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.

Copolymers of 2-methacryloyloxyethyl phosphorylcholine (MPC) as biomaterials

Copolymers of 2-methacryloyloxyethyl phosphorylcholine (MPC) showed good hemocompatibility as hypothesized. The hypothesis was surfaces having phosphorylcholine groups by polymerization of MPC could accumulate phospholipids from blood stream and show good blood compatibility. We designed and prepared a methacylate having a phosphorylcholine group. While it was possible to introduce them by polymer reactions, polymer reaction is not always good method to prepare the desired pure surface. This must be very important point to consider biomaterials, as we have to apply them in our body without any adverse effects. The hypothesis was confirmed by changing copolymer composition. The adsorption amount of phospholipids on the surfaces increased with increasing the MPC units in the copolymers. On the other hand, increasing MPC units in MPC copolymers decreased adsorption amount of peptides. There is limitation in blood compatibility tests in vitro due to unstable characteristics of blood itself. We evaluated them with series of blood compatibility tests, in vitro, ex vivo and in vivo, on coated PMMA beads, modified hollow fibers for hemodialysis and 2 mm small diameter blood vessels, respectively. These data suggested MPC is a promising methacrylate to develop good blood contacting devises, which may not require systemic anticoagulation. Conventional blood compatible biomaterials were not suitable to make permeable membranes. But MPC is soluble in water and we could prepare permeable membranes to various solutes by the copolymerization. Introduction of MPC copolymers on cellulose and polysulfone hollow fiber membranes gave them nonthrombogenicity but it did not give adverse effect on their permeability. These data suggested that it is possible to apply them to hemodialyzers, oxygenators and percutaneous glucose sensors to keep diabetic patients easier. MPC surfaces are good hydrogel to minimize damage on tissues by lubricating between organs and the coated devices. They do not induce denaturation of peptides, which is beneficial to keep activities of enzymes longer. And poly-MPC dissolved is applicable to stabilize several bioactive peptides in aqueous phase. So MPC polymers are useful to minimize fouling by inhibiting the adsorption of bioactive proteins. MPC has high potential to develop many varieties of new biomaterials useful in so-called biotechnology. MPC and their copolymers are commercially available from NOF (Tokyo, Japan) and Biocompatibles (UK, as PC technology).

Influence of dentinal polyelectrolytes on wet demineralized dentin, a bonding substrate

The objective of this study was to show the influence of dissolved dentinal polyelectrolytes on the characteristics of dentin (bonding substrate) demineralized by citric acid in the absence or presence of ferric chloride. The demineralizing agent was an aqueous mixture of 0, 1, 3, or 10% ferric chloride in 10% citric acid (10-0, 10-1, 10-3, 10-10, respectively). The hypothesis was that the concentration of dissolved dentinal noncollagenous substances, mainly polyelectrolytes soluble in water, must be decreased by their aggregation with ferric ions, which changes the characteristics of demineralized dentin, the rates of demineralization, and dehydration. Cervical bovine dentin was prepared in 3 x 2 x 2-mm blocks, each weighing 20.0 +/- 0.5 mg. The rate of demineralization was investigated by measuring the weight loss resulting from demineralization by immersion in 10 mL of conditioner at 2-h intervals. The dehydration rate of wet demineralized dentin was determined using two methods: (1) weight loss in a desiccator under 263 Pa pressure and (2) differential scanning calorimetry (DSC). Twenty, 12, 8, and 4 h were required to complete demineralization of the blocks with the 10-0, 10-1, 10-3, and 10-10 solutions, respectively. The 10-10 wet demineralized dentin showed the highest rate of dehydration, followed in descending order by the 10-3, 10-1, and 10-0 specimens. Ferric chloride in dentin conditioners provided both a higher rate of dentin demineralization and a higher dehydration rate of wet demineralized dentin. These results suggest that in the presence of ferric chloride, a decreasing amount of dissolved polyelectrolytes aggregated with ferric ions in the substrates may increase the permeability of dentin to water and citric acid. Improvement of monomer permeability is essential to the preparation of good hybridized dentin, providing a more stable and reliable bonding and also protecting the dentin and pulp from infection. A further study of bonding substrates is required in order to understand the role of hybridized dentin in improved dental treatment.

Preparation of non-thrombogenic materials using 2-methacryloyloxyethyl phosphorylcholine

This review addresses the non-thrombogenic characteristics of copolymers based on 2-methacryloyloxyethyl phosphorylcholine (MPC), originally developed by Nakabayashi and colleagues. The hypothesis underlying these developments was that such materials would adsorb phospholipids from blood, yielding surfaces with good natural blood compatibility. Methacrylates were found to have excellent properties for this copolymerisation. The characteristics of the MPC copolymers relevant to the improved blood compatibility were minimisation of protein adsorption through an increase in the amount of free water in the MPC hydrogels, which prevents protein conformational change and increased protein stability in solution. Non-thrombogenicity has been evaluated by in vitro, ex vivo and in vivo procedures. Non-thrombogenic dialysis membranes and a durable glucose biosensor have been developed using this MPC copolymer.

Effect of dentin conditioners on wet bonding of 4-META/MMA-TBB resin

PURPOSE

By altering either ferric chloride concentration in 10% citric acid (1% ferric chloride = 10-1; 5% ferric chloride = 10-5; 10% ferric chloride = 10-10) or conditioning periods with an aqueous mixture of 1% citric acid and 1% ferric chloride (1-1), the influence of dentin substrate on bond strength and hybridized dentin in wet bonding of 4-META/MMA-TBB resin was examined.

MATERIALS AND METHODS

Dentin surfaces of fresh bovine incisors were conditioned either with 10-1, 10-5, or 10-10 mixtures for 10 s (10-1-10s, 10-5-10s, 10-10-10s groups) or with a 1-1 mixture for 5, 10, 30 or 60 s (1-1-5s, 1-1-10s, 1-1-30s, 1-1-60s groups). Rinsed, demineralized dentin samples were kept wet, primed with 5% 4-META in acetone for 60 s, and bonded with 4-META/MMA-TBB resin. Bonded specimens were trimmed to a mini-dumbbell shape for tensile testing. The cross sections of bonded specimens were modified with HCl and NaOCl in order to assess the hybrid layer. The fractured surfaces of specimens and the hybridized dentin were investigated with SEM.

RESULTS

No significant difference (p > 0.01) in tensile strength was identified between 10-1-10s and 10-5-10s groups (30 MPa), 10-10-10s and 1-1-5s groups (15 MPa), and the three groups conditioned by 1-1-10s, -30s and -60s (40 MPa). The thickness of the hybrid layer increased with increasing either ferric chloride or conditioning periods.

CONCLUSION

The concentration of ferric chloride in 10% citric acid for wet bonding must be less than 5% in order to provide a reliable bond. When applied from 10 to 60 s, the 1-1 conditioner provided hybridized dentin with reliable tensile bond strength. The thickness of the hybrid layer did not influence the tensile bond strength.

Beneficial effects of synthetic phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate), on stratum corneum function

The effects of a newly synthesized phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) [poly(MPC-co-BMA)], on the water barrier function and water-holding capacity of the stratum corneum were examined by measuring transepidermal water loss (TEWL) and electrical conductance of the skin surface. On the backs of four NC mice, the epidermal permeability barrier was abrogated by cellophane tape stripping 30 times. The skin was then treated with 0.1% poly(MPC-co-BMA) or distilled water twice daily for the following 3 days. Poly(MPC-co-BMA) reduced TEWL significantly compared with the control after the first treatment (P = 0.044) and this effect was observed for 3 days. In human skin, water-holding capacity was measured at 5, 10, 15, 30 min and 1, 2, and 4 h after the application of poly(MPC-co-BMA) or distilled water to both volar forearms of 21 healthy volunteers. Skin treated with poly(MPC-co-BMA) showed significantly greater ability to retain water at all time points. Poly(MPC-co-BMA) is the first synthetic material that can enhance both the water barrier function and water-holding capacity of the stratum corneum. Our results indicate that this substance may be useful clinically in the treatment of dry skin.

Effect of Phenyl-P/HEMA acetone primer on wet bonding to EDTA-conditioned dentin

OBJECTIVES

The purpose of this study was to examine the effect of 2-methacryloyloxyethyl phenyl phosphoric acid (Phenyl-P)/2-hydroxyethyl methacrylate (HEMA) acetone-based primer on moist dentin surfaces that were preconditioned with ethylenediaminetetraacetate (EDTA) to remove the smear layer.

METHODS

Bovine dentin were prepared with 180-grit paper, conditioned with 0.5M EDTA (pH 7.4) for 60s followed by water rinsing and then blot drying. Each surface was then primed with Phenyl-P/30 wt% HEMA in acetone for 10s followed by blot drying. A light-cured bonding agent was then applied, cured and trimmed to give dumbbell-shaped specimens. The Phenyl-P concentration ranged from 1 to 20 wt%. During the bonding procedure, no compressed air was used. After storage in water at 37 degrees C for one day, tensile bond strengths were measured and analyzed using one-way ANOVA. Dentin discs treated under the same conditions were observed under a scanning electron microscope (SEM).

RESULTS

When the concentration of Phenyl-P was 12 wt%, the highest mean tensile bond strength was obtained (27 MPa). It was significantly higher than that of the 3, 5, 15 or 20 wt% groups (9-11 MPa) (p<0.05). The samples of 1 wt% group were all broken during trimming the dumbbell-shaped specimens. SEM observations showed a 1 microm-thick layer of hybridized dentin after polished cross-sections were chemically challenged with 6N HCl for 30s and then 1% NaOCl for 60 min.

SIGNIFICANCE

The experimental Phenyl-P/HEMA acetone primer is effective in bonding resin to EDTA-conditioned dentin. Acetone as a solvent for Phenyl-P/HEMA primer has the clinical advantage of not requiring an air-stream to evaporate the solvent. The experimental bonding procedure can minimize the skin irritation by HEMA.

Preservation of platelet function on 2-methacryloyloxyethyl phosphorylcholine-graft polymer as compared to various water-soluble graft polymers

The chemical structures of water-soluble polymers grafted onto PE surfaces affect platelet function when the platelets contact the polymer surfaces. To improve our understanding of this effect, this study sought to control the blood/materials interaction on the surfaces of polyethylene (PE) by grafting with various water-soluble polymers. Such polymers as poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), poly(acrylamide) (PAAm), poly(N-vinylpyrrolidone) (PVPy), and poly[monomethacryloyl poly(ethylene glycol)] (PMPEG) were grafted on low-density PE sheets by photoinduced graft polymerization. Both the PE bags modified with water-soluble polymers and those nonmodified were prepared by heat processing. Activation of platelets after storage in the PE bags was evaluated by measuring the cytoplasmic free calcium ion concentration ([Ca(2+)]i). The concentration of [Ca(2+)]i of platelets in contact with the PE surface grafted with PMPC was the same as that of native platelets and significantly less than that in contact with other PE surfaces grafted with water-soluble polymers. The number of adherent platelets was effectively decreased on PE surfaces grafted with PMPC and PMPEG, as compared with nontreated PE. The aggregation ability of platelets was also measured after storage of platelet-rich plasma in the PE bags. The PE surface grafted with PMPC effectively maintained aggregation ability as compared with both the nontreated PE and with PE grafted with PAAm, PVPy, and PMPEG. It was concluded that for preserving platelet function, PMPC was the most effective of these water-soluble polymers used for surface modification.

Preparation of nanoparticles composed with bioinspired 2-methacryloyloxyethyl phosphorylcholine polymer

The poly(L-lactic acid) nanoparticles immobilized with 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, which has excellent blood compatibility, were prepared by a solvent evaporation technique using the water-soluble amphiphilic MPC polymer as an emulsifier and a surface modifier. The diameter and zeta-potential of the obtained nanoparticles strongly depended on the concentration of the MPC polymer. When the nanoparticles were prepared in 1.0 mg/ml of an MPC polymer aqueous solution, the diameter was 221 nm which was determined by atomic force microscopy and dynamic light scattering measurements. The X-ray photoelectron spectroscopic analysis indicated that the phosphorylcholine groups of the MPC unit were located at the surface of the nanoparticles, that is, the MPC polymer was immobilized on the PLA particles and the surface zeta-potential was -2.5 mV. Various hydrophobic fluorescence probes could permeate through the MPC polymer layer and adsorb on the PLA surface. The amount of bovine serum albumin adsorbed on the nanoparticles was significantly smaller compared with that on the conventional polystyrene nanoparticles. It is suggested that the nanoparticles immobilized with the MPC polymer have the potential for use as both a novel drug carrier and diagnostic reagent which can come in contact with blood components.

Evaluation of the frictional properties of an elastomer with enhanced lipid-adsorbing ability

Wear particle production in load-bearing orthopaedic implants is one of the major factors currently limiting the service life of the implant. Most of the research carried out to date in attempting to solve this problem has used the approach of finding more wear-resistant biocompatible material pairs. In contrast, other researchers have attempted to reduce wear by encouraging elastohydrodynamic film formation through the use of elastomeric bearing surfaces. Unfortunately, these elastomeric bearing surfaces have poor tribological properties when a fluid film is not present. Boundary lubrication of an elastomeric orthopaedic bearing may alleviate some of these difficulties. The purpose of this research was to fabricate and characterize an elastomeric material that had a surface capable of specifically adsorbing a naturally occurring boundary lubricant. Dipalmitoyl phosphatidylcholine (DPPC) has been previously shown to be able to act as a boundary lubricant at stresses that occur in human load-bearing joints such as the hip and knee; therefore, DPPC was chosen for use in this study. It was expected that in an aqueous liposome suspension the static coefficient of friction microseconds of such a material would be lower, and increase less quickly over time, than a similar material without an ability to adsorb specifically DPPC when articulated against a polished chrome steel ball bearing. The lipid-adsorbing elastomer did not possess the desired tribological properties. This result was attributed to the polymer adsorbing the DPPC in the liposome phase and not in the bilayer phase, and interaction among the polymeric surface, DPPC and water. This approach to lubricating orthopaedic bearings was shown to have some merit, but a great deal of work needs to be done before such an approach can be used on a clinically available material.

Effect of phospholipidic boundary lubrication in rigid and compliant hemiarthroplasty models

Hemiarthroplasty may benefit from materials which produce lower friction and improved boundary lubrication protection during start-up conditions. The purpose of this study was to evaluate the effect of phospholipidic boundary lubrication in both rigid and compliant hemiarthroplasty. An in vitro model was designed to dissociate the relative contribution of implant material compliance and the presence of phospholipid to the overall friction of a hemiarthroplasty contact using bovine articular cartilage. Normal bovine articular cartilage was articulated against four flat materials using reciprocating motion: (a) borosilicate glass: (b) borosilicate glass coated with dipalmitoylphosphatidylcholine (DPPC); (c) polyurethane (PU) elastomer (Tecoflex SG93A, a medical-grade aliphatic thermoplastic PU, Thermedics Incorporated. Woburn, Massachusetts); and (d) surface-coated PU (Tecoflex SG93A substrate coated with lipid-attracting copolymer poly[methacryloyloxyethyl phosphorylcholine (MPC)-co-butyl methacrylate (BMA)]. Tests were conducted in physiologically simulated tribological conditions for a non-conformal point contact. Friction and lubrication analysis was performed using both static and kinetic coefficients of friction mu measured for each group as a function of time for a sliding distance of up to 60 m. Results showed that the inclusion of supplemental phospholipid, DPPC, on a rigid substrate significantly decreased mu in comparison with the control (cartilage-glass). Additionally, removal of phospholipid components from the articular cartilage surface produced a significantly greater start-up mu in comparison with normal cartilage at the test onset. The use of a material with a lower modulus resulted in lower mu for the entire duration of the test. Polyurethane elastomer coated with the lipid-attracting copolymer, poly(MPC-co-BMA), resulted in the lowest frictional response. As seen in this study, the improvement of low-modulus hemiarthroplasty may involve the optimization of chemical modification and incorporation of lipid-attracting MPC copolymers onto compliant materials. However, further tests are warranted to determine whether lipid-attracting MPC copolymers perform as well during long-time, in vivo wear studies.

Bonding to dentin with a self-etching primer: the effect of smear layers

OBJECTIVE

The purpose of this study was to investigate the effect of smear layers on the tensile bond strength to human dentin. Bond strength was determined on dumbbell-shaped specimens to determine the feasibility for clinical use of a self-etching primer.

METHODS

The dentin of extracted human teeth was exposed by grinding with either #180 or #600 abrasive paper. A self-etching primer was then applied to the prepared dentinal surfaces and left undisturbed for 30s. It was then air-dried and a photocured bonding agent applied and irradiated for 20s. A composite resin was then added to the primed dentin and light-cured for 60s to complete the bonded assemblies. Mini-dumbbell specimens (3.0 x 2.0 mm2) were prepared from the bonded samples. These specimens were stored in 37 degrees C water for 24h before tensile loading to failure at a crosshead speed of 1.0 mm/min. Surfaces of fractured specimens, both resin and dentin, were examined under a scanning electron microscope (SEM).

RESULTS

Significantly different tensile bond strengths (TBS) of 10.0+/-7.2 and 28.5+/-5.2MPa were found for #180- and #600-prepared dentin, respectively (p<0.01). The former specimens fractured within the hybridized, relatively coarse smear layer, while the latter demonstrated adhesive failure between the composite resin and an attached PMMA rod, not between the dentin and applied adhesive agent.

SIGNIFICANCE

The presence and quality of a smear layer yields significantly different bond strengths to prepared human dentin, in vitro. However, a TBS of 10+/-7MPa is evidently adequate, since self-etching primers have been well accepted in dental clinics.

Semi-interpenetrating polymer networks composed of biocompatible phospholipid polymer and segmented polyurethane

2-Methacryloyloxyethyl phosphorylcholine (MPC) polymers, which have excellent biocompatibility, have been receiving increasing attention in biomedical and bioengineering fields; however, the mechanical strength of the hydrated MPC polymers is not sufficient for use in these fields as a bulk material. Therefore, we hypothesized that a novel material might be realized by reinforcing the MPC polymer network with segmented polyurethane (SPU). Semi-interpenetrating polymer networks (IPNs) composed of crosslinked MPC polymer and SPU were prepared. The mechanical properties of the IPN membrane were significantly improved compared with those of the MPC polymer membrane. Three-dimensional polymer networks of the MPC polymer in the IPNs were observed after solvent extraction of SPU. An X-ray photoelectron spectrum analysis revealed that the MPC units were exposed on the IPN surface. When the IPN was alternately soaked in water and ethanol, the swelling ratio was found to be completely reversible and no disintegration of the network structure was observed. The permeation coefficient of 1, 4-di(2-hydroxyethoxy)benzene through the IPN membrane was 1.11 x 10(-7) cm(-2)s(-1). The amount of adsorbed protein and the number of adherent platelets on the IPN membrane were effectively reduced compared with those on SPU. We concluded that IPNs composed of the MPC polymer and SPU are a new bulk biomaterial, which possesses both blood compatibility and good mechanical properties.

In vivo evaluation of the bond strength of adhesive 4-META/MMA-TBB bone cement under weight-bearing conditions

In order to minimize the problems associated with implant fixation using acrylic bone cement, we studied a new adhesive bone cement that consists of 4-methacryloyloxyethyl trimellitate anhydryde (4-META) and methylmethacrylate (MMA) as monomers, tri-n-butylborane (TBB) as an initiator, and PMMA powder (4-META/MMA-TBB cement). It shows remarkable adhesive properties to metal and bone in vitro. The purpose of this study was to evaluate the strength of the bond of the cement to both metal and bone in vivo under weight-bearing conditions. Metal prostheses were implanted in the right femora of 12 rabbits using either adhesive 4-META/MMA-TBB cement or the conventional PMMA cement, as the control, for fixation. After 4 and 12 weeks, both femora were excised and the same operations were performed in the left femora in vitro. Eighteen femora were sectioned for the mechanical assessment of the bone-cement and cement-implant interfaces. 4-META/MMA-TBB cement had a significantly higher interfacial shear strength than the conventional PMMA cement: 201 N and 90 N, on average, for the implant-cement interface (p<0.01); and 138 N and 89 N, on average, for the bone-cement interface (p<0.01), at 12 weeks. The present results suggest the efficacy of 4-META/MMA-TBB cement in providing greater fixation of implants to bone and promise a firmer intramedullary fixation than the control conventional PMMA cement.

Prevention of fibrous layer formation between bone and adhesive bone cement: in vivo evaluation of bone impregnation with 4-META/MMA-TBB cement

We have studied a new adhesive bone cement, that consists of 4-methacryloyloxyethyl trimellitate anhydride (4-META) and methylmethacrylate (MMA) as monomers, tri-n-butyl borane (TBB) as the initiator, and polymethylmethacrylate powder (4-META/MMA-TBB cement). This cement has shown remarkable adhesive properties to bone in vitro. In this study, we assessed the interface in vivo periodically. The femora of rabbits were fenestrated and filled with either the 4-META/MMA-TBB cement or a conventional polymethylmethacrylate cement. The animals were killed after 1, 4, 12, and 24 weeks to analyze the interface by optical microscopy and transmission electron microscopy. Optical microscopic examinations showed that the cured 4-META/MMA-TBB adhesive cement bonded to bone directly for 24 weeks, whereas a fibrous tissue layer was observed between the bone and cured conventional cement at 12 weeks after the operation. The transmission electron microscopy views of 4-META/MMA-TBB cement bonded to bone demonstrated a unique "hybridized bone" with the cement in the subsurface of the substrate in every case. The formation of the hybridized bone indicates the bonding mechanism of the adhesive cement to bone, which prevents the fibrosis intervention between bone and cement. These results suggest that the biomechanical and adhesive properties of 4-META/MMA-TBB cement make it a useful bone-bonding agent in orthopedic surgery.

The effect of phosphoric acid concentration on resin tag length and bond strength of a photo-cured resin to acid-etched enamel

OBJECTIVES

To determine the relationship between depth of penetration and tensile bond strength of a photo-cured resin to phosphoric acid etched enamel, and the efficacy of enamel etchants that are less aggressive than a concentration of 10% H3PO4.

METHODS

The tensile bond strength and length of tags produced by a photo-cured (20 s) resin consisting of pre-polymerized TMPT/silica in 3% HNPM-TEGDMA on acid-etched enamel was determined. The enamel etchants tested were various concentrations (3-65%) of phosphoric acid. The resin was applied to enamel samples that had been abraded with No. 600-grit SiC paper and acid etched (30 s) to create test specimens that were loaded to fracture on a testing device. The HCl-treated, then cut specimens, were examined under scanning electron microscopy and light microscopy.

RESULTS

The tensile bond strength (10 MPa) of resin to enamel, pre-treated with various acid concentrations did not vary significantly. But resin tag length was found to decrease significantly from 22 microns for 35% H3PO4 to 12 microns for 20% H3PO4 to 9 microns for 5, 10 and 65% H3PO4 to 5 microns for 3% H3PO4.

SIGNIFICANCE

These findings suggest that the length of the tags created by the tested photo-cured resin on phosphoric acid-etched enamel contributes little to the bond strength of the test specimens, and that the adhesive strength of the resin to H3PO4 etched enamel is mainly attributable to the resin's ability to penetrate between the enamel crystallites and rods. Further, enamel pre-treatment by phosphoric acid etchants of concentrations lower than 10% may be satisfactorily employed. The use of less aggressive acid concentrations might minimize any potential adverse effects to enamel substrates.

Effect of etchant variation on wet and dry dentin bonding primed with 4-META/acetone

OBJECTIVE

To collect data that explains the advantage, if any, of wet bonding versus dry bonding to dentin, and to more clearly understand the mechanism of wet bonding.

METHODS

Bovine dentin samples were prepared with #600-grit paper and were divided into four groups of six each. The first six specimens were etched with 10% citric acid and 3% ferric chloride for 10 s then rinsed and blot-dried (Gr. 1: 10-3:W). The second six were etched with 10% citric acid and 3% ferric chloride then rinsed and air-dried (Gr. 2: 10-3:D). The third six were etched with 10% citric acid for 10 s, rinsed and blot-dried (Gr. 3: 10-0:W). The fourth group of six samples was etched, rinsed and air-dried (Gr. 4: 10-0:D). All groups were primed with 5% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in acetone for 60 s and an acrylic rod was bonded to the samples using a 4-META/methyl methacrylate (MMA)-tri-n-butyl borane (TBB) resin. The samples were fashioned into dumbbell-shaped specimens and stressed in tension until bond failure, to determine tensile bond strengths. Fractured surfaces were examined by scanning electron microscopy.

RESULTS

The mean tensile bond strengths of specimen groups were found to be 18.9 (8.1) MPa (Gr. 1: 10-3:W), 18.1 (1.7) MPa (Gr. 2: 10-3:D), 11.9 (4.4) MPa (Gr. 3: 10-0:W) and 5.4 (2.8) MPa (Gr. 4: 10-0:D). There was no statistically significant difference between Grs. 1 and 2 (p > 0.01), or between Grs. 1 and 3 (p > 0.05). The TBS of Gr. 4 (10-0:D) was significantly lower than the others (p < 0.01). The 5% 4-META in acetone primer was apparently quite effective in improving monomer impregnation into demineralized dentin resulting in increased resin content within the hybridized dentin.

SIGNIFICANCE

Effective dentin bonding depended upon the etchants employed. 10-0 etching and air-drying caused the demineralized dentin to collapse in which case wet bonding became necessary to obtain good TBS data. The specimens demineralized with 10-3 did not collapse, even when air-dried; consequently both wet and dry bonding proved effective for obtaining high tensile bond strength data.

Short-term in vivo evaluation of small-diameter vascular prosthesis composed of segmented poly(etherurethane)/2-methacryloyloxyethyl phosphorylcholine polymer blend

A small-diameter vascular prosthesis with potential for clinical use was prepared from a Dacron prosthesis coated with nonthrombogenic polymeric materials. As a coating material, segmented poly(etherurethane) (SPU; Tecoflex 60) was blended with a phospholipid polymer, 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, which has excellent blood compatibility. The Dacron prosthesis, 2 mm in diameter, was immersed in a solution of the SPU/MPC polymer blend and dried to evaporate the solvent. The SPU/MPC polymer prosthesis was nonwater permeable and could be sewn to a natural vessel by a microsurgical technique. The SPU solution was used instead of the SPU/MPC polymer blend solution to prepare a control prosthesis (SPU prosthesis). The SPU/MPC polymer prosthesis and the SPU prosthesis were placed as interposition grafts in rabbit carotid arteries. A massive red thrombus became attached to the surface of the SPU prosthesis as early as 90 min after implantation. In the SPU/MPC polymer prosthesis case, the surface was maintained clear even after 5-day implantation. These observations indicated that the MPC polymer in the SPU could improve the nonthrombogenicity of SPU, and the SPU/MPC polymer blend had potential for preparation of small-diameter vascular prostheses.

Restoration of segmental bone defects in rabbit radius by biodegradable capsules containing recombinant human bone morphogenetic protein-2

Recombinant human bone morphogenetic protein-2 (rhBMP-2) was encapsulated in biodegradable poly(DL-lactide-co-glycolide) (PLGA) capsules to regenerate bone by controlling the release rate of rhBMP-2. The rhBMP-2/PLGA capsules containing 12 microg of rhBMP-2 were implanted in seven 15-mm segmental defects of rabbits radii to examine the healing capacity of the rhBMP-2/PLGA capsules. For the control group, four segmental defects were left empty and two were implanted with ghost PLGA capsules. Healing of the defects was followed for 24 weeks and periodically evaluated by radiographs and histological examination. Mechanical testing was applied to three regenerated bone samples at 24 weeks postoperatively when the mature cortex was observed. Mechanical properties of regenerated bone were not significantly different from normal intact bone statistically. Histologically, the rhBMP-2/PLGA capsules disappeared completely during the process of bone regeneration. These results increased possibilities for clinical application of rhBMP-2/PLGA capsules.

Chemical modification of silk fibroin with 2-methacryloyloxyethyl phosphorylcholine. II. Graft-polymerization onto fabric through 2-methacryloyloxyethyl isocyanate and interaction between fabric and platelets

2-Methacryloyloxyethyl phosphorylcholine (MPC) was grafted onto silk fabric in a two-step heterogeneous system through the vinyl bonds of 2-methacryloyloxyethyl isocyanate (MOI) modified on the fabric. First, habutae silk fabric was modified with the MOI monomer in anhydrous dimethyl sulfoxide using di-n-butyltin (IV) dilaurate and hydroquinone at 35 degrees C. The saturated weight gain of modified MOI monomer on the fabric was 7.3 wt% versus the original silk. Second, graft polymerization with MPC onto the MOI modified silk was conducted using 2,2'-azo bis[2-(2-imidazolin-2-yl)propane dihydrochloride] (VA-044) as an azo polymerization initiator. The weight of the grafted MPC eventually gained was about 26.0 wt%. The MOI-modified and MPC-grafted silk fabrics were analyzed by Fourier transform infrared (FT-IR) spectroscopy. To confirm the improved biocompatibility of the silk fabric, platelet adhesion was preliminarily tested measuring lactate dehydrogenase. The number of platelets adhering to polyMPC-grafted silk fabric decreased by about one tenth compared to original and MOI-modified silk after 60 min of contact with human platelet-rich plasma (1.0 x 10(6) platelets cm(-2)).

Small diameter vascular prosthesis with a nonthrombogenic phospholipid polymer surface: preliminary study of a new concept for functioning in the absence of pseudo- or neointima formation

The purpose of this study was to prepare a small diameter vascular prosthesis functioning without pseudointima formation. A nonthrombogenic phospholipid polymer, the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, has a cell membrane-like structure and has demonstrated strong nonthrombogenicity. We have recently prepared 2 kinds of vascular prostheses, 2 mm in diameter, composed of the MPC polymer and segmented polyurethane (SPU). One includes 7.5 wt% MPC polymer (SPU/MPC[7.5] prosthesis), and the other includes 10.0 wt% (SPU/MPC[10] prosthesis). These prostheses were placed in rabbit carotid arteries and were retrieved at 1 and 4 weeks after implantation. A pseudointima was observed at 4 weeks on the SPU/MPC(7.5). For the SPU/MPC(10), the surface was macroscopically clear without a pseudointima even after a 4 week implantation. It appears that the SPU/MPC(10) prosthesis, functioning without a pseudointima, possesses a stronger nonthrombogenicity and would be more applicable for clinical use.

Stabilization of an antibody conjugated with enzyme by 2-methacryloyloxyethyl phosphorylcholine copolymer in enzyme-linked immunosorbent assay

The purpose of this study was to develop a novel synthetic stabilizer of enzyme-linked antibody in the enzyme-linked immunosorbent assay (ELISA). The water-soluble amphiphilic phospholipid polymer, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-styrene (St)] was synthesized, and its stabilizing functions for the antibody were compared with conventional stabilizers of the antibody conjugated with enzyme (enzyme-antibody conjugate), such as bovine serum albumin (BSA) and casein. In the absence of the stabilizer, the remaining immunologic activity decreased to about 10% of its initial value after 37 days. The same tendency was observed even when the enzyme-antibody conjugate in 1.0 wt % BSA solution was used as a stabilizer. In 1.0 wt % casein solution, the immunologic activity decreased to 29% of the initial value after 37 days. On the other hand, in 0.1 wt % and 1.0 wt % poly(MPC-co-St) solution, the activity remained 74% and 92% of the initial value, respectively. The effects of poly(MPC-co-St) on the stabilization of the enzyme-antibody conjugate depended on the concentration of poly(MPC-co-St). During the ELISA procedure, not only did poly(MPC-co-St) have no effect on the reaction between the antigen and the antibody, but it also had no effect on the reaction between the enzyme and the substrate. These results indicate that poly(MPC-co-St) has the ability to suppress the denaturation of protein, enzyme, and antibody. We concluded that water-soluble poly(MPC-co-St) is an effective synthetic stabilizer in the ELISA.

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.

The effect of the chemical structure of the phospholipid polymer on fibronectin adsorption and fibroblast adhesion on the gradient phospholipid surface

The interaction between biocomponents and the polyethylene (PE) surface modified with poly[omega-methacryloyloxyalkyl phosphorylcholine (MAPC)] was considered taking into account the surface characteristics, i.e., density, mobility, and orientation of the poly(MAPC). The PE surface, grafted gradually with the poly(MAPC) was prepared by corona irradiation method. The amount of peroxide produced on the PE surface which was determined with 1,1-diphenyl-2-picryl-hydrazyl, increased with an increase in the energy of the corona. The surface density of the poly(MAPC) was increased with an increase in the amount of the peroxides produced by the corona irradiation. The orientation and mobility of the poly(MAPC) grafted on the PE surface was evaluated with 1,6-diphenyl-1,3,5-hexatriene. The orientation of the poly[6-methacryloyloxyhexyl phosphorylcholine (MHPC)] which has six methylene chains between the phospholipid polar group and the backbone was higher than that of other poly(MAPC)s. The mobility of the poly(MAPC) decreased with an increase in the methylene chain length in the MAPC unit. The fibronectin adsorption on the gradient PE sheet grafted with poly(MAPC) was determined with enzyme-labeled immunoassay. The amount of adsorbed fibronectin on the PE grafted with poly[2-methacryloyloxyethyl phospohorylcholine(MPC)] and poly(MHPC) decreased with an increase in their surface density. Especially, the PE sheet grafted with the poly(MHPC) was effectively reduced compared with other poly(MAPC)s. On the poly[10-methacryloyloxydecyl phosphorylcholine (MDPC)], there is a minimum amount of adsorbed fibronectin. The fibronectin adsorption pattern on the PE sheet grafted with poly(MAPC) was quite different from the chemical structure of the MAPC unit. The human normal diploid fibroblasts (WI-38 cells) were cultured on the gradient PE sheet grafted with poly(MAPC) changing the concentration of seeded WI-38 cells. The adhesion behavior of the WI-38 cells was different depending on the concentration of the seeded WI-38 cells. When the concentration was low, the number of the adherent WI-38 cells had the same tendency as fibronectin adsorption. The gradient PE sheet grafted with the poly(MHPC) effectively reduced WI-38 cells adhesion even when the concentration of the WI-38 cells was high. The biocompatibility of polymer surfaces can be improved by highly oriented phosphorylcholine group.

Total hip arthroplasty using bone cement containing tri-n-butylborane as the initiator

We performed total hip arthroplasty (THA) using a special acrylic self-curing bone cement (Bonemite), which contains tri-n-butylborane as the initiator. Its maximum temperature at curing is lower than that of a conventional bone cement (CMW). Fifty-eight THAs using Bonemite and 35 THAs using CMW were followed up for more than 8 years (12.5 years on average). At the 10-year follow-up, the survival rates, using revision surgery or aseptic loosening impending revision as the endpoint for failure, were 92.2% for the patients in the Bonemite group and 91.0% for those in the CMW group. No statistical differences were observed between the patients in these two groups with regard to survival rate (p = 0.39). Bonemite showed no clear superiority compared with CMW, although the results suggest that Bonemite is safe and reliable for clinical use and stable in situ for long time.

Behavior of blood cells in contact with water-soluble phospholipid polymer

Omega-Methacryloyloxyalkyl phosphorylcholine (MAPC) polymer, which has various methylene chain lengths between the phosphorylcholine group and the backbone, was synthesized with attention to formation of the biomembrane. The effect of water-soluble poly(MAPC) on the function and activation of blood cells was evaluated to determine the interaction between blood cells and the MAPC polymer. The poly(MAPC) and the MAPC copolymer with a small amount of fluorescent units were synthesized by a conventional radical polymerization technique. Using a fluorescence spectrometer, it was determined that the MAPC polymer was adsorbed on the plasma membrane of platelets when the platelets were suspended in an aqueous solution of the MAPC copolymer. The hemolytic activity of poly(MAPC) was less than that of other water-soluble polymers, such as poly(ethylene glycol) and poly(1-vinyl-2-pyrrolidone) (PVPy). The change in the plasma membrane fluidity of platelets on contact with poly(MAPC) was determined with 1,6-diphenyl-1,3,5,-hexatriene. The plasma membrane fluidity of platelets decreased with an increase in the methylene chain length of the MAPC unit. The aggregation activity of platelets after contact with poly(MAPC) was also evaluated, but no significant difference between that of polymer-contacted platelets and native platelets was observed. Finally, the activity of platelets on contact with poly(MAPC) was determined by measuring the cytoplasmic calcium ion concentration ([Ca2+]i) in platelets. The increase in [Ca2+]i in the platelets after contact with poly(MAPC) was similar to that of native platelets. We conclude that the poly(MAPC) reduced platelet activation even though the poly(MAPC) adsorbed on the membrane surface of the platelets. In particular, poly(10-methacryloyloxydecyl phosphorylcholine) significantly reduced platelet activation compared with PVPy.

Modification of polysulfone with phospholipid polymer for improvement of the blood compatibility. Part 2. Protein adsorption and platelet adhesion

Protein adsorption and platelet adhesion from human plasma on polysulfone (PSf) membranes modified with 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer were studied. The modification was carried out by blending of the MPC polymer in the PSf. The amount of protein adsorbed on the PSf/MPC polymer blend membrane was significantly decreased with an increase in the composition of the blended MPC polymer. The distribution of the specific proteins adsorbed on the membrane surface was also determined by a gold-colloid immunoassay. Albumin, gamma-globulin and fibrinogen were observed on every membrane surface after contact with plasma. However, in the case of the blended membrane, the density of the adsorbed proteins decreased compared with that of original PSf membrane. That is, the MPC polymer blended in the membrane could function as a protein-adsorption-resistant additive. The number of platelets adhered on the PSf membrane was reduced, and change in the morphology of adherent platelets was also suppressed by the modification with the MPC polymer. Therefore, the PSf/MPC polymer blend membrane had improved blood compatibility compared with the PSf membrane.

Modification of polysulfone with phospholipid polymer for improvement of the blood compatibility. Part 1. Surface characterization

To improve the surface blood compatibility of polysulfone (PSf) membranes, we prepared novel polymeric additives which have suitable blood compatibility. They were polymers with a phosphorylcholine group, a 2-methacryloyloxyethyl phosphorylcholine (MPC) unit. The MPC polymer could be blended with polysulfone by a solvent evaporation method during membrane processing, and a transparent membrane could be obtained. The mechanical properties of the blend membrane were similar to that of the original PSf membrane. Surface analysis of the blend membrane by X-ray photoelectron spectroscopy and dynamic contact angle measurement revealed that the MPC unit in the polymeric additive was concentrated on the surface of the membrane. The blend membrane significantly reduced plasma protein adsorption compared with that of the PSf membrane.

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.

Combination of EDTA conditioner and phenyl-P/HEMA self-etching primer for bonding to dentin

OBJECTIVES

The purpose of this study was to examine a new bonding system, combining an ethylenediaminetetraacetic acid (EDTA) conditioner and the 2-methacryloyloxyethyl phenyl phosphoric acid (Phenyl-P)/2-hydroxyethyl methacrylate (HEMA) self-etching primer with a dumbbell-shaped specimen for tensile test.

METHODS

Bovine dentin was prepared with a 180-grit paper, conditioned with EDTA, primed with Phenyl-P/HEMA and applied with a light-cured bonding agent, then trimmed to the dumbbell-shaped specimen. After storage in water at 37 degrees C for one day, the tensile bond strength was measured and the hybridization was evaluated by scanning electron microscopy (SEM).

RESULTS

When the demineralized dentin with EDTA was primed with 1 wt% Phenyl-P in 30 wt% aqueous HEMA for 10 s, the highest tensile bond strength (22 MPa) was obtained. The SEM views showed that the fractured surface after the tensile test was due to cohesive failure in the cured resin and the 1 micron-hybridized dentin was identified. When the concentration of Phenyl-P and the priming period were increased, tensile bond strength significantly decreased and adhesive failure appeared on the fractured surface.

SIGNIFICANCE

Combining the EDTA conditioner and Phenyl-P/HEMA primer afforded high-quality hybridization and good bond strength. This bonding system was promising for bonding resin to human dentin.

Improvement of blood compatibility on cellulose hemodialysis membrane: IV. Phospholipid polymer bonded to the membrane surface

To improve the surface blood compatibility on a cellulose hemodialysis membrane, 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers with a phospholipid polar group were immobilized on the surface through covalent bonding. The MPC polymers had a carboxylic group, which can react with hydroxyl groups on the cellulose membrane, and were synthesized by conventional radical polymerization. The reaction between the MPC polymers and the cellulose membrane was carried out in a heterogeneous system using a condensation reagent. Surface analysis of the modified membrane by X-ray photoelectron spectroscopy revealed the immobilization of the MPC polymer on the surface. The mechanical strength and permeability for a solute of the membrane did not change even after the modification. The modified cellulose membrane was blood-compatible, as determined by the prevention of adhesion, deformation, and aggregation of platelets after contact with platelet-rich plasma. Based on these results, it is concluded that the MPC polymers may be a useful material for improving the blood compatibility of cellulose hemodialysis membranes.

The role of recombinant human bone morphogenetic protein-2 in PLGA capsules at an extraskeletal site of the rat

Bone morphogenetic protein-2 (BMP-2) is a member of the transforming growth factor-beta (TGF-beta) superfamily and has strong bone-inductive activity in vivo. To examine the role of BMP-2 in an extraskeletal site of rat using a controlled release system of peptides, we encapsulated the recombinant human BMP-2 (rhBMP-2) with poly(DL-lactide-co-glycolide) (PLGA) and implanted the rhBMP-2/PLGA capsules in the subcutaneous area of rats. Upon histochemical examination, it was found that bone-inducing cells having alkaline phosphatase (ALP) activity appeared around the capsules by the suitably released rhBMP-2. In addition, the temporal histological examination showed that direct bone formation without cartilage occurred in the process of this ectopic bone induction. These data indicate that the role of rhBMP-2 in the extraskeletal site of rats is to induce the differentiation of mesenchymal cells into the osteoblasts.

Platelet adhesion on the gradient surfaces grafted with phospholipid polymer

We have synthesized omega-methacryloyloxyalkyl phosphorylcholine (MAPC) polymers as new blood-compatible materials, with attention to the surface structure of the biomembrane and investigated their blood compatibility. The blood compatibility observed on the MAPC polymers is due to their strong affinity to phospholipids. When the blood comes in contact with the MAPC polymer, phospholipids in the plasma preferentially adsorb on the surface, compared with the plasma proteins or cells. The adsorbed phospholipids construct a biomembrane-like structure on the MAPC polymer surface. The MAPC polymers then have an excellent blood compatibility. In this study, we prepared a gradient poly(MAPC)-grafted polyethylene (PE) surface using a corona discharge treatment method to clarify the effect of the chemical structure of the MAPC unit on the blood compatibility of the MAPC polymers. The surface composition of MAPC and the hydrophilicity on the poly(MAPC)-grafted PE surface were determined by X-ray photoelectron spectroscopic (XPS) analysis and contact angle measurement with water, respectively. The phosphorus/carbon (P/C) ratio determined by the XPS analysis increased, but the water contact angle decreased with increasing corona irradiation energy. These results indicated that the surface density of the MAPC unit was increased. More than 2.5 cm from the starting point of the corona irradiation, the P/C ratio and water contact angle of the surface achieved a constant level. Thus, the surface was completely covered with the grafted poly(MAPC) chain. The effect of the methylene chain length of the MAPC unit on surface properties was also observed. The phospholipid polar group of the MAPC unit was effectively exposed on the surface as the chain length became longer. Moreover, the hydrophobicity of the surface was increased with the increase in the methylene chain length of the MAPC unit. The number of platelets adhering to the poly(MAPC)-grafted PE surface was reduced from the same point where the P/C ratio became constant.

Performance of adhesive bone cement containing hydroxyapatite particles

A new acrylic bone cement which can adhere to both bone and prostheses was developed based on a methyl methacrylate (MMA) monomer containing 4-methacryloyloxyethyl trimellitate anhydride (4-META) as adhesion promoting agent. Moreover, hydroxyapatite (HA) particles were introduced into the 4-META cement as a bone compatible filler. The mechanical strengths of an acrylic bone cement without 4-META decreased drastically with an increase in the percentage of HA particles in the cement. However, the mechanical strengths of the HA-containing 4-META cement did not change in the same way as that of the 4-META cement without HA due to adhesion between the cement HA particles and matrix. The HA particles did not affect the adhesion of the 4-META cement to bone and metals. Implantation of the 4-META cement and the HA-containing 4-META cement in animals demonstrated that these cements did not disturb bone ingrowth and the new bone was able to contact the cement directly. The 4-META cements, with and without HA particles, could adhere to bone in vivo.

The durability of adhesion to phosphoric acid etched, wet dentin substrates

OBJECTIVE

The purpose of this study was to investigate the influence of remaining non-resin-impregnated, phosphoric acid demineralized dentin upon the long-term durability of specimens that were wet-bonded to bovine dentin substrates.

METHODS

Prepared bovine dentin samples were etched with 65% phosphoric acid then rinsed with water and kept wet during application of 5 wt% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in acetone primer. This was followed by application of a photocured dentin-bonding agent consisting of 4-methacryloyloxyethyl trimellitate anhydride/triethyleneglycol dimethacrylate-camphorquinone/N-phenylglycine (4-META/TEGDMA-CQ/NPG). The tensile bond strength (TBS) of bonded specimens was determined after immersion in 37 degrees C water for various time intervals. Generated data were analyzed for statistical significance by one-way ANOVA and Duncan's New Multiple Range Test (p < 0.05). The dentin side of the tensile-load-fractured specimens was examined under optical and scanning electron microscopes (SEM).

RESULTS

TBS decreased from 6.6 +/- 1.0 MPa after 1-day water immersion to 3.4 +/- 1.7 MPa after 1 month of water immersion. After 6 months of water immersion, TBS was found to be 3.9 +/- 0.9 MPa and this decreased to 2.0 +/- 1.0 MPa for specimens immersed in water for 1 year, a statistically significant difference (p < 0.05). Optical microscopic and SEM observations disclosed failure patterns within demineralized, non-resin-impregnated dentin that increased with the period of water immersion.

SIGNIFICANCE

The bond durability to wet dentin was poor when demineralized dentin was not resin-impregnated, resulting in exposure of collagen fibrils which hydrolyzed during long periods of water immersion.

A tensile test to facilitate identification of defects in dentine bonded specimens

OBJECTIVES

To determine the efficacy of a miniaturized dumbbell test procedure designed to more easily identify defect(s) in bonded dentine test specimens.

METHODS

Extracted human dentine substrates were pre-conditioned with 10-3 solution for 10, 30 or 60 s prior to dentine bonding with 4-META/MMA-TBB resin. Miniaturized dumbbell-shaped test specimens were prepared from the resin bonded samples. After 24 h storage in 37 degrees C water, the specimens were tensile-loaded to failure. Fractured surfaces and cross-sections were examined and compared under scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

RESULTS

Cohesive failure within the bonding resin was observed in specimens pre-conditioned for 10 s. The tensile bond strength of these was excellent. Bond strengths of specimens that were pre-conditioned for 30 and 60 s were significantly lower, and defects in these specimens, formerly difficult or impossible to identify, were readily identified under SEM and TEM microscopy.

CONCLUSION

The proposed method of tensile stressing to failure and microscopically examining fractured miniaturized dumbbell-shaped test specimens is a simple and reproducible test procedure. The protocol is capable of clearly elucidating defective resin infiltration of demineralized dentine in bonded interfaces. These defects are difficult to visualize by conventional and/or ISO recommended methods.

Why do phospholipid polymers reduce protein adsorption?

The amount of plasma protein adsorbed on a phospholipid polymer having a 2-methacryloyloxyethyl phosphorylcholine (MPC) moiety was reduced compared to the amount of protein adsorbed onto poly[2-hydroxyethyl methacrylate (HEMA)], poly[n-butyl methacrylate (BMA)], and BMA copolymers with acrylamide (AAm) or N-vinyl pyrrolidone (VPy) moieties having a hydrophilic fraction. To clarify the reason for the reduced protein adsorption on the MPC polymer, the water structure in the hydrated polymer was examined with attention to the free water fraction. Hydration of the polymers occurred when they were immersed in water. The differential scanning calorimetric analysis of these hydrated polymers revealed that the free water fractions in the poly(MPC-co-BMA) and poly(MPC-co-n-dodecyl methacrylate) with a 0.30 MPC mole fraction were above 0.70. On the other hand, the free water fractions in the poly(HEMA), poly(AAm-co-BMA), and poly(VPy-co-BMA) were below 0.42. The conformational change in proteins adsorbed on the MPC polymers and poly(HEMA) were determined using ultraviolet and circular dichroism spectroscopic measurements. Proteins adsorbed on poly(HEMA) changed considerably, but those adsorbed on poly(MPC-co-BMA) with a 0.30 MPC mole fraction differed little from the native state. We concluded from these results that fewer proteins are adsorbed and their original conformation is not changed on polymer surfaces that possess a high free water fraction.

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

A new adhesive bonding material for the cementation of implantable devices in otologic surgery

BACKGROUND

Presently, there are no U.S. Food and Drug Administration (FDA)-approved adhesive bone cements for the surgical fixation of prosthetic materials in the middle ear. A promising new cement, 4-META/MMA-TBB opaque resin, has shown remarkable adhesive properties as a bone cement in vivo. The cement is composed of 4-methacryloyloxyethyl trimellitate anhydride (4-META) and methyl methacrylate (MMA) as monomers and tri-n-butyl borane (TBB) as an initiator.

METHODS

An electromagnetic semiimplantable hearing device presently under development was implanted into the middle ear of six cats using 4-META/MMA-TBB resin to cement a titanium-encased magnet to the incus. The animals were subsequently killed (at a mean of 9.6 months) to assess the (temporal bones and specifically the magnet-incus complex in each animal.

RESULTS

The titanium-encapsulated magnet was firmly adherent to all incuses without any failure of the cement-bone interface. Histopathologic examination of the implanted temporal bones demonstrated lack of middle ear inflammation. Transmission electron microscopy of the incuses demonstrated a unique "hybrid layer" in the bone-side subsurface of the bone-cement interface that elucidates the mechanism of interfacial adhesion.

CONCLUSIONS

Our investigation highlights the special biomechanical properties as well as the biocompatibility of 4-META/ MMA-TBB resin that make it an attractive bone-bonding agent for use in otologic surgery, including its potential usefulness during ossicular reconstruction.

Enhanced strength in cemented stem fixation using adhesive acrylic cement as a metal coating material

One cause of aseptic loosening of cemented total hip arthroplasty is mechanical weakness at the interface between the metal stem and the cured bone cement. Adhesive acrylic bone cement containing 4-methacryloyloxyethyl trimellitate anhydride (4-META) was applied as a metal coating material to increase the strength of the cemented fixation. The 4-META cement has 2-3 times greater tensile bond strength to metals than does commercial acrylic bone cement. The shear strength of the coated metals fixed with bone cement was approximately 4 times greater in SUS-304 and 3 times greater in titanium (Ti) alloy than those of uncoated metals, and this strength did not decrease after 1 week's immersion in saline. The coating process using the 4-META cement can be performed at normal room temperature, so that metal stems for bone cement fixation could be coated during the course of an operation resulting in potentially improved results of total hip arthroplasty.

Preparation of an effective light-cured bonding agent for orthodontic application

OBJECTIVE

The purpose of this study was to prepare a light-cured adhesive applicable for orthodontics by mixing monomers and a polymerized reactive organic composite filler (prepolymerized trimethylolpropane trimethacrylate-filler, TMPT-filler).

METHODS

The monomer component was a mixture of 3.0 wt% 2-hydroxy-3-(2-naphthoxy)propyl methacrylate (HNPM) in triethylene glycol dimethacrylate. This was applied to extracted bovine tooth enamel after acid etching with 65 wt% phosphoric acid for 30 s. After 24 h in 37 degrees C water, the tensile bond strength was measured, and the data were analyzed with Duncan's new multiple range test (p < 0.01 or 0.05).

RESULTS

The tensile bonding strength to enamel etched with 65 wt% phosphoric acid was 13.1 +/- 0.5 MPa, and the thermal stability of the bond was excellent. SEM examination of the cross-sectioned specimens modified with HCl demineralization showed that when the diffusion time prior to light irradiation was only 1 min, a well-developed resin honeycomb-like structure was created in the enamel surface in the formulation containing HNPM.

SIGNIFICANCE

Monomer impregnation beyond the etched enamel surface was important for resin-enamel bonding, increasing bonding strength and thermal stability. HNPM was effective in enhancing monomer diffusion and impregnation of the etched enamel surface.

Effect of reduced protein adsorption on platelet adhesion at the phospholipid polymer surfaces

We prepared polymers having a phospholipid polar group, poly [omega-methacryloyloxyalkyl phosphorylcholine (MAPC)-co-n-butyl methacrylate(BMA)], as new biomedical materials and evaluated their blood compatibility with attention to protein adsorption and platelet adhesion. The total amount of proteins adsorbed on the polymer surface from human plasma was determined, and the distribution of adsorbed proteins on the plasma-contacting surface was analyzed. The amount of proteins adsorbed on every poly (MAPC-co-BMA) was small compared with that observed on polymers without the phospholipid polar group. However, there was no significant difference in the amount of adsorbed proteins on the poly(MAPC-co-BMA) even when the methylene chain length between the phospholipid polar group and the backbone in the MAPC moiety was altered. Platelet adhesion on the polymer surface from a platelet suspension in a buffered solution was evaluated with and without plasma treatment on the surface. When a rabbit platelet suspension was brought into contact with the poly(BMA) surface after treatment with plasma, many platelets adhered and aggregated. However, a reduced amount of platelet adhered on the poly(BMA) was found in the case of direct contact with the platelet suspension. On the other hand, the poly(MAPC-co-BMA)s could inhibit platelet adhesion under both conditions. Based on these results, it can be concluded that the proteins adsorbed on the surface play an important role in determining the platelet adhesion and suppression of the protein adsorption on the surface, which is one of the most significant ways of inhibiting platelet adhesion.

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.

Bone morphogenetic protein encapsulated with a biodegradable and biocompatible polymer

To develop a controlled release system for bone morphogenetic protein (BMP), poly(DL-lactide-co-glycolide) (PLGA) capsules containing BMP were prepared by an interfacial precipitation method using a water-in-oil-in-water emulsion. The surface morphology, particle size distribution, and hydrolytic degradation rate of the PLGA capsules were examined. The encapsulation yield and release rate of BMP in vitro were measured using fluorescein isothiocyanate-labeled BMP. The amount of BMP released from PLGA capsules increased between days 3 and 5. In addition, the effectiveness of BMP encapsulated in PLGA to induce bone formation in vivo was also examined by subcutaneous implantation in rats. Complete digestion of the capsules and new bone formation including bone marrow were identified by histologic examination of harvested tissues at 3 weeks after implantation. These results demonstrated that encapsulation of BMP with PLGA could be a promising method to induce bone in clinics.

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.

Bonding to intact dentin

It has been reported that the presence of a smear layer on dentinal substrates can compromise bonding. Typically, smear layers are removed by acidic agents that selectively extract calcium salts from dentin surfaces to leave a collagen-rich substrate. Acid-conditioned dentin (i.e., demineralized) is then primed and an adhesive agent applied. In the present study, we removed smear layers by "polishing" dentin specimens with a hydroxyapatite paste and ultrasonication. Bonding procedures were carried out by means of an aqueous solution of 20% 2-methacryloyloxyethyl phenyl phosphoric acid (phenyl-P) and 30% 2-hydroxyethyl methacrylate, referred to as 2OP-30H, a "self-etching primer". The 20P-30H solution was applied to "intact" dentin (i.e., non-demineralized) for either 30 or 60 s. Control samples received no application (O s) of the self-etching primer. Mean tensile bond strengths (10 MPa) were similar in both the 30-second- and 60-second-primed groups. The widths of formed hybrid layers varied from 0.3 +/- 0.2 micron at O s application (control) to 2.1 +/- 0.3 micron for the 30-second group and 4.1 +/- 0.2 micron for the 60-second group. SEM and TEM observations revealed that the 20P-30H self-etching primer created diffusion channels into "intact" calcium-rich dentin which permitted monomer to infiltrate dentin substrates. Hybrid layers identified under microscopic examination demonstrated resistance to both HCI and NaOCI treatments, suggesting that the hybrid layer was not defective, and that bonding was stable.

Effect of phosphoric acid concentration on wet-bonding to etched dentin

OBJECTIVE

This study was conducted to investigate the influence of phosphoric acid (H3PO44) demineralization of dentin during smear layer removal prior to dentin bonding.

METHODS

Bovine dentin was pre-treated with either 10 wt% or 35 wt% phosphoric acid for 30 s. Substrates were then rinsed and either kept moist or air-dried before a light-cured bonding system was applied. The adhesive system consisted of a 5 wt% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in acetone primer, and a photocured bonding agent, 4-META/triethylene glycol dimethacrylate-camphorquinone/N-phenylglycine (4-META/TEGDMA-CQ/NPG). Tensile bond strengths of bonded specimens were measured, and specimens were examined with a scanning electron microscope (SEM). Data obtained were subjected to two-way ANOVA and Duncan's New Multiple Range test to examine statistically significant differences (p < 0.05).

RESULTS

Improved tensile bond strengths were measured when the 4-META/acetone primer was applied to wet dentin that had been etched with 10 wt% H3PO4 compared with similarly etched but dry dentin samples. However, when the dentin was etched with 35 wt% H3PO4, there was no significant difference in tensile bond strength between wet and dry specimens. SEM examination of the fractured surfaces revealed a number of cohesive failures in the demineralized dentin. Microscopic examination of cross sections of these surfaces indicated that resin impregnation was inadequate and that the hybrid layers in the cohesively fractured specimens were defective.

SIGNIFICANCE

Phenomena observed in this investigation suggest that the channels between the H3PO4-denatured collagen fibers were difficult to preserve, so adhesive monomer impregnation of these substrates was impaired in a considerable number of test specimens.