Biomedical Engineering Reference
In-Depth Information
2.1 Introduction
Hierarchical assembly of nanofi brils is ubiquitous in many biological tis-
sues such as bone, muscle, and intestine, which plays important roles in
enabling these tissues to perform specialized functions. Bone, for example,
is made up of hierarchically assembled mineralized collagen fi brils with
a precisely ordered organization of crystals of the mineral hydroxyapatite
(Ca 10 (PO4) 6 (OH) 2 , HA) in and around collagen matrix. The hierarchical
assembly of natural bone has been thought to be due to its unique per-
formances, including excellent intensity and toughness. Therefore, many
efforts have concentrated on the thorough understanding of the processes
and mechanisms involved in the formation of the unique architectures.
These investigations have not just improved our understanding of colla-
gen-mediated biomineralization in calcifi ed tissues, but have also offered
new ideas in the design and fabrication of new functional materials with
biomimetic strategies.
Large bone defects, which are mostly caused by trauma, tumors or dis-
eases, are quite common problems in a clinical setting with a high demand
for bone substitutes. Current therapies of bone replacement include the use
of autograft, allograft, or artifi cial bone material. Although autologous bone
grafts are widely recognized as the “gold standard” for healing large bone
defects, autologous transplantation in a clinical setting is limited because
of the limited graft quantity, donor site morbidity and infection or pain to
patients from secondary surgery [1, 2]. As for allografts, the main problem is
the potential risk of transmitting diseases and the immunological response
[3]. Therefore, it is quite necessary and crucial to develop a promising alter-
native to autografting and allografting. As we all know, many kinds of bone
graft substitutes, such as HA, bioactive glass ceramics and poly(methyl
methacrylate), have been developed and widely used for bone replacement
and bone defect fi lling. However, these bone materials are not biodegrad-
able or bioactive and do not match the requirements of bone regeneration
and remodeling as permanent implantations. In recent years, bone tissue
engineering has made great progress in large bone defects repair by creat-
ing novel artifi cial constructs to direct bone regeneration [4]. And the design
and fabrication of synthetic biomaterials are the crucial elements of bone
tissue engineering. According to biomimetic strategies, HA and collagen, as
the main components of natural bone, have been consequentially applied
for the synthesis of artifi cial bone materials [5-8]. In this sense, the most
promising approach for bone regeneration is to realize a real bioactive arti-
fi cial bone material mimicking the compositions, hierarchical organization,
and biological functions of bone tissues.
In this chapter, we will highlight the current understanding of the
microstructures and hierarchical organization of mineralized collagen
fi brils in calcifi ed tissues, as well as recent work involving biomimetic
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