Measurement of Biomimetic Deposition of Calcium Phosphate in Real Time Using Complex Capacitance

Deposition of minerals, particularly calcium phosphates such as hydroxyapatite, is an important process in the formation of hard tissues such as bone. Herein, a new, affordable, straightforward and nondestructive method based on complex capacitance spectroscopy, an application of electrochemical impedance spectroscopy, is described which allows repeated and real-time measurements of the same sample throughout the calcium phosphate deposition process. In contrast with end-point assays which require large numbers of samples to obtain useful time-course data, this method allows the kinetics of deposition to be measured using a single sample by measuring the impedance of a pair of interdigitated electrodes at a range of frequencies as the layer of mineral is deposited. Changes in the complex capacitance curve over time with deposition can be compared with images of the coating deposited on model substrates, and show different behavior depending on the composition of the coating and the conditions of deposition.