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Biomedical subjects

N Nakabayashi

Publications and source records attributed to N Nakabayashi.

At least 73 records · Page 4Linked to original sources
PubMed1995

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.

Adsorption↗
PubMed1995

Adhesion and cytokine production by monocytes on poly(2-methacryloyloxyethyl phosphorylcholine-co-alkyl methacrylate)-coated polymers.

Human monocytes isolated from peripheral venous blood were assayed for their ability to adhere to various polymers. The culture supernatants were also assayed for the cytokines, interleukin-1 beta (IL-beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). The polymers evaluated for adherence and cytokine production included Pellethane, polyethylene and poly[n-butyl methacrylate (BMA)] coated with poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-alkyl methacrylate] copolymers. In some experiments the test polymers were adsorbed with fibrinogen or IgG prior to the addition of monocytes. MPC copolymer-coated materials inhibited monocyte and macrophage adhesion after 1 and 8 days of culture relative to corresponding uncoated polymers and tissue culture polystyrene (TCPS). The degree of inhibition by coated Pellethane compared to uncoated Pellethane was the greatest, while inhibition of adhesion by coated poly(BMA) was the least compared to uncoated poly(BMA). However, adhesion was significantly decreased on both coated and uncoated poly(BMA) by day 8. While IL-1 beta, IL-6, and TNF-alpha release was variably influenced by polymer coating, release was consistently inhibited relative to TCPS on day 1. However, cytokine production was not inhibited compared to corresponding uncoated polymers on day 1. With or without protein preadsorption, IL-1 beta release was not detectable in the supernatants of any polymer on day 8, IL-6 production was diminished on day 8, and TNF-alpha production was sustained on day 8. Overall, MPC copolymer-coated and uncoated poly(BMA) were the least stimulating, while TCPS was the most stimulating.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatible Materials↗
PubMed1995

Fabrication and characterization of dipalmitoylphosphatidylcholine-attracting elastomeric material for joint replacements.

Wear debris associated with the polyethylene components of total joint replacements has been shown to induce bone resorption which contributes to implant loosening. In an effort to promote lubrication and reduce wear in artificial hip joints, the use of the cushion bearing concept has been proposed previously; however, an elastomeric material tested as a cushion bearing has been shown to have poor tribological properties during initiation of motion from rest. The goal of this project was to fabricate and characterize an elastomer that has the ability to attract to its surface naturally occurring boundary lubricants from an aqueous solution. The test elastomer and appropriate controls were characterized using fluorescence, electron spin resonance and X-ray photoelectron spectroscopy. The test elastomer was found to have an enhanced ability to attract dipalmitoylphosphatidylcholine, a known physiological boundary lubricant. A cushion bearing that also encourages boundary lubrication represents a potential improvement over currently existing orthopaedic implant-bearing materials.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

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

Surface modification of segmented polyurethanes (SPUs) was carried out using new blood compatible polymers having both phospholipid polar groups and urethane bonds in the side chains. The polymers were composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), n-butyl methacrylate (BMA) and methacrylate with a urethane bond (MU). The MPC copolymers were soluble in ethanol. The SPU membranes were immersed in an ethanol solution of MPC copolymers and dried in vacuo for coating. The surface formed was completely covered with the MPC copolymer which was confirmed by X-ray photoelectron spectroscopic analysis. The polymer coatings were hardly detached in water, ethanol and 40% aqueous solution of ethanol compared with poly(MPC-co-BMA) which did not have the MU moieties. Therefore, the MU moieties had affinity for the SPU. The surface modification of the SPUs suppressed platelet adhesion effectively after contact with platelet-rich plasma for 180 min.

Biocompatible Materials↗
PubMed1995

Hemocompatible cellulose dialysis membranes modified with phospholipid polymers.

Hemocompatibility is one of the most important properties for hemodialysis membranes. For improvement of the hemocompatibility on a cellulose dialysis membrane, modifications with new blood-compatible phospholipid polymers were carried out. These methods included a direct grafting of the phospholipid monomer on the membrane surface, coating the membrane surface with a water-soluble graft copolymer composed of a cellulose backbone and phospholipid polymer as a branch, and covalent bonding with a reactive phospholipid polymer on the membrane surface. These modified membranes could reduce protein adsorption as well as complement activation and platelet adhesion on the surface without any adverse effects on the membrane performance.

Absorption↗
PubMed1995

Intra-oral bonding of 4-META/MMA-TBB resin to vital human dentin.

PURPOSE: To investigate and compare the in vivo and in vitro tensile bond strengths of a 4-META/MMA-TBB adhesive resin (Superbond C&B, C&B-Metabond) to human dentin. MATERIALS AND METHODS: Caries-free teeth present on patients and scheduled for extraction for orthodontic reasons were used. Flat dentin surfaces were prepared and a 4-META/MMA-TBB resin applied. After 10 minutes, the teeth were extracted. Extracted caries-free teeth were also used and treated similarly. Tensile bond strength was evaluated and all specimens were sectioned immediately after bond testing, after polishing the debonded area or after treating the surfaces with HCl acid. RESULTS: Data were analyzed statistically, and no significant differences could be determined between third molars and first premolars, and in vivo and in vitro specimens. Further, tensile stress fractured specimens were examined under scanning and transmission electron microscopy. Widths (+/- 5 microns) of hybrid layers and impregnation of adhesive monomers into 10-3 solution demineralized vital human dentin substrates were essentially similar to those observed in extracted samples. The adhesive resin penetrated tubules to form resin tags, unimpeded by intra-tubular fluid under physiologic pressure in intra-orally prepared specimens. A hybrid layer formed on resin tags to seal against microleakage and pulpal attack by bacteria and their by-products. An acid-resistant hybrid layer was also observed in enamel. Finally, hydroxyapatite crystals that were encapsulated by polymerized 4-META/MMA-TBB resin was observed at the bases of resin-reinforced hybrid layers in the human dentin substrates. This observation is consistent with earlier findings and appears to be essential in maintaining durable dentin bonds.

Acrylic Resins↗
PubMed1995

Development of a ferrocene-mediated needle-type glucose sensor covered with newly designed biocompatible membrane, 2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate.

To prepare the long-life and stable glucose sensor, we developed the ferrocene-mediated needle-type glucose sensor covered with newly designed biocompatible membrane, 2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate (MPC-co-BMA) membrane. In this membrane, the hydrophilic phosphorylcholine chains were grafted on the hydrophobic polymer surface. 1. The poly(MPC-co-BMA) membrane inhibited platelet activation and protein adhesion on the surface, showing excellent biocompatibility. These results suggested that the hydrophilic phospholipids chains might have the potential for suppressing activation and adsorption of biochemical molecules. 2. The ferrocene-mediated needle-type glucose sensor covered with poly(MPC-co-BMA) membrane achieved excellent results in vitro. Subcutaneous tissue glucose concentrations were measured in a wide range from 1.7 to more than 16.7 mmol/l. The correlation between subcutaneous tissue (Y) and blood (X) glucose concentrations was Y = 1.04X + 0.12 (r = 0.98). The subcutaneous tissue glucose concentrations could be monitored precisely for 7 days without any in vivo calibrations, and for 14 days by introducing in vivo calibrations. We therefore conclude that this sensor is stable and reliable, as compared to any other glucose sensors we developed.

Adult↗
PubMed1994

Hemocompatibility on graft copolymers composed of poly(2-methacryloyloxyethyl phosphorylcholine) side chain and poly(n-butyl methacrylate) backbone.

To improve the hemocompatibility on hydrophobic biomedical materials by a simple coating technique, graft copolymers composed of a hydrophilic side chain with phospholipid polar groups and a hydrophobic backbone were synthesized. The hydrophilic chain had phospholipid polar groups, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)], and the hydrophobic backbone was poly[n-butyl methacrylate (BMA)]. Because the graft copolymers obtained could dissolve in ethanol, they could be used as a coating material. When the poly(MPC-graft-BMA) was coated onto a poly(BMA) membrane, the composition of the MPC units on the surface was maintained in the bulk graft copolymer even after immersion in water. Protein adsorption on the membrane coated with the graft copolymer from human plasma detected by a gold-colloid labeled immunoassay was drastically decreased compared with that on glass and the original membrane. Moreover, blood cell adhesion, activation, and aggregation on the membrane after contact with human citrated whole blood were suppressed by the coating of the graft copolymer. These results clearly show that the poly(MPC-graft-BMA) is a suitable material for improving hemocompatibility on the biomedical devices because of its protein adsorption and cell adhesion resistant properties.

Adsorption↗
PubMed1994

Selective adhesion of platelets on a polyion complex composed of phospholipid polymers containing sulfonate groups and quarternary ammonium groups.

We investigated the effects of electrical charges on cell-polymer interactions of poly[2-methacryloyloxyethyl phosphorylcholine(MPC)-co-n-butyl methacrylate (BMA)] (PMB) having excellent blood compatibility, by copolymerizing anionic or cationic methacrylates with MPC and BMA. A polyion complex (PIC) composed of anionic and cationic MPC copolymers was also prepared. When the cell adhesion on these polymer surfaces from rabbit whole blood was evaluated, we observed a considerable reduction in cell adhesion on the MPC copolymers compared with that on poly(BMA), even when the MPC copolymer was electrically charged. On the other hand, many platelets selectively adhered to the PIC surface from whole blood, but the adherent platelets maintained a discoid shape. The amount of adenosine triphosphate (ATP) in platelets adherent on the PMB or the PIC from a platelet-rich plasma (PRP) was more than 75% of that in the original PRP, which indicated that the activity of these platelets remained high. However, in the platelets adherent to poly(BMA), only a small amount of ATP remained. Protein adsorption on the polymer surface from human plasma was investigated using a gold-colloid-labeled immunoassay against albumin gamma-globulin, and fibrinogen. Many of these proteins adsorbed on poly(BMA), whereas a small amount of protein was observed on the MPC copolymers that had an electrical charge. Albumin adsorption and suppression of gamma-globulin and fibrinogen adsorption were found on the PIC. Therefore, the introduction of electrical charges in the PMB did not have an adverse effect on cell adhesion and protein adsorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1994

Measurement methods for adhesion to dentine: the current status in Japan.

Adhesive test in vitro is performed to evaluate bonding materials. This paper describes methods of measuring adhesion to dentine currently used in Japan, and considers advantages and disadvantages. Various tests are used in Japan. Many factors-dentine substrate, storage conditions, bond strength test method-affect bonding to dentine. Bond strength test methods employed are divided into: tensile bond test and shear bond test. The test method used for the best prediction of clinical performance in bond strength evaluation is discussed. There has also been interest in bonding stability. At present, it may be difficult to propose an optimal standardized measuring method. Standardized experimental conditions in vitro which can simulate conditions in vivo are still under investigation.

Adhesiveness↗
PubMed1994

Improvement of hemocompatibility on a cellulose dialysis membrane with a novel biomedical polymer having a phospholipid polar group.

To improve surface hemocompatibility on cellulose hollow fibers for hemodialysis, newly designed hemocompatible polymers with a phospholipid polar group, 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers, were introduced on the surface through two different methods: direct grafting of MPC on the surface, or coating of a water-soluble cellulose grafted with MPC. The MPC was polymerized using cerium ion as an initiator in the cellulose hollow fibers, and the poly(MPC) chains were grafted directly on the surface. Another modification of the cellulose hollow fibers was attempted by coating them with a water-soluble graft copolymer composed of a poly(MPC) side chain and a cellulose backbone. The coating process from an aqueous solution of the graft copolymer was very convenient, and the graft copolymer on the surface was not detached even after water circulated into the hollow fibers. These cellulose hollow fibers modified with MPC polymers displayed excellent hemocompatibility such as prevention of blood cell adhesion and aggregation after contact with blood without an anticoagulant. The permeability of the hollow fibers did not decrease as a result of these modifications. From these results, it is clearly suggested that introduction of the MPC units was effective for improving the hemocompatibility of the hollow fibers for hemodialysis.

Animals↗
PubMed1994

Effect of methylene chain length in phospholipid moiety on blood compatibility of phospholipid polymers.

To investigate the effects of the methylene chain length between the phospholipid polar group and the backbone on blood compatibility of a phospholipid polymer, copolymers of omega-methacryloyloxyalkyl phosphorylcholine (MAPC) with n-butyl methacrylate (BMA) were synthesized. The methylene chains were ethylene (n = 2), tetramethylene (n = 4), and hexamethylene (n = 6). Every MAPC copolymer with an MAPC mole fraction in the range of 0.1-0.3 was soluble in ethanol but only swelled in water, and the equilibrium water fraction of the water-swollen MAPC copolymer membrane decreased with the length of the methylene chain. When a rabbit platelet-rich plasma was applied on the MAPC copolymer surface with an 0.1 MAPC mol fraction for 180 min, the number of adhered platelets depended on the length of the methylene chain in the MAPC moiety of the copolymer. The amount of phospholipid adsorbed on the MAPC copolymer from human plasma was larger than that on hydrophobic poly(BMA) and increased with the length of the methylene chain in the MAPC moiety. That is, the reduction of platelet adhesion corresponded to the increase in the amount of phospholipid adsorbed on the MAPC copolymer.

Adsorption↗
PubMed1994

Bonding to ground dentin by a phenyl-P self-etching primer.

Increasingly higher concentrations of Phenyl-P in 30% HEMA were used as dentin conditioners to improve the bonding of adhesive resins to smear layers. The maximum bond strength (10.4 MPa) was obtained at a concentration of 20% Phenyl-P. Transmission electron microscopy of fractured, lightly smeared, and compactly smeared dentin demonstrated that 20% Phenyl-P in 30% HEMA demineralized the dentin surface by partially dissolving mineral crystals from around collagen. When applied to smear layers, this resin system demineralized the smear layer and incorporated it into the applied resin which penetrated a short distance into the underlying dentin, thereby creating a hybrid layer that contained the original smear layer. This single-step conditioner/primer offers several advantages over previous bonding systems by permitting a single solution to serve as both a conditioner and a primer.

Animals↗
PubMed1994

Polymeric biomaterials: influence of phosphorylcholine polar groups on protein adsorption and complement activation.

The introduction to polymeric biomaterials of phosphorylcholine polar groups represents an approach towards the development of materials with improved blood compatibility. In this respect, two biomaterials, one a copolymer of butyl methacrylate and 2-methacryloyloxyethylphosphorylcholine (MPC), (poly(BMA-co-MPC) and the other, MPC-grafted Cuprophan, were examined with respect to their influence on protein adsorption and complement activation. Protein adsorption was studied by measurement of the adsorption of radiolabelled single proteins (albumin and fibrinogen), while complement activation was measured using radioimmunoassay for C3a des Arg. The investigation demonstrated that the polymers containing phosphorylcholine polar groups can achieve a marked reduction in protein adsorption and complement activation and supports the utilization of phosphorylcholine polar groups as a means of improving the compatibility of biomaterials for blood-contacting applications.

Adsorption↗
PubMed1993

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.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1993

Tissue response of apatite-filled resin cement and titanium-reinforced apatite dental implants in dogs.

Abutment and root portion divided two-piece dental implants were designed to modify the one-piece dense hydroxyapatite (D-HAP) implant. The initial placement of the root portion endosseously ensured an aseptic environment and physical stability for the implant during the bone healing period. The outer D-HAP shell of the root portion was fortified by an inner titanium cylinder and cemented with an adhesive resin cement containing 4-methacryloyoxyethyl trimellitate anhydride (4-META) and reinforced by fine apatite filler. Upon attaining integration of the bone and implant, the abutment was screwed and fixed into the screw hole of the root portion. The tissue response of both the apatite-filled resin cement and root portion of the two-piece implant was studied by animal canine experiments. Light and electron microscopic examination of specimens taken from experimental animal tissue showed bone contacted directly not only the exposed apatite filler at the surface of the apatite-filled resin cement, but also the resin portion. These findings of direct bone contact suggested that the tissue response of apatite-filled resin cement was approximately similar to the usual D-HAP. Because most of the surface of the outer D-HAP shell of the root portion came in contact with bone, it prevented the deposition of contamination on the D-HAP surface during the manufacturing procedures of the root portion.

Animals↗
PubMed1993

Bonding durability of photocured phenyl-P in TEGDMA to smear layer-retained bovine dentin.

The long-term durability of a photocured resin bond to ground bovine dentin with its smear layer retained was investigated. The bonding resin that was employed was composed of 5.0 wt% 2-(methacryloxy)ethyl phenyl hydrogen phosphate (phenyl-P) as a diffusion-promoting monomer, 0.5 wt% camphorquinone as a photosensitizer, and 0.5 wt% N-phenylglycine as a reducing agent in triethyleneglycol dimethacrylate. Following polymerization of the bonding resin, a composite resin was placed and photocured for 60 seconds. Prepared specimens were stored in 37 degrees C water for 1 day, 6 months, and 1 year. Measured tensile bond strengths were 6.7 MPa after 1 day of storage, 4.1 MPa after 6 months of storage, and 2.8 mPa after 1 year of storage. Examinations of the interfaces after fracture under tensile loading suggested that long-term water-immersion weakened the bonds between the photocured adhesive resin and the smear layer-retained dentin because there was insufficient diffusion of the adhesive resin through the retained smear layer.

Animals↗