Scaffolds for Tissue Engineering - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 5

bone defects are autologous bone grafts, autogenous bone grafts or alternatively
metals and ceramics. If the bone is taken from another part of the patient's own
body, it is referred as autologous bone grafts. For bone healing and regenera-
tion, autologous bone provides osteogenic cells and essential osteoinductive fac-
tors (Rose and Oreffo 2002 ). It also imparts relatively better chance of success.
Nevertheless, the limitations of autograft tissues are that the availability of this
type of tissues are inadequate for the required applications (Rose and Oreffo
2002 ).
Allografts which refer to tissues taken from some other's body, may introduce
the risks of immunological rejection problem and of transmission of pathogens
from donor to host (Spitzer et al. 2002 ; Yaszemski 2004 ). Another limitation of
allograft is the rate of incorporation of host tissue is commonly lower than that of
autograft.
Potential substitutes to bone grafts could be metals and ceramics (Yaszemski
2004 ). Metals which could offer immediate mechanical support at the defect site
but as it exhibits poor overall integration with respect to the host tissue, may also
fail due to fatigue loading. Ceramics have the disadvantage of brittleness and have
low tensile strength and cannot be applied in the locations such as significant tor-
sion, bending, or shear stress.
1.2.4 Needs for Bone Tissue Engineering
Bone tissue engineering, which is a new strategy, provides a prospective solution
to regenerate bone in a reliable, economical and physiologically acceptable man-
ner and has emerged as an alternative to bone-grafting procedures over the past
decades in order to overcome the various limitations of current grafting procedures
and bone substitute biomaterials (Chen et al. 2006 ). In order to regenerate bone
tissue, there are three key elements: osteogenic progenitor cells, osteoinductive
growth factors and osteoconductive scaffolds (Schieker et al. 2006 ). Scaffolds,
which act as temporary substrate, facilitate necessary support for cells to prolif-
erate and to maintain differentiated function of the cells, are major component
among various strategies such as cell-based and factor-based strategies. In fact, the
applicability and success of bone tissue engineering depends on the performance
of the scaffolds.
1.3 Requirements for Scaffolds for Bone Tissue Engineering
It has been mentioned in ASTM F2150-02 (ASTM 2002 ) that a scaffold is a
support, delivery vehicle, or matrix to facilitate the migration, binding, or trans-
port of cells or bioactive molecules that is used to replace, repair, or regenerate