Adsorption of plasma proteins and adhesion of platelets onto novel polyetherurethaneureas--relationship between denaturation of adsorbed proteins and platelet adhesion

Improved corrosion resistance and biocompatibility of a calcium phosphate coating on a magnesium alloy for orthopedic applications

In this study a calcium phosphate (Ca–P) coating was fabricated on the surface of an AZ31 alloy by a chemical deposition process, and the in vitro and in vivo studies were carried out on a Ca–P-coated and uncoated AZ31 alloy to determine the effect of Ca–P coating on the corrosion behavior and biocompatibility of the AZ31 alloy. The morphology and composition of the Ca–P coating were characterized by scanning electron microscopy and energy dispersive spectroscopy. The corrosion behavior of the Ca-P coating was evaluated by a static immersion test and the effects of the Ca–P coating on biocompatibility were also investigated by in vitro cell experiments and in vivo animal experiments. The results indicated that the Ca–P coating reduced the in vitro and in vivo corrosion rates of the AZ31 alloy. Cell experiments showed significantly good adherence and high proliferation on the Ca–P-coated AZ31 alloy than those on the uncoated AZ31 alloy ( P < 0.05). The blood cell aggregation tests showed that the Ca–P-coated AZ31 alloy had decreased the blood cell aggregation compared to the uncoated AZ31 alloy. The animal experiments showed that the uncoated AZ31 alloy degraded more rapidly than the Ca–P-coated AZ31 alloy and the Ca–P coating provided significantly good biocompatibility, thus suggesting that the Ca–P coating not only slowed down the corrosion rate of the AZ31 alloy, but also improved its biocompatibility. Therefore, the Ca–P-coated AZ31 alloy can be considered as a promising biomaterial for orthopedic applications.

Drug-carrying albumin film for blood-contacting biomaterials

Surface-induced thrombosis is a major complication in the development of blood-contacting medical devices. Serum albumin has the ability to bind to a wide variety of compounds, including drugs, and neither cells nor proteins adsorb to an albumin-coated surface. These properties of albumin are useful for improving the blood compatibility of biomaterial surfaces. In the present study, we prepared a water-insoluble film by cross-linking pharmaceutical grade recombinant human serum albumin aiming to the clinical applications, and loaded the film with a synthetic antiplatelet drug, cilostazol. The resultant film possessed native albumin characteristics such as drug binding ability and resistance to cell adhesion. Mouse fibroblast L929 cells did not adhere on the albumin film, just as they did not adhere on native albumin-coated surfaces. Furthermore, when the albumin film carrying cilostazol was placed in PBS containing Tween-80, the release of cilostazol was sustained over 144 h. The results indicate that the surface coating with thus prepared albumin film can confer the biomaterials with antithrombogenic surface by virtue of its non-adhesiveness to cells and its release of cilostazol.

Hemocompatibility of heparin-coated surfaces and the role of selective plasma protein adsorption

Although several studies have shown that heparin-coated surfaces reduce the activation of both the complement system and the coagulation system, there is still inadequate understanding of the factors initiating and controlling blood activation at these surfaces. We investigated the adsorption profile of 12 common plasma proteins (and the platelet receptor CD41) to a heparin coating (Carmeda BioActive surface (CBAS)) compared to uncoated controls (PVC) by using an in vitro whole blood Chandler-Loop model. Surface bound proteins were studied kinetically by a direct ELISA technique. Western blots were performed on the SDS eluates in order to detect adsorbed cleavage products and denatured proteins. Changes in plasma levels of neutrophil activation markers, platelet activation, coagulation activation, complement activation and the inflammatory response were measured by conventional ELISAs. This study showed significant differences in adsorption patterns among the heparin-coated and the uncoated surfaces, notably for fibronectin, fibrinogen, C3 and high molecular weight kininogen (HMWK). The kinetic studies confirmed the results obtained from Western blots and indicated specific adsorption profiles of plasma proteins. We assume that at least some of the improved blood compatibility of the heparin-coated surfaces may be ascribed to the selective uptake and cleavage of plasma proteins.

Glutardialdehyde induced fluorescence technique (GIFT): a new method for the imaging of platelet adhesion on biomaterials

One of the major limitations of biomaterials used in medicine is the adhesion and subsequent activation of platelets upon contact with blood. The development of new or modified materials necessitates adequate methods for the detection and quantification of platelet/material interactions. These interactions are commonly investigated by means of scanning electron microscopy (SEM), radioisotope and immunological techniques, or by quantification of released platelet contents. Given the lack of a simple, rapid, and inexpensive assay, we developed a novel method for the accurate assessment of platelet adhesion after contact with foreign surfaces, which enables quantitative measurements as well as imaging of the platelet shape change, and which omits conventional or immunological staining and time-consuming preparative steps. The glutardialdehyde induced fluorescence technique (GIFT) uses the epifluorescence of glutardialdehyde-fixed platelets detected by fluorescence microscopy and is suitable for opaque and transparent materials. Combined with computer-aided image analysis, numbers of adherent platelets, platelet-covered surface, and average platelet spread area can be determined as markers of surface thrombogenicity. To validate the technique, four materials of different thrombogenicity [polypropylene (PP), poly(D,L-lactide) (PDLLA), 2-hydroxyethyl-methacrylate-grafted PDLLA (PDLLA-HEMA), and heparin-coupled PDLLA-HEMA] were investigated by GIFT and SEM. We found concordant results with SEM and GIFT with the following ranking of thrombogenicity: PP > PDLLA > PDLLA-HEMA > or = PDLLA-HEMA-heparin. GIFT significantly discriminated between the investigated materials. The surface modifications led to improved thromboresistance with reduced platelet adhesion and shape change. The main advantages of GIFT as compared with SEM are: no vacuum-drying or dehydration, less time-consuming procedure, fixation and fluorescence "staining" in one step, and suitability for computer-aided image analysis allowing quantitative assessment of platelet adhesion as well as imaging of the platelet shape change with high-contrast images. In conclusion, GIFT is a valid, rapid, and simple method for the quantitative determination of platelet/material interactions intended for the evaluation of thrombogenicity of biomaterials surfaces.

Blood compatible aspects of poly(2-methoxyethylacrylate) (PMEA)--relationship between protein adsorption and platelet adhesion on PMEA surface

Platelet adhesion and spreading is suppressed when a poly(2-methoxyethylacrylate) (PMEA) surface is used, compared with other polymer surfaces. To clarify the reason for this suppression, the relationship among the amount of the plasma protein adsorbed onto PMEA, its secondary structure and platelet adhesion was investigated. Poly(2-hydroxyethylmethacrylate) (PHEMA) and polyacrylate analogous were used as references. The amount of protein adsorbed onto PMEA was very low and similar to that absorbed onto PHEMA. Circular dichroism (CD) spectroscopy was applied to examine changes in the secondary structure of the proteins after adsorption onto the polymer surface. The conformation of the proteins adsorbed onto PHEMA changed considerably, but that of proteins adsorbed onto PMEA differed only a little from the native one. These results suggest that low platelet adhesion and spreading are closely related to the low degree of the denaturation of the protein adsorbed onto PMEA. PMEA could be developed as a promising material to produce a useful blood-contacting surface for medical devices.

Protein adsorption on low-temperature isotropic carbon: I. Protein conformational change probed by differential scanning calorimetry

This is the first of a set of articles on protein adsorption on low-temperature isotropic carbon (LTIC), a reputed blood compatible material. Surface-induced conformational changes of albumin, fibrinogen, and some small proteins were measured by differential scanning calorimetry (DSC) on LTIC powders and colloidal silica. The LTIC surface significantly alters the DSC response (denaturation?) in proteins studied in different buffer solutions. We use the term "denaturation" to refer to altered protein behavior in the adsorbed state. Hydrophobic interactions between LTIC and the proteins are thought to be the major driving force. The presence of air at the water-carbon interface seems to prevent the surface denaturation of fibrinogen. The silica surface greatly denatures albumin but only slightly denatures fibrinogen. Because LTIC is considered to be a nonthrombogenic material, but silica is considered to be a thrombogenic one, whether a surface denatures adsorbed proteins cannot be the sole criterion for its blood compatibility. The latter largely depends on what protein the surface denatures, and in what sequences.

Heparin-coated cardiopulmonary bypass circuits

The indications for heparin-coated extracorporeal circuits cannot be defined or limited at present. Clinical investigation remains at an early stage of development. In situations where the risk of systemic anticoagulation is high, this technology would seem to hold great promise. Examples include extracorporeal lung assist and resuscitation from accidental hypothermia. Some have also suggested the use of heparin-coated circuits for percutaneous bypass in cardiopulmonary resuscitation. A significant advantage might also accrue in noncardiac surgical procedures requiring cardiopulmonary bypass, such as complex cerebral aneurysm or arteriovenous malformation resections, resections of the tracheal carina, or bilateral lung transplantations. Its role in routine cardiac surgical procedures remains uncertain, but the work of von Segesser et al suggests a need for continued investigation in that setting using reduced levels of systemic anticoagulation. That endeavor will be greatly assisted by the recent development of heparin-coated cardiotomy reservoirs. Although heparin-coated circuits have been safely used for extracorporeal lung assist with little or no systemic anticoagulation, prospective studies are clearly needed to determine if this approach is advantageous, and it would seem appropriate to develop heparin coating for silicone-based membrane oxygenators.

Adsorption of a novel fluorescent derivative of a poly(ethylene oxide)/poly(butylene oxide) block copolymer on octadecyl glass studied by total internal reflection fluorescence and interferometry

We have used total internal reflection fluorescence (TIRF) to measure the adsorption kinetics of a newly synthesized fluorescent derivative of a triblock copolymer comprising two poly(ethylene oxide) arms connected by a poly(butylene oxide) segment. The composition is (EO)400 (BO)55 (EO)400, in which EO represents ethylene oxide, BO represents butylene oxide, and one or both of the terminal OH groups of the two (EO)400 arms are labeled with tetramethylrhodamine. The poly(butylene oxide) segment binds to hydrophobic octadecyl glass, used as a substratum. The TIRF signal is shown to be derived almost entirely from surface-adsorbed polymer. This facilitates calculation of adsorption isotherms from 0.1-0.005% bulk polymer solution by means of diffusion kinetics. Information about the effective thickness of the adsorbed polymer, determined by optical interference microscopy, corresponds with what is known about the conformation of similar molecules at interfaces and indicates monolayer adsorption on the glass.

Synthesis and nonthrombogenicity of fluoroalkyl polyetherurethanes

New polyetherurethanes carrying fluoroalkyl substituents in the side chains were synthesized from N,N-di(hydroxyethyl)heptadecafluorooctyl-sulfonamide (a chain extender), 4,4'-disocyanatodiphenylmethane, and poly(tetramethylene glycol). Various kinds of polyetherurethanes having different tensile properties were prepared by changing the content of fluoroalkyl chain extender or the molecular weight of poly(tetramethylene glycol). The surface of a film made from the fluoroalkyl polyetherurethane was strongly water-repulsive. The in vitro thrombus formation on the fluoroalkyl polyetherurethanes was reduced by increasing the content of chain extender for the same molecular weight of poly(tetramethylene glycol). Protein adsorption, platelet adhesion, and platelet activation on the fluoroalkyl polyetherurethanes were also investigated.

Competitive adsorption of albumin against collagen at solution-air and solution-polyethylene interfaces

The adsorption of human serum albumin (HSA) from the binary mixtures with collagen was monitored at solution-air and solution-polyethylene interfaces by the in situ measurements. The results clearly demonstrate that on both interfaces albumin is the only adsorbing protein within a large collagen solution concentration range. At the albumin concentration equal to 0.005 mg/mL, the presence of collagen in solution results in the enhancement of albumin adsorption at solution-air interface relative to its adsorption from the single protein system. The same phenomenon is manifested at the solution-polyethylene interface, although the increase in albumin adsorption at this interface occurs at the albumin concentration equal to 0.01 mg/mL. These results are attributed to the lowering in the solution-air and solution-polyethylene interfacial tensions, and thus to the increase in the spreading characteristics of albumin in the presence of collagen molecules. The desorption experiments carried out with a buffer solution on polyethylene surfaces reveal the irreversibility of adsorbed albumin from both the single and the binary mixtures with collagen. When after 20 h of adsorption from the solutions containing albumin only, collagen was added to these solutions or when the samples after that period of time were first rinsed with a buffer and then with a collagen solution, the amounts of albumin remaining at the surfaces were in both cases reduced by one-half.

Introducing a selectively biodegradable filament wound arterial prosthesis: a short-term implantation study

This article introduces a new compliant and selectively biodegradable filament wound vascular graft and reports the findings of a short-term implantation study. A basic feature of filament winding is its ability to tailor and better control the mechanical properties of the prosthesis, so that a closer match with the anisotropic properties of native arteries is achieved. The elastomeric vascular grafts comprise poly(ether urethane urea) fibers (Lycra) embedded in a two-component matrix consisting of poly(ether urethane) (Pellethane) and a highly flexible poly(ethylene glycol)/poly(lactic acid) biodegradable segmented copolymer (PELA). Typical tensile modulus values fall in the few megapascals (MPa) range, this being comparable to that of natural arteries. The wound graft exhibits excellent handling and suturability characteristics as well as enhanced burst strength. Furthermore, due to its biodegradable constituent, the prosthesis combines minimal intraoperative blood loss and high healing porosity. The graft displays initially negligible in vitro water permeation, which increases gradually with time. In this short-term study, the prostheses were implanted in the canine carotid, and their biological performance was compared to that of expanded Gore-Tex. The luminal surface of the wound grafts was coated with a thin layer of pseudointima, strongly adhered to the prosthesis surface. Contrasting with the very stiff Gore-Tex grafts, the filament wound prostheses retained their high compliance, being highly pulsatile upon explanation. Histological studies fully corroborated these findings, underscoring the healing properties of these new filament wound vascular prostheses.

[Model for immunologic testing of biomaterials]

Corrosion products and electric fields are capable of changing proteins to antigens, thus permitting the immunological system to identify the biomaterial as foreign. The reaction between corrosion products and a macro-molecule also leads to an antigen (carrier antigen), such as conformational changes of a macro-molecule, e.g. a protein, caused by the electric field at the implant surface (modified macro-molecule antigen). While the sensitivity to corrosion and the effectiveness of galvanic elements is measurable by electrochemical methods, suitable methods of determining the field strength in the vicinity of biomaterial surfaces are still unavailable. The influence of the double layer of uncoated and coated titanium surfaces on the conformation of proteins and their conversion to antigens are investigated with polyclonal antibodies capable of identifying the unchanged protein despite adsorption to the surface. 14C-marked Bovine Serum Albumin serves as a model protein. Determination of the total number of protein molecules adsorbed is effected via the detection of the emitted electrons. The quotient of the concentration of natural proteins to the concentration of adsorbed molecules gives the biocompatibility index, which is independent of the surface area, and gives an indication of the expected biocompatibility of the material. The results of the biological tests of titanium and two coating materials on titanium were confirmed in an animal experiment. It is possible that in the future immunological tests may replace experiments in animals.

Enhancement of cell growth on growth factor-immobilized polymer film

Insulin, transferrin and collagen were immobilized on the surface of hydrolysed poly(methyl methacrylate) films. Mouse STO fibroblasts were cultured on the protein-immobilized films. Growth factors remained immobilized without detachment and accelerated cell growth in a more potent manner than free or adsorbed growth factors. Immobilized collagen enhanced the flattening of adhered cells in the early stages of cell adhesion, but did not enhance cell growth significantly.

Synthesis and antithrombogenicity of heparinized polyurethanes with intervening spacer chains of various kinds

Heparin was immobilized to polyetherurethaneurea membrane by covalent or ionic bondings with intervening spacer chains having different lengths and different terminal functional groups. The amount of immobilization of heparin and the release rate of immobilized heparin were controlled by the nature and the mode of bonding of spacer chains. The heparinized polyetherurethaneurea membranes became more in vitro antithrombogenic and suppressed more strongly the adhesion and activation of platelets, as the amount of immobilization increased. It was also shown that the membrane to which the low-molecular-weight fraction of heparin was immobilized was less stimulating to platelets.

Adsorption of plasma proteins and platelet adhesion on to polydimethylsiloxane/poly(gamma-benzyl L-glutamate) block copolymer films

A-B-A-type block copolymers of four different compositions were synthesized, in which A and B represent poly(gamma-benzyl L-glutamate) and polydimethylsiloxane segments, respectively. Among the block copolymers and their surface-modified derivatives, those containing 40-70 mol% polydimethylsiloxane and having water contact angles ranging from 50 degrees to 85 degrees were found not to induce conformational change of plasma proteins upon adsorption. It was also observed that the number of adhered platelets and the rate of serotonin release from adhered platelets increased when plasma proteins underwent conformational change upon adsorption. These experimental observations indicate that hydrophobic-hydrophilic block copolymers having a certain composition do not induce conformational change of plasma proteins upon adsorption and do not adhere to and activate platelets, thus leading to a suppression of thrombus formation.

Attachment and proliferation of fibroblast cells on polyetherurethane urea derivatives

Interactions of novel polyetherurethane urea derivatives with fibroblast cells as well as with plasma proteins were investigated. Fibronectin, which is a cell adhesion protein, was found to be very active in attaching fibroblast cells onto a heparinized polyetherurethane urea: its activity was found to be strongly dependent on the surface properties of the material. Fibronectin was easily adsorbed by the heparinized polyetherurethane urea, but the degree of its adsorption to the material in competition with other proteins was so low that cell attachment to polyetherurethane ureas was decreased by heparinization. Different degrees of cell attachment onto different materials due to different adsorptivities of plasma proteins were considered. Proliferation of fibroblast cells was suppressed on cationic polyetherurethane urea but unaffected on other derivatives of polyetherurethane urea. Since specific suppression of cell proliferation was not observed on the heparinized polyetherurethane urea, the latter material was expected to be useful as a long-term antithrombogenic material in vivo.