*2.5. Surface Properties*

A contact angle meter (DIGIDROP DGD-DI, GBX, Dublin, Ireland) was used to measure the contact angle of aluminum templates with various structures. The contact angles of the surfaces of Al template with flat-structure, micro-structure, nano-structure, and micro/nano-structure are discussed. 5 points were measured on each specimen. Deionized water (0.5 μL) was dropped on the template surface. The three states of solid/gas/liquid affected the liquiddrop stability, the use of computer-controlled photography (25/s) captured images and converted the image files. The obtained data of measured contact angle were made into charts.

A MultiMode 3D scanning probe atomic force microscope (DI 3100, Advanced Surface Microscopy, Indianapolis, IN, USA) was utilized to determine the surface roughness of Al templates with various structures. The atomic force microscope (AFM) was also applied to measure the surface profile of aluminum templates with different structures. The authors measured the surface roughness of each test template at 5 measurement points. The scanning range of each measurement point was 5 × <sup>5</sup> <sup>μ</sup>m2. The surface morphology of Al templates with various structures was analyzed by SEM (JSM-6700F, JOEL, Peabody, MA, USA).

#### *2.6. Cell Culture*

In the phosphate-buffered saline (PBS) buffer allocation method, PBS and deionized water were mixed in ratio of 1:9. The PBS was put in a sterilized bottle and stored in a refrigerator at 4 ◦C. Dulbecco's Modified Eagle Medium from HyClone Co. (South Logan, UT, USA) was added to 10% PBS and 1% penicillin (HyClone Co.). The MG63 cell line (ATCC CRL-1427) was used in the cell culture. MG63 is a human bone precursor cell (human osteogenic sarcoma). MG63 cells are utilized in experimental research of the in vitro attachment and proliferation of bone cells. The microculture tetrazolium test (MTT) is 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide. It is a yellow compound that accepts hydrogen ions. It acts on the respiratory chain of living cell lines. Cracking its tetrazolium ring using succinate dehydrogenase and cytochrome C yields a blue formazan crystal. In this study, the crystal was dissolved in dimethyl sulfoxide, and its optical density (OD) was measured using an ELISA machine (Anthos 2020, Biochrom, Cambridge, UK). The OD value indicated the cell activity.
