Nanotechnology for Regenerative Medicine

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