Using synthetic bioresorbable polymers for orthopedic tissue regeneration - Durability and Reliability of Medical Polymers - page 123

scaffolds. 35 the in vitro cell culture revealed that the resulting nanofiber
provided an excellent osteoinductive and osteointegrative environment.
However, one of the major problems with PlGa scaffolds is the lack of
osteoconductivity compared with the current gold standard of allograft. 36 the
use of natural materials to coat the scaffolds used, is expected to increase
osteoblast adhesion and to allow bone to express normal physiological
function. To test this hypothesis, PLGA substrates were modified with
coatings of collagen, chitosan, or N -succinylchitosan, and then used as
scaffolds to evaluate their effects on osteoblast attachment, proliferation,
and differentiation. 37 the results demonstrated that the pore size did not
affect the osteoblast phenotype, but there was an increased cell attachment
and proliferation owing to collagen, and an increase differentiation owing
to chitosan and N -succinylchitosan.
these results promoted new strategies for modifying microenvironments
to increase osteoblast adhesion, proliferation and differentiation on PlGa
scaffolds, a strategy that might be useful for tissue regeneration. as a result,
PLGA implants have proven to be versatile, support sufficient cell growth
to be used commercially, and can be readily fabricated into highly porous
scaffolds with different structures and sizes to fit anatomical bone defects. 38,39
furthermore, devices made of amorphous PlGa have not caused clinically
significant foreign body reactions. 15

6.2.4 Comparing poly( a -hydroxy acids)
Copolymers, rather than homopolymers, are preferred for clinical application
and they are thought to be associated with diminished risks of inflammatory
reactions. 15 Polymers based on lactic and glycolic acids are still popular
scaffold materials especially for orthopedic applications, such as bone,
cartilage, and meniscus, as outlined in several reviews. 22,40,41 each of these
polymers, as well as various modifications or combinations of them, are
capable of delivering cells or growth factors to target tissues while also
providing a three-dimensional scaffold for cell function. 42,43
Porous Pla/PGa copolymer has been proposed as a successful
biodegradable matrix for tissue engineering for both bone and cartilage
regeneration and osteoblasts are observed to adhere better to and produce
more extracellular matrix proteins on Pla/PGa copolymer than on other
osteocompatible bioresorbable materials.
Polyesters also have a major disadvantage. Most of them degrade by
a bulk degradation mechanism, 44,45 which leads to the accumulation of
acidic products within the polymer bulk that can cause late non-infectious
inflammatory responses when released in a sudden burst upon structure
breakdown. 46 An inflammatory response to poly( a -hydroxy acids) was also
found to be triggered by the release of small particles during degradation

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