A new nondestructive method for assessing bioengineered artificial tissue

May 09, 2023

(Nanowerk News) Engineering organs to replace damaged hearts or kidneys in the human body may seem like something out of a sci-fi movie, but the foundations for this technology are already there. In the emerging field of tissue engineering, living cells are grown in artificial scaffolds to form biological tissues. But to evaluate how successfully cells develop into tissues, researchers need reliable methods for monitoring cells as they move and proliferate.

Now, scientists at the National Institute of Standards and Technology (NIST), US Food and Drug Administration (FDA) and National Institutes of Health (NIH) have developed a noninvasive method for counting living cells in three dimensions (3D). ) scaffold. The technique real-time images millimeter-scale regions to assess cell viability and how cells are distributed within the scaffold — an important capability for researchers fabricating complex biological networks from simple materials such as living cells.

Their findings have been published in Journal of Biomedical Materials Research Part A (“Three-dimensional, label-free measurement of cell survival in tissue engineered scaffolds using optical coherence tomography”). A 3D volume sample of live cells in a gel captured using a non-invasive imaging technique called optical coherence tomography. Its volume is approximately 1 millimeter by 1 millimeter by 1 millimeter. The white objects in the sample volume are live cells. (Image: G. Babakhanova, NIST)

First, the researchers created a 3D scaffold system made of networks of polymer molecules that can hold large amounts of water, forming a type of material known as a hydrogel. The 3D hydrogel is then embedded with a type of human white blood cell that can reproduce endlessly.

Cells can be very sensitive to the environment in which they grow: If a researcher wants to study the growth of bone cells rather than breast tissue, the cells need to be cultured under different conditions. In addition, the scaffolding that houses the cells is also made of different materials and can be used for various purposes.

“The scaffold holds things together, and provides a microenvironment for whatever you want a cell to do. You can tune the scaffold to direct cells to behave in a certain way,” says NIST biologist Carl Simon.

The team then used a non-invasive imaging technique called optical coherence tomography (OCT), which is similar to an ultrasound test, except that sound waves use light waves.

“To determine whether a cell is alive, we analyzed the optical signals created due to the movement of organelles within the cell,” said NIST physicist Greta Babakhanova, first author of the paper. The researchers detect organelle movement by shining light through the cell. They classified cells as alive or viable when the organelles moved, indicated by changes in the transmitted light.

The NIST method is non-invasive, and there is no cutting or staining of the sample. This method is also label-free: Cells do not need fluorescent molecules known as “labels” to be attached to them to be visible. The former methods require constant contact with the sample, which can be damaging and expensive and affects results. The new technique also reduced the time the researchers spent on their measurements from a few hours to a few minutes.

This method is also different from previous methods which rely on two-dimensional flat samples. “The downside to existing techniques is that you can measure a number of cells, but you don’t know where they are. With this method we can image one millimeter cube of the hydrogel and see where the cells are in the gel,” says Babakhanova.

The 2D approaches also don’t work well because they don’t mimic the 3D microenvironment that cells experience in the body, says Babakhanova.

As a next step, the researchers are looking at applying the technique to study other properties, such as the structure of biofabricated networks. “OCT methods may be able to measure nondestructive specific structures that develop as tissues mature in real time as a measure of their readiness for implantation,” said Simon.

Meanwhile, the method has fulfilled an unmet need in tissue engineering, with its ability to monitor the number and arrangement of cells in an artificial scaffold without having to disassemble and destroy it.

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