Augmented delivery, controlled-release

Biomaterials, a relatively new class of materials, are natural or S3mthetic substances used to treat, augment or replace a tissue, organ, or function of the body. Biomaterials encompass a broad range of functions including tissue engineering, controlled-release drug delivery, and bioadhesives. 

The controlled-release micropump (Figure 2) is a recently invented device that uses the principles of membrane transport and controlled release of drugs to deliver insulin at variable rates (20,26). With a suitable supply of insulin connected to the pump, the concentration and/or pressure difference across the membrane results in diffusion or bulk transport through the membrane ). This process is the basal delivery and requires no external power source. Augmented delivery is achieved by repeated compression of the foam membrane by the coated mild-steel piston. The piston is the core of the solenoid, and compression is effected when current is applied to the solenoid coil. Interruption of the current causes the membrane to relax, drawing more drug into the membrane in preparation for the next compression cycle. 

Pressure-Difference Driving Force. The effect of a l- xm polycarbonate microporous filter on basal and augmented delivery in the controlled-release micropump due to a pressure difference is shown in Figure 3. As the pressure difference was lowered (i.e., as the liquid level dropped in the falling head permeameter) the basal flow rate was reduced to less than 0.2 mL/day (pressure difference, approximately 0.8 cm H20). At this basal rate, operation with a 100-U/mL reservoir becomes practical. More importantly, the degree of augmentation was increased to more than 10 X from the... 

The mechanism of action of the controlled-release micropump is unclear. With a pressure difference, the rapid oscillatory movement of the piston during augmented delivery may be responsible for the increased delivery rate by lowering the overall resistance of the micropump to bulk flow (35). When only a concentration difference exists, on the other hand, augmentation can be attributed to a pressure difference superimposed during piston movement on the basal concentration difference, or to a mixing effect associated with piston movement. The physical relationship between piston movement and augmentation remains to be defined. 

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