Acid-Sphingomyelinase Triggered Fluorescently Labeled Sphingomyelin Containing Liposomes in Tumor Diagnosis after Radiation-Induced Stress

In liposomal delivery, a big question is how to release the loaded material into the correct place. Here, we will test the targeting and release abilities of our sphingomyelin-consisting liposome. A change in release parameters can be observed when sphingomyelin-containing liposome is treated with sphingomyelinase enzyme. Sphingomyelinase is known to be endogenously released from the different cells in stress situations. We assume the effective enzyme treatment will weaken the liposome making it also leakier. To test the release abilities of the SM-liposome, we developed several fluorescence-based experiments. In in vitro studies, we used molecular quenching to study the sphingomyelinase enzyme-based release from the liposomes. We could show that the enzyme treatment releases loaded fluorescent markers from sphingomyelin-containing liposomes. Moreover, the release correlated with used enzymatic activities. We studied whether the stress-related enzyme expression is increased if the cells are treated with radiation as a stress inducer. It appeared that the radiation caused increased enzymatic activity. We studied our liposomes’ biodistribution in the animal tumor model when the tumor was under radiation stress. Increased targeting of the fluorescent marker loaded to our liposomes could be found on the site of cancer. The liposomal targeting in vivo could be improved by radiation. Based on our studies, we propose sphingomyelin-containing liposomes can be used as a controlled release system sensitive to cell stress.     

Characterization of enzymatically synthesized amylopectin analogs via asymmetrical flow field flow fractionation

Asymmetrical flow field flow fractionation (AF4), when coupled with multi-angle laser light scattering (MALLS), is a very powerful technique for determination of the macromolecular structure of high molar mass (branched) polysaccharides. AF4 is a size fractionation technique just as size exclusion chromatography (SEC), nevertheless can overcome some crucial problems found in SEC analysis especially in starch like structures. This paper describes a detailed investigation of the macromolecular structure of two groups of well-defined synthetic amylopectin analogs – synthesized via an in vitro enzyme-catalyzed reaction using the enzymes phosphorylase b from rabbit muscle and Deinococcus geothermalis glycogen branching enzyme (Dg GBE). Size, molar mass distributions and structural data were studied by AF4 coupled with online quasi-elastic light scattering (QELS) and multi-angle light scattering (MALLS).     

Retention of Eucalyptol,a Natural Volatile Insecticide,in Delivery Systems Based on Hydroxypropyl‐β‐Cyclodextrin and Liposomes

Eucalyptol (Euc) is a natural monoterpene with insecticide effects. Being highly volatile and sensitive to ambient conditions, its encapsulation would enlarge its application. Euc‐loaded conventional liposomes (CL), cyclodextrin/drug inclusion complex, and drug‐in‐cyclodextrin‐in‐liposomes (DCL) are prepared to protect Euc from degradation, reduce its evaporation, and provide its controlled release. The liposomal suspension is freeze‐dried using hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) as cryoprotectant. The liposomes are characterized before and after freeze‐drying. The effect of Euc on the fluidity of liposomal membrane is also examined. A release study of Euc from delivery systems, in powder and reconstituted forms, is performed by multiple head extraction at 60 °C after 6 months of storage at 4 °C. CL and DCL suspensions are homogeneous, show nanometric vesicles size, spherical shape, and negative surface charge before and after freeze‐drying. Moreover, HP‐β‐CD does not affect the fluidity of liposomes. CL formulations present a weak encapsulation for Euc. The loading capacity of eucalyptol in DCL is 38 times higher than that in CL formulation. In addition, freeze‐dried DCL and HP‐β‐CD/Euc inclusion complex show a higher retention of eucalyptol than CL delivery system. Both carrier systems HP‐β‐CD/Euc and Euc‐loaded DCL decrease Euc evaporation and improve its retention. Practical Applications: Eucalyptol is a natural insecticide. It is highly volatile and poorly soluble in water. To enlarge its application, its encapsulation in three delivery systems (conventional liposomes, cyclodextrin/drug inclusion complex, combined system composed of cyclodextrin inclusion complex and liposome) is studied. In this paper it is proved that cyclodextrin/eucalyptol inclusion complex and eucalyptol‐in‐cyclodextrin‐in‐liposome are effective delivery systems for encalyptol encapsulation, retention, and release.     

Nanoliposomes for encapsulation and delivery of the potential antitumoral methyl 6-methoxy-3-(4-methoxyphenyl)-1H-indole-2-carboxylate

A potential antitumoral fluorescent indole derivative, methyl 6-methoxy-3-(4-methoxyphenyl)-1H-indole-2-carboxylate, was evaluated for the in vitro cell growth inhibition on three human tumor cell lines, MCF-7 (breast adenocarcinoma), A375-C5 (melanoma), and NCI-H460 (non-small cell lung cancer), after a continuous exposure of 48 h, exhibiting very low GI50 values for all the cell lines tested (0.25 to 0.33 μM). This compound was encapsulated in different nanosized liposome formulations, containing egg lecithin (Egg-PC), dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylglycerol (DPPG), DSPC, cholesterol, dihexadecyl phosphate, and DSPE-PEG. Dynamic light scattering measurements showed that nanoliposomes with the encapsulated compound are generally monodisperse and with hydrodynamic diameters lower than 120 nm, good stability and zeta potential values lower than -18 mV. Dialysis experiments allowed to monitor compound diffusion through the lipid membrane, from DPPC/DPPG donor liposomes to NBD-labelled lipid/DPPC/DPPG acceptor liposomes.     

Manufacturing of 3D-Printed Microfluidic Devices for the Synthesis of Drug-Loaded Liposomal Formulations

Microfluidic technique has emerged as a promising tool for the production of stable and monodispersed nanoparticles (NPs). In particular, this work focuses on liposome production by microfluidics and on factors involved in determining liposome characteristics. Traditional fabrication techniques for microfluidic devices suffer from several disadvantages, such as multistep processing and expensive facilities. Three-dimensional printing (3DP) has been revolutionary for microfluidic device production, boasting facile and low-cost fabrication. In this study, microfluidic devices with innovative micromixing patterns were developed using fused deposition modelling (FDM) and liquid crystal display (LCD) printers. To date, this work is the first to study liposome production using LCD-printed microfluidic devices. The current study deals with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes with cholesterol (2:1) prepared using commercial and 3D-printed microfluidic devices. We evaluated the effect of microfluidic parameters, chip manufacturing, material, and channel design on liposomal formulation by analysing the size, PDI, and ζ-potential. Curcumin exhibits potent anticancer activity and it has been reported that curcumin-loaded liposomes formulated by microfluidics show enhanced encapsulation efficiency when compared with other reported systems. In this work, curcumal liposomes were produced using the developed microfluidic devices and particle sizing, ζ-potential, encapsulation efficiency, and in vitro release studies were performed at 37 °C.     

Phospholipid liposomes: Preparation,characterization, and uses

Rhodopsin and cyclic guanosine monophosphat (cGMP)-dependent channel proteins are isolated from the rod outer segment disk membranes of dark-adopted bovine retinae and incorporated in liposomes, prepared by the method of detergent removal dialysis. The ion channel does not lose its transport function (release of Ca²⁺ ions by injection of cGMP) when incorporated in a liposome. Its activity depends on the degree of protein solubilization and the kind of detergent used. The highest activity is obtained by use of the detergent CHAPS. Shape, size, and size distribution of the liposomes are deduced from elastic and quasi-elastic light scattering, the liposome number density by viscometry, and the photopigment or Ca²⁺ content by optical absorbance. The liposomes are heterogeneous with respect to size and shape. Small unilamellar liposomes (R_h = 80 nm) and a narrow size distribution (U_D = 0.16) are obtained by using the detergent CHAPS. With increasing rhodopsin content per liposome, the hydrodynamic radius R_h increases and at the same time the shape of a liposome converts from a sphere to a prolate ellipsoid. The amount of entrapped Ca²⁺ per liposome reaches its maximum value when the Rhodopsin nearest-neighbor distance approaches its minimum value. This suggests an intermembrane protein-lipid-protein lattice, which serves as barriere for Ca²⁺. The influence of temperature or total used Ca²⁺ content is less profound. Increasing temperature yields slightly smaller liposomes.     

The selective delivery of anticancer agents using target-sensitive liposomes

Target-sensitive (TG-S) liposomes having modified antibodies on their surface were employed to study the release of calcein and the selective delivery of the anticancer agents, doxorubicin (DOX) and methotrexate (MTX). The release of calcein from TG-S liposome occurred when the various target cells were contacted with liposomes and it was proportionally increased with the increase of antibody affinity to the target cells. Increasing the concentration of antigen molecules (major histocompatibility, MHC) on the surface of RMA-S, the release of calcein and drugs from TG-S liposomes contacting with RMA-S also rised. The destabilization of TG-S liposomes was only induced above a threshold density of surface antigen on the target cell membrane. The growth inhibition of specific target cells by the liposomal drugs was always stronger than that of the non-specific ones. For specific target cells, the IC₅₀ of liposomal DOX was about 2 times greater than that of free DOX, on the while, for non-specific target cells, more than 5 times. This indicates that the liposomal drugs were transferred preferentially to the specific target cells than the non-specific ones. Based on this phenomenon, the TG-S liposomal MTX were also applied for the selective elimination of the specific target cells in the mixed culture of specific and non-specific target cells.     

Efficient preparation of liposomes encapsulating food materials using lecithins by a mechanochemical method

In order to evaluate to the feasibility of using lecithins for nanocapsules including functional food materials, liposomes were prepared from different commercially available lecithins (SLP-WHITE, SLP-PC70 and PL30S) by the Bangham method, and their physicochemical properties were examined by using a confocal laser scanning microscopy (CLSM) and the measurements of trapping efficiency. There was little difference in the trapping efficiency among the three types of liposomes. In all cases, the trapping efficiency clearly increased with an increase of the lecithin concentration up to 10 wt % , and the maximum efficiency reached at approximately 15%. CLSM observation showed the particle size of liposomes prepared from SLP-WHITE is significantly smaller than that prepared from other lecithins. In addition, liposomal solution prepared from SLP-WHITE remained well dispersed for at least 30 days, while two other liposomal solutions showed a phase separation due to aggregation and/or fusion of liposomes. These results indicated that SLP-WHITE is the most appropriate for the preparation of stable liposomes with well dispersed among the lecithins tested. SLP-WHITE liposomes were then prepared by the mechanochemical method using a homogenizer and microfluidizer, aiming at improving the preparation efficiency and liposome stability. The particle size of the prepared SLP-WHITE liposomes decreased with increasing inlet pressure and the number of processed cycles, and reached between 73 and 123 nm based on the measurement using dynamic light scattering. Moreover, freeze-fracture transmission electron microscopy revealed that the prepared liposomes are small unilamellar vesicles (SUV) with a diameter of approximately 100 nm. The extract of Curcuma longa Linn. (Ukon), which contains curcumins as a functional food material, was then subjected to the mechanochemical method with SLP-WHITE to give liposomes including the functional materials. Interestingly, the trapping efficiency of the liposomes for curcumins was found to reach over 85%. From these results, the present mechanochemical method is very likely to allow us to efficiently prepare stable and functional liposomes from the low-cost lecithin. The method may thus have a potential for manufacturing practical nanocapsules, which serves as a novel carrier of functional food materials.     

多肽型阳离子脂质体的研究进展

多肽型阳离子脂质体作为一种重要的非病毒基因载体,克服了其他阳离子脂质体转染效率低、具有一定细胞毒性的缺点,在基因转运方面具有广阔的应用前景。在近年来多肽型阳离子脂质体研究的基础上,论述了多肽型阳离子脂质体在类脂的结构设计、脂质体制备及其在基因转运方面应用的研究现状,展望了多肽型阳离子脂质体的发展方向。     

Characterization of poly (N‐vinyl formamide) by size exclusion chromatography–multiangle light scattering and asymmetric‐flow field‐flow fractionation–multiangle light scattering

The molar mass and the radius of gyration of three poly N‐vinyl formamide (polyNVF) synthesized in aqueous solution polymerization were characterized using two different fractionation techniques: size exclusion chromatography (SEC) and asymmetric‐flow field‐flow fractionation (AF4) coupled with a multiangle light scattering (MALS) and a refractive index (RI) detector. For the sake of comparison, the polymers were also characterized by MALS using the Zimm plot approach (no fractionation). The dn dc^?1 of the poly (N‐vinyl formamide) was measured (0.1564 mL g^?1) and it was found to be insensitive to the molar mass (in the range 150–450 kDa) and also to the eluents used (DDI water or mixed eluent DDI water/acetonitrile (80 : 20) at pH = 5.5). Interestingly, the concentrations of the samples injected in the SEC and AF4 should be different because concentrations in the range of 20–40 mg mL^?1 used for the AF4 caused overloading and anomalous elution in the SEC and hence misleading molar masses. At adequate concentrations in each fractionation equipment, the molar masses were in reasonable good agreement although AF4/MALS provided larger values than the other two techniques likely because samples were not filtered before injection. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42434.     

Effect of PEG lipid on fusion and fission of phospholipid vesicles in the process of freeze-thawing

The effects of freeze-thawing on the sizes and size distribution of egg yolk phosphatidylcholine (EggPC) liposomes in the presence of 0-40 mol% distearoylphosphatidylethanolamine-polyethyleneglycol 2000 (DSPE-PEG2000) prepared by detergent removal method were studied by quasielastic light scattering (QELS), gel exclusion chromatography, and freeze-fracture electron microscope. Especially, gel exclusion chromatography successfully provided the size distribution of polydisperse vesicle suspension. The mean diameters of the liposomes, which had originally large size, decreased with increase in the number of freeze-thawing cycles. On the contrary, the mean diameters of the liposomes, which had originally small size, increased with increase in the numbers of freeze-thawing cycles. After freeze-thawing over 10 times, the liposomal mean diameters fell into a range from 80 to 150 nm in spite of their original size. Gel exclusion chromatography showed that in the process of freeze-thawing of the liposomes containing DSPE-PEG 2000, two opponent events, one is fission and the other is fusion, occurred at the same time.     

Glucose-Sensitive Liposomes Incorporating Hydrophobically Modified Glucose Oxidase

Glucose-sensitive liposomes were prepared by incorporating hydrophobically modified glucose oxidase (EC 1.1.3.4.) into the liposomal bilayer of dioleoylphosphatidylethanolamine and cholesteryl hemisuccinate. For the release test, calcein, a fluorescence marker, was entrapped in the liposomes. The liposomes were stable under neutral conditions in terms of calcein release but an extensive release was observed under acidic conditions. In the experiment of glucose concentration-dependent calcein release, no release was observed for 180 min when the suspension of liposome was free of glucose. With a glucose concentration of 50 mg/dL, no appreciable amount of calcein was released for the first 20 min, and then the release rate was accelerated. At 200 mg/dL glucose concentration which is diagnostic and indicative for insulin-dependent diabetes, the lag time of calcein release became shorter and a faster response was obtained. When glucose concentration further increased to 400 mg/dL, the calcein release rate and the degree of release in 180 min were almost the same as the values when the glucose concentration was 200 mg/dL. The glucose concentration-dependent release is due to pH change, since the suspension of liposomes became acidic during the release experiments.     

Increasing Transfection Efficiency of Lipoplexes by Modulating Complexation Solution for Transient Gene Expression

Transient gene expression is a suitable tool for the production of biopharmaceutical candidates in the early stage of development and provides a simple and rapid alternative to the generation of stable cell line. In this study, an efficient transient gene expression methodology using DC-Chol/DOPE cationic liposomes and pDNA in Chinese hamster ovary suspension cells was established through screening of diverse lipoplex formation conditions. We modulated properties of both the liposome formation and pDNA solution, together called complexation solutions. Protein expression and cellular cytotoxicity were evaluated following transfection over the cell cultivation period to select the optimal complexation solution. Changes in hydrodynamic size, polydispersity index, and ζ potential of the liposomes and lipoplexes were analyzed depending on the various pH ranges of the complexation solutions using dynamic light scattering. The transfer of lipoplexes to the cytosol and their conformation were traced using fluorescence analysis until the early period of transfection. As a result, up to 1785 mg/L and 191 mg/L of human Fc protein and immunoglobulin G (bevacizumab), respectively, were successfully produced using acidic liposome formation and alkaline pDNA solutions. We expect that this lipoplex formation in acidic and alkaline complexation solutions could be an effective methodology for a promising gene delivery strategy.     

pH-dependent release property of dioleoylphosphatidyl ethanolamine liposomes

pH-sensitive liposomes were prepared by a detergent removal method. Dioleoylphosphatidylethanolamine (DOPE) and cholesteryl hemisuccinate (CHEMS) were combined for the preparation of the liposomes so that the molar ratios of DOPE to CHEMS are 9/1, 8/2, 6/4 and 5/5. On transmission electron micrographs, hundreds of nm sized-multilamella vesicles were observed. The degrees of fluorescence quenching were approximately 70–80%, indicating that closed vesicles were formed. According to the results of the pH-dependent release experiment with the liposome composed of DOPE/CHEMS (5/5), no significant release was observed in the pH region ranging from 6 to 8. At pH of 5, an appreciable amount of calcein was released. The patterns of pH-dependent releases from liposomes composed of DOPE/CHEMS (6/4) and DOPE/CHEMS (8/2) were almost the same as those from liposomes composed of DOPE/ CHEMS (5/5). With the liposomes composed of DOPE/CHEMS (9/1), unlike the other liposomes described above, almost 90% release was observed at pH 6. In this case, since the amount of a complementary molecule, CHEMS, is relatively small, the liposomes would be subjective to destabilization even at a small change in the degree of deionization of the carboxylic group. This may explain why the liposome of DOPE/CHEMS (9/1) exhibits a significant release at a relatively high pH, pH 6.0.     

脱氧氟尿苷脂质体的制备

目的建立脱氧氟尿苷(DFUR)脂质体的制备工艺。方法采用逆向蒸发法制备DFUR脂质体,并以包封率为参考指标,进行正交试验优化该脂质体的配方。以优化的配方制备脂质体,观察其微观形态,测定粒径、包封率及稳定性,并进行体外释药实验。结果制备DFUR脂质体的最佳配方为:卵磷脂/胆固醇(摩尔比)为2∶1,有机相/水相(体积比)为5∶1,DFUR浓度为2mg/ml,磷酸盐缓冲液pH值为7.0。以此配方制备,脂质体包封率可达52.15%。3批DFUR混悬液,粒径小于220nm的粒子比率均在70%以上,显微镜下观察可见,脂质体呈球形或椭圆形,粒径范围在0.15μm～1.00μm之间。4℃保存49d,脂质体的稳定性良好。其累积释放率远低于原料药浓度。结论已建立了DFUR脂质体的制备工艺,该工艺操作简便可靠,所需设备简单,稳定性较好,可用于包埋水溶性药物。     

Biophysical studies and intracellular destabilization of pH-sensitive liposomes

We examined changes in membrane properties upon acidification of dioleoylphosphatidylethanolamine/cholesterylhemisuccinate liposomes and evaluated their potential to deliver entrapped tracers in cultured macrophages. Membrane permeability was determined by the release of entrapped calcein or hydroxypyrene-1,3,6-trisulfonic acid (HPTS)-p-xylene-bis-pyridinium bromide (DPX); membrane fusion, by measuring the change in size of the liposomes and the dequenching of octadecylrhodamine-B fluorescence; and change in lipid organization, by³¹P nuclear magnetic resonance spectroscopy. Measurement of cell-associated fluorescence and confocal microscopy examination were made on cells incubated with liposomes loaded with HPTS or HPTS-DPX. The biophysical studies showed (i) a lipid reorganization from bilayer to hexagonal phase progressing from pH 8.0 to 5.0, (ii) a membrane permeabilization for pH<6.5, (iii) an increase in the mean diameter of liposomes for pH<6.0, and (iv) a mixing of liposome membranes for pH<5.7. The cellular studies showed (i) an uptake of the liposomes that were brought from pH 7.5–7.0 to 6.5–6.0 and (ii) a release of ∼15% of the endocytosed marker associated with its partial release from the vesicles (diffuse localization). We conclude that the permeabilization and fusion of pH-sensitive liposomes occur as a consequence of a progressive lipid reorganization upon acidification. These changes may develop intracellular after phagocytosis and allow for the release of the liposome content in endosomes associated with a redistribution in the cytosol.     

Multifunctional liposomal drug delivery with dual probes of magnetic resonance and fluorescence imaging

Many liposomal drug carriers have shown great promise in the clinic. To ensure the efficient preclinical development of drug-loaded liposomes, the drug retention and circulation properties of these systems should be characterized. Iron oxide (Fe₃O₄) magnetic nanoparticles (MNPs) are used as T2 contrast agents in magnetic resonance imaging (MRI). Gold nanoclusters (GNCs) contain tens of atoms with subnanometer dimensions; they have very low cytotoxicity and possess superb red emitting fluorescent properties, which prevents in vivo background autofluorescence. The aim of this study was to develop dual imaging, nanocomposite, multifunctional liposome drug carriers (Fe₃O₄-GNCs) comprising MNPs of iron oxide and GNCs. First, MNPs of iron oxide were synthesized by co-precipitation. The MNP surfaces were modified with amine groups using 3-aminopropyltriethoxysilane (APTES). Second, GNCs were synthesized by reducing HAuCl₄·3H₂O with NaBH4 in the presence of lipoic acid (as a stabilizer and nanosynthetic template). The GNCs were grown by adsorption onto particles to control the size and stability of the resultant colloids. Subsequently, dual Fe₃O₄-GNCs imaging probes were fabricated by conjugating the iron oxide MNPs with the GNCs via amide bonds. Finally, liposome nanocarriers were used to enclose the Fe₃O₄-GNCs in an inner phase (liposome@Fe₃O₄-GNCs) by reverse phase evaporation. These nanocarriers were characterized by dynamic light scattering (DLS), fluorescence spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectrophotometry, superconducting quantum interference device (SQUID), nuclear magnetic resonance (NMR) imaging and in vivo imaging systems (IVIS). These multifunctional liposomal drug delivery systems with dual probes are expected to prove useful in preclinical trials for cancer diagnosis and therapy.     

The effect of liposome on dyeing mohair/wool blends

The aim of this study was to examine the use of liposome in the dyeing of wool and mohair fibres with acid dyestuffs. Soybean lecithin and cholesterol were used to form the liposome membrane utilised in the dyebath. Liposome production was performed according to the thin lipid layer method (Bangham Method) using a rotary evaporator. Two different forms of liposome were used for dyeing wool and mohair fibres. In its first form, liposome was utilised as an auxiliary agent, where it was added to a conventional dyebath at the beginning of the process. In its second form, dyes were encapsulated with liposome and then used in dyeing. The effects of these two different forms of liposome were compared with conventional dyeing. Dyeing was carried out at depths of shade of 0.5%, 1.0% and 2.0% using three different concentrations of liposome (0.33%, 0.66% and 1.33%). An analysis of K/S values, fastness to washing, and the alkali solubility of fibres was conducted. The fibre samples dyed in the presence of liposome exhibited very good fastness to light (grade 8). The wash fastness test results of the liposomal‐dyed samples were significantly better (grade 4‐5) than for those samples which were conventionally dyed. In the presence of liposome, the tensile strength of fibres was 20 gf, whereas it was 11 gf without liposomes.     

Solubilization of phospholipid bilayer caused by surfactants

The interaction of surfactants with liposomes eventually leads to the rupture of such structures and the solubilization of the phospholipid components. In this paper, solubilization is regarded as a decrease in light scattering of liposome suspensions. To this end, in accordance with the nomenclature, adopted by Lichtenberg, three parameters were considered as corresponding to the effective surfactant/lipid molar ratios (Re) at which light scattering starts to decrease, Re_sat; reaches 50% of the original value, Re₅₀; and shows no further decrease, Re_sol. These parameters corresponded to the Re at which the surfactant (i) saturated the liposomes, (ii) resulted in a 50% solubilization of vesicles and (iii) led to a total solubilization of liposomes. The surfactants tested were the nonionic surfactant octylphenol ethoxylated with 10 units of ethylene oxide or Triton X-100 (OP-10EO), two anionic surfactants, sodium dodecyl sulfate and sodium dodecyl ether sulfate, and an amphoteric surfactant dodecyl betaine (D-Bet). Unilamellar liposomes formed by egg phosphatidylcholine containing increasing amounts of phosphatidic acid were used. The Re parameters were the lowest for D-Bet, followed by OP-10EO, whereas the anionic surfactants always showed the highest values regardless of the electrical charge of the lipid bilayers. These parameters seem also to be inversely related to the critical micelle concentration (CMC) of the surfactant, except for OP-10EO. Moreover, the CMC values of the surfactant/lipid systems at 0.5 mM lipid concentration corresponded in all cases to the surfactant concentration at which liposomes were saturated by surfactants. As a consequence, this ratio can be regarded as an interesting parameter associated with the mixed micelle formation in liposome solubilization.     

Clusters of Phospholipid Vesicles as Platforms for Glucose Oxidase‐Catalyzed Reaction in a Bubble‐Column Bioreactor

Clusters of negatively charged liposomes encapsulated with glucose oxidase were prepared in the presence of Ca²⁺ and used to catalyze the oxidation of glucose in an external loop airlift bubble column. The clusters exhibited higher catalytic activity compared to nonclustered glucose oxidase‐containing liposomes (GOLs) when the liposome membranes were incorporated with cholesterol. The clusters were structurally altered in shear flow to give sufficient interfacial area accessible to glucose. The reactivity of GOL clusters could be modulated on the basis of lipid composition of the membranes which affected the mode of interaction among liposomes through Ca²⁺. Part of GOL clusters could be separated from the reaction mixture by centrifugation, which would be advantageous for reusing liposomal catalysts. The liposome clusters can be the platforms to regulate the catalytic performance of glucose oxidase in the airlift.