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Plastics can include antimicrobial properties for use in medical devices—including this HyGentic PA from BASF (photo courtesy of BASF).
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The custom-made orsthesis worn by racing cyclist Michael Teuber was made from polyamide by a laser sintering additive manufacturing method using CAD data (photo courtesy of Ortema).
Single-use syringes, cannulas and beyond
Be it contact lenses, intubation tubes, single-use syringes or cannulas, more than half of all medical products manufactured around the world are made of plastics. But even beyond these mass-produced articles, the prospects for polymer materials in medical technology look rosy. This is a fast-growing market—and one which will remain expansive and lucrative, given the increasing world population and longer life expectancy along with rising expectations regarding health care. At the same time, this is a field governed by a permanent pressure to innovate because of the often extremely short life cycles of the products involved. Market experts will have ample opportunity to track the advances made and the growth of plastics in medical applications at K 2013, the international trade fair for plastics and rubber, which is being staged in Düsseldorf on October 16-23.
In the middle of the last century, around 1950, the total volume of plastics produced worldwide amounted to just 1.5 mn tonnes. However, the curve has risen steeply in the following years and decades. Today, some 280 mn tonnes of alternative polymer materials are now being synthesised at locations all over the world. And the requirement for them will continue to grow as our planet’s population increases.
About one fifth of global plastics output is currently produced in Europe. After China, the European continent is the second-largest supplier of plastics, still ranking ahead of North America, the other Asian states and the Middle East. Of the roughly 47 mn tonnes of plastics processed in Europe, almost 40% are used for packaging, 21% for civil engineering and construction, only 8.3% in the automotive industry, and 5.4% in the electrical and electronics industry. The rest is spread across such diverse areas as sport and leisure, toys, household goods, furniture, agricultural uses, and—not least—medical technology. No exact percentages are available here because of the blurred distinctions as to where medical technology starts and ends. But one thing is clear: only technically sophisticated and high-quality plastic grades find their way into healthcare applications.
The EU: With a growth rate approaching 9% in 2010 and 6% in 2011, the medical technology sector lies substantially above the figures for most other industries, but also quite a bit higher than the rate of growth of Germany’s GDP, which amounted to only 3% in 2011. Turnover by German enterprises in this market has been estimated at approximately €21 bn for 2011 by Spectaris, the German industry association of businesses in the optical, medical and mechatronic technologies. Almost two thirds of this sum (65%) is earned through export business. More than one third (40%) of these exports go to EU countries, and 12% to other European countries. About 20% of total exports are generated through business with North America, a respectable 17% with customers from the Asian region, although the emphasis here is quite clearly on the Chinese market.
It is interesting to note in this context that, according to Spectaris, the mostly medium-sized companies involved in medical technology invest nearly 10% of their sales in their R&D activities. This is double the percentage that German companies in general invest in research and development (R&D). It also shows that the sector is not only very willing to innovate but is obliged to do so, and that all sights are set on further expansion. A recently published study undertaken by the German Federal Ministry of Economics, Innovationsimpulse in der Gesundheitswirtschaft, which means Innovation momentum in the health care industry confirms this positive trend. It forecasts annual growth of 5% regarding the growth opportunities for medical technology in the near future.
Of abrasion and deception: Not everything always runs smoothly. Sometimes, unexpected problems arise with polymer products. For example, knee replacement implants have been known to develop undesirable wear. The plastic lining (generally made of PE) between metal components abrades under the stress it is subjected to. As the Deutsches Ärzteblatt (the German Medical Association’s science journal) writes, this abrasion continuously causes minute particles to be detached which are suspected of promoting wear of the bones around the implant in the long term. Furthermore, it was found during a current research project at the University of Heidelberg that particles also detach from the metal surface. Intense efforts are therefore now being made to reduce the detected wear on implants.
For the stated new study in Heidelberg, the biomechanics specialists at the university are using a motion simulator to mimic the stresses applied to an implant system over a three-year period. The scope of this investigation is not necessarily always the rule, as illustrated by a scandal which shook the otherwise antiseptic and squeaky clean world of medical technology. All the controls and checks had obviously failed here: half a million women from all over the world, including many German nationals, had had breast implant surgery using implants from the south French company Poly Implant Prothese (PIP). Some of the implants were made of low-cost industrial-grade silicone that is usually intended for use as a construction material. Reports are that documentation had been manipulated with the intent to deceive inspection authorities, such as the TÜV Rheinland in Germany, which was responsible for certifying the implants.
Feverish efforts are now being made to ensure that such tragic cases will not recur. However, such instances are very much the exception and not the rule, as evidenced by the long-standing symbiosis of synthetic materials and health care. Plastics were already being used in medical technology even before synthetics began to write their commercial success story from the mid 20th century onwards. In 1936, William Feinbloom made the first contact lenses in the USA from polymethyl methacrylate (PMMA), a polymer material that first achieved fame under the trademark Plexiglas. Around 1949, Harold Ridley, another American, succeeded in implanting the first intraocular lens made of PMMA. In later years, this became a standard surgical procedure. Today, however, in some cases the original synthetic material has been replaced by another one: modern intraocular lenses are made of an advanced silicone elastomer.
While early last century, many World War I invalids had to make do with wooden prostheses, the trend to using plastics to make artificial limbs was well under way by the mid 20th century. Currently, sophisticated composite constructions made of plastics reinforced with carbon fibres (CRP) are being used to make unusual prostheses, such as those used by the exceptional South African athlete Oscar Pistorius (known as Blade Runner). On another scale, the cannulas, single-use syringes and intravenous drip bags which are used in large quantities in hospitals, laboratories or health centres have been on the market since the early 1960s at least, and are available in a variety of plastic materials. And here is another impressive statistic: according to research by the Schmalkalden University of Applied Sciences, a total of 16 bn single-use syringes are used every year around the world.
The trend towards thin-walled components: The demands made on a polymer material intended for use in medical technology were always high, but they have risen even further in recent years. In addition to high resistance to chemicals (including the often very aggressive cleaning substances used in healthcare settings), sterilisability and good optical performance, the processability of the material (for injection moulding, extrusion, welding, and so on) has become an important selection criterion. New requirements have arisen from the continuing trend towards thin-walled components, in order to be able to maintain high quality standards in products for healthcare technology even when saving on material and weight.
The longer life expectancy of people in industrialised nations is also posing new challenges: Implants and regenerative medicine are moving into the foreground as a result of health-related restrictions experienced by an increasingly aging population. The German Society for Thoracic and Cardiovascular Surgery, DGTHG—Deutsche Gesellschaft für Thorax- Herz- und Gefäßchirurgie—recorded a total of 80,000 operations involving heart-lung machines (HLMs) in 1995. A year later, the figure had risen to 87,000, climbing to nearly 100,000 in 2001. Today the number of operations requiring HLMs probably lies at about 200,000.
Moreover, almost 70,000 pacemaker systems are implanted annually in Germany, and the number of stents worldwide is estimated at 4 mn. Roughly 55,000 patients in Germany rely on dialysis machines, which consist mostly of plastic materials. Intramolecular lenses, heart valve prostheses and oxygenerators are required in addition to intracorporal blood pumps and extracorporal heart support systems.
And synthetic materials are required for all of these medical systems, surrogates and implants—not just any such materials, but specific, biocompatible and physiologically safe grades. This is not always easy to achieve, as one example clearly illustrates.
In 2002, more than 1,000 different models of dialysers were being offered on the world market, with membranes made of at least 10 different types of polymers. At a congress staged in Friedrichshafen in the spring of 2012 by the German Society of Engineers, the VDI—Verein Deutscher Ingenieure—a paper by the University of Hannover stressed that the selection of a suitable material for biomedical implant technology can be problematic. The paper was entitled entitled Plastics in Medical Technology and summarised the dichotomy faced by designers of plastic medical devices. Two conflicting aims have to be resolved. A biocompatible material selected for a particular application must not damage the organism around it, but it must also not be impaired in its function by the effects of the biological environment it will be used in.
Silicone resins and silver ions: Silicone resins have won their place among the materials of choice for medical technology applications in everyday clinical use. In terms of volume, they make up 3-5% of all polymers employed in this area. As stated at the VDI congress by Wacker Chemie, a large German manufacturer of silicone rubber, the material fulfils the stringent requirements for pharmaceutical applications. The material is said to be not only biocompatible but also free of organic plasticisers and stabilisers and, as a purely synthetic substrate, contains no ingredients of animal origin.
Silicone elastomers, it has been claimed, show good mechanical properties over a broad temperature range and are resistant to a large number of common cleaning agents and disinfectants.
A further benefit of polymer materials on offer to medical processors are grades with antimicrobial finishes. They can help to significantly reduce the number of infections due to microorganisms in clinical environments. Thermoplastics, for example, can be given effective antimicrobial properties through the addition of metallic salts. Zinc oxide is used to avoid discolouration of end products. Even in low concentrations, silver-based additives can achieve good antimicrobial effects. A new styrene-butadiene block copolymer (SBC) recently launched on the market by German chemical company BASF also contains antimicrobially acting silver ions (see image). Available in granular form and excellently suited for injection moulding, the new material—says its manufacturer—is highly effective against a large variety of fungi and diverse bacteria. Moreover, articles for medical use made from the material can be disinfected by conventional methods.
And nanotechnology, too, has long established itself in the health care industry where it is playing an increasingly important role in medical technology in particular. According to Frank Schröder-Oeynhausen, managing director at the Center for Applied Nanotechnology (CAN) in Hamburg, Germany, it allows the targeted production of completely new materials and the improvement of existing ones. Nanoparticles can be used, for example, to create antibacterial surfaces, coated implants, contrasting tooth fillings or novel nanocomposites. Nanoscale contrast agents can enhance existing imaging processes in diagnostics. And, as Mr Schröder-Oeynhausen reports, nanoscale systems such as liposomes, micelles or polymer nanoparticles can also be used as transport systems to deliver active ingredients directly to diseased tissue.
Prostheses using additive manufacturing methods: It goes without saying that medical technology also uses advanced product development methods such as additive manufacturing (AM). As the technical journal Plastverarbeiter (in English, plastics processor) writes, the rate of innovation in this field depends to a very large extent on AM of genuinely functioning parts for prototyping. It can be used to configure the first specimen parts right through to prostheses based on existing CAD files, but the methods used in AM offer further attractive opportunities. Within a very short time, series parts can be made from a wide range of different materials, such as plastics, using computer aided design (CAD) data, without the need for moulds.
CAD data and AM helped professional cyclist Michael Teuber back into the saddle and even onto the podium following a traffic accident which resulted in him being paralysed. Through intensive training, the cyclist was able to reactivate the muscles in his thighs. An orsthesis (see image in slideshow) now helps to transfer the force from his thigh muscles directly to the pedals of the racing bike. The success of this speaks for itself and for Teuber: the athlete has four paralympic medals—three gold and one silver. The orsthesis, which is to no small extent responsible for Teuber’s success, was produced from polyamide using CAD data and a laser sintering process, a common AM technology.
All the other areas in which plastics help to make people’s lives easier and advance medical technology are excellently documented at the Medica and Compamed trade fairs, a highly successful combination spanning the entire process chain and complete range of medical products, machines and devices. As many as 130,000 visitors streamed to Medica last year, of whom around 16,000 were specifically interested in what Compamed had to offer. Taking place again this year on towatds the end of November, these two events provide yet another opportunity to learn all about current developments in medical technology, beyond the cannulas, single-use syringes and other mass-produced articles. A month earlier, on October 16-23, K 2013 will open another window on the topic when the halls with exhibiting machine manufacturers will be revealing the latest trends in manufacturing medical products by the various processes involved for engineering plastics.