Over the past few decades, several thermogelling materials have been extensively developed for biomedical applications. The thermogelling materials can be easily injected and solidified at the specific target tissue for biomedical application[1].
Recently, we examined the thermogelling properties of methoxy polyethylene glycol-b-poly(ε-caprolactone) (MC) as thermogelling block copolymers to apply in biomedical field[2]. More recently, we examined the thermogelling properties of MC diblock copolymers derivatized with carboxylic acid group, tertiary amine group, and zwitterionic sulfobetaine in the end position in MC chain[3].
Based on the previous studies, thus, we hypothesized that introducing chloride (MC-Cl), azide (MC-N3) and amine (MC-NH2) functional pendant groups into the MC end position could alter the thermogelling behavior of the MC copolymer in aqueous solutions.
The preapred diblock copolymers exhibited characteristic 1H- and 13C-NMR peaks for MC, MC-Cl, MC-N3, or MC-NH2. Aqueous solutions of diblock copolymers were prepared by dissolving diblock copolymers at 80°C in deionized water. At room temperature, diblock copolymer solutions formed a translucent liquid that flowed when tilted.
The thermogelling behavior was monitored by measuring the solution viscosity as a function of temperature. At low temperatures, MC-Cl, MC-N3 and MC-NH2 solution were a homogeneous solution with a viscosity of 1 cP. As the temperature was increased from room temperature, the MC-Cl, MC-N3 and MC-NH2 solutions exhibited gel-like behavior at an onset temperature marked by an increase in the viscosity.
The sol-to-gel phase transition of thermogelling diblock copolymers depended on the composition of diblock copolymers and the identity of the functional group in the pendant position. The diblock copolymer solutions exhibited viscosities of 3.6 x 105–6.6 x 105 cP. The viscosity may be correlated with the strength of the gel formed by thermogelling diblock copolymers.
These results indicate that a thermogelling properties of diblock copolymers depended on both the type of functional pendant group and the composition of diblock copolymers. We conclude that the diblock copolymers with functional pendant group designed in this study can be used as potential thermogelling materials for drug and cell.
References:
[1] J. I. Kim, D. Y. Kim, D. Y. Kwon, H. J. Kang, J. H. Kim, B. H. Min and M. S. Kim, “An Injectable Biodegradable Temperature-Responsive Gel with an Adjustable Persistence Window” Biomaterials, 33, 2823-2834, 2012.
[2] M. S. Kim, H. Hyun, K. S. Seo, Y. H. Cho, G. Khang, H. B. Lee, “Preparation and characterization of MPEG-PCL diblock copolymers with thermo-responsive sol-gel-sol behavior” Journal of Polymer Science Part A: Polymer Chemistry, 44, 5413-5423, 2006.
[3] S. W. Shim, D. Y. Kwon, J. H. Park, H. J. Chun, Y. J. Koh and M. S. Kim, "Preparation of zwitterionic sulfobetaine end-functionalized poly(ethylene glycol)-b-poly(caprolactone) diblock copolymers and examination of their thermogelling properties" Journal of Polymer Science Part A: Polymer Chemistry, 52, 2185-2191, 2014.