Biomedical Engineering Reference
In-Depth Information
Ultimately, the most desirable starting material for cellular therapies is a tissue-specific
stem cell whose rate of self-renewal and commitment to differentiation can be controlled.
Further, if such a source could be made nonimmunogenic, most of the problems associated
with tissue procurement would be solved. The variability in the tissue manufacturing
process would be reduced and would make any quality assurance (QA) and quality control
(QC) procedures easier.
Cryopreservation
The scientific basis for cryopreservation involves several disciplines, including basic
biophysics, chemistry, and engineering. Current cryopreservation procedures are clinically
accepted for a number of tissues, including bone marrow, blood cells, cornea, germ cells, and
vascular tissue. Recent experience has shown that, in general, the same procedures cannot be
applied to human cells that have been grown ex vivo. New procedures need to be developed
and implemented. Any cryopreservation used in existing cellular therapies that rely on
ex vivo manipulation call for freezing the primary tissue prior to the desired manipulation.
6.6 FUTURE DIRECTIONS: FUNCTIONAL TISSUE ENGINEERING
AND THE “-OMICS” SCIENCES
6.6.1 Cellular Aspects
Some cell populations that are to be transplanted may contain subpopulations of
unwanted cells. The primary example of this is the contamination of autologously harvested
hematopoietic cell populations with the patient's tumor cells. Ideally, any such contamination
should be removed prior to transplantation. Similarly, many biopsies are contaminated with
accessory cells that may grow faster than the desired parenchymal cells. Fibroblasts are a
difficult contaminant to eliminate in many biopsies, and they often show superior growth
characteristics in culture. For this reason, it is difficult to develop primary cell lines from
many tumor types.
6.6.2 Functional Tissue Engineering
Tissue engineering is distinguished from cell biology by the focus on the emergent func-
tion that arises from the organization of large numbers of cells into higher-order structures,
variously called
, depending on the level of anatomical complexity and
structural integration. The reengineering of complex human anatomical structures such as
limbs or organ systems is by definition a systems-engineering problem. Though it can be
argued that all tissue functions arise from fundamental cellular mechanisms, the system-
level organization of tissues and organs confers function that is not possible to achieve with
individual cells or masses of unorganized cells in a scaffold. A pile of bricks does not provide
the functionality of a house, nor does a crate full of car parts function like an automobile.
Analogously, engineered tissues must be viewed at the systems level, and the success or
failure of the engineering effort ultimately rests upon a quantitative assessment of the
organ-level function of the engineered tissue or organ. The use of molecular biological
tissues
or
organs
