近红外光响应氧化石墨烯/微凝胶复合智能水凝胶

设计合成了一种包含氧化石墨烯（GO）片层、聚（N-异丙基丙烯酰胺）（PNIPAM）微凝胶球体和PNIPAM链段的复合结构水凝胶。通过控制聚合时间得到负载双键且粒径不同的PNIPAM微凝胶,将其作为交联点与N-异丙基丙烯酰胺（NIPAM）聚合,GO作为纳米填料掺入水凝胶体系,GO片层上的含氧基团与NIPAM上的胺基产生氢键物理交联。此方法制备的复合水凝胶同时具有温度敏感和近红外光敏感特性,通过改变GO浓度、微凝胶的合成时间、NIPAM浓度等条件,水凝胶的光敏感性和温度敏感性得到提升。相比于传统PNIPAM水凝胶,此种复合水凝胶能够对光响应,实现非接触式控制形变,且响应速率快、响应程度高,可应用于光控开关等领域。     

Effect of poly(ethylene glycol)-derived crosslinkers on the properties of thermosensitive hydrogels

Three crosslinkers, poly(ethylene glycol) diacrylate (PEGDA), glycerol ethoxylate triacrylate (GETA) and citric acid-(PEG acrylate)₃ (CA-PEGTA) derived from poly(ethylene glycol) (PEG) were synthesized at first. The three series of poly (N-isopropylacrylamide) (PNIPAAm) hydrogels were prepared by photopolymerization with the crosslinkers and compared with a hydrogel based on commercial crosslinker, N,N′-methylene bis-acrylamide (NMBA). The influence of the crosslinker structures and contents on the swelling behaviour, mechanical properties, and drug release of the hydrogels was investigated. The results showed that the hydrogels based on PEGDA and NMBA exhibited the highest and the lowest swelling ratio, respectively. The content of crosslinker of all hydrogel series showed good thermosensitivity and thermo-reversibility. The critical gel transition temperature (CGTT) appeared at 32 °C for the hydrogel based on NMBA, but appeared at about 34 °C for other hydrogels due to higher hydrophilicity of the crosslinker. In the mechanical properties, three-arms crosslinker GETA and CA-PEGTA led to higher mechanical strength than a linear crosslinker PEGDA. A hydrogel based on GETA (NG6) showed the highest shear modulus of 656.9 kPa and Young’s modulus of 1655.0 kPa. The hydrogels containing higher content of crosslinker revealed lower swelling ratio and higher mechanical strength. In the drug release, the hydrogels with higher swelling ratios showed higher drug absorbed. The highest release percentage of caffeine and vitamin B12 for hydrogel based on PEGDA (NP6) could reach 68.3% and 75.4%, respectively. In addition, the bound water and toxicity of the hydrogels were also investigated.

     

Dual pH‐ and temperature‐responsive hydrogels with extraordinary swelling/deswelling behavior and enhanced mechanical performances

pH‐ and temperature‐responsive semi‐interpenetrating nanocomposite hydrogels (NC hydrogels) were prepared with surface‐functionalized graphene oxide (GO) as the crosslinker, N‐isopropylacrylamide (NIPAM) as the monomer, and chitosan (CS) as an additive. The effects of 3‐(trimethoxysilyl)propylmethacrylate‐modified GO sheets and CS content on various physical properties were investigated. Results show that PNIPAM/CS/GO hydrogels undergo a large volumetric change in response to temperature. Swelling ratios of PNIPAM/CS/GO hydrogels are much larger than those of the conventional organically crosslinked PNIPAM hydrogels. The deswelling test indicates that the deswelling rate was greatly enhanced by incorporating CS into the hydrogel network and using the surface‐functionalized GO as the crosslinker. The pH‐sensitivity of PNIPAM/CS/GO hydrogels is evident below their volume phase transition temperature. Moreover, the PNIPAM/CS/GO hydrogels have a much better mechanical property compared with traditional hydrogels even in a high water content of 90%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41530.     

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。     

Preparation and Controlled Drug Release Characteristics of Thermoresponsive PEG/Poly (NIPAM-co-AMPS) Hydrogels

Thermosensitive hydrogels were prepared by free radical polymerization of N-isopropylacrylamide (NIPAM) and 2-acrylamido-2-methylpropanesulphonic acid (AMPS) in presence of polyethylene glycol (PEG) as macroinitiator. The incorporation of functional monomer in the hydrogel was confirmed by infrared spectroscopy. The equilibrium swelling ratio (ESR), deswelling rate, volume transition temperature, and surface morphology of synthesized hydrogels are found to be dependent on concentration of AMPS monomer in the feed composition. The equilibrium swelling ratio (ESR) and water retention properties increase with increasing AMPS concentration in hydrogels and decrease with increasing salt concentration in external medium. The hydrogel with high dose of AMPS has high loading efficiency of theophylline drug, whereas the in-vitro release of the drug is delayed for a prolonged period in swollen gels above LCST of PNIPAM.     

自交联法合成相转变温度范围窄的聚(N-异丙基丙烯酰胺)水凝胶微球

在不使用交联剂的情况下,采用无皂乳液聚合法合成自交联聚(N-异丙基丙烯酰胺)(PNIPAM)水凝胶微球。固体13C NMR分析结果表明,PNIPAM水凝胶微球中存在因链转移反应形成的自交联点。自交联PNIPAM水凝胶微球的相转变温度范围很窄,接近非连续体积相转变行为。合成过程中反应温度、反应时间、引发剂用量对微球粒径和溶胀比有比较明显的影响,这些因素对微球的相转变温度及其范围的影响均很小。     

Functionalization of hybrid poly(n‐isopropylacrylamide) hydrogels for Escherichia coli cell capture via adsorbed intermediate dye molecule

Poly(n‐isopropylacrylamide) Laponite (PNIPAM‐Lap) hybrid hydrogels, which use the synthetic clay Laponite as a crosslinker, permanently adsorb cationic laser dyes out of solution. This proof‐of‐concept expounds on this capability by adsorbing an intermediate dye molecule and using it as the foundation for successfully conjugating microbial antibodies to the surface of a PNIPAM hydrogel. The study involves using acriflavinium chloride molecules, adsorbed by a PNIPAM‐Lap hydrogel from an acriflavine laser dye solution, as an intermediate molecule to attach antibodies raised against E. coli to the hydrogel and demonstrate cell capture. Furthermore, this system exemplifies a novel biotechnological platform for greatly expanding PNIPAM hydrogels' capabilities and applicability through conjugation chemistry to surface‐bound molecules. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41557.     

Preparation of antimicrobial polycarboxybetaine‐based hydrogels for studies of drug loading and release

A series of cationic poly(N‐isopropyl acrylamide) (PNIPAM)‐g‐poly(carboxybetaine ester) (PCBMAE) hydrogels were prepared by reversible addition–fragmentation chain‐transfer polymerization with PCBMAE precursors reacting with N‐isopropyl acrylamide in the presence of N,N′‐methylene bisacrylamide. These hydrogels exhibited excellent antimicrobial activities against Staphylococcus aureus and could switch to nontoxic zwitterionic hydrogels after hydrolysis. Nonionic tetracycline hydrochloride (TCHC) and anionic sodium salicylate (SA) were selected to evaluate the loading capacities and release kinetics of the cationic hydrogels. We found that the loading efficiencies of TCHC in the PNIPAM‐g‐PCBMAE hydrogels were approximately twice as high as those of SA. However, the cumulative release amount of TCHC was lower than that of SA from the corresponding cationic hydrogel at 37°C. In addition, the PNIPAM‐g‐PCBMAE hydrogels exhibited accelerated release rates of both TCHC and SA with increasing content of (2‐carboxymethyl)?3‐acryloxyethyldimethylammonium chloride methyl ester. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39839.     

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.     

Thermoresponsive nanocomposite hydrogels with high mechanical strength and toughness based on a dual crosslinking strategy

The practical application of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels are severely limited by their poor mechanical properties. Herein, we reported a series of dual crosslinked (DC) PNIPAM hydrogels with superior mechanical properties prepared by simple copolymerization of N-isopropylacrylamide and sodium acrylate (SA) in the laponite RDS suspension, following by a soaking process in multivalent metal cations (e.g., Ca²⁺, Al³⁺, Fe³⁺) aqueous solutions to form ionic coordination interactions with  COO groups of copolymer side chains. The effect of laponite RDS, AANa (sodium acrylate), and metal cation (e.g., Fe³⁺) concentrations on the mechanical properties and deswelling properties of the DC hydrogels are evaluated. The DC hydrogel prepared with 10 w/v% laponite RDS, 0.25 mol/L AANa and 0.45 mol/L Fe³⁺ possesses the best mechanical properties (ca. 1.1 MPa of tensile strength, 9.1 MPa of compression strength at 80% of compression strain, 1.4 MPa of elastic modulus and 1.3 MJ/m³ of toughness). Moreover, we also discovered that the DC hydrogels crosslinked by Fe³⁺ showed better mechanical properties due to the larger charge and ion radius of Fe³⁺.     

Novel Thermoreversible Injectable Hydrogel Formulations Based on Sodium Alginate and Poly(N-Isopropylacrylamide)

Novel injectable thermoreversible hydrogel compositions with semi-interpenetrating network structure were prepared through the addition of sodium alginate (SA) to poly(N-isopropylacrylamide) (PNIPAM) aqueous solutions. The addition of the hydrophilic alginate strongly improved the stability against syneresis of the 15 wt% PNIPAM hydrogels formed at 37°C from less than 15 min in the absence of alginate to more than 7 days in the presence of 4 wt% SA. Besides the SA concentration, the hydrogel stability depended on the molecular weight and polydispersity of PNIPAM, being lower when a high molecular weight fraction was present. The phase transition temperature (T_ph) of the PNIPAM aqueous solutions decreased with alginate concentration, while the dynamic viscosity and elastic modulus of the hydrogels increased. By decreasing the PNIPAM molecular weight and polydispersity, the dynamic viscosity and elastic modulus of the PNIPAM–alginate hydrogels formed above T_ph diminished, while their viscoelastic behavior changed from predominantly elastic to predominantly viscous.     

Effect of functional groups on physicochemical and mechanical behavior of biocompatible macroporous hydrogels

The increasing interest in studying the properties of biocompatible hydrogels is due to their possible applications in bioengineering. Properties of hydrogels based on N-isopropylacrylamide (NIPAM) and the effect caused by copolymerization with 2-acrylamido-2-methylpropanesulfonic acid (AMPS) or N-acryloyl-tris-(hydroxymethyl)aminomethane (HMA) were investigated. Hydrogels were synthesized by free radical polymerization at room temperature or by cryogelation at − 18 °C. The presence of different functional groups (isopropyl, − SO₃⁻, and –OH) and thermal conditions of polymerization affected the morphology and physicochemical and mechanical properties of hydrogels. Scanning electron microscopy (SEM) revealed the presence of macropores created by cryogelation with the morphology of the pores dependent on chemical composition of the copolymer. Poly(NIPAM-co-HMA) has spherical and isolated pores, whereas PNIPAM and Poly(NIPAM-co-AMPS) showed ellipsoidal interconnected pores. Three different water states were detected by differential scanning calorimetry (DSC), indicating the presence of nano- and macropores. Elastic modulus (E) was measured to be around 3–6.5 kPa by uniaxial compression. However, higher E values (20–30 kPa) and an anisotropic mechanical response were observed for PNIPAM and PNIPAM-co-AMPS hydrogels with ellipsoidal pores, a behavior that is almost similar to that of cartilage and bone tissues. Cytocompatibility studies using bovine fibroblasts (BFs) indicated good cell attachment and proliferation on PNIPAM-based hydrogel surfaces, although initially the cell adhesion varied depending on the composition of the surface. These hydrogels could be an interesting choice for the development of scaffolds in tissue engineering.     

Dual Cross‐Linked Hydrogels with High Strength,Toughness, and Rapid Self‐Recovery Using Dynamic Metal–Ligand Interactions

A dual cross‐linking design principle enables access to hydrogels with high strength, toughness, fast self‐recovery, and robust fatigue resistant properties. Imidazole (IMZ) containing random poly(acrylamide‐co‐vinylimidazole) based hydrogels are synthesized in the presence of Ni²⁺ ions with low density of chemical cross‐linking. The IMZ‐Ni²⁺ metal–ligand cross‐links act as sacrificial motifs to effectively dissipate energy during mechanical loading of the hydrogel. The hydrogel mechanical properties can be tuned by varying the mol% of vinylimidazole (VIMZ) in the copolymer and by changing the VIMZ/Ni²⁺ ratio. The resultant metallogels under optimal conditions (15 mol% VIMZ and VIMZ/Ni²⁺ = 2:1) show the best mechanical properties such as high tensile strength (750 kPa) and elastic modulus (190 kPa), combined with high fracture energy (1580 J m^?2) and stretchability (800–900% strain). The hydrogels are pH responsive and the extent of energy dissipation can be drastically reduced by exposure to acidic pH. These hydrogels also exhibit excellent anti‐fatigue properties (complete recovery of dissipated energy within 10 min after ten successive loading–unloading cycles at 400% strain), high compressive strength without fracture (17 MPa at 96% strain), and self‐healing capability due to the reversible dissociation and re‐association of the metal ion mediated cross‐links.     

PNIPAM/锂藻土纳米复合凝胶微球的制备及其弹性力学性能

利用微流控技术,以锂藻土作为交联剂,成功制备得到温度响应型聚（N-异丙基丙烯酰胺）（PNIPAM）与锂藻土的纳米复合凝胶微球,并利用一种简单的微步进单轴压缩装置,分别在25℃和37℃下对具有不同锂藻土含量的PNIPAM/锂藻土纳米复合凝胶微球的弹性力学性能进行系统研究。该微步进单轴压缩装置主要包括三个部分：一个程控进样器用以实现对凝胶微球的微步进压缩,一套配有高分辨率数码相机的侧视光学系统用以记录凝胶微球受压时发生的形变,一台精密电子天平作为力传感器用来记录凝胶微球在特定形变下所受的外力。研究结果表明,纳米复合凝胶微球在25℃和37℃下的形变量H与所受压力F的实验数据与Hertz弹性接触理论方程呈现良好的拟合关系,证明了PNIPAM/锂藻土纳米复合凝胶微球在25℃和37℃下均具有弹性形变行为。同时,随着锂藻土含量的增加,PNIPAM/锂藻土纳米复合凝胶微球的温敏性降低,但其杨氏模量增大。具有相同锂藻土含量的纳米复合凝胶微球,由于温度升高凝胶体积收缩、凝胶结构变得致密,因此在37℃下的杨氏模量大于其在25℃下的杨氏模量。研究结果可为PNIPAM/锂藻土纳米复合凝胶微球的设计与实际应用提供指导。     

通过RAFT聚合方法合成具有高强度和高溶胀率的纳米水凝胶

为了得到具有高强度和高溶胀率的纳米水凝胶(NCgels),N-异丙基丙烯酰胺通过可逆加成断裂链转移(RAFT)聚合的方法,插层在含有质量分数为0.25%～15%的可扩展的有机化的蒙脱土(Clay-S)层间并交联。结果表明,与传统水凝胶相比,该水凝胶的强度和溶胀性能得到了很大提高,并且对温度的变化具有较快的响应速率。以质量分数为5%的蒙脱土,链转移剂的质量分数为0.5%制备的纳米水凝胶为例,该水凝胶在20℃的溶胀率为450,而传统水凝胶在相同温度时的溶胀率仅为20;该水凝胶在1min内失去75%的水,在4min内失去约90%的水,而传统水凝胶在15min内仅失去66%左右的水。     

Synthesis and swelling properties of a pH‐ and temperature‐dual responsive hydrogel by inverse microemulsion polymerization

A novel pH‐ and temperature‐dual responsive hydrogel was synthesized by inverse microemulsion polymerization, using itonic acid (IA) as pH‐responsive monomer, N‐isopropylacrylamide (NPAM) as thermo‐responsive monomer and acrylamide (AM) as the nonionic hydrophilic monomer. Factors affecting water and salt absorption, as well as swellability of the dual responsive hydrogels, such as IA/NPAM mass ratio and crosslinker amount, were investigated. pH‐ and temperature‐sensitivity and dynamic viscoelasticity behaviors of the dual responsive hydrogels were also studied. The dual responsive responsive hydrogels showed suitable water and salt absorbency, remarkable pH‐, and temperature‐sensitivity, adjustable swellability and enhanced viscoelastic behaviors under high stress. Water absorbency and pH‐sensitivity increased while salt absorbency and temperature‐ sensitivity decreased with increasing IA/NIPAM mass ratio. Both water absorbency and salt absorbency increased first with crosslinker amount increased to 0.2 wt %, and then decreased with increasing crosslinker amount. Temperature‐induced shrinkage range of the dual responsive hydrogels was higher and broader than that of the conventional poly(N‐isopropylacrylamide) hydrogel. TEM indicated that the as‐synthesized hydrogel particles were regular and spherical‐like in shape and had the mean particle size of 49nm in the range of 30–78 nm. FTIR indicated the structure of the dual responsive hydrogels. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42139.     

羟丙基纤维素RAFT聚合温敏性聚（N异丙基丙烯酰胺）水凝胶的合成及表征

用羟丙基纤维素(HPC)接枝的多链转移官能基大分子链转移剂,通过可逆加成断裂链转移(RAFT)聚合制备了羟丙基纤维素接枝聚(N-异丙基丙烯酰胺)(PNIPAM)水凝胶(HPC-g-PNIPAM hydrogel),研究了HPC相对分子质量、RAFT分子接枝密度以及HPC和NIPAM质量比对水凝胶微观形貌、低临界溶解温度(LCST)以及溶胀性能和机械性能的影响。结果表明,HPC大分子RAFT聚合PNIPAM能获得具有高溶胀比和快速响应性能的水凝胶;HPC的引入能提高水凝胶机械强度。RAFT聚合方法和少量大分子纤维素RAFT分子的引入会略微降低LCST,但当HPC组分增加到一定量,又会使LCST升高。     

聚N异丙基丙烯酰胺/黏土纳米复合自修复水凝胶的制备及性能

以N异丙基丙烯酰胺(PNIPA)为单体,纳米黏土硅酸镁锂(LXG)为交联剂,通过原位聚合反应制备了一种具有自修复功能的高分子/纳米黏土复合水凝胶。探讨了单体和黏土配比、单体与分散剂配比等参数对水凝胶成胶性能的影响。重点对该复合水凝胶自修复机理及性能进行评价。结果表明,当单体与黏土比例为1.5~2：1,单体与分散剂比例为1：10时水凝胶成胶性能良好;水凝胶的溶胀性能随黏土含量的增加而下降,最大溶胀率为12.8 g/g;合成的水凝胶在室温下无需任何修复剂,24 h即可实现损伤断面的良好修复,自修复效率最高为43.1 %。     

UV-induced synthesis of chitosan-<Emphasis Type="Italic">g</Emphasis>-polyacrylamide semi-IPN superabsorbent hydrogels

Superabsorbent hydrogels of chitosan-g-polyacrylamide with N,N′-methylene-bis-acrylamide as a crosslinker were prepared via UV irradiation in the absence of photoinitiator under homogeneous conditions. The product was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy to confirm the formation of hydrogels. The transparent hydrogels have been observed to exhibit as much as 2987% swelling in acidic solution. In addition, the hydrogel which hydrolyzed for 6 h (0.24 × 10³ min) can have a water uptake of 106 times its weight (5300% swelling for 0.5 g hydrogel). The effect of several variables such as time, temperature, pH, acrylamide/chitosan ratio, crosslinker amount, and different media was explored. Finally, the prepared hydrogel have been used in adsorption of Zn(II) ions from water with high removal efficiency (0.636 meq g⁻¹ or 20.8 mg g⁻¹) at pH = 7. The experimental data of the adsorption equilibrium from Zn(II) solution fit well with the pseudo-second-order model.     

Thermosensitive poly(n‐isopropylacrylamide) hydrogels bonded on cellulose supports

A two‐step initiation and polymerization process was developed for the preparation of two series of hydrogel–cellulose composites with distinctively different morphologies and swelling behaviors. Hydroentangled cotton cellulose fibers were optimally initiated in 20 mM aqueous ammonium cerium(IV) nitrate for 15 min and then polymerized in aqueous solutions of N‐isopropylacrylamide (NIPAAm) monomer and N,N′‐methylene bisacrylamide (BisA) crosslinker. The extents of hydrogels on the cellulose solids could be controlled by variations in the concentrations of the monomer and crosslinker as well as the NIPAAm/BisA solution‐to‐solid ratios. The two series of hydrogel–cellulose composites formed were hydrogel‐covered/filled cellulose (I) and cellulose‐reinforced hydrogel (II) composites. Series I composites were synthesized with NIPAAm/BisA solutions below the liquid saturation level of the cellulose; this led to pore structures (size and porosity) that depended on both the extent and swelling of the grafted hydrogels. Series II composites were polymerized in the presence of excessive NIPAAm/BisA solutions to produce cellulose solids completely encapsulated in the hydrogels. All the cellulose‐supported hydrogels exhibited lower extents of phase transition over a wider temperature range (28–40°C) than the free poly(N‐isopropylacrylamide) hydrogels (32°C). These findings demonstrate that hydrogels can be used to control the pore structure of cellulose and can be supported with cellulose fibers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 999–1006, 2003