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Posted: Jul 05, 2011
Implants of the future: bioactive, corrosion resistant and antibacterial
(Nanowerk News) The interaction of materials with biological tissues and organisms and their adaptation to them play an important role in the development of implants. The term biocompatibility is used to describe a material's capability to exist in harmony with body tissue. The revision rate of implant materials used in clinical practice is sometimes as high as 10 per cent. This is mainly due to the formation of wear particles or the accumulation of corrosion products in the tissue surrounding the implant. The major reason for both these occurrences is the difference in the surface and volume characteristics of the implant and the organism as well as the inability of the implant to adapt to the organism.
New developments, including some in the field of nanobiotechnology, are expected to bring improvements. In general, the production of functional implants depends on the adherent layer between the coating and the basic material. An imperfect layer leads to cracks, body fluid entering the implant and corrosion of the implant material that then needs to be removed, which is unsatisfactory for patients, doctors and the health system alike.
Companies that develop implants make every effort to adapt the mechanical characteristics of bone implants to those of living bones and bone tissue. However, these efforts are often associated with the disadvantage that the surface of the implant is not hard enough or that the implants are not resistant enough to wear, particularly those made of stainless steel and titanium alloys. Companies around the world are therefore working to develop appropriate surface modifications (specific texture and surface roughness).
Popular materials with disadvantages
Titanium has long been the material of choice for the production of medical implants. This is mainly due to its excellent biocompatibility, which means that titanium implants bond optimally to human tissue. However, implants with more flexibility and elasticity are difficult to produce with titanium due to its brittle and inflexible properties, which can lead to an implant quickly becoming non-functional and needing to be changed prematurely. In order to improve this situation, there is a trend towards using implant materials of artificial and biological origin, but which are nevertheless characterised by insufficient biocompatibility and might in consequence lead to foreign body or immunological reactions, and even to the incapsulation of the implant. The biocompatibility of plastic implants can be improved by functionalizing their surfaces with suitable coatings or by adding drugs (i.e. drug eluting implants).
Increasing biocompatibility with nanoparticles
Biomaterials that will be used for the production of implants in the future are characterised as bioactive. Such materials stimulate and initiate the formation of new body tissue on their surface when the material has been specifically treated. At present, different methods from the field of nanobiotechnology can already be used to stimulate desired cellular processes. The goal of nanobiotechnology is to improve, or initially render possible the trouble-free synchronisation and compatibility between biological and technical systems. Drug-eluting systems are one of several nanobiotechnological methods used for this purpose. Nanoparticles such as dendrimers and polymer capsules are used to transport drugs that increase the biocompatibility of the implant to the designated target, thereby preventing the early release of the drug and undesired autoimmune reactions.
Besides the specific structuring of surfaces in the nanometre and micrometre range, which improves the adhesion and proliferation of cells, the targeted induction of abiotic surface mineralization of implant materials is another method to improve the osseointegration of implants (i.e. the formation of a direct structural and functional connection between living bone and the surface of an artificial implant). In addition to being resistant to wear and corrosion, biomaterials of the future also need to be biologically degradable in order to enable degradation in the body if necessary, thereby avoiding a second surgical intervention to remove the implanted material. Future research is also focusing on developing implants with an antibacterial surface.