Surface molecular mobility and platelet reactivity of segmented poly(etherurethaneureas) with hydrophilic and hydrophobic soft segment components

Khang

et al. 1998

J. Biomed. Mater. Res.

100

Functional group gradients were prepared on low-density polyethylene (PE) sheets. The surface density of grafted functional groups was gradually changed along the sample length by way of corona discharge treatment with gradually increasing power following graft copolymerization of acrylic acid (AA), sodium p-styrene sulfonate (NaSS), or N,N-dimethyl aminopropyl acrylamide (DMAPAA). AA and NaSS are negatively chargeable and DMAPAA is positively chargeable in phosphate-buffered saline or plasma solution at pH 7.3-7.4. The prepared functional group gradient surfaces were characterized by measurement of the water contact angle, by electron spectroscopy for chemical analysis, and by Fourier transform infrared spectroscopy in the attenuated total reflectance mode. All these measurements indicated that the functional groups were grafted onto the PE surfaces with gradually increasing density. The platelets adhered to the functional group gradient surfaces along the sample length were counted and observed by scanning electron microscopy. It was observed that the platelet adhesion to the gradient surfaces decreased gradually with the increasing surface density of functional groups. This may be related to the hydrophilicity of the surfaces. The DMAPAA-grafted surface showed a large amount of platelet adhesion, probably due to its positive charge character, while the AA-grafted surface, which is charged negatively, showed poor platelet adhesion. However, the NaSS-grafted surface, which is also charged negatively, showed a relatively large amount of platelet adhesion. This may be associated with the existence of an aromatic ring close to the ionizable group in NaSS. It seems that surface functional groups and their charge character, as well as wettability, play important roles for platelet adhesion.

Section: Interaction Of Platelets With the Gradient Surfacesmentioning

confidence: 94%

Platelet adhesion onto chargeable functional group gradient surfaces

Khang

et al. 1998

J. Biomed. Mater. Res.

100

“…The fact that platelets in the presence of plasma proteins are more adhered to the hydrophobic surfaces than hydrophilic ones also was observed by other research groups. 30,31 To see the effect of plasma proteins on platelet adhesion behavior, PPP, which contains more than 200 kinds of different plasma proteins, 32 was adsorbed onto the wettability gradient PE surfaces for 1 h at 37°C. The plasma protein-adsorbed gradient surface was analyzed by ESCA.…”

Section: Platelet Adhesion and Plasma Protein Adsorption On The Gradimentioning

confidence: 99%

Platelet adhesion onto wettability gradient surfaces in the absence and presence of plasma proteins

1998

J. Biomed. Mater. Res.

156

A wettability gradient was prepared on lowdensity polyethylene (PE) sheets by treating them in air with a corona from a knife-type electrode the power of which increased gradually along the sample length. The PE surfaces oxidized gradually with the increasing corona power and a wettability gradient was created on the surfaces, as evidenced by the measurement of water contact angles, Fourier transform infrared spectroscopy in the attenuated total reflectance mode, and electron spectroscopy for chemical analysis. The wettability gradient surfaces prepared were used to investigate the adhesion behavior of platelets in the absence and presence of plasma proteins in terms of the surface hydrophilicity/hydrophobicity of polymeric materials. The platelets adhered to the wettability gradient surfaces along the sample length were counted and examined by scanning electron microscopy (SEM). It was observed that the platelet adhesion in the absence of plasma proteins increased gradually as the surface wettability increased along the sample length. The platelets adhered to the hydrophilic positions of the gradient surface also were more activated (possessed more pseudo pods as examined by SEM) than on the more hydrophobic ones. However, platelet adhesion in the presence of plasma proteins decreased gradually with the increasing surface wettability; the platelets adhered to the surface also were more activated on the hydrophobic positions of the gradient surface. This result is closely related to plasma protein adsorption on the surface. Plasma protein adsorption on the wettability gradient surface increased with the increasing surface wettability. More plasma protein adsorption on the hydrophilic positions of the gradient surface caused less platelet adhesion, probably due to platelet adhesion inhibiting proteins, such as high-molecular-weight kininogen, which preferably adsorbs onto the surface by the so-called Vroman effect. It seems that both the presence of plasma proteins and surface wettability play important roles for platelet adhesion and activation.

“…Since nitrogen is only present in the hard segment, the ratio of N ls to C ls corresponds to the relative surface concentration of hard segments [17]. Only one of the treated elastomer specimens did not have its N/C ratio increased (Tables IV-VI).…”

Section: Correlation Of Elemental Property Changes With Structural Dementioning

confidence: 99%

Structural degradation of polyurethane-based elastomeric modules

Stevenson

Kusy

1995

J Mater Sci: Mater Med

Degradative characteristics were studied using specimens of three polyurethane-based elastomeric modules that were treated in solutions of varying acidity, oxygen content and temperature. After periods of 10 and 100 days, molecular weight distribution changes, mechanical property changes and elemental chemistry changes were studied using gel permeation chromatography (GPC), stress-relaxation testing and X-ray photoelectron spectroscopy (XPS), respectively. As determined through analyses of the molecular, mechanical, and elemental changes after treatment, the degradative mechanism was influenced by whether the polyurethane was polyester-based or polyether-based, and the degree of structural degradation was influenced by the type and duration of conditioning treatment. Degradation of the polyester-based materials after treatment was dominated by a chain scission mechanism; conversely, the degradation of the polyether-based material was dominated by a crosslinking mechanism. Among the conditioning treatments, the combined effects of an increase in acidity, oxygen content and temperature most influenced the degree of degradation with time, with the increase in temperature having the greatest effect of any of the single variables investigated.