Researchers are optimizing micro-3D printing technology for micro-needles

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

The approach uses a two-photon polymerization (2PP) process, a high-precision 3D printing method that is particularly skilled at fabricating complex microstructures with nanometer resolutions. 2PP has taken off steam in the academic field in recent years, in microfluidic devices, photonics, microoptics, and medical devices such as microneedle sets.

The multinational research team has now carried out a parametric optimization of the 2PP process, specifically for the development of polymeric microneedles with complex characteristics such as side channels.

An example of a common microneedle patch. Photo by Georgia Tech.

Descend to the nanoscale with microneedles

Although conventional hypodermic needles are used to extract blood samples and inject compounds into the vein, microneedles and their miniature form factors have a set of new applications. This includes the delivery of transdermal medications through the skin barrier, the removal of small biologics for diagnosis, as well as cosmetic procedures.

Micro-needles can be made of all kinds of materials, such as metals, silicon, glass, and even ceramics. Polymeric microneedles are particularly noteworthy for their biocompatibility and mechanical stability.

Polymer variants can be 3D printed via 2PP, but selecting the optimal printing parameters to create a usable range of microneedles often involves extensive testing. According to the research team, there is also limited research on the optimization of printing parameters, making the procedure tedious.

That’s not to say it’s not worth doing, as scientists at Stanford University and the University of North Carolina at Chapel Hill (UNC) have recently printed a vaccine patch in 3D, saying it has more protection than a regular vaccine shot. When applied directly to the skin, the microneedle patch reportedly gave an immune response ten times greater than a vaccine given to an arm muscle, which was painless.

In addition, at the University of Kent and the University of Strathclyde, researchers have developed a new pre-printed micro-needle device that uses microelectromechanical systems (MEMS) to closely monitor the delivery of transdermal drugs. Called 3DMNMEMS, the device was developed with the goal of customizing clinical treatment and allowing medical professionals to dose patients according to their needs.

Scientists at Stanford University and UNC are using 3D printing to create a micro-needle vaccine patch.  Photo via UNC.
Scientists at Stanford University and UNC are using 3D printing to create a micro-needle vaccine patch. Photo via UNC.

Optimized microprinting process

For the project, the team used a Nanoscribe Photonic Professional GT 3D printer. The study printed some micro-needle test samples with different process parameters to identify the optimal combination. Eventually, they received a laser power of 80 mW, a print speed of 50,000 μm / s, and cutting distances of 0.5 μm to 0.7 μm.

Both scanning speeds and laser power were found to have a significant effect on the construction result, resulting in faster scanning speeds resulting in lower (worse) polymerization levels.

Now looking at the geometry of the microneedles, the team found that an array with a tip height of 300µm had the poorest performance to meet the applied load. On the other hand, a series of micro-needles with a length of only 150 µm can withstand a load of 50% higher before breaking. The printed parts also had a side channel design that formed a microfluidic channel that ran through the epidermis. Upon reaching the subcutaneous region, these channels could be used to deliver drugs and control biomarkers.

In skin penetration tests performed on pig carcasses, microneedles were highly successful as long as they had no cytotoxicity or inflammatory effect.

After all, the researchers were able to develop an optimized 3D printing process for polymeric microneedles, but they confirm that the technique can also be applied to other high-resolution microstructures.

Further details of the study can be found in the document ” Parametric optimization of two-photon Direct laser writing process for manufacturing polymeric microneedles’.

Photonic Professional GT2 3D printer.  Nanoscribe photo.
Nanoscribe Photonic Professional GT2 3D Printer. Nanoscribe photo.

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The highlighted image shows an example of a common microneedle patch. Photo by Georgia Tech.

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