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Year in Review: Bioengineers make headway on human body parts

New techniques produce mimics of brain, liver, heart, kidney, retina

ALMOST BRAIN  A cross section of an immature lab-grown approximation of a human brain reveals neurons (green) and neuron-producing stem cells (red).

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Baron Victor von Frankenstein would have admired the bounty of body parts scientists crafted in the lab this year.

Lab-grown lumps of liver, bits of brain and clumps of heart, kidney and retinal cells can now mimic the functions of organs grown the old-fashioned way.

Scientists have no plans to assemble a monster, of course. Artificial organs may instead one day help repair or even replace a person’s damaged tissues. But that day is still many years away, says retinal cell researcher Robin Ali of University College London. “Making a neuron in a dish is exciting, but it’s not a therapy,” he says. 

In the last few years, researchers have learned how to turn embryonic stem cells into all sorts of different cell types, such as skin cells, heart cells and neurons (nerve cells). These cells are good research tools: Scientists can watch how lab-grown neurons behave in a culture dish and test their responses to drugs.

But to be clinically useful, the cells need to team up and form tissues and organs that researchers can transplant into patients. Getting cells to organize into these three-dimensional structures is tricky. In the lab, cells often stretch out in flat sheets stuck to the surface of a dish. 

This year, several research groups tackled the problem using a clever trick: They grew cells in structural scaffolds made of gel or the hollowed-out shells of real organs. The scaffolds can cue cells to grow and give them a physical framework to hook up in three dimensions. 

“When cells are bound to just each other, they’re very fragile — they will fall apart,” says tissue engineer Shay Soker of Wake Forest School of Medicine in Winston-Salem, N.C. 

The scaffold technique helped drive this year’s bioengineering boom. As part of a recipe to grow human brain tissue, researchers at the Austrian Academy of Sciences in Vienna and colleagues injected stem cells into droplets of gelatinous protein goo. The goo balls grew into primitive brain buds about the size of BB pellets. Neurons inside the buds could mimic some abilities of human brain tissue, such as transmitting electrical signals (SN: 9/21/13, p. 5).

Gel scaffolds also helped researchers craft mini-livers from stem cells. After transplantation into mice, the tiny organs could hook up to the blood supply and break down drugs (SN: 8/24/13, p. 16). Ali and colleagues used similar scaffolds to transform stem cells into rudimentary retinas. Primitive retinal cells injected into mice’s eyes linked up with the optic nerve and developed into mature light-sensing tissue (SN: 8/24/13, p. 16). 

Gel-based frameworks are good for supporting small clusters of cells, Soker says. But to make bigger clumps of tissue, scientists need to figure out how to re-create the large-scale architecture of organs. This year two research groups took a crack at the challenge by borrowing structures from existing organs.

By stripping the innards from rat kidneys and mouse hearts, and then loading the husks with new cells, researchers bio­engineered organs similar to the originals (kidney shown below). The renovated organs could filter waste or spontaneously contract (SN: 5/18/13, p. 14; SN Online: 8/15/13).

Still, refilling the shells of organs with fresh cells is like taking an apartment building and swapping out the tenants, Soker says. Eventually, tissue engineers want to erect an entire organ without relying only on existing frameworks. One day scientists may be able to 3-D print these frameworks, or weave them together using technologies from the textile industry, Soker says.

But before people with damaged livers or kidneys receive transplants crafted from scratch, patients might see simpler artificial tissue replacements with lab-grown bone, skin and cartilage, Ali predicts. 

He thinks these replacements could happen within the next 10 years. Now, he says, “The cutting edge is to work on the biology of transplantation.” Safely transferring artificial organs into people’s bodies might inspire more than just mad scientists to shout, “It’s alive!”

See all top science stories of 2013 

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