Synthesis of phospholipid polymers having a urethane bond in the side chain as coating material on segmented polyurethane and their platelet adhesion-resistant properties

Reduction of surface-induced platelet activation on phospholipid polymer

omega-Methacryloyloxyalkyl phosphorylcholine (MA-PC) polymers which have been synthesized with attention to the surface structure of a biomembrane show excellent blood compatibility, i.e., resistance to protein adsorption and blood cell adhesion. To clarify the stability of platelets in contact with the MAPC polymer surfaces, cytoplasmic free calcium concentration ([Ca2+],) in the platelets was measured. A platelet suspension was passed through a column packed with various polymer beads after treatment with plasma, and the [Ca2+]i in the platelets eluted from the column was measured. The [Ca2+]i in contact with the MAPC polymers, i.e., poly[2-methacryloyloxyethyl phosphorylcholine-co-nbutyl methacrylate (BMA)] (PMEB) and poly(6-methacryloyloxyhexyl phosphorylcholine-co-BMA) (PMHB), was less than that in contact with poly(BMA). However, poly(10-methacryloyloxydecyl phosphorylcholine-co-BMA) (PMDB) was not effective in suppressing the increase in [Ca2+]i, and thus was at the same level as in the poly(BMA). This result indicated that platelets in contact with PMEB or PMHB were less activated compared with those in contact with PMDB and poly(BMA). Moreover, the state of the platelets adhered to these polymer surfaces, both morphologically and immunologically, was examined. Scanning electron microscopic observation of the polymer surface after contact with a platelet suspension revealed that many platelets adhered and changed their shape on the poly(BMA). The numbers of adhetent platelets were reduced on all MAPC polymer surface. The relative amount of alpha-granule membrane glycoprotein (GMP-140) which appears on the cell membrane by activation of platelets on the PMEB surfaces was less than that on poly(BMA) and poly(2-hydroxyethyl methacrylate). These results suggest that PMEB and PMHB suppressed not only platelet adhesion but also activation of the platelets in contact with these surface.

Stabilization of Liposomes Attached to Polymer Surfaces Having Phosphorylcholine Groups

The adsorption state of liposomes on a polymer surface containing a phosphorylcholine group, that is, omega-methacryloyloxyalkyl phosphorylcholine (MAPC) polymer, was evaluated using a quartz crystal microbalance and an atomic force microscope. After a quartz crystal resonator coated with the MAPC polymer or poly[2-hydroxyethyl methacrylate (HEMA)] was equilibrated with distilled water, the quartz crystal was contacted with a dipalmitoylphosphatidylcholine (DPPC) liposomal suspension. The resonance frequency change during liposome adsorption on the poly(HEMA)-coated resonator was larger than that on the MAPC polymer-coated resonator. The temperature response based on the phase transition of adsorbed DPPC liposomes, that is, the liquid crystalline state to gel state, on the MAPC polymer-coated resonator was more sensitive than that on the poly(HEMA)-coated resonator. Moreover, when the DPPC liposomes adsorbed on the polymer surfaces were disintegrated with a nonionic surfactant, it took longer for the frequency to return to the initial value of the poly(HEMA)-coated resonator than to that of the MAPC polymer-coated resonator. According to atomic force microscopic observation of the polymer surface after treatment with the liposomal suspension, the DPPC liposomes adsorbed on the MAPC polymers maintained their spherical shape well. We conclude that DPPC liposomes adsorbed on the poly(HEMA) surface can penetrate a hydrated layer and its ordered structure. On the other hand, DPPC liposomes may adsorb to the MAPC polymer surface without change in their original structure. Copyright 1997Academic Press

Protein adsorption and platelet adhesion on polymer surfaces having phospholipid polar group connected with oxyethylene chain

We evaluated the blood compatibility of various amphiphilic polymers, that is, n-butyl methacrylate (BMA) copolymers with methacrylates having a phosphorylcholine (PC), hydroxy (OH) or methoxy (MeO) group as an end polar group in the oxyethylene side chain. The amount of proteins adsorbed on the PC-polymer from human plasma was smaller than that on not only the poly(2-hydroxyethyl methacrylate) and poly(methyl methacrylate) but also the OH-polymer and MeO-polymer. The PC group could weaken the interaction between plasma proteins and polymer surfaces. The amount of adsorbed proteins on the PC-polymer decreased with an increase in the mole fraction of the PC units in the polymers. We could observe an effect of the oxyethylene chain length (n is the number of repeating units of oxyethylene) on protein adsorption between n = 2 and n = 3. The platelet adhesion on these polymer surfaces was evaluated using rabbit platelet-rich plasma. On the polymers without the PC group, that is, poly(BMA), OH-polymer, and MeO-polymer, many platelets adhered and a considerable shape change in the adherent platelets occurred. On the other hand, the PC-polymers could effectively suppress platelet adhesion. The platelet adhesion behavior on the polymers was strongly dependent on the adsorbed proteins. Platelet adhesion was completely inhibited on all of the PC-polymers studied having a 0.3 PC unit mole fraction. However, it was observed that the oxyethylene chains on the PC-polymers with a 0.1 PC unit mole fraction affected platelet adhesion.

Improved blood compatibility of segmented polyurethane by polymeric additives having phospholipid polar group. II. Dispersion state of the polymeric additive and protein adsorption on the surface

To improve the blood compatibility of a segmented polyurethane (SPU), phospholipid polymer, i.e., 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymerized with cyclohexyl methacrylate or 2-ethylhexyl methacrylate, was blended into SPU as a polymeric additive. The blending was achieved by a solvent-evaporation technique from a homogeneous solution containing both the SPU and the MPC polymer. Surface analysis of the SPU membrane blended with the MPC polymer (SPU/MPC polymer membrane) revealed that the MPC polymer was concentrated at the surface of the SPU membrane which contacted the substrate, Teflon, compared with that which contacted air during the membrane-formation period. The dispersion state of the MPC polymer in the SPU membrane was evaluated in detail by staining the MPC unit with osmium tetraoxide. When sonication was applied during preparation of the mixed solution containing SPU and the MPC polymer, the dispersion of the MPC polymer in the SPU membrane was different from that without sonication. That is, the size of the domains of the MPC polymer became smaller but the number of the domains increased. The amount of the MPC polymer mixed with SPU affected the dispersion state. Plasma proteins adsorbed on the SPU/MPC polymer membrane surface after contact with human plasma were detected by gold-colloid-labeled immunoassay. Both albumin and fibrinogen were observed on the SPU membrane; however, the amount of these proteins was reduced on the SPU/MPC polymer membrane. Thus it was concluded that the blood compatibility of the SPU was effectively improved by the blending of the MPC polymer.

Improved blood compatibility of segmented polyurethanes by polymeric additives having phospholipid polar groups. I. Molecular design of polymeric additives and their functions

To improve the blood compatibility of a segmented polyurethane (SPU), 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer was blended with the SPU. The MPC was copolymerized with cyclohexyl methacrylate (CHMA) or 2-ethylhexyl methacrylate (EHMA), and the MPC polymers obtained could be dissolved in the same solvent as the SPU (Tecoflex 60). The blended membranes composed of SPU and MPC polymers were prepared by a solvent evaporation method. A small amount of MPC polymer in the blended membrane leached out after immersion in water for 10 days. The X-ray photo electron spectra indicated that the MPC moieties were located at the surface of the SPU membrane blended with poly(MPC-co-CHMA). On the other hand, the poly-(MPC-co-EHMA) was located homogeneously in the SPU membrane. The mechanical properties of the SPU membrane, as determined by tensile stress-strain measurements, changed very little even after addition of the MPC polymers. Blood compatibility of the blended membrane was evaluated by blood-cell adhesion on the surface when the membranes were placed in contact with rabbit whole blood or platelet-rich plasma. The addition of MPC polymer in the SPU membrane dramatically reduced cell adhesion. It is concluded that the blending of the MPC polymer in the SPU membrane is an effective method for imparting nonthrombogenicity.

A new haemocompatible phospholipid polyurethane based on hydrogenated poly(isoprene) soft segment

A new haemocompatible phospholipid polyurethane based on hydrogenated poly(isoprene) glycol (HPIP) and 4,4'-methylendiphenyl diisocyanate (MDI) was synthesized using 2-[bis(2-hydroxyethyl)methyl-ammonio]ethylstearylphosphate (BESP) and 1,4-butanediol (BD) as chain extender. The bulk and surface characteristics of this material was investigated by differential scanning calorimetry (DSC), dynamic viscoelasticity and tensile property measurements, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and contact angle measurement. This polymer possessed a hydrophobic surface revealed by contact angle measurement. The haemocompatibility of this polyurethane was evaluated by platelet rich plasma (PRP) contacting studies and scanning electron microscopy (SEM) observation using medical grade poly(vinyl chloride) (PVC) as the reference. The results show that this new polyurethane had relatively lower platelet adhesion and limited shape change for the attached platelets compared to PVC. The clotting time of the materials in contact with platelet poor plasma (PPP) was 99, 75, and 62 s and in contact with PRP was more than 240, 100, and 86 s for new polyurethane, PVC, and glass, respectively. This new phospholipid polyurethane is expected to have wide applications as coating or structural material for blood-contacting medical equipment due to its outstanding haemocompatibility and excellent mechanical strength.