We have a problem, every year the number of patients with chronic kidney disease increases while the number of patients living on hemodialysis increases as well. This leads for an ever increasing need for dialysis which ultimately may exceed our ability to provide it. Patients enter the system on one end and should theoretically receive kidney transplantation on the other end. However transplantation programs are not able to keep pace with demand and the population on dialysis continues to grow. What if we could create our own kidneys?
The kidney is an organ whose anatomy has been fairly well known for some time. Modern dialysis is based on replication of some of the functions of the normal kidney. The simplest function to replicate would be the ability to filter. The filtration system of the kidney consists of what is known as glomerulus a highly specialised group of cells which somehow retain things that we need such as large proteins and simultaneously filter out small toxins that are dissolved in the blood.
The obvious observation is that this is a size selective process and the glomerulus is acting as a strainer or seive. Thus the design of modern dialysis filters is on this basis. However in the normal kidney blood flows down a set of tubes these tubes are rightly called tubules and the combination of the glomerulus and its tubule is called a nephron. A dialysis machine functions essentially as only half of this structure. There is no current commerically available machine that replicates tubular function.
If tubules were simply pipes that connected the filter to the repository of urine known as your bladder then this would be easily replicated. However each tubule is lined by cells which continually analyse the constituents of the fluid passing by it, altering it if necessary along the way by adding to it or removing things that we need to retain within our body to support life.
Recently however a paper on biomedical engineering of kidney tubules was published. This paper proposes the development of a kidney tubule on a chip. Utilizing tissue culture technique an artifical tubule would be created by transplanting either living cells from an existing kidney or tubule cells grown in culture onto a membrane and passing fluids along it in a similar manner to the normal kidney. If the cells function as they do within the normal kidney then they should be able to modify the fluid and essentially create urine.
By combining the filtration ability of existing dialysis technology with something similar to this tubule on a chip we would have a filter in series with a tubule. This is a design which is already proven to work in everyone reading this article. This would be a first step that would hopefully plug the short term need for better more physiologic renal replacement therapy.
However in the long term miniaturization of the filtration apparatus with a similar cell on chip technology may lead to truly wearable dialysis machines. Of course the smaller we make things the better and if a wearable machine can be made small enough why could it not be implanted under the skin or in the abdomen? Artificial kidneys anyone?
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