Bioactive Glass-Based Coatings and Modified Surfaces: Strategies for the Manufacture, Testing, and Clinical Applications for Regenerative Medicine - Biological and Biomedical Coatings: Processing and Characterization - page 426

(e.g., bone) and soft tissues (e.g., collagen). After 60 mol% silica content, glass compositions
are no longer bioactive.
Coating metallic load-bearing implant surfaces with bioactive glasses offers a promising
approach to improving the rate and quality of osteointegration and possibly extending
implant lifetime by making metallic implant surfaces bioactive. Using high-temperature
methods, thick coatings (>100 μm) have been explored. Their development has been lim-
ited due to glass interactions with the implant metallic surfaces resulting in a reduction
and even loss of bioactivity coupled with low glass/metal interfacial strength. Mismatches
in TECs have resulted in coating failure during manufacture while low compressive
strength of second-generation glasses has limited their usefulness as coating materials.
Glass-ceramic compositions offer improvements in compressive strength and research is
currently focused on developing new compositions of bioactive glasses with TECs match-
ing metallic substrates. In an attempt to avoid TEC mismatch, lower temperature coat-
ing process have been explored. These have resulted in thin (<100 μm) bioactive coatings.
Based on PVD techniques developed for other applications, bioactive glass coatings are
superior in that bioactivity is not compromised by the coating process, and coating compo-
sitions and thicknesses can be precisely controlled. Metallic substrate/glass coating inter-
facial strength are also much stronger. In addition, coating bioactivity can be significantly
increased by coating metallic substrates with third-generation materials. Sol-gel bioactive
glasses exhibit bioactivity with compositions that are much simpler (three-component sys-
tems) and ingredients that are purer than melt-derived bioactive glasses. Inherent poros-
ity offers surface areas that are significantly higher than melt-derived bioactive glasses
accounting, in part, for their significantly higher bioactivity rates resulting in faster tissue
ingrowth and mechanical bonding. For regenerative medicine applications, bioactive glass
coatings can transform polymeric bioinert scaffolds into bioactive scaffolds without com-
promising scaffold degradation rates.
Nanotechnology offers an exciting new strategy to further improve the bioactivity of
implant surfaces by allowing materials to mimic host tissue extracellular matrix form and
function (third-generation biomaterials), thus providing a genetic stimulus for bone tissue
regeneration. Although the fundamental mechanisms by which cell functions are regu-
lated by nanoscopic features remain unresolved, research has recently focused on creating
nanoscopic bioactive glass-powder-based coatings and nanoscopically modified bioactive
glass surfaces. It is too early to predict what the clinical impact of these materials will be,
but it is almost certain that third-generation bioactive glasses that elicit specific genetic
responses will be the next generation.
References
[1] Black, J. 2006. Biological Performance of Materials. Fundamentals of Biocompatibility , 4th edn. CRC
Press, Boca Raton, FL.
[2] Paital, S.R., Dahotre, N.B. 2009. Calcium phosphate coatings for bio-implant applications: mate-
rial, performance factors and methodologies. Mater. Sci. Eng. R 66, 1-70.
[3] Balamrugan, A., Rajeswari, S., Balossier, G., Rebelo, A.H.S., Ferreira, J.M.F. 2008. Corrosion
aspects of metallic ceramics—an overview. Mater. Corros . 59(11), 855-869.
[4] Osborn, J.F. 1979. Biomaterials and their use in implants. Schweiz. Mschr. Zahnheilk . 89, 1138.