Scaffolds for Tissue Engineering - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 14

behavior, biodegradation kinetics of PLA can be modified by blending. Blends
of PLA with poly(d-lactide) (PDLA) can be used to prepare novel hydrogels and
microspheres for biomedical alpplications (Yu 2009 ). It was reported that drug
delivery system particles were fabricated from l-configured peptides such as insu-
lin with PDLA, PDLA-b-PEG, PDLA-b-PEG/PDLA, PLLA/PDLA or PLLA-
b-PEG/PDLA-b-PEG (Yu 2009 ).
As biodegradable PHB is very brittle and prone to thermal degradation, in order
to improve its mechanical properties and processability, blending with another pol-
ymer can be done. There are several reports on the blending of PHB with other
biodegradable polymers including poly(l-lactic acid-co-ethylene glycol-co-adipic
acid) (Yoon et al. 1996 ), PCL (Kumagai and Doi 1992a ), PHBV (Kumagai and
Doi 1992b ). The properties and biodegradability of polymer blends containing
either PHB or PHBV was reviewed by Verhoogt and co-workers (Verhoogt et al.
1994 ).
The spherulitic structure, growth rate and melting behavior of blends of PHB
and PLA using polarized light microscopy were studied and the results indicated
that low-molecular weight PLA (M n = 1,759) was miscible in the melt whereas a
blend of high molecular weight PLA (M n = 159,400) with PHB exhibited bipha-
sic separation (Blümm and Owen 1995 ).
Blends of PLLA with two kinds of PHB with different molecular weights were
prepared by Park and co-workers by the solvent casting method (Park et al. 2004 ).
It was reported from DSC analysis that the system was immiscible over the entire
composition range. It was also found that the mechanical properties of all the sam-
ples were improved. A good interfacial adhesion between two polymers and the
reinforcing role of PLLA components led to enhanced mechanical properties to
the PLLA content (Park et al. 2004 ).
It was reported that the presence of a second component in the blend with
PHBV, whatever its chemical nature, is sufficient to perturb the crystallization
behavior of highly crystalline PHBV and enhance hydrolytic degradation (Renard
et al. 2004 ). The introduction of polar carboxylic groups in side-chains led to an
increase in the degradation rate as carboxylic groups promote water penetration
into the polymer (Renard et al. 2004 ).
1.4.4 Composites
Composite materials are solids containing two or more distinct constituent
materials or phases on a scale larger than the atomic (Park and Bronzino 2003 ).
Composite materials usually exhibit controllable mechanical properties such as
stiffness, strength, toughness etc. Ceramic/polymer composites exhibit the best
characteristics of each constituent, i.e. the toughness of polymer and stiffness of
ceramic. Artificial ceramic/polymer composites are usually produced as analogue
biomaterials for bone substitute as natural bone is a collagen/apatite composite.
Synthetic polymer/naturally derived polymer composite scaffold composed of