Stabilization of Liposomes Attached to Polymer Surfaces Having Phosphorylcholine Groups

Pickering emulsion templated soft capsules by self-assembling cross-linkable ferritin-polymer conjugates

Oil-in-water (o/w) and water-in-oil (w/o) Pickering emulsions were prepared using ferritin-polymer conjugates. UV cross-linking stabilised the particle assembly around the fluid droplets. The resulting soft protein-polymer capsules were transferred to a medium of equal polarity as the inside of the capsule, creating water-in-water (w/w) and oil-in-oil (o/o) capsules.

Liposome characterization by quartz crystal microbalance measurements and atomic force microscopy

This chapter reviews liposome characterization by quartz crystal microbalance (QCM) measurements and atomic force microscopy (AFM). In many studies, AFM imaging is simply used to image liposomes with resolution often that does not allow morphological analysis. Although liposome size can be obtained by processing AFM images, it is found that liposomes flatten upon surface adsorption or immobilization. Liposome stability and stiffness have been characterized by using AFM imaging or AFM force measurements, although the latter method, using a microsphere attached on the AFM cantilever, seems more appropriate to limit liposome damage and to obtain more quantitative analysis, such as the Young's modulus. Investigation of liposome layers by QCM revealed that liposomes can be detected from a combined analysis of frequency and bandwidth shifts. However, QCM by itself provides only limited information on liposomes. QCM can be used to assess the presence of a layer and also to discriminate between rigid and viscoelastic ones. Liposome properties have been derived from QCM curves, but often this requires making hypotheses that are difficult to assess. AFM and QCM analyses need to be combined with other techniques to provide complementary information.

Arraying of intact liposomes into chemically functionalized microwells

Here, we describe a protocol to bind individual, intact phospholipid bilayer liposomes, which are on the order of 1 microm in diameter, in microwells etched in a regular array on a silicon oxide substrate. The diameter of the wells is on the order of the liposome diameter, so only one liposome is located in each well. The background of the silicon oxide surface is functionalized with a PEG oligomer using the contact printing of a PEG silane to present a surface that resists the adsorption of proteins, lipid material, and liposomes. The interiors of the wells are functionalized with an aminosilane to facilitate the conjugation of biotin, which is then bound to Neutravidin. The avidin-coated well interiors bind the liposomes whose surfaces contain biotinylated lipids. The specific binding of the liposomes to the surface using the biotin-avidin linkage, together with the resistant nature of the background and the physical confinement of the wells, allows the liposomes to remain intact and to not unravel, rupture, and fuse onto the surface. We demonstrate this intact arraying using confocal laser scanning microscopy of fluorophores specifically tagging the microwells, the lipid bilayer, and the aqueous interior of the liposome.

Phospholipid polymer surfaces reduce bacteria and leukocyte adhesion under dynamic flow conditions

Persistence of infection can occur when the host immune response is compromised because of the presence of a foreign implant. Surface modification of biomaterials with phospholipid polymers may enhance biocompatibility and reduce incidence of infection by impeding bacterial and leukocyte adhesion. A rotating disk model, which generates shear stress from 0 to 18 dynes/cm(2), was used to characterize adhesion of neutrophils, monocytes, and bacteria in phosphate-buffered saline (PBS) or 25% human serum on polyethylene terephthalate surfaces coated with a phospholipid polymer, poly[omega-methacryloyloxyalkyl phosphorylcholine (MAPC)-co-n-butyl methacrylate (BMA)]. The material designated PMB30 contains a methylene chain length, (CH(2))(n), of n = 2, whereas PMHB30 contains a chain length of n = 6. In PBS, bacterial adhesion was shear stress dependent with the lowest bacterial density observed on PMB30. However, the presence of serum proteins eliminated shear stress and surface chemistry effects in addition to bacterial adhesion reduced to <10% of adhesion in PBS. Trends for leukocyte adhesion in serum demonstrated shear dependence with PMB30 exhibiting the lowest cell density throughout the range of shear stresses. In conclusion, modification of the polyethylene terephthalate surfaces with phospholipid polymers resulted in reduced bacterial and leukocyte adhesion. Furthermore, shortening the methylene chain length of the MAPC copolymer most effectively reduced adhesion.

Effects of complexation between liposome and poly(malic acid) on aggregation and leakage behaviour

The design and development of novel pH-sensitive liposomes were investigated to improve the release of liposome-encapsulated chemicals. Stable liposomes comprising of L-alpha-dipalmitoylphosphatidylcholine (DPPC) and poly(carboxylic acid) were prepared and characterized. Poly(malic acid) (PMLA) was chosen as a fusogen, because of its excellent biodegradability in physiological regions. Octyl groups introduced in the poly(malic acid) worked as anchors at the surface of the liposomes and made a remarkable contribution to complexing. The interaction between the liposomes and the polyacids was studied in terms of the change in size of the liposomes. The influences of molecular weight and amounts of polymer upon their characteristics, especially fusion, were discussed. The influences of pH change with respect to the association behavior of the liposomes such as aggregation and fusion were estimated by the particle size of the liposomes, turbidimetry of the solution and resonance energy transfer assay. From the results of these studies, it was shown that more tightly complexed liposomes aggregated and fused more positively with increasing acidity of the solution. The leakage of calcein entrapped in the inner aqueous phase of the liposomes increased with decreasing pH. The effect of pH on the liposome aggregation in a solution qualitatively paralleled that found in the leakage behavior.

Phosphorylcholine-containing polyurethanes for the control of protein adsorption and cell attachment via photoimmobilized laminin oligopeptides

In this study, we synthesized a biomaterial whose surface inhibits non-specific protein and cell attachment. The polymer was designed to mimic the external cell plasma membrane properties through the introduction of particular chemical constituents of the cell membrane: phospholipid polar headgroups. This was done by copolymerizing phosphorylcholine (PC) groups into a polyurethane polymer backbone (PCPUR). Peptides known to induce specific cell attachment were subsequently bound to the surface of this copolymer in a photoadressible manner to obtain surfaces that allowed the attachment of cells in a specific pattern. Two polymers with different phosphorylcholine concentrations were synthesized and their bulk and surface properties were characterized through differential scanning calorimetry, wettability measurements, angle-resolved X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Protein and lipid adsorption investigation using optical waveguide light mode spectroscopy showed that the irreversible adsorption of both proteins and lipids is drastically reduced as a result of simultaneous contributions of the PC groups, molecular mobility and strong hydrophilicity of the polymers. Consequently, this leads to a marked reduction in the cellular attachment response, which further decreases with increasing PC concentration. Finally, when the polymer surface was photo-derivatized, attachment of the neural NG108-15 cell line occurred only on the areas of the PCPUR where the laminin CDPGYIGSR peptide sequence was photoimmobilized. Cell attachment was nevertheless found to be non-specific with respect to the peptide sequence used and reasons for such results are therefore discussed.

Interfacial adsorption of polymers and surfactants: implications for the properties of disperse systems of pharmaceutical interest

This review considers basic aspects of the interfacial adsorption of polymers and surfactants, with particular reference to the relevance of these processes for the formulation of pharmaceutical disperse systems. First, we discuss different approaches to the interpretation of adsorption isotherms, paying particular attention to systems containing more than one adsorbate. Second, we consider the implications of adsorption for the properties of suspensions, emulsions, and colloidal systems, particularly as regards the use of polymers and surfactants for stabilizing disperse systems, for controlling flocculation, and for modifying the biopharmaceutical behavior of colloidal drug carriers. Finally, we present a number of representative examples of the importance of adsorption of macromolecules in pharmaceutical systems.

Competitive adsorption between phospholipid and plasma protein on a phospholipid polymer surface

The competitive adsorption of proteins and phospholipids on omega-methacryloyloxyalkyl phosphorylcholine (MAPC) polymer was evaluated in this study. Albumin, fibrinogen, and dimyrstoyl phosphatidylcholine (DMPC) were used as model components. The amount of DMPC adsorbed on the MAPC polymers increased with an increase in the MAPC unit composition of the polymer. The methylene chain length of the MAPC unit was another factor influencing the DMPC adsorption when the MAPC unit composition of the MAPC polymer was low. The state of albumin and DMPC liposome adsorbed on the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was determined by dynamic contact angle (DCA) measurement. The adsorption strength of albumin on the MPC polymer was weaker than that on the poly[n-butyl methacrylate (BMA)], that is, the albumin was detached from the MPC polymer during the rinsing process. On the poly(BMA) surface, no difference in the shape of the DCA loops before and after contact with the DMPC liposomal suspension was observed. Fibrinogen adsorption on the MAPC polymer was detected by gold-colloid labeled immunoassay. The amount of fibrinogen adsorbed on every MAPC polymer surface was reduced by addition of the DMPC liposome in the fibrinogen solution. The number of platelets adhered on the MAPC polymer was also decreased when the DMPC liposome was present in the fibrinogen solution during pretreatment. We concluded that phospholipids were preferentially adsorbed on the MAPC polymer surface compared with plasma protein and that the adsorbed phospholipids played an important role in showing an excellent blood compatibility on the MAPC polymer.