The medical market will be a high growth area for nanoscale coatings over the next 5-10 years, and this is reflected in the high number of companies exploiting technology in this area, especially in the multi-billion dollar anti-microbial segment. According to Cosmetic Science Technology, the global market in 2010 for medical textiles was approximately $16 billion.
Nanocoating products have been commercialized in life sciences & healthcare as anti- bacterial surfaces for medical catheters, have been added to paints and lacquers used to coat operating tables, door knobs and door handles in hospitals and also as ultra-hard porous coatings for surgical and orthopaedic implants such as screws, plates or joint implants.
In medical facilities it is necessary to equip materials and surfaces with a high level of hygiene, using antimicrobial agents to protect them against bacteria and other micro organisms, to prevent infections caused by bacteria and contribute significantly to reducing health costs. Drug-resistant bacteria, the so-called “superbugs,” are a growing problem in hospitals worldwide and poor hygiene among staff is often blamed for the spread of such infections. The Centers for Disease Control and Prevention (CDC) estimates that roughly 1.7 million hospital-associated infections, from all types of bacteria combined, cause or contribute to 99,000 deaths each year. Other estimates indicate that 10%, or 2 million, patients a year become infected, with the annual cost ranging from $4.5 billion to $11 billion. There has been a growing use of anti-bacterial and superhydrophilic coating in medical devices in recent years to combat these problems. The increased need by an ageing population for spinal, orthopaedic and dental medical devices will also boost demand for medical device nanostructured coatings.
Properties
Nanomaterials have key implications for the development of future biomaterials via the surface modification of medical devices to enhance their biological interface.
They are currently used in the following applications:
• Carbon nanotubes in bone cements (Graphene is also being developed for the same application);
• Nano hydroxyapatite paste for bone void and dental filling;
• Nano-crystalline diamond-coated dental implants
• Polycrystalline nanoceramics in dental restorative materials;
• Nanosilver or other nanomaterials (e.g. Nano hydroxyapatite), as coatings on implants and catheters;
• Graphene coated cardiovascular stent
• Nanosilver used as an anti-inflammatory, anti-fungal and anti-viral, anti-biofilm, and antibacterial agent in wound dressings and medical textiles.
Anti-infective nanoscale coating materials improve the efficacy of indwelling and implantable medical devices, while reducing the risk of deadly medical device-related infections.
Self-cleaning coatings have application for improved biocompatible surfaces able to prevent cells from adhering to implanted medical devices.
Many medical device coatings attempt to reduce bacterial infection by releasing active biocides. These biocides may not protect against new bacterial strains, and may actually promote the evolution of resistant strains. Moreover, the biocides can prove toxic to surrounding tissues.
Anti-microbial
There are a number of companies producing anti-microbial nanocoatings for medical devices and surfaces in hospitals. Benefits of nanomaterials include long lasting anti-microbial effect, constant release of the active substance, effectiveness against bacteria and other micro-organisms, no chemical impurities, easy processing, no changes to the characteristics of the equipped material, and no later discolouration of the equipped material. Biogate Ag (www.bio-gate.de) equips materials and surfaces in all areas where a high level of hygiene is needed with its antimicrobial agents, consisting out of elemental silver, to protect them against bacteria and other micro organisms. ItN Nanovation (www.itn-nanovation.de) also manufactures products in this market that are added to paints and lacquers used to coat operating tables, door knobs and door handles in hospitals and surfaces in sanitary facilities. AeonClad Coatings (www.aeonclad.com) nanocoatings increase biocompatibility by treating the surfaces of medical devices, stents, and catheters with ultra thin, ultra smooth coatings that better prevent protein and bacterial attachment.
Nanosilver
Nanosilver has been incorporated in numerous medical applications including diagnostics, wound care, drug delivery, medical devices and coatings. Nanosilver coated polymers have been incorporated into plastic catheters, for their antibacterial and disinfecting effect. The antimicrobial effect of nanosilver has been successfully used in medical textiles for a number of years in hospital clothing and anti-microbial dressings, diabetic socks, scaffolds, sterilization materials in hospitals, and contraceptive devices. Nanocrystalline silver wound dressing inhibit the growth of bacteria allowing wounds to heal more quickly. Nanosilver particles are coated onto fibres via:
• mixing in a polymer (master batch) before being spinning it into fibres. This is applied, e.g., in polyester and cellulose acetate fibres, resulting in firm integration into the fibre, leading to a long lasting antibacterial effect.
• applied on the fibre surface as a finish. In this method, adhesion strength, and thus the effective duration can vary greatly. Weakly bound nanoparticles can suffer from poor adhesion after just a few washes.
Nanosilver is also used as an antibacterial additive for poly (methyl methacrylate) (PMMA), used in bone implants. Nanosilver is also used in dentistry for making artificial teeth and in eye care for coating contact lenses. DocuGuard uses silver-based paper to protect hospital case notes and medical files against the proliferation of bacteria.
The antimicrobial effect of silver is based on the release of silver ions (Ag+). Bacteria are killed by Ag+-ions. The EU biocide directive applicable from September 2013 onwards requires that nanosilver (when it is used as a biocide) be approved for textiles and declared on the products. Kimberley Clark (www.iflo.com) is a large company that produces nanosilver coatings for catheters. Most of the coatings based on silver are widely regarded as being costly and there are concerns over leaching of sliver ions into the environment and of silver nanoparticles through the skin.
Anti-fouling
Biofouling is often responsible hospital-acquired and device-based infections that are a major cause of mortality in the U.S. and other parts of the world. Biofouling of implantable medical devices remains a serious problem, for example in the form of thrombus formation on cardiovascular devices and bacterial biofilm formation on catheters and other medical devices. Easy to clean nanocomposite sol gel coatings are currently used to coat medical devices and equipment. Anti-fouling nanocoatings prevent bacterial attachment and colonization on a device surface. They are biocompatible and act against all bacterial strains, including those that resist other biocides.
Implants and medical devices
There is growing demand for advanced coatings to control the interactions between biomedical implants and the surrounding biological environment. For cardiovascular stents specifically, materials such as nitinol, 316L stainless steel are often used in implant manufacturing due to their superior mechanical properties. However, their metallic nature results in poor hemo- and bio-compatibility. The biocompatibility of medical devices, stents, and catheters is improved with ultra-thin, ultra smooth coatings that better prevent protein and bacterial attachment. These nanocoatings allow for prevention of bio film, lubrication and cell adhesion for medical implants. Under development are: biocompatible nanostructured implant surfaces and TiO2 coated stents; and better performing and cheaper to produce artificial retinas and cochlear that are more body friendly, and mimic more closely nature’s light/sound receptor and transmission systems. Nanotechnology has also opened up innovative techniques for producing bone-like synthetic nanopowders and hydroxyapatite coatings. Nanoscale coatings of hydroxyapatiteare used for superior biocompatible coatings for implants.
According to Nanointerface Technology, Inc. (www.nanointerfacetech.com), the hip, knee and dental implants have a worldwide market size of $15 billion dollar with growth rate of 15-25%. Companies developing nanocoatings for implants include Inframat (www.inframat.com) and Debiotech SA (www.debiotech.com).
Orthopaedic surgeons have made great improvements in the operating procedures of hip and knee implants. But there has been no increase in the lifespan of hip or knee implants because the quality of coatings on the implants has not improved over the decades. As well as their high stability, chemical versatility and biocompatibility silica nanoparticles are employed in artificial implants due to the osteogenic property of the resultant composites. Nanocrystalline metalloceramic coatings have been applied to orthopedic and dental implants for increased biocompatibility, and can provide a huge increase in binding to bone proteins compared to conventional coatings. Nanoporous alumina is also under development for use on titania alloys.
Nanovis Incorporated (www.nanovisinc.com) is developing nanopatterned implant surfaces for the degenerative spine implant market. Acrymed, Inc. (www.acrymed.com) develops anti-infective nanosilver coatings for implants. Namos GmbH (www.namos.de) also produces nanostructured functional surface coatings for implants.
