Fabrication of Three-Dimensionally Deformable Metal Structures Using Precision Electroforming.

It is difficult to fabricate three-dimensional structures using semiconductor-process technology, because it is based on two-dimensional layered structure fabrication and the etching of thin films. In this study, we fabricated metal structures that can be dynamically deformed from two-dimensional to three-dimensional shapes by combining patterning using photolithography with electroforming technology. First, a resist structure was formed on a Cu substrate. Then, using a Ni sulfamate electroforming bath, a Ni structure was formed by electroforming the fabricated resist structure. Finally, the resist structure was removed to release the Ni structure fabricated on the substrate, and electroforming was used to Au-plate the entire surface. Scanning-electron microscopy revealed that the structure presented a high aspect ratio (thickness/resist width = 3.5), and metal structures could be fabricated without defects across the entire surface, including a high aspect ratio. The metallic structures had an average film thickness of 12.9 µm with σ = 0.49 µm, hardness of 600 HV, and slit width of 7.9 µm with σ = 0.25 µm. This microfabrication enables the fabrication of metal structures that deform dynamically in response to hydrodynamic forces in liquid and can be applied to fields such as environmental science, agriculture, and medicine.

Detection of cancer cells in whole blood using a dynamic deformable microfilter and a nucleic acid aptamer.

Cancer cell count in the blood of cancer patients is extremely low. If these cells are easily detectable, cancer diagnosis may be possible by simply using a blood test, thus reducing patient burden. This study aimed to develop a cancer detection device by combining a microfilter that can be dynamically deformed and a nucleic acid aptamer that has a specific binding ability to cancer cells for easy detection. The cancer detection device was fabricated by photolithography, electroforming, and three-dimensional printing. The cancer cell detection ability of the fabricated device was evaluated using 1 mL of blood samples spiked with different concentrations of cancer cells. The lowest concentration of cancer cells in the blood was 5 cancer cells/1 mL blood. The fabricated microfilters specifically detected cancer cells in the blood successfully at exceedingly low concentrations. Moreover, the cancer detection experiment results using human whole blood revealed that cancer detection could be performed with higher accuracy using the fabricated cancer detection device compared to pre-existing cancer detection equipment (e.g., CellSearch system, Veridex). These findings provide important insights into the use of cancer cells in the blood as a diagnostic approach for cancer.

A dynamically deformable microfilter for selective separation of specific substances in microfluidics.

To study an environmental or biological solution, it is essential to separate its constituents. In this study, a 3D-deformable dynamic microfilter was developed to selectively separate the target substance from a solution. This microfilter is a fine metallic nickel structure fabricated using photolithography and electroplating techniques. It is gold-coated across its entire surface with multiple slits of 10-20 µm in width. Its two-dimensional shape is deformed into a three-dimensional shape when used for fluid separation due to hydrodynamic forces. By adjusting the pressure applied to the microfilter, the size of the gap created by deformation can be changed. To effectively isolate the target substance, the relationship between the solution flow rate and the extent of microfilter deformation was investigated. The filtration experiments demonstrated the microfilter's ability to isolate the target substance with elastic deformation without undergoing plastic deformation. Additionally, modification of the microfilter surface with nucleic acid aptamers resulted in the selective isolation of the target cell, which further demonstrates the potential application of microfilters in the isolation of specific components of heterogeneous solutions.