Abstract
Several electrical fields are known to be present in bone tissue as originally described by Fukada and Yasuda in the year 1957. Intrinsic voltages can derive from bone deformation and reversely lead to mechanical modifications, called the piezoelectric effect. This effect is used in the clinic for the treatment of bone defects by applying electric and magnetic stimulation directly to the bone supplied with an implant such as the electroinductive screw system. Through this system a sinusoidal alternating voltage with a maximum of 700 mV can be applied which leads to an electric field of 5–70 V/m in the surrounding bone. This approach is established for bone healing therapies. Despite the established clinical application of electrical stimulation in bone, the fundamental processes acting during this stimulation are still poorly understood. A better understanding of the influence of electric fields on cells involved in bone formation is important to improve therapy and clinical success.
To study the impact of electrical fields on bone cells in vitro, Ti6Al4V electrodes were designed according to the pattern of the ASNIS III s screw for a 6-well system. Osteoblasts were seeded on collagen coated coverslip and placed centred on the bottom of each well. During four weeks the cells were stimulated 3×45 min/d and metabolic and alkaline phosphatase (ALP) activity as well as gene expression of cells were analysed. Furthermore, supernatants were collected and proteins typical for bone remodelling were examined.
The electrical stimulation did not exert a significant influence on the metabolic activity and the ALP production in cells over time using these settings. Gene expression of BSP and ALP was upregulated after the first 3 days whereas OPG was increased in the second half after 14 days of electrical stimulation. Moreover, the concentration of the released proteins OPG, IL-6, DKK-1 and OPN increased when cells were cultivated under electrical stimulation. However, no changes could be seen for essential markers, like RANKL, Leptin, BMP-2, IL-1beta and TNF-alpha.
Therefore, further studies will be done with osteoblasts and osteoclasts to study bone remodelling processes under the influence of electrical fields more in detail. This study was supported by the German Research Foundation (DFG) JO 1483/1-1.
