Biomimetic Synthesis of Self-Assembled Mineralized Collagen-Based Composites for Bone Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 41

critical to control bone formation in three dimensions (3D) using the bone
tissue engineering approach. The 3D scaffold materials were designed to
mimic the bone-forming components of autograft, in order to facilitate the
growth of vasculature into the material, and provide an ideal environment
for bone formation [79-81]. Many researchers have fabricated HA and
collagen composite by mixture or self-organization, followed by cross-
linkage or uniaxial pressing to develop a large size material [82, 83].
Du et al. has developed a bone-like nano-hydroxyapatite/collagen
(nHAC) composite by mineralizing the type I collagen sheet [64, 84].
This material is bioactive and biodegradable. However, its mechanical
properties are too weak for practical application. In order to improve the
mechanical strength and the forming ability of the material, a new bone
tissue engineering scaffold material, nano-HA/collagen/poly(lactic acid)
(nHAC/PLA) has been developed base on mineralized collagen fi brils
[85, 86]. First, the collagen molecules and nano-HA are assembled into
mineralized fi brils. Next, the mineralized collagen fi brils are assembled
into parallel fi bril bundles aligned along their longitudinal axis. The fi bril
array patterns also show the same pattern as seen in bone. The assembled
mineralized collagen fi brils are found to distribute uniformly in the PLA
matrix. The freeze-drying technique is used for keeping the nHAC compo-
nent as initial status on the fi nal in-patient use [86]. The material is similar
to natural bone in main composition and hierarchical microstructure. On
the histological level, interconnecting porous structure of the natural bone
also can be found in the top hierarchical level of the nHAC/PLA scaffold
composite. The suitable macroporous structure is important in order to
obtain good implant incorporation through rapid vascularization, bone
ingrowth and possible remodeling. In addition, the surface of composite
gradually appeared smoother by biodegradation which is benefi cial for
the cells spreading out. This composite, combined with high compatibility
and high strength, provides a promising scaffold in both traditional bone-
defect repair and in bone tissue engineering.

2.4.1.2 Injectable Bone Cement: Nano-HA/Collagen/Calcium Sulfate

Hemihydrate (nHAC/CSH)

The solid block is diffi cult to carve into the appropriate shape for irregu-
lar bone defects. Therefore, handling of this material in a clinical setting
would be diffi cult, particularly when it is used in augmenting bony sur-
faces [87]. Mixture of calcium sulfate hemihydrates (CaSO 4 ·1/2H 2 O, CSH)
and nHAC could form moldable cement that greatly enhance the han-
dling characteristics. CSH itself has a long clinical history as a bone graft
substitute, known as plaster or gypsum for its self-setting ability in situ
after fi lling the defect, the lack of infl ammatory response, or the promo-
tion of bone healing [88-91].