A
new type of bone cement is unlikely to cause infection as it contains porous
silica particles that slowly release antibiotics into the body
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 problems1. The bone cement slowly releases
antibiotic drugs, which should dramatically reduce infection rates and the need
for further interventions.
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.”
The A*STAR-affiliated researchers contributing to
this research are from the Institute
of Chemical and Engineering Sciences
References
- Shen, S.-C. et al. Mesoporous silica nanoparticlefunctionalized poly(methyl
methacrylate)-based bone cement for effective antibiotics delivery. Journal
of Materials Science: Materials in Medicine 22, 2283–2292
(2011). |article
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