| 摘要 |
PURPOSE: To justify a cannula position, to control and/or to prevent diffusion of a drug, by making a hydrophilic layer and hydrophobic layer with a predetermined composition, swelling in contact with an aqueous medium to soften generally, and controlling that velocity of swelling and softening. CONSTITUTION: The total cross section of a hydrophilic layer is necessary to account for at least about two thirds of the total cross section of a wall 25 of a cannula structure 10, and desirable to account for at least about three fourths of the total cross section of the wall 25. A hydrophilic material is necessary for such a material that swells at a volume ratio larger than 1.3:1, when it comes in contact with an aqueous medium such as a body fluid or tissue. A hydrophobic layer 12 or 14 is thin enough to keep a state bonded to each the other layer 12 or 14, and flexible. A resistance of a concerned hydrophobic layer against swelling expansion of the hydrophilic layer 12 or 14 must not be so large as to prevent that a cross section of an inner hole 36 increases at least about 20% at 37 deg.C. Velocity of softening and swelling is controlled at which longitudinal part the concerned complex cannula structure 10 is softened and swelled. |
