Yes, theoretically, it is possible to manufacture the self-defense knuckle spike keychain using 3D printing technology. By converting the design of the keychain into a 3D model and using suitable 3D printing materials like plastic, a similar-looking and functional keychain can be produced on a 3D printer.

If you have access to 3D printing equipment and the necessary knowledge, you can download or design a suitable 3D model for the self-defense knuckle spike keychain and print it out. This way, you can provide your girlfriend or family members with a self-defense tool for unforeseen situations.

However, it is important to abide by local laws and regulations regarding the manufacturing and use of any self-defense tools. Additionally, ensure proper training and education on the safe use of the self-defense knuckle spike keychain to avoid accidental injuries or improper usage.