Special topics: medical uses of polyurethane
The medical uses of polyurethanes (PU) are in many ways similar to more prosaic applications of foams, elastomers, coatings, and adhesives and in certain ways very distinctive. Virtually, every patent or academic publication on a medical application states that the material attributes of PU as a class make them ideal for medical use. Among the required PU properties valued for these applications are fatigue resistance, abrasion resistance, ability to design for biodegradability or chemical resistance, biocompatibility, wettability by bodily fluids, and ability to be fabricated into useful shapes [1,2]. However, medical uses of PU are also substantially more complex than other uses due to the numerous ways an organism has of rejecting a foreign body and the extreme wear potential in many uses. PU can be susceptible to the numerous ways immune systems attack such as by hydrolysis, oxidation, and various enzymatically driven chain scission processes . In addition, an immune system may simply colonize and coat a foreign object creating a source of thrombus (blood clots), sclerosis due to calcification, infection due to opportunistic growth, and occlusion of annular prostheses [4-6]. The criticality of performance creates a market for specialty monomers that would otherwise be too small volume and, by extension, too expensive to be commercially viable.
MARKETS AND PARTICIPANTS
The size of the medical PU market is very small by the standards of the PU industry. Accurate segmentation is difficult due to myriad small and specialty uses, but the analysis of available estimates is that 2012 global volumes were approximately 35
FIGURE 11.1 Patent activity from 1990 to 2014 of various industrial polyurethane producers and producers of biomedical products. Except for Bayer, which has a large life sciences businesses, PU manufacturers do not participate meaningfully in this market. 2700 total patents filed worldwide and 680 filed patents by participants in Figure 11.1.
million pounds of PU building blocks sold for medical applications. However, not including items such as mattress covers, protective gloves, and condoms, the high-performance medical market is closer to 10 million pounds with a compound annual growth rate of approximately 5% [7-9]. Volumes are split between North America, Europe, and Asia . It is reasonable to expect that medical PU will find increasing use in the Asia-Pacific region .
Because of stringent performance and regulatory requirements for medical applications and attendant risks for performance failures, the value of PU in the medical segment is approximately 100 million dollars . The majority of applications for which urethanes find medical use are associated with the requirements of an aging population (i.e., pacemakers, catheters, valves, etc.) . Furthermore, the amount of innovation required to meet medical requirements, and developed in anticipation of future requirements, is astonishing. An analysis of corporate activity shows that with the exception of Bayer (which has a very sizable life sciences business), the large multinational PU manufacturers of PU components are not participating in the medical market. Instead, innovation is primarily an activity of medical device makers and, to a limited extent, universities and national laboratories (Fig. 11.1). Almost all of this activity has occurred since 1990.
The flexibility to make nearly any functional material with PU chemistry is represented by the breadth of applications that have been patented. Segmentation of PU applications according to function is shown in Figure 11.2. It shows patent activity in virtually every medical device application. The intensity of coating innovation for medical devices in many cases reflects innovation for coating a thermoplastic polyurethane (TPU) rather than a specific PU coating [14, 15].
The activity of individual companies reflects the need for corporate competitive advantage and defense against other market participants. The similarities and distinctions
FIGURE 11.2 Distribution of patents from 1990 to 2014 filed on biomedical uses of polyurethane by technology. 2700 patents represented in the distribution.
between companies actively innovating are interesting and instructive. For instance, Medtronic is a manufacturer of numerous implantable technologies such as heart pacemakers, stents, catheters, and other surgically important products. Figure 11.3 documents the proportional areas of Medtronic Inc. PU-related patent activity by technology segment for the years 1990-2014 and the numerical activity by year. Figure 11.4 is a similar analysis for activity by Bayer AG. As mentioned previously, much of the coating innovation is related to non-PU coatings applied to a PU surgical product for a specific function. The same is true for adhesive activity. Many of the patents represent innovations improving adhesion of PU to another specific substrate or to specific biological cells [16, 17]. An interesting phenomenon in the analysis is the increasing interest in medical PU intellectual assets until the years 2009-2010 after which there was a pronounced decrease in activity. The causes for this may originate in economic or public policy concerns but are not mirrored in patent activity filed in the Chinese language on medical PU (Fig. 11.5).