Understanding the Impact of Surface Modification on Polyurethane Blood Compatibility

The interaction of blood with biomaterials is a critical consideration in biomedical applications, particularly for devices such as vascular grafts. Recent studies have highlighted that the cationization of polyetherurethanes (PEUs) can significantly increase their acute thrombogenic potential, leading to heightened adhesion of platelets and fibrinogen. In contrast, surfaces designed with zwitterionic characteristics—exhibiting both positive and negative charges—demonstrate enhanced thromboresistance. This phenomenon is attributed to how positive ions are embedded within the material while negative ions are preferentially exposed at the surface, creating an environment that is less conducive to clot formation.

Lelah et al. have further explored the interplay of surface charge and blood compatibility, proposing that a synergistic effect arises from the dual charge of zwitterionic PEUs. This synergy enhances protein adsorption, which is crucial for improving biocompatibility. Additionally, factors such as the isoelectric point (pI) of the proteins and the zeta potential of the polyurethane surface must be considered in experimental designs to accurately assess their interactions with blood components.

The discussion of hydrophilicity in relation to blood response gained traction in the 1980s, emphasizing the importance of surface characteristics that promote water absorption. It was found that optimizing the hydrophobic-hydrophilic ratio could significantly reduce platelet adhesion, thereby enhancing blood compatibility. Interestingly, research revealed that slightly hydrophilic cationomer PEUs exhibited greater platelet and fibrinogen uptake than their neutral counterparts, indicating that the relationship between hydrophilicity and blood response is not straightforward.

In the late 1980s, innovative techniques for modifying polyurethanes emerged, aimed at improving their blood compatibility. These included chemical incorporation, grafting, and various coating methods. Extraction processes on polyurethane block copolymers, for example, demonstrated the potential to enhance blood compatibility by significantly lowering ex vivo platelet deposition levels. The effectiveness of these extraction methods lay in their ability to remove low molecular weight components, thereby modifying the surface characteristics of the polyurethanes.

Grasel et al. expanded on this research by examining the effects of extraction using various media, such as methanol, toluene, and acetone, on the blood response of standard polyurethane block copolymers. Their findings reinforced the notion that careful manipulation of the polymer's surface can yield significant improvements in biocompatibility. As the field progresses, understanding the complex interactions between polymer properties and biological responses remains essential for the development of effective biomedical devices.