Projects that utilize large volumes of nonmetallic materials of planetary protection concern pose a challenge to their bioburden budget, as the most conservative value of 30 spores/cm3 is typically used. The standard laboratory procedures do not provide any direction into the methodologies to understand the embedded bioburden within such nonmetallic components such as adhesives, insulation, or paint. A project can elect to conduct a destructive hardware study to experimentally derive a sourcespecific encapsulated microbial density, and the experimental value can be utilized for a project.
A tailored, novel, destructive hardware technology employing a household box grater was developed to assess the embedded bioburden within the adhesives, insulation, and paint for the Mars Science Laboratory (MSL) project. Similar technologies used for the destructive analyses of nonmetallic components include chemical/solvent-based methods, blenders, mortar and pestle crushing, French press, pulverizing, and bead beating methods. These similar technologies are typically lethal to viable biological cells due to the excess generation of heat or adverse chemical interactions that render cells non-viable. These typical destructive hardware methodologies proved ineffective in breaking up the material into suitable size particles due to the material composition of the adhesives, insulation, and paint. Therefore, a novel approach had to be devised.
Samples were placed on a sterile tray and cut into three 5×5 cm pieces. The cut piece was wiped with a sterile wipe and 2-propanol. The cleaned material was then grated gently on the smallest grading plane on the box grater into sugar-crystal-sized pieces. The box grater approach is advantageous due to the ease and ability of the entire system to be sterilized, minimal (or negligible) impact to recontamination if performed in a Class 100 flow bench, and controllable heat generation upon material destruction. The recovery percentages of spores seeded on flight or surrogate materials were <10% for surrogate and <50% for flight, and could be applicable along with other chemical or physical technologies.
This work was done by James N. Benardini, Fabian Morales, Wayne W. Schubert, Gayane A. Kazarians, and Robert C. Koukol of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48299