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Actuation of Ferromagnetic Fibre Networks to improve Implant Longevity

Final Report Summary - AFFINITY (Actuation of Ferromagnetic Fibre Networks to improve Implant Longevity)

Creating “smart” biomedical devices with the potential for controlled actuation* in vivo has been a long-standing scientific pursuit in therapeutic medicine. Affinity focused on a bone regeneration scaffold, based on ferromagnetic fibres, designed to accelerate bone healing at the bone-to-implant interface by the application of an external magnetic field of less than 1 Tesla (field lower than those employed for diagnostic purposes). The implant design involves the introduction of a magneto-active porous layer, based on interconnected networks of slender fibres, in the proximal region of the implant. By applying an external magnetic field in vivo, the fibres deform elastically and generate internal stresses/strains within the in-growing bone. Mechanical deformation is known to be highly beneficial in promoting bone growth, provided the associated strain lies in the therapeutic range. The treatment would be applied during the period immediately after the operation (i.e. the critical period for bone in-growth) and can be adopted either in a clinical or home setting.
A highly porous network made of bonded 444 ferritic (magnetic) stainless steel fibres has been developed as a model for magneto-mechanical stimulation of in-growing cells. Network architecture characterisation, magneto-mechanical response investigations, various modeling activities, systematic in vitro cell culture studies and magneto-mechanical actuation experiments have been carried out to understand the key performance requirements for this application and how they can be controlled.
The strains exerted on the bone cells as they grow into the fibre network are strongly dependent on the network architecture and the magnitude of the imposed magnetic field. Networks with large inter-joint spacings and low joint density (fibre-fibre joints) are desirable, so that the network exhibits relatively large distortions under the influence of a magnetic field. There is also scope in creating graded structures with high porosity near the surface but increased density near the network/implant interface.
Our results suggest activation of BMP2 signaling during magneto-mechanical actuation. Bone morphometric proteins (BMPs), especially BMP2, play a pivotal role in adult skeletal development and bone formation. The optimal exposure period, applied field and frequency have yet to be established.

*devices in which controlled physical motion or force is triggered by an external signal or stimulus