| Description |
Different types of osmotic pumping devices, requiring a constant flow rate of 1 uL/hr for 1 year and capable of operation at pressures between 0 and 150 psig and temperatures between -5 and 121 °C, are designed, developed, and tested. The design is completely self-sustaining and self-contained. The design employed is capable of operation in any orientation and the solvent supply for the pump is pressurized to avoid phase changes that would inhibit functionality of the devise. During development, different semipermeable materials are considered, including cellulose acetate, acetate plus, polyethersulfone, polyimide, porous ceramics, and porous glass. The osmotic pumping devices using cellulose acetate membranes offered satisfactory results for temperatures up to 50 °C while overcoming back pressures up to 150 psig. The devices using polyimide as the semi-permeable membrane performed similarly to cellulose acetate with increased temperature performance up to and including 75 °C. The devices using porous glass could handle temperatures up to 121 °C, but could not operate above 50 °C when pressures above 25 psig were applied. Acetate plus, polyethersulfone, and porous ceramic membranes never produced functional osmotic pumping devices. None of the devices operate properly when temperatures above 75 °C are applied. The designs of the osmotic devices utilize unique methods for: (i) membrane retention, (ii) onboard water reservoir, and (iii) flow activation or |
