Biological Indicator Spore Layering for Reliable Sterilization Monitoring
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Solution Overview
Problem
Biological indicators often become sterile before the end of a sterilization cycle due to significant spore kill in pre-exposure conditioning phases, leading to unmonitored portions of the cycle and potential false positives from spore stacking, which can result in incomplete sterilization detection.
Innovation Solution
A biological indicator design with 70-95% of the spore deposit in a single layer and 5-30% in a stacked configuration, ensuring spore coverage throughout a substantial part of the cycle without survival at the end of a successful sterilization process, using a carrier with controlled spore stacking and a compartmentalized structure for growth media contact post-cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the spore population density is increased to extend monitoring coverage into the exposure phase, then the sterilization cycle monitoring is improved, but uncontrolled spore stacking occurs which leads to false positives
Solution Approach 1:
The spore deposit is designed with non-uniform local characteristics: the central region has a first spore population density while the peripheral region has a second spore population density that is 1.5 to 10 times higher. This local quality variation allows different regions to serve different functions - the central region provides baseline monitoring while the peripheral region extends coverage into the exposure phase without causing excessive overall stacking
Solution Approach 2:
The spore deposit is segmented into distinct central and peripheral regions with different spore densities. This segmentation allows the indicator to simultaneously achieve extended monitoring coverage through the higher-density peripheral region while maintaining reliability through the controlled lower-density central region, preventing false positives from uncontrolled stacking
2Loss of time
If the spore population density is increased to delay complete spore kill, then the monitoring coverage into exposure phase is extended, but spore stacking increases causing false positives
Solution Approach 1:
Different spore population densities in central versus peripheral regions create local quality variations that allow the system to extend monitoring time without generating harmful false positives. The peripheral region's higher density delays complete spore kill to extend coverage, while the central region's lower density maintains detection accuracy
3Reliability
If spores are deposited in high concentration to ensure coverage throughout sterilization cycle, then monitoring effectiveness is improved, but uncontrolled stacking protects underlying spores from sterilant exposure
Solution Approach 1:
The spore deposit is divided into central and peripheral segments with controlled density ratios. This segmentation ensures that while the peripheral region has sufficient spore concentration to extend monitoring coverage, the overall controlled stacking prevents complete blockage of sterilant exposure to underlying spores, maintaining monitoring reliability
Data Source
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AI summary
This invention relates to a biological indicator, comprising: a carrier; and a spore deposit on the carrier, wherein from about 70% to about 95% of the area of the spore deposit comprises spores residing in a single spore layer, and the remainder of the area of the spore deposit comprises spores residing in a stacked configuration.