Cells and Materials


Back-scattered electron (BSE) imaging allows the visualization and evaluation of mineralized bone structures down to the micrometer range. To produce undecalcified bone sections with adequate structural and surface integrity, bone specimens are usually resin-embedded, followed by cutting, grinding , and polishing procedures. In samples prepared this way, so-called "ultracracks" were detected as black clefts in the lamellar bone matrix by BSE-imaging at magnifications ranging from 1000x to 3000x. By charging phenomena in the secondary electron (SE) mode of the scanning electron microscope (SEM), these clefts can be proven to be open cracks in the sample surface, and thus, as being created after embedding. These "ultracracks" seem to be a swelling effect of the bone matrix when it is exposed to water on the sample surface, followed by shrinking during drying . They did not occur, when water-free preparation techniques, like micromilling, were used and all water contact with the sample surface was avoided. This observation using the BSE-technique in SEM, and the simple method of discrimination between cracks existing before embedding and cracks newly generated during or after embedding, seem important for ultrastructural investigations of mineralized bone tissue, particularly for the evaluation of microcracks after loading or for the study of bone-implant interfaces.