Osmotically-Driven Micro-Dispense Pump

Dr. Phil Ligrani:    p_ligrani@msn.com

  • Applicable to low flow rate therapeutic and diagnostic biomedical delivery systems
  • Generic nature of pump allows for implementation in other applications
  • Capable of accurately and continuously delivering one m l/hr for up to one week
  • Relies on water-powered osmotic microactuator, requiring no external power source
  • Miniature size enables portability, mobility and unobtrusive usability

As the driving mechanism of many microfluidic devices, micropumps have been the focus of much microsystems research over the past twenty years. This collective effort has resulted in a diverse assortment of micropumps employing a broad range of working principles and utilizing a wide variety of fabrication methods. Traditionally, micropump development has centered on minimizing device dimensions and on maximizing flow rates. However, emerging applications in the biomedical field are redirecting some research efforts on low flow rate biocompatible micropumps. These applications include both therapeutic and diagnostic systems, described below.

Therapeutic applications include external and internal drug delivery devices. The efficacy of a drug can be greatly enhanced by the method of delivery. Using micropumps to deliver drugs in a highly controlled regime exploits this characteristic in a manner not possible with traditional drug delivery methods (i.e. oral tablets and injections). Other benefits of microscale therapeutic devices include potentially increased mobility and reduced interference with normal actions of the user.

Diagnostic applications include biological assays and cell adhesion analyses. Using micropumps reduces the volume of biological fluid needed for various processes and can decrease process time. Additionally, arrays of microdiagnostic devices could replace larger equipment, even to the point of being handheld.

Because biomedical devices are often used in life-critical applications, there are numerous important considerations. These include biocompatibility (both the drug/device and device/environment interfaces), reliability, durability, environmental stability, accuracy, delivery scalability, flow delivery (continuous vs. pulse flow), portability, reusability, back pressure range and power consumption. While biocompatibility is always an important consideration, other considerations vary in importance depending on the device application.

Current micropump research at the University of Utah explores an innovative low flow rate pump compliant with the many of demands of biomedical applications: an osmotically-driven mechanical dispense pump. The actuation of the micro-dispense pump is accomplished as water, driven by a chemical potential, crosses an osmotic membrane and enters a salt chamber. This increase in volume in the salt chamber forces an expansion membrane to deflect into a drug reservoir. As the expansion membrane pushes into the reservoir, the drug is dispensed via an outlet port. The size of the present device is on the order of several millimeters. Devices planned for the future will be smaller.

The osmotically-driven micro-dispense pump has the following advantages: continuous operation without batteries or external power supply; sustainable dispense rate for the duration of the dispensing period; truly continuous flow delivery; high pressure generation capable of overcoming backpressures; biocompatibility due to careful selection of materials and processes; portability due to miniaturization.

Characteristic lengths and volumes of microfluidic devices (Nguyen and Wereley 2002)

Osmotic test apparatus. Water flows through the osmotic membrane on the left side of object shown into the salt chamber, displaces the expansion membrane, and forces the contents of the reservoir to be forced out via the tubing shown on the right.

Copyright Trademarks Ligrani Research Group 2009