Over the past few years, 3D printing of electronics have become a promising technology due to their potential appli­cations in emerging fields such as nano­electronics and nano­photonics. Among 3D microfabrication technologies, multiphoton litho­graphy (MPL) is considered the state-of-the-art amongst the micro­fabrication methods with true 3D fabrication capability, excellent level of spatial and temporal control, and the versatility of photo­sensitive materials mostly composed of acrylate-based polymers/monomers or epoxy-based photo­resists. When looking at this future of production of microscale organic electronics, Mohammad Reza Abidian at the Univer­sity of Houston Cullen College of Engineering sees their potential for use in flexible electronics and bioelec­tronics, via multiphoton 3D printers. 

“We introduced a new photo­sensitive resin doped with an organic semiconductor material (OS) to fabricate highly conductive 3D micro­structures with high-quality structural features via MPL process,” Abidian said. They showed that the fabrication process could be performed on glass and flexible substrate poly(dimethyl­silosane). They demonstrated that loading as low as 0.5 wt % OS into the resin remarkably increased electrical conductivity of printed organic semi­conductor composite polymer over 10 orders of magnitude. “The excellent electrical conductivity can be attri­buted to presence of OS in the cross-linked polymer chains, providing both ionic and electronic conduction pathways along the polymer chains,” Abidian said. 

To demonstrate the potential electronic appli­cations based on the OS composite resin, his team fabricated various microelectronic devices, including micro-printed circuit board, which comprises various electrical elements, and an array of micro­capacitors. Three dimensional bioprinting of organic semiconductor microdevices based on MPL has potential in biomedical appli­cations including tissue engineering, bioelectronics and biosensors. Abidian’s team successfully incor­porated bioactive molecules such as laminin and glucose oxidase into the OS composite micro­structures (OSCMs). To confirm that the bioactivity of laminin was retained throughout the entire MPL process, primary mouse endothelial cells were cultured on OS composite micro­structures. Cells seeded on laminin incor­porated OSCMs displayed evidence of adherence to substrate, proli­feration, and enhanced survival. 

“We also assessed the biocompati­bility of the OS composite structures by culturing lymphocytes, namely splenic T-cells and B-cells, on the fabricated surfaces and compared them with control surfaces. After seven days of culture, OS composite polymers did not induce cell mortality with approxi­mately 94 percent cell viability compared to the control surfaces,” Abidian said. “In addition, the potential effect of OS composite polymers on cell activation was also studied. After seven days of culture, there was no significant difference in the expression of activation markers on the lymphocytes between OS composite structures and control surfaces.” 

Finally, Abidian proposed a maskless method based on MPL for fabrication of bioelectronics and biosensors. They fabricated a glucose biosensor similar to Michigan style neural electrodes. Glucose oxidase, an enzyme for the specific recognition of glucose, was encapsulated within the solidified OS composite micro­electrodes via the MPL process. The biosensor offered a highly sensitive glucose sensing platform with nearly ten-fold higher sensitivity compared to previous glucose biosensors. In addition, this biosensor exhibited excellent speci­ficity and high reproduci­bility. 

“We anticipate that the presented MPL-compatible OS composite resins will pave the path towards production of soft, bioactive, and conductive microstructures for various appli­cations in the emerging fields of flexible bioelec­tronics, biosensors, nano­electronics, organ-on-chips, and immune cell therapies,” Abidian said. (Source: U Houston)

Reference: O. Dadras-Toussi et al.: Multiphoton Lithography of Organic Semiconductor Devices for 3D Printing of Flexible Electronic Circuits, Biosensors, and Bioelectronics, Adv. Mat. 34, 2200512 (2022); DOI: 10.1002/adma.202200512

Link: Dept. of Biomedical Engineering, University of Houston, Houston, USA