Investigation of alginate beads for gastro-intestinal functionality, Part 2: In vivo characterisation

This paper summarises work undertaken to visualise and characterise alginate gel beads, in vivo, in the human gastro-intestinal tract using magnetic resonance imaging (MRI). Two types of alginate beads were investigated: “strong” (strongly gelled) and “weak” (weakly gelled) beads, each prepared by long and short exposures to a calcium chloride gelling bath, respectively. Ten volunteers attended the study centre, on two different occasions, and consumed a different bead type on each visit. Before consuming the bead meal, the volunteers consumed 50 ml of Calogen® (a fatty preload) which converted gastric motility to a fed pattern and delayed the emptying of the non-nutrient model bead meal from the stomach. Gastric emptying of the bead meal was dominated by the fatty preload, with the median half-emptying time 48 min for both bead types. Gastric sieving of the strong beads occurred with the percentage of the meal remaining at 60 min significantly higher for the strong bead meal compared to the weak bead meal. Both types of gelled beads were clearly visualised by MRI in both the stomach and the small intestine, with beads being more visible in the ileum compared to the jejunum and duodenum. The water proton transverse relaxation time, T2, of the beads was measured in the stomach. After an initial increase, T2 decreased slightly over time from the initial in vivo measurement. In the first paper of this series, we correlate in vitro T2 shortening with formation of a more dense gel network. These in vivo investigations suggest that changes in the gel beads, within the GI tract, could be monitored using T2.