Strategies for the chemical analysis of highly porous bone scaffolds using secondary ion mass spectrometry

Understanding the distribution of critical elements (e.g. silicon and calcium) within
silica-based bone scaffolds synthesized by different methods is central to the optimization of
these materials. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used to
determine this information due to its very high surface sensitivity and its ability to map all the
elements and compounds in the periodic table with high spatial resolution. The SIMS image
data can also be combined with depth profiles to construct three-dimensional chemical maps.
However, the scaffolds have interconnected pore networks, which are very challenging
structures for the SIMS technique. To overcome this problem two experimental methodologies
have been developed. The first method involved the use of the focused ion beam technique to
obtain clear images of the regions of interest and subsequently mark them by introducing
fiducial marks; the samples were then analysed using the ToF-SIMS technique to yield the
chemical analyses of the regions of interest. The second method involved impregnating the
pores using a suitable reagent so that a flat surface could be achieved, and this was followed by
secondary ion mapping and 3D chemical imaging with ToF-SIMS. The samples used in this
work were sol–gel 70S30C foam and electrospun fibres and calcium-containing silica/gelatin
hybrid scaffolds. The results demonstrate the feasibility of both these experimental
methodologies and indicate that these methods can provide an opportunity to compare various
artificial bone scaffolds, which will be of help in improving scaffold synthesis and processing
routes. The techniques are also transferable to many other types of porous material.