Haemocompatibility of polymer having phospholipid polar groups evaluated by monoclonal antibody method

Investigation into potential mechanisms promoting biocompatibility of polymeric biomaterials containing the phosphorylcholine moiety

Phosphorylcholine (PC) moieties were chemically attached to surfaces of polymer microparticles by addition of 2-methylacryloyloxyethyl phosphorylcholine monomer to the seeded, semi-continuous polymerisations of methyl methacrylate (MMA) and butyl acrylate (BA). The surface of the bio-functionalised polymer microparticles was principally characterised using X-ray photoelectron spectroscopy (XPS), dynamic nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), acoustophoresis and enzyme-linked immunosorbent assays (ELISA). It was found that the persulphate initiating species are concealed behind the phosphorylcholine containing monomer sequence located on the surface of the microparticles. The combination of analytical techniques showed that the surfaces of the polymer microparticles are extremely mobile above the glass transition temperature of the co-polymer and able to rearrange depending on the environment in which they are placed. This allows the phosphorylcholine moiety to be preferentially expressed at the surface in aqueous media, but not so in the dry state or conditions of ultra-high vacuum. In terms of the nature of the biocompatibility of phosphorylcholine containing polymers, no evidence was found for the irreversible structuring of water molecules around the phosphorylcholine moiety in the wet state. The results of this work suggest that a more likely contributory reason for the protein-resistant nature of phosphorylcholine containing polymers is the mobility of the phosphorylcholine moiety. Increases in biocompatibility correspond with increases in the hydrophilicity of a polymer surface when phosphorylcholine is preferentially expressed. A large free water fraction may be present in the phosphorylcholine containing monomer sequence, as part of a hydrogel structure located at the surface of the polymer microparticles. This, coupled with concomitant modification of the local electrical double-layer very close to the surface may also play a critical role in reducing protein-surface interactions.

Suppression of the inflammatory response from adherent cells on phospholipid polymers

The expression of interleukin-1beta (IL-1beta) messenger RNA (mRNA) in macrophage-like cells cultured on phospholipid polymers was evaluated to determine the extent of the inflammatory response. As phospholipid polymers, poly(2-methacryloyloxyethyl phosphorylcholine(MPC)-co-n-butyl methacrylate(BMA)s (PMBs) were synthesized. Poly(ethylene terephthalate) (PET), poly(2-hydroxyethyl methacrylate) (PHEMA), and segmented poly(ether urethane) (Tecoflex 60) were used as reference biomedical polymers. The protein adsorption onto the polymer surfaces from a cell culture medium was determined. The amount of the total protein adsorbed onto the PMBs was lower than that adsorbed onto the reference polymers, and the amount of adsorbed protein decreased with an increase in the MPC units in the PMBs. Human premyelocytic leukemia cell line (HL-60) was used, and the expression of IL-1beta mRNA was investigated with the reverse transcription polymerase chain reaction (RT-PCR) method. When HL-60 cells were cultured on PMBs, the expression of IL-1beta mRNA in the cells was much less than that on the reference polymers. In particular, the expression of IL-1beta mRNA in HL-60 cells cultured on the PMBs containing more than 10 mol % MPC units was not detected. This corresponded to the reduced amount of adsorbed proteins on the PMB surfaces. These results suggest that the PMBs effectively suppressed the activation and inflammatory response of adherent macrophagelike cells.

Preparation and performance of protein-adsorption-resistant asymmetric porous membrane composed of polysulfone/phospholipid polymer blend

To obtain protein-adsorption-resistant membrane for hemodialysis, we prepared a polymer blend composed of polysulfone and 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer (PSf/MPC polymer). The content of the MPC polymer in the PSf was 7 and 15 wt%. The asymmetric porous membrane was obtained by the dry/wet membrane processing method. The surface characterization of the PSf/MPC polymer membrane by X-ray photoelectron spectroscopy revealed that the MPC polymer located at the surface. The mechanical strength of the PSf/MPC polymer membrane did not change compared with that of the PSf membrane. On the other hand, the permeability of solute below a molecular weight (Mw) of 2.0 x 10(4) through the PSf membrane increased with the addition of the MPC polymer, which is considered to be an effect of the hydrophilic character of the MPC polymer. The amount of protein adsorbed on the PSf membrane from plasma was reduced by the addition of the MPC polymer. The permeability of low-molecular-weight protein (Mw = 1.2 x 10(4)) did not change even after the PSf/MPC polymer membrane was contacted with plasma protein solution for 4 h, whereas it decreased dramatically in the case of the PSf membrane. Platelet adhesion was also effectively suppressed on the PSf/MPC polymer membrane. Based on these results, the MPC polymer could serve as a doubly functional polymeric additive, that is, to generate a protein-adsorption-resistant characteristic and to render the membrane hydrophilic.

Phosphorylcholine-based polymers and their use in the prevention of biofouling

This article provides an overview of work carried out on the synthesis and non-fouling properties of phosphorylcholine (PC)-containing polymers. The concept of biomimicry is outlined and the major classes of synthetic PC-based materials described. Studies on the interaction of these materials with various proteins are collated and the mechanism for their protein-resistant nature is discussed. Similarly, cellular interactions are also reviewed, with ex-vivo and in-vivo clinical data provided to demonstrate the usefulness of these materials for improving the properties of medical devices.

Inhibition of fibroblast cell adhesion on substrate by coating with 2-methacryloyloxyethyl phosphorylcholine polymers

Fibroblast adhesion and growth behavior were examined on various polymers coated on a poly(ethylene telephthalate) (PET) substrate. The polymers are poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylatel copolymer (PMB)s with different MPC unit compositions, and poly(2-hydroxyethyl methacrylate). Surface analysis by dynamic contact angle measurement revealed that the mobility of the polymer chain on the PET substrate depended on the MPC unit composition, but there was no significant difference between the PMBs with 3-10 mol% MPC units and poly(HEMA). Fibronectin adsorption on the polymer surface from a cell culture medium was determined by immunoassay. The adsorbed fibronection was evenly distrubuted in every polymer, however, the amount was reduced with an increase in the MPC unit composition in the PMB. This result suggested that the MPC unit could weaken the interaction between the polymer surface and proteins. When fibroblast L-929 cells, were cultured on the polymers, the cells adhered and the number of cells increased on not only the hydrophobic poly(BMA) but also on the hydrophilic poly(HEMA). However, the number of cells that adhered on the PMB surface decreased with an increase in the MPC unit composition. This was a result of the fibronectin adsorption behavior. Thus, it could be concluded that since the PMB could suppress cell adhesion proteins e.g. fibronectin, the PMB showed excellent cell adhesive resistance properties.

Adsorption-desorption of proteins on phospholipid polymer surfaces evaluated by dynamic contact angle measurement

Adsorption-desorption of plasma protein on various polymer membranes was evaluated by a dynamic contact angle (DCA) measurement using the Wilhelmy plate method. Poly(ethylene terephthalate) (PET) was used as a substrate membrane; we examined this membrane coated with hydrophilic polymers such as poly[2-methacryloyloxethyl phosphorylcholine (MPC)-co-n-butyl methacrylate (BMA)] or poly[2-hydroxyethyl methacrylate (HEMA)]. Although the zeta-potential of the PET membrane was negative, the coating with poly(MPC-co-BMA) induced increase of value to nearly zero. The DCA loops observed on the polymer membranes after protein adsorption were unity and hysteresis of the loop was reduced. In the cases of protein adsorbed on both the PET and the poly(HEMA) membranes, the shape and hysteresis of the loops were almost same during the rinsing process with a phosphate-buffered solution (PBS). However, the hysteresis of the DCA loops that appeared on the protein-adsorbed poly(MPC-co-BMA) membrane became large during the rinsing process with the PBS, and the shape of the DCA loop returned to its non-protein-adsorbed state. Therefore, proteins adsorbed on poly(MPC-co-BMA) could desorb more readily than those on PET and poly(HEMA) because of the weak interaction between poly(MPC-co-BMA) and the proteins.

Effects of phospholipid adsorption on nonthrombogenicity of polymer with phospholipid polar group

Polymers with phospholipid polar groups, 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers, have excellent nonthrombogenic properties. The effects of adsorption of phospholipids on platelet adhesion and activation on the MPC copolymer with n-butyl methacrylate (BMA) were investigated with particular attention to the structure of the phospholipids adsorbed onto the polymer surface. The electrical nature of the phospholipids adsorbed on the polymer surface affected the thrombogenicity of the polymer. On the MPC polymer surface treated with an aqueous liposomal solution of acidic phospholipids, phosphatidylserine, platelet adhesion and activation occurred to a greater extent when compared to a poly(MPC-co-BMA) surface. However, on the MPC polymer surface treated with electrically neutral phosphatidylcholines, reduced thrombogenicity could be observed. Therefore, the adsorption of the phosphatidylcholines was an important factor in reducing the thrombogenicity on the polymers. Moreover, by comparison of the poly(MPC-co-BMA) to a poly(BMA), platelet adhesion and activation on these polymer surfaces depended on the adsorption state of the phosphatidylcholines. The amount of phosphatidylcholine adsorbed on the poly(MPC-co-BMA) increased with an increase in the MPC mole fraction of the copolymer. This indicates that the MPC moieties have affinity for the phosphatidylcholines. We conclude that the poly(MPC-co-BMA) can adsorb large amounts of phosphatidylcholines and that these phospholipids organize themselves. The organized adsorption layer of the phosphatidylcholines on the surface, which construct biomembrane-like surfaces, can reduce platelet adhesion and activation effectively.