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Posted: Apr 25, 2012

Nanoparticle-based bone cement is less likely to cause infections

(Nanowerk News) Many countries are facing the problem of an ageing population, and it is estimated that the number of people aged 85 or over in the world will triple over the next fifty years. This rise in number is set to be accompanied by an increase in the prevalence of ailments that are common among the elderly, as well as the need for treatments, not least hip and knee replacements. Despite strict hygiene controls, however, it has been reported that one to three percent of patients suffer infections after hip and knee replacement surgery.
Shou-Cang Shen at the A*STAR Institute of Chemical and Engineering Sciences and co-workers have now developed a new type of bone cement that is less likely to cause problems (see paper in Journal of Materials Science: Materials in Medicine: "Mesoporous silica nanoparticle-functionalized poly(methyl methacrylate)-based bone cement for effective antibiotics delivery"). The bone cement slowly releases antibiotic drugs, which should dramatically reduce infection rates and the need for further interventions.
X-ray of the pelvis after a hip replacement
X-ray of the pelvis after a hip replacement.
Conventional bone cements commonly use a polymer called PMMA for fixing new bone implants. They may also contain antibiotics that are released quickly into the body within one to two days. Worse still, a portion of the antibiotics may stay trapped within the bone cement, unable to be released. Shen and co-workers introduced porous silica particles that carry antibiotics inside them into the PMMA. By carefully optimising the amount of drug used, the new bone cement could release more than 70% of the antibiotics from the nanoparticles over 80 days.
The researchers found that particle size and particle number within the bone cement were critical to ensuring maximum drug release. There also had to be enough nanoparticles to ensure that they form a 'network' for delivering the drugs to the cement boundaries. More importantly, the particles had to be small enough so that a homogenous distribution through the cement could be achieved. If the particles were too large, there were an insufficient number and they not distributed evenly enough to create the network needed for drug diffusion to the surface.
One thing that concerns the researchers is the potential detrimental effect of the mechanical properties of the cement as a result of the incorporation of these nanoparticles. Joint replacements are load-bearing components and so their mechanical properties are critical to performance. Shen found that the bending modulus was somewhat affected though still retained 90% of its original capability. The compressive strength was completely retained despite the presence of the silica nanoparticles.
"Our next step is to make multifunctional nanoparticles for bone cements which both release drugs and are detectable to X-rays," says Shen. "Bone cements that appear opaque to X-rays could allow for post-surgery observation and diagnosis of any problems."
Source: A*STAR
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