Modeling and Numerical Analysis of a Cervical Spine Unit - Biologically Responsive Biomaterials for Tissue Engineering - page 147

Fig. 7.8 3D views of the core and shell bodies

The error number is usually proportional with several factors: the native number of
points, smoothness of the mesh, geometrical dimensions, and complexity of the
geometry. Due to these factors, the inner solid experiences more errors than the
outer solid.
Using the surface module of the software, the inadequate surfaces were erased or
modified. The manual procedure consists of the following steps:

• Erasing the inadequate surfaces

• Drawing a 3D spline to divide a large inadequate surface into smaller good

ones
Replenishing the empty surfaces •

This task can also be automatically done but with less chances of success, the
simple vertex repositioning being not enough. When all the surfaces from both vol-
umes were enclosed, the conversions into solid bodies were automatically made.
In the next stage the two solids were combined in one part by matting their ori-
gins as coincident. Using Boolean subtraction method, the inner body (core) was
eliminated from the outer solid, having as result a new shell body. In this way, the
core and the shell bodies were created (see Fig. 7.8 ).
The reason of having two solids rather than one is obvious: the core corresponds
to the spongy vertebral bone, and will get the spongy bone properties, whereas the
shell corresponds to the cortical bone, and will get suitable properties.
The desired multi-solid body represents the assembly of the core and shell solids.
For relative positioning of the bodies the origins were set as coincident. This opera-
tion was possible because the origin of the parts is identical. The coincidence of the
origins is derived from the reconstruction stage, where the point clouds were
exported from the same processed images. The multi-solid body of the cervical
vertebra is presented in Fig. 7.9 .
The reconstruction stages of the cervical vertebra can be extended to any ele-
ments of the human body. The required conversion stages from CT images to solid
objects can be synthetically presented as a transformation protocol (see Fig. 7.10 ).