MSU Researchers Continue to Probe Hole Threats

Researchers are working to clarify initial findings that suggest that pressure differentials (PD) experienced during transportation do encourage microbial ingress into sterile barrier systems. The work is just one phase in a project that set out in 2004 to answer this question: What is the smallest hole that will cause a sterility breach in sterile medical packaging?

Laura Bix, PhD, assistant professor at Michigan State University’s (MSU) School of Packaging, continues to lead researchers. In 2006, work by graduate student Jane Severin evaluated the effect of PDs on trays with nonporous lid stock, which had intentional defects of either 10- or 100-µm holes. Severin found that all samples subjected to PDs that mimic 8000 ft in altitude had “significantly more colony-forming units than did those that were not subjected to PD. But even those samples had some growth,” says Bix.

“With 100-µm holes, you will see growth with or without PD. But Severin’s tests with 10-µm-hole trays showed that the majority of those with growth had PD, and at least one without PD had growth,” Bix adds.

Ondrea Kassarjian is working with Bix to repeat the methodology Severin used “in order to be sure there were no false positives or negatives,” says Kassarjian, who also serves as training programs manager for Lansmont Corp.

All trays will be tested on a microflow detection system from ATC. Visual inspection and microbial challenge aerosolization will also be performed. Smith & Nephew has sterilized the packages and returned them to MSU to begin tests.

Later phases of the study will involve subjecting trays with 100-µm holes packaged in solid-bleached-sulfate cartons to PDs to evaluate microbial ingress.

“Eventually, we may go with some sort of mathematical probability to determine, based on a given microbial concentration, flow rate, and hole size, what the probability of something falling in with or without PD is,” Bix points out. “The deeper we get into it, it appears that it is all about probability. It is almost like determining a sterility assurance level.”

It may be too early to “assume that a 10-µm hole presents a threat,” Bix says. “We are using a high microbial concentration, and a porous lid stock would forgive some of the PD.”

Study results could one day help packagers balance risk and economics. For more information on the research or to help fund the research, contact Bix at 517/355-4556 or at bixlaura@msu.edu.