A simulation method to analyze chemo‐mechanical behavior of swelling‐induced shape‐memory polymer in response to solvent

A network of thermally responsive shape‐memory polymers (SMPs) could imbibe a quantity of solvent molecules to swell, and subsequently induces a chemical potential change in polymer. When an equilibrium is reached between the mechanical load and the chemical potential of polymer network and solvent, the SMP polymer usually swells with a field of inhomogeneous and anisotropic deformation, which is considered to be equivalent to a hyperelastic field. We implement this theory in the free‐energy function equation, and analyze examples of swelling‐induced deformation and shape recovery behavior. This work may provide a powerful tool to study complex swelling‐induced shape‐memory behavior of SMPs in response to the immersing solvents. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Release of fluorescent markers from phase‐separated gelatin‐maltodextrin hydrogels

Genipin‐crosslinked gelatin‐maltodextrin phase‐separated hydrogels consisting of gelatin‐continuous or bicontinuous microstructures were developed to regulate swelling and release behavior of four fluorescent markers of varying molecular weights [(fluorescein (332 Da) and FITC‐dextrans (FD) (4000–250,000 Da)]. Bicontinuous hydrogels showed significantly greater swelling than gelatin‐continuous hydrogels under all conditions (at pH 1.5 and 7.4 and three genipin/gelatin crosslinking ratios) (P < 0.05). With both microstructures, fluorescein showed the largest release rate and total release followed by FD 4000 Da, FD 40,000 Da, and FD 250,000 Da (P < 0.05). Marker molecular weight, pH, and crosslink ratio all affected the rate and amount of release. The mode of transport for the solvent and all markers was Fickian or slightly anomalous, with diffusional exponent (n) values ranging from 0.35 to 0.64. These results demonstrated that with the proper combination of crosslink density, solvent pH, and microstructure, hydrogels with a specified swelling behavior may be developed. This, coupled with a marker of appropriate size, can lead to controllable levels and rates of release. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

温度和pH响应型水凝胶的制备及性能研究

采用双丙酮丙烯酰胺、丙烯酰胺和丙烯酸为原料,以N,N'-亚甲基双丙烯酰胺为交联剂,2-酮戊二酸为光引发剂,采用光引发聚合方法制备了具有温度和pH响应型水凝胶。研究了水凝胶在不同温度和pH条件下的溶胀性能。结果表明,随着温度的升高,水凝胶的溶胀率降低,随着pH的增加,水凝胶的溶胀率增加,表现出明显的温度、pH双重响应性。     

Dual‐responsive semi‐interpenetrating network beads based on calcium alginate/poly(N‐isopropylacrylamide)/poly(sodium acrylate) for sustained drug release

To improve the mechanical strength of natural hydrogels and to obtain a sustained drug‐delivery device, temperature‐/pH‐sensitive hydrogel beads composed of calcium alginate (Ca‐alginate) and poly(N‐isopropylacrylamide) (PNIPAAm) were prepared in the presence of poly(sodium acrylate) (PAANa) with ultrahigh molecular weight (M_η ≥ 1.0 × 10⁷) as a strengthening agent. The influence of PAANa content on the properties, including the beads stability, swelling, and drug‐release behaviors, of the hydrogels was evaluated. Scanning electron microscopy and oscillation experiments were used to analyze the structure and mechanical stability of the hydrogel beads, respectively. The results show that stability of the obtained Ca‐alginate/PNIPAAm hydrogel beads strengthened by PAANa the alginate/poly(N‐isopropyl acrylamide) hydrogel bead (SANBs) was significantly improved compared to that of the beads without PAANa (NANBs) at pH 7.4. The swelling behavior and drug‐release capability of the SANBs were markedly dependent on the PAANa content and on the environmental temperature and pH. The bead sample with a higher percentage of PAANa exhibited a lower swelling rate and slower drug release. The drug release profiles from SANBs were further studied in simulated intestinal fluid, and the results demonstrated here suggest that SANBs could serve as a potential candidate for controlled drug delivery in vivo. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

HPMC水凝胶溶胀性能的影响因素研究

制备了一系列具有不同相对分子质量和取代度的羟丙基甲基纤维素(HPMC)水凝胶,并用称重的方法对凝胶的溶胀性能进行了研究,考察了温度、pH值、溶剂类型、取代度和相对分子质量对HPMC水凝胶溶胀性能的影响。结果显示,HPMC水凝胶的平衡溶胀度随温度的升高而减小;其溶胀行为受溶剂影响显著,而受溶液pH值的影响不明显;而取代度和相对分子质量都对凝胶溶胀行为有较大的影响。     

Swelling behavior of chitosan/poly(acrylic acid) complex

This study investigates the improved swelling behavior of chitosan/poly(acrylic acid) complex by solvent (methanol, ethanol, and acetone) extraction. The complex is developed by photoinitiated free‐radical polymerization of acrylic acid in the presence of chitosan. The swelling ratio of the complexes depends on the cosolvency effect of poly(acrylic acid) to the extracted solvent, which in turn affects the polymer network structure and ionic states characterized by dynamic force microscopy (DFM), Raman, and FT‐IR spectroscopy. The DFM investigation displays the improved structural changes of the polymer network structure after solvent extraction and its relation to the improved swelling property of the chosen system in different environmental conditions (pH, solvent, and salt concentration) are discussed. A high swelling ratio of about 600 times its dry weight is observed in water as well as in low salt and solvent concentration after methanol extraction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2930–2940, 2004     

Gum arabic–acrylic superabsorbing hydrogel hybrids: Studies on swelling rate and environmental responsiveness

The swelling rate and the environmental sensitivity of novel superabsorbent gum arabic–acrylic hydrogel hybrids were investigated. The swelling kinetics of the hydrogel hybrids was studied by means of a Voigt‐based viscoelastic model. The effects of concentration of the initiator, crosslinker, and the monomer ratio on the swelling rate were studied. The superswelling properties of the hydrogel hybrids were evaluated in various environmental pH, salinity and solvent–water mixtures. The optimally prepared hydrogel, MR5, showed a reproducible on–off switching behavior when the swelling medium was alternatively changed between distilled water and alkaline solutions. The hydrogel hybrid MR5 was also tested to be swollen and deswollen alternatively in distilled water and sodium chloride solution. The sorption–desorption behavior was found to be quite repeatable. A similar capability was interestingly observed when a calcium chloride solution with the same molar concentration was used. The swelling changes of the hydrogel hybrid were examined in various water–solvent systems including the aqueous solutions of methanol, ethanol, acetone, ethylene glycol, glycerol, and dimethylsulfoxide. One and/or two volume‐phase transitions were induced by the nonsolvents. The transitions were explained according to the solubility parameters of the solvents and water–solvent mixtures. The swelling–deswelling capability of the hydrogel in alternatively changed solvent–water mixtures was also studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5667–5674, 2006     

pH敏感性P(AAm-co-AA)半互穿网络水凝胶的制备、表征及溶胀动力学研究

以N,N-亚甲基双丙烯酰胺(N,N-MBA)为交联剂、过硫酸钾(KPS)为引发剂,采用自由基交联共聚法合成了具有pH敏感性的半互穿网络水凝胶聚丙烯酰胺-co-丙烯酸[P(AAm-co-AA)],通过傅立叶红外光谱、差热分析研究了水凝胶的结构及热稳定性.水凝胶的溶胀研究表明,随着缓冲溶液pH值的增大平衡溶胀率增大;在不同...     

The effect of PEG(400)DA crosslinking agent on swelling behaviour of acrylamide-maleic acid hydrogels

Summary Acrylamide (AAm)-maleic acid (MA) hydrogels with different monomer ratios were prepared in an aqueous solution by radical polymerization using a new crosslinking agent, polyethyleneglycol (400) diacrylate (PEG (400) DA) and also using N, N’-methylenebisacrylamide (NMBA) for comparison purpose. The hydrogels were characterized by acid group content and FTIR spectroscopy. Their swelling and deswelling behavior were studied as a function of maleic acid content, pH and crosslinking agent. Incorporation of MA in hydrogels significantly increased their swelling ability and their equilibrium degree of swelling (EDS) values changed between 100–269 g water/g polymer in water while AAm polymers swollen less (22–23 g water/g polymer). The AAm hydrogels showed Fickian type diffusion but the all AAm-MA hydrogels showed non-Fickian type behavior. Their swelling degree increased with the increase of pH of the external medium and an instantaneous increase was observed near a pH value of 7.0. The use of PEG (400) DA instead of NMBA as a crosslinking agent also increased the swelling rate and capacity of the gel. The swelling constant (K) and the diffusion coefficient (D) of hydrogels were also increased. The swelling-deswelling cycles in acidic-basic solutions showed that they could be used as pH responsive gels without any decrease in swelling capacity.     

Swelling behavior of crosslinked hydroxypropylcellulose films retaining cholesteric liquid crystalline order,II. Effects of temperature,solvent, and pH

Crosslinked hydroxypropylcellulose (HPC) films were cast from the cholesteric liquid crystalline HPC solution in methanol. The films retained the cholesteric liquid crystalline order. The dependences of swelling behavior of our films in water and propanol on temperature and on pH of the solvent were determined. The response of our films to the changes in water, temperature and in pH was discussed. In water, the equilibrium swelling ratio (B_e) decreased with temperature whereas B_e increased with temperature in propanol. For a given composition of water and propanol, B_e was independent of temperature. B_e in the acidic solvents was higher than in the alkaline solvents. The response data to the stepwise change in temperature revealed that the deswelling behavior was more rapid than the swelling behavior in water, and the swelling-deswelling behavior was reversible. The response to the stepwise change in pH was almost the same as that of the change in temperature, but the surface of the film was attacked by the acid and became fluffy with increasing soaking time.     

Characterization and caffeine release properties of N‐isopropylacrylamide/hydroxypropyl methacrylate copolymer hydrogel synthesized by gamma radiation

Research efforts have been devoted to demonstrate that the temperature sensitivity characters of poly(N‐isopropylacrylamide)(PNIPAAm) can be applied in the field of drug carriers. A copolymer hydrogel of N‐isopropylacrylamide/hydroxypropyl methacrylate (NIPAAm/HPMA) was synthesized by gamma irradiation. The nature of bonding was characterized by FTIR spectroscopy, whereas the thermal stability was characterized by thermogravimetric analysis (TGA). The influence of NIPAAm/HPMA composition on the swelling properties in water, at different temperatures and different pH values was studied. The release characters of caffeine drug from NIPAAm/HPMA hydrogels were also investigated. The gel fraction of NIPAAm/HPMA was found to increase slightly by increasing the ratio of HPMA in the initial solution. The IR spectra indicate the formation of copolymer hydrogels, whereas the TGA study showed that the NIPAAm/HPMA copolymer hydrogels displayed higher thermal stability than NIPAAm hydrogel. PNIPAAm hydrogel showed higher swelling in water than NIPAAm/HPMA hydrogels. Based on Fick's law, it was demonstrated that the diffusion of water into NIPAAm/HPMA is controlled. It was found that the main parameters affecting the drug release behavior from the hydrogels are composition and pH. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of ultrastable eu‐complex/polystyrene composite luminescent nanoparticles using a solvent swelling method

Nanoparticles composed of Eu‐complex, Eu(TTA)₃Phen, and polystyrene (PS) were successfully synthesized through an improved solvent swelling method. The unstable Eu(TTA)₃Phen could be protected by the hydrophobic shell of PS nanoparticles. This method is very appropriate to embed unstable luminescent molecules into polymer nanoparticles. The as‐synthesized luminescent PS nanoparticles have been turned out to be water‐dispersible, strong red luminescent, ultrastable in strong acid and alkali, and luminescence lifetime enhanced. A cell imaging assay was further carried out and strong luminescent signal could be obtained, which showed that the as‐synthesized luminescent Eu‐complex/PS nanoparticles are a good candidate to be used as luminescent nanoparticles in tumor cell detection. This solvent swelling method is simple, easy to scale‐up, and has great potential in the preparation of other luminescent nanoparticles. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Multifunctional sensors based on silicone hydrogel and their responses to solvents,pH and solution composition

In this paper, multicomponent silicone hydrogels were prepared by the copolymerization of the hydrophobic silicon‐containing monomer bis(trimethylsilyloxy) methylsilylpropyl glycerol methacrylate with two hydrophilic monomers 2‐hydroxyethyl methacrylate and N‐vinyl pyrrolidone. The response of the silicone hydrogels to different stimuli was evaluated by observing the swelling ratios of the hydrogels. The results show that the hydrogels display different responses to variations in pH and solvent. Multifunctional sensors were then prepared based on the silicone hydrogels to detect the pH value of solutions, the types of solvent and the ethanol percentage in water. The results could be obtained by visual inspection and the sensors were reusable. © 2016 Society of Chemical Industry     

Solvent swelling behavior of Permian-aged South African vitrinite-rich and inertinite-rich coals

Two South African coals similar in rank and age, but different in maceral composition, were studied using solvent swelling. Inertinite-rich Highveld coal (dominated by semifusinite) and vitrinite-rich Waterberg coal were evaluated for swelling extent and swelling rate using N-methylpyrrolidone (NMP) and CS₂/NMP. A stop-motion videography method was developed to study individual particle swelling behavior. This method allowed observation of overshoot and climbing-type swelling, as well as swelling kinetics. Single-particle swelling experiments showed that both coals exhibited overshoot-type and climbing-type swelling. The inertinite-rich coal swelled much faster (in both solvents) than the vitrinite-rich coal. The swelling in CS₂/NMP was faster for both coals. Kinetic parameters showed that solvent swelling was governed by relaxation (super-Case II relaxation) of the coal structure. X-ray computed tomography was conducted over a 50 h swelling period in NMP for single particles of each coal. Anisotropic swelling was observed in all the particles (swelling greater perpendicular to the bedding plane than parallel to it). The subtle changes in molecular structure, fine structural and physical differences resulted in significant differences in solvent swelling behavior.     

Interpenetrating polymer networks based on poly(acrylic acid) and gelatin. I: Swelling and thermal behavior

This article describes the synthesis of full and semi-interpenetrating polymer networks (IPNs) based on poly(acrylic acid) and gelatin as polymers 1 and 2, which were crosslinked sequentially using N,N′-methylene bisacrylamide (B_Am) and glutaraldehyde, respectively. Various samples were prepared by taking varying amounts of acrylic acid and gelatin in the initial feed. Sequential IPNs were prepared by first polymerizing and crosslinking acrylic acid in the presence of gelatin using redox initiators (ammonium persulphate and sodium metabisulphite) and B_Am as a crosslinking agent. Gelatin present in the firm gels was then crosslinked using 4% glutaraldehyde. Characterization of these gels was done by measuring their swelling behavior as a function of pH, temperature, and time. Percent swelling increased with increasing amounts of acrylic acid. The swelling ratio was also determined in the pH range of 1 to 12. Acid/alkali or buffers were used for maintaining pH. A significant increase in the percent swelling was observed when pH of distilled water was above 10. On the other hand, in the case of buffer, the swelling ratio increased with increasing the pH, and a maxima was observed at pH 8.4. A further increase in pH resulted in a decrease in the swelling ratio. Thermal and morphological characterization was done using thermogravimetric analyzer and scanning electron microscopy, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 217–227, 2001     

Investigation of mechanical and thermodynamic properties of pH‐sensitive poly(N,N‐dimethylaminoethyl methacrylate) hydrogels prepared with different crosslinking agents

pH‐sensitive poly(N,N‐dimethylaminoethyl methacrylate) hydrogels were synthesized by free‐radical crosslinking polymerization using two different crosslinking agents; tetraethylene glycol dimethacrylate (TEGMA) and N,N′‐methylenebis(acrylamide) (BAAm). The influence of the polymerization factors such as the type of the crosslinking agent and the gel preparation concentration on the swelling behavior, the gel strength, the effective crosslinking density and the average chain length between the crosslink points for the resulting hydrogels was investigated. The results of the equilibrium swelling measurements in water showed that the linear swelling ratio of the resulting hydrogels increases with increasing gel preparation concentration. The swelling ratio of PDMAEMA hydrogels crosslinked with BAAm is larger than those for hydrogels crosslinked with TEGMA over the entire range of the polymer network concentration. The hydrogels exhibit very sharp pH‐sensitive phase transition in a very narrow range of pH between 7.7 and 8.0. From the mechanical measurements, it was also found that the linear swelling ratio of resulting hydrogels depends on the crosslinking density and also the type of the crosslinker used in the preparation. The resulting hydrogels are thought to be good candidates for pH‐sensitive drug delivery systems. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

醚化海藻酸钠-丙烯酸-聚乙烯醇高吸水树脂在环境介质中的溶胀行为

以N,N-亚甲基双丙烯酰胺为交联剂,过硫酸铵-亚硫酸氢钠为引发剂,采用水溶液法合成了醚化海藻酸钠-丙烯酸-聚乙烯醇高吸水性树脂.考察比较了树脂在不同pH值缓冲溶液和盐溶液中的平衡含水率.结果表明,在酸性介质中,凝胶的溶胀过程为—COO^-的质子化过程控制,溶胀过程表现出non-Fickian动力学行为; 在碱性介质中,溶胀过程主要由溶剂扩散控制,表现出Fickian动力学行为,随着pH值升高,凝胶的平衡含水率升高; 在离子强度相近时,树脂在pH缓冲溶液中的溶胀率比在单价盐离子溶液中低,但比在二价盐溶液中高.对聚合物-溶剂的相互作用机理进行了探讨.     

Enhanced swelling and responsive properties of an alginate-based superabsorbent hydrogel by sodium p-styrenesulfonate and attapulgite nanorods

In this work, a series of sodium alginate-g-poly(sodium acrylate-co-sodium p-styrenesulfonate)/attapulgite (NaAlg-g-poly(NaA-co-NaSS)/APT) superabsorbent composites were prepared by graft copolymerization using N,N’-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate as an initiator. Fourier transform infrared spectroscopy revealed that NaA and NaSS had been grafted onto NaAlg, and APT participated in polymerization reaction through reactive –OH groups. The introduction of proper amount of NaSS and APT induced the improved surface morphology, swelling capacity, and swelling rate. Moreover, the swelling behaviors of the superabsorbent composites were remarkably influenced by various salt medium, pH buffer solutions and organic solvents, and especially an intriguing swelling–deswelling behavior was observed with altering water/organic solvent ratio.     

Surfactant-Modified Poly(acrylamide-co-acrylamido propane sulphonic acid) Hydrogels

Recent advances in drug delivery have been directed towards the design of a number of intelligent systems for the treatment of various diseases. In this regard, we developed novel surfactant-modified hydrogels which are synthesized from acrylamide (AM) and acrylamido propane sulphonic acid (AMPS), in the presence of a surfactant (Latemul PD-104) using ammonium persulfate/N,N,N′,N′–tetramethylethylene diamine (APS)/(TMEDA) as an initiating system and N,N′-methylenebisacrlyamide (MBA) as a crosslinker. The hydrogel formation was confirmed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The variation in the hydrogel networks formation employing different levels of synthetic parameters was verified by swelling studies. Influences of salt, biological fluids, and buffer solutions on the developed systems were also investigated. It was found that, compared to PAM hydrogel, all the surfactant-modified hydrogels were responsive towards salt concentration and pH. A robust drug release behavior was observed from surfactant-modified hydrogel systems.     

Swelling Properties of Chemically Crosslinked Poly(acrylamide-co-maleic acid) Hydrogels

ABSTRACT

Chemically crosslinked poly(acrylamide-co-maleic acid) [poly(AAm-co-MA)] hydrogels were prepared by simultaneous free radical copolymerization of acrylamide (AAm) with maleic acid (MA) in presence of di or tri functional crosslinking agents using ammonium persulfate-N,N,N′,N′-tetramethylethylenediamine (APS-TMEDA) redox-initiating system. The poly(AAm-co-MA) hydrogels formation was confirmed by IR studies. The influence of crosslinkers such as N,N′-methylene-bis-acrylamide (MBA) and 2,4,6-triallyloxy-1,3,5-triazine (TATA) on swelling/de-swelling characteristics were studied in detail for poly(AAm-co-MA) hydrogels containing different amounts of maleic acid. The present investigation also deals with the influence of concentration of crosslinker and initiator on the swelling behavior of poly(AAM-co-MA) hydrogels. The effect of various salts on swelling capacity was studied. In addition, the effect of simulated biological fluids and pH solutions on the swelling of hydrogels was also studied in detail.