system application_number US 29369681 A description device 10 as used for the purpose of the invention consists of a wall 11 or housing made of a substantially polymeric material this material is preferrably rigid and it permits pressure to be exerted against it without any major change in its shape or dimensions thereby assuring thatpressure generated in device 10 is exerted against container 13 housing 11is made from a semipermeable polymer that regulates the passage of fluid into the device the semipermeable polymers suitable for forming the wall are polymers that display selective water permeability the phrase selective water permeability as used herein denotes polymers that are permeable to the passage of water and essentially impermeable to the passage of solute the semipermeable polymers act in cooperation with the hydrophilic hydrogels in the device and govern the passage of water through the wall into the device generally the semipermeable polymer will have a water permeability of 0 01 to 10 cc cm 2 hr or day or longer typical semipermeable polymers suitable for forming the wall include cellulose acylate cellulose diacylate cellulose triacylate cellulose acetate cellulose diacetate cellulose triacetate cellulose polymers having at least one acyl group with the remaining degrees of substitution on the anhydroglucose units selected from hydrogen hydroxal and hydrocarbyl the volume of water that passes through the wall can be further controlled by selecting cellulose.