Researchers are optimizing micro-3D printing technology for microneedles

Researchers at the University of Birmingham and the University of South Queensland are studying the use of micro-3D printing technology to create microneedles.

The approach uses a process called two-photon polymerization (2PP), a form of high-precision 3D resin printing that is particularly adept at making complex microstructures with nanometer resolutions. 2PP has gained steam in academia in recent years with applications in microfluidic devices, photonics, microoptics and medical devices such as microneedle arrays.

The multinational research team has already performed parametric optimization of the 2PP process, specifically for the development of polymer microneedles with complex functions such as side channels.

Example of a conventional microneedle patch. Photo by Georgia Tech.

Down to the nanoscale with microneedles

While conventional hypodermic needles are commonly used to extract blood samples and deliver compounds intravenously, microneedles and their miniature form factors have their own set of new applications. This includes transdermal drug delivery across the skin barrier, withdrawal of small bioassays for diagnosis, and even cosmetic procedures.

Microneedles can be made of any material such as metals, silicon, glass and even ceramics. Polymer microneedles, in particular, have been declared for their biocompatibility and mechanical stability.

Polymer variants can indeed be 3D printed using 2PP, but choosing the optimal printing parameters to create a usable array of microneedles often involves extensive testing. According to the research team, there is also limited research when it comes to optimizing printing parameters, which makes it a difficult procedure.

But that doesn’t mean it’s not worth it, as researchers at Stanford University and the University of North Carolina at Chapel Hill (UNC) recently printed a 3D vaccine patch that they say provides more protection than the typical vaccine. . Applied directly to the skin, the microneedle patch reportedly delivers an immune response ten times greater than the vaccine delivered to the arm muscle, while being painless.

Elsewhere, at the University of Kent and the University of Strathclyde, researchers have previously developed a new 3D printed microneedle device that uses microelectromechanical systems (MEMS) to closely control transdermal drug delivery. Called 3DMNMEMS, the device is designed to customize clinical treatment and allow healthcare professionals to dose their patients based on their needs.

Researchers at Stanford University and UNC use 3D printing to create a microneedle vaccine patch.  Photo by UNC.
Researchers at Stanford University and UNC use 3D printing to create a microneedle vaccine patch. Photo by UNC.

Optimized microprint process

To carry out the project, the team used a Nanoscribe Photonic Professional GT 3D printer. The study involves printing a number of microneedle samples with different process parameters to identify the optimal combination. In the end, they opted for a laser power of 80 mW, a print speed of 50,000 µm / s and cutting distances between 0.5 µm and 0.7 µm.

It has been found that both the scanning speed and the laser power have a significant impact on the construction result, with higher scanning speeds leading to lower (worse) levels of polymerization.

Now looking at the geometry of the microneedles themselves, the team found that an array with a long peak height of 300 µm has the worst performance in response to the applied load. On the other hand, an array of microneedles with a length of only 150 µm can withstand loads up to 50% higher before breaking. The printed parts also have a side channel design that forms a microfluidic channel crossing the epidermis. Reaching the subcutaneous area, these channels can be used to deliver drugs and monitor biomarkers.

In skin penetration tests performed on pig carcasses, microneedles were very successful, but showed no cytotoxicity or inflammatory effects.

Eventually, the researchers were able to develop an optimized 3D printing process for polymer microneedles, but argued that the technique could be applied to other high-resolution microstructures.

Further details of the study can be found in the article entitled “Parametric optimization of a two-photon process of direct laser writing for the production of polymer microneedles”.

Photonic Professional GT2 3D printer.  Photo by Nanoscribe.
Nanoscribe Photonic Professional GT2 3D printer. Photo by Nanoscribe.

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The presented image shows an example of a conventional microneedle patch. Photo by Georgia Tech.

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