Poly(N-isopropylacrylamide) Hydrogels Crosslinked by Small-Molecular Crosslinkers Through Click Chemistry

A well-defined azido-poly(N-isopropylacrylamide) (PNIPA) was prepared by reversible addition-fragmentation chain transfer polymerization of NIPA and glycidyl methacrylate followed by the azidization of pendant epoxyl groups. Then the polymer was crosslinked via Click chemistry by bis- or tetra-alkynyl terminated compounds, which were synthesized through esterification of 1,3-propanediol and pentaerythritol with propiolic acid and 6-heptynoic acid, to fabricate PNIPA hydrogels. And the swelling properties of obtained hydrogels were studied as functions of crosslinker dosage and species. The results showed that the decrease of crosslinker dosage or increase of chain length thereof could enhance swelling capacities of hydrogels due to bigger free volumes within networks; the functionality of crosslinkers almost had no influence on swelling properties of hydrogels. In addition, no obvious distinction was found for lower critical solution temperature and swelling response to a temperature jump during reswelling and deswelling course, no matter what and how much crosslinker was used.     

Temperature-dependent transparency of poly(HPMA-co-DMA) hydrogels: effect of synthesis parameters

The acrylic comonomers hydroxypropyl methacrylate (HPMA) and N,N-dimethylaminoethyl methacrylate (DMA) have been used in several earlier studies to produce pH-responsive hydrogels. However, these same monomers can also be used to prepare hydrogels that are highly responsive to temperature. One manifestation of this temperature sensitivity is a sharp decrease in hydrogel optical transparency that occurs when the temperature exceeds a critical transition value. For example, a hydrogel that exhibits a swelling transition at the physiological pH value of 7.4 has a transition temperature of about 45 °C when the environmental salt concentration is 0.15 M. The value of the transparency transition temperature is shown to depend on hydrogel synthesis parameters such as comonomer mole ratio, crosslinker mole ratio, and even initiator concentration. By reducing the mole ratio of the crosslinker tetraethylene glycol dimethacrylate (TEGDMA), the transition temperature can be lowered by as much as 15 °C. Environmental salt concentration and solvent polarity are also shown to influence the transition temperature.     

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.     

化学交联聚乙二醇水凝胶的制备方法

对化学交联聚乙二醇基水凝胶的研究进展进行了综述.介绍了该类水凝胶的制备方法,包括几种常见的前体制备方法和常用的交联方法,并讨论了影响水凝胶溶胀性能和力学性能的几种因素.     

快速响应聚(N-异丙基丙烯酰胺)水凝胶的制备及性能

以N-异丙基丙烯酰胺为单体、N,N′-亚甲基双丙烯酰胺为交联剂、过硫酸铵为引发剂、N,N,N,′N′-四甲基乙二胺为加速剂,在不同浓度的羧甲基纤维素的水溶液中,在低温下聚合/交联制备了一系列快速响应的温度敏感性聚(N-异丙基丙烯酰胺)水凝胶。用SEM观察了其表面形态,测定了不同温度下达到平衡时水凝胶的溶胀比,研究了水凝胶的去溶胀动力学。结果表明,与传统水凝胶相比,该水凝胶的溶胀性能有所提高,并且对温度的变化具有较快的响应速率。以质量分数为0.75%的羧甲基纤维素水溶液中制备的水凝胶为例,该水凝胶在20℃时的溶胀比为21.4,而传统水凝胶在相同温度时的溶胀比仅为12.9;该水凝胶在1 m in内失去60%的水,在4 m in内失去约80%的水,而传统水凝胶在15 m in内仅失去66%左右的水。     

Investigation of pH sensitivity of poly(acrylic acid‐co‐acrylamide) hydrogel

It was found that the upper critical solution temperature (UCST) of poly(acrylic acid‐co‐acrylamide) hydrogel decreases with increase in pH. The UCST of samples equilibrated in a buffer at pH 2.5 was 33.7 °C, whereas it shifted to below 0 °C when swollen in buffers above pH 10. FT‐IR showed that COOH group of acrylic acid ionized gradually in alkaline media. The morphology change of the hydrogel swollen in different buffers was studied by environmental scanning electron microscopy (ESEM). ESEM images showed that the pore size of the sample increased with increase in pH, and in strongly basic media the three‐dimensional network was replaced by a ‘sausage‐like’ or ‘desert‐like’ structure. A study of the pH‐dependent release of cefazolin sodium was also carried out. Copyright © 2003 Society of Chemical Industry     

聚乙烯己内酰胺的制备与表征

以乙烯己内酰胺单体(VCL)为原料,偶氮二异丁腈(AIBN)为引发剂,在水溶液中通过自由基聚合合成了聚乙烯己内酰胺. 考察了引发剂用量、溶剂用量、聚合反应时间和聚合反应温度对产物分子量和产率的影响,阐述了水溶液中自由基聚合的反应机理. 在VCL:AIBN:H2O=1:0.05:15(质量比),75℃下反应5 h的优化工艺条件下,产率能达到97%,并通过凝胶渗透色谱仪测定了聚合物的平均分子量. 以红外光谱和核磁共振对产品结构进行了表征,用分光光度计测定其临界溶解温度为32℃.     

Fabrication and Characterization of Macroporous Poly(Ethylene Glycol) Hydrogels Generated by Several Types of Porogens

Polymer scaffolds play an important role in tissue engineering applications. Poly(ethylene glycol) based hydrogels have received a lot of attention in this field because of their high biocompatibility and ease of processing. However, in many cases they do not exhibit proper tissue invasion and nutrient transport because of their dense structure. In the present work, several approaches were developed and compared to each other to produce interconnected macroporous poly(ethylene glycol) hydrogels by including different types of porogens in the photocrosslinking reaction. The swelling capacity of the resulting hydrogels was analyzed and compared to non-porous hydrogel samples. Moreover, the obtained materials were characterized by means of mechanical properties and porosity using rheometry, scanning electron microscopy, and mercury intrusion porosimetry. Results showed that interconnected and uniform pores were obtained when a porogen template was used during hydrogel fabrication by photocrosslinking. On the other side, when the porogen particles were dispersed into the macromer solution before matrix photocrosslinking the interconnexion was negligible. The templates must be dissolved before the hydrogel's cell-seeding in vitro, while the dispersed porogen can be used in situ in the in vitro seeding tests.     

Adjusting Some Properties of Poly(methacrylic acid) (Nano)Composite Hydrogels by Means of Silicon-Containing Inorganic Fillers

The present work aims to show how the main properties of poly(methacrylic acid) (PMAA) hydrogels can be engineered by means of several silicon-based fillers (Laponite XLS/XLG, montmorillonite (Mt), pyrogenic silica (PS)) employed at 10 wt% concentration based on MAA. Various techniques (FT-IR, XRD, TGA, SEM, TEM, DLS, rheological measurements, UV-VIS) were used to comparatively study the effect of these fillers, in correlation with their characteristics, upon the structure and swelling, viscoelastic, and water decontamination properties of (nano)composite hydrogels. The experiments demonstrated that the nanocomposite hydrogel morphology was dictated by the way the filler particles dispersed in water. The equilibrium swelling degree (SDe) depended on both the pH of the environment and the filler nature. At pH 1.2, a slight crosslinking effect of the fillers was evidenced, increasing in the order Mt < Laponite < PS. At pH > pKa_MAA (pH 5.4; 7.4; 9.5), the Laponite/Mt-containing hydrogels displayed a higher SDe as compared to the neat one, while at pH 7.4/9.5 the PS-filled hydrogels surprisingly displayed the highest SDe. Rheological measurements on as-prepared hydrogels showed that the filler addition improved the mechanical properties. After equilibrium swelling at pH 5.4, G’ and G” depended on the filler, the Laponite-reinforced hydrogels proving to be the strongest. The (nano)composite hydrogels synthesized displayed filler-dependent absorption properties of two cationic dyes used as model water pollutants, Laponite XLS-reinforced hydrogel demonstrating both the highest absorption rate and absorption capacity. Besides wastewater purification, the (nano)composite hydrogels described here may also find applications in the pharmaceutical field as devices for the controlled release of drugs.     

in situ thermal gelation of water-soluble poly(N-isopropylacrylamide-co-vinylphosphonic acid)

A copolymer based on N-isopropylacrylamide (NIPAAm) and vinylphosphonic acid (VP) was synthesized to investigate its thermal gelation behaviors in the presence of calcium ion. The copolymer showed a variety of temperature-sensitive phase transition properties as a function of temperature. In an aqueous solution, it exhibited 3 distinctive phase transitions with gradually increasing the temperature: a transparent solution state, a cloudy and white solution state (sol), and a white and semisolid (gel) state. Particularly, in situ reversible sol-gel transition behaviors could be observed over a wide range of temperatures in the presence of varying concentrations of calcium ion. This physical gel that initially was formed homogeneously without changing its dimension in the solution container tended to slowly phase-separate out into a polymer-rich phase and a water-rich phase over the following several days, indicating that a synerisis occurred. The in situ thermal gelation behavior was utilized in the controlled release formulation of a model compound. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1947–1953, 1998     

Preparation and Gel Properties of Poly[hydroxyethylmethacrylate-co-poly(ethylene glycol) methacrylate] Copolymeric Hydrogels by Photopolymerization

Copolymeric hydrogels based on 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methacrylate (PEGMA) and isopropanol as a diluent were prepared by photopolymerization. The swelling kinetics, mechanical properties, drug release behaviors, and the interaction between various drugs and the present copolymeric gels were investigated in this study. The results showed that the addition of PEGMA could effectively increase the equilibrium water content and the diffusion coefficient and penetration velocity of water though the gels. Although Young's modulus increased with the increase of PEGMA content, the resulting gels had smaller elongation and more brittle characteristics. The drug release behavior was strongly dependent on the interaction between the present copolymeric gels and drugs such as caffeine, crystal violet (CV), phenol red, and vitamin B₁₂.     

Tensile Fatigue of Poly(Vinyl Alcohol) Hydrogels with Bio‐Friendly Toughening Agents

Inspired by the avoidance of toxic chemical crosslinkers and harsh reaction conditions, this work describes a poly(vinyl alcohol)‐based (PVA) double‐network (DN) hydrogel aimed at maintaining biocompatibility through the combined use of bio‐friendly additives and freezing–thawing cyclic processing for the application of synthetic soft‐polymer implants. This DN hydrogel is studied using techniques that characterize both its chemical and mechanical behavior. A variety of bio‐friendly additives are screened for their effectiveness at improving the toughness of the PVA hydrogel system in monotonic tension. Starch is selected as the best additive for further tensile testing as it brings about a near 30% increase in ultimate tensile strength and maintains ease of processing. This PVA–starch DN sample is then studied for its tensile fatigue properties through cyclic, strain‐controlled testing to develop a fatigue life curve. Though an increase in monotonic tensile strength is observed, the PVA–starch DN hydrogel does not bring about an improvement in the fatigue behavior as compared to the control. Although synthetic hydrogel reinforcement is widely researched, this work presents the first fatigue analysis of its kind and it is intended to serve as a guide for future fatigue studies of reinforced hydrogels.     

缩醛化乙烯醇-丙烯酸钠共聚物的合成及温敏性质

首先合成了室温下可溶于水的聚乙烯醇-丙烯酸钠共聚物(PVA-co-AANa),然后部分缩醛后得到一系列不同缩醛度(DA)、不同相对分子质量和单体组成的高分子材料(APVA-co-AANa),该材料具有温敏性。用FTIR和1HNMR表征了其结构。通过APVA-co-AANa水溶液在不同温度的浊度测定,考察了母体PVA-co-AANa相对分子质量、DA和单体组成对APVA-co-AANa的低临界溶解温度(LCST)的影响,发现APVA-co-AANa的DA越高、分子链越长、AA组分用量越小,相对LCST越低。而且,APVA-co-AANa水溶液还表现出盐敏性,LCST随NaCl用量增加而降低。APVA-co-AANa膜的AFM表面形貌的变化也证实了APVA-co-AANa的温敏性。     

Swelling and Diffusion Properties of Poly(acrylamide-co-maleic acid) Hydrogels: A Study with Different Crosslinking Agents

Crosslinked hydrogels comprising acrylamide (AAm) and maleic acid (MA) were synthesized by free radical polymerization in presence of a crosslinker using ammonium persulfate (APS) and N,N,N¹,N¹-tetramethylethylenediamine (TMEDA) as initiator and activator, respectively. The crosslinked hydrogel formation was confirmed by IR analysis. The swelling/de-swelling characteristics were studied in detail for crosslinked poly(acrylamide-co-maleic acid) [poly(AAM-co-MA)] hydrogels containing different amounts of maleic acid. Four different crosslinkers such as 1,2-ethyleneglycol dimethacrylate (EGDMA), 1,4-butanediol diacrylate (BDDA), 1,6-hexanediol diacrylate (HDDA), and diallyl phthalate (DP) were utilized to study their influence on the swelling behavior of the hydrogels. The effect of reaction parameters such as the concentration of crosslinker and initiator on swelling capacity of the crosslinked poly(AAm-co-MA) hydrogels was also investigated. Further, the influence of various salts, simulated biological fluids, and pH solutions on the swelling pattern of hydrogels was studied extensively. Phase separation morphology of crosslinked hydrogels was also studied by differential scanning calorimetry. The morphology of crosslinked hydrogels were revealed using scanning electron microscopy (SEM).     

The Effect Acetic Acid has on Poly(N-Vinylcaprolactam) LCST for Biomedical Applications

The aim of this research was to synthesize Poly(N-vinylcaprolactam) (PNVCL) with the incorporation of hydrophilic acetic acid with thermosensitive N–vinylcaprolactam for potential drug delivery applications. Preparation of the heterogeneous mixture involved photopolymerization of a combination of N–vinylcaprolactam and acetic acid at different ratios. By altering the feed ratio, hydrogels were synthesized to have lower critical solution temperature close to physiological temperature. This ability to shift the phase transition temperature of PNVCL provides excellent flexibility in tailoring transitions to suit physiological temperature, inheriting great potential in drug delivery.     

pH–temperature responsive poly(HPA‐Co‐AMHS) hydrogel as a potential drug‐release carrier

In this study, a novel pH–temperature‐responsive copolymer was first synthesized by the radical copolymerization between HPA (2‐hydroxypropyl acrylate and 2‐hydroxyisopropyl acrylate) and AMHS (aminoethyl methacrylate hydrochloric salt). The molecular structure of the corresponding copolymer has been confirmed by ¹H‐NMR and FTIR. The lower critical solution temperature of the resulting copolymer exhibited a considerable dependence upon the ratio of monomers and pH value in the medium. On the basis of the copolymer, a hydrogel as drug release carrier was prepared via the introduction of a crosslinker, N,N′‐methylenebisacrylamide. The swelling behaviors of hydrogel in the different pH value, temperature, and NaCl concentration have indicated that the hydrogel showed a remarkable phase transition at 31.5°C. The swelling ratio was increased with an increasing of pH value, especially in the greater pH values. By the use of caffeine as a model drug, we investigated the caffeine‐controlled release from hydrogel systematically as a function of pH value, temperature, and crosslinker content. The caffeine release was sensitive to the temperature. Only 55% caffeine was released from the hydrogel at room temperature, whereas ～ 92% caffeine diffused into the medium at 37°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Tunable temperature‐ and shear‐responsive hydrogels based on poly(alkyl glycidyl ether)s

We describe the synthesis, characterization and direct‐write 3D printing of triblock copolymer hydrogels that have a tunable response to temperature and shear stress. In aqueous solutions, these polymers utilize the temperature‐dependent self‐association of poly(alkyl glycidyl ether) ‘A’ blocks and a central poly(ethylene oxide) segment to create a physically crosslinked three‐dimensional network. The temperature response of these hydrogels was dependent upon composition, chain length and concentration of the ‘A’ block in the copolymer. Rheological experiments confirmed the existence of sol–gel transitions and the shear‐thinning behavior of the hydrogels. The temperature‐ and shear‐responsive properties enabled direct‐write 3D printing of complex objects with high fidelity. Hydrogel cytocompatibility was also confirmed by incorporating HeLa cells into select hydrogels resulting in high viabilities over 24 h. The tunable temperature response and innate shear‐thinning properties of these hydrogels, coupled with encouraging cell viability results, present an attractive opportunity for additive manufacturing and tissue engineering applications. © 2018 Society of Chemical Industry     

Preparation of glycopolypeptides bearing mannose moieties and biphenyl pendants and their upper‐critical‐solution‐temperature‐type thermoresponsive properties in alcohol/water solvent mixtures

A series of glycopolypeptides with constant main‐chain lengths and various compositions of mannose moieties and biphenyl pendants were synthesized by copper‐mediated 1,3‐dipolar cycloadditions. ¹H NMR and Fourier transform IR (FTIR) analysis confirmed the molecular structures of the resulting polypeptides. FTIR analysis characterized the molar contents of the mannose pendants and α‐helical conformations in the solid state. Glycopolypeptides conjugated with tetra‐O‐acetyl‐d ‐(+)‐mannopyranoside showed a reversible upper‐critical‐solution‐temperature‐type (UCST‐type) phase behavior both in MeOH/H₂O and EtOH/H₂O binary solvent mixtures depending on the weight percentage of alcohols (f_w). Incorporation of a low content of biphenyl pendants (≤0.20) can broaden the range of f_w at which polymers showed UCST‐type phase behaviors. The UCST‐type transition temperature (T_pt) was highly related to the incorporation of biphenyl pendants, polymer concentrations, and the nature and weight percentage of alcohols. It decreased as the polymer concentration decreased and increased on incorporation of biphenyl groups. © 2016 Society of Chemical Industry     

Thermodynamic investigation of thermoresponsive xanthan‐poly (N‐isopropylacrylamide) hydrogels

Polysaccharide‐based hydrogels, such as xanthan maleate/poly(N‐isopropylacrylamide) (PNIPAAm) interpenetrated polymer networks, are thermostimulable materials of interest for the controlled release of biologically active components due to conformation changes at the low critical‐solution temperature (LCST) PNIPAAm phase transition. The phase transition of these interpenetrated polymer network hydrogels, where PNIPAAm is in a ‘confined’ environment, was examined by high resolution magic angle spinning nuclear magnetic resonance and differential scanning calorimetry. High resolution magic angle spinning nuclear magnetic resonance spectroscopy allows the accurate determination of LCST and an evaluation of the corresponding thermodynamic data. More particularly, the evolution of these data as a function of the composition of the hydrogel, and of the external parameters such as pH and ionic strength, was considered. LCST shows a minimal value with increasing xanthan content. Moreover, it was possible to calculate, as a function of temperature, the fraction of NIPAAm which remains uncollapsed. The data obtained for pure PNIPAAm hydrogels are in good agreement with recently published results. The phase transition of PNIPAAm in a diphasic hydrogel is broader when PNIPAAm is ‘confined’ within an interpenetrated polymer network than in a pure PNIPAAm crosslinked network. The widening of the transition with increasing xanthan content indicates a reduction of the PNIPAAm interchain aggregation in a network structure. Copyright © 2011 Society of Chemical Industry     

Evaluation of Antibacterial Activity of Nanostructured Copolymers of Poly (Naphthylamine)

The present preliminary investigation highlights for the first time the antibacterial activity of copolymers of nanostructured poly (naphthylamine) (PNA) with aniline (PNA-co-PANI) and o-toluidine (PNA-co-POT) against E. coli and S. aureus. The antibacterial effect of these nanosized polymers was found to be much higher than that reported for pristine polyaniline. The chemical structure and morphology of the copolymers was found to play a significant role in deciding the antimicrobial efficiency of the copolymers. A proposed mechanism of antimicrobial effect has also been suggested. Our results indicate that the antimicrobial effects of the copolymers could be useful ingredients for biomaterials used in the development of food packaging and medical devices.