Exploring the Impact of Additives in Biomedical Polyurethanes

Biomedical polyurethanes (PUs) are increasingly being enhanced with various additives to improve their performance, particularly in applications involving contact with biological systems. Recent studies have highlighted the significant role of additives like Advawax® 240 and ethylene-bis-stearamide in altering the surface properties of these materials, leading to a more hydrocarbon-rich environment. This transformation can enhance compatibility with biological tissues by potentially reducing calcification and material degradation.

Research by Ratner and colleagues demonstrated that the integration of Advawax® 240 into PUs can create surfaces with notable hydrocarbon characteristics. This innovative approach has been further validated by Briggs, who discovered the presence of ethylene-bis-stearamide on the surface of Pellethane™ materials. This specific amide-lubricant is recognized for its balanced internal and external lubricating properties, which can be crucial for optimizing the hemocompatibility of medical devices.

However, the choice of additives is critical, as different blends of Advawax® are commercially available, each with varying effects on material properties. While Ratner and Paynter's work indicated that these hydrocarbon-rich surfaces could lower platelet consumption in vivo, conflicting results emerged from Bandekar and Sawyer’s investigations. Their findings suggested that increased amounts of bis-amide processing wax actually led to heightened platelet activation, emphasizing the complexity of biological interactions with synthetic materials.

The contrasting results from these studies highlight the necessity of careful experimental design in evaluating the hemocompatibility of biomedical materials. For instance, Ratner and Paynter employed in vivo models using arterio-venous shunts in baboons, which generally yield more applicable insights than in vitro methods used by Bandekar and Sawyer. This raises important questions about the reliability of different testing approaches in predicting the biological responses to polymer additives.

Additionally, the role of external lubricants, as explored by Hari and Sharma, further complicates the narrative around protein adsorption on PU surfaces. Their work showed that certain lubricants can encourage the adsorption of fibrinogen while discouraging albumin adhesion, suggesting a potential pathway for enhancing blood compatibility in synthetic materials. This information is pivotal as it indicates that selective surface modifications can lead to improved interactions between biomedical devices and biological fluids.

Lastly, the use of plasticizers in PUs cannot be overlooked. These additives are crucial for enhancing flexibility but can also pose challenges due to their tendency to leach from the polymer matrix. This aspect is particularly concerning in applications like tubing for transporting hydrophobic fluids, where the loss of plasticizer can compromise material performance over time. Understanding these dynamics is essential for the continued development of effective biomedical polyurethanes.