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Methodology

The kidneys essentially serve as the filter system of the body, responsible for removing metabolic waste

from the blood. Additionally, properly functioning kidneys have to regulate the balance of water and

important molecules such as sodium and chloride as well as the nutrients that the body (via reabsorption).

The replacement kidney that we have designed must be able to efficiently carry out these fact without

having potentially adverse effects on the patient.

Our design was based on a design from the Implantable Artificial idney !orporation. The dimensions of 

the artificial kidney were ideal as a replacement for the actual organ, however we made modifications to

the membranes material used within the system in order to ma"imi#e the efficiency of the artificial

kidney. The membranes used were derived from microelectromechanical systems ($%$&) (this will be

discussed later).

The artificial kidney consisted of ' chambers, each consisting of a pair cartridges contain two membranes.

The first three chambers contained membranes intended to carry out ultrafiltration via reverse osmosis,

these chambers were also pressuri#ed to the normal blood pressure while the membranes of the

remaining two chambers were intended to reabsorb any needed molecules via osmosis or diffusion.

iffusion occurs when a system is not at e*uilibrium. Osmosis is the diffusion of li*uid molecules across

a semipermeable membrane. In these two phenomena, molecules move from an area of high

concentration to an area of low concentration.

The five chambers were separated by a dividing wall. Tall narrows slots were placed within the dividing

wall, between the five chambers, thus acting as the means of fluid transition from one chamber to the

ne"t. The artificial kidney is connected to the circulatory circuit via a tube e"tending from the iliac artery

to the entrance of the first chamber. The blood will be flowing at a rate of roughly +' ml per minute each

day.

-ater and other small molecules ( /0 amu) will continue on through the second membrane in the two

cartridges, out into collecting areas. 1rea and any larger molecule (2/0.0/ amu) will not pass through the

second (outer3most) membranes in the first cartridges instead it will be channeled out special drain ports

to a waste collecting area.

-ater and other substances filtered from the blood in the first reverse osmosis chamber are transferred

from the outer collecting areas to the two osmosis or diffusion feed chambers without passing through the

second and third chambers. At this point, using any of the following processes4 absorption, osmosis,

solvent drag, diffusion and ion e"change, the substance will selectively re3enter the blood stream.

Additionally, the blood is would be transporting mainly larger molecules. The blood pressure inside the

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last two chambers and the filtrate on the outside of the in5ection membranes would now be near e*ual

 pressures. ynamic diffusion would occur as a result and, until a state of e*uilibrium is reached, some of

the small molecules (water, sodium, calcium) would move to the region where they are less concentrated.

The main component of the artificial kidney is the material used for the membranes. The performance

capabilities of the membrane will ultimately decide the efficiency and effective of the artificial kidney

designed. Additionally, it should be relatively unreactive when in the body. A suitable material would

have a membrane system with uniform pores. The presence of such can effectively reduce resistance to

fluid flow while maintaining molecular selectivity compared to polydisperse (non3uniform) porous

materials. !ontrolled pore shape also provide additional reductions in hydraulic resistance (resistance to

flow of a fluid in for eg. a pipe) when compared with round or irregular pores.

It is for this reason, that microelectromechanical systems ($%$&) 6based membranes were used in the

design. $ore specifically, silicon $%$&3based substrates were used as the membranes. $%$& refers to

miniaturi#ed mechanical and electro3mechanical element devices and structures that are made using the

microfabrication techni*ues. &urface micromachining can be used to control on a nanoscale, the si#e and

geometry of the membrane pores. The biocompatibility of silicon3based $%$& substrates has been

shown to be inert and relatively nonto"ic after being assessed using international standards. This suggest

that the material would remain stable for a very long period of time without posing any sever harm to the

 patient.