Appeal No. 2005-1608 Page 4
Application No. 10/424,327
paragraph of page 10 of the specification. Here, the specification indicates that “PMP hollow
fibers have a natural tendency to shrink which increases with temperature.” It is said that, “in
preferred embodiments of the invention, the PMP fabric 36 is preshrunk prior to winding.” The
specification further states that “a preferred method of preshrinking and stabilizing the fabric is
to heat the fabric to about 15 °C above the expected operating temperature for approximately 2
to 8 hours, preferably 4 hours.” All references to “pre-shrunk” in the specification are to a
process operation of pre-shrinking by heating. Therefore, we cannot agree with Appellants that
“pre-shrunk” is a structural limitation per se in the context of Appellants’ claims. Because “pre-
shrunk” references a process step, this limitation can only serve to differentiate the claimed
structure from the prior art structure on the basis of the structure that arises due to the operation
of pre-shrinking. While Appellants are correct that they are free to define the device by what it
does rather than by what it is, In re Swinehart, 439 F.2d 210, 212, 169 USPQ 226, 228 (CCPA
1971), such a method of claim drafting carries the risk that the claims will not distinguish the
structure from that of the prior art. In re Schreiber, 128 F.3d 1473, 1478, 44 USPQ2d 1429,
1432 (Fed. Cir. 1997).
Appellants argue that “pre-shrunk” is a structural limitation in the claim because it is cast
in a product claim format and is it used in the past-tense form instead of the “ing” form of the
verb, i.e., pre-shrinking as used in process claims. This is not persuasive because whether the
claim recites the limitation as a positive process step or more subtly references the process by
using a past-tense verb form, the words still reference a process operation. See In re Brown, 459
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