Amino acids as cryoprotectants for liposomal delivery systems

Afzal-Ur-Rahman Mohammed, Allan G.A. Coombes, Yvonne Perrie*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Liposomes provide an efficient delivery system for solubilisation and delivery of both small and macro molecules. However, they suffer from the disadvantage of instability when stored as aqueous dispersions. Cryoprotection of the liposomal systems provides an effective approach to overcome poor stability whilst maintaining formulation characteristics, although, the formulation of a freeze-dried product requires the consideration of not only the selection of an appropriate cryoprotectant, but also needs careful consideration of the processing parameters including pre-freezing conditions, primary and secondary drying protocols along with optimisation of cryoprotectant concentration. This current work investigates the application of amino acids as potential cryoprotectants for the stabilisation of liposomes, and results indicate that amino acids show biphasic nature of stabilisation with 4 mol of cryoprotectant per mole of the lipid exhibiting optimum cryoprotection. The investigations of process parameters showed that the pre-freezing temperatures below the glass transition of the amino acids followed by drying for over 6 h resulted in stable formulations. Studies investigating the efficiency of drug retention showed that the cryoprotection offered by lysine was similar to that shown by trehalose, suggesting that amino acids act as effective stabilisers. ESEM analysis was carried out to monitor morphology of the rehydrated liposomes. © 2007 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)406-413
Number of pages8
JournalEuropean Journal of Pharmaceutical Sciences
Issue number5
Publication statusPublished - Apr 2007


  • amino acids
  • cryoprotectants
  • environmental scanning electron microscopy
  • freeze drying
  • liposomes
  • stability


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