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by Prof. Thomas Webster
Nanotechnology offers new engineering tools that can help us address the
design problems associated with building better implants. In the context of
biomedical engineering, recent technological advancements mean that we now have
the ability to manipulate materials (and their surfaces) with nanometer scale
accuracy. This allows us to create biomaterials with features the same size as
the proteins and cells with which our implant will interact.
Attempting to have cells traverse conventional sized materials is analogous
to asking a human to travel across shear cliffs and rugged valleys, but
nanomaterials offer an implant interface with features that more closely
resemble the natural tissue onto which cells normally travel (and create
themselves). Although there are other reasons for nanomaterials to affect cells
differently than conventional biomaterials, it seems as though just making their
surfaces resemble natural tissues can promote cell growth.1
The above result is important because the central goal in designing an
effective implant is to encourage the growth of good cells and discourage the
activity of bad cells. Good and bad are relative terms, but in the case of bone
implants; bone cell growth should be encouraged, and the growth of bacteria and
excessive immune cell activity should be avoided.
The positive effect of bone cell growth and the negative effect of bacteria
growth on implants are more obvious than the detrimental effect of overactive
immune cells. Much like scar tissue that forms on your skin, overactive immune
cells can lead to granular scar tissue formation on the surface of implants
leading to implant failure. Macrophages, cells that are part of the body's
immune system, are among the biological players that contribute to scar tissue
formation inside the body. Excessive macrophage activation should be avoided to
avoid granular tissue formation on the surface of the implant.
Recent studies are beginning to confirm that nanotechnology can be used to
design a more effective implant. It is now possible to make implant surfaces
that more closely resemble native bone in both surface roughness and chemistry
than traditional implants. These new biomimetic surfaces are biocompatible and
show good bone cell growth.2 The same is true for
many other organs in the body from the heart to the brain.
Additionally, just modifying implant surfaces to be nanorough has positive
outcomes. These nanorough surfaces make it possible to independently modulate
the growth rates of bone cells, bacteria and immune cells on the surface of
implanted materials. For instance, scar forming macrophage cells are less active
on nanomaterials than on conventional biomaterials, while bone cells are more
active on nanomaterials.3,4 In
addition to this result, wear debris from implants with nanoscale surface
features is less toxic to the surrounding tissue than that from conventional
implants.5 Moreover, recent studies have
demonstrated that nanostructured surfaces reduce bacterial colonization.6,7 The above results suggest that
nanotechnology can be used to design a more effective implant reducing the need
for revision surgeries.
References
1. Bruder JM et al. 2007, J Biomater Sci Polym Ed.,
18(8):967-82.
2. Zhang et al. 2008, Int J Nanomedicine, 3(3):
323–334.
3. Khang D et al. 2009, Acta Biomater.
5(5):1425-32.
4. Webster et al. 2000, Biomaterials,
21(17):1803-10.
5. Gutwein et al. 2003, Biomaterials,
25(18):4175-83.
6. Puckett, SD et al. 2009 Biomaterials 31 (4)
706-713
7. Taylor EN et al. 2009 Int J Nanomedicine. 4:145-52
Copyright AZoNano.com, Professor Thomas Webster (Brown
University)