Objectives Thanks to their biocompatibility and biodegradability, poly-lactide (PLA) and poly-(lactide-co-glicolide) (PLGA) are approved by the FDA for human clinical applications and different controlled release formulations, based on these polymers, are actually marketed. Water, acting as a plasticiser, might drastically change polymer features, compromising the performance of the drug delivery system. Experimental PLGA RG502H, RG503H, and RG504H have been casted on CaF2, and analyzed by FTIR in dry and completely wet state. Spectra were collected in the range of 20-70°C. Results For the three dry polymers several vibrational signals located in the 1000- 2000 cm-1 frequency range, show temperature-dependent intensity changes. In particular, the absorbance of the bands ascribed to C=O and O-C-O stretching, CH3 and CH bending, and CH3 rocking modes, plotted as a function of temperature, evidences an inflection point corresponding to the Tg region determined by DSC measurements. Differences between the first and the second heating ramp, due to the cancellation of polymer thermomechanical history, are also observed. The C=O and O-C-O stretching bands of the completely hydrated RG503H sample shift to lower frequencies compared to the signal of dry polymeric films at 20 °C. Moreover, these bands slightly upshift upon temperature rising, downshifting back after subsequent cooling at 20 °C. These findings can be rationalized considering the formation of O-H....O hydrogen bonds between water and PLGA groups and suggest the presence of nonfreezable (bound) water in the completely hydrated polymer. Direct information on water structuring within the polymer matrix are obtained by analysing the O-H stretching region (3100-3700 cm-1). The high intensity detected for the hydrated polymer drastically reduces with increasing temperature due to the loss of freezable (unbound) water. Thus, the OH distribution detected after cooling back the sample at 20 °C, can be ascribed to water molecules which remain trapped into the polymer matrix. Interestingly, this OH band is very broad and partially structured, showing components assigned to OH oscillators involved either in very weak (3600 cm-1) or very strong cooperative (3200 cm-1) hydrogen bonds. Similar features have been observed for hydration water “confined” in a hydrophobic solvent. Conclusions The reproducibility of the data obtained with different PLGA, namely Resomer RG504H, RG503H, and RG502H, confirms the ability of FTIR to detect the glass-to-rubber transition on one side, and investigate the state of water in water/PLGA mixtures on the other.
EFFECT OF TEMPERATURE AND WATER ON POLY(LACTIDE-CO-GLYCOLIDE) INVESTIGATED BY FT-IR SPECTROSCOPY
PAOLANTONI, Marco;BLASI, PAOLO;RICCI, Maurizio;SASSI, Paola
2012
Abstract
Objectives Thanks to their biocompatibility and biodegradability, poly-lactide (PLA) and poly-(lactide-co-glicolide) (PLGA) are approved by the FDA for human clinical applications and different controlled release formulations, based on these polymers, are actually marketed. Water, acting as a plasticiser, might drastically change polymer features, compromising the performance of the drug delivery system. Experimental PLGA RG502H, RG503H, and RG504H have been casted on CaF2, and analyzed by FTIR in dry and completely wet state. Spectra were collected in the range of 20-70°C. Results For the three dry polymers several vibrational signals located in the 1000- 2000 cm-1 frequency range, show temperature-dependent intensity changes. In particular, the absorbance of the bands ascribed to C=O and O-C-O stretching, CH3 and CH bending, and CH3 rocking modes, plotted as a function of temperature, evidences an inflection point corresponding to the Tg region determined by DSC measurements. Differences between the first and the second heating ramp, due to the cancellation of polymer thermomechanical history, are also observed. The C=O and O-C-O stretching bands of the completely hydrated RG503H sample shift to lower frequencies compared to the signal of dry polymeric films at 20 °C. Moreover, these bands slightly upshift upon temperature rising, downshifting back after subsequent cooling at 20 °C. These findings can be rationalized considering the formation of O-H....O hydrogen bonds between water and PLGA groups and suggest the presence of nonfreezable (bound) water in the completely hydrated polymer. Direct information on water structuring within the polymer matrix are obtained by analysing the O-H stretching region (3100-3700 cm-1). The high intensity detected for the hydrated polymer drastically reduces with increasing temperature due to the loss of freezable (unbound) water. Thus, the OH distribution detected after cooling back the sample at 20 °C, can be ascribed to water molecules which remain trapped into the polymer matrix. Interestingly, this OH band is very broad and partially structured, showing components assigned to OH oscillators involved either in very weak (3600 cm-1) or very strong cooperative (3200 cm-1) hydrogen bonds. Similar features have been observed for hydration water “confined” in a hydrophobic solvent. Conclusions The reproducibility of the data obtained with different PLGA, namely Resomer RG504H, RG503H, and RG502H, confirms the ability of FTIR to detect the glass-to-rubber transition on one side, and investigate the state of water in water/PLGA mixtures on the other.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
