormone, other molecular forms of the hormone, and other proteins shows enough high selectivity of artificial gel antibodies.

Investigação do processo de absorção de água de hidrogéis de polissacarídeo: efeito da carga iônica, presença de sais, concentrações de monômero e polissacarídeo

Neste trabalho foi reportada a caracterização de hidrogéis constituídos por metilcelulose (MC) e poliacrilamida (PAAm) preparados pelo processo de reticulação cruzada. As propriedades espectroscópicas e morfológicas foram investigadas por espectroscopia no infravermelho com transformada de Fourier e microscopia eletrônica de varredura, respectivamente. O efeito da carga iônica, presença de sais, concentrações de monômero AAm e polissacarídeo MC na absorção de água e nas propriedades cinéticas dos hidrogéis foi detalhadamente investigado. Os resultados indicaram que o decréscimo da concentração de MC ou aumento da concentração de AAm, carga iônica do contra-íon do sal de cloreto e a presença de fertilizante no meio externo de intumescimento provocaram diminuição significativa na absorção de água dos hidrogéis. O mecanismo de absorção de água dos hidrogéis de PAAm-MC em água seguiu o modelo de difusão Fickiana; já o mecanismo dos hidrogéis intumescidos em sais (cloreto ou fertilizante) seguiu o modelo de transporte anômalo. Pela alta e rápida absorção de água, as matrizes porosas e tridimensionais compostas por PAAm e MC podem em potencial ser aplicadas na agricultura como veículos carreadores.

Gelation Rheology and Water Absorption Behavior of Semi-Interpenetrating Polymer Networks of Polyacrylamide and Carboxymethyl Cellulose

Gelation rheology and swelling behavior of novel semi-interpenetrating polymer network (semi-IPN) hydrogels based on polyacrylamide are described. These hydrogels were prepared by solution cross-linking of partially hydrolyzed polyacrylamide and carboxymethyl cellulose (CMC), using chromium triacetate. Effects of CMC content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels increased with increasing CMC content. Enhancement of storage modulus was more than two times for the semi-IPN gels containing 50 wt% CMC. It was also found that increasing the CMC content decreased the loss factor, indicating that the elastic properties of this gelling system increase more strongly than the viscous properties. The swelling ratio of the semi-IPN gels in tap water, NaCl and CaCl2 solutions, and synthetic oil reservoir water slightly decreased as the concentration of the CMC increased. The improved storage modulus and slightly decreased swelling capacity in oil reservoir water make these semi-IPN hydrogels potentially good candidates for excess water treatment in oil recovery applications.

Preparation of hollow ZSM-5 crystals in the presence of polyacrylamide

Hollow ZSM-5 crystals were successfully synthesized through a simple one-step hydrothermal crystallization method in the presence of polyacrylamide (PAM) as template. The influences of crystallization temperature, PAM concentration, and the type of PAM on the morphology and pore structure of hollow ZSM-5 zeolite as well as the stability and formation mechanism of hollow structure were investigated. Hollow ZSM-5 crystals could be synthesized by adding three types of PAM with different surface groups. Crystallization temperature and PAM concentration played crucial roles in the formation of hollow ZSM-5 crystals. Low crystallization temperature or high PAM concentration was beneficial for the formation of hollow ZSM-5 crystals with embedded large voids in the framework structure. Egg-shell like hollow ZSM-5 crystals formed with less amount of PAM at high temperature due to the decomposition of the PAM network. Moreover, the surface walls of those hollow ZSM-5 crystals possessed microporous crystalline framework. Hollow ZSM-5 crystals exhibited good thermal and hydrothermal stability, and anti-pressure ability. ZSM-5 crystallization in the presence of PAM was in good agreement with the surface-to-core crystallization process. The fast growth of ZSM-5 nuclei on the surfaces of PAM hydrogel resulted in the formation of single crystals with hollow structure after they consumed the synthesis gel and ZSM-5 nuclei in the PAM hydrogel network.