Using Dynamic Imaging Particle Analysis to Characterise Biologics

In recent years we have seen an increase in the role of biologics in medicine. Biologics are medicinal products that are created by biologic processes instead of chemical synthesis; these include products such as blood, vaccines, gene therapy, allergenics or somatic cells. Because of the increased role of biologics, the need to characterise particulate matter within those biologics has increased as well. In this article, we’ll take a look at how dynamic imaging particle size analysis is being used to characterise particulates in biologics, as well as some of the factors that need to be considered when using the technology.

The early days: Light Obscuration

In the early days of particle analysis in biologics, analysts used light obscuration techniques to attempt characterisation, but this method meant they faced a few hurdles. These were as follows:

The transparency of aggregated proteins

Biologics are subject to protein aggregation — that is, the formation of larger particles from a combination of smaller ones. Because aggregated proteins are transparent or “soft”, they are much tougher to detect than opaque particles, and light obscuration technology was not always able to detect them.

The amorphousness of aggregated proteins

The shape of the aggregates vary from circular to strand-like shapes. Light obscuration devices are capable of measuring size, but they assume that the particles are spherical in shape. Because aggregates could be absolutely any shape, many measurements were inaccurate.

The biologics are delivered through pre-filled syringes

This could result in silicone droplets being present, and might also result in inflated particle counts.

The introduction of Dynamic Imaging

A dynamic imaging particle size analyser, on the other hand, is capable of making various measurements even if the particle is transparent. It works by capturing digital microscopic images of biologic particles as they make their way through a flow cell. The result is a more detailed description of the particle and its shape, which also allows for analysts to recognise the difference between aggregates and silicone droplets.

Dynamic Imaging limitations

It would seem, then, that dynamic imaging has solved the problem of characterising biologics — but that’s not to say that the technology is perfect. In particular, there are three factors that analysts must consider whenever characterising biologics with the use of dynamic imaging. These are:

Resolution

Digital images don’t show the real world in the same way that the human eye does. Instead, images are pixelated, which means dynamic imaging systems can only count particles that are no smaller than 1µm, and can only differentiate shape for particles larger than 2-3µm. Electron microscopy is needed to measure particles smaller than these limits, but such a technique has many shortcomings of its own.

Colour threshold

Images are not only limited in size; they are also limited in their colour scale. Because imaging systems are backlit, particles in the optical path reduce the light that passes through to the camera sensor and, as such, the incoming pixel intensity becomes darker. This works fine for opaque particles, but not so well for the transparent protein aggregates. Additionally, the amorphous nature of the aggregates causes light to bend awkwardly around the structure, creating further confusion.

Image quality and sharpness

This great effects on the precision of particle measurements. The less sharp the image, the lower the accuracy when attempting biologic characterisation.

Finding a particle size analyser

Particle size analysers play a key role in biologics, so it’s important that you one you use is of a high quality and from a trusted supplier. ATA Scientific offers a range of quality particle size analysers perfect for characterising particulates in biologics. Contact us today for more information.