Physicochemical Studies on Artificial Surface/Protein/Platelet Interactions

Abstract

To highlight the mechanisms of artificial surface/protein/platelet interactions, results obtained by various methods have been integrated to elucidate some of the correlations between phenomena which occur at the macromolecular level and subsequently influence those at the cellular level, such as platelet adhesion. Microcinematographic evidence obtained under the controlled conditions of the Stagnation Point Flow Experiment (SPFE) indicate that, even on glass, platelet adhesion commences only after 30-60 sees of exposure to native blood. This lag period is consistent with diffusion kinetics predicting the arrival of plasma proteins should overhwelmingly precede that of the cellular components. During the lag period, native plasma proteins collide with the artificial surface and, in most cases, adsorb with surface-induced conformational changes. The energy for altering the secondary protein structure is supplied by the heat of adsorption. The extent of adsorption and structural alterations depend upon both the type of protein and the molecular architecture of the artificial surface, viz., the number density and orientation of polar, H-bonding, etc. groups accessible to proteins. Using microparticulate glass (< μ dia.) and a microcalorimeter sensitive to ±0.00001° C in 100 ml of sample volume, serum albumin was found to adsorb, release heat, and desorb in a conformationally altered state. In contrast, γ-(7S)-globulin and fibrinogen underwent irreversible multilayer attachment releasing (1.0-1.7) χ 103 Kcal/mole of protein adsorbed directly to the glass surface. Proteins in the second, etc. sorbed layers released much smaller heats. The electrophoretic mobility of the same particles coated with varying amounts of the same proteins confirmed that the relatively greatest conformational change occurred in the protein layer directly attached to the artificial surface. On homologous Nylons exposed under identical hemodynamic conditions in the SPFE, the surface number density of platelets remaining adherent at points of identical shear was proportionate to the polar force contribution of those surfaces. These results indicate that the protein layer which settles first, is acting as a “proportional transformer” mediating the effects of artificial surfaces onto platelets.

Microcalorimetry of the adsorption of lysozyme onto polymeric substrates

“…Nyilas et al [3,4] and Filisko et al [5] examined the adsorption of blood proteins onto various surfaces and obtained results suggesting that initially adsorbed protein undergoes more conformational change than does a subsequent layer. Using a semi-quantitative approach, Norde and Lyklema [6] resolved the integral adsorption heat into its components for the adsorption of albumin and ribonuclease onto polystyrene.…”

“…Koutsoukos et al [8] measured ads H for the adsorption of albumin on hematite under varying conditions of charge on the protein and the substrate, finding maximal evolution of heat near the isoelectric point of the protein. Several authors [3][4][5][6][7][8][9] have obtained exothermic heats upon adsorption of protein onto like-charged substrate, indicating that Coulomb forces do not necessarily dominate spontaneous adsorption.…”

Structure and Properties of Membrane Surfaces of A-B-A Tri-Block Copolymers Consisting of Poly(γ-methyl D,L-glutamate) as the A Component and Polybutadiene as the B Component

“…In this work, we discuss the preparation, structure, and surface characteristics of A-B-A tri-block copolymers consisting of DL-isomers of poly(ymethyl glutamate) as the A component and polybutadiene as the B component. Conformation studies ofpoly(y-methyl D,L-glutamate) have been made by et al 15 and Nakajima et af.1 6 and show that the helical content in the membranes steadily decreases from 100% to 80% as the fraction of the Dresidue is increased from 0 to 50%. Furthermore, these authors found that the helical content of the right-handed a-helical form for poly(y-methyl D,Lglutamate) in which D-residue is 50% equals the helical content of the left-handed form.…”

“…Poly-a-amino acids have been investigated for various biomedical materials, such as hemodialysis membranes and synthetic vascular prostheses. 2 -4 Block copolymers containing poly-a-amino acid as one component should be excellent biomedical materials, since it has been reported by Lyman et al, S Nyilas et a/., 6 and Okano et al 7 that the microheterophase structure characteristic of the block copolymers plays an important role in blood compatibility. In fact, biomembranes have a microhet-erophase structure composed of both hydrophilic and lipophilic domains.…”

Factors Contributing to the Properties of Fluoropolymer Barrier Films

“…Values were obtained using the graphical method o f Fowkes (30) ancl y ,~ \values from tlie literature (31). For the control 1' I:OMA films, Y ,~, was very close to the y, value, indicating n o polar contril~ution.…”