ASTM Update

Barbara Kanegsberg and Ed Kanegsberg, August 2005

WE PERIODICALLY PROVIDE UPDATES on the progress of the ASTM F04.15.17 Task Group on Cleanliness of Biomedical Devices to develop standard methods to assess the cleanliness of biomedical devices [1]. The May 2005 ASTM Committee Week meetings in Reno, NV included both a committee meeting of the F04.15.17 Task Group to fine-tune the proposed standard and a half-day symposium. The Symposium on Cleanliness of Implants was an information-laden, thought-provoking session consisting of fourteen contributed reports and studies on cleaning methodologies and analytical methods to assess cleanliness.

General Trends
The international makeup of both the presentations and attendees at the symposium reflects an overwhelming, world-wide concern for cleanliness issues. The presentations also illustrate an increasing awareness that contamination issues are far more complex than sterilization. This complexity is due not only to the diversity of product sizes, shapes, and purposes. It is also due to the large numbers of potential contaminants and to the diverse methods to either~ remove these contaminants or to assess the degree of contaminant removal. A number of presenters noted that contamination could be introduced at any stage of the manufacturing process including assembly, inspection, packaging, transport, and handling. The presentations of cleaning methods covered a range of aqueous, organic solvent, and non-liquid (specifically plasma) approaches.

Presentations addressing cleanliness validation highlighted the variety of available analytical techniques. In addition to the proposed gravimetric standard for overall contamination determination, the merits of additional sensitive, specific methods such as Fourier Transform Infrared Spectroscopy {FTIR), X-Ray Photoelectron Spectroscopy (XPS), Total Organic Carbon (TOC), and Gas Chromatography-Mass Spectroscopy (GC-MS) were discussed.

Some Specific Presentations
The symposium presentations were informative and thought-provoking. We shall highlight a few of the specific presentations.

Researchers from the University of South Australia reported [2] on a plasma technique to clean hydrox~ yapatite (HA) coated pins that are used for surgical treatment of bone fractures. The study elucidated another aspect of device manufacture, the importance of understanding the surface chemistry (surface quality or surface attributes). XPS revealed silicon contamination on the HA coating that was traced to a rubber cap that protects the pin from its plastic package. The plasma technique removed the contaminant.

A technique developed by Hyperflo, Inc. [3] utilizes modulation of pressure to target contaminants. Under reduced pressure and controlled temperature, "pre-boiling" bubbles tend to grow on uneven areas of a surface. Therefore, discrete surface contaminants would tend to be targeted. When the pressure is subsequently increased, the implosive energy of the bubble creates sufficient force to detach the contaminant.

A comparative study performed at Stryker Howmed-ica Osteonics [4] indicates that citric acid may be a promising substitute for nitric acid passivation of metallic instruments. Citric acid is safer to handle and less costly to dispose of.

Two presentations illustrate both the utility and potential pitfalls of ultrasonic techniques for cleaning or extraction. A validation of a gravi-metric extraction method such as that being developed by the FO4.15.17 Task Group was presented by Wright Medical Technology, Inc [5]. An adherent buffing compound was extracted from porous bead coated metallic coupons. Using ultrasonics in hexane, extraction times of up to six hours were needed to obtain sufficient extraction. BFK Solutions LLC, presented a discussion of ultrasonic parameters for cleaning or extraction methods [6]. Ultrasonics is a very complex, not fully understood process, with many parameters. Although it is a powerful tool for cleaning, ultrasonic action can cause product damage under some conditions. Several examples of product surface modification were presented, including indications of surface alteration after one hour or less of ultrasonic exposure.

Following the Symposium, the Task Force continued to fine-tune an initial proposed standard for gravimetric determination of residual contaminants in metal implantable devices. In anticipation of standard approval, complex coupons to emulate test devices are being developed for use in round-robin testing.

References:
1. B. Kanegsberg, E. Kanegsberg. "Measuring Contamination in and out of the Clean-room," A2C2 Magazine, (October, 2003; July, 2004).
2. S. Kumar and W. Skinner. "Plasma Cleaning of a Commercially Available Hydroxya-patite-coated External Fixation Pin by the Radio Frequency Glow Discharge Technique," ASTM Symposium on Cleanliness of Implants, Reno, NV, (May 18, 2005).
3. C. Frederick, D. Gray. "Sub-Sub Micron Cleaning Using Vacuum Cavitational Streaming (VCS)," ibid.
4. J. Phillips. "A Comparitive Study between Citric Acid and Nitric Acid for Use in Passi. vation of Metal Instruments," ibid.
5. M.T. Hooper, J.P. Mosley. "Validation of a Gravimetric Procedure for Recovery of Processing Materials from Porous Coated Implants," ibid.
6. B. Kanegsberg and E. Kanegsberg. "Parameters in Ultrasonic Cleaning for Implants and other Critical Devices," ibid.

Barbara Kanegsberg and Ed Kanegsberg are independent consultants in critical cleaning, precision cleaning, surface preparation, and contamination control. They are the editors of “Handbook for Critical Cleaning,” CRC Press. Contact them at BFK Solutions LLC., 310-459-3614; info@bfksolutions.com; www.bfksolutions.com.