Researchers optimize micro-3D printing technology for microneedles

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Researchers from the University of Birmingham and the University of Southern Queensland are exploring the use of micro-3D printing technology to create microneedles.

The approach relies on a process called two-photon polymerization (2PP), a form of highly precise resin 3D printing that is particularly adept at fabricating complex microstructures with nanometer resolutions. 2PP has gained momentum in the academic sphere in recent years, with applications in microfluidic devices, photonics, micro-optics, and medical devices such as microneedle arrays.

The multinational research team has now performed parametric optimization of the 2PP process, specifically to develop polymeric microneedles with complex features such as side channels.

An example of a conventional microneedle patch. Photo via Georgia Tech.

Get down to the nanoscale with microneedles

While conventional hypodermic needles are commonly used to extract blood samples and administer compounds intravenously, microneedles and their miniaturized form factors have their own set of novel applications. This includes transdermal drug delivery across the skin barrier, collection of tiny biological samples for diagnostic purposes, and even cosmetic procedures.

Microneedles can be made of all kinds of materials such as metals, silicon, glass and even ceramics. Polymer microneedles, in particular, are renowned for their biocompatibility and mechanical stability.

Polymer variants can indeed be 3D printed via 2PP, but selecting the optimal print parameters to create a usable microneedle array often involves extensive testing. According to the research team, research is also limited when it comes to optimizing print settings, making it a strenuous procedure.

That’s not to say it’s not worth doing, as scientists from Stanford University and the University of North Carolina at Chapel Hill (UNC) recently 3D printed a vaccine patch. which they say provides better protection than a typical vaccine. Applied directly to the skin, the micro-needle patch would have delivered an immune response ten times greater than that of a vaccine administered into a muscle in the arm, while being painless.

Elsewhere, at the University of Kent and the University of Strathclyde, researchers have already developed a novel 3D-printed microneedle device that uses microelectromechanical systems (MEMS) to tightly control transdermal drug delivery. Named 3DMNMEMS, the device was developed with the aim of personalizing clinical treatment and allowing medical professionals to dose their 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.

An optimized micro-printing process

To complete the project, the team used a Nanoscribe Photonic Professional GT 3D printer. The study involved printing a number of microneedle test samples with varying process parameters to identify an optimal combination. Finally, they opted for a laser power of 80 mW, a printing speed of 50,000 µm/s and cutting distances between 0.5 µm and 0.7 µm.

Scan speed and laser power have been shown to have significant impacts on the outcome of constructs, with faster scan speeds resulting in lower (worse) levels of polymerization.

Now looking at the geometry of the microneedles themselves, the team found that an array with a long tip height of 300 µm had the poorest performance in response to applied load. On the other hand, an array of microneedles just 150 µm long could withstand up to 50% higher loads before breaking. The printed parts also featured a side channel design that formed a microfluidic channel through the epidermis. Reaching the subcutaneous region, these channels could be used to deliver drugs and monitor biomarkers.

In skin penetration tests performed on pig cadavers, the microneedles gave great success while exhibiting no cytotoxic or inflammatory effects.

Ultimately, the researchers were able to develop a 3D printing process optimized for polymer microneedles, but say the technique could also be applied to other high-resolution microstructures.

Further details of the study can be found in the article titled “Parametric Optimization of the Direct Two-Photon Laser Writing Process for the Fabrication of Polymer Microneedles”.

The Photonic Professional GT2 3D printer.  Photo via Nanoscribe.
Nanoscribe Photonic Professional GT2 3D printer. Photo via Nanoscribe.

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The featured image shows an example of a conventional microneedle patch. Photo via Georgia Tech.

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