Biomedical Engineering Reference
In-Depth Information
16.1 Introduction
Recently, numerous biodegradable polymeric biomaterials have
been employed for devices for orthopedic surgery, scaffolds for
tissue engineering, and vehicles for the drug delivery system.
Implanted biomaterials and drug delivery vehicles have been
reported to induce sequential events of immunologic reactions in
response to injury caused by implantation procedures and result in
acute inflammation marked by a dense infiltration of inflammation-
mediating cells at the materials-tissue interface.
1
-
5
Prolonged irri-
tations provoked by implanted biomaterials advance acute inflam-
mation into a chronic adverse tissue response characterized by the
accumulation ofdense fibrotic tissue encapsulating the implants.
3
PLGA is a member of a group of poly(
α
-hydroxy acid) that is
among the few synthetic polymers approved for human clinical
use by the Food and Drug Administration (FDA). Consequently, it
has been extensively used and tested for scaffold material as a
bioerodible material due to good biocompatibility, relatively good
mechanical property, lower toxicity, and controllable biodegradabil-
ity. It has been clinically utilized for three decades as sutures, bone
plates, screws, and drug delivery vehicles, and its safety has been
proved in many medical applications.
1
PLGA degrades by non-
specific hydrolytic scission of its ester bonds into their original
monomers, lactic acid and glycolic acid. During these processes,
there is very minimal systemic toxicity; however, in some cases, the
acidic degradation products can decrease the pH in the surround-
ingtissue,whichresultsinalocalinflammatoryreaction andpoten-
tially poor tissue development, as shown in Fig. 16.1.
6
Also, its poor
mechanicalstrength,smallporesize,andhydrophobicsurfaceprop-
erties for cell seeding have limited itsusage.
Currently, biomaterials are endowed with biocompatibility
through three different methods: coating with hydrophilic mole-
cules,modifyingsurfacecharacteristicsusingphysiochemicalmeth-
ods, and impregnating bioactive substances. Previous reports
showed that application of a mineral layer or localized deliv-
ery of an anti-inflammatory agent such as a corticosteroid with
cytokine could effectively suppress inflammation and fibrosis of the
implant.
7
Although the methods of such studies are experimentally
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