Are Natrelle Inspira and Mentor Memory Gel Both Gummy Bear Silicone?

All silicone breast implants are made with polydimethylsiloxane molecules cross-linked to each other. The fewer crosslinks, the more liquid (oily) the silicone is, and more crosslinking yields more and more cohesive silicone gels. The present fifth generation of silicone gel implants (Memory Gel by Mentor, or Natrelle by Allergan) are both cohesive gels that do not leak or exhibit "silicone bleed" from the implant shell beyond microscopic molecular amounts that are substantially less than in previous generations of silicone gel implants (these were the ones that could rupture, leak, or stimulate inflammatory reaction and capsular contracture.) The present implants were engineered by both implant manufacturers to address and deal with these issues, and are much more cohesive than previous versions.

The "gummy bear" implant is an even more cohesive (more crosslinking), form-stable, teardrop-shaped, textured-surface implant that has been used in several studies that are hoped to lead to FDA approval. They are not yet available to the general population or plastic surgeons outside these studies (which I believe are presently closed). There are pros and cons to these implants that your surgeon can discuss.

At this point in time, both the Mentor Memory Gel and Allergan Natrelle silicone gel implants represent the best FDA-approved implants available, and are comprised of a soft but cohesive gel that does not ooze or leak if these implants are cut or punctured. They are NOT, however, as firm and form-stable as the shaped "gummy bear" study implants that have not yet received FDA approval.

No implant (or any implantable device) is guaranteed to "last a lifetime." However, silicone gel breast implants do not "wear out," nor do they automatically need replacement after any set period of time. The present generation of cohesive silicone gel implants will likely outlast your own anatomic changes or desire for different size or position, which are the most common reasons for re-operation,  NOT implant "failure!"

This is certainly a point of confusion for many patients.  Highly cohesive silicone gel implants are what are referred to as "gummy bear" breast implants because the silicone polymers in these implants have greater cross-linking, which allows them to be form-stable such that if they are cut in half there will be two separate halves like a gummy bear candy.  The older silicone gels had more of a liquid consistency and would spill out when cut, which led to the development of cohesive silicone gel implants followed by highly cohesive silicone gel (gummy bear) breast implants.  
Since your question in 2011, Allergan (Natrelle), Mentor, and Sientra have each received FDA approval and released their version of highly cohesive silicone gel (gummy bear) breast implants in the United States.  Inspira is the name of Allergan's Natrelle round implant with a higher silicone fill percentage.  Inspira now comes in "Responsive" (cohesive but not highly cohesive), "Cohesive" (most form-stable highly cohesive), and most recently "Soft-Touch" (highly cohesive but less form-stable than the "Cohesive").  The greater the cohesivity, the less the deformability and chance of visible rippling.  The quality of implants continues to improve with new advancements every few years.  Most implant companies recommend changing the implants every 10 years, but this does not need to be done if you are not having any problems with your implants.
Ziyad Hammoudeh, MD