Aug 15, 2024 In this 3DHEALS event recap, we venture into the side of 3D bioprinting that features components at the micro- and nanometer scale. Our panel of 3D microfabrication experts covered 3 different techniques — two-photon polymerization, projection micro stereolithography, and superluminescent light projection — and a wide range of applications, including cell scaffolds, microfluidics, and metallic structures. Here are some of the highlights from our event earlier this year.
Two-photon polymerization (2PP) for cell scaffold fabrication
One of 3D printing’s core strengths is its customizability. Methods for printing such as two-photon polymerization (2PP) are enabling this customization at the scale of cells and are changing the way we create in vitro models. Among the growing number of use cases, researchers from Delft University of Technology have used 2PP printing to fabricate many tiny pillars either forming an array or covering a 3D cage scaffold for microglial cells to grow on. These pillars, 0.2 micrometers in diameter and 2.5 micrometers in height, enabled them to influence the microglial cells, achieving higher proportions of the desired cell shapes.
Accelerating the creation of these 3D microglial scaffolds behind the scenes is Nanoscribe, and Dr. Benjamin Richter, the company’s Application Manager, talked to us about the tools helping to drive this research forward.
Nanoscribe develops a lineup of 2PP printers, achieving feature sizes down to 100 nanometers. 2PP is the use of a laser, such as that in the near-infrared, to solidify a resin. Such laser beams can be controlled with rotating galvo mirrors and focused with an objective lens. Users of the company’s Quantum X bio printer start with a CAD file, then load a substrate and resin for printing, and finally remove non-solidified material in post-processing.
Dr. Richter shared how they can print smooth cube scaffolds with organic pore shapes that provide favorable conditions for cell growth. Due to 2PP printing’s high resolution, smooth surfaces can be obtained. Such cubes can be used for a variety of applications, including cell culturing, tissue fabrication, and cell migration studies.
They can also print complex meshes with embedded capillary structures that have holes between 1 and 5 microns. These mesh structures are designed as 350 x 175 x 175 micron subunits, which can be repeated and joined together to create larger tissue-like formations.
A clip from our event below shows these structures as well as how the company is using artificial intelligence to expand the 2PP design space.
Beyond cubic structures, Dr. Richter described how they can use their 2PP printers to create 3D mesh scaffolds 800 micrometers in height and 2 millimeters in diameter that fits within the small organoid wells of a microfluidic chip in 4 minutes. These scaffolds can also be printed with a biodegradable material that degrades over time as the organoid grows.
They can also fabricate multi-material scaffolds, which can be time-consuming to align if done manually. Now, the company’s printers can start the structure with a cell repelling resin (PEGDA) and perform automatic alignment using printed fiducial markers to subsequently apply a cell attractive resin (IP-S) at the precise position.
Projection micro stereolithography (PμSL) and microfluidic chips
Another key application of 3D microfabrication is the manufacturing of microfluidic chips to reliably grow in vivo-like tissues. Here, we turn to Dr. Chunguang Xia, CTO and Co-Founder of Boston Micro Fabrication (BMF), who is using projection micro stereolithography (PμSL) to make these chips.
Unlike 2PP printing which solidifies its resin within a small spot-like focal volume where two photons are likely to be absorbed at the same time, PμSL creates a 2D image using ultraviolet light on resin. Dr. Xia’s company BMF produces a series of PμSL printers with 2, 10, and 25 μm optical resolutions. Their newer printers offer faster printing speeds by having their software analyze where to use a finer resolution and a lower resolution for the rest of the print.
Dr. Xia talked about the company’s A10 BioChip, a device with 70 channels to harbor the growth of tissue. These 80-micron diameter channels feature pores of approximately 7 microns that allow for the movement of nutrients and waste. Such material exchange enables the growth of larger tissue structures, avoiding the death of interior cells. These chips open up opportunities for more cost- and time-effective drug and cosmetic testing.
They have shown that capillary perfusion within their microfluidic chips leads to the growth of thick and large colorectal HCT116 tumors compared to the lack of large tumor formation without such perfusion. These cancer-on-a-chip technologies can help pave the way for new drug efficacy tests, adding to the options researchers have to study these cells in vitro.
Dr. Xia also mentioned their tests on growing human liver cells within the biochip. After culturing for 7 days, these liver cells had greater viability compared to those grown in 2D. As an example of overdose drug testing, they demonstrated that their perfused liver-on-a-chip model results in lower cell viability levels at different acetaminophen concentrations compared to 2D and static cultures. Further research can then explore the use of this higher drug sensitivity to better simulate the toxicity of certain medications and their potential side effects in humans.
Superluminescent light projection (SLP) for nanoscale metallic structures
A critical consideration of 3D microfabrication techniques is the trade-off between resolution and cost. Jungho Choi, a Ph.D. candidate in Mechanical Engineering at Georgia Tech, is developing techniques to break this trade-off, specifically for nanoscale metallic structures.
The microfabrication of functional metallic structures may one day prove useful for small devices in healthcare. For example, electronics that adhere to the skin for patient monitoring and other biosensors will require specialized forms of cost-effective manufacturing.
Fabrication of nano-scale metallic structures remains a challenge: Choi pointed out that current techniques can only produce small volumes or are expensive. A 30-micron resolution inkjet metal printer can cost more than 250,000 U.S. dollars. Such costs may become a hurdle for low and medium-volume manufacturing.
In a clip from our event below, Choi talked about his work in creating a low-cost optical system using superluminescent light projection (SLP) that can create structures less than 250 nm. Instead of a costly femtosecond laser employed in nanoscale printing, they use a significantly cheaper superluminescent light emitting diode (SLED) and create focused light spots using an objective lens.
Light from the SLED is reflected off a digital micromirror device, which is an array of many microscopic mirrors that can be switched on to form a spatial pattern, similar to selectively turning on pixels of a computer screen to create an image. Light reflected from the activated mirrors is then passed through a collimating lens and then an objective lens, ultimately hitting the ink and forming the metal nanostructures.
They observed that by annealing their nanowires on a hot plate, the printed silver nanoparticles merge, increasing the contact area between them and achieving conductivity levels about 1/18th that of bulk silver, comparable to multi-photon photoreduction printing. Choi is looking to build upon this work to create 3D features as well as perform multi-material prints with polymers in the future.
Join us for our future 3DHEALS events
3D microfabrication has immense potential for future applications, with avenues in Dr. Richter’s two-photon polymerization, Dr. Xia’s projection micro stereolithography, and Choi’s superluminescent light projection. Techniques such as the ones featured by our panelists open up the world of micro- and nano-scale devices to 3D printing for healthcare. To join our events live and stay up to date with 3D bioprinting, subscribe to receive updates for our upcoming webinars.
About the Author:
Peter Hsu
Peter Hsu is an editorial intern for 3DHEALS. He is currently an undergraduate at the University of Illinois Urbana-Champaign and studies bioengineering with a focus on cell and tissue engineering. He is also minoring in computer science with interests in artificial intelligence and image processing. Peter conducts research on using computer vision methods to analyze human tissue images and improving the robustness of machine learning workflows. He is interested in the use of AI to assist tissue engineering and bioprinting research for medical applications. He is passionate about science communication and leads STEM outreach lessons at schools in the central Illinois area.
Related Links:
3D Microfabrication 2.0 (On Demand, 2024)
3D Microfabrication: Medical Applications (On Demand, 2022)
3D Printing Organ on a Chip, Microfluidics Devices (On Demand, 2023)
Event Recap: Point of Care 3D Printing
Event Recap: 3D Bioprinting Biofabricating Skin Components
Event Recap: Point of Care 3D Printing
Event Recap: 3D Printing and AI in Orthopedics
Event Recap: Innovation in Melt-Electrowriting (MEW) & 3D Printing
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