Electrospinning of PCL/PVP blends for tissue engineering scaffolds

Currently, one of the main drawbacks of using poly(ε-caprolactone) in the biomedical and pharmaceutical fields is represented by its low biodegradation rate. To overcome this limitation, electrospinning of PCL blended with a water-soluble poly(N-vinyl-2-pyrrolidone) was used to fabricate scaffolds with tunable fiber surface morphology and controllable degradation rates. Electrospun scaffolds revealed a highly immiscible blend state. The incorporated PVP phase was dispersed as inclusions within the electrospun fibers, and then easily extracted by immersing them in cell culture medium, exhibiting nanoporosity on the fiber surface. As a striking result, nanoporosity facilitated not only fiber biodegradation rates, but also improved cell attachment and spreading on the blend electrospun scaffolds. The present findings demonstrate that simultaneous electrospinning technique for PCL with water-soluble PVP provides important insights for successful tuning biodegradation rate for the PCL electrospun scaffolds but not limited to expand other high valuable biocompatible polymers for the future biomedical applications, ranging from tissue regeneration to controlled drug delivery.     

双酚A缩水甘油醚/乙二胺环氧树脂的热分解行为

采用傅里叶红外光谱法研究了双酚A缩水甘油醚/乙二胺环氧树脂(DGEBA/EDA)在不同温度时分解残留物的红外吸收光谱;利用热分析技术考察了DGEBA/EDA从室温到600℃之间的热解反应。结果表明,DGEBA/EDA环氧树脂在氮气中分解时存在一个热解阶段,最低热解活化能为195.74 kJ/mol。色谱-质谱联用(GC/MS)分析DGEBA/EDA环氧树脂热解残留物,表明在热解过程中主要生成苯酚、对异丙基苯酚和双酚A。讨论了DGEBA/EDA环氧树脂热解的机理。经热解后的残留环氧树脂的热稳定性降低明显,环氧树脂发生了明显的化学裂解。     

聚乙烯吡咯烷酮/聚(乙烯-乙烯醇)共混膜的制备及其油水分离性能

将聚乙烯吡咯烷酮(PVP)与聚(乙烯-乙烯醇)(EVAL)共混,采用浸没沉淀法制备了PVP/EVAL共混膜,并用于油水乳液分离过程。通过全反射红外光谱、扫描电子显微镜、拉伸试验、接触角测试等对膜的组成、结构形态、机械性能、亲水性进行了表征,并研究了PVP添加量对共混膜油水分离性能的影响。结果表明:添加PVP能较显著地改变EVAL膜的结构,且共混膜的机械强度和亲水性得到明显改善,当PVP添加量为10 wt%(PVP在铸膜液中的质量分数)时,其拉伸强度和断裂伸长率分别为纯EVAL膜的1.88倍和1.34倍。当PVP添加量为4 wt%时,油水分离稳定通量为纯EVAL膜的1.81倍,截留率为92.2%,比纯EVAL膜略高。PVP添加量为10 wt%的PVP/EVAL共混膜清洗后通量恢复率由纯EVAL膜的51%增至77.98%。     

稀溶液黏度法研究醋酸纤维素/聚乙烯吡咯烷酮共混物的相容性

以冰醋酸为共溶剂,利用乌氏黏度计在25℃研究了醋酸纤维素(CA)、聚乙烯吡咯烷酮(PVP)以及不同组成的CA/PVP共混物(CA的质量分数分别为0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9)的粘性行为。基于稀溶液黏度法确定的4种相容性判据(Δb,Δb’、Δ[η]m和α)探讨CA/PVP共混体系的相容性。实验结果表明,当醋酸纤维素在CA/PVP共混体系中的质量分数低于0.12或者在0.8～0.91范围内时,CA与PVP是相容的,其余的组成体系都是不相容的。因此,CA/PVP共混体系是部分相容体系。     

Composite of DGEBA/TBA epoxy blend and amine-functionalized carbon nanotube: Structural,thermal, nonflammability,and EMI shielding studies

Novel blend of diglycidyl ether of bisphenol-A (DGEBA) and tetrabromo bisphenol-A (TBA) was reinforced with acid-functionalized (MWCNT-F) and amine-functionalized multi-walled carbon nanotube (MWCNT-A). DGEBA/MWCNT-A displayed fine tubular morphology with open nanotube ends, while DGEBA/TBA/MWCNT-A displayed somewhat aggregated morphology due to lesser filler content. DGEBA/TBA/MWCNT-A system showed maximum enhancement in decomposition temperature (T₀ = 404°C, T_max = 583°C). Glass transition temperature and Limiting oxygen index of DGEBA/TBA/MWCNT-A were also higher (221°C and 55%) compared with other systems. DGEBA/TBA/CNT-A 0.1 had crystalline morphology with diffractions at 12.7° and 26.09°. Novel nanocomposite revealed EMI shielding effectiveness of ～15.05–15.18 dB, i.e., suitable for aerospace applications.     

PLLA/PVP共混静电纺丝形貌表征及性能研究

采用静电纺丝法制备了PLLA/PVP共混纤维膜,通过SEM、接触角表征了纤维膜的形貌以及亲水性能,同时测定了纤维膜的力学性能,探讨了共混液中PVP的比例对纤维膜形貌、亲水性能及力学性能的影响。结果表明:随着共混液中PVP比例的增大,PLLA的亲水性得到改善,但纤维的强力却迅速下降。当PVP的比例为40%和50%时,接触角接近零。SEM分析结果显示:纤维丝上孔的孔径和密度随着PVP比例的增大而发生改变。     

混合比及后处理对混合环氧/热塑性树脂复相体系动态力学特征的影响

以热塑性树脂(TP)/双酚A二缩水甘油醚(DGEBA)及二苯基甲烷四缩水甘油胺(TGMDA)混合环氧树脂的复相体系为基础,采用动态力学分析手段研究了在相同热塑性树脂含量的条件下,混合比例对混合环氧/热塑性树脂的动态力学性能中tanδ曲线的特征峰位置、峰形等的影响,以及在经高温后处理后曲线特征峰的变化.结合树脂断口分析,结果显示:混合环氧在固化反应过程中对热塑性树脂的高粘度高阻碍性的响应是不同的,tanδ曲线上的主峰主要由TP的转变构成而次级峰则主要由DGEBA环氧固化物的转变构成.高温后处理使树脂体系有利于分相及固化网络的完善.在复相体系中,连续相主要由TP及TGMDA环氧固化网络构成,DGEBA环氧主要存在于分散相中.     

Novel PVP/PVA hydrogels for articular cartilage replacement

Poly(vinyl alcohol) (PVA) hydrogel has been considered as a very interesting and promising material for articular cartilage replacement. The most vital shortcoming of PVA hydrogels is that their mechanical properties are difficult to meet the requirements of articular cartilage. In the present work, blend hydrogels based on PVA and poly (vinyl pyrrolidone) (PVP) were prepared by repeated freezing and thawing method. Such hydrogel had similar internal three-dimensional structure and water content (approximately 75%) as nature articular cartilage. The mechanical and tribological properties were investigated to find out that change of mechanical and tribological properties of PVP/PVA hydrogels were significantly dependent on PVP content and freezing–thawing cycles. The blend hydrogel with 1 wt.% PVP had the best mechanical properties and the friction system consisting of such blend hydrogel and stainless steel ball exhibited a mixed lubrication regime especially under bovine serum lubrication. The results established that such hydrogel would be a novel attractive material for articular cartilage replacement.     

Dissolution rate and stability study of flavanone aglycones,naringenin and hesperetin,by drug delivery systems based on polyvinylpyrrolidone (PVP) nanodispersions

Objective: To study the dissolution behavior, the release mechanism and the stability of nanodispersion system of aglycones with PVP. Methods: The nanodispersion system of polyvinylpyrrolidone (PVP)/naringenin–hesperetin was prepared using the solvent evaporation method. The chemical stability (compatibility) of naringenin and hesperetin in the prepared dispersions was studied under accelerated conditions for 3 months. The evaluation of physical stability was performed by X-ray diffraction analysis (XRD) and by comparing the dissolution profile before and after storage at high temperature and moisture (40ºC, RH 75%). Results: The dissolution rate of naringenin and hesperetin released was dramatically increased in the nanodispersion system of PVP/naringenin–hesperetin (80/20, w/w). The release mechanism of both flavanone aglycones was better described by the diffusion model (Higuchi model). Also it was found that the rate-limiting step that controlled the release of naringenin and hesperetin in the nanodispersion system was dissolution of the carrier (PVP). Conclusions: During accelerated degradation analysis, for 3 months at high temperature and moisture, PVP nanodispersion system showed enhanced chemical compatibility and physical stability. The physical evaluation (obtained from XRD analysis) of PVP/naringenin–hesperetin (80/20, w/w) in the selected storage conditions did not show any crystallization of flavanone aglycones in the PVP nanodispersion system or any change in their release profile.     

Hyperbranched polymers as modifiers of epoxy adhesives

A novel hyperbranched poly(amide-ester)s (HBP) has been synthesized through the AB₂ approach in one-step polycondensation without solvents. The synthesized HBP has been characterized and used as filler for epoxy resin with the aim obtain materials which exhibit improved toughness. Composites containing 6% and 12% wt/wt of HBP in diglycidylether of bisphenol A (DGEBA) were produced and characterized. Results obtained from DMA tests showed that HBP has good compatibility with the epoxy resin. Impact tests proved that composites containing 12% HBP showed an improvement of about 25% on impact strength with respect to neat DGEBA. Moreover, adhesive properties were evaluated in terms of the lap-shear strength value of composite joints bonded using the investigated blend. Results showed an improvement of shear strength value of DGEBA added with 12% HBP with respect to neat DGEBA. The water uptake behavior was also evaluated.     

Reaction-induced phase separation in an epoxy/low molecular weight solvent system

Blends based on a stoichiometric mixture of diglycidyl ether of bisphenol A (DGEBA) and 2,2-bis(4-amino-cyclohexyl)methane (ACHM) and cyclohexane as low molecular weight solvent were studied. The polymerization kinetics data experimentally obtained at different temperatures (30–60°C) were accurate fitted using a mechanistic model. The effect of the solvent over the polymerization rate was analyzed. No influence of the presence of the solvent was found up to 20 wt% of cyclohexane in the sample. The thermodynamic analysis using Flory-Huggins model allowed determination of the initial miscibility of binary blends containing DGEBA/cyclohexane and pseudo-binary mixtures of DGEBA/ACHM/cyclohexane. The presence of ACHM increases the DGEBA/cyclohexane initial solubility. The reaction-induced phase separation was described using a conversion-composition transformation phase diagram. It indicates that phase separation takes place by a nucleation and growth (NG) mechanism. The appropriate selection of composition of the blend and polymerization conditions led to final materials with a desired closed cell porous morphology.     

Effect of PVP loading on pervaporation performance of poly(vinyl alcohol) membranes for THF/water mixtures

This work reports an experimental study on the pervaporative dehydration of an industrial solvent tetrahydrofuran (THF) using a blend membrane of PVA/PVP crosslinked with maleic acid. The influence of feed composition and permeate pressure on the pervaporation flux and selectivity has been investigated. The membrane was found to exhibit a water flux of 0.007 kg/m² h with a water selectivity of infinity for dehydration of 97% THF at 30 °C. FTIR of the blend was carried out to interpret its behavior on the basis of interactions between carbonyl groups of the cationic PVP and hydroxyl groups of the neutral PVA polymer. X-ray diffraction and sorption studies were carried out to study the degree of crystallinity and polymer–liquid interactions. The variation in film morphology was examined by scanning electron microscopy (SEM). Pervaporation experiments showed that high selectivity and promising permeability were obtained with a 9:1 blending ratio of PVA/PVP membrane crosslinked with 5 wt% maleic acid.     

Thermal stability,morphology, and X-ray diffraction studies of dynamically vulcanized natural rubber/chitosan blends

The thermal degradation behavior of cross-linked Natural Rubber/Chitosan (NR/CS) blends was studied by thermogravimetric analysis (TGA). Dicumyl peroxide (DCP) was selected as a cross-linking agent. Peroxide-cured NR/CS blends exhibit very good overall thermal properties. The activation energy of degradation was analyzed using the Horowitz–Metzger equation. Vulcanization of rubber phase in the blend increased the activation energy. From the activation energy values, it is found that among the series of the blend compositions, NR₈₅CS₁₅ blend vulcanized with 3 pphr DCP exhibits better thermal stability. Better adhesion between the two phases with the incorporation of DCP is achieved which results in an enhancement in the thermal stability. The DSC curve shows that, the T _g of chitosan in the blend increased to 242 °C by dynamic vulcanization. The morphology of the vulcanized blends was studied by scanning electron microscopy. More uniform distribution was exhibited by the vulcanization of NR phase in the blend. X-ray diffraction (XRD) study shows an enhancement in the crystallinity by vulcanization.     

添加剂对PVC/PVB共混超滤膜性能的影响

通过干-湿相转化法,制备聚氯乙烯（PVC）/聚乙烯醇缩丁醛（PVB）共混平板超滤膜;考察了3种不同型号的PVB型号、添加剂聚乙二醇（PEG）和聚乙烯吡咯烷酮（PVP）在铸膜液中的含量的不同对共混超滤膜性能的影响。结果表明PVB对PVC共混改性可有效改善膜的性能,在不同型号的PVB中PVB-60T对膜亲水性和分离性能改善最为显著;当PEG含量为5%,PVP含量分别为5%和1%时,PVC/PVB共混膜分离性能较佳,纯水通量为510.1L/（m2.h）,截留率为98%。     

pH-sensitive hydrogels based on semi-interpenetrating network (semi-IPN) of chitosan and polyvinyl pyrrolidone for clarithromycin release

The aim of this study was to develop a pH-sensitive chitosan/polyvinyl pyrrolidone (PVP) based controlled drug release system for clarithromycin. The hydrogels were synthesized by cross-linking chitosan and PVP blend with glutaraldehyde to form a semi-interpenetrating polymer network (semi-IPN). These semi-IPNs were studied for their content uniformity, swelling index (SI), mucoadhesion, wettability, in vitro release and their release kinetics. The hydrogels showed more than 97% content of clarithromycin. These hydrogels showed high swelling and mucoadhesion under acidic conditions. The swelling may be due to the protonation of a primary amino group on chitosan. In acidic condition, chitosan would be ionized, and adhesion could have occurred between the positively charged chitosan and the negatively charged mucus. In the alkaline condition, less swelling and mucoadhesion was noticed. In vitro release study revealed that formulation containing chitosan (2% w/v) and PVP (4% w/v) in the ratio of 21:4 showed complete drug release after 12 h. Release profile showed that all the formulations followed non-Fickian diffusion mechanism. The cross-linking and compatibility of clarithromycin in the formulation was studied by Fourier transform infrared (FTIR) spectroscopic analysis, differential scanning calorimetry (DSC) and powder X-ray diffraction (p-XRD) study, which confirmed proper formation of semi-IPN and stability of clarithromycin in the formulations. The surface morphology of semi-IPN was studied before and after dissolution in simulated gastric fluid (SGF, pH 1.2) which revealed pores formation in membrane after dissolution. The results of study suggest that semi-IPNs of chitosan/PVP are potent candidates for delivery of clarithromycin in acidic environment.     

Control of self organization in conjugated polymer fibers

We propose new strategy to facilitate the fabrication of conjugated polymer fiber with higher oriented structures, which focused on electrospinning of a blend solution of regioregular poly(3-hexylthiophene) (rr-P3HT) and poly(vinyl pyrrolidone) (PVP). SEM observation revealed that the blend system forms homogeneous composite nanofibers. This system exhibits the specific feature of strong interchain contribution of P3HT from UV-vis absorption, fluorescence spectroscopic, XRD, and photoelectron spectrometric (for HOMO levels) investigations. We also demonstrate the removal of the PVP component from the P3HT/PVP composite fibers through the selective extraction and such strong interchain stacking of pristine P3HT fiber mat can be remarkably maintained.     

Lithium ion conducting solid polymer blend electrolyte based on bio-degradable polymers

Lithium ion conducting polymer blend electrolyte films based on poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) with different Mwt% of lithium nitrate (LiNO₃) salt, using a solution cast technique, have been prepared. The polymer blend electrolyte has been characterized by XRD, FTIR, DSC and impedance analyses. The XRD study reveals the amorphous nature of the polymer electrolyte. The FTIR study confirms the complex formation between the polymer and salt. The shifts in T _g values of 70 PVA–30 PVP blend and 70 PVA–30 PVP with different Mwt% of LiNO₃ electrolytes shown by DSC thermograms indicate an interaction between the polymer and the salt. The dependence of T _g and conductivity upon salt concentration has been discussed. The ion conductivity of the prepared polymer electrolyte has been found by a.c. impedance spectroscopic analysis. The PVA–PVP blend system with a composition of 70 wt% PVA: 30 wt% PVP exhibits the highest conductivity of 1·58 × 10^???6 Scm^???1 at room temperature. Polymer samples of 70 wt% PVA–30 wt% PVP blend with different molecular weight percentage of lithium nitrate with DMSO as solvent have been prepared and studied. High conductivity of 6·828 × 10^???4 Scm^???1 has been observed for the composition of 70 PVA:30 PVP:25 Mwt% of LiNO₃ with low activation energy 0·2673 eV. The conductivity is found to increase with increase in temperature. The temperature dependent conductivity of the polymer electrolyte follows the Arrhenius relationship which shows hopping of ions in the polymer matrix. The relaxation parameters (ω) and (τ) of the complexes have been calculated by using loss tangent spectra. The mechanical properties of polymer blend electrolyte such as tensile strength, elongation and degree of swelling have been measured and the results are presented.     

Preparation of PVP/MEH-PPV composite polymer fibers by electrospinning and study of their photoelectronic character

Ultrafine polyvinylpyrrolidone (PVP)/poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) composite fibers were successfully prepared by electrospinning of PVP/MEH-PPV blend solutions in solvent mixtures of 1,2-dichloroethane/chlorobenzene. Composite polymer fibers with smooth surface were obtained using solutions in which MEH-PPV's concentration was 1.0 (wt.%). Compared with the MEH-PPV solution and bulk, PVP/MEH-PPV fibers show a significant blue shift, a stronger intensity of fluorescence and a higher surface photovoltage (SPV). The morphology of fibers has been characterized by scanning electron microscopy (SEM) and fluorescence microscopy.     

聚乙烯吡咯烷酮含量对聚偏氟乙烯/聚醚砜共混膜性能和结构的影响

采用二甲基乙酰胺为溶剂,聚乙烯吡咯烷酮(PVP K90)为致孔性添加荆,研究了PVP的浓度对聚偏氟乙烯/聚醚砜(PVDF/PES)共混膜的收缩率、纯水通量、牛血清蛋白(BSA)截留率和膜结构的影响.在PVP含量为5%时,共混膜的收缩率最低,水通量取得极大值,截留率有一极小值.     

pH-sensitive hydrogels based on semi-interpenetrating network (semi-IPN) of chitosan and polyvinyl pyrrolidone for clarithromycin release

The aim of this study was to develop a pH-sensitive chitosan/polyvinyl pyrrolidone (PVP) based controlled drug release system for clarithromycin. The hydrogels were synthesized by cross-linking chitosan and PVP blend with glutaraldehyde to form a semi-interpenetrating polymer network (semi-IPN). These semi-IPNs were studied for their content uniformity, swelling index (SI), mucoadhesion, wettability, in vitro release and their release kinetics. The hydrogels showed more than 97% content of clarithromycin. These hydrogels showed high swelling and mucoadhesion under acidic conditions. The swelling may be due to the protonation of a primary amino group on chitosan. In acidic condition, chitosan would be ionized, and adhesion could have occurred between the positively charged chitosan and the negatively charged mucus. In the alkaline condition, less swelling and mucoadhesion was noticed. In vitro release study revealed that formulation containing chitosan (2% w/v) and PVP (4% w/v) in the ratio of 21:4 showed complete drug release after 12?h. Release profile showed that all the formulations followed non-Fickian diffusion mechanism. The cross-linking and compatibility of clarithromycin in the formulation was studied by Fourier transform infrared (FTIR) spectroscopic analysis, differential scanning calorimetry (DSC) and powder X-ray diffraction (p-XRD) study, which confirmed proper formation of semi-IPN and stability of clarithromycin in the formulations. The surface morphology of semi-IPN was studied before and after dissolution in simulated gastric fluid (SGF, pH 1.2) which revealed pores formation in membrane after dissolution. The results of study suggest that semi-IPNs of chitosan/PVP are potent candidates for delivery of clarithromycin in acidic environment.