A downhole tool for use in a wellbore having a tool body with a blade assembly slidably mounted thereon and movable between a retracted and an outwardly extended position. A switching unit is provided at a path electrically connecting the motor generator and the inverter. The optical member 15 is received on the backside by receiving members 21 and 24 provided respectively in a holder 17 and a lamp holder 16, while being held from the front by a frame 18. Such method and apparatus are also useful in controlling the amount of change in bulk density or amount of settling of a packaged product during shipping or handling. The therapeutic material is preferably a heparin or heparin derivative or analog which renders the material antithrombotic as an implantable or invasive device.