In the human body, living tissue responds dynamically to mechanical stimulation, ranging from the tissue macro-scale to the cellular microscale, and converts it into a biochemical signalling. This mechanism is known as mechanotransduction and is crucial in the development of several tissues. One of the goals of tissue engineering is to create in vitro mimics of human tissue by replicating the complex structures of native tissue. Since mechanotransduction has been identified as a morphogenic driver of tissue development, controlled external stimulation of tissue is an essential tool towards that goal. Polymeric biomaterials particles can facilitate the attachment of cells and subsequently their differentiation into a specific tissue type. The use of an external magnetic stimulus allows, by using the particle as the probe, the remote, local, mechanical stimulation of cells and tissues. In this study, a new technique is developed to provide magneto-mechanical stimulation to cells encapsulated in alginate beads. Spherical alginate beads with and without magnetic properties are produced by using the extrusion dripping method. The magnetic actuation of beads loaded with pure iron microspheres, provides indirect mechanical compression to the surrounding beads with encapsulated cells. In comparison with Iron oxide nanoparticles loaded alginate beads, the magnetic alginate beads developed in this project can apply local stimulation to cells with a higher magnetic force and at a larger distance. They also avoid the risk of cell contamination by inhibiting the leakage of Iron microspheres from the beads to the surrounded cells.
At first, the production parameters of the alginate beads using the syringe pump are investigated. By modifying the alginate concentration, iron volume fraction and the Optiprep concentration of the initial solution, we control respectively the sphericity, the magnetic force generated and the iron dispersion in the beads. The magnetic properties of the iron microspheres are evaluated. Finally, the magnetic manipulation of the beads takes place in a hydrogel medium with controlled viscosity while the magnetic response of the beads to the external magnetic field is measured and the generated force is calculated.