Effects of flow rate and solution concentration on in situ protein adsorption behavior

Exposure of plasma proteins on Dacron and ePTFE vascular graft material in a perfusion model

OBJECTIVES

to compare the exposure of plasma proteins adsorbed onto three vascular graft materials (polytetrafluoroethylene ePTFE and two modifications of polyethyleneterephthalate Dacron).

METHODS

surface exposure of fibronectin, vitronectin, thrombospondin, antithrombin III, IgG, high molecular-weight kininogen, fibrinogen, albumin and plasminogen was studied by incubation with radiolabelled antibodies in a perfusion model. Perfusion times with human plasma were 1, 4, 24 and 48 hours.

RESULTS

all proteins could be detected at 1, 4, 24 and 48 hours after the start of perfusion. Overall, the least amount of proteins adsorbed onto ePTFE.

CONCLUSIONS

the low adsorption of proteins onto ePTFE may be one of the reasons for the lower incidence of infections reported with this material.

Protein depositions on one hydrocephalus shunt and on fifteen temporary ventricular catheters

Biomaterials are commonly used in modern medicine. Proteins are adsorbed to the surface of the biomaterial immediately after insertion. This report demonstrates the presence of adsorbed proteins in one infected cerebrospinal shunt from a child with hydrocephalus and on fifteen temporary ventricular catheters from adult patients with spontaneous or traumatic brain injuries. Depositions of vitronectin, fibrinogen and thrombospondin-fibronectin to some extent--on the shunt surface was imaged by field-emission scanning electron microscopy. Vitronectin, fibronectin, fibrinogen, and thrombospondin on the ventricular catheters were shown with radio-actively labelled antibodies. Furthermore, protein adsorption from human cerebrospinal fluid to heparinized and unheparinized polymers was studied under flowing conditions in vitro. On heparinized polymer, significantly reduced levels of vitronectin, fibronectin, and thrombospondin were exposed, as measured after 4 hours in vitro perfusion. After 24 hours perfusion, the differences in protein exposition between heparinized and unheparinized polymers were substantially reduced.

Biocompatibility issues in hemodialysis

Hemodialysis, as a life-saving treatment modality for uremic patients, implies a repeated and compulsory contact of blood with foreign materials. As a consequence, biocompatibility problems are unavoidable. The same applies for the material used for the creation of vascular access, and for the alternative dialysis method, CAPD (continuous ambulatory peritoneal dialysis), although each system might cause its own and specific problems. Although in early dialysis the focus has been on maintenance of life and elimination of toxins, later on the important morbid implications of this lack of biocompatibility have been recognized. Eight major problems will be discussed, especially in the perspective of recent new findings in this field: (1) coagulation and clotting; (2) complement and leukocyte activation; (3) susceptibility to infection; (4) leaching or spallation; (5) surface alterations of solid materials; (6) allergic reactions; (7) shear; (8) transfer of compounds from contaminated dialysate. After description of the major biochemical and clinical implications of these problems, ways to prevent morbid events and future perspectives will be described.

Amount and surface structure of albumin adsorbed to solid substrata with different wettabilities in a parallel plate flow cell

In this article we studied the adsorption of serum albumin to substrata with a broad range of wettabilities from solutions with protein concentrations between 0.03 and 3.00 mg.mL-1 in a parallel-plate flow cell. Wall shear rates were varied between 20 and 2000 s-1. The amount of albumin adsorbed in a stationary state was always highest on PTFE, the most hydrophobic material employed and decreased with increasing wettability of the substrata. Increasing stationary amounts of adsorbed albumin were observed with increasing wall shear rates at the lowest protein concentration. Inverse observations were made at the highest protein concentration. Transmission electron micrographs of replicas from the albumin-coated substrata showed that proteins were mostly adsorbed in islandlike structures on the hydrophobic substrata. The tendency to form islandlike structures was shear rate- and concentration-dependent and disappeared gradually going to more hydrophilic substrata. On glass, the most hydrophilic material employed, a homogeneous, well distributed, fine knotted, reticulated structure was found. In conclusion, this study demonstrates that both the amount of adsorbed albumin as well as the surface structure of the adsorbed proteins are regulated by the substratum wettability. This observation may well account for the fact that substratum properties can be transferred by an adsorbed protein film to the interface with adhering cells or microorganisms.

Topographic and dynamic radioisotopic investigations of interactions between biomaterials and blood components

Functional investigations using radionuclides to study protein adsorption and platelet adhesion onto biomaterials are described. The authors' novel methods use radiotracers with a dynamic technique. This allows direct observation of the interaction between blood, or simpler biological substances, and artificial materials. Several radiotracers were used in this study, including 111In-platelets, 123I-fibrinogen, 123I-antithrombin III, and 99mTc-tagged red blood cells. The detectors employed were a semiconductor diode or gamma-camera equipped with special collimators. The acquisition and treatment of data were performed with an original device. These methods allowed precise comparisons, especially between platelet adhesion upon different materials in the form of tubes and also protein adsorption and desorption. The results are discussed in terms of materials to be used for work in vivo.

Adsorption of plasma proteins to the derivatives of polyetherurethaneurea carrying tertiary amino groups in the side chains

Polyetherurethaneureas carrying tertiary amino groups in the side chains were synthesized, quaternized, and heparinized. The adsorption of plasma proteins to the polyurethane derivatives was investigated using Fourier-transform infrared, surface fluorescence, ultraviolet, and circular dichroism spectroscopy. Bovine gamma-globulin and bovine plasma fibrinogen were easily adsorbed to hydrophobic polyurethanes and denatured. It was found that the beta structure was generated during the irreversible conformational change of the proteins on adsorption to hydrophobic polyurethane materials. On the other hand, bovine serum albumin was easily adsorbed to hydrophilic quaternized and heparinized polyurethanes without a serious conformational change. The conclusion was drawn that a polymer material that selectively adsorbs bovine serum albumin in a native state could be antithrombogenic.

Adsorption of plasma proteins to the derivatives of polyaminoetherurethaneurea: the effect of hydrogen-bonding property of the material surface

Polyaminoetherurethaneureas bearing tertiary amino groups in the main chain (M-PAEUU) were synthesized, quaternized (Q-M-PAEUU) and heparinized (H-M-PAEUU). With increasing portions of diisocyanate and with decreasing portions of polyaminoether in the feed, M-PAEUU containing more hydrogen-bonded urea carbonyl groups was prepared. With increasing hydrogen-bonding character of M-PAEUU, the adsorbed bovine serum albumin (BSA) was more denatured. By quaternization of M-PAEUU, the protein adsorption increased, but the denaturation of adsorbed proteins was suppressed. With increasing ratio of hydrogen-bonded urea carbonyl groups in Q-M-PAEUU, the adsorptions of BSA, bovine serum gamma-globulin (B gamma G), and bovine plasma fibrinogen (BPF) were decreased, but the degree of denaturation of adsorbed proteins was increased. In the adsorption to H-M-PAEUU, both the amount and the degree of denaturation of adsorbed proteins were strongly decreased. The dynamic adsorption experiments of plasma proteins showed the behaviors which are similar to the equilibrium adsorption experiments. The decrease of hydrogen-bonded urea linkages and the increase of hydrophilicity by quaternization and heparinization of the polymer surface may be favorable for building up a hydration layer on the surface, thus suppressing the denaturation of plasma proteins which may trigger blood clotting and thrombus formation.

FTIR-ATR studies of the effect of shear rate upon albumin adsorption onto polyurethaneurea

The effect of wall shear rate upon albumin adsorption onto a polyurethaneurea, Biomer, was studied using FTIR-ATR spectroscopy. In these experiments, nondiffusion controlled adsorption was observed from 10 mg/ml solutions at known wall shear rates. Results show that increasing wall shear rate during adsorption does not significantly affect the adsorption kinetics, but does decrease the rate of protein desorption. These results suggest that albumin adsorbed at higher shear rates is more tightly bound to the surface. Comparison of the data to simple mathematical models suggests that more than one layer of protein adsorbs in 2 h.

Evaluation of in vivo adsorption of blood elements onto hydrogel-coated silicone rubber by scanning electron microscopy and fourier transform infrared spectroscopy

Three hydrogel formulations consisting of 2-hydroxyethyl methacrylate (HEMA) copolymerized with N-vinyl pyrrolidone (NVP) were incorporated into silicone rubber by irradiation-induced polymerization. These coatings were chosen to represent different degrees of hydrophilicity, and they changed the hydrophobic character of the silicone rubber surface to that of hydrophilic. These composite materials and the silicone rubber comparison material were used as femoral artery-to-vein (A-V) shunts and were removed at 15 min, an approximate time representative of an initial buildup stage of blood elements on test surfaces. Data obtained by scanning electron microscopy (SEM) were used to determine the type and amount of adhering blood cells and fibrin at the time interval described. One-half of each specimen was used for Fourier Transform Infrared (FT-IR) analysis to provide a direct comparison of the relative amounts of protein present on the silicone rubber and the three hydrogel composite samples. The combined SEM and FT-IR analyses were performed on A-V samples from three dogs. Differences in the response of blood to the surfaces were found by the combined SEM and FT-IR analyses. The more hydrophilic a hydrogel grafted surface, the less fibrin and cellular elements were seen deposited on it. This is not interpreted as an indication of less reactivity, but is more likely due to thrombus buildup and a degree of subsequent embolization (a tearing of sections of the platelet matting away from a surface, revealing an area that again can be covered.

Characterization of protein adsorption on soft contact lenses. I. Conformational changes of adsorbed human serum albumin

Adsorption of human serum albumin on three different soft contact lens surfaces (lathe cut and spin cast crosslinked PHEMA and spin cast PHEMA/MAA) was studied. Using ATR--FTIR spectroscopy the spectra of the adsorbed protein were obtained at different times of adsorption. Structural changes were detected, initially characterized by an increase in hydrogen bonding and after that by involvement of the protein hydrophobic side chain residues. At long adsorption times, the protein becomes denatured, its alpha-helix content is drastically reduced and the amounts of random coil and beta-sheet conformations are increased. ATR-FTIR and circular dichroism studies of albumin solutions reveal similar conformational changes to those experienced by the adsorbed protein. Differences in the adsorption behaviour for the hydrogel surface, indicate the importance of the hydrophilicity, surface regularity and the chemical composition of the contact lens surfaces as the controlling parameters in the protein adsorption phenomena.

Surface analysis of biomedical polymers by attenuated total reflectance-fourier transform infra-red

An infra- red approach has been developed to characterize hydrophilic biomaterials, particularly contact lenses. Water was utilized as the optical coupling agent between the sample and the ATR element. This method enables the study of hydrophilic polymers in their natural aqueous environment and simultaneously solves the optical contact problem that usually arises when the ATR technique is used. Some studies were made utilizing this approach: dry and hydrated samples were structurally compared; also, a depth profiling study and a surface comparison were made on soft contact lenses fabricated by different industrial processes. Finally, the three dimensional orientation of one hydrated structure was characterized.

Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRAS) of fibrinogen adsorbed on metal and metal oxide surfaces

We have investigated the possibilities of using Infrared Reflection Absorption Spectroscopy in the study of the interaction of proteins with metal surfaces. Structural information can be obtained since the infrared radiation at the metal surface interacts only with dipole transition moments perpendicular to the metal surface. Fibrinogen spontaneously adsorbed from solution onto gold, titanium and aluminum was used as model systems. The infrared studies were carried out on dried protein films. The amide I bands of fibrinogen adsorbed on the metal surfaces shift towards higher frequencies (ca. 20 cm-1) relative to the same band in buffer solution. The magnitude of these shifts indicates that conformational change of the protein occurs upon adsorption on metal surfaces. The change in conformation of the fibrinogen also can partly be due to one week of drying at room temperature. The amide I and amide II bands show a slightly different behaviour in terms of frequency and intensity for each metal-protein system studied. The side chains appeared to be more substrate sensitive than the peptide group. Orientational effects were observed for a number of side-chain related groups.