What is micro-scale 3D printing? Lessons learned from the Mayo Clinic

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These 3D-printed microneedles – viewed through a scanning electron microscope – are pictured next to a traditional 29-gauge hypodermic needle. A human hair is approximately as wide as the 100-micron scale marker in the picture. [Image courtesy of Mayo Clinic]

Micro-scale 3D printing has the potential to revolutionize medical device development.

Seth Hara and Renc Saracaydin, Mayo Clinic

The Mayo Clinic Engineering Division is an integrated engineering team that provides engineering support and services to researchers and clinicians across the enterprise. To meet their needs, the engineering team adopted micro-scale 3D printing.

Micro-scale 3D printing in medical device development is still relatively new. As this technology continues to mature, the field will continue to find exciting new opportunities to advance the practice of medicine.

As the name suggests, micro-scale 3D printing is the use of additive manufacturing techniques to produce structures with features as small as a few microns. To put it all to scale, a human hair is about 100 µm (microns) in diameter; that is, one tenth of a millimeter or four thousandths of an inch. The ability to 3D print at such a small scale opens the door to a variety of applications in the biomedical sector.

This technology can additively fabricate 3D microfluidic chips to be used for diagnostic blood testing, cell sorting, drug discovery, and organoid synthesis, to name a few applications. It can be used to fabricate drug delivery systems such as microneedle arrays to enable painless and efficient self-administration of drugs or vaccines. Additionally, it enables the fabrication of porous architectures or scaffolds that can be used to guide cell growth and proliferation for regenerative medicine applications such as the treatment of spinal cord injuries. Beyond these cutting-edge applications, micro-scale 3D printing enables the fabrication of connectors, fasteners, and other critical ancillary components for medical devices.

Seth Hara Mayo Clinic

Seth Hara is a senior engineer in Mayo Clinic’s Engineering Division and director of the Microfabrication Laboratory. [Photo courtesy of Mayo Clinic]

Microscale 3D printing takes shape

Over the past decade, a wave of 3D printing technologies have become commercially available. Some of the most common are material extrusion, vat light curing, powder bed fusion, and material jetting. Although these technologies are able to fabricate relatively large components with high repeatability and reliability, they often struggle to reduce features below a few hundred microns.

However, with advances in optics, microelectromechanical systems (MEMS) and materials science, new technologies capable of 3D printing at the microscopic scale have emerged. Proprietary names for some of these technologies are micro-stereolithography (µSLA), micro-digital light processing (µDLP), micro-stereoprojection lithography (PuSL), and two-photon polymerization (2PP).

The principle of operation of these technologies is similar (except for 2PP, which will be explained later). A viscous light-cured resin is exposed to visible or ultraviolet (UV) light depending on the desired part geometry. When light interacts with the resin, it hardens the resin and turns it into a rigid polymer. Specifically, the energy provided by UV light creates reactive species called free radicals that covalently bind to monomers and/or oligomers to initiate the photopolymerization reaction.

As more molecules are bound together, the reaction propagates until it is complete. This reaction leads to long polymer chains which can be interconnected depending on the type of resin used. This process is repeated for each layer until the final piece is made. What enables these technologies to print at the microscale is their ability to highly localize the light-curing reaction through the use of custom resin chemistry and high optical resolution ranging from 1-5 µm.

2PP, on the other hand, operates in a different regime and uses resin chemistry that requires two femtosecond pulses to light-cure an extremely localized focal volume. This allows free volume structures to be printed with submicron resolution, exchanging the larger build volumes that can be achieved with older technologies.

Renc Clinic Saracaydin Mayo

Renc Saracaydin works on microscale additive manufacturing as a graduate microfabrication intern at Mayo Clinic. [Photo courtesy of Mayo Clinic]

The Challenges of Microscale 3D Printing

As with any emerging technology, there are many challenges and obstacles that must be overcome to realize the full potential of micro-scale 3D printing. New materials must be developed to take advantage of advances in optical technology, and processes must be tuned so that light-curing is contained in small volumes while adequately forming secure bonds.

Once the parts are printed, post-processing presents another set of challenges. As with any resin-based print, uncured resin must be removed from cavities and lumens. This is often accomplished by immersing the part in a bath of solvent and agitating the solution. Micro-scale prints, however, can be vulnerable due to their small features and therefore shaking should be done carefully – if at all – to avoid damage and breakage. This is made even more difficult by the intricate patterns and small volumes designed in microscale parts, which often require more agitation to properly remove all of the uncured resin. These competing requirements highlight the critical need for tuning strategies and process design for microscale prints.

Micro-scale 3D printing for medical device development adds an additional level of complexity to processing considerations. Materials that allow microscale printing often do not have a long history of biocompatibility and must be carefully tested for the intended application. Additionally, the printing process itself must be evaluated and monitored to verify that the material properties of the final part are repeatable and safe. If the printed part is to be used in an application requiring sterilization, strategies should be put in place at the design stage to ensure that the selected sterilization process will not adversely impact the material properties of the part. room and that all surfaces are properly sterilized.

This is an exciting chapter for additive manufacturing and medical device development. Micro-scale 3D printing opens up new possibilities and provides tools for researchers and engineers to develop the next generation of medical devices.

As the challenges facing this new technology are addressed, micro-scale 3D printing is likely to be a common and enabling manufacturing tool in this highly innovative field.

Renc Saracaydin is pursuing a master’s degree in materials science and engineering at the University of California, Los Angeles, and is working on microscale additive manufacturing as a microfabrication graduate trainee at Mayo Clinic.

Seth Hara is a senior engineer in Mayo Clinic’s Engineering Division and director of the Microfabrication Laboratory. He has a background in bioMEMS and obtained his Ph.D. in Biomedical Engineering from the University of Southern California.

The opinions expressed in this article are those of the author alone and do not necessarily reflect those of MedicalDesignandOutsourcing.com or its employees.

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