In pharmacology research, scientist frequently use drug infusion study in animals to examine the long term effect of a chemical on the body. An osmotic pump is an implanted device that release a steady flow of chemical over time. However, osmotic pumps come in various sizes and models, picking the right fit for your experiment can be crucial to your study design.

How does the osmotic pump Work?

The osmotic pump works by principles of osmolarity. When implanted in the body, the proprietary salt inter-layer absorbs moisture from the body and expand at a steady rate, displacing the drug payload stored in the storage capsules to the target site.

The osmotic pump can be implanted in the abdominal cavity or under the skin to replace IP or Subcutaneous injections. Alternatively, it can also provide intracranial, muscular and vein infusion when connected to a cannula implant, muscle or vein catheter.

How to Pick the right osmotic pump for Your study design?

When purchasing your osmotic pump, there are three main parameters to consider:

Drug Payload Volume Determines the size of your osmotic pump. Pumps that are too large can cause damage to the internal organs or increase risk of the implant being ripped out of the skin when co-housed. In general, we recommend the 100uL model for mice, 200uL model for rats and 2mL models for larger organisms.

The Release Duration determines the time frame of which the drug payload is released. This parameter determines the flow rate of the osmotic pump and should match your intended study duration. Note that the osmotic pump will generally continue to provide drug flow 2-3 days after the designed duration.

However, the pump should not be left in the body for longer than that duration as it would continue to absorb moisture, eventually causing the outer membrane to burst open. This can lead to the salt content being exposed to the muscle or the internal organ of the animal, causing irritation and eventually termination.

The Drug Concentration Although the drug volume and the flow rate is determined by the animal model and the study design, the amount of chemicals delivered to the animal can be adjusted by varying the concentration of the drug compound in the solvent. The concentration of the compound should be determined as follow:

Where C is the desired concentration, n is the amount of chemical designed for the animal per day and R is the hourly flow rate marked on the container.

Other Things to Look Out For

Chemical compatibility of the solvent need to be examined before conducting the experiment. Certain solvents such as alcohol can dissolve the outer membrane causing the salt content to leak out. Therefore extreme care should be taken when loading the capsule. Other chemicals can lead to failure if they dissolves the inner drug capsule, or if it is too viscous causing the capsule to burst. As a rule of thumb, also check with the list of compatible solvents provided by the vendor. Always use solvents with Viscosity under 100k cP.

If you are using a solvent outside of the vendor recommended list, you should either contact the manufacturer, or order a compatibility test vial to check for chemical compatibility before doing the implant.

Exact Flow Rate of the pump differs between batch as per manufacturer’s specification. however the flow rate within a batch is relatively stable. Therefore the flow rate of each case of osmotic pump will be marked with a flow rate reflecting the flow rate of the batch. When calculating the concentration of the payload, always use this flow rate measurement to yield more accurate result!