For the experiments, a gadolinium(III)-chelate contrast agent was selected, which is known to have the lowest possible toxicity. However, at high concentrations, it is still potentially toxic for cells and tissue spheroids, because of the osmotic pressure imbalance due to excessive use of ions in the paramagnetic medium. An obvious dilemma - high concentration of gadolinium enables magnetic levitation but is relatively toxic, whereas a low, non-toxic concentration of gadolinium does not allow magnetic levitation with permanent magnets. The solution is to perform the levitation at a low concentration of gadolinium but taking advantage of very high magnetic fields. 

Using a magnetic field of up to 31 T, researchers from Moscow, Maastricht, and Nijmegen performed magnetic levitational assembly of tissue constructs from living spheroids. The construct from tissue spheroids partially fused after 3 hours of levitation. The analysis of viability after prolonged exposure to the magnetic field showed the absence of significant cytotoxicity or morphology changes in the tissue spheroids. This means that the high magnetic field acts as a non-toxic, temporal, and removable support. The researchers demonstrate that formative biofabrication of tissue-engineered constructs from tissue spheroids in high magnetic fields is a promising research direction.