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Terahertz Spectroscopy: An Investigation of the Structural Dynamics of Freeze-Dried Poly Lactic-co-glycolic Acid Microspheres

1
Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, UK
2
Biopharmaceutical Development, AstraZeneca, Granta Park, Cambridge CB21 6GH, UK
*
Author to whom correspondence should be addressed.
Pharmaceutics 2019, 11(6), 291; https://doi.org/10.3390/pharmaceutics11060291
Received: 23 April 2019 / Revised: 30 May 2019 / Accepted: 11 June 2019 / Published: 20 June 2019
(This article belongs to the Special Issue PLGA Based Drug Carrier and Pharmaceutical Applications)
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Abstract

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 characterization was performed by morphology measurements, scanning electron microscopy, and helium pycnometry. The THz-TDS data show two distinct transition processes, T g , β in the range of 167–219 K, associated with local motions, and T g , α in the range of 313–330 K, associated with large-scale motions, for the microspheres examined. Using Fourier transform infrared spectroscopy measurements in the mid-infrared, we were able to characterize the interactions between a model polypeptide, exendin-4, and the PLGA copolymer. We observe a relationship between the experimentally determined T g , β and T g , α and free volume and microsphere dynamics. View Full-Text
Keywords: terahertz spectroscopy; microspheres; drug delivery; formulation development; PLGA; molecular mobility terahertz spectroscopy; microspheres; drug delivery; formulation development; PLGA; molecular mobility
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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    Doi: 10.17863/CAM.40737
    Link: https://doi.org/10.17863/CAM.40737
    Description: All raw data that was acquired for the experiments presented in this manuscript.
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Shmool, T.A.; Hooper, P.J.; Kaminski Schierle, G.S.; van der Walle, C.F.; Zeitler, J.A. Terahertz Spectroscopy: An Investigation of the Structural Dynamics of Freeze-Dried Poly Lactic-co-glycolic Acid Microspheres. Pharmaceutics 2019, 11, 291.

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