Extruded sheet with a density greater than 300 kgm3, or preferably greater than 400 kgm3, made of biodegradable materials of synthetic andor natural origin, suitable for use in the production of chew toys for domestic pets. In a cathode active material contained in a cathode, a coating layer is provided on at least part of a complex oxide particle containing at least lithium and cobalt. A first cell using a first RAT, under certain circumstances, may be permitted to enter a powered down state such that less power is consumed. The bottom of the first connector is formed with a first trough. These methods find use a number of applications, such as in preparing inner ear cells for in vitro screening for agents that are toxic to inner ear cells, for in vitro screening for agents that prevent against, mitigate, or reverse the toxic effects of such agents, and for in vitro screening for agents that promote otoregeneration.