In Vitro Use of ALZET Pumps

ALZET pumps are used in a variety of applications in vitro, such as cell culture. The key considerations are:

Temperature

The pumping rate for ALZET pumps is temperature dependent. Nominal rates for each pump model assume 37°C. Note that temperatures above 42°C have been found to cause fluctuating delivery rates and are not recommended. Predict the pumping rates of ALZET pumps at different temperatures.

Osmolality

Nominal pumping rates provided for ALZET pumps assume that the fluid surrounding their outer membrane is at normal mammalian osmolality (310 milliosmols/L) which is equivalent to an osmotic pressure of 7.5 atm. Note that these formulae are useful for osmotic pressures in the range of 0-25 atm. Predict the pumping rates of ALZET pumps at different osmolalities.

Water source

Proper operation of the ALZET pump requires that the outer membrane be completely surrounded by aqueous solution for the entire infusion period. For example, placing the pump in saline-filled test tubes suffices.

Exciting work has been conducted using ALZET pumps in vitro, including sending them into space!

Examples of In Vitro Applications

ALZET Pumps on Spacelab
Lorenzi et al. at the Swiss Federal Institute of Technology studied the effects of microgravity on hamster kidney cells aboard Spacelab during the IML-1 mission in 1992. Model 2001 ALZET pumps were used to exchange the cell culture medium in flight. The authors reported that “the osmotic pump delivered sufficient fresh medium to support cell growth in the perfusion chambers.” Pg. 37. (Microgravity Sci Technol 1993; VI/1:34-38)

ALZET Pumps Deployed in the Ocean
Imagine if in order to reach your study’s subjects you had to drive to the coast, charter a boat, and navigate the open sea. Consider the challenges if each test sample had to be retrieved from an ocean depth of 3800 meters under variable weather conditions. These are but a few of the obstacles faced by chemical oceanographers at the Monterey Bay Aquarium Research Institute (MBARI) and Moss Landing Marine Laboratories (MLML) in Monterey, California, as they study ocean chemical cycles on large temporal and spatial scales.¹ To circumvent some of these difficulties, Jannasch et al. adapted ALZET osmotic pumps in a unique application to perform reagent addition and sampling functions in a self-contained, continuous flow analyzer which determines nitrate concentrations in sea water during long-term, deep sea deployment.

The pumping action of modified ALZET pumps draws seawater into a miniature manifold, past reagent-bearing ALZET pumps, a cadmium-reducing surface and a photodiode detector. The catalyzed reduction of nitrate to nitrite is followed by production of an azo dye, which is picked up by the detector. A datalogger, which powers the electronic components, converts the detector’s signal to voltages and then amplifies, digitizes and stores the data.

Data from one month’s operation of the analyzer in both a fresh water aquarium and the kelp tank at the Monterey Bay Aquarium agreed well with nitrate measurements made by standard methods. Barnacle and algae growth on the analyzer’s external surface did not affect its operation, constituting an important victory over biofouling. Development of the analyzer continues at MBARI and MLML because of its many advantages over field sample collection and analysis. In fact, three analyzers are currently operating on a deep sea mooring off of Bermuda in the Atlantic Ocean.³ Jannasch et al assert that "the inherent simplicity and small size of osmotic pumps allow the analyzers to be used to continually monitor dissolved chemicals at remote sites for limnological, estuarine, and oceanographic studies." ²

1. Johnson KS, Coale KH & Jannasch HW. Anal Chem 1992; 64 (22): 1065A-1075A.
2. Jannasch HW, Johnson KS & Sakamoto CM. Anal Chem 1994; 66 (20):3352-3361.
3. Jannasch HW, personal communication, August 9, 1995.