Jul 7, 2017 | By David

A pioneering new technique is currently being trialled for 3D bio-printing, which has the potential to revolutionize the way biological tissues are engineered. The new method, which was developed by researchers at the National University of Singapore, involves using laser technology to give a much higher degree of control over the micro-environment in which the cell cultures are developed, offering a broad range of advantages and a vastly improved final product.

Typically, 3D bio-printing involves implanting cells into a miniature scaffold-like structure, where they can replicate to eventually form a new tissue in a way that is partially directed by the bio-engineers who design the scaffold. However, this method does have some drawbacks and limitations -the cell growth can be very low-density, and cell diffusion in the bulk can be very slow and uneven.

A huge range of other methods have been suggested and trialled, including using micro-fluidic processes or controlling cell replication using magnetics or robotic technology. Most of these so-called ‘top-down assembly’ processes also present some limitations, such as a restricted material selection and limited bio-compatibility.

A newer alternative that has had some success is light-directed technology. This technique often makes use of what are referred to as ‘optical tweezers’, high-intensity lasers that can give a high level of control over the manipulation of objects at the micro-scale. The lasers are controlled by an automated motor, programmed with a virtual 3D model, which directs the replication of cells into the desired structure or pattern. The problem with this method is that the high power of the lasers can lead to damage of the biological sample cells.

Ideally, 3D printing of tissues would be carried out using a light-directed assembly technique that used relatively low-powered lasers. Some promising research has recently been carried out suggesting that this is now a possibility. The groundbreaking research project was carried out by Dinh Ngoc Duy, Rongcong Luo, Maria Tankeh Asuncion Christine, Weikang Nicholas Lin, Wei-Chuan Shih, James Cho-Hong Goh, and Chia-Hung Chen- PhD students from the Department of Biological Engineering at the National University of Singapore. The results of the novel NIR (near-infrared laser) method for 3D printing with stem-cell laden microgel were published in renowned online journal Wiley, and a U.S patent has also been filed for the technique.

The innovation of the team was to make use of gold nano-rods (GNRs), which were implanted into the micro-environment. The presence of these metallic rods meant that more light was absorbed from the laser and subsequently converted into heat energy.  Because of the improved thermal absorption provided by the gold nano-rods, more control over structures is possible with lower intensity lasers, and different building units can be integrated.

In order to test out the improved precision and integration of different units, a special hydrogel was used. Absorbed thermal energy creates convection currents in this hydrogel, and having control over the direction of these thermal convection currents enables the construction of specific structures. By directing the laser, it is possible to assemble the particles in a specific way without requiring any kind of scaffold.

According to the paper, ''The mesenchymal stem-cell-seeded hydrogel microparticles are prepared as functional building blocks to construct scaffold-free tissues with desired structures.'' In this case, the ''building blocks'' for the structures were the stem cells within the hydrogel, and the NIR method enabled the desired biological structures to be successfully built in the micro-environment in a short amount of time.

The low laser-intensity NIR approach offers more control over the direction of the convection currents (and therefore over the construction of the structure) without sacrificing 'throughput' for different applications, as there is less damage to the biological sample.The paper refers to NIR lasers as the ‘golden tool’ in surgery, as they have the potential to work in ways that no previous 3D printing method has. The unprecedented level of precision that the technology offers means that it could have a huge range of uses- not just bio-printing but also regenerative medicine, tissue engineering and bio-fabrication for advanced manufacturing.



Posted in 3D Printing Technology



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