The Role of Biodegradable Engineered Scaffold in Tissue Engineering - Biomaterials Science and Engineering - page 154

scale to favor tissue integration and vascularization, (2) be made from material with
controlled biodegradability or bio - resorbability, (3) appropriate surface chemistry to favor
cellular attachment, differentiation and proliferation, (4) possess adequate mechanical
properties to match the intended site of implantation and handling, (5) should not induce
any adverse response and, (6) be easily fabricated into a variety of shapes and sizes (Liu et
al., 2007; Sachlos et al., 2003).
Due to control scaffold degradation and mechanical integrity, cell-scaffold interaction as
well as cell functon, one must have access to a range of materials. Therefore, an appropriate
fabrication method is required with which it is possible to have a structure with different
independent parameters and materials (Yarlagadda et al., 2005).
It is worth to mention that degradation of synthetic polymers, both in vitro and in vivo
conditions, releases by - products. For example, for PLLA releasing Lactic acid during
degradation, causes reducing the pH, which further accelerates the degradation rate due to
autocatalysis which later affects cellular function. (Sachlos & Czernuszka, 2003, as cited
Reed and Gilding, 1981)
In addition to degradation rate and by - products, certain physical characteristics of the
scaffolds must be considered when designing a substrate to be used in tissue engineering
applications. For instance, in order to allow proper cell attachment, the scaffold must have a
large surface area which can be achieved by creating a highly porous polymeric foam. In
these foams, the pore size should be large enough to allow cells to penetrate through the
pores, to maximize nutrient and oxygen diffusion, interstitial fluid and blood flow into the
interior of the scaffold, to manipulate tissue differentiation (Yarlagadda et al., 2005, as cited
Le Huec et al. 1995; Tsuruga et al., 1997). These characteristics (porosity and pore size ) often
depend on the material and method of scaffold fabrication (Mikos&Temenoff, 2000, as cited
Mooney et al., 1999; Nam et al. 2000)
2.2 Decent materials for scaffolds fabrication
In order to have an effective function, an ideal scaffold must possess the optimum structural
parameters, conductivity to the cellular activities leading to neo - tissue formation; these
include cell penetration and migration into the scaffold, cell attachment onto the scaffold
substrate, cell spreading and proliferation and cell orientation. Such scaffold design
parameters are now described with reference to these cellular activities. One of the first
considerations when designing a scaffold for tissue engineering is the choice of material.
The three main material types which have been successfully investigated to be applied in
developing scaffolds include (i) natural polymers, (ii) synthetic polymers, and (iii) ceramics
(Willerth & Sakayama - Elbert, 2007; Radulescu et al., 2007).
2.2.1 Natural materials
Natural polymers commonly derived from protein or carbohydrate polymers have been
used as scaffolds for the growth of several tissue types. In the area of tissue engineering, for
example, scientists and engineers look for scaffolds on which it may successfully grow cells
to replace damaged tissue. Typically, it is desirable for these scaffolds to be: biodegradable,
non - toxic / non-inflammatory, mechanically similar to the tissue to be replaced, highly
porous, encouragement of cell attachment and growth, easy and cheap to manufacture, and
capable of attaching with other molecules (Elmstedt, 2006; Cuy, 2004). Here some examples
of natural polymers that have been previously studied for biomaterials application are
reviewed.