Authors: Jacob Andrews - Technical Director of Filtration Technologies 
Angie Young – Medical Marketing Coordinator 

There are many important considerations when choosing a filter for your medical device application.  Ultimately, it is essential that the filter is fit-for-purpose, meaning it meets the critical to quality (CTQ) requirements of your application.  Because not every application has the same CTQs, a filter that is suitable in one application may present unacceptable risk in another application.  This post discusses key filter attributes and their impact on the filter’s ultimate suitability for use.  These attributes will be discussed in greater detail in future posts. 

As an example, a filter that is used to protect a pump or sensor in a medical device may represent one level of criticality – typically bypass of the filter in such applications may lead to premature repair or even replacement the device.  In contrast, the bypass of a filter used as a sterile boundary in surgical applications, endoscope reprocessing, and many other applications can result in patients being exposed to bacteria, viruses or other harmful contaminants.  In these most critical applications, the use of 100% integrity testing to ensure there is no filter bypass is paramount to patient safety whereas such testing may not be required in less-critical applications. 

The first example, however, also highlights the importance of accurately and completely assessing the risk of filter’s failure in use – even in applications which typically may not be considered critical.  If failure of a sensor or pump (due to bypass of the filter intended to protect it) would result in a catastrophic failure and/or a risk to patient safety, additional qualification and testing may be required – beyond what is typical for a pump protector filter. 

In addition to the filter’s reliability and associated release testing requirements, the filter’s performance, compatibility, size, connectivity, and regulatory compliance attributes must be chosen or designed to meet your project and device requirements. 

Typical performance attributes of a filter include its retention efficiency (ability to remove contaminants of different sizes), flow rate versus differential pressure, and liquid repellency.  These attributes are impacted significantly by the application and therefore need to be chosen with a detailed understanding of the intended use.  As an example, a filter’s retention capability will differ significantly in liquid versus gas and both liquid retention and repellency may be significantly impacted by nature of the liquid (for instance the presence of surfactants) and usage conditions (time, temperature, pressure).  

A filter’s size and connectivity may offer convenience to a device user or may be critical to the proper function or design of the device itself.  The use of drip-free and gendered quick-connect fittings can improve ease of installation / removal, prevent improper installation, and protect the device from damage caused by spillage.  In applications where filter orientation is critical for proper function or where sensitive device parts can be damaged by spillage, implementation of these features into the filter design can reduce the risk of failure in use. 

Given the multitude of variables (application conditions and filter attributes) that impact a filter’s fitness for use in a medical device application, off the shelf (standard) filter products are often unable to satisfy all user requirements.  In some cases, medical device development engineers are able to ‘work around’ a standard product offering – for instance by increasing the overall device size to accommodate an over-sized standard filter or by adding tubing and adaptors to achieve the desired fitting connection and location.  However, in many cases standard filters are unable to meet the risk-based requirements of the intended use (e.g. where 100% integrity testing is needed) or workarounds are undesirable (e.g. due to the increased risk of leakage in the case where extra adapters are needed).  In these cases, medical device design engineers can optimize their designs and reduce their development cycle without compromise (by eliminating re-designs and workarounds) through the use of purpose-built customized filter solutions. 

Through co-development between medical device design engineers and filter applications and design engineers, the size, shape, connectivity, materials, and quality/regulatory attributes of the filter are selected to meet the specific requirements demanded by the intended use.  Further, through validation, qualification, and quality control testing, the filter’s reliability and fitness for use is assured.  The result is filtration-enabled medical device designs that are simpler, faster to market, and successful. 

Saint-Gobain offers engineered filtration solutions that can be customized for your application.  For more information contact us at www.medical.saint-gobain.com/contact-us.