No, The silicone in breast implants is not bulletproof. The CNN article cited in the claim does not explicitly say or imply that silicone breast implants are bulletproof. CNN stated that “The implant caused the change in the trajectory of the bullet”, while the woman still suffered a gunshot wound, broken rib, and ruptured implant. Because the woman in this story still suffered a gunshot wound which ruptured her implant it does not appear that her breast implant was bulletproof, although it may have deflected the bullet and saved her life. This is an isolated incident in which a breast implant was not bulletproof, and in order to fully assess this claim it seems necessary to examine other cases, as it is possible other silicone breast implants could be bulletproof.
According to the National Library of medicine, There have been several cases in which a bullet's trajectory is altered by a breast implant. This is similar to the CNN article, although this still does not cite any case in which a breast implant has stopped a bullet from entering the body. Although the NLM found “a 20.6% decrease in penetration compared with that seen with no implant”, meaning that the silicone in breast implants does have the ability to slow or decrease the velocity of a bullet. However, the NLM failed to cite any case in which a silicone implant has stopped a bullet's penetration.
NLM’s findings are supported by Christopher Pannucci, a plastic surgeon from Utah. Through a study he conducted, he found that “there is a good chance the penetration stoppage power of the implant will be less than 20%”. While it does seem true that silicone breast implants have some ability to deflect a bullet, or soften the impact, the claim that silicone breast implants are bulletproof seems an extreme hyperbole. The claim appears to be untrue.
Sources:
https://www.cnn.com/2020/04/21/americas/breast-implant-bullet-wound-wellness-intl-scli/index.html
https://pmc.ncbi.nlm.nih.gov/articles/PMC9949879/
https://www.dr-adams.com/blog/can-a-breast-implant-stop-a-bullet/