The role of carbohydrate in platelet adhesion to foreign surfaces

Sung Wan Kim - Early events in blood/material interactions

Sung Wan Kim's initial efforts as an independent investigator were focused on improving the understanding of the early events in blood/material interactions with the goal to develop blood compatible materials for application in medical devices and prostheses. These initial efforts were centered around blood protein adsorption on biomaterials and related mechanisms of thrombus formation (thrombosis). Ultimately, Sung Wan's efforts were expanded to studies of the non-thrombogenic nature of heparinized biomaterials, prostaglandin biomaterials, and block copolymer systems. These studies were supported by two NIH grants for 22 and 19 years, respectively, and a NIH Career Development Award. Moreover, these studies resulted in over 140 peer-reviewed publications and training of many students and postdoctoral scientists. The intent of this paper is to identify key concepts, papers, and contributions by Sung Wan and his colleagues that fall within the four aforementioned research categories. In this context, many of Sung Wan's early efforts contributed directly to Utah's biomaterials efforts and the Total Artificial Heart program at the time, while providing the foundation for the productive international Triangle Collaboration as well as his following work in polymer-controlled drug releasing systems.

Elastin as a nonthrombogenic biomaterial

Surface-induced thrombosis is a significant issue for artificial blood-contacting materials used in the treatment of cardiovascular diseases. The development of biomaterials and tissue-engineered constructs that mimic the vasculature represents a way to overcome this problem. Elastin is an extracellular matrix macromolecule that imparts arterial elasticity where it comprises up to 50% of the nonhydrated mass of the vessel. In addition to its critical role in maintaining vessel integrity and elastic properties under pulsatile flow, elastin plays an important role in signaling and regulating luminal endothelial cells and smooth muscle cells in the arterial wall. Despite its well-established significance in the vasculature and its growing use as a biomaterial in tissue engineering, the hemocompatibility of elastin is often overlooked. Past studies pointing to the potential of arterial elastin and decellularized elastin as nonthrombogenic materials have begun to be realized, with elastin scaffolds and coatings displaying increased hemocomptibility. This review explores the mechanisms of elastin's nonthrombogenicity and highlights the current problems limiting its wider application as a biomaterial. We discuss the benefits of constructing biomaterials encompassing the relevant mechanical and biological features of elastin to provide enhanced hemocompatibility to biomaterials.

Quantitative analysis of protein adsorption on a planar surface by Fourier transform infrared spectroscopy: lysozyme adsorbed on hydrophobic silicon-containing polymer

The adsorption of hen egg white lysozyme onto a solid polytris(trimethylsiloxy)silylstyrene (pTSS) surface from a D(2)O solution at pD 7 containing 100 mM NaCl and 10 mM sodium deuterated phosphate was monitored at 25 degrees C by Fourier transform infrared spectroscopy using the attenuated total reflection (ATR) method. The infrared spectrum attributed to only the adsorbed lysozyme was derived from the observed spectrum, and the amount of adsorbed lysozyme was determined as a function of time and lysozyme concentration. The kinetics of adsorption could be decomposed into two components, one of which was a process with a time constant of larger than 4 h(-1) and the other was a process with one of about 0.1 h(-1). These spectra showed that the lysozyme adsorbed in the faster process had a higher beta-structure content than the dissolved lysozyme. It was also found that the slower adsorption induced some conformational change in the lysozyme adsorbed in the faster process and/or that adsorbed in the slower process. After adsorption for 24 h, the pTSS surface was rinsed out with lysozyme-free solution. The resultant spectra of the surface indicated that the lysozyme adsorbed in the faster process was bound irreversibly on the surface and was changed to a conformer with a higher beta-structure content during the slower process. The experimental procedures and the theoretical applications for such a quantitative analysis in the ATR spectroscopic method are presented in detail.

Protein adsorption on low temperature isotropic carbon: V. How is it related to its blood compatibility?

Based on our research on blood protein interactions with low temperature isotropic carbon (LTIC) and data from the literature, we propose that the carbon surface has strong interactions with adsorbed proteins. In this paper we focus on how a relatively blood-compatible material interacts with plasma proteins. We present our results on the structure and properties of the LTIC surface utilizing SEM, STM, XPS, and contact angle measurements. We briefly review protein adsorption on LTIC using DSC, impedance, radioisotopes, and two-dimensional gel electrophoresis. LTIC is characterized by a microporous, oxidized, hydrophobic, and domain mosaic structure. Surface polishing smoothens the roughness and removes the porosity, while largely destroying the ordered atomic texture, making the surface more random and more amorphous. The LTIC surface denatures all adsorbed proteins studied. The rate of protein adsorption is high and the surface concentration is large. The LTIC surface adsorbs all proteins without preference. The surface also tenaciously retains proteins such that they cannot be displaced by buffer or exchanged by proteins in solution. We conclude that LTIC accomplishes its blood compatibility through a passivating film of strongly adsorbed bland proteins, which do not interact with platelets nor participate in blood coagulation. We also suggest mechanisms for the production of such a film by the LTIC surface.

Haemocompatibility of invasive sensors

In recent years the importance and utilisation of invasive chemical sensors have increased, especially in respect to their function and behaviour in a biological environment. This review aims to highlight the development of various sensors and reflect on the problems which can occur when the sensors come into contact with blood. Thus their haemocompatibility is a key area of importance. A clear understanding of their interaction with plasma proteins at the point of interface is fundamental as this determines their ultimate capability to function safely and effectively. There is also an overview of various techniques that have been developed, together with a broad summary of inherent problems which may arise when aiming to improve the haemocompatibility of invasive sensors for in vivo applications.

Antithrombogenic heparin-bound polyurethanes

Many kinds of heparin-bound polyurethanes have been developed. Polyurethanes are a family of elastomers displaying better blood-compatibility than other polymeric materials. It is useful to modify this material by heparinization. Several approaches to heparinization have been devised: 1) a general method of heparinization, applicable to all polymeric materials, 2) a heparinization method specific to polyurethanes, and 3) the design of heparinizable polyurethane derivatives. These three approaches are first explained in detail. Then, the antithrombogenic mechanism of the heparinized polymers is discussed. Finally, the interactions of the heparinized polymers with blood coagulation factors, plasma proteins, and platelets are discussed.

Platelet adhesion and prevention at blood-polymer interface

It has been proposed that adsorbed glycoproteins such as fibrinogen and gamma-globulin induce platelet adhesion at blood-polymer interfaces. The importance of oligosaccharide groups in the glycoproteins proved to be responsible for platelet adhesion and aggregation via possible complex formation. Several studies have provided evidence that the proposed mechanism was involved in platelet adhesion on polymer surfaces. To minimize or prevent platelet adhesion on polymers, prostaglandins (PGs), potent inhibitors of platelet aggregation and PG-heparin (HEP) conjugate, were combined with polymers via physical dispersion or chemical immobilization on the surfaces. Albumin-HEP conjugate-adsorbed surfaces also showed significant reduction of platelet adhesion.

Synthesis and antithrombogenicity of anionic polyurethanes and heparin-bound polyurethanes

Two kinds of novel antithrombogenic polyurethane materials were synthesized. One of them is a polyetherurethane with anionic charges on the film surface, and the other is a polyetherurethaneurea to which heparin was covalently bound. The mechanism of their antithrombogenicity was investigated. The anionic polyetherurethane selectively adsorbed albumin, did not cause a conformational change of plasma proteins adsorbed, and suppressed the adherence and deformation of platelets but did not deactivate the blood-clotting system, thus leading to a moderate antithrombogenicity. The heparin-bound polyetherurethaneurea was not favorable for the selective adsorption of albumin, caused the denaturation of plasma proteins adsorbed, and induced the adherence and deformation of platelets but deactivated the blood-clotting system, leading to excellent antithrombogenicity. For the investigation of blood-material interaction, the importance of a multiparameter estimation of the activation of platelets and the blood-clotting system was indicated.

Interaction of polystyrene/poly(gamma-benzyl L-glutamate) and poly(methyl methacrylate)/poly(gamma-benzyl L-glutamate) block copolymers with plasma proteins and platelets

A-B-type block copolymers, consisting of polystyrene (PST) or poly(methyl methacrylate) (PMMA) forming segment (A) and poly(gamma-benzyl L-glutamate) (P[Glu(OBzl)]) segment (B), were synthesized and the thrombus formation on these block copolymer films was investigated in relation to the adsorption of plasma proteins and the activation of platelets. The relative amount of thrombus formation was higher on homopolymers than on block copolymers. The amount of thrombus formation became less, with decreasing content of P[Glu(OBzl)] in the PST block copolymers and with increasing content of P[Glu(OBzl)] in the PMMA block copolymers. Adsorption of bovine serum albumin(BSA), bovine gamma-globulin (B gamma G) and bovine plasma fibrinogen(BPF) onto polymer films was also investigated. More proteins were adsorbed and denatured when adsorbed onto PST and PMMA than onto block copolymers. With increasing content of P[Glu(OBzl)] in the PST block copolymers, the degree of denaturation of adsorbed proteins increased, while the amount of protein adsorption was unaffected. Conversely, with increasing content of P[Glu(OBzl)] in the PMMA block copolymers, the degree of denaturation of adsorbed proteins decreased, while similarly the amount of protein adsorption was unaffected. Adhesion of platelets from platelet suspension (WP) to polymer films coated with one of the plasma proteins showed that the activation of adhered platelets was suppressed when there was a lower degree of denaturation of coated proteins. In the same experiments using platelet-rich plasma(PRP), neither the number of platelets adhered nor the degree of activation of the adhered platelets was correlated with the composition of the polymer films.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Platelet adhesion onto microcapsule membranes with different degrees of sulfonation

Microcapsules having different numbers of sulfonic acid groups on their surfaces were prepared by the interfacial polycondensation method. Platelets adhered to these capsules, and the rate and degree of platelet adhesion were found to be remarkable on those microcapsules that had high surface charge compared to those with low surface charge. This trend was strengthened by the coating of the capsules with plasma, while the electrophoretic mobilities of the plasma-coated capsules showed a considerable reduction and no appreciable difference between the respective mobilities could be observed. This trend suggest that the adsorption of plasma components on microcapsules, and not their surface negative charge, affected platelet adhesiveness directly. In connection with the glycosyl transferase hypothesis, the adsorption pattern and its effect on platelet adhesion of albumin, gamma-globulin, and fibrinogen were examined. The protein adsorption pattern varied depending on both the type of protein and the magnitude of negative charge on the microcapsule surface, but its effect on platelet adhesion was not fully consistent with the glycosyl transferase hypothesis. It was concluded from the findings that the surface negative charge of the capsules strongly affected the composition, molecular orientation, and/or configuration of the adsorbed plasma components, which probably induced the differences in platelet adhesiveness depending on the magnitude of surface negative charge of the microcapsules.

The influence of heparinized polymers on the retention of platelets aggregability during storage

The change in aggregability of the platelets stored in the storage tube fabricated from a newly developed heparinized hydrophilic polymer (H-RSD) has been studied in comparison with plasticized poly(vinyl chloride) (PVC) which is widely used for blood bags. Rabbit blood was directly withdrawn into the storage tube containing an anticoagulant from the carotid. Then the tube was mechanically sealed with screw cocks and centrifugated to prepare platelet-rich plasma (PRP) in the tube and again mechanically clamped to separate the PRP from the residual precipitate. The PRP was stored in situ in the storage tube at room temperature under agitation. During storage, the change in the aggregability of the PRP induced by adenosine diphosphate (ADP) was studied and the morphological change in the platelets adhered onto the inner surface of the storage tube was observed by scanning electron microscopy. In the H-RSD tube, the aggregability was maintained during two-day storage, while in the PVC tube, the aggregability was completely lost after one-day storage. The scanning electron microscopic studies demonstrated that the reduction in the aggregability of the stored platelets is closely correlated with the morphological deformation of the platelets adhered onto the surface of the storage tube.

Role of protein and fatty acid adsorption on platelet adhesion and aggregation at the blood-polymer interface

Thrombus formation on a foreign surface is a complicated process, involving many factors. However, there is little doubt that a foreign surface adsorbs plasma proteins upon blood contact and that the nature of this adsorbed layer may determine the mechanism of platelet adhesion and aggregation. The adhesion and aggregation of platelets play an important role in the initial events of thrombus formation on a foreign surface. In this work, adsorption studies using human blood plasma were done on several polymer surfaces. Some drugs which prevent platelet adhesion were utilized to verify the proposed mechanism for platelet adhesion which includes glycosyl transferase reaction. Also, adsorption and release of fatty acid salts, including fatty acid-bonded albumin, were investigated at different polymer interfaces. It is postulated that adsorbed fatty acid salts are released from the surface upon contact with plasma to form a high local concentration of fatty acid, and that this fatty acid suspension would cause platelet aggregation at the interface.