The sterility of the filtration device is one of the important factors in the successful of the steam sterilization
Sterilization of filters considering factors includes: applications emphasizing weak -chemical conditions, vulnerable to damage of filter membranes, components heat- excessive temperature, mechanical – high differential pressure, chemical – structural materials. Filters should be sterilized in accordance with field recommendations and must be validated for the intended purpose of each sterilization process: consideration of the effect on filtration performance, integrity, stability, precipitates and leaches, post-sterilization integrity testing to confirm that the filters are not damaged during sterilization
The most common sterilization methods: 1. steam sterilization 2. online sterilization
Filter assembly preparation is very important, for it is important to protect the sterile filter components, microbial barrier can be avoided after sterilization of pollution, and it must allow the steam get into the sterilization with filter, the filter air inlet and outlet must be free to exhaust, cycles of the differential could damage the integrity of the filter. Pre-packaged items have only enough packaging material to protect critical surfaces and allow free transfer of saturated steam, thus to sterilize the filter, minimizing the usage of sterilizing tape is required. In addition, the filter manufacturer’s specifications should be consulted when establishing a pressure sterilization process for the filter composition. If the filter is sterilized outside the room where it is placed, it should ensure proper support to prevent deformation. Air removal is one of the main difficulties encountered in autoclave sterilization. Initial vacuum and steam purge cycles are used to remove air in the initial stage of sterilization to prevent cold spots which will result in the incomplete sterilization. Sterilization temperature is generally required to be greater than 121℃ to achieve the sterilization effect of filter components. A slow discharge should be used at the end of the sterilization process to avoid excessive differential pressure passing through the filter during the cooling phase. After sterilization, the filter should be took out in time, and cannot be kept inside the autoclave for long time to prevents oxidation damage from hot air
Online sterilization also known as SIP, the filter housing can withstand a pressure of 15-30psig (1-2bar). For the filter element, the pressure difference in the steam process is the main consideration. At the steam temperature, the high steam flow can lead to high pressure difference, so install pressure gauges upstream and downstream of the filter to monitor the pressure difference. And it should avoid large downstream systems or large volumes of steam passing through the filter assembly. Steam should be directed through the filter and directly into the large downstream system. And free drainage and removal of condensate is also important, the filter might adsorb to hydrophobic filters and dry hydrophilic filters, resulting in high differential pressure. Steam cannot initially pass through a wet hydrophilic filter, which must be heated to allow steam to flow through. Upstream vents and drains are fully open to allow steam to flow through the filter element. Once free steam flow is able to pass through the filter element, the vents and drains can be throttled. The pressure of steam should be gradually increased to avoid excessive differential pressure and enhance the removal of condensed water. In the cooling process, it should avoid reverse pressure, filter shell cooling faster than the kernel, make the upstream steam pressure drops rapidly, pressure and temperature remains in the filter core, which may lead to a temporary high reverse pressure difference and the damage of the filter, by the positive air pressure at the upstream, the gas could keep positive pressure when getting through the filter.