I found quite a few mesh errors in the original wireframe skeleton model, so I went back to the source and rebuilt the entire skeleton model with a cleaner and smoother mesh.

I also enlarged the model to make its printing size more appropriate. In the slicing software, you can freely adjust the model's scale as needed.

In addition, I also created an extra base and integrated it into the model. This way, the model is not only easier to adhere to and print smoothly, but also provides a flat and stable support base for the internal filling, making the overall effect even better.

The print in the picture is made of silver PLA material, and it is enlarged by 150% and printed with a layer height of 0.2mm.

The model has been verified as a "manifold" model in Rhino 3D, and after my inspection, there are no gaps or errors in the mesh.

If you encounter errors or holes in the model when using slicing software, it is likely due to the software having difficulty accurately analyzing complex and fine geometries, or that some parameter settings need to be optimized to better adapt to these tiny geometrical features.
In addition, appropriately enlarging the model size can also effectively alleviate such problems.

Please note: The mesh of this model fully complies with the manifold standard and has no holes at all! If your slicing software still indicates the presence of holes, it is likely due to complex geometric details causing calculation confusion in the software, or the relevant parameter settings need further adjustment. We recommend that you carefully check and confirm all settings multiple times, or enlarge the model to a larger size for printing.This is particularly important in areas such as the nose and eyes.

[Updated on July 22, 2019]
I have completely cleaned up and optimized the mesh, and now there are no overlapping surfaces or open gaps in the model, which is almost in a perfect state.

[Updated on July 20, 2019]
I repaired the base part and simplified it significantly

To make it easier for everyone to modify and repurpose the models, I've provided both the STL files and the original Blender project files. Of course, if you want to use these resources for further creation, please be sure to show respect and remember to credit the original author - philnelson, as well as Garygeo, who designed the basic skeleton model! :)