Lower critical solution temperature versus volume phase transition temperature in thermoresponsive drug delivery systems

M. Constantin, M. Cristea, P. Ascenzi, G. Fundueanu

Research output: Contribution to journalArticlepeer-review

Abstract

One of the most subtle problem in the characterization of thermoresponsive polymers is the evaluation of the relationship between the lower critical solution temperature (LCST) of the linear polymer and the volume phase transition temperature (VPTT) of the corresponding hydrogel. Here, the LCST and the onset temperature of linear poly(N-isopropylacrylamide-co-N-hydroxymethyl acrylamide) has been determined under pseudo-physiological conditions by cloud point (CP) measurements and by microcalorimetric analysis. The LCSTs, as well as the onset temperatures, determined by the CP method, decrease with increasing the concentration of the polymer solution. On the contrary, microcalorimetric analyses give almost the same values for LCSTs and the onset temperatures regardless of polymer concentration. The VPTT of the hydrogel, determined by the blue dextran method, was found to be closely similar to the LCST of the concentrated polymer solution (10%, w/v), determined by the CP method. In fact, the hydrogel could be considered as a concentrated polymer solution whose concentration could be related to the amount of water retained by the hydrogel. Hydrogel microspheres have been also reported to release diclofenac, a drug model system, in a pulsating way at temperatures slightly below and above the VPTT.

Original languageEnglish
Pages (from-to)839-848
Number of pages10
JournalExpress Polymer Letters
Volume5
Issue number10
DOIs
Publication statusPublished - Oct 2011

Keywords

  • Cloud point
  • Lower critical solution temperature
  • Smart polymers
  • Thermoresponsive hydrogels
  • Volume phase transition temperature

ASJC Scopus subject areas

  • Polymers and Plastics
  • Materials Chemistry
  • Chemical Engineering(all)
  • Organic Chemistry
  • Physical and Theoretical Chemistry

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