Projection-based stereolithography for direct 3D printing of heterogeneous ultrasound phantoms

Abstract

Modern ultrasound (US) imaging is increasing its clinical impact, particularly with the introduction of US-based quantitative imaging biomarkers. Continued development and validation of such novel imaging approaches requires imaging phantoms that recapitulate the underlying anatomy and pathology of interest. However, current US phantom designs are generally too simplistic to emulate the structure and variability of the human body. Therefore, there is a need to create a platform that is capable of generating well-characterized phantoms that can mimic the basic anatomical, functional, and mechanical properties of native tissues and pathologies. Using a 3D-printing technique based on stereolithography, we fabricated US phantoms using soft materials in a single fabrication session, without the need for material casting or back-filling. With this technique, we induced variable levels of stable US backscatter in our printed materials in anatomically relevant 3D patterns. Additionally, we controlled phantom stiffness from 7 to >120 kPa at the voxel level to generate isotropic and anisotropic phantoms for elasticity imaging. Lastly, we demonstrated the fabrication of channels with diameters as small as 60 micrometers and with complex geometry (e.g., tortuosity) capable of supporting blood-mimicking fluid flow. Collectively, these results show that projection-based stereolithography allows for customizable fabrication of complex US phantoms.

Mechanical Behavior of 3D Printed Poly(ethylene glycol) Diacrylate Hydrogels in Hydrated Conditions Investigated Using Atomic Force Microscopy

“…The exposure gradient through the layer and the double exposure of the top section of each layer results in a gradient cross-linking density across each printed layer. This exacerbates the gradient of cross-linking degree and adversely affects the mechanical properties across the thickness of the layer, which agrees with the results in Figure …”

“…This exacerbates the gradient of cross-linking degree and adversely affects the mechanical properties across the thickness of the layer, which agrees with the results in Figure 2. 24 In our previous study, we found that the monolithic sample, which did not contain the QY photoabsorber in its prepolymer solution, had the highest degree of cross-linking and highest E, as indicated by both 1 H NMR spectra and nanoindentation measurements. On the other hand, the multilayer sample, which had the highest concentration of QY photoabsorber, exhibited a lower degree of cross-linking as well as E. This observation suggests that a higher concentration of QY photoabsorber in the prepolymer solution leads to a reduction in the degree of cross-linking in the cross-linked hydrogel, as shown in Figures 2id,iid, and 3a,b.…”

“…Despite the aforementioned advantages, previous studies have reported the existence of cross-linking gradients in photo-cross-linked 3D printed multilayer PEGDA hydrogels that result in inhomogeneous properties, e.g., E , across the printed layers. − To date, atomic force microscopy (AFM) measurements were carried out in dried and cryosectioned biostructures; hence, there is a clear need for improving the fundamental understanding of outer surface properties of 3D printed multilayer hydrogels in realistic conditions. The research reported herein addresses this knowledge gap by systematically and thoroughly mapping the elastic behavior on the outer surface of 3D printed multilayer PEGDA hydrogels using AFM measurements in the hydrated state. − While the findings presented herein are limited to elastic behavior, they provide a much-needed baseline understanding of the outer surface variation in E within the layer and across the entire structure that remained elusive prior to this study.…”

Nanoindentation Response of 3D Printed PEGDA Hydrogels in a Hydrated Environment

“…46,47 Any inhomogeneity or gradient in crosslinking within each layer is attributed to the absorption of the UV light by the photoabsorber in the prepolymer solution resulting in a spatial decay of light intensity during the crosslinking process. 48,49 There was no obvious change in the monolithic mono-1200 μm-3 s and mono-1200 μm-15 s in terms of their visual appearance, as there is no interlayer interface within the structure (Figure 4cii, right). High magnification cross-sectional SEM images of vacuum-dried multilayer PEGDA showed imperfections that appear as pockets of voids, both at interfaces and within printed layers.…”

“…Interface failure could be due to the residual stress at the interface between the top section of the previously printed layer and the bottom section of the newly formed layer. The top section is assumed to be sufficiently cross-linked as it is closer to the UV light, while the bottom section is farther away from the UV light and is assumed to be less cross-linked in comparison. , Any inhomogeneity or gradient in cross-linking within each layer is attributed to the absorption of the UV light by the photoabsorber in the prepolymer solution resulting in a spatial decay of light intensity during the cross-linking process. , There was no obvious change in the monolithic mono-1200 μm-3 s and mono-1200 μm-15 s in terms of their visual appearance, as there is no interlayer interface within the structure (Figure cii, right). High magnification cross-sectional SEM images of vacuum-dried multilayer PEGDA showed imperfections that appear as pockets of voids, both at interfaces and within printed layers .…”