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Howmedica Osteonics Corp. v. Zimmer

June 13, 2007


The opinion of the court was delivered by: Walls, Senior District Judge


In this action brought by Howmedica Osteonics Corp. ("Howmedica") for infringement of four of its patents relating to medical implants, defendants Zimmer, Inc., Zimmer Austin, Inc., and Smith & Nephew, Inc. move jointly for summary judgment on the issues of invalidity and non-infringement as to three of those patents. Defendants' motion for summary judgment on invalidity asks the Court to determine that numerous patent claims are invalid because they contain an equation term ("Arrhenius' equation") which is not amenable to definite construction by a person of ordinary skill in the art. Defendants' motion for summary judgment on non-infringement principally argues that Howmedica is foreclosed from proving infringement because it has not disclosed in discovery the precise manner in which defendants' products infringe its patents.

Having considered the parties' written submissions and oral arguments, the Court grants defendants' motion for summary judgment on invalidity. Accordingly, it will not address the motion for summary judgment on non-infringement.


A. Parties and Procedural History

Howmedica is a New Jersey corporation that manufactures and markets medical implants such as artificial knee and hip implants. Starting in 1993, Howmedica filed a series of related patents that disclose processes for irradiating and then heating polymers used in medical implants. The treatment increases the oxidation resistance of the polymer. A polymer with greater oxidation resistance retains its physical properties better, which makes it more suitable for use in medical implants because it deteriorates more slowly in the body.

Defendants Zimmer, Inc., Zimmer Austin, Inc., and Smith & Nephew, Inc. are also corporations in the business of manufacturing and marketing medical implants. In February 2005, Howmedica filed suit against defendants, alleging that they had violated 35 U.S.C. § 271 by infringing four of Howmedica's patents relating to polymeric materials used in medical implants. These four patents are U.S. Patent No. 6,174,934 B1 (filed Jan. 23, 1998) ("the '934 Patent"); U.S. Patent No. 6,372,814 B1 (filed June 28, 2000) ("the '814 Patent"); U.S. Patent No. 6,664,308 B2 (filed Jan. 8, 2002) ("the '308 Patent"); U.S. Patent No. 6,818,020 B2 (filed June 13, 2003) ("the '020 Patent") (collectively, "the patents-in-suit"). Howmedica claims that four of the defendants' products, Longevity, Prolong, Durusul, and XLPE, infringe on these patents.

In January 2006, after considerable discovery, the parties filed reciprocal Markman motions requesting that the Court construct numerous patent claims. On July 27, 2006, defendants filed the present motion for summary judgment. The Court decided the Markman motions in April 2007. The parties argued the motion for summary judgment on May 15, 2006.

Defendants move for summary judgment on the issues of noninfringement and the invalidity of the asserted claims of Howmedica's '934, '814, and '308 Patents. They argue that they are entitled to summary judgment on invalidity because the Howmedica patent claims at issue do not provide precise boundaries to the inventions they disclose. Defendants also seek summary judgment on non-infringement because Howmedica is unable to demonstrate how defendants' products infringe on these three patents. As said, the Court will not reach the issue of non-infringement because it finds the patents invalid.

B. The Invention

1. Background

Howmedica's patents describe a process for making medical implants from a polymer, typically ultra-high molecular weight polyethylene ("UHMWPE"), that has been irradiated and then heated. Irradiating and then heating the polymer in an oxygen-free environment for a defined period of time at a defined temperature will cause chemical reactions that make the polymer stronger by forming cross-links between polymer chains.

The initial irradiation of the polymer causes chemical bonds between sections of the polymer molecule to undergo scission (to split). Scission creates free radicals, or atoms and molecules which have unpaired electrons in their outermost electron shell. Free radicals are highly reactive because unpaired electrons in the outermost shell allow an atom or molecule to form bonds more easily by sharing those electrons with other atoms or molecules.

The free radicals created by irradiating a polymer will react in two different ways. First, they will cause post-irradiation degradation of the polymer, i.e., further scission. Second, they will bond to one another and become inert. This latter process is called cross-linking. If the polymer is irradiated while exposed to oxygen, the free radicals will cause a significant amount of post-irradiation degradation of the polymer in comparison to the amount of cross linking. In contrast, if the polymer is irradiated in an inert atmosphere, more cross-linking and less post-irradiation degradation will occur. When the ratio of chain scission reactions to cross-linking reactions is lower, the polymer retains its qualities better over time. In other words, irradiating the polymer in an inert atmosphere creates a stronger material than irradiating it in oxygen.

2. Howmedica's Improvement on Prior Art

Howmedica cites two principal types of prior art in its patents. First, Howmedica cites patents that disclose irradiation of polymers (in the form of medical devices and otherwise) out of contact with oxygen to prevent post-irradiation oxidation. Second, Howmedica cites patents that describe heating processes which improve the physical characteristics of ultra-high molecular weight polyethylene.

Howmedica's patent avowedly improves on prior art by disclosing a process whereby the polymer is irradiated and then heated for such a period of time that allows for a desired level of free radical cross-linking to occur. Both steps, irradiation and heating, take place out of contact with oxygen. Heating the polymer "helps free radicals . . . to migrate in the plastic matrix to meet other neighboring free radicals for cross-linking reactions." '934 Patent, 5:53-55. The patent specifications state that the post irradiation heating step has to be of a sufficient duration and temperature to reduce the number of free radicals "to a minimal or an accepted level." '934 Patent, 7:05-07.

3. Arrhenius' Equation

The '934, '814, and '308 Patent claims at issue in the motion for summary judgment all define the range of sufficient heating time and temperature combinations by referring to Arrhenius' equation. These claims state that the implant material is heated at a temperature and for a time at least equivalent to 50EC for 144 hours ...

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