In recent years many studies have demonstrated stimulatory effects of pulsed electromagnetic fields (PEMF) on biological tissue.However, controversies have also surrounded the research often due to the lack of knowledge of the different physical consequences of static versus pulsed electromagnetic. PEMF is widely used for treating fractures and non-unions as well as for treating diseases of the joints. Furthermore, new research has suggested that the technology can be used for nerve regeneration and wound healing although conclusive clinical trials, besides those for fracture healing, are still lacking. Despite the apparent success of the PEMF technology very little is known regarding the coupling between pulsed electrical fields and biochemical events leading to cellular responses. Insight into this research area is therefore of great importance. In this review we describe the physical properties of PEMF-activated electrical fields and explain the typical set up for coils and pulse patterns.Furthermore, we discuss possible models that can account for mechanisms by which induced electric fields are able to enhance cellular signaling. We have emphasized the currently well-documented effects of PEMF on cell function from tissue culture and animal studies as well as from studies describing clinical effects on bone growth, nerve growth and angiogenesis. We believe this relatively new technology can become relevant for treating a variety of physiological conditions demanding enhanced cellular activity.
INTRODUCTION
Since the mid-1950s it has been known that bone becomes electrically polarized when deformed as in a fracture, and this led to the discovery that the application of weak electric fields increases the formation and growth of bones (osteogenesis). However, the invasive technique of implanting current inducing electrodes on the broken bone in order to increase the bone growth severely restricted the use of this new method. Since the mid-1970s the non-invasive technique of inducing electric currents in bones by use of PEMF has been widely used to speed up fraction repair (Basset et al, 1977; Basset et al, 1981) and this method has been approved by the Food and Drug Administration (FDA) in USA. In the late 1970s it was found that application of PEMF resulted in a significant and reproducible enhancement in the regeneration of nerve fibers exposed to a lesion and, since then, the PEMF technique has been successfully applied to stimulate growth and regeneration of various types of nerve cells both in vitro and in vivo (Sisken et al, 1989; Longo et al, 1999; Macias et al, 2000). More recently evidence has been found, showing that application of PEMF has therapeutic benefits in the treatment of painful inflammation of bone joints (osteoarthritis) as well as in wound healing (Trock et al, 1994; Patino et al, 1996). The latest findings show, that low frequency, PEMF is capable of inducing cell proliferation in several cell culture models, of which especially cultures of cartilage cells (chondrocytes) has been tested vigorously, in the hope of obtaining a treatment for rheumatism and other cartilage-based diseases (Pezetti et al.,1999; De Mattei et al, 2001). From the first discovery of its effects, the clinical spectrum for treatment of various afflictions with PEMF has been ever-broadening and the recent findings suggest that new uses for clinical PEMF-therapy may well be under way.
The articles cited above are only a small extract of the large amount of research articles available, documenting the effects of PEMF. Common to them all is the fact that application of PEMF stimulates or enhances growth-related responses of cells. A connection between the pulsed electromagnetic fields and the events responsible for cell growth must therefore exist, and in this review we outline the most attractive models accounting for this interaction.
