We look at how nanomaterials are allowing for new technological developments in medical implants.
The medical implants industry encompasses implantable cardioverter defibrillators, cardiac resynchronization therapy devices, pacemakers, tissue and spinal orthopedic implants, hip replacements, phakic intraocular lenses and cosmetic implants. According to Nanointerface Technology, Inc., the hip, knee and dental implants have a worldwide market size of $15 billion dollar with growth rate of 15-25%.
Medical implants such as orthopaedic implants and heart valves are made of titanium and stainless steel alloys, primarily because they are biocompatible. However, these metal alloys have a lifespan of 10-15 years and may wear out within the lifetime of the patient. They also might not achieve the same fit and stability as the original tissue, and in a worst case scenario, the host organism might reject the implant altogether. There are also often difficulties in getting bone to adhere to the metal implants.
To address these problems researchers and product developers are turning to nanomaterials. The properties sought for medical implants such as mechanical stability, thermal/electrical conductivity, diffusion, water absorption, biostability and biocompatibility are all greatly enhanced at the nanoscale. The response of host organisms (including at the protein and cellular level) to nanomaterials is different than that observed to conventional materials and they offer many potential advantages over conventional materials. Nanostructured materials can stimulate self-healing cell responses or can increase the biocompatibility of implants. Nanomaterials are also being utilized the coating of vascular stents. Nanoporous alumina and hydroxyapatite coatings increase biocompatibility and thus efficient stenting. Companies developing these coatings include Inframat (www.inframat.com) and Debiotech SA (www.debiotech.com).
Application of nanomaterials in medical implants include:
Silica nanoparticles
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. In breast implants the silicone rubber shell is reinforced with nanosilica so implants appear to be homogeneous and crystal clear.
Nanocoatings
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. 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. Nanocoatings allow for prevention of bio film, lubrication and cell adhesion for medical implants. Poor lubrication in medical implants generates wear particles; increased lubrication afforded by nanocoatings helps to prevent this. Nanoporous alumina is also under development for use on titania alloys.
Carbon nanotubes
Carbon nanotubes can be used for improving the strength of orthopaedic implants. Nanotubes have been added to bone cement composites due to their enhanced fatigue performance, which can lead to improved longevity of the life of the implant.
Hydroxyapatite nanoparticles
Hydroxyapatite (HA) and tricalciumphosphate (TCP) nanoparticles are on the market in synthetic bone graft substitutes. Nanostructured hydroxyapatite has several advantages over hydroxyapatite of larger particle size in its use in bone tissue engineering due to its higher surface area and consequently higher reactivity, which offers better cellular response.
Nanostructured hydroxyapatite is being produced for hip, knee and dental prostheses by US companies Inframat, Inc., Fluidinova (www.fluidinova.com) and Spire Biomedical, Inc (www.spirecorp.com).
Other products include Ostim (www.aap.de/en/Produkte/Orthobiologie/…/Ostim/index_html) from aap Implante (www.aap.de) in Germany (HA), VITOSS from Orthovita, Inc. (www.orthovita.com) in the USA (TCP), Cem-Ostetic™ and Bi-Ostetic™ bone void fillers from Berkeley Advanced Biomaterials Inc. and NanOss Bone Void Filler (HA) from Pioneer Surgical (www.pioneersurgical.com).
Other nano enabled implantable device products on the market include:
• Retinal implants: OptobionicsCorp (http://optobionics.com), Retinal Implant AG (www.retina-implant.de), Intelligent Medical Implants (www.imidevices.com)
• Dental implants incorporating nanoscale calcium phosphate crystals: Biomet (www.biomet.co.uk)
• Pacemakers utilizing spintronics: St. Jude Medical, Inc. (www.sjm.com), NVE Corporation (www.nve.com)
• Hearing aids incorporating spintronic sensors: Starkey Laboratories, Inc. (www.starkey.com).
