Biomedical Engineering Reference
In-Depth Information
therapeutic systems in order to replace the nonbiodegradable materials.
This evolution is aimed at helping injured tissues or repairing diseased tis-
sues with delivery of pharmaceutical and bioactive molecules to enhance
tissue regeneration [71]. Both synthetic- and naturally-derived biodegrad-
able polymeric materials have been investigated as biomaterials for bone
tissue regeneration and reconstruction. The most common degradable
polymeric materials used as matrices for polymer nanocomposites prepa-
ration (Table 5.2) for bone tissue engineering application is described in
the following sections.
5.4.1
Synthetic Biodegradable Polymers and Nanocomposites
Synthetic biodegradable polymers are attractive candidate materials for
biomedical applications such as drug delivery devices, orthopaedic fi xa-
tion devices and different types of tissue engineering scaffolds [72, 73].
The materials include poly(lactic acid) (PLA), poly(glycolic acid) (PGA),
poly(dioxanone) and poly(caprolactone) (PCL), and their copolymers have
been accepted worldwide for use as medical devices [72]. The other impor-
tant synthetic biodegradable polymers which are currently used in biomed-
ical applications are polyphosphazenes, polyanhydrites, and poly(amino
acids). However, the polyester-based materials have shown signifi cant
prospects and, therefore, the next section will focus on the preparation of
polymer nanocomposites using PLA, PCL, PGA and their copolymer as
matrix materials. Synthetic biomaterials are generally biologically inert and
have more predictable properties than natural polymers. For applications
like bone tissue regeneration, the material should have a certain level of bio-
logical activity, therefore strategies have been developed to incorporate bio-
logical motifs such as HAp and TCP nanoparticles into the polymer matrix.
5.4.1.1
Poly(Lactic Acid) Nanocomposites
The poly(L-lactide) (PLLA) is a semicrystalline and bioresorbable poly-
mer, and the resorption kinetics of PLLA is different from that of poly(D,L-
lactide) (PDLLA). It requires more than 2 years to be completely resorbed
[73]. PLLA exhibits a wide range of suitable properties including high
mechanical strength, low elongation, and high values of the following:
modulus, stiffness, chemical and impact resistance, good wear and fric-
tion. All these properties make PLLA a better candidate material than
amorphous polymers for load-bearing orthopaedic applications [73-76].
Many researchers have reported that the bioactivity of PLA-based mate-
rials for bone fracture repair can be enhanced by incorporation of HAp
nanoparticles into the matrix. The reports provided details of sample
preparation protocols, mechanical properties, interface structure, biocom-
patibility and biodegradability of the PLA-HAp nanocomposites [74-82].
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