Computed axial lithography (CAL) is an emerging volumetric additive manufacturing technology which presents unique opportunities in layerless ultra-rapid fabrication. However, the required process control places particular demands on computing and delivering the appropriate 3D distribution of optical energy, as well as monitoring the solidifying structure within the photo-resin. For example, continued reaction after tomographic exposure is not currently accounted for and could lead to higher degree-of-conversion than designed and consequent feature dilations. Color Schlieren Tomography (CST) is developed as an in-situ metrology tool to monitor volumetrically the internal refractive index and the forming geometry. Major improvements of CST in real-time computation and processing of 3D reconstruction have enabled event-driven patterning control such as auto-termination. With this technique, we monitored the polymerization process in real-time during and after termination of the exposure period signaled by an index-volume termination criterion. Monitoring of continued polymerization after termination (dark polymerization) shows that the refractive index change can rise to 10 times higher than its value at termination. The time-resolved 3D reconstruction data provided by CST can be used for chemical kinetics modeling and development of compensation schemes.
Volumetric additive manufacturing is a novel 3D printing method to form parts in a single exposure, in contrast to traditional stereolithography 3D printing which builds parts layer-by-layer. Photopolymerizable resin is exposed with grayscale images from different angles over 360 degrees to deliver a 3D distribution of light energy which cures the resin to form the desired part. The exposure images are calculated using computed tomography (CT), the same principles which are used to convert X-ray images obtained during a computerized axial tomography (CAT) scan to reconstruct a 3D volume of the patient. A digital micromirror device is used to project the sequence of calculated exposure images into a cylindrical vial of resin as it is rotated thus exposing over 360 degrees. The polymerization kinetics of the resin, the alignment of the resin vial to the projected images, and the uniformity of the illumination field are all tightly coupled together and must all be understood and controlled to generate quality parts. Projecting a good image is challenging as the vial and resin are essentially a strong cylindrical lens located at the image plane, and the desired build space is not a plane but a volume. We perform an analysis of the cylindrical lensing on the image quality (and thus the print quality) and investigate methods to correct for the lensing. We demonstrate different methods to improve print quality and discuss the benefits and limitations of each technique.
Lower-dimensional photopolymerization based additive manufacturing techniques have several drawbacks that currently limit the applicability and scope of 3D printing, including: topological constraints, the requirement for numerous complex support structures that later need to be removed, long print times for complex geometries, relative motion between the liquid resin and printed part, as well as debilitating mechanical weakness and anisotropy resulting from the inherently layered structure of the parts. We propose and demonstrate a novel volumetric 3D printing technique based on one of the most ubiquitous computational imaging methods in the field: computed axial tomography. Computed axial lithography (CAL) is a vat photopolymerization technique that exposes the entire resin volume by projecting images from a multiplicity of angles. The technique is a physical implementation of the filtered back projection algorithm for tomographic reconstruction. We use constrained non-convex optimization in order to generate images that are projected into the resin in order to sculpt a 3-dimensional energy dose that cures the desired arbitrary geometry. This eliminates the requirement for supports and enables complex and nested structures that were previously challenging or impossible to print. Further, the process is layer-less and does not involve any relative motion between the resin and the printed part, which has positive implications for mechanically isotropic part strength. We demonstrate support-less printing of complex geometries containing 10^8-10^9 voxels in 2-4 minutes, orders of magnitude faster than comparable techniques.
The utility and accuracy of computational modeling often requires direct validation against experimental measurements. The work presented here is motivated by taking a combined experimental and computational approach to determine the ability of large-scale computational fluid dynamics (CFD) simulations to understand and predict the dynamics of circulating tumor cells in clinically relevant environments. We use stroboscopic light sheet fluorescence imaging to track the paths and measure the velocities of fluorescent microspheres throughout a human aorta model. Performed over complex physiologicallyrealistic 3D geometries, large data sets are acquired with microscopic resolution over macroscopic distances.
Although real-time PCR (RT-PCR) has become a diagnostic standard for rapid identification of bacterial species, typical
methods remain time-intensive due to sample preparation and amplification cycle times. The assay described in this
work incorporates on-chip dielectrophoretic capture and concentration of bacterial cells, thermal lysis, cell
permeabilization, and nucleic acid denaturation and fluorescence resonance energy transfer assisted in-situ hybridization
(FRET-ISH) species identification. Identification is achieved completely on chip in less than thirty minutes from receipt
of sample compared to multiple hours required by traditional RT-PCR and its requisite sample preparation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.