2.3. Design of the Needle Management Module

The needle management mechanism is of great importance to avoid damage to the tissue, or even perforation in the worst case. Figure 3 shows the design and working mechanism of the needle management module. The tattooing module can slide forward and backward inside the capsule shell for needle extrusion and retraction, respectively. Since the head dome is in the way and prevents forward mobility, the key locks its linear motion. The key must be rotated 90 degrees clockwise to unlock both the injection needle’s linear motion and the key’s linear motion. The tattooing module can roll along with the permanent magnet’s rotation because it is not connected to the capsule’s outer shell. This rolling motion around the axial axis of the capsule body can be realized by the magnetic field produced by the EMA system. To allow for this rotation motion, the head dome is modified with a needle railway that facilitates the needle rotation within 90°. After rotating clockwise, the key and hole become concentric and enable the linear motion of the key and the injection needle. In this case, a magnetic force can be employed to extrude and retract the injection needle. In the extrusion status, the key is placed inside the hole. In contrast, a counterclockwise magnetic field is needed to rotate the key to the initial position, which is 90° away from the hole, following the withdrawing motion of the injection needle to lock its linear motion.

Design of the needle management module with the head dome (left) and control mechanism (right). The blue arrow indicates the rotation magnetic field direction B. A drawing of the head dome is shown in Appendix A.

In this section, we present the overall system, design, and working principle of the tattooing module and the needle management module. In summary, the tattooing process consists of the following steps: