The market for plastic medical devices is growing despite the global economic slowdown. The medical device market is therefore quite optimistic to achieve double digit growth at 15% in Asia, 10-12% in America, and 6-8% in Europe for 2009 and 2010. Although medical devices may differ widely in design and use characteristics, certain factors determine susceptibility of a device to microbial contamination and biofilm formation: duration of use, number and type of organisms to which the device is exposed, flow rate and composition of the medium in or on the device, device material construction and conditioning films on the device.
FIve percent to 10% of hospital patients acquire hospital related infections in the United States alone. The most common post operative infections are urinary tract infection, surgical site infection and pneumonia. These post operative infections prolong the patient’s hospital stay by about four to five days, increasing cost of hospitalisation. Almost 30% of these infections are considered to be preventable. Many of these infections occur due to formation of biofilms of implanted medical devices. Microbial biofilms develop when microorganisms adhere to a submerged surface and produce extracellular polymers that facilitate adhesion to a surface that may be inert, nonliving material or living tissue. Biofilms can develop on the simplest of medical devices, such as contact lenses, or on more complex items such as prosthetic joints, mechanical heart valves and pacemakers. Hence, the medical device industry is challenged to develop biomaterials with inbuilt antimicrobial surface properties without deterioration in processability and low surface migration or lower leachable substances, for reducing device-centered infection. But most approaches to date have used drug-eluting compounds or coatings that are eventually consumed. It is much more desirable to have easily processed biomaterials with good wet-strength and long-term efficacy without leachable additives, drugs or biocides. A growing risk of hospital originated infections is causing the industry to increasingly turn to antimicrobial plastics for application in medical devices that can protect against pathogens while remaining cost-effective. The basic requirements for antimicrobials used as either biostabilizers or active ingredients are:
- Low toxicity to humans, animals, and the environment (during manufacture and under conditions of use)
- Easy application
- Compatibility with processing aids, other additives
- No negative impact on properties or appearance of the plastic article, its storage stability, or useful life
To make plastic products antimicrobial, self-assembling monolayer end groups (SAMEs) are emerging as a solution. These two-dimensional SAME end groups use nanotechnologies. These terminals SAME groups are added to the backbone of polymer provide antimicrobial properties. Self assembling monolayer end groups (SAME) technology is the second generation of surface modifying end groups (SMEs). Bioactive SAME groups could include drug functionality such as heparin, biological groups such as peptides, or surface functionality for post device fabrication surface reactions. Self assembling monolayer (SAM) technology has demonstrated that bioactive 'head groups' can be appended to alkane chains as a method of creating model surfaces for in vitro research. Ideally, the chemistry used during such model studies could then be applied to actual medical devices to further improve clinical outcomes. However, SAM technologies are not easily transferred to medical device applications due to the fragility of such systems. SAME technology is a breakthrough that is capable of providing polymers with "SAM-like" engineered surfaces. Relative to backbone chains, polymer end groups are more mobile, in part because they are often tethered to the backbone by a single, flexible covalent bond. Their mobility allows them to diffuse from the bulk, and assemble in the polymer surface to affect surface composition. This occurs spontaneously if the presence of the end groups in the surface reduces system interfacial energy. Simple hydrophobic end group may diffuse to an air interface, while purely hydrophilic end groups may enrich a polymer surface when exposed to aqueous body fluids. SAME technology utilizes very specific hydrophobic or hydrophilic spacer groups, and a head group chemistry chosen for the particular application. The spacer groups will "self-assemble" at the surface through either hydrophobic or hydrophilic interactions, and thus present the head group as the outermost monolayer of the polymer.
A polyurethane material with permanently bonded antimicrobial surface properties has been developed by DSM PTG (Polymer Technology Group). The polymer with surface-active alkyl ammonium chloride end groups has demonstrated antimicrobial action against gram-positive bacteria in a range of laboratory studies. Very small amounts of biologically active end groups are permanently incorporated into the polymer during its synthesis. After being extruded or molded into a medical device, the new material modifies its own surface as a result of the polymer's surface activity and self assembly of its novel end groups. In this way the antimicrobial groups are concentrated on the surface where they are needed. No secondary coating processes or treatments are required to provide the necessary antimicrobial properties, which reduces manufacturing times and the cost of goods. The polymers exhibit low water absorption, excellent strength and processability, high molecular weight, and effective contact-killing of Gram-positive bacteria relative to controls.
Anti-Crobe antimicrobial POM polymers are a family of acetals targeted at high performance polymer applications such as medical devices exposed to environments where heat, moisture and nutrients can promote bacterial and fungal growth. Anti-Crobe antimicrobial polymers resist bacteria throughout the part. Parts made from Anti-crobe polymers help resist bacterial growth in all kinds of difficult applications and environments that can cause odor, contamination, discoloration and slime growth. These resins are NSF Standard 61 Drinking Water Systems components listed, giving the benefits of antimicrobial part protection in potable water application as there are no health concerns from contaminates leaching into water. Materials that restrict the growth of microorganisms on equipment and surfaces in the medical environment help control the potential for infection in hospitals, clinics and doctor's offices. These engineering plastics by Ticona give medical designers a tool to apply to demanding applications that can benefit from resistance to bacteria and fungi. The material works by inhibiting bacteria's ability to reproduce. The inorganic, antimicrobial technology built into this acetal series is present throughout the polymer matrix and not just on the surface as with coatings. This means its protection won't abrade or scratch off, so it can continue to limit microbial growth over the long term. This deterrent to bacteria and fungi also keeps them from attacking the plastic and causing the odors, stains, biofilms and loss in mechanical properties that can compromise product performance. Many components and surfaces touched by medical staffs or patients are candidates for these new antimicrobial grades, as are hard-to-reach-and-clean areas that can foster microbial growth. The polymers' high lubricity also makes them ideal for sliding parts, such as those in hospital beds. The materials are dimensionally stable, abrasion resistant, and tolerant to low temperatures. In addition, they give good surface aesthetics in molding. As a naturally white polymer, they can be tinted or color coded. They also have a high resistance to chemicals and withstand continuous exposure to hot water at 82 C (180F) and intermittent exposure to water at 100º C (212º F) or more. They can be sterilized by all common chemical, thermal, and irradiative sterilization methods. The polymers were developed for use where polyolefins and other commodity plastics cannot meet performance specifications. The polymers do not protect users or others against disease-causing or food-borne bacteria as antimicrobial properties apply only to the molded part.
Bayer Material Science has developed two grades of antimicrobial PC with different levels of efficacy for use in medical device applications to meet a growing demand for products that can help inhibit the growth of bacteria. These are based on attaching silver ions on the backbone of PC polymer. Bayer is using an inorganic silver nanoadditive to control growth of bacteria on the surface of medical devices. The nano particles' high surface area makes the silver additive highly efficient. The company says the additive can potentially control the generation of Gram-positive (bacillus, listeria, staphylococcus) and Gram-negative (e-coli, salmonella) bacteria. Stain testing shows that bacteria on untreated PC grow unabated, while bacteria growth on the antimicrobial PC is virtually nonexistent. Potential applications are IV and urological systems, and housings for diagnostic/hospital equipment.
Patented polymer technology has yielded an altogether new type of antimicrobial that provides permanent protection at much less cost than conventional silver-based additives while eliminating common problems like discoloration, opacity and concerns about heavy metals, by BIOSAFE, Inc. Tradenamed BIOSAFE, the new antimicrobial protects plastics from staining and degradation caused by bacteria, mold, mildew, and fungi and does not compromise end-product safety by migrating out of the plastic or being rubbed off the surface, according to the company. The additive does not compromise optical properties when used with high-clarity resins. It provides an environmentally sustainable means of prolonging the useful life of consumer and industrial products and addresses the growing demand among the healthcare community for hygienic cleanliness in medical products for hospitals and doctors' offices. As a nontoxic polymer that renders plastic surfaces permanently antimicrobial, it eliminates the safety issues of leaching antimicrobials and does so while actually reducing the cost of effective end-product protection. It takes one to four hours to achieve effective microbial reductions on plastic surfaces. BIOSAFE products can be incorporated by standard mixing and compounding techniques and they contain no volatile organic compounds, heavy metals, arsenic, or polychlorinated phenols. Toxicity tests have shown them to cause no irritation or sensitization in skin contact. BIOSAFE chemistry is FDA listed as a modifier to medical devices and has received its EPA label approval. The spread of infection in hospitals and the development of antibiotic-resistant strains of bacteria is nationally recognized as a critical healthcare problem, one that the antimicrobial can help solve through its use in catheters, wound dressings, and high-contact environmental surfaces such as door knobs and countertops.
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