A number of clinical conditions such as the loss of kidney and liver function result in increased concentrations of toxic substances in the blood. The high levels of these molecules, which arise through the natural metabolic process as well as from an activated immune system, makes sufferers ill and forces them to spend considerable amounts of time in hospital.
One of the main treatments for people with this condition is haemodialysis. In haemodialysis the patient’s blood is passed through a filter, known as a dialyser, which contains a semi-permeable membrane. The patient’s blood flows along one side of the membrane and on the other side there is dialysis fluid. This fluid is made up of ultra pure water and salts mimicking the ionic composition of blood plasma.
The membrane has minute holes in it that allow small molecular weight toxic substances, such as urea, that have built up to diffuse out of the blood into the dialysis fluid. Normally these toxic substances would be filtered out by the kidneys.
A major problem with haemodialysis is that the so-called middle or medium sized molecules, for example small proteins and polypeptides, are not removed effectively from the blood as the membrane pores are not large enough to allow these to pass through. Increasing the pore size of membranes risks contamination of blood by bacteria and endotoxins, which may be present in the dialysis fluid on the other side of the membrane, and loss of the large blood proteins that are essential to life, for example albumin.
Researchers from the University’s Department of Chemical Engineering are developing a carbon based sponge-like adsorbent, which would be able to soak up the middle molecules from blood, in a process called blood filtration or haemoperfusion.
Blood from the patient is removed from the body using a catheter and passed through a column containing the carbon adsorbent, much like the domestic water filters used in many homes. The middle molecules, which are harmful for the patient, are removed by the process of adsorption as they stick to the surface of the carbon and the cleansed blood is returned back to the patient.
A large part of the development process for the new carbon absorbent will be in overcoming the problems encountered when blood comes into contact with an artificial surface. This often activates the body’s immune system which, recognising the surface as being alien to it, initiates emergency measures to attack and destroy it. In developing this new technique the research team will have to ensure that it is biocompatible to enable it to be used in blood purification therapies.
Dr. Danish Malik, who is leading the research, said: “Development of a combined dialysis and adsorption-based detoxification system, where the carbon column removes the middle molecules whilst the dialyser clears the excess water and small molecular weight molecules, would be an ideal solution to current problems.
“This technology would substantially reduce the cost of acute and chronic renal treatment as well as significantly improve the quality of life for thousands of dialysis users by improving the purification of their blood.”
The two-year research project is being funded by the Engineering and Physical Sciences Research Council (EPSRC).