Saving Cells – Safer Method for Filtering Sensitive Biological Products

For many years, engineers have worked to efficiently filter valuable bio-process products on an industrial economic scale. The challenge has been to push rates up without incurring high shear rates and resultant cell lysis, which would cause loss of yield. High shear can destroy delicate and valuable biological materials such as proteins, blood, algae and yeasts, and also brings with it a requirement for higher flow rates, which in turn raises pumping costs.

Inventors at the University of Oxford have developed two very elegant solutions to this dilemma, each of which would allow bio-process engineers to “have their cake and eat it” – i.e. achieve high flux AND low shear. Both technologies are improvements upon the existing practice of using ceramic block or tubular membrane filters, allowing users to obtain breakthrough performance without incurring massive disruption.

The first method is an insert that could be applied to existing tubular membrane filters (TMF) as an add-on. It can be used to achieve excellent mixing at low rates of flow and with a laminar flow pattern. This combination helps to minimise cell damage in the filtration of sensitive materials as high filtration fluxes are obtained at much lower feed flow rates than are currently achieved using existing equipment. The method has been successfully used for ultrafiltration of protein solutions with high flux and negligable fouling; separation of plasma from whole blood by microfiltration and separation of high concentration yeast suspensions. All of these important processes can be achieved more effectively at a much lower cost if the insert method is adopted.

The second method or “Helical Groove” ceramic block membrane filter would be a suitable replacement for an existing ceramic block filter element. Normally the performance of these filters is limited by the efficiency of fluid mixing. The helically grooved internal structure of the new membrane allows optimisation of radial mixing as the surface area of the filter is increased. The inherent properties of the filters are also important and include excellent chemical and thermal stability and rigidity. From a practical point of view they are easy to sterilise and can be easily adapted for use in large-scale units.

The inventions are now the subject of granted patents and a ten-tube microfiltration module is available for demonstration purposes. Companies interested in developing these systems for commercial applications should contact Isis Innovation Ltd.