Biomedical Engineering Reference
In-Depth Information
matrix of natural scaffold provides not only a physical support for cells, but also plays an important
role in the cell proliferation and differentiation or cell-mediated morphogenesis. The scaffold of bio-
materials has been designed and prepared for the local environment of tissue regeneration. The scaf-
folds should be biodegradable to disappear from the body and should occur simultaneous with bone
regeneration at the site of defect. In addition, the degradation products should not be toxic and rather
should be cleared by metabolism.
If the surrounding tissue of bone defect has a high potential toward regeneration, bone tissue
will be newly formed in the scaffold implanted into the bone defect by seeded cells or cells infil-
trated from the surrounding tissues. However, when the regeneration potential is very low, bone
regeneration will not always be expected similarly. In this situation, it is practically possible to
utilize growth factors to accelerate the induction of bone regeneration. Recent research develop-
ments in biology and medicine reveal that growth factors play an important role in proliferation
and differentiation of cells
in vitro
and
in vivo
[3]
. However, by direct injection alone of the growth
factor solution into the target site to be regenerated, we cannot always guarantee that the growth
factors will induce tissue regeneration. This is because the growth factors generally have very short
half-lives
in vivo
, since they are rapidly cleared from the site of injection or deactivated enzymati-
cally or by antibodies. Consequently, increased dose quantity and frequency may be necessary for
bone regeneration. This often causes adverse effects. As one trail to efficiently enhance the
in vivo
biological efficacy of growth factors, it is practically possible to make use of drug delivery sys-
tems (DDS). For example, a growth factor can be incorporated into a carrier matrix for controlled
release in order to be applied to the site to be regenerated. It is likely that this delivery system
efficiently enhances the local residence of the growth factor in the target site for a prolonged time
period, resulting in promoted tissue regeneration.
14.2
SCAFFOLDING BIOMATERIALS
Regenerative medicine is an interdisciplinary field that combines engineering and biological sciences
in order to develop techniques that enable the restoration, maintenance, or enhancement of living
tissues and organs. Its fundamental aim is the production of natural tissue with the ability to restore
missing organ or tissue function, which the organism has not been able to regenerate under physi-
ological conditions. This will result in improving the health and quality of life for millions of people
worldwide and to give resolution to the present limitations including rejection of implanted organs,
low quantity of donors, etc.
[4]
. Tissue engineering needs scaffolds to serve as substrates for seed-
ing cells and as a physical support in order to guide the formation of the new tissue. The majority
of the used techniques utilize three-dimensional polymeric scaffolds, which are composed of natural
or synthetic polymers. Synthetic materials are attractive because their chemical and physical proper-
ties (e.g., porosity, mechanical strength) can be optimized for particular applications. The polymeric
scaffolds structures are endowed with a complex internal architecture, channels and porosity that pro-
vide sites for cell attachment, and maintenance of differentiated function without hindering prolifera-
tion. Ideally, a polymeric scaffold for tissue engineering should have the following characteristics: (1)
to have appropriate surface properties that promote cell adhesion, proliferation, and differentiation;
(2) to be biocompatible; (3) to be highly porous, with a high surface area to volume ratio, and
an interconnected pore network for cell growth and flow transport of nutrients and metabolic waste;
