Biomedical Engineering Reference
In-Depth Information
onmentally-friendly polymeric materials (Smith, 2005). Biopolymers include
polysaccharides such as cellulose, starch, alginate and chitin/chitosan,
carbohydorate polymers produced by bacteria and fungi (Chandra and
Rustgi, 1998), and animal protein-based biopolymers such as wool, silk,
gelatin and collagen. Naturally-derived polymers combine biocompatibility
and biodegradability. One of the advantages of naturally-derived polymers
is their ability to support cell adhesion and function. However, these
materials have poor mechanical properties. Many of them are also limited in
supply and can therefore be costly (Johnson et al., 2003).
Polyvinyl alcohol (PVA), poly(
-caprolactone) (PCL), poly(lactic acid)
(PLA), poly(glycolic acid) (PGA), poly(hydroxy butyrate) (PHB) and poly
(butylene succinate) (PBS) are examples of polymers of synthetic origin
which are biodegradable (Platt, 2006). In today's commercial environment,
synthetic biopolymers have proven to be relatively expensive and available
only in small quantities, with limited applications that include the textile,
medical and packaging industries. However, synthetic biopolymers can be
produced on a large scale under controlled conditions and with predictable
and reproducible mechanical properties, degradation rate and microstruc-
ture (Platt, 2006; Sinha Ray and Okamoto, 2003a).
One of the most promising synthetic biopolymers is PLA because it is
made from agricultural products. PLA is not a new polymer, but recent
developments in the capability to manufacture the monomer economically
from agricultural products have placed this material at the forefront of the
emerging biodegradable plastics industries.
PLA, PGA and their copolymers, poly(lactic acid-co-glycolic acid)
(PLGA) are also extensively used in tissue engineering for treating patients
suffering from damaged or lost organs or tissue (Ma, 2004; Langer and
Vacanti, 1993). They have been demonstrated to be biocompatible, they
degrade into non-toxic components and have a long history of degradable
surgical sutures with gained FDA (US Food and Drug Administration)
approval for clinical use. PCL and PHB are also used in tissue engineering
research.
The task of tissue engineering demands a combination of molecular
biology and materials engineering since, in many applications, a scaffold is
needed to provide a temporary artificial matrix for cell seeding. In general,
scaffolds must meet certain specifications such as high porosity, proper pore
size, biocompatibility, biodegradability and proper degradation rate (Quirk
et al., 2004). The scaffold must provide sufficient mechanical support to
maintain stresses and loadings generated during in-vitro or
ε
in-vivo
regeneration.
For some of the aforementioned applications, enhancement of the
mechanical properties is often needed (Tsivintzelis et al., 2007). This could
be achieved by the incorporation of nanoparticles, such as hydroxyapatite
