Biomedical Engineering Reference
In-Depth Information
3.4 Yield
Yield can be defined as the number of cells obtained for each medicinal product. GMPs
guidance requires yield validation, but in our experience this can be difficult to perform. In
fact, yield is, more than the other specifications, subjected to variables that make quite
problematic the required standardization. Intrinsic variability due to patient, cartilage
quality or cell growth capacity do not completely depend from operators or process
conditions and cannot be totally controlled. When we started our process we had yield
validation data allowing a cell seeding onto the biomaterial of 1x10
6
cells per cm
2
. Lately,
after more than 90 cultures, this initial specification has been replaced by a range of values:
0.1 ÷ 1.1x10
6
cells per cm
2
. To accept and apply this new yield scale we had to re-validate the
process and the products verifying that each value of the range was able to guarantee the
development of viable and cartilage-like engineered tissues.
Fig. 8. Osteocalcin immuno-staining on engineered constructs (20X). The image from one
representative sample shows that the protein is not present (no red areas were observed
using fast red substrate). Biomaterial fibers are indicated by arrows. Biomaterial fibers are
indicated by arrows.
