Biomedical Engineering Reference
In-Depth Information
37.1 Introduction
Bone is composed of osteocytes surrounded by a rigid, highly cal-
cified organic matrix. Although bone has good mechanical proper-
ties, it often undergoes damage or suffers defects resulting from
tumor reconstruction, chronic infection, or traumatic bone loss.
There is a great need therefore for bone graft materials for vari-
ous bone applications. Autologous bone grafting is widely accepted
as the gold standard for the treatment of bone defects.
1
However,
the supply of autografts is limited and donor site morbidity is also
a concern along with the required prolonged operation times.
2
The
alternative of allogeneic bone has potential risks of disease trans-
mission and infection.
3
In order to avoid the problems associated
with either autologous or allogeneic bone grafts, many synthetic
bone graft materials, such as titanium alloy, ceramics, and poly-
mers, have been used as bone-substitute materials during the past
decades.
4
However, these substitute matrices have specific disad-
vantages in biocompatibility, degradability, osteogenic capability,
and histochemical responses by the host tissue. It became neces-
sary to find a promising alternative of autogenous bone for graft-
ing indications. Bone tissue engineering is a recently developed,
exciting approach for the repair of bone defects.
5
,
6
Recently, stud-
ies of three-dimensional scaffold materials have become a crucial
element of bone tissue engineering. The three-dimensional scaf-
fold materials were designed to mimic one or more of the bone-
forming components of autografts, in order to facilitate the growth
of vasculature into the material, and provide an ideal environment
for bone regeneration.
7
-
9
Therefore, as a surrogate of the natural
bone, an ideal bone tissue engineering scaffold should simulate
both the components and the structure of natural bone. Previous
studies have revealed that natural bone is a representative exam-
ple with a typical hierarchically ordered organization. Bone tissues
are mainly constructed from nanosized hydroxyapatite (HA) crys-
tals and a collagen framework in which the crystals form, resulting
in a highly complex but ordered mineral-organic composite mate-
rial by self-assembling.
10
In this paper we have used the concept
of self-assembling defined by Whitesides and Grzybowski,
11
that
is, self-assembling is the autonomous organization of components
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