How does it work?
ALZET pumps operate because of an osmotic pressure difference between a compartment within the pump, called the salt sleeve, and the tissue environment in which the pump is implanted. The high osmolality of the salt sleeve causes water to flux into the pump through a semipermeable membrane which forms the outer surface of the pump. As the water enters the salt sleeve, it compresses the flexible reservoir, displacing the test solution from the pump at a controlled, predetermined rate. Because the compressed reservoir cannot be refilled, the pumps are designed for single-use only.
The rate of delivery by an ALZET pump is controlled by the water permeability of the pump’s outer membrane. Thus, the delivery profile of the pump is independent of the drug formulation dispensed. Drugs of various molecular configurations, including ionized drugs and macromolecules, can be dispensed continuously in a variety of compatible vehicles at controlled rates. The molecular weight of a compound, or its physical and chemical properties, has no bearing on its rate of delivery by ALZET pumps.
The volume delivery rate of ALZET pumps is fixed at manufacture. ALZET osmotic pumps are available with a variety of delivery rates between 0.11 and 10 µL/hr and delivery durations between 1 day and 6 weeks. While the volume delivery rate of the pump is fixed, different dosing rates can be achieved by varying the concentration of agent in the solution or suspension used to fill the pump reservoir.
A more complete and technical explanation of the operation of ALZET osmotic pumps can be found in the following reference.
Theeuwes F and Yum SI. Principles of the design and operation of generic osmotic pumps for the delivery of semisolid or liquid drug ormulations. Ann Biomed Eng 1976, 4(4): 343-353.