Welcome to Ask a Biogeek, a column about cutting-edge biology by UC Berkeley researcher Terry Johnson. Knowing which organs you can live without is all well and good, but wouldn't you rather have replacement organs? Tissue engineers already have some pretty good ones if you happen to lose your skin or severely damage your bones. And there are some other organs we're cooking up for you too, as long as you can hold out for a few more years.

Tissue engineered skin has been used on humans since 2001, though initially it was merely a replacement for cadaver skin as a temporary solution for burn patients whose skin was damaged too extensively to consider skin grafts. More permanent solutions designed to more closely mimic the structure of skin are on the way, with several different designs currently under research or in the clinic. We're a long way from a tissue engineered donor-free face transplant, but we'll get there. There are non-medical benefits to this work as well - a variation on tissue engineered skin called Episkin is being marketed in Europe as an alternative to animal testing of cosmetics.

One of the advantages of skin from an engineer's point of view is that it's easy to feed. Thin sheets do not require a system of blood vessels to supply the cells inside the sheet with adequate oxygen and fuel. Cartilage is another tissue that can do pretty well without a vasculature, and has a tendency to heal poorly - a combination that sends clinical researchers off to write grants. If you're looking at total knee replacement in the future, keep in mind that there's already one therapeutic alternative and several others in the works.

If you're a sports fan, at one time or another you've probably had your team's season imperiled by a player's torn ligament. While these lingering injuries may be a boon to broadcasters and sports writers, for athletes they can be career-ending events. A biodegradable polyester combined with cells from undamaged ligament may be the solution - in rabbit knees, these engineered ligament replacements already rival transplants. The thing about a transplant is, that transplant tissue has to come from somewhere. If from another body, you've got tissue rejection to look forward to. If from you, getting there requires a scalpel and seriously good painkillers. These engineered alternatives, using cells from the patient cultured outside of the body, do a lot less hurting to get to the healing.

Most bone breaks heal on their own with a little immobilization, but not all, and fractures aren't the only problem one can have with bone. A man in Finland lost his upper jaw to a tumor, but doctors were able to create a replacement. A biomaterial scaffold was created in the shape of the missing part, then seeded with mesenchymal stem cells from a culture of the cells in a sample of the patient's fat. The whole device was then implanted in the man's abdomen, where it was given nine months to develop before being removed and implanted into the jaw. That may sound a little roundabout, but considering the only other option was hacking enough bone out of the man's leg to rebuild the jaw, you can see the attraction. Similar work has been done in Germany using the patient's back as an incubator instead of the abdomen, giving you a potential choice of scars as well.

If that same fellow ended up a few teeth shy, or you're worried about encroaching denturehood, engineered teeth are possible as well - in mice. Until it's working in humans, I strongly suggest you floss regularly.

There's a lot of exciting work in kidneys, but if you know any potential donors try and stay on their good side. There are already a few tissue engineered bladders engaged in their usual duties inside patients.

Heart disease is a leading cause of death in the United States, and to some, the holy grail of tissue engineering. Replacing clogged blood vessels or valves with healthy engineered tissue would save lives and wear and tear on the parts of the body where we usually go scrounging for healthy vessels to replace the damaged bits with. It doesn't get much tricker than a complete engineered heart transplant - a machine that requires incredible timing, physical power, a highly specific vasculature, and most importantly, a vanishingly small failure rate. One approach is to cheat - that is, take an existing donor heart and remove all of the cells, leaving the structure intact. The deheartinated hearts are then seeded with heart cells from the would-be patient. Rat hearts treated in this manner can be coaxed into beginning to beat anew, though as of yet not hard enough to replace an ailing ticker.

Do you have questions you've always wanted to ask a biogeek? You can email me at tdj@io9.com.