In vitro degradation testing of hydrogels – concept and case study of gellan gum degradation in water

Over the past two decades, hydrogels have become an indispensable tool for cell culture and regenerative medicine, in part due to their swelling and degradation capabilities. Degradable hydrogels present the advantage of improved biocompatibility and flexibility concerning the diffusion and stability properties. The testing of hydrogel degradation in vitro before its targeted application is required but the evaluation methods are precarious. One of the main obstacles is the manipulation of very soft hydrogels. The samples are often very delicate and measured parameter such as mass may be problematic to determine.
Several strategies to determine mass loss of hydrogels exist, including weighing the wet mass using closed containers, and lyophilization to determine dry mass [1]. Common issues in the experimental setup include errors being introduced by handling and touching the samples, as well as remaining incubation media that is difficult to separate from the gel. Here, we propose a degradation testing setup using a holder for the hydrogel sample and present degradation test results using gellan gum-based hydrogels. As a simple concept study, we incubate hydrogels samples in ultra-pure water and monitor weight change over 24h. Our demands for the method are: 1. the hydrogels are fully surrounded by the incubation medium; 2. it is possible to remove excess liquid; and 3. the sample can be moved without harming.
Gellan gum (GG) is an anionic polysaccharide that easily forms self-supporting hydrogels in the presence of cations, and has been investigated as artificial cell matrix and other tissue engineering applications [2] We have further investigated the modification of GG for extrusion-based applications, and are using an oxidized gellan gum (GGox), prepared using sodium iodate reaction, where a portion of the rhamnose sugars in the structure have been opened and carry aldehyde groups [3].