Snow blasting cleans medical and pharma parts resources-efficiently

The suitability of snow blasting technology for cleaning medical and pharmaceutical products was investigated in a joint project. Until now, liquid-based cleaning processes with very high resource consumption have been used for this purpose.

The necessary surface cleanliness of medical and pharmaceutical products is usually achieved during their manufacture using liquid-based cleaning processes, which require an enormous amount of energy and water. In order to effectively reduce the use of resources, the material compatibility of the dry QuattroClean snow jet cleaning technology on various product-typical surfaces of medical and pharmaceutical products was investigated as part of a joint project funded by Invest BW with industrial partners and the Fraunhofer IPA and NMI institutes at the University of Tübingen. The results of the tests, which included in-vitro cytotoxicity tests as well as VOC and SVOC analyses, confirm the suitability of the cleaning process for a wide range of applications. In order to lower the approval hurdles, an extensive basic validation for life science applications was carried out in parallel.

In the manufacture of medical and pharmaceutical products, a cleaning process is suitable if contaminants are safely removed and a product-specific defined level of cleanliness is stably achieved. At the same time, changes to or damage to the product surface of the items to be cleaned must be avoided. Classic, liquid-based cleaning processes fulfill these requirements for a wide range of materials used for life science products.

This experience is not yet widely available for the dry CO2 snow jet cleaning process "QuattroClean". The aim of the joint project with five industrial partners as well as the Fraunhofer Institute for Manufacturing Engineering and Automation IPA and the NMI Natural and Medical Sciences Institute at the University of Tübingen was therefore to prove the suitability of the process in principle for cleaning a wide range of materials typically used in medicine and pharmaceuticals.

The primary aim was to prove that the mechanical forces of the snow crystals do not change, impair or damage the surface. In addition, the aim was to determine whether the thermal load and/or the chemical properties of the carbon dioxide affect the surfaces or the biocompatibility of the materials, for example by releasing cytotoxic material components.

The tests were carried out with test specimens made of stainless steel 1.4301 and 1.4305 with different surface textures as well as polyether ether ketone (PEEK), polyether (PE), polyoxymethylene (POM), Nitinol, cobalt-chrome and glass vials.

For the basic validation by Fraunhofer IPA, the surfaces of the test specimens were examined microscopically (light and/or scanning electron microscope) in their initial state. Subsequent cleaning was carried out under worst-case conditions: The test specimens were continuously irradiated locally in the center and at the edge with the CO2 snow at a high pressure of twelve bar for ten seconds.

Evaluation with regard to surface changes

The subsequent microscopic evaluation of the surfaces using a light and scanning electron microscope showed no impairments such as structural changes, damage, changes in surface roughness, flaking, etc. on the surfaces. It was found that slightly protruding burrs on the phase edges were partially removed. No cracks formed on glass vials as a result of the cleaning and no propagation of existing cracks was observed. Using a fluorescent penetrant, it was also possible to prove that the snow crystals did not cause any additional stresses in the glass. Similarly, abrupt exposure to cold and subsequent warming of the vials to ambient temperature did not lead to any microcracks.

Evaluation of biocompatibility

In vitro cytotoxicity tests according to DIN EN ISO 10993-12: 2021-05 and DIN EN ISO 10993-12: 2021-08 confirmed that the CO2 snow does not have any negative effects on cell vitality. The VOC and SVOC analyses carried out in accordance with ISO 16017-1 resulted in Tenax values within or below the measurement limits.

Material compatibility with stainless steels

The NMI tested the material compatibility of quattroClean snow blast cleaning on stainless steel 1.4301 and 1.4305 in even greater detail. The surfaces were examined before and after treatment with the CO2 snow blast using photoelectron spectroscopy. The comparisons and analyses showed that cleaning the stainless steels with the process does not lead to any material changes and can be classified as compatible with the material.

The extensive investigations have demonstrated the suitability of QuattroClean snow jet technology for a wide range of applications in the medical and pharmaceutical industries as a resource-saving cleaning process. It is a dry cleaning process for full-surface and localized applications that uses liquid, recycled carbon dioxide as a cleaning medium. It is passed through a wear-free two-substance ring nozzle and expands into fine snow crystals as it exits. These are bundled by a separate, ring-shaped jet of compressed air and accelerated to supersonic speed. The cleaning effect is based on a combination of thermal, mechanical, solvent and sublimation effects when the easily focused jet of compressed air hits the surface to be cleaned. With regard to particulate residual contamination, cleanliness levels in the sub-micrometer range are reproducibly achieved. In the case of filmic contamination, the cleaning result is comparable to that of other ultra-fine cleaning processes such as wet-chemical and plasma cleaning. Removed contaminants are extracted in the compact cleaning cell, preventing recontamination of the parts and contamination of the environment. As the crystalline carbon dioxide completely sublimates during the process, the residue-free cleaned surfaces are dry - there is no need for time-consuming and energy-intensive rinsing and drying processes.

For optimum adaptation of the cleaning solution to the respective component geometries, requirements and production situation, the manufacturer offers various modular solutions and individually planned systems, including cleanroom-compatible versions, for example for high-purity applications. This includes media treatment for the liquid carbon dioxide, which ensures a purity of 99.995 percent; the compressed air quality is 1.2.1. Process validation and design are carried out on a customer and application-specific basis through tests in the manufacturer's cleanroom-based technical center (OM-8/25).