Thursday, 18 April 2019

Terahertz Spectroscopy: An investigation of the Structural Dynamics of Freeze-Dried PLGA Microspheres

Hooper, Philippa J., Gabi Kaminski, and J. A. Zeitler. "Terahertz Spectroscopy: An investigation of the Structural Dynamics of Freeze-Dried PLGA Microspheres." (2019).
Biodegradable poly lactic-co-glycolic acid (PLGA) microspheres can be used to encapsulate peptide and offer a promising drug delivery vehicle. In this work we investigate the dynamics of PLGA microspheres prepared by freeze-drying and the molecular mobility at lower temperatures leading to the glass transition temperature, using temperature-variable terahertz time-domain spectroscopy (THz-TDS) experiments. The microspheres were prepared using a water-in-oil-in-water (w/o/w) double emulsion technique and subsequent freeze-drying of the samples. Physical characterisation was performed by morphology measurements, scanning electron microscopy (SEM), and helium pycnometry. The THz-TDS data show two distinct transition processes, T<sub>g,β</sub> in the range of 167-219 K, associated with local motions, and T<sub>g,α</sub> in the range of 313-330 K associated with large-scale motions, for the microspheres examined. Using FTIR measurements in the mid-infrared we were able to characterise the interactions between a model polypeptide, exendin-4, and the PLGA copolymer. We observe a relationship between the experimentally determined T<sub>g,β</sub> and T<sub>g,α</sub> and free volume and microsphere dynamics. 
… Terahertz Time-Domain Spectroscopy (THz-TDS) The THz-TDS spectra were acquired using a commercial TeraPulse 4000 instrument across the spectral range of 0.2 − 2.2THz (TeraView, Cambridge, UK). The sample temper …

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