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Peer-reviewedCC BY 4.0International Journal of Molecular Sciences

Analysis of Local Free Volume and Hydration in Pharmaceutical Polymer Films Using Positron Annihilation Lifetime Spectroscopy

  • Mariam Majida Shokoya1,2
  • Károly Süvegh3
  • Zsófia Vilimi2,4
  • Nikolett Kállai-Szabó2,4
  • Romána Zelkó1,2
  • István Sebe1,2
4 affiliations
  1. 1University Pharmacy Department of Pharmacy Administration, Semmelweis University, 7-9 Hőgyes Street, 1092 Budapest, Hungary
  2. 2Center for Pharmacology and Drug Research & Development, Semmelweis University, 1085 Budapest, Hungary
  3. 3Department of Nuclear Chemistry, Institute of Chemistry, Faculty of Science, Eötvös Loránd University, 1518 Budapest, Hungary
  4. 4Department of Pharmaceutics, Faculty of Pharmaceutical Sciences, Semmelweis University, 7-9 Hőgyes Street, 1092 Budapest, Hungary
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Abstract

The relationship between the nanoscale free volume of pharmaceutical polymer films and their hydration behavior remains poorly understood. Eight pharmaceutical polymers were screened at three concentration levels within a quality-by-design framework; only two poly(vinyl alcohol) grades (PVA EG-30P and EG-40P), hydroxypropyl cellulose (HPC), and sodium alginate (Na-alginate) formed continuous films. These were characterized by positron annihilation lifetime spectroscopy (PALS), loss on drying (LOD), and swelling analysis. PALS clearly differentiated HPC, Na-alginate, and PVA, whereas the two PVA grades were similar and the concentration had only a minor effect. HPC showed the largest free volume holes (86.7–89.5 Å3), and Na-alginate the smallest holes (36.9–39.6 Å3) together with the highest LOD (20.2–21.6%). Across the 12 polymer–concentration combinations, the free volume hole volume correlated inversely with LOD (Spearman ρ = −0.85) but not with the equilibrium swelling index, as both HPC and Na-alginate swelled considerably more than PVA. Thus, PALS discriminates film-forming pharmaceutical polymers and reflects their residual water content, but the free volume of the air-dried films does not predict their swelling capacity.

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Cite

BibTeXRIS
BibTeX
@article{shokoya2026analysis,
  title = {{Analysis of Local Free Volume and Hydration in Pharmaceutical Polymer Films Using Positron Annihilation Lifetime Spectroscopy}},
  author = {Mariam Majida Shokoya and Károly Süvegh and Zsófia Vilimi and Nikolett Kállai-Szabó and Romána Zelkó and István Sebe},
  journal = {International Journal of Molecular Sciences},
  year = {2026},
  month = oct,
  doi = {10.3390/ijms27219518},
  url = {https://www.mdpi.com/1422-0067/27/21/9518},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Analysis of Local Free Volume and Hydration in Pharmaceutical Polymer Films Using Positron Annihilation Lifetime Spectroscopy
AU  - Mariam Majida Shokoya
AU  - Károly Süvegh
AU  - Zsófia Vilimi
AU  - Nikolett Kállai-Szabó
AU  - Romána Zelkó
AU  - István Sebe
PY  - 2026
DA  - 2026/10/24
JO  - International Journal of Molecular Sciences
DO  - 10.3390/ijms27219518
UR  - https://www.mdpi.com/1422-0067/27/21/9518
AB  - The relationship between the nanoscale free volume of pharmaceutical polymer films and their hydration behavior remains poorly understood. Eight pharmaceutical polymers were screened at three concentration levels within a quality-by-design framework; only two poly(vinyl alcohol) grades (PVA EG-30P and EG-40P), hydroxypropyl cellulose (HPC), and sodium alginate (Na-alginate) formed continuous films. These were characterized by positron annihilation lifetime spectroscopy (PALS), loss on drying (LOD), and swelling analysis. PALS clearly differentiated HPC, Na-alginate, and PVA, whereas the two PVA grades were similar and the concentration had only a minor effect. HPC showed the largest free volume holes (86.7–89.5 Å3), and Na-alginate the smallest holes (36.9–39.6 Å3) together with the highest LOD (20.2–21.6%). Across the 12 polymer–concentration combinations, the free volume hole volume correlated inversely with LOD (Spearman ρ = −0.85) but not with the equilibrium swelling index, as both HPC and Na-alginate swelled considerably more than PVA. Thus, PALS discriminates film-forming pharmaceutical polymers and reflects their residual water content, but the free volume of the air-dried films does not predict their swelling capacity.
SN  - 1422-0067
ER  -