Effect of Hydration on Physicochemical Properties of End-Capped PLGA

Abstract

The objective of this study was to assess the physicochemical effects of hydrating a hydrophobic end-capped poly(lactide-coglycolide) (PLGA) polymer in the liquid and vapor state. PLGA RG503 polymer was incubated at 37 ∘ C in 0.5% polyvinyl alcohol (PVA) solution and at 90% RH. Samples were withdrawn at predetermined intervals and changes to polymer properties like glass transition temperature (T g ), moisture uptake, molecular weight change, and % acid number were determined using differential scanning calorimetry, Karl Fisher titrimetry, gel permeation chromatography, and acid base titrimetry, respectively. Study results showed that T g was depressed instantaneously upon hydration, indicating that bulk water acted as a plasticizer of hydrophobic end-capped PLGA. T g values decreased to levels below the incubation temperature when hydrated in 0.5% PVA solution but not in 90% RH. The drop in T g exhibited a linear relationship ( 2 > 0.99) to the amount of water uptake by the polymer; higher moisture uptake was noted with liquid water. Removal of moisture from the polymer matrix resulted in recovery of T g , only up to a period of 14 days. Presence of water in liquid or vapor form caused a reduction in molecular weight of the polymer and a corresponding increase in % acid number over the duration of the study.

Potential Roles of the Glass Transition Temperature of PLGA Microparticles in Drug Release Kinetics

“…When PLGA (Resomer RG503H, 50:50, 30 kDa) was exposed to water, T g decreased by about 15 °C within an hour even at room temperature, e.g., 47.7−32.7 °C. 29 Similar results were observed with ester end-capped PLGA (Resomer RG503, 50:50, 38 kDa). The fact that the T g decreases below the body temperature within 1 h (even in 30 min) implies profound changes in the PLGA properties as soon as the drug release process begins.…”

“…If T g - T b < 7 °C, the PLGA formulation will reach an equilibrium in 6 h (Figure ). The T g of PLGA polymers has been shown to decrease by 15 °C in an hour as the polymers absorb water and surfactants. , The T g of PLGA polymers is known to decrease linearly at a rate of 6.03 ± 0.57 °C per mass% of water absorbed . Thus, it is likely that the T g - T b is close to 0 °C, and equilibrium will be reached within an hour.…”

Glass Transition Temperature of PLGA Particles and the Influence on Drug Delivery Applications

“…After incubation in 0.5% PVA solution, the dried PLGA polymer had a T g approximately 15 °C higher than the wet polymer, and T g recovery was achieved upon removing the moisture content ( Figure 8 ). After 14 days’ incubation, lower PLGA chains were found, indicating that degradation of PLGA occurred [ 93 ].…”

“… T g of PLGA under different post-treatment [ 93 ]. Reproduced from D’Souza, S. et al, Advances in Biomaterials 2014, 2014, under Creative Commons Attribution 4.0 International License ( (accessed on 13 February 2022)).…”

Fabrication of Poly(lactic-Co-Glycolic Acid)/Calcium Phosphate Bone Cement Composite: Synthesization of Calcium Phosphate From Crab Shells

“…The quantization of Tg is needed to ensure the Tg of PLGA is not shifted to a temperature lower than the temperature of human body. The CaP/PLGA bone cement composite which composed of PLGA, was soft and viscoelastic [32]. This property was steeply transformed into a glassy state when the temperature reached 45.15 o C. The bone cement composite was then gradually become harder until it reached the Tg peak of 103.38 o C. Heat treatment more than the Tg peak, drastically caused the bone cement composite to melt into a liquid phase.…”