One of the ways to prevent CAUIT is unidirectional flow by generating the negative pressure in the drainage system. For this purpose, at first, we used a sponge (For more information see Drainage Sponge). But, the sponge has some problems. First of all, it applies all the pressure at once to the bladder and does not regulate it, and may damage the bladder tissue. Also, it is not reliable system because, at the beginning of the process, the pressure is high but after a while (near an hour) it decrease dramatically. Therefore we decided to redesign the system and employed water beads instead of the sponge.

Water beads are considered as a superabsorbent polymer (SAP) and usually made of Sodium Polyacrylate and Polyacrylamide. We found that when they are in the impermeable bag and exposed with a liquid, they absorb the liquid and get swell and create new void volume between themselves. As a result, the pressure in the bag decreases and negative pressure is generated. As they swell more, the pressure decreases more.

Accordingly, the drainage bag was filled with the particular amount of the water beads and vacuum was applied to the bag, then the system was run and the generated pressure and the flow rate was measured to optimize the system. In addition, a bacterial test was designed to evaluate the effect of negative pressure via water beads on bacterial growth in the bladder mimicking container.