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Microneedling System

Background

   Microneedling is a minimally invasive procedure used to create micro-injury to stimulate collagen production, and using radio frequencies to deliver thermal energy and produce collagen network remodeling leading to skin shrinkage as a result. The goal of the micro-needling procedure is to reduce wrinkles and heal scars on the skin surface by penetrating the skin, which causes damage to the dermis layer. Thus, it will stimulate collagen production. Our sponsors, Dr. Duncan and Dr. Dobke are both plastic surgeons that would like to create a new micro-needling device that is capable of delivering the desired agent through hollow needles. Additionally, the delivery of radiofrequency energy to the skin. The agent delivered will further reduce wrinkles and scars more effectively than the micro-needling device available on the market. Microneedling procedure is now being used for a very wide range of applications including skin aging, acne scars, and post-traumatic scars. In terms of microneedles structure, the solid microneedles made from silicone and stainless steel are broadly applied within the drug delivery industry. Hollow microneedles are developed to transport cosmeceuticals into the skin.

Figure 1: Microneedling Device

Objective

    The main objective of this project is to optimize tissue rejuvenation procedures, by designing, building and clinically testing the system that combines all three modalities, the device should be multifunctional performing micro-needling, delivering cosmeceuticals via pores in hollow needles and generating radio frequencies concurrently or separately.

    Goals:

• Minimize the injection agent waste.

• Replaceable and disposable cartridge (hollow needles).

• Delivery of biological agents.

Theory

    The behavior of the micro-needling cartridge is governed by the extended Bernoulli with the following assumptions. First, the flow is laminar and the velocity in the syringe is assumed to be zero due to the big difference in size between the syringe and the needle (~30 times bigger) and also assuming no minor head losses to simplify the equation. There is viscous friction in the syringes and the analysis needs to take into consideration the entrance regime from the syringe to the needle. 

     (eq1)

        (eq2)

Where

P is pressure (Pascal).

p is the density of the injection agent (mass / volume^3).

g is gravitational constant (distance / time^2).

F is the applied force (Newton).

A is the cross-sectional area (distance^2).

V is the velocity (distance/time).

z is the displacement (distance).

m' is the mass flow rate (mass per time).

    Assuming everything is constant in the final equation to represent a relationship between mass flow rate and the diameter of the needle we get the equation described below. This theoretical trend matches the risk reduction testing result trends. 

            (eq3)

            Where m' is the mass flow rate (mass per time).

            D is the diameter of the hollow needles (length).

Figure 4: The 3D CAD Design of the Microneedling Cartridge

    The micro-needling design consists of two major mechanisms: the vertical oscillation mechanism and the injection mechanism. The micro-needling cartridge includes several major components. It contains the storage tank with a syringe, and the silicone insulation layer.

    The vertical oscillation mechanism is composed of a spring and a rod. The purpose of the rod is to connect and lock with the driving pen, which regulates the depth and the speed of the skin penetration. The spring is to secure the rod in place and improves the vertical oscillation while, preventing any horizontal oscillation that will introduce torsion into the system during operation.

Figure 5: The Axial Oscillation Mechanism

    The injection mechanism consists of the storage tank and the insulation layer. The storage tank is to store the injection agents such as blood plasma and nano-fats. The silicone insulation layer is to prevent any leakage from the storage tank into the electrical board that contains the hollow microneedles.

Figure 6: Storage Tank with Luer Lock Connector

Testing Results

    The goal of the mass flow rate test is to examine the mass flow rate through the hollow needles with various needle sizes under different applied forces. 

Figure 7: Mass Flow Rate Result

    The graph showed the trend between measured mass flow rate and needle diameter, the gray line represents a constant applied force/mass of 299 grams and the blue line represents a higher force of about 490 grams. The result showed that the higher the applied force the higher the mass flow rate for the same needle size.

Prototype Performance

    The testing that was carried out on both prototypes were mostly visual. For example, to ensure that the prototype capability of delivering the agent, a towel is placed under the prototype while it is operating and observe the water droplets on the towel. After that, the prototype was disassembled to check if any of the fluid agents are left out in the cartridge or if anything was leaking.

    The final prototype achieved the objective of delivering the agent. The cartridge is locked to the driving pen. In terms of the vertical oscillation performance, it successfully achieved the axial oscillation within the design of the spring attachment. The spring allows the cartridge to return to its original position and keeps the rod in place, meaning the rods were able to overcome the situation where it would be completely pushed out of the cartridge. Furthermore, the piston attached to the driving rod was able to push most of the fluid out of the storage tank, minimizing the dead space. The storage tank also remains fixed during operation.