Injectable Thermosensitive Poly(ethylene glycol)–poly(-caprolactone)–poly(ethylene glycol) Hydrogels: Optimal Synthesis Conditions and Sol-gel-sol Transition Behaviour

Abstract

Hydrogels are polymeric materials containing amphiphilic networks that can absorb a large amount of physiological fluid without damaging their structure. By following the two-step procedure of caprolactone ring-opening reaction and coupling PEG-PCL blocks with hexamethylene diisocyanate (HMDI), injectable thermosensitive poly(ethylene glycol)–poly(-caprolactone)–poly(ethylene glycol) (PEG–PCL–PEG, PECE) hydrogels are successfully fabricated. The PECE hydrogels are characterized in terms of physical-chemical properties and “sol-gel-sol” phase transition by Proton Nuclear Magnetic Resonance (1H-NMR) and Fourier Transform Infrared spectroscopy (FT-IR). Effects of several factors (temperature, time reaction, and mole ratios of reactants) on the properties of the PECE hydrogels are also investigated to determine the optimal synthesis conditions. The results show that the structure and physical-chemical properties of the PECE are significantly affected by the investigated factors, especially the ratio of reactants. The optimal condition for the first stage is determined at 130 °C, 10 h, and a PEG/PCL mole ratio of 1:2; and for the second stage is 80 °C, 8 h, and HMDI/PEG mole ratio of 1:1. Furthermore, the PECE hydrogels are soluble at room temperature and become “gel” at human body temperature. The features of polymer structure such as the balance between hydrophilic and hydrophobic groups, and the length of PCL and PEG have a great impact on the phase transition behavior of the PECE.