Biomedical Engineering Reference
In-Depth Information
cells
Tissue defect
Scaffold
Release carrier of
growth factor
FIGURE 14.2
Schematic illustration of tissue regeneration based on principle of tissue engineering.
materials for bone tissue engineering because it is well recognized that they are compatible to natural
bone tissue and osteoconductive
[5,6]
. However, HAp is not practically degraded under physiological
conditions and remains inside the regenerated bone tissue. Therefore, as one trial to control the
in-
vivo
degradability, the HAp is combined with organic materials, such as collagen or glycolide-lactide
copolymers
[7]
. The combination is effective in manipulating the biodegradability and mechanical
properties of the HAp scaffolds. On the other hand, β-TCP is advantageous from the viewpoint of
the biodegradability, although brittle compared with HAp. Several requirements should be considered
in the design of three-dimensional scaffolds for bone tissue engineering. Firstly, the scaffold should
have sufficient porosity for cell proliferation, differentiation, and ingrowth, resulting in promoted
bone regeneration. Higher porosity (e.g., more than 90%) is important for scaffolds to be suitable for
promoting bone regeneration. The pore size is one of the key factors for the scaffold design. It has
been reported that the pore size ranging between 150 and 400 μm is preferable for the bone regen-
eration
[8]
. High interconnectivity between the pores is also desirable for homogenous cell seeding
and distribution, oxygen and nutrient supply, and excretion of metabolic waste from the cell-scaffold
constructs. It has been widely accepted that the cell-scaffold interaction is greatly influenced by the
porous structure of the scaffold. In addition, the scaffold requires suitable surface properties because
the cell behavior is greatly influenced by roughness, topography, wettability, charge, and chemical
composition of scaffold surface.
Figure 14.2
indicates tissue regeneration based on the principle of
tissue engineering.
14.3
GROWTH FACTORS
Tissue engineering is designed to regenerate natural tissues or create biological substitutes for defec-
tive or lost organs by making use of cells. Considering the usage of cells in the body, there is no
doubt that sufficient supply of nutrients and oxygen to the transplanted cells is vital for their survival
and maintenance of function, otherwise, only a small number of cells pre-seeded in the scaffold or
migrated into the scaffold from the surrounding tissue would survive. Rapid formation of a vascular
network at the transplanted site of cells is promising to provide cells with the vital nutrient and oxy-
gen supply. This process of generating new microvasculature, termed neovascularization, is a process
