Dead Dirt and Bio-Dirt
Barbara Kanegsberg & Ed Kanegsberg, April 2003
The medical world has long understood the importance of minimizing microbes
and other bio-based contaminants. Because implantable biomedical devices have
become smaller, more widely-used, and are expected to function reliably for
many years, all sources of contamination must be minimized.
Absolute cleanliness is probably an unknowable and unachievable goal. However, the maximum acceptable level of residual contamination, along with analysis and documentation of appropriate surface characteristics, is more readily determined. To this end, biomedical device manufacturers, along with regulators and other experts in the field, have established a team, the ASTM F04.15.17 Cleanliness Testing Task Force, to develop testing standards for biomedical devices. These standards will assist in establishing how clean is “clean enough,” or how clean is acceptably clean. The group has defined the project to include newly-manufactured implantable, non-resorbed medical devices made of metal, ceramics, plastics, or composites. Ultimately the task force is expected to establish multiple testing standards dealing with the cleanliness of biomedical devices.
The task force has generated a list of possible categories of residues
(Table 1). Some members indicated the desirability of establishing
acceptable limits
of the residues. Those involved in such critical manufacturing activities
as wafer fabrication, optics, aerospace, and even automotive applications
will
find many of the contaminants hauntingly familiar because, although biomedical
devices have particularly stringent performance and reliability requirements,
these contaminants occur throughout the manufacturing world.
The list of categories could grow; for example, thin-film organic residue of cleaning agents might be suggested as an addition. Further, desirable surface additives may need to be distinguished from contamination (see Kanegsberg and Chawla, “Beneficial Contamination,” A2C2, January and February, 2002.)
In addition, because the manufacture of biomedical devices often involves
multiple materials and multiple fabrication processes, contamination
stemming from operations
that occur during initial fabrication or metalworking operations that
occur outside of the cleanroom, or even at sub-vendor or supplier facilities,
may warrant consideration.
Beyond the value for biomedical device manufacturers, the task force
may produce standards of potential utility to a host of manufacturing
applications.
The
task force is considering details of sampling, extraction, and analysis
techniques, including specific determinations to complement the more
commonly-used gravimetric
approaches. There are issues of testing variability, so the group
may work with NIST to prepare reference specimens of known contamination
for round-robin
studies, as well as for process validation and calibration.
The next activity is a one-day workshop focusing on issues of cleanliness
for newly manufactured biomedical devices, scheduled for May 7, 2003
at the Westin
Crown Center, Kansas City, MO. The workshop will include presentations
by invited experts in the field of cleaning and cleanliness standards,
as well
as those
involved in producing or monitoring medical devices. To facilitate
information exchange, the workshop will involve both presentations
and roundtable
discussions. On the following day, the Cleanliness Testing Task Force
will work on standards
outlining sample preparation techniques, methods of analysis, and
ultimately on acceptable residue levels. In a highly competition-sensitive
and
heavily regulated world, this laudable collaborative effort is worthy
of support.
For additional information about the workshop and the task force, contact Stephen Spiegelberg, Cambridge Polymer Group, 617-629-4400, ext. 12.Email, Web Site
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.
