Screen Printing Microneedle Coating Precision
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Solution Overview
Problem
Existing methods for coating microneedles with drugs are not precise, easy, or mass producible, often resulting in limited drug delivery due to viscosity constraints and capillary phenomena, making it difficult to control the amount of drug coated on the microneedles effectively.
Innovation Solution
A method using a screen printer with a mask plate and spatula to coat microneedles, adjusting parameters like aperture diameter, viscosity, clearance, and spatula pressure to achieve precise and quantitative coating of high molecular physiologically active substances, preventing coagulation and phase separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ink jet method is used to coat microneedles, then selective coating to microneedles is achieved, but the releasable amount is limited to picoliter order and viscosity is limited to lower side
Solution Approach 1:
The patent replaces the ink jet method with a screen printing method, substituting a mechanical printing system for a droplet ejection system. This allows coating solutions with higher viscosity (up to 10,000 cps) to be applied in controllable amounts to microneedles, overcoming the picoliter limitation of ink jet methods while maintaining selective coating capability.
2Quantity of substance
If immersion-drying cycle is repeated to coat large amount of drug, then coated amount is increased, but concentration of coating solution increases gradually and wicking phenomenon occurs
Solution Approach 1:
The patent replaces the immersion-drying cycle with a screen printing method where a coating solution is applied once in a controlled manner. The screen plate with apertures positioned at specific depth prevents the solution from reaching the basal surface, eliminating capillary wicking and preventing concentration changes that would occur with repeated immersion cycles.
Solution Approach 2:
The screen plate acts as an intermediary element between the coating solution reservoir and the microneedles. It controls the depth of solution application and prevents direct contact between the solution and the basal surface of microneedles, thereby preventing capillary wicking and maintaining solution concentration stability.
3Manufacturing precision
If cylindrical roller is used to control coating solution level, then selective coating is achieved, but viscosity is limited to about 500 cps or lower
Solution Approach 1:
The patent replaces the cylindrical roller mechanism with a screen printing system. The screen plate with precisely positioned apertures allows coating solutions with viscosity up to 10,000 cps to be applied controllably, expanding the viscosity range from 500 cps to 10,000 cps while maintaining precise coating amount control.
4Manufacturing precision
If mask phase method is used to coat microneedle tip, then drug coating only on microneedle is achieved, but drying step requires time and residual mask phase remains
Solution Approach 1:
The patent replaces the mask phase method with direct screen printing. The coating solution is applied directly to microneedles through screen plate apertures without requiring a separate mask phase layer, eliminating the time-consuming drying step and avoiding residual mask phase contamination while maintaining precise coating location control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise, easy, and mass producible coating of microneedles with high molecular physiologically active substances, ensuring homogeneous solutions and controlled coating amounts, enhancing the convenience and efficiency of microneedle devices.
Implementation Method 1
the capillary phenomenon occurs depending on the surface tension of a coating solution used, causing the wicking phenomenon wherein the solution extends to the basal surface (root portion) of microneedle
Implementation Method 2
a spatula is pressed to a surface of the mask plate
Implementation Method 3
inserting microneedles of a microneedle device to the apertures filled with the coating solution to coat the microneedles
Data Source
Figure 1(a)~2
Figure 3(a)~4(c)
Figure 5~6
AI summary
The present invention provides a method of coating microneedles by which the microneedles mounted on a microneedle device are coated accurately and easily in a mass-producible manner. In this method, a microneedle device (22) with a plurality of microneedles (21) is mounted on a table (23), while a mask plate (25) with a plurality of apertures (24) is fixed to a frame member (26), and a coating solution (27) is drawn in the direction of arrow A on the mask plate (25) using a spatula (28) to fill the apertures (24) with the coating solution. The microneedles (21) are inserted in the apertures (24) before or after the filling of the apertures (24) with the coating solution (27) to coat the microneedles (21).