Biomedical Engineering Reference
In-Depth Information
does not always lead to the formation of apatite in SBF even though it bonds extensively to
bone in vivo [18].
Morphological Testing
Scanning electron microscopy (SEM) has been used extensively to give high-resolution
surface images of biomaterials [21]. Figure 9.10 shows typical apatite morphologies with
increased immersion in SBF solution and human blood serum solution. Even higher-
resolution techniques are being employed to image submicron surface features that are
being engineered onto the bioactive glass surface reaction layers. Atomic force microscopy
(AFM) is the most common technique used.
Atomic Force Microscopy
Invented in 1985 by Gerd Binnig and Christoph Gerber, AFM has become widely used to
generate high-resolution* images of surfaces at the nanoscale [22]. One of the advantages
of AFM is that it can image the nonconducting surfaces.
In addition to surface roughness characterization, it has been widely adopted as a mor-
phological characterization tool to image microscopic and nanoscopic surface features.
AFM has been used to image apatite formation on metallic substrates and even surface
peptide adsorption on polymeric substrates. Little sample preparation is required for imag-
ing with the AFM. In most cases it is as simple as drying the sample. In some instances
spotting a few microliters of solution on the coating to be tested has been used.
For a detailed explanation of the AFM technique, the reader should refer to the excellent
review by Mayer [22].
In Vitro Cellular Testing
Included in the first phase of the NAMSA characterization approach, cell culture allows
detailed investigation of early, acute cellular responses at the bioactive glasses interface.
Cellular responses under characterization on candidate material surfaces of interest
include:
• Degree of surface adhesion and proliferation
• Rate and quality of extracellular matrix produced from test cells
• Enabling the complexity of in vivo interactions to be broken down and investi-
gated as a study of responses to isolated, specific test cell lines
Since bioactive glass surfaces provide a substrate (surface roughness, porosity, etc.)
coupled with surface reaction layer chemistries (e.g., controlled release of ionic dissolu-
tion products and doped growth factors, adsorption of growth factors added to culture
medium) to control cell growth and differentiation, bioactive surfaces, and their disso-
lution products are tested using either qualitative or quantitative approaches listed in
Table 9.10.
*
The width of a DNA molecule is loosely used as a measure of resolution, because it has a known diameter of
2.0 nm.
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