Membrane Materials and Applications for In Vitro Diagnostics

Industrially manufactured membranes play a vital role in the effectiveness of in vitro diagnostics instruments and procedures, such as protein assays and liquid/gas filtration applications. In this article, we cover some of the different types of membranes available for use in the field of in vitro diagnostics, the key features and characteristics, and applications for use.

Characteristics of Membranes for In Vitro Diagnostics

Various membranes have distinctive characteristics that suit them to specific applications. Below we explore some of the main attributes for evaluating membranes.

Pore Size

Pore size relates to the size of the particles that the membrane can trap. The measurement (in µm) refers to the minimum diameter of the particles filtered from the fluid.

Membranes used in ultrafiltration, however, consider the nominal molecular weight limit (NMWL) of substances rather than the pore size of a membrane.

Pore size and NMWL are not the ultimate measures of the effectiveness of a membrane. Also for consideration is the filtration application when selecting the best-suited material.

Flow Rate

The flow rate of a membrane determines how fast a stream passes through the filter. It is affected by the pore size, membrane thickness, pore architecture, among other attributes. 

Membrane selection is typically based on the required retention and flow rate. A high NMWL rating increases the flow rate but reduces retention and vice versa.

Extractables

These are contaminants from the apparatus or filter that end up in the final filtrate. They can result from:

• breakdown of the filter material
• Impurities washed off the filter
• Residual chemicals from the manufacturing process

The quality of the membrane material used can have a considerable impact on the integrity of the filtrate.

Chemical Compatibility

Filter material should be compatible with the chemical properties of the filtered fluid and the prevailing filtration conditions. Otherwise, it can jeopardize the structural integrity of the membrane. The surface should not adsorb the desired solute. For instance, when biomolecules come into contact with some polymer-based membranes, they get bound on the surface until saturation. Adsorption can hurt the productivity of a filtration procedure.

Types of Filter Membranes and Their Uses

Taking a closer look at several membranes and their application. 

Polyethersulfone (PES)

PES membranes are hydrophilic and non-specific protein adsorptive filters with high flow rates. They come in many pore sizes and diameters, and the filtrate demonstrates minimal extractables.

The filters are resistant to chemical action over the 1-14 pH values. For this reason, they are ideal for the filtration of aqueous solutions and various pharmaceutical solutions and solvents.

Regenerated Cellulose (RC)

Membranes made of regenerated cellulose are also hydrophilic, high flow-rate, and low-adsorption filters. They are suitable for almost all fluids, including solvents, since they can withstand pH 3-12. Their asymmetric architecture reinforced with nonwoven cellulose makes the filters long-lasting.

Polyamide Membranes (PA)

Apart from being hydrophilic, PA membranes are resistant to many organic solvents and alkaline solutions. They are also excellent for the filtration and sterilization of aqueous solutions for analytical determination. They are applicable where a membrane material of relatively high adsorption is necessary.

Polytetra-Fluorethylene (PTFE)

PTFE membranes are hydrophobic membranes that can filter air, gas, and chemicals like acids and solvents of all pH levels. To use them for aqueous solutions, you need to pre-wet them with methanol or ethanol. They have multiple pore sizes for most filtering applications.

Conclusion

Filter membranes for in vitro diagnostics come in different materials and construction engineered for various purposes. They vary in pore sizes, flow rates, pH tolerance, and other properties.