Two-Photon Laser Photolithography Produces Precise Microstructured Tissue Scaffolds

Andrew Wan, Jackie Y. Ying, and co-workers from the Institute of Bioengineering and Nanotechnology at A*STAR Research (Singapore) have developed a photolithography method that can be used to fabricate precise microstructured 3-D tissue materials. This method of creating 3-D tissue scaffolds with well-defined microstructures could eventually aid in the repair of such human organs as kidneys and livers. "Fine microstructures are important as they allow us to better define the interactions between cells, which in turn leads to better scaffold function," Wan explains.

Typical approaches for fabricating scaffolds involve physical processes that lead to poorly defined and heterogeneous pore geometry. While layer-by-layer methods such as soft lithography can be used to form layered structures with microscopic internal patterns, this method results in materials that lack the fine structure desired for advanced tissue engineering.

To create well-defined microstructures, Wan and his team developed a two-photon laser scanning photolithography technique that excites crosslinkable molecules in the polymer to form a dense polymer network that replicates a computerized design. This design is generated using software that converts a drawing of a scaffold into digital information. The actual 3-D scaffold is obtained by washing away the unreacted molecules using an organic solvent.

The researchers successfully used their approach to fabricate a small cube composed of microscopic pores in just two hours. The scaffold reproduced the original design with high-resolution and fidelity and was also highly transparent and easily observed using fluorescence microscopy.

Evaluating the performance of the porous cube for liver tissue engineering, the researchers discovered that primary liver cells, or hepatocytes, cultured on the scaffold exhibited good cell attachment, viability, and cell-cell interactions. And unlike cells seeded on flat polymer surfaces, these hepatocytes produced more of the liver-specific compounds albumin and urea.  

Because complex organs such as the liver consist of more than one cell type, the researchers are currently attempting to use microstructured scaffolds to produce patterned cocultures of cells. "These 3-D spatially defined cocultures would allow us to better reproduce the function of the tissue or organ that we would like to engineer," Wan says. This technique, the researchers add, would be particularly useful for studying cell-drug interactions and developing effective therapies.