If you have to replace a part of the body, it's not necessary to replace it with an exact replica of what was there before: it just has to perform the same job, and perform that job at least as well. With this in mind, the medical research community has in recent years produced a range of ways to sculpt biological materials, such as collagen, as well as produce biodegradable scaffolding material that can be colonized by a patient's own cells to build new tissue. Thanks to these and other closely related technologies, many of the structural components of the body will be amenable to clinical repair and replacement via scaffolds and bioartificial prosthetics by the time the 2020s have rolled around - the list includes joints, bones, muscles, tendons, soft tissues of the face, and so forth.
I noticed two recently publicized advances from the biomaterials research community today, and here they are for your consideration:
Biomedical engineers at Johns Hopkins have developed a new liquid material that in early experiments in rats and humans shows promise in restoring damaged soft tissue relatively safely and durably. The material, a composite of biological and synthetic molecules, is injected under the skin, then "set" using light to form a more solid structure, like using cold to set gelatin in a mold. ... The researchers created their composite material from hyaluronic acid (HA), a natural component in skin of young people that confers elasticity, and polyethylene glycol (PEG), a synthetic molecule used successfully as surgical glue in operations and known not to cause severe immune reactions. The PEG can be "cross-linked" - or made to form sturdy chemical bonds between many individual molecules - using energy from light, which traps the HA molecules with it. Such cross-linking makes the implant hold its shape and not ooze away from the injection site.
We've engineered [spinal] discs that have the same structural components and behave just like real discs," says Bonassar. "The hope is that this promising research will lead to engineered discs that we can implant into patients with damaged discs." ... Bonassar's lab, which focuses on the regeneration and analysis of musculoskeletal tissue, engineered artificial discs out of two polymers - collagen, which wraps around the outside, and a hydrogel called alginate in the middle. They seeded the implants with cells that repopulate the structures with new tissue. Remarkably, as opposed to artificial implants today that degrade over time, the scientists are seeing that the implants get better as they mature in the body, due to the growth of the cells.