Biomedical Engineering Reference
In-Depth Information
features such as pore shape, pore wall morphology and interconnectivity
between pores of the scaffolding materials are also suggested to be
important for cell seeding, migration, growth, mass transport and tissue
formation (Ma, 2004).
Natural scaffolds made from collagen are fast being replaced with
ultraporous scaffolds made from biodegradable polymers. Biodegradable
polymers are attractive candidates for scaffolding materials because they
degrade as new tissues are formed, eventually leaving nothing foreign in the
body. The major challenges in scaffold manufacture lie in the design and
fabrication of customizable biodegradable constructs with desirable proper-
ties that promote cell adhesion and cell porosity, along with mechanical
properties that match the host tissue with predictable degradation rate and
biocompatibility (Ma, 2004; Mohanty et al., 2000; Langer and Vacanti,
1993).
The biocompatibility of the materials is imperative. The substrate
materials should not elicit an inflammatory response nor demonstrate
immunogenicity of cytotoxicity. The scaffolds must be easily sterilizable in
both surface and bulk to prevent infection (Gilding and Reed, 1979). For
scaffolds used in bone tissue engineering, a typical porosity of 90% with a
pore diameter of ca 100
m is required for cell penetration and a proper
vascularization of the ingrown tissue (Karageorgiou and Kaplan, 2005).
Another major class of biomaterials for bone repair is bioactive ceramics
such as HA and calcium phosphates (Kim et al., 2004; Hench, 1998). They
show appropriate osteoconductivity and biocompatibility because of their
chemical and structural similarity to the mineral phase of native bone, but
are inherently brittle and have poor shape ability. For this reason, polymer/
bioactive ceramic composite scaffolds have been developed for applications
in bone tissue engineering. They exhibit good bioactivity, manipulation and
control microstructure in shaping to fit bone defects (Zhang and Ma, 1999).
μ
17.3 Synthetic biopolymers and their nanocomposites
for tissue engineering
The extensive research literature on nanocomposites (e.g. polymer/layered
silicate) is covered in several reviews (e.g. Okada and Usuki, 2006; Gao,
2004; Sinha Ray and Okamoto, 2003b; Alexandre and Dubois, 2000). The
study of nanocomposites has gained momentum. This new class of materials
is now being introduced in structural applications such as gas barrier films,
flame retardant products and other load-bearing applications (Okamoto,
2006a). Among these nanocomposites, biopolymer-based nancomposites or
green nanocomposites are considered to be a stepping stone towards a
greener and more sustainable environment. Green nanocomposites are
