Characterization of phosphatidylcholine/polyethylene glycol‐lipid aggregates and their use as coatings and carriers in capillary electrophoresis

Abstract

PEG-stabilized lipid aggregates are a promising new class of model membranes in biotechnical and pharmaceutical applications. CE techniques, field-flow fractionation, light scattering, quartz crystal microbalance (QCM), and microscopic techniques were used to study aggregates composed of 1-palmitoyl-2-oleyl-sn-glycero-phosphatidylcholine (POPC) and PEG-lipid conjugates. The PEG-lipids, with PEG molar masses of 1000, 2000, and 3000, were 1,2-diacyl-sn-glycero-3-phosphoethanolamine-N-[methoxy-(PEG)] derivatives with either dimyristoyl (DM, 14:0) or distearoyl (DS, 18:0) acyl groups. The 80/20 mol% POPC/PEG-lipid dispersions in HEPES at pH 7.4 were extruded through 100 nm size membranes. Asymmetrical flow field-flow fractionation (AsFlFFF), photon correlation spectroscopy (PCS), and dynamic light scattering (DLS) were used to determine the sizes of POPC and the PEGylated aggregates. All methods demonstrated that the DSPEG-lipid sterically stabilized aggregates were smaller in size than pure POPC vesicles. The zeta potentials of the aggregates were measured and showed an increase from -19 mV for pure POPC to -4 mV for the POPC/DSPEG3000 aggregates. Atomic force microscopy (AFM), electron cryo-microscopy (EM), and multifrequency QCM studies were made to achieve information about the PEGylated coatings on silica. Lipid aggregates with different POPC/DSPEG3000-lipid ratios were applied as capillary coating material, and the 80/20 mol% composition was found to give the most suppressed and stable EOFs. Mixtures of low-molar-mass drugs and FITC-labeled amino acids were separated with the PEGylated aggregates as carriers (EKC) or as coating material (CEC). Detection was made by UV and LIF.

Dynamic coating of SU‐8 microfluidic chips with phospholipid disks

“…Following modification, the zeta potentials were only $20% of the initial values (À8.7 to À5.2 mV) and very close to those earlier obtained for mere POPC/DSPEG3000 disks (i.e. À3.970.7 mV in 9 mM HEPES buffer at pH 7.4) [37]. The reason for the seemingly better POPC/DSPEG3000 surface coverage for SU-8 microparticles than that for SU-8 microchannels is not fully characterized, but it is likely that the surface topography greatly affects the lipid assembly so that microparticles are more favorable regarding dense packing of the disk-like lipid aggregates.…”

“…In a previous work, DSPEG-stabilized POPC lipid aggregates with varying PEG chain lengths (i.e. varying molar masses) were utilized for modification of fused-silica capillaries [37] and their effects on analyte interactions with the coated capillary wall were studied using the lipids either as carriers (i.e. EKC) or coating material (i.e.…”

“…In this study, we examined the affinity of POPC/DSPEG3000 disks to three different microchip materials, namely SU-8, PDMS, and Borofloat glass. The preconditioning and coating conditions as well as PEG chain length and molar ratio were adopted from previous work [37,42], based on optimization done with respect to EOF stability in fused-silica capillaries. Here, no disks were present in the BGE after coating, hence the conditions resembled those of the CEC mode throughout the study.…”

“…The phospholipid disks comprised POPC with 20 mol% of DSPEG3000 as a stabilizing agent and were prepared as previously reported [37]. Briefly, appropriate amounts of POPC and PEG-lipid stock solutions in chloroform were mixed to obtain the desired composition.…”

Asymmetrical flow field-flow fractionation technique for separation and characterization of biopolymers and bioparticles

“…From the MALS data it was concluded that empty liposomes and liposomes encapsulated hemoglobin (LEHb) are spherical, while actin modified LEHb have a thin-disk shape. AsFlFFF has been also used to characterize the liposome sizes in the development of new stabilized particle/polymer/proteincovered liposomes, such as liposome encapsulating hemoglobin [108], and that of polyethylene glycol-lipid aggregates containing various types of polyethylene glycol-functionalized lipids [109].…”