3D printing of optical materials: an investigation of the microscopic properties

3D printing technologies are currently enabling the fabrication of objects with complex architectures and tailored properties. In such framework, the production of 3D optical structures, which are typically based on optical transparent matrices, optionally doped with active molecular compounds and nanoparticles, is still limited by the poor uniformity of the printed structures. Both bulk inhomogeneities and surface roughness of the printed structures can negatively affect the propagation of light in 3D printed optical components. Here we investigate photopolymerization-based printing processes by laser confocal microscopy. The experimental method we developed allows the printing process to be investigated in-situ, with microscale spatial resolution, and in real-time. The modelling of the photo-polymerization kinetics allows the different polymerization regimes to be investigated and the influence of process variables to be rationalized. In addition, the origin of the factors limiting light propagation in printed materials are rationalized, with the aim of envisaging effective experimental strategies to improve optical properties of printed materials.Comment: 8 pages, 3 figure

Impact of size effects on photopolymerization and its optical monitoring in-situ

Photopolymerization processes are exploited in light exposure-based 3D printing technologies, where either a focused laser beam or a patterned light sheet allows layers of a UV curable, liquid pre-polymer to be solidified. Here we focus on the crucial, though often neglected, role of the layer thickness on photopolymerization. The temporal evolution of polymerization reactions occurring in droplets of acrylate-based oligomers and in photoresist films with varied thickness is investigated by means of an optical system, which is specifically designed for in-situ and real-time monitoring. The time needed for complete curing is found to increase as the polymerization volume is decreased below a characteristic threshold that depends on the specific reaction pathway. This behavior is rationalized by modeling the process through a size-dependent polymerization rate. Our study highlights that the formation of photopolymerized networks might be affected by the involved volumes regardless of the specific curing mechanisms, which could play a crucial role in optimizing photocuring-based additive manufacturing

Neurosurgical Applications of Magnetic Resonance Diffusion Tensor Imaging

Magnetic Resonance (MR) Diffusion Tensor Imaging (DTI) is a rapidly evolving technology that enables the visualization of neural fiber bundles, or white matter (WM) tracts. There are numerous neurosurgical applications for MR DTI including: (1) Tumor grading and staging; (2) Pre-surgical planning (determination of resectability, determination of surgical approach, identification of WM tracts at risk); (3) Intraoperative navigation (tumor resection that spares WM damage, epilepsy resection that spares WM damage, accurate location of deep brain stimulation structures); (4) Post-operative assessment and monitoring (identification of WM damage, identification of tumor recurrence). Limitations of MR DTI include difficulty tracking small and crossing WM tracts, lack of standardized data acquisition and post-processing techniques, and practical equipment, software, and timing considerations. Overall, MR DTI is a useful tool for planning, performing, and following neurosurgical procedures, and has the potential to significantly improve patient care. Technological improvements and increased familiarity with DTI among clinicians are next steps

Local mechanical properties of electrospun fibers correlate to their internal nanostructure.

This is the final version of the article. Available from the publisher via the DOI in this record.The properties of polymeric nanofibers can be tailored and enhanced by properly managing the structure of the polymer molecules at the nanoscale. Although electrospun polymer fibers are increasingly exploited in many technological applications, their internal nanostructure, determining their improved physical properties, is still poorly investigated and understood. Here, we unravel the internal structure of electrospun functional nanofibers made by prototype conjugated polymers. The unique features of near-field optical measurements are exploited to investigate the nanoscale spatial variation of the polymer density, evidencing the presence of a dense internal core embedded in a less dense polymeric shell. Interestingly, nanoscale mapping the fiber Young's modulus demonstrates that the dense core is stiffer than the polymeric, less dense shell. These findings are rationalized by developing a theoretical model and simulations of the polymer molecular structural evolution during the electrospinning process. This model predicts that the stretching of the polymer network induces a contraction of the network toward the jet center with a local increase of the polymer density, as observed in the solid structure. The found complex internal structure opens an interesting perspective for improving and tailoring the molecular morphology and multifunctional electronic and optical properties of polymer fibers.V. Fasano and G. Potente are acknowledged for confocal and SEM images, respectively. The authors also gratefully thank S. Girardo for high-speed imaging of the polymer jet and E. Caldi for assistance in the SNOM measurements. We gratefully acknowledge the financial support of the United States-Israel Binational Science Foundation (BSF Grant 2006061), the RBNI-Russell Berrie Nanotechnology Institute, and the Israel Science Foundation (ISF Grant 770/11). The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement 306357 (ERC Starting Grant “NANO-JETS”)

Mechanics of Hydrogenated Amorphous Carbon Deposits from Electron-Beam-Induced Deposition of Paraffin Precursor

Many experiments on the mechanics of nanostructures require the creation of rigid clamps at specific locations. In this work, electron-beam-induced deposition(EBID) has been used to depositcarbonfilms that are similar to those that have recently been used for clamping nanostructures. The film deposition rate was accelerated by placing a paraffin source of hydrocarbon near the area where the EBIDdeposits were made. High-resolution transmission electron microscopy, electron-energy-loss spectroscopy, Raman spectroscopy, secondary-ion-mass spectrometry, and nanoindentation were used to characterize the chemical composition and the mechanics of the carbonaceous deposits. The typical EBIDdeposit was found to be hydrogenated amorphous carbon (a-C:H) having more sp2- than sp3-bonded carbon.Nanoindentation tests revealed a hardness of ∼4GPa and an elastic modulus of 30–60GPa, depending on the accelerating voltage. This reflects a relatively soft film, which is built out of precursor molecular ions impacting the growing surface layer with low energies. The use of such deposits as clamps for tensile tests of poly(acrylonitrile)-based carbon nanofibers loaded between opposing atomic force microscope cantilevers is presented as an example applicatio

3-D Nanofibrous Electrospun Multilayered Construct is an Alternative ECM Mimicking Scaffold

Abstract Extra cellular matrix (ECM) is a natural cell environment, possesses complicated nano-and macroarchitecture. Mimicking this three-dimensional (3-D) web is a challenge in the modern tissue engineering. This study examined the application of a novel 3-D construct, produced by multilayered organization of electrospun nanofiber membranes, for human bone marrow-derived mesenchymal stem cells (hMSCs) support. The hMSCs were seeded on an electrospun scaffold composed of poly e-caproloactone (PCL) and collagen (COL) (1:1), and cultured in a dynamic flow bioreactor prior to in vivo implantation. Cell viability after seeding was analyzed by AlamarBlue TM Assay. At the various stages of experiment, cell morphology was examined by histology, scanning electron microscopy (SEM) and confocal microscopy

Enhanced Electrospinning of Active Organic Fibers by Plasma Treatment on Conjugated Polymer Solutions

Realizing active, light-emitting fibers made of conjugated polymers by the electrospinning method is generally challenging. Electrospinning of plasma-treated conjugated polymer solutions is here developed for the production of light-emitting microfibers and nanofibers. Active fibers from conjugated polymer solutions rapidly processed by a cold atmospheric argon plasma are electrospun in an effective way, and they show a smoother surface and bead-less morphology, as well as preserved optical properties in terms of absorption, emission, and photoluminescence quantum yield. In addition, the polarization of emitted light and more notably photon waveguiding along the length of individual fibers are remarkably enhanced by electrospinning plasma-treated solutions. These properties come from a synergetic combination of favorable intermolecular coupling in the solutions, increased order of macromolecules on the nanoscale, and resulting fiber morphology. Such findings make the coupling of the electrospinning method and cold atmospheric plasma processing on conjugated polymer solutions a highly promising and possibly general route to generate light-emitting and conductive micro- and nanostructures for organic photonics and electronics

The role of parental achievement goals in predicting autonomy-supportive and controlling parenting

Although autonomy-supportive and controlling parenting are linked to numerous positive and negative child outcomes respectively, fewer studies have focused on their determinants. Drawing on achievement goal theory and self-determination theory, we propose that parental achievement goals (i.e., achievement goals that parents have for their children) can be mastery, performance-approach or performance-avoidance oriented and that types of goals predict mothers' tendency to adopt autonomy-supportive and controlling behaviors. A total of 67 mothers (aged 30-53 years) reported their goals for their adolescent (aged 13-16 years; 19.4 % girls), while their adolescent evaluated their mothers' behaviors. Hierarchical regression analyses showed that parental performance-approach goals predict more controlling parenting and prevent acknowledgement of feelings, one autonomy-supportive behavior. In addition, mothers who have mastery goals and who endorse performance-avoidance goals are less likely to use guilt-inducing criticisms. These findings were observed while controlling for the effect of maternal anxiety

Reinforcing medical authority: clinical ethics consultation and the resolution of conflicts in treatment decisions

Despite substantial efforts in the past 15 years to professionalise the field of clinical ethics consultation, sociologists have not re‐examined past hypotheses about the role of such services in medical decision‐making and their effect on physician authority. In relation to those hypotheses, we explore two questions: (i) What kinds of issues does ethics consultation resolve? and (ii) what is the nature of the resolution afforded by these consults? We examined ethics consultation records created between 2011 and mid‐2015 at a large tertiary care US hospital and found that in most cases, the problems addressed are not novel ethical dilemmas as classically conceived, but are instead disagreements between clinicians and patients or their surrogates about treatment. The resolution offered by a typical ethics consultation involves strategies to improve communication rather than the parsing of ethical obligations. In cases where disagreements persist, the proposed solution is most often based on technical clinical judgements, reinforcing the role of physician authority in patient care and the ethical decisions made about that care.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154312/1/shil13003.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154312/2/shil13003_am.pd