Researchers funded by the National Institute of Biomedical Imaging and Bioengineering (NIBIB) have created a new type of tissue chip that can better represent human tissues compared with current chips, and can be more widely used for drug testing. By engineering the chips as a silk gel, the researchers circumvented many of the problems with existing devices. The new chip also has the potential to someday be an implantable treatment itself.
Tissue chips are collections of cells that mimic both the anatomy and physiology of a tissue or organ, making it possible to test treatments in the lab more accurately than using cells grown in a single layer in a dish. To engineer a tissue outside the body, the cells need a three-dimensional structure on which to grow. Such scaffolds are often made of polydimethylsiloxane (PDMS), a silicon-based polymer, and contain microfluidic chambers, representing blood vessels or respiratory tracts, running through them.
These microfluidic systems have various advantages. Some systems are great for developing and testing treatments in the lab; some allow living cells to be embedded within them, while others can replicate a variety of tissue types (bone and bone marrow, say). Other systems have qualities that may allow them to be implanted in the body as part of the treatment itself; one such quality is the ability to eventually degrade away when no longer needed. But, none of the current biomaterials can do all of the above. PDMS is particularly problematic because it is non-degradable, and it sucks up lipids, such as fat molecules or steroid hormones. Many potential medications are lipid based, so PDMS absorbs them before their effects can be measured, making it difficult to test drugs. Additionally, an implant made of PDMS would absorb the body’s lipids, and since lipids are vital to the body’s function, a PDMS microchip can’t be implanted in humans.