Patent infringement defenses are various and are different in the scope of their applications. For patent owner to consider filing a lawsuit of patent infringement, it is important that he/she and his/her team of patent attorneys be fully aware of the possible defenses the other side may bring into the case. Patent laws and regulations may often be simple to understand at fair glance, however, their applications in actual infringement action lawsuits and litigation can prove to transform the legislation from simple and understandable to confusing and complex. 

In certain cases, there aspects of the law that may be used effectively as defense to an infringement case that is not entirely obvious. Such a instance is evident with the repair doctrine, also known as the doctrine of repair and reconstruction. This type of patent infringement defense is typically used or applied when a case of indirect patent infringement or induced patent infringement is introduced. 

Repair doctrine also applies to what is considered as a combination patent, where a combination of parts, in their assembled state, create an innovation that is eligible for and granted patent rights. However, when each component is separate, or not part of the completed invention, each part is not patented under the combination patent because of exclusions or ineligibility by proper patent laws. Therefore, the combination patent only protects the completed or assembled combination of those parts. 

The patent infringement action arises when a lawful purchaser of a combination patent product or invention uses replacement parts to repair the innovation. Under patent laws, the transaction of sale of the product from the patent owner or licensed party to the purchaser or consumer, it is implied that the right to repair such product is granted, regardless of where or from whom the replacement parts are purchased. In other words, the replacement parts do not need to be purchased from the patent owner or inventor. 

This is what is referred to as repair doctrine. Patent infringement does not apply because of the fact that the patent owner does not have exclusive rights to the components of the combination or assembled patented invention; the patent only applies to the finished product. The repair doctrine is extended to also include if such repair or replacement of components actually modifies the original patented product or design. The repair doctrine protects the consumer from direct patent infringement, while concurrently protecting the third party selling the replacement parts from indirect patent infringement. 

However, patent infringement can still be applicable if the repair or replacement of the components of a combination patent invention occurs before those components have run their course or have been rendered inoperable. Patent holders and owners have pushed to limit the extent to which repair doctrine can be applied, and is now solely used to refer to worn out or inoperable components. However, in recent years, the idea of repair doctrine only applying to worn out parts or components has been steadily rejected and the idea that any readily replaceable part may be repaired or replaced at any given time, without inducing any kind of patent infringement. 

Commonly, when it relates to patents, first sale doctrine will also be referred as exhaustion doctrine, or doctrine of exhaustion for the purpose of avoiding confusion when differentiating between the different types of intellectual property. First sale doctrine is a regulation that implies a patent license with certain sales of a patented product by the patent owners or inventors. Exhaustion simply refers to the idea that a patent owner will essentially “exhaust” or lose certain rights and protection after their patented product is initially sold or used at the commercial level. The patent owner will still have certain rights and protections as applicable by patent laws, but certain control over those rights will be exhausted once that product, invention, or innovation enters the commercial market and used by consumers. 

It is also important to note that once a patent right is considered to be under “exhaustion,” that the same product is to be considered as such at an all encompassing level. In other words, if those rights become “exhausted” as considered by the rule of first sale doctrine in a particular area, the same will be enforced in other areas as well. Because first doctrine sale or the exhaustion doctrine is often applied to imply a license through the sell of a patented product, it will also be used with another defense to further provide for a stronger argument. The exhaustion doctrine is very commonly used with claims of patent-related estoppel. 

The concept of exhaustion doctrine seems to be quite ordinary and easily applicable in litigation procedures, but often enough, there are other issues that are considered that will render first sale doctrine more complicated than it seems. In certain cases, patent lawyers will often analyze the actual sale of patented product to a particular party in order to evaluate if such a transaction was a real sale versus an implied license agreement. If there is no sale to be accounted for, then first sale doctrine can be used as a defense in the sense that, under its definition, those rights have not been “exhausted” and the owner of the patent may then eligible to file suit for patent infringement. The first sale doctrine can be used on both sides of a patent infringement suit, as long as the patent lawyers have the knowledge and skill to apply the exhaustion doctrine in the favor of their clients.

Out of the possible defense strategies that can be considered during a patent infringement case and litigation, patent misuse can be considered the most powerful and assertive patent infringement defense. The reason for patent misuse being a great patent infringement defense lies in the fact that it renders the owner of the patent in question quite powerless in terms of managing to obtain any positive outcome out of the infringement suit. 

Furthermore, it also renders the patent itself as useless, and may be revoked regardless if it was already protected under proper registration and United States trademark laws. Patent misuse refers to certain types of prohibited behavior undertaken by the owner of the patent seeking infringement action. Generally speaking, there are three ways in which a patent owner can commit patent misuse:

         The patent owner or holder commits violations of the antitrust laws

         The patent owner or holder improperly or willfully expands the scope or claims of the patent with ill intentions.

         The patent owner or holder is found to commit inequitable conduct in obtaining a patent and abusing the inherent rights granted upon such issuance

It is the responsibility of the defendant and his/her patent attorneys to appropriately and vehemently prove that the plaintiff and/or owner of the patent is guilty of patent misuse in order to render the patent infringement suit invalid. Furthermore, the patent in question will be considered to be unenforceable as a result of patent misuse. In many cases, however, the patent will only be denied on a temporary basis. 

The patent may be reinstated after the finding of patent misuse as long as the practices are abandoned and correcting any ill effects of such misuse. However, if the patent infringement defense can prove that the patent misuse occurred in the process of obtaining the patent rights, the patent will not be reconsidered and will be rendered as void and canceled. It is important to note that the patent infringement defense of patent misuse can still be enforced, regardless if such misuse actually harmed the defendant in any way by the abuse of the patent rights. 

This also extends to the fact that if the infringement case is valid, and the patent was in fact infringed, the patent owner will not be able to retain the inherent patent rights and be compensated due to abuse and patent misuse. An example that would constitute patent misuse would be if a person or company purchases many patents regarding distinct and widely used products, such as a water pump. The owner of these patents could possibly establish a type of monopoly on water pumps, for it renders it impossible for others to produce a similar product without infringing on the patents. 

Though there is nothing wrong in owning various patents to a particular type of product, it can be deemed that such a practice is for the purpose of establishing a type of monopoly, which would allow the owner of these patents to enact infringement lawsuits to anyone developing a water pump. This would be grounds for a violation of antitrust laws, and also be considered patent misuse. 

An example of patent misuse expanding the scope of patent rights and protection could be if the owner of a patented product or owner enters a licensing agreement with another party, and forces them to sign the contract stating that royalties are to be paid beyond the life or term of the patent. This is an example of willfully expanding the scope of a patent for ill purpose and willful intention, and thus is a form of patent misuse.