Smart Implants
Nanotechnology and orthopedics: on the threshold of creating intelligent bone implants
NanoNewsNet by materials Nanowerk: Nanotechnology research lays the foundation for smart implantsImagine intelligent medical implants that can constantly monitor their condition while in the body and automatically respond to changes such as infection by releasing antibacterial drugs.
Thanks to nanotechnology, medical research is rapidly approaching this goal.
The medical implantable device market is huge and continues to grow rapidly – in the US alone it has reached an annual turnover of $23 billion and is expected to grow by 10 percent annually over the next few years. Among the sales leaders are cardiological defibrillators and resynchronizers, pacemakers, orthopedic implants for the treatment of the spine, prosthetics of large joints, intraocular lenses and cosmetic implants. Nearly 500,000 hip and knee replacement surgeries are performed annually in the United States alone, and approximately the same number of patients need bone reconstruction due to injuries or birth defects. Every year, 16 million Americans lose their teeth and need dental implants.
The main problem that scientists and doctors have to face on the way to a successful and long-term service of artificial joints remains wear and infection of implants. Studies have shown that during the operation of orthopedic implants, the smallest particles of their materials, both metals and plastics, are formed. A large number of such particles causes a cascade of events that can eventually destroy the bone around the implant (a process known as osteolysis). The resulting "loosening" of the implant leads to the fact that the artificial joint can no longer perform its function. Diagnosis of the implant condition is based on X-ray and other imaging methods. These technologies are not sensitive enough, do not give a picture in real time and require hospitalization of the patient. Surgical operations to replace such prostheses are not only more complex and expensive than primary prosthetics of joints, but also less effective.
A new study shows that the quality of bone implants can be significantly improved. A film of polypyrrole deposited on their surface can be used as an electrically controlled device for the isolation of drugs. Using antibiotics or anti–inflammatory agents injected into the polymer coating by electrodeposition, Brown University scientists have demonstrated that these drugs can be isolated from polypyrrole "on demand" – when voltage is applied - and control the behavior of cells, that is, suppress inflammation and kill bacteria.
Polypyrrol is a conductive polymer coated with carbon nanotubes (photo:
EMSL/Flickr)
"Polypyrrol is a traditionally conductive polymer that can be synthesized by electrochemical methods in the form of a thin film on conductive materials," explains Thomas J. Webster (Thomas J. Webster). The possibility of its use has been studied in the field of corrosion protection and the development of electrode coatings, electrochemical biosensors, semiconductor devices, as well as in bioelectronics and other fields. However, although it has established itself as a promising material with significant capabilities in the field of biomedicine and controlled drug delivery, its potential role in reducing infection and suppressing inflammatory reactions in orthopedics has not been sufficiently investigated.
Reporting their results in the January online issue of the journal Nanotechnology, Webster and his colleagues presented proof of concept for the development and evaluation of on-demand delivery of drugs in situ from polypyrrol, using as an example penicillin/streptomycin (antibiotics to combat gram-positive and gram-negative bacteria) and dexamethasone (glucocorticoid used in clinical in practice as an anti-inflammatory and immunosuppressive agent). With their experiments, scientists have proved that medicines can be removed from the coating of bone implants on demand in order to reduce both septic and aseptic inflammation.
This work is a continuation of earlier research by Webster's nanomedical Laboratory, which demonstrated that such nanostructured materials can affect and promote bone growth.
To create their polymer coatings, scientists first grew multilayer carbon nanotubes (about 55 nm in diameter) on anodized nanotube titanium by chemical vapor deposition (CVD) with cobalt as a catalyst. The polypyrrol monomers were oxidized either with antibiotics or dexamethasone prior to electrochemical polymerization of the polypyrol around carbon nanotubes.
On the left is polypyrrol electrodeposited on ordinary titanium,
on the right – on multilayer carbon nanotubes
(photo: Webster Lab, Brown University)
"In our latest study, anionic drugs bound electrostatically inside a thin polyporrole film were released when a negative voltage was applied," explains Webster. "During the first five cycles, we observed the release of anionic molecules from a thin polypyrrole film and their reverse movement caused by a constant process of reduction and oxidation. Peaks of penicillin/streptomycin release caused by drug recovery disappeared after 15 cycles of cyclic voltammetry. The peak of dexamethasone recovery was observed after 25 cycles and disappeared after 40 cycles."
The increase in the amount of drugs released after electrical excitation was significant up to 5 cycles. The combined release of penicillin/streptomycin and dexamethasone was close to 80 percent of the initial amounts of drugs, and subsequent cycles did not cause their release.
Although scientists have found that at higher voltages or with longer periods of its supply, polypyrrol can be over-oxidized and loses its electrical activity, carbon nanotubes maintain and prolong its electroactivity due to their excellent conductive properties.
Webster notes that polypyrrol can be saturated not only with antibiotics and drugs such as dexamethasone, but also with many other biomolecules – growth factors, peptides, enzymes, antibodies, proteins, etc., in order to change their biological, physical, chemical and electrical properties and obtain a controlled isolation system applicable in many biomedical applications.
In addition, polypyrrol can be integrated into implantable chips to output a signal to a biological environment.
"These preliminary results lay the foundation for the development of intelligent drug delivery technologies for use in orthopedics, capable of using closed-loop information reading to control the administration of drugs based on this information," says Webster. "Both carbon nanotube-based sensors and controlled drug delivery systems can be an excellent means of extending the use of orthopedic implants, allowing implants to kill bacteria, show less sensitivity to prolonged inflammatory reactions and, ultimately, enhance the process of bone formation."
Mentioned publications:
Electrically controlled drug release from nanostructured polypyrrole coated on titaniumGreater osteoblast functions on multiwalled carbon nanotubes grown from anodized nanotubular titanium for orthopedic applications
Multiwalled carbon nanotubes enhance electrochemical properties of titanium to determine in situ bone formation
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