Preparation of PEO-b-PPO-b-PEO/α-cyclodextrin supramolecular hydrogels hybridized with exfoliated graphite nanoplates

Abstract

In this work, an effective method was developed to prepare novel PEO-b-PPO-b-PEO (EPE)/α-cyclodextrin (α-CD) supramolecular hydrogels containing exfoliated graphite nanoplates (xGNPs) by mixing an aqueous solution of α-CD with an aqueous dispersion of xGNPs at the presence of amphiphilic EPE copolymer. The EPE copolymer played three important roles in the preparation process: (1) as an exfoliating agent to break expanded graphites into xGNPs under ultrasonication, (2) as a dispersant to stabilize xGNPs in the aqueous solution, and （3）as a component to form the inclusion complexes with α-CD. The resultant xGNPs/EPE/α-CD hybridized hydrogels were characterized by scanning electron microscopy, wide-angle X-ray diffraction, differential scanning calorimetry, and Fourier transform infrared spectroscopy, which confirmed not only the formation of supramolecular hydrogel structure but also the homogenous dispersion of xGNPs in the hydrogel matrix. It was found that the existence of xGNPs can accelerate the speed of gel formation in comparison with that of the native EPE/α-CD hydrogel. Additionally, the water-retention ability and the release behavior of vancomycin hydrochloride for the xGNPs/EPE/α-CD hybridized hydrogels were investigated.     

Search for a Steric Penultimate Effect: Copolymerization of 2,3,4-Trimethyl-3-pentyl Methacrylate with Styrene

The hindered monomer, 2,3,4-trimethyl-3-pentyl methacrylate (I), was synthesized for penultimate effect studies. Since it readily homopoiymerized (km¹¹¹≠ 0) and readily copolymerized with styrene, copolymerizations of I with styrene were carried out at 60°C in benzene with AIBN as initiator. The conversion to copolymer and the copolymer composition were determined by using GLC techniques. Composition-conversion data was analyzed by performing a computerized nonlinear least-squares fitting to the integrated form of the penultimate model equation. The experimental design included the use of optimized M¹°/M²° ratios. The penultimate reactivity ratios calculated from these data were r¹′ = 0.23, r¹′= 0.59, r² = 0.59, r²′ = 1.34. Thus, when I is the penultimate unit, a terminal styryl radical prefers to add styrene, whereas when styrene is the penultimate unit, terminal styryl radicals prefer to add I. These results constitute the best evidence for a steric penultimate effect yet available in the literature from composition-conversion studies. However, the case is not yet proved. Further studies to strengthen this conclusion are proposed.     

Novel Supports Based on Polysaccharides for Sustained‐Release of Isosorbide Dinitrate

Novel supports based on carboxymethylcellulose (CMC), crosslinked with epichlorohydrin (EPC), and microparticles based on acetylphthalylcellulose (APC), for sustained‐release of isosorbide dinitrate (Isoket, Ik), were obtained. The drug has been included into CMC hydrogels through diffusion from ethanol‐water solution. Studies about the ethanol–water ratio influence on including the drug have shown an increased amount of included drug at higher content of water in the alcohol‐water mixture. Isoket–ACP microparticles have been obtained by drug and polymer co‐precipitation from emulsified aqueous solution.

The kinetics for “in vitro” release of Ik from polymeric materials, in simulated conditions for intestinal tract medium, where the drug is preferentially absorbed, has been analyzed. The experimental data have shown a “zero” order kinetic for drug release, which is characteristic for systems controlled by diffusion.     

The Copolymerization of Alkenes with Maleic Anhydride

The investigations presented deal with the experimental results of the copolymerization of maleic anhydride (MAn) with alkenes. The course of the reaction is explained by the overall rate of the copolymerization (v _Br), which correlates with the solution viscosity of the copolymer, and the dependence of the v _Br maximum on the mole ratio of the monomers at constant total monomer concentration. The use of solvents with increasing donor power leads to increased complexing of the free MAn molecules and of the MAn radical chain ends. The results demonstrate that, for low 1-alkenes, the addition of the MAn chain radical is the rate-determining step of the copolymerization. As the substituents on the olefinic double bond become larger or the double bond shifts to the 1,2-position, the addition of MAn to the hydrocarbon radical becomes more and more the rate-determining step. On the other hand, an increase of the CT complexation of the MAn polymer radical by use of donor solvents decreases the alkene addition rate.     

Molecular Hydrogels with Esterase-like Activity

The development of molecular hydrogels that can be applied for mimicking bioactive molecules attracts extensive interests of researchers in fields of self‐assembly. In this study, we reported on several molecular hydrogels based on naphthylacetic acid‐peptides containing L‐histidine formed by the heating‐cooling process. All hydrogels exhibited higher activity to hydrolyze 4‐nitrophenyl acetate (4‐NPA) than the free L‐histidine probably due the high density of L‐histidine residue at the surface of self‐assembled nanofibers. To calculate the 4‐NPA hydrolysis rates, the Michaelis‐Menten enzyme kinetics model was made. Among these gels, the gel of Nap‐GFFYGHY possesses the highest enzyme activity of making the ester bond cleavage, which is approximately 25 times higher than that of the control (free L‐histidine and Nap‐GFFYGYY). These results indicate that molecular hydrogels with self‐assembled nanofibers have great potential for the generation of self‐assembled multivalent materials.     

Alginate‐Based Microcapsules with a Molecule Recognition Linker and Photosensitizer for the Combined Cancer Treatment

A reactive template method was used to fabricate alginate‐based hydrogel microcapsules. The uniform and well‐dispersed hydrogel capsules have a high drug loading capacity. After they are coated by a folate‐linked lipid mixture on the surface, the capsules possess higher cell uptake efficiency by the molecule recognition between folate and the folate‐receptor overexpressed by the cancer cells. Moreover, in this bioconjugate, the lipid could remarkably reduce the release rate of hydrophilic doxorubicin from the hydrogel microcapsules and encapsulate the hydrophobic photosensitizer hypocrellin B. The biointerfaced capsules could be used as drug carriers for combined treatment against cancer cell proliferation in vitro; this was much more effective than chemotherapy or photodynamic therapy alone.     

Mathematical modeling and sustained release property of a 5-fluorouracil imprinted vehicle

In the present research, a type of imprinted hydrogels, in which 5-fluorouracil is complexed non-covalently to the monomers and cross-linked into the hydrogel matrix, is synthesized in order to evaluate the possibility of their applications in sustaining the release of 5-fluorouracil due to the drug’s heightened interactions with the imprinted binding sites. Because of the hydrophility, hydrogels can absorb large amounts of water. As a result, drug release mechanisms are different from hydrophobic polymers. Mathematical model has been established to predict the drug release from the hydrogel matrix as a function of time. The drug release mechanism when immersed in release medium is discussed based on mathematical analysis. Swelling studies are performed and the capability of the hydrogels to reload 5-fluorouracil in aqueous solutions is evaluated. In vitro release studies after reloading are conducted. Mathematical analysis suggest that drug release kinetics from the hydrogels fit Fickian mechanism, further evaluation of the fitness for different hydrogel types reveal that the conformation of binding sites can play a very important role in deciding the kind of drug release mechanism. Experiments reveal that all hydrogels show swelling property. The imprinted hydrogels bind much more 5-fluorouracil than non-imprinted ones, and they sustain 5-fluorouracil release better than non-imprinted hydrogels. This research indicates that the imprinted hydrogels would be a potential promising device for drug delivery.     

Efficiency of Superparamagnetic Nano Iron Oxide Loaded Poly(Acrylamide-co-Maleic acid) Hydrogel in Uptaking Cu2+ Ions from Water

A novel superparamagnetic iron oxide nanoparticles loaded poly(acrylamide-co-maleic acid) hydrogel (superparamagnetic PAM hydrogel) has been synthesized and cross-linked by methylene bisacrylamide for the investigation of its efficiency in uptaking copper ions from aqueous solution by batch method. The swelling behavior of the hydrogel was investigated. Metal ion uptake capacity of the adsorbent was evaluated in the light of varying pH, contact time, temperature, adsorbent dose, and different copper ion concentration. The synthesized superparamagnetic PAM was characterized by FTIR and XRD analysis. The structure and coating of the magnetic nanoparticles were characterized by XRD and FTIR analysis respectively. The adsorption data was fitted well in the Langmuir, Freundlich, and Temkin models and various static parameters were calculated. It is stated that this hydrogel could be regenerated efficiently (>97%) and used repeatedly.     

聚乙烯醇/壳聚糖复合水凝胶的物理化学性质

测定了聚乙烯醇(PVA)和壳聚糖(CS)复合水凝胶的平衡含水量、熔融焓、等温溶胀动力学和非等温失水动力学等性质,讨论了水凝胶的组成和制备参数对这些性质的影响.结果显示:PVA/CS复合水凝胶具有适宜于软骨修复替代材料的网络结构和平衡含水量.CS与PVA复合减弱了凝胶的结晶度,但却增强了水与凝胶支架的相互作用.尽管水凝胶力学拉伸强度有所降低,但却优化了凝胶的生物相容性和降解能力.PVA/CS复合水凝胶是一种潜在的软骨修复材料,作为一种理论研究的模型体系,它将促进热力学在复杂医用材料方面的应用.