No abstract

. Microscopic and mesoscale optical imaging techniques allow for three-dimensional (3-D) imaging of biological tissue across millimeter-scale regions, and imaging phantom models are invaluable for system characterization and clinical training. Phantom models that replicate complex 3-D geometries with both structural and molecular contrast, with resolution and lateral dimensions equivalent to those of imaging techniques ( ), have proven elusive. We present a method for fabricating phantom models using a combination of two-photon polymerization (2PP) to print scaffolds, and microinjection of tailored tissue-mimicking materials to simulate healthy and diseased tissue. We provide a first demonstration of the capabilities of this method with intravascular optical coherence tomography, an imaging technique widely used in clinical practice. We describe the design, fabrication, and validation of three types of phantom models: a first with subresolution wires (5- to diameter) arranged circumferentially, a second with a vessel side-branch, and a third containing a lipid inclusion within a vessel. Silicone hybrid materials and lipids, microinjected within a resin framework created with 2PP, served as tissue-mimicking materials that provided realistic optical scattering and absorption. We demonstrate that optical phantom models made with 2PP and microinjected tissue-mimicking materials can simulate complex anatomy and pathology with exquisite detail.

The ability to print high-resolution (< 10 µm) three-dimensional (3D) features is important in numerous existing and emerging applications such as tissue engineering, nanoelectronics, photovoltaics, optics, biomedical devices etc. The current chapter is focused on a subset of high-resolution printing techniques that exploit micro and nanofluidics features to attain high resolution. Here these approaches are referred as fluidics assisted high-resolution 3D printing. Salient examples of such techniques are electrohydrodynamic printing, direct-write assembly, aerosol jet printing, etc. The chapter starts with a brief introduction and discussion on the challenges of high-resolution printing. This is followed by a section on fundamental mechanisms of droplet, jet and filament formations, and their role in deciding the print resolution. Commonalities between different printing techniques (e.g. the physics of jet breakup and role of capillary stresses) are highlighted in order to provide a systematic understanding and context. Next the fluid mechanics features determining the print resolution and quality are discussed in detail. This includes sections on the role of ink rheology, evaporation rate, nozzle size, substrate and nozzle wetting properties (i.e. surface energy) and dynamic effects such as drop impact and spreading, stability of printed liquid lines and liquid filaments etc. Wherever relevant, literature on much more established inkjet printing techniques is also exploited to provide a context for the high-resolution printing and clarify the distinct benefits and challenges that emerge at progressively higher resolutions. In the wetting and surface energy section, features of dippen lithography and transfer printing, two popular techniques for two-dimensional high-resolution printing, are also briefly introduced for completeness. Lastly, the chapter ends with a summary and brief perspective on future research trends in this area.