Approximately 3 million pounds of PU are consumed per year in the making of catheters [18,19]. A catheter is a hollow tube inserted into the body for any number of procedures. They include removal of fluids such as urine or draining of fluids resulting from infection such as those that would be encountered from an internal abscess. Additionally, they are used for remote positioning of cardiac stents or balloon angioplasty. In addition, they can be critical components of other cardiac
FIGURE 11.3 Patent activity for Medtronic Corporation for the years 2000-2014: (a) by technology segment and (b) by year. 59 patents filed during this time.
procedures including ablative procedures and electrophysiology testing. Many materials have been employed for catheter construction including polyvinyl chloride, polyethylene, silicones, perfluorinated polyethylene, and nylons. PU are among the preferred materials due to their flexibility, ability to engineer to the correct stiffness without kinking in use, ease of processing to appropriate form, low
FIGURE 11.4 Patent activity for Bayer AG for the years 2000-2014: (a) by technology segment and (b) by year. 92 patents filed during this time.
coefficient of friction when wet with water, and relatively low susceptibility to bacterial colonization. The reduced susceptibility to bacterial complication is particularly important since infection is one of the most prevalent complications associated with cardiovascular procedures [20, 21]. It has been cited that between 30 and 40% of infusion therapy-related infections are complications associated with catheters beginning as local infections and potentially progressing to systemic. In this regard, it has also been reported that PU has one of the lowest susceptibilities to staphylococcus infection, possibly due to low surface adhesion energies [22, 23].
FIGURE 11.5 Number of patents filed in the Chinese language from 1990 to 2013. Total number=317.
Coatings for catheter tips with biocides for the purpose of reducing the risk of infection are a common area of patent activity [24, 25].
With the significant demands placed on a material for catheter application, it is perhaps surprising that TPUs utilized for catheters are relatively mundane. It is common for patents to specify the brand name and grade without mention of composition. In fact, it is common in medical literature and patents for the authors to simply cite "a urethane" or "PU" catheter available from a specific manufacturer. Typical medical grades of TPU are simple, and examples of their formulation are given in Table 11.1. The preference of polyether polyols over polyester polyols for catheter applications is associated with their superior low-temperature flexibility and their superior resistance to hydrolysis . The simplicity of polymer design creates robustness and reliability and performance. It also makes for a predictable and reproducible substrate for subsequent surface treatments improving specific catheter functions and antibiotic performance .