Scaffolds for Tissue Engineering - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 13

derivatives and their combinations (Ratner 2004 ; Wang 2004 ). These inorganic
materials are widely considered to be osteoconductive which means their surface
properties support osteoblastic cells adhesion, growth and differentiation. These
materials have the capacity to bind and concentrate bone morphogenetic proteins
(BMPs) in vivo. Over the past three decades, hydroxyapatite (HA), which is simi-
lar to the mineral component of natural bone, has been extensively studied and
now used for bone tissue repair (Wang 2004 ). Efforts have thus been made to form
non-porous HA/PHB and HA/PHBV composites for bone tissue repair utilizing
the osteoconductive property of HA (Chen and Wang 2002 ). For bone tissue engi-
neering, biodegradable composite scaffolds containing HA appear to hold great
promises.
Tricalcium Phosphate (TCP) is a bioresorbable ceramics which is nonporous
(or porous) resorbable ceramics which are designed to be slowly replaced by bone.
The most frequently encountered TCP polymorphs in the field of bioceramics are
α -and β -TCP (Wang 2004 ). The dissolution rate of TCP was investigated. They
increased in the following order:
HA < β − TCP < α − TCP < TTCP
There are several factors which can cause the biodegradation of calcium phos-
phate ceramics. The rate of biodegradation increases as:
• Surface area increases (powders > porous solid > dense solid)
• Crystallinity decreases
• Crystal perfection decreases
• Crystal and grain size decreases
• Ionic substitutions
It was reported that TCP has slightly higher toughness than HA. It has been
found from most of the reports that TCP is biodegradable and β -TCP has been
accepted and used as a biocompatible, resorbable material for bone repair in the
form of ceramic blocks, granules, and calcium phosphate cements (Wang 2004 ).
1.4.3 Biodegradable Polymer Blends
Blending of biodegradable polymers can improve the performance and reduce
expense. Blends of natural polymers with synthetic polymers can be used to
improve the degradation properties. PLA is biodegradable and non-toxic to
the human body (Ikada and Tsuji 2000 ; Garlotta 2001 ; Albertsson 2002 ; Gupta
et al. 2007 ; Yu 2009 ). PLA possesses high mechanical performance similar to
some commercial polymers such as polyethylene and poly(ethylene terephtha-
late) (PET). Because of good biodegradability and very low toxicity, PLA based
materials have been widely used for biomedical and pharmaceutical applica-
tions such as fixation of fractured bone and matrices for drug delivery systems.
Depending on their applications, the physical properties and biodegradation