Cuige Lu

Hydrophobically associated hydrogels based on acrylamide and anionic surface active monomer with high mechanical strength

In this work, a physically cross-linked hydrogel (HA gels) with high mechanical strength is synthesized via micellar copolymerization of acrylamide (AAm) and an anionic surface active monomer (surfmer), sodium 9 or 10-acrylamidostearic acid (NaAAS) without any adscititious surfactant or chemical cross-linkers. SEM and DLS characterizations indicate that the surfmer formed multi-micellar aggregates with 80–90 nm diameters above its critical micelle concentration, and serve as a crosslinked-center to endow the obtained hydrogel a robust three-dimensional architecture. Compared with the chemically cross-linked hydrogel, HA gels exhibit unusual swelling–deswelling behavior in water and a pulsatile swelling–deswelling behavior is exhibited with alternating pH changes from 5 to 10 because the presence of carboxyl in the surfmer, demonstrating a smart characteristic of the hydrogel. Moreover, the presence of the surfmer greatly improve the mechanical properties of HA gels. A hydrogel containing 20% (mol/mol) surfmer shows a compression strength of 22.50 MPa at a strain of 90% and can be elongated to 13 times its original length. Furthermore, the HA gels show a significant hysteresis recovery after large deformation, underlying a serious energy-dissipation mechanism. This uncommon swelling behavior and mechanical properties of the HA gels result from its special characteristic of cross-linked units. A self-healing ability is expected for this physical hydrogel in future applications in biotechnology.

In situ hydrogel constructed by starch-based nanoparticles via a Schiff base reaction.

Polysaccharide-based hydrogels are remarkable materials for the biomedical fields because of its excellent biodegradation and biocompatibility. In this work, a novel polysaccharide-based hydrogel was fabricated by in situ crosslinking of starch-based nanoparticles and polyvinylamine. Starch was decorated with cholesterol group and aldehyde groups. TEM and DLS showed that the cholesterol modified oxidation starch (OCS) exhibited a core-shell nanoparticles with mean size of ∼143 nm in aqueous. The hydrogel was then synthesized via Schiff base reaction. Rheological measurements demonstrated the incorporation of cholesterol groups not only reduced the gel time but also improved the storage modulus of the hydrogel compared with the oxide starch crosslinked hydrogel. SEM showed the OCS based hydrogels possess a well-defined porous structure. Furthermore, doxorubicin (DOX) was used as model drug to investigate the control and release properties of OCS hydrogels. This OCS hydrogel would be a promising drug carrier for biomedical applications.

Synthesis of poly(2-(2-methoxyethoxy)ethyl methacrylate) hydrogel using starch-based nanosphere cross-linkers

Biodegradable thermosensitive hydrogels have attracted great interest because of their potential in biomedical applications. Herein, we present a novel, thermoresponsive poly(2-(2-methoxyethoxy)ethyl methacrylate) hydrogels with starch-based nanospheres as cross-linkers (NMH). NMHs exhibit a narrow lower critical phase transition temperature (LCST) range and high mechanical strength compared with conventional, small molecular cross-linked hydrogels (CMH). Fourier transform infrared (FT-IR) spectroscopy confirms that the NMHs are degradable in aqueous medium. The phase transition temperature of the NMHs is ∼4°C compared with ∼25°C for CMH. The NMHs can sustain strength of 12.2MPa, 10 times more than that of CMH. Moreover, the deswelling rate of NMHs is faster than CMH. The different concentrations of nanospheres can efficiently regulate the various properties of NMHs. The NMHs have excellent properties because of its even network structure formed by nanosphere cross-linkers.

Pickering polymerization of styrene stabilized by starch-based nanospheres

Here, we present a novel nanoparticle derivate from natural polysaccharide as a stabilizer for the Pickering polymerization of styrene. In this process, amphiphilic starch-based nanospheres (SNPs) were fabricated from starch octenyl succinic ester through a nanocoprecipitation process as a Pickering stabilizer. The effects of the SNP concentration, size and pH value on the Pickering polymerization are investigated in detail. The polystyrene (PS) particle morphology transforms from bare PS particles to raspberry-like structures with an increase in the SNP content. The linear relationship between the inverse diameter of the PS particles and the SNP content allows for an estimation of the coverage of SNPs on the PS particle surface. Moreover, the size of the PS particles can be regulated by the SNP size. The microstructure of the PS particles can also be regulated by the pH value of the reaction medium. Finally, a possible mechanism for the formation of the PS particles with different morphologies is proposed.

In situ crosslinkable hydrogels formed from modified starch and O-carboxymethyl chitosan

An in situ hydrogel based on oxidation cholesterol starch (OCS) and O-carboxymethyl chitosan (CMCT) that is completely devoid of potentially cytotoxic small molecule cross-linkers and does not require complex manoeuvres or catalysis has been formulated and characterized. The network structure was created by Schiff base formation. The mechanical properties, internal morphology and swelling ability of the injectable hydrogel were examined. Rheological measurements demonstrated that increasing the concentration of the monomer improved the storage modulus. SEM showed that the hydrogel possessed a well-defined porous structure. In addition, the Schiff base reaction was acid sensitive. Under acid conditions, the hydrogel could hydrolyse quickly compared with high pH conditions. Doxorubicin (DOX) was used as a model drug to investigate the control and release properties of the hydrogel. The cytotoxic potential of the hydrogel was determined using an in vitro viability assay with L929 cells as a model and the results revealed that the hydrogel was non-cytotoxic.

Thermally Induced Multimicellar-Aggregate-to-Vesicle Transition for a Dentritic Starch Ester

Smart polymer nanoparticles are of great interest owing to their response for internal or external stimuli, such as pH, temperature, magnetic field, redox potential, light, and so on. Moreover, the introduced intelligent groups can be used as a reversible switch to modulate the hydrophilic/hydrophobic balance, resulting in drastic changes in the sizes and shapes of the final self-assembly aggregates. Some excellent examples have been reported and, based on amphiphatic copolymers, show that the reversible micelle-to-vesicle transition is responsive towards the stimuli of temperature; the time taken for this thermally induced transition can be in the order of weeks. Waxy corn starch is a naturally occurring dentritic polysaccharide that has been a fantastic material in the biomedical field due to its biodegradability, biocompatibility, and high disease site selectivity. However, because of its irregular molecular architecture and higher polydispersity, it is rarely involved in the supramolecular self-assembly system. Herein, we report a fast, thermally induced micelle-tovesicle transition based on natural polysaccharide derivatives (S-NIPAM-AC). The waxy corn starch ester, decorated with a temperature-sensitive group of poly(N-isopropylacrylamide) (PNIPAM), can undergo self-assembly in aqueous media to form a nanosphere. In addition, this large nanoaggregate is composed from unimolecular micelles units, which act as the basic responsive units and reorganize at high temperature to transform the microstructure of nanoaggregates from micelles to vesicles. The commercially available waxy corn starch was firstly grafted with NIPAM by free radical copolymerization using ammonium cerium nitrate as an initiator, and the obtained polymer was then esterified by using acetic anhydride. The structural feature of S-NIPAM-AC (MN (GPC)= 345,000 Da, MW/MN= 3.75, see the Supporting Information, Figure S1) was characterized by H NMR spectroscopy (see the Supporting Information, Figure S2) and illustrated in Scheme 1. The graft ratio of NIPAM and degree of substitution (DS) of acylation (AC) is 25.7 % and 2.41, respectively. The self-assembly of S-NIPAM-AC was conducted by using a nanoprecipitation procedure. Deionized water was added into the stirred THF solution of S-NIPAM-AC followed by volatilization at 20 8C to exhaustively remove the THF, giving a final concentration of approximately 2 mgmL . A typical TEM image of the spherical micelles is shown in Figure 1 A. The amplified TEM photos revealed the fine structures within a large micelle and provided direct evidence that the large micelle is composed by small spherical building units. For dentritic polymers, Yan and Haggs have pointed out that the large micelles are multimicellar aggregates (MA) with the basic building units of unimolecular micelles, and this aggregation may be maintained by the cooperative interaction between hydrogen bond and hydrophobic association interaction during the self-assembly process. In addition, dynamic light scattering (DLS) characterization also indicated the coexistence of nanoparticles with dimensions of around 11 and 175 nm in the aqueous solution of obtained micelles (Figure 1 B). Therefore, we could identify the larger ones as the MA, and the smaller ones as the [a] Dr. Y. Tan, Dr. K. Xu, Dr. C. Lu, Dr. C. Liu, Prof. Dr. P. Wang Key Laboratory of Ecomaterial Polymers Changchun Institute of Applied Chemistry Chinese Academy of Sciences 130022 Changchun (P.R. China) Fax: (+86) 431-526-2629 E-mail : pxwang@ciac.jl.cn Supporting information for this article (including experimental details and additional H NMR/DLS/TEM data) is available on the WWW under http://dx.doi.org/10.1002/chem.201101060. Scheme 1. The potential structural feature of a dentritic starch ester. PNIPAM =poly(N-isopropylacrylamide), Ac= acyl.

The astonishing progress in performance of hydrogel triggered by the structure evolution of cross-linking junctions

Novel microgel composite hydrogels characterized with the structural evolution of crosslinking junctions were prepared. Under the pH stimulus, the high-strength hydrogels exhibit a drastic and sudden volume phase transition, which derives from the dissociation and association of crosslinks.

A novel poly(acrylic acid-co-acrylamide)/diatomite composite flocculant with outstanding flocculation performance

Series of anionic flocculants with outstanding flocculation performance, poly(acrylic acid-co-acrylamide)/diatomite composite flocculants (PAAD) were successfully prepared through aqueous solution copolymerization and applied to flocculate from oil-field fracturing waste-water. The structure of PAAD was characterized by Fourier transform infra-red spectroscopy, (13)C nuclear magnetic resonance and X-ray diffraction tests, and its properties were systematically evaluated by viscometer, thermogravimetry analysis and flocculation measurements. Furthermore, the influences of various reaction parameters on the apparent viscosity of flocculant solution were studied, and the optimum synthesis condition was determined. The novel composite flocculants exhibited outstanding flocculation properties. Specifically, the dosage of composite flocculants that could make the transmittance of treated wastewater exceed 90% was only approximately 12-35 ppm, which was far lower than that of conventional flocculants. Meanwhile, the settling time was lower than 5 s, which was similar to that of conventional flocculants. This was because PAAD flocculants had a higher absorption capacity, and larger chain extending space than conventional linear flocculants, which could refrain from the entanglement of linear polymer chains and significantly improve flocculation capacity.

Dynamic Properties of Polyampholyte Hydrogel Elucidated by Proton NMR Spin-spin Relaxation Time

Abstract1H spin-spin relaxation time(T2) measurement of polyampholyte hydrogel poly(methylacrylic acidacryloyloxyethyl trimethylammonium chloride)[P(MA-DAC)] in different pH, ionic strength and temperature was carried out to reveal the molecular mobility. Spontaneous volume transition of the polyampholyte hydrogel was also investigated by spin-spin relaxation time measurement. Meanwhile T2 and the proton component fraction were acquired to study the swelling behaviour of the hydrogel. Moreover the changes of T2 characterized the molecular mobility of polyampholyte hydrogel in various swelling states. And the results suggest that the mobility of the main chains and a few free side chains(the long T2) of P(MA-DAC) was dominated by the mesh size in the hydrogel network, depending on the swelling ratio(Q) and the mobility of the side chains(the short T2) was influenced by electrostatic interaction between different charges in polymer side chains. Finally the T2 measurements of P(MA-DAC) hydrogel in the spontaneous swelling-deswelling process demonstrated the electrostatic interaction of the charged side chains caused deswelling behavior. At the same time, the mobility state transition temperature of the charged side chains was also studied by the 1H spin-spin relaxation time measurements, and the transition activation energy of the side chains is 2.72 kJ.