Final Design

Figure 1: Final Microneedling Device Design

    The micro-needling device design consists of a driving pen and the micro-needling cartridge. There are several major components of the micro-needling cartridge: the outer layer, pushing rod with mechanical spring, the storage tank, Luer lock connector, the silicon sealing layer, and a layer with 9 pins hollow microneedles. 

Storage Tank Design (Transmission Channel)

Figure 2: Storage Tank Design

    Storage tank design stemmed from the sponsor’s requirement to deliver cosmetics during the procedure while providing a sterile environment for the cosmetics injection, within the scope of this project different storage tank concepts were explored. After further considerations, the team managed to narrow them to two design concepts, further explained in table 1.

Figure 3: Silicon Sealing Layer

    The purpose of the silicon seal layer is to prevent any agent leakage from the storage tank. Its dimension is 15 mm in diameter. The material of this insulation layer is silicon because of three reasons. First, silicon is electrically insulated therefore to prevent any potential damage to the device due to contact between the insulation layer and electrical layer at the bottom of the device. Second, the hollow needles need to penetrate through the insulation layer to reach the inside of the storage so the injection agent can pass through the hollow needles and inject it into the dermis. Silicon is a good material in this case because it is a polymer with self-seal characteristics (the silicon will auto seal itself when the 32 gauge hollow needles penetrated it). 

    Another alternative goal of this silicon insulation layer is to prevent any liquid injection agent from the storage tank. The silicone allows the needle to move through the material with the least amount of friction. It is also a material capable of preventing leakage with its auto-seal character. 

Driving Rod

Figure 4: Driving Rod

    The dimension of the pushing rod is 48 mm in height with the piston design of 11.8 mm in diameter. The rod is 3D printed and its material is Vero Clear, which consists of the tensile strength of 50 - 65 MPa and flexural strength of 75-110 MPa. The top design of the rod is connect to the driving pen, which generate the axial oscillation. The piston-like design is to push the injection agent into the hollow needles and transmit the agents into the dermis. The pushing rod design consists of two rods, which connected to the layer with hollow needles. 

Hollow Needles Layer

Figure 5: Hollow Needles Layer

    During operation, the hollow needles are impacted by shear force and axial force. The purpose of the hollow needles is to penetrate vertically into the dermis and transmit the injection agents into the dermis. The goal is to avoid any needle fracture or breakage during the operation. 

*Note: Smaller length, test not valid.

Table 2: Comparison of Various Needles Size

    The micro-needling device consists of 9 32-gauge hollow needles. The 32-gauge hollow needles satisfy the following design requirements. First, its inner diameter is able to transmit the injection agent into the dermis and reach the targeting area of the operation. Second, it satisfies the force testing, which able to uphold a shear force of 0.7167 Newton and a failure axial force of 3.03 Newton. 

Outer Layer

Figure 6: Outer Layer

    The outer layer is manufactured using clear polycarbonate via CNC machining. The outer layer consists of different features. First, it has two different components: the top part and the cylindrical bottom part. The top part is responsible for connection with the driving pen. There is a guiding channel in the cylindrical bottom part, which used to minimize the radial oscillation during operation. The dimension of the outer layer is 26.5 mm in diameter and 38.5 mm in length. The building material of the top part is Vero Clear and the material of the cylindrical bottom part is polycarbonate. 

    Another purpose of the outer layer is to eliminate any unnecessary radial oscillation or vibration. The top part of the outer layer has a Luer lock like design, which locks to the driving pen to avoid any misalignment between the driving rod and the driving pen, as well as fully constraint the needle cartridge to the driving pen during operation. 

Executive Summary

    The device showed achievement in working as desired: delivery of cosmetics, and the hollow needles being able to avoid any failure modes. However, there are a few issues that could be fixed. One concern is the vibration of the needle layer radially; and this was resolved by adding two guiding channels to the inside of the outer cover, where the driving rod will slide through and be supported in place. In this way, the movement generated by the driving pen will only move the needles in the axial direction avoiding any unnecessary radial vibrations.

    The final prototype has performed the delivery of cosmetics through hollow needles, and it proved that the path of fluids delivery is successful. On the other hand, the final prototype experienced issues during the attachment of the needles to the base layer which in turn caused the prototype to fail to provide an oscillation of the needles, this issue would be resolved with implementing an automatic manufacturing method of the cartridge instead of using the manual abilities in a very tight space.