Critical organ failure can only be solved by organ transplants. However, the supply of organs is far lower than the demand, and immunological reactions make everything more difficult. An alternative to this problem is to grow pigs whose organs can be transplanted into humans, a process called xenotransplantation. Both genetically engineered pigs and human-pig chimeras could potentially be used as organ donors. However, their use is surrounded by doubts and ethical concerns. Would you accept a heart grown in a pig?

Some References: 

Xenotransplantation Review

Video on xenotransplantation

BBC article on human-pig chimeras