Biomaterials 25 (2004) 4805–4815 Magneto-mechanical stimulation of bone growth in a bonded array of ferromagnetic fibres Athina E. Markaki, T. William Clyne* Department of Materials Science and Metallurgy, Cambridge University, Pembroke Street, Cambridge, Cambs CB2 3QZ, UK Received 10 July 2003; accepted 24 November 2003 Abstract A brief experimental and theoretical study is presented into the elastic deformation of bonded arrays of ferromagnetic fibres, when subjected to an external magnetic field. Material made of such fibre arrays is of potential interest for certain biomedical applications, such as prosthetic implants. Externally imposed magnetic fields could be used to generate mechanical strains in surrounding tissue, with possible physiological benefits. It is shown that it should be possible to generate strains within embryonic bone cell networks, forming within such a fibre array, which are sufficient to stimulate enhanced growth. The effects outlined here could thus form the basis of surgical or therapeutic advances. r 2004 Elsevier Ltd. All rights reserved. Keywords: Porosity; Magnetism; Scaffold 1. Introduction It is well established [1,2] that healthy bone growth is promoted by the imposition of mechanical stress. Associated strains within the bone need to reach levels of at least about 1millistrain in order to stimulate significant beneficial effects [3–5]. Prosthetic implants must support substantial loads, but equally important is that they should adhere well to the surrounding bone and that they should not be so stiff as to shield it from the development of stress [6–8]. The latter two require- ments would be well satisfied by making implants from porous and permeable metallic materials. Most metals have a stiffness (Young’s modulus) of around 100– 200GPa, whereas that of cortical bone is about 5–30GPa. Porosity levels would thus need to be relatively high, in order to bring the stiffness of such metal down sufficiently to match that of bone. Such high porosity would also favour bone in-growth and hence good adhesion. Provided the channels are similar in size [9] to pores in bone (B100–250 mm), and the material, or a coating on it, is biocompatible [10,11], such bone in- growth is known to occur readily—see Fig. 1. It is something of a challenge to ensure that such highly porous material is sufficiently strong [12] to satisfy substantial load-bearing requirements, but structures such as strongly bonded metallic fibres do show promise in this regard. Such a porous implant could be regarded as a scaffold for tissue growth, a concept now well established for many reconstructive physiological therapies [13].A scaffold must be bio-compatible and there has been extensive work on identification of the materials and surface treatments exhibiting such compatibility. A novel emerging concept [14] is that of an active scaffold—i.e. one which actively promotes healthy physiology. During and after initial bone in-growth, substantial benefits might accrue from being able to stimulate mechanical movement of the scaffold and/or to generate internal stresses within the growing bone. Such mechanical stimulation would differ slightly from purely bio-chemical activity, but might lead to similar types of benefit. In principle, such mechanical movement could, for example, be stimulated by a temperature change, either as a consequence of differential thermal expansion in a bi-material structure or via a shape memory transforma- tion [15]. However, the scope for inducing significant temperature changes within an organism, without risking physiological damage, is very limited indeed. A potentially more attractive stimulation technique is to ARTICLE IN PRESS *Corresponding author. Tel.: +44-1223-334332. E-mail address: twc10@cam.ac.uk (T.W. Clyne). 0142-9612/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2003.11.041