In situ rheological measurements of the external gelation of alginate

Abstract

Direct mixing of alginate and divalent cations such as Ca 2+ generally produces heterogeneous gels that form almost instantaneously. Therefore, is particularly difficult to measure the rheological properties of this gelation event due to the rapid gelation kinetics. In this study, the gelation of alginate when exposed to a solution of CaCl 2 was measured by using a modified rheometer. This modification involved attaching a petri dish to the lower plate of the rheometer into which, filter paper impregnated with CaCl 2 solution was added. A semipermeable membrane was then placed above the filter paper as a barrier to prevent the filter paper imbibing the gel. Samples of 4%w/w alginate were loaded onto the semi-permeable membrane and measurements were taken using 55mm parallel plate geometry. Measurements of G′ and Gʺ were determined as a function of time to monitor gelation. Once gelation was complete the filter paper was removed and replaced with filter paper impregnated with calcium chelators (EDTA, sodium citrate) to assess the degradation of the gel. The results showed that this technique was suitable for analysing the external gelation of alginate with a sharp increase in G′ in the first three minutes which then plateaued over the remainder of the test. It was also shown that gel stiffness reduced to a greater extent on exposure to EDTA compared with sodium citrate. This method is not only suitable for measuring rapid gelation kinetics on exposure to cross-linkers, but has potential applications in modelling the in situ gelation behaviour in simulated physiological environments. Graphical AbstractHighlights: A novel method for the rheological measurements of the gelation of alginate from an external source of calcium ions  Simple modification of a commercial rheometer  Can be used to measure the degradation of alginate gel on exposure to calcium chelators  Potential model for measurements of in situ gelation

Preparation of Succinoglycan Hydrogel Coordinated With Fe3+ Ions for Controlled Drug Delivery

“…These observations implied that when a dynamic load is applied, the Fe 3+ -SG hydrogels have a strong physical gel structure, indicating a highly elastic response with a comparatively small dissipation in energy [35,36]. In addition, the slope of G' of the Fe 3+ -SG hydrogel is close to zero, which indicated that the storage modulus and angular frequency were associated with the dynamics of the hydrogel network [37]. Succinolgycan also coordinated with Fe 2 + , thus, high concentrations of Fe 2+ ions would be expected to increase the storage modulus and became a gel.…”

Behavior of In Situ Cross‐Linked Hydrogels with Rapid Gelation Kinetics on Contact with Physiological Fluids

“…Neither of these methods, however, offers suitable experimental simulation of rapid gelation behavior in physiological conditions. Recently in our laboratories, we have demonstrated the experimental monitoring of the external gelation of alginate by modifying a commercially available rheometer . In this paper, we have explored the potential of this modification, as an experimental simulation of in situ gelation on exposure to simulated physiological environments using gellan gum as a model in situ gelling delivery system ( Figure ).…”

In-vivo vascular application via ultra-fast bioprinting for future 5D personalised nanomedicine

“…For example, changing the development speed on a machine with a subtractive technology, the surface roughness alteration does not modify the mechanical characteristics, but using the additive manufacturing technology to realise cake decorations, its morphology changes, with the functional aim of the object (aesthetics). Thus, the assessment of the parameters is directly related with the functionality of the 5D object and in the case of the soft tissue development we have to take in consideration drops accidentally falling down or the creation of vascular channel to bring, where required, the gelation fluid for the morphology long-term fixation and dedicated tests 33,34,[36][37][38][39][40][41] are required to better explore any manufactured object and each possible customisation.…”