Tissue engineering - Orthopaedic Biomaterials in Research and Practice - page 235

regenerative medicine/engineering
While tissue engineering is more clearly defined, regenerative medicine
is more difficult to differentiate from tissue engineering and to define.
It is widely characterized as a field where stem cells drive embryonic
formation, or where inductive organizers induce a blastema to regenerate
a tissue, ultimately aimed at reforming damaged tissues and organs in
humans. Regenerative medicine concerns itself primarily with stem cell
plasticity and cloning, when nuclear transfer, transdifferentiation, and
cell fusion are measures to modulate the stem cell differentiation path-
way. Experiments in the cloning of animals, such as frogs, lambs, and
sheep, have shown how genetic material from an adult cell can be used to
re-express every gene to build an entirely new animal. However, the pos-
sibility of cloning humans raises extreme ethical concerns. Commercial
development has been inhibited by inefficiencies in the cloning process
owing to problems with reprogramming a cell's DNA in the search for
new eggs. During cloning, an adult nucleus is implanted into an egg,
which must erase the adult genome's epigenetic marks in order to re-
express them. The addition of chemicals or proteins to adult cell nuclei
to bypass the need for eggs may help accelerate development in this field.
Regenerative medicine, sometimes known as reparative medicine, is
also defined as the regeneration and remodeling of tissue in vivo for the
purpose of repairing, replacing, maintaining, or enhancing organ func-
tion, and the engineering and growing of functional tissue substitutes in
vitro for implantation in vivo as a biological substitute for damaged or
diseased tissues and organs.
Genetic engineering
Genetic engineering has also been used to describe some aspects of tis-
sue engineering. Genetic engineering is a process in which recombinant
DNA technology is used to produce certain desirable traits into organ-
isms. For example, a genetically engineered animal is one that contains a
recombinant DNA construct producing a new trait. Conventional breed-
ing methods have been used to produce more desirable traits in animals,
but genetic engineering is a much more targeted and powerful method
of introducing desirable traits. The first known experiments in genetic
engineering brought engineered human insulin in the late 1970s. Since
then, there has been work to create animal models of human diseases,
as well as gene therapy where defective human genes are replaced with
functional copies.
In simple terms, the first step in the genetic engineering process is to
isolate the selected gene that is intended for insertion into an organism.
There are two options for isolation. The first uses restriction enzymes to
cut the DNA into fragments and gel electrophoresis to separate them out
according to length. An alternative employs polymerase chain reaction
to amplify up a gene segment, which can then be isolated through gel
electrophoresis. If the DNA sequence of the gene is known, then it can