Page 239 - Biodegradable Polyesters

9.1 Tissue Engineering in Medicine and the Polymeric Materials Needed 217

(a) (c)

(b) (d)

Figure 9.2 Schematic scaffold with living into pores of the scaffold, and (d) cell colo-
cells on it: (a) cell culture medium where nize pores and creates its own extra cellular
O and nutrients supplied from liquid cell matrix (the arrows show the direction of O 2
2
culture medium, (b) cell seeded onto scaf- and nutrients supply).
fold, (c) proliferation and migration of cells
and Drug Administration (FDA) of the United States for certain applications
and were readily processable into a variety of shapes and forms using melt and
solvent techniques [8]. The polymers that degraded by hydrolysis leaving natural
metabolic intermediates and the resorption rates could be designed to vary
from months to years depending on the ratio of the monomers. In addition, the
polymers could potentially be manufactured to provide controlled release of
hormones and growth factors.
In addition to the chemical properties of the material, physical properties such
as surface area for cell attachment are essential. Various methods of creating pores
in these materials to increase surface area are used. Scaffolds formed using differ-
ent techniques, including fiber bonding, solvent casting/particulate leaching, gas
foaming, and phase separation are known, which result in different porosity, pore
size, and promotion of tissue growth [9].
To achieve the goal of tissue reconstruction, scaffolds must meet some specific
requirements. A high porosity and an adequate pore size are necessary to facili-
tate cell seeding and diffusion throughout the structure of both cells and nutri-
ents. Biodegradability is often an essential factor as scaffolds should preferably be
absorbed by the surrounding tissues without the necessity of surgical removal. The
rate at which degradation occurs has to coincide as much as possible with the rate
of tissue formation: this means that while cells fabricate their own natural matrix
structure around themselves, the scaffold is able to provide structural integrity