Biomedical Engineering Reference
In-Depth Information
13.4.2.1.1 POLY(GLYCOLIC ACID) ( PGA ). PGA, a polymer of glycolic acid
(GA), is highly crystalline and degrades relatively faster within the body due to its
hydrophilic nature. However, the rates of degradation depend on the molecular
weight, size, and surface area of the scaffold made of PGA [157]. The degradation
product of PGA is glycolic acid, which can at times be a limiting factor due to its
acidic nature. Nevertheless, PGA is desirable in many biomedical applications
such as surgical sutures due to its high tensile strength, biocompatibility and
biodegradability [158]. High crystallinity of PGA limits its solubility in organic
solvents, the only exception being highly fl uorinated compounds such as 1,1,1,3,3,3
hexafl uoro-2-propanol (HFP). Boland et al. used the aforementioned solvent
system for successful electrospinning of PGA and obtained fi bers in the range
of 0.22
m at concentrations of 67-mg/mL PGA concentration and
143-mg/mL PGA concentration, thereby demonstrating the dependence of fi ber
diameter on polymer concentration [159].
μ
m to 0.88
μ
13.4.2.1.2 POLY(LACTIC ACID) (PLA). A polymer of lactic acid (LA), PLA is
well known for its hydrophobicity, biocompatibility and biodegradability.
Even though it is a crystalline polymer like PGA, its hydrophobicity enables
relatively slower degradation rates. Unlike PGA, PLA is soluble in a variety of
organic solvents due to the presence of an additional methyl group that also
renders its hydrophobicity. High mechanical strength of PLA favors its potential
application in load bearing applications. The variation in properties of PLA (both
physical and chemical) is due to the presence of methyl group on the alpha carbon
of lactic acid. Thus, the possible variations are poly (L-lactic acid) (PLLA),
poly(D-lactic acid) (PDLA) and poly(DL-lactic acid) (PDLLA). Poly(DL-lactic
acid) (PDLLA) is amorphous with low mechanical strength as compared to the
D- and L-forms of PLA. Dong et al. reported the synthesis of PDLLA fi bers
and demonstrated that N, N-dimethyl formamide (DMF) was a better solvent
than acetone for the electrospinning of PDLLA [160]. In addition, they studied
the role of an additive-triethylbenzylammonium chlorate (organic salt) and
demonstrated that the fi ber diameter decreased from 500 nm to 100-200 nm
following the addition of an organic salt due to the increased conductivity of the
solution [160] .
13.4.2.1.3 POLY(LACTIC - CO - GLYCOLIC ACID) ( PLGA ). PLGA is a copoly-
mer of LA and GA with its degradation rates and mechanical properties amena-
ble for tailoring by altering the ratio of LA and GA. The rate of degradation of
the copolymer can be decreased by increasing the glycolic acid content and can
be increased by increasing the lactic acid content. PLGA is one of the most com-
monly used polymers in tissue engineering as it supports cell adhesion and prolif-
eration, in addition to being biodegradable and biocompatible. A study by Katti
et al. demonstrated the infl uence of various parameters like polymer solution
concentration, orifi ce diameter, and voltage on the morphology and diameter of
electrospun PLGA nanofi bers using THF : DMF (1 : 1) as the solvent system [82] .
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