ADDITIVE MANUFACTURING FOR BONE LOAD BEARING APPLICATIONS - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 245

FIGURE 11.8
(a) Bulk porosity characteristics and compressive strength measurements of cylindrical samples with small, large,
and dual particle size composition, with ( p < 0.05). For each trial, ( n = 10). (*) Illustrates Tukey HSD statistical
pairwise similarity. (b) Sintered samples with large, small, and dual powder composition.
11.6 NANOCOMPOSITE BONE SUBSTITUTES
11.6.1 NANOMATERIALS, LIMITATIONS, AND OPPORTUNITIES
Bone is inherently a nanocomposite, which serves as a mechanical support to the body and also a res-
ervoir for essential minerals ( James et al., 2011; Murugan and Ramakrishna, 2005 ).There have been
many studies on the development of synthetic bone substitutes such as ceramic-based and polymer-
based materials. In addition to certain requirements of these materials like high mechanical strength,
biodegradability, and biocompatibility, they should be shaped into 3D porous structures to fit into the
defected part of the bone. Osteoconductivity of the scaffolds is of great importance since it determines
the rate of osteoblast cell infiltration and proliferation. The scaffolds should also be degraded with a
similar rate to the bone healing process and the yield of degradation must not provoke immune re-
sponses in the body. Commonly, all these requirements are not obtained through a single-phase mate-
rial and there is a significant need for the development of multiphase materials (i.e. composites with
similar physical and structural properties to bone). Bone is composed of a nanocomposite known as
ECM which consists of an organic matrix, osteoid, and an inorganic phase as reinforcement. Fibrous
protein and collagen are the main components of the organic matrix, whereas the inorganic phase is
mainly made of carbonate-substituted hydroxyapatite (HA) crystals. The mineral is not pure HA and
some traces of magnesium, carbonate, and zinc elements are mostly detected in the structure. In addi-
tion, calcium-to-phosphorous ratio is not constant and might undergo significant variations at the same
bone site, but in different populations or age groups ( Rogel et al., 2008; Crystals et al. 2006 ).
For bone grafting, ceramic materials, such as calcium phosphates and hydroxyapatite, are conven-
tionally employed as fillers and coatings. Although they provide good osteoconductivity, their scaffolds
are brittle and undergo detrimental failure under load. They also suffer from slow biodegradability,