Learning The Basics About Dialysis Membranes

As Joe Cosgrove has already said in this blog, dialysis is a method used on patients who have End Stage Renal Disease (ESRD) and whose kidneys are not able to filter blood properly in order to remove waste from it.

Renal Dialysis Technician

Image courtesy of wistechcolleges at Flickr.com

As the dialysis process needs to filter blood waste, it should use a membrane in order to do so. Nowadays, most of these membranes are artificial ones, made out of polymer compound and blends. The most common polymer used to manufacture dialysis membranes is regenerated cellulose. However, many companies have developed modified cellulose membranes and even synthetic polymer membranes that are useful to filter blood.

Dialysis membranes are used clinically to remove waste from the patient’s’ blood. Most of this waste is made of uremic toxins that would otherwise cause blood intoxication. Besides removing waste, these membranes are responsible for providing the lacking dialysate ions the body needs to properly function.

As the number of patients who need dialysis increases so does a number of dialysis membranes that are required to treat them. Every year, at least 70 million square meters of dialysis membranes are used in the world. The most common type of dialysis membranes that is used to remove accumulated toxins is made of hollow fibers. A hollow fiber membrane included numerous materials, such as cellulose and other synthetic polymers.

Related: Which dialyser membrane to choose?

A Bit Of History

At first, dialysis membranes were made of cotton or cotton derived fibers. These membranes were thought to be natural ones and their structure would activate blood leukocytes and their immunity response. Due to this, the body started to develop inflammatory responses and finally, it was concluded that those membranes were not biocompatible with the body.

In time, scientists started to develop polymers made of both natural and synthetic compounds in order to mitigate the body’s response and further development of inflammatory reactions. This is how it was concluded that cellulose was more biocompatible to the body and didn’t cause as many reactions as cotton would do. Research institutions started to develop cellulosic membranes that were highly more compatible to the body and modified cellulosic membranes were born.

Many membranes have been developed over the years. Currently, we can find synthetic membranes with higher filtration capacity due to the larger size of their pores. This way, synthetic membranes can remove more particles than “natural” ones would do. This is how, besides the low flux cellulose membranes, five types of high-flux synthetic membranes can be found in the market today.

Characteristics

Biocompatibility: This characteristic describes how a membrane can cause a biological or biochemical effect on the body. In other words, is there is an inflammatory reaction in the body, the membrane is not biocompatible because it activated the leukocytes and made them react. This usually happens when natural fibers are not modified.

The main cause of death in dialysis patients is caused by these inflammatory responses. When healthcare providers use synthetic materials, patients have a better response to the dialysis treatment. This happens because high-flux synthetic polymers don’t activate leukocytes as unmodified cellulose membranes do, therefore they are considered to be more biocompatible to the body and their mortality rate associated with them is lower.

Impermeability: This characteristic is related to the membrane’s impermeability to dialysate impurities such as bacteria. Dialysate can be easily contaminated by other substances, allowing dangerous substances enter the body through the membrane directly to the blood stream.

Those membranes with larger pores, paradoxically, have fewer chances of filtering bacteria directly to the blood stream. This happens because membranes with larger pores are more absorbent that those with smaller pores. This way, synthetic membranes or cellulose modified membranes can absorb more bacterial products of dangerous substances for the body. These membranes are considered to be more impermeable to impurities.

However, it is recommended to use pure dialysate on patients, simply to avoid taking any potential risk that may affect the patient’s health. Using a synthetic membrane can be understood as taking an additional precaution.

Adsorption: As it was said before, membranes used during the dialysis process need to be absorbent. This way, they can remove any potential threat present in the dialysate fluid. There are some peptides, necrosis factors, and other substances that should be absorbed by the membrane in order to keep the body healthy.

In order to increase the membrane’s capacity to absorb impurities, most dialysis machines also include other inner systems such as beads with special properties meant to absorb harmful substances. This way, the absorption capacities won’t rely exclusively on the membrane, but also on the dialysis machine.

Filtered

Image courtesy of Amy at Flickr.com

Pore size: This characteristic varies from one material to another. Natural membranes have smaller pores and synthetic membranes have larger pores. Nowadays, scientists and researchers have created new synthetic materials and compounds that allow membranes to have larger pores, increase the flux and properly remove harmful substances.

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