Short of building completely synthetic organs, one of the areas of synthetic biology with the greatest promise is the development of artificial tissues – replacement material for damaged hearts, livers, and other parts of the body. However, one of the major difficulties has been to create tissue that takes on appropriate shapes. Most of the cells used for synthetic tissue are grown in vitro literally on a glass plate. The arrangement of the developed cells is flat; the tissue needs to be in 3-D.
A new technique, nicknamed ‘micromasonry’ has been developed by researchers at the Massachusetts Institute of Technology – Harvard Division of Health Sciences and Technology. A gel like material is used to hold the tissue cells together as it hardens into what might be called cell ‘bricks.’
The process of engineering body tissue starts with live tissue of the kind desired, say, from the liver. Enzymes are used to digest (remove) the natural material that holds the cells together. The cells are transferred to a Petri dish environment where they can be grown and manipulated. What this doesn’t do, however, is develop the appropriate new binding structures that make up tissue. The hard part is mimicking the often very complicated ‘microarchitecture’ of natural tissue such as the vascular system (veins, capillaries). This is where micromasonry comes in.
The ‘bricks’ are a combination of the appropriate cells and a polymer called polyethylene glycol (PEG), a common plastic-like coating used in many medical applications. The type of PEG used in this research starts as a liquid, which is layered over the cells to be used in a brick. When the PEG-coated cells are exposed to light, the liquid hardens into a gel and cubes about 100 to 500 millionths of a meter are created. Then these cell-gel cubes or ‘bricks’ can be used like building blocks (or biological Legos) to fill out a template created of a silicon based polymer (more like a solid plastic). The whole combination of template and bricks is then coated with PEG and illuminated again to form a solidified shape. Then the template material is removed. What remains is an artificial tissue, complete with the necessary internal structures such as veins and capillaries. The whole process is remindful of the sculpturing and casting procedures used by artists – and indeed there is, at least for now, nearly as much art in this technique as science.
Ali Khademhosseini, assistant professor of HST, and former HST postdoctoral associate Javier Gomez Fernandez describe the work in a paper published online in the journal Advanced Materials.
Other researchers have developed a technique called organ printing to create complex 3-D tissues, but that process requires a robotic machine that is not in widespread use. The new technique does not require any special equipment. “You can reproduce this in any lab,” says Gomez Fernandez. “It’s very simple.”