Characterizing the impact of thermal gels on isotachophoresis in microfluidic devices

Thermally reversible Pluronic gels have been employed as separation matrices in microfluidic devices in the analysis of biological macromolecules. The phase of these gels can be tuned between liquid and solid states using temperature to vary fluidic resistance and alter peak resolution. Although separations in thermal gels have been characterized, their effect on isotachophoresis has not. This study used fluorescein as a model analyte to evaluate isotachophoretic preconcentration as a function of thermal polymer concentration and temperature. Results demonstrated that increasing polymer concentration in microfluidic channels increased the apparent analyte concentration. A critical minimum of 10% (w/v) Pluronic was required to achieve efficient preconcentration with maximum focusing occurring in 20 and 25% polymer gels. Temperature of the thermal gel also impacted analyte focusing. Most efficient focusing was achieved at 25°C with diminishing analyte accumulation at higher and lower temperatures. Under optimal conditions, isotachophoretic preconcentration increased an additional threefold simply by including thermal gels in the system. This approach can be readily implemented in other applications to increase detection sensitivity and measure low-concentration analytes within simple microfluidic devices.     

SIMS depth profiling of polymer blends with protein based drugs

We report the results of the surface and in-depth characterization of two component blend films of poly(l-lactic acid) (PLLA) and Pluronic surfactant [poly(ethylene oxide) (A) poly(propylene oxide) (B) ABA block copolymer]. These blend systems are of particular importance for protein drug delivery, where it is expected that the Pluronic surfactant will retain the activity of the protein drug and enhance the biocompatibility of the device. Angle dependant X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) employing an SF₅⁺ polyatomic primary ion source were both used for monitoring the surfactant's concentration as a function of depth. The results show an increased concentration of surfactant at the surface, where the surface segregation initially increases with increasing bulk concentration and then remains constant above 5% (w/w) Pluronic. This surface segregated region is immediately followed by a depletion region with a homogeneous mixture in the bulk of the film. These results suggest the selection of the surfactant bulk concentration of the thin film matrices for drugs/proteins delivery should achieve a relatively homogeneous distribution of stabilizer/protein in the PLLA matrix. Analysis of three component blends of PLLA, Pluronic and insulin are also investigated. In the three component blends, ToF-SIMS imaging shows the spatial distribution of surfactant/protein mixtures. These data are reported also as depth profiles.     

Synthesis and Characterization of pH- and Temperature-sensitive Hydrogels of Poly (Styrene-alt-Maleic Anhydride)-co-Pluronic for Drug Release

A pH- and temperature-sensitive hydrogel of poly(styrene-alt-maleic anhydride) -co-Pluronic P123 (PSMA-P123) was prepared by the reaction of anhydride groups (MA) on PSMA with the hydroxyl groups on Pluronic (triblock polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide, HO(CH₂CH₂O)₂₀(CH₂CH(CH₃)O)₇₀ (CH₂CH₂O)₂₀OH). The effect of proportions between PMSA and P123 on the gel fraction was determined. The effects of pH value and temperature on swelling ratio of the hydrogels were evaluated. Scanning electron microscopy was used to observe the morphology of the hydrogels. Differential scanning calorimetry was employed to characterize the thermo-sensitivity of the hydrogel. The drug-release behavior of the hydrogels was investigated by using chloromycetin as a model drug. The effect of temperature and pH on the release of chloromycetin from the hydrogels was studied. These results showed that PSMA-P123 hydrogels, being pH- and temperature-sensitive and reversible, appeared to be of potential for biomedical materials, especially for drug release applications.     

Effect of poly(γ‐glutamic acid) on the gelation of Pluronic F127

The gelation of Pluronic F127 aqueous solution was investigated in the presence of sodium poly(γ‐glutamate) (PGA). The gelation temperature was determined based on the tube inversion technique. The gelation temperature increased greatly when the ratio of PGA to F127 was 0.2, and then decreased at higher ratios. The enthalpy of gelation (ΔH_gel) was calculated based on the model of Eldridge and Ferry. A splitting in the model was observed when the PGA/F127 ratio was 0.2 which yielded both a maximum and a minimum of ΔH_gel. These results indicate that PGA can significantly affect the gelation of F127. Copyright © 2008 John Wiley & Sons, Ltd.     

Pluronic L61 accelerates flip-flop and transbilayer doxorubicin permeation

It has recently been found that Pluronics (block copolymers of ethylene oxide, EO, and propylene oxide, PO) favor the permeability and accumulation of anthracycline antibiotics, for example doxorubicin (Dox), in tumor cells. In an effort to understand these results, the interaction of EO(2)/PO(32)/EO(2) (Pluronic L61) with unilamellar egg yolk vesicles (80-100 nm in diameter) was examined. A partition coefficient K(p)=[Pl](membrane)/[Pl](water)=45 was determined. This corresponds to adsorption of about 20 polymer molecules to the surface of each vesicle in a 20 microM polymer solution. Despite this rather weak adsorption, Pluronic has a substantial effect upon the transmembrane permeation rate of Dox and upon the phospholipid flip-flop rate within the bilayers. Thus, the Dox permeation rate increases threefold and the flip-flop rate increases sixfold in 20 microM Pluronic. The two rates increase linearly with the amount of adsorbed polymer. The obvious ability of Pluronics to increase the mobility of membrane components may have important biomedical consequences.     

(PAA-b-F127-b-PAA)-Blg复合物的合成及乳化性能

采用原子转移自由基聚合(ATRP)方法合成了PtBA-b-F127-b-PtBA(PtBA为聚丙烯酸叔丁酯), 经三氟乙酸水解得到PAA-b-F127-b-PAA(PAA为聚丙烯酸). 进一步通过碳二亚胺的水溶性衍生物1-(3-二甲氨基丙基)-3-乙基碳二亚胺盐酸盐(EDC?HCl)在水溶液中成功地耦合β-乳球蛋白(Blg)和PAA-b-F127-b-PAA. 蛋白的三级构象没有受到反应条件的影响. 与纯Blg相比, (PAA-b-F127-b-PAA)-Blg复合物的乳化性能大大提高.     

Stabilization and activation of Pluronic micelles for tumor-targeted drug delivery

In order to be used as drug carriers, Pluronic micelles require stabilization to prevent degradation caused by significant dilution accompanying IV injection. This article studies three routes of Pluronic micelle stabilization. The first route was direct radical crosslinking of micelles cores which resulted in micelle stabilization. However, this compromised the drug loading capacity of Pluronic micelles. In the second route, a small concentration of vegetable oil was introduced into diluted Pluronic solutions. This decreased micelle degradation upon dilution while not compromising the drug loading capacity of oil-stabilized micelles. The third route was a novel technique based on polymerization of the temperature-responsive LCST hydrogel in the core of Pluronic micelles. The hydrogel phase was in a swollen state at room temperature, which provided a high drug loading capacity of the system. The hydrogel collapsed at physiological temperatures which locked the core of micelles thus preventing them from fast degradation upon dilution. This new drug delivery system was called Plurogel®. Phase transitions in Plurogel® caused by variations in temperature or concentration were studied by the EPR. The effect of Pluronic concentration in the incubation medium on the intracellular uptake of two anti-cancer drugs was studied. At low Pluronic concentrations, when the drugs were located in the hydrophilic environment, drug uptake was increased, presumably due to the effect of a polymeric surfactant on the permeability of cell membranes. In contrast, when the drugs were encapsulated in the hydrophobic cores of Pluronic micelles, drug uptake by the cells was substantially decreased. This may be advantageous in the prevention of undesired drug interactions with normal cells. Ultrasonication enhanced intracellular drug uptake from dense Pluronic micelles. These findings permitted the formulation of a new concept of a localized drug delivery.     

Effect of dynamic high pressure microfluidization on structure and stability of pluronic F127 modified liposomes

Pluronics modified liposomes have been prepared and shown to enhance stability of liposomes in our previous reports. In this study, we intended to evaluate the effect of dynamic high pressure microfluidization (DHPM) on the structure and stability of pluronic F127 modified liposomes. The results indicated that the particle size of F127 modified liposomes was decreased from 1180.6?nm to 73.5?nm after DHPM treatment. Meanwhile, the morphology was changed from irregularly multilamellar vesicle to spherically unilamellar structure. Structural characteristics were examined by fourier transformed infrared spectrometer, differential scanning calorimetry and X-ray powder diffraction. The subtle difference of structure might be attributed to the incorporation of PPO chains into the bilayer caused by DHPM treatment. Stability studies indicated that DHPM treatment could enhance the storage and membrane stability of F127 modified liposomes. This study may provide more insight to understand the effect of preparation method on the structure and stability of F127 modified liposomes.     

CO_2诱导的五嵌段非离子共聚物与阴离子氟碳表面活性剂的相互作用

聚合物-表面活性剂复合物在诸多工业领域都具有重要的应用潜力,但利用CO_2气体调节复合物的相互作用及微观聚集体形貌鲜见报道。本文基于三嵌段共聚物普兰尼克F127制备了五嵌段共聚物聚甲基丙烯酸二乙氨基乙酯-block-聚氧化乙烯-block-聚氧化丙烯-block-聚氧化乙烯-block-聚甲基丙烯酸二乙氨基乙酯(PDEAEAM-b-F127-b-PDEAEMA)。通过聚合物溶液pH和电导率的变化研究了PDEAEAM-b-F127-b-PDEAEMA的CO_2刺激响应性,应用动态光散射和透射电子显微镜考察了PDEAEAM-b-F127-b-PDEAEMA与阴离子氟碳表面活性剂在CO_2刺激作用下的相互作用。结果表明,CO_2/N_2的交替通入可以使PDEAEAM-b-F127-b-PDEAEMA产生相应的质子化/去质子化过程,从而可逆地改变PDEAEAM-b-F127-b-PDEAEMA溶液的pH值和电导率;质子化/去质子化过程可以"开关"共聚物与阴离子氟碳表面活性剂之间的静电吸引作用,使体系中的聚集体在球形胶束与蠕虫状胶束之间发生可逆转变。CO_2可控的聚合物-表面活性剂复合物的形貌转变为构建气体响应的软材料提供了一种新的思路。     

Biocompatibility Study of Curcumin-Loaded Pluronic F127 Nanoformulation (NanoCUR) against the Embryonic Development of Zebrafish (Danio rerio)

Curcumin (CUR) has been studied for its biomedical applications due to its active biological properties. However, CUR has limitations such as poor solubility, low bioavailability, and rapid degradation. Thus, CUR was nanoformulated with the application of polymeric micelle. Previous studies of CUR-loaded Pluronic F127 nanoformulation (NanoCUR) were generally prioritized toward cancer cells and its therapeutic values. There are reports that emphasize the toxicity of CUR, but reports on the toxicity of NanoCUR on embryonic developmental stages is still scarce. The present study aims to investigate the toxicity effects of NanoCUR on the embryonic development of zebrafish (Danio rerio). NanoCUR was synthesized via thin film hydration method and then characterized using DLS, UV-Vis, FTIR, FESEM, and XRD. The toxicity assessment of NanoCUR was conducted using zebrafish embryos, in comparison to native CUR, as well as Pluronic F127 (PF) as the controls, and ROS assay was further carried out. It was revealed that NanoCUR showed an improved toxicity profile compared to native CUR. NanoCUR displayed a delayed toxicity response and showed a concentration- and time-dependent toxicity response. NanoCUR was also observed to generate a significantly low reactive oxygen species (ROS) compared to native CUR in ROS assay. Overall, the results obtained highlight the potential of NanoCUR to be developed in clinical settings due to its improved toxicity profile compared to CUR.