User-defined Shape Research Articles

Solvent-free synthesis of biostable segmented polyurethane shape memory polymers for biomedical applications.

Biostable shape memory polymers that remain stable in physiological conditions are beneficial for user-defined shape recovery in response to a specific stimulus. For potential commercialization and biocompatibility considerations, biomaterial synthesis must be simple and scalable. Hence, a library of biostable and cytocompatible shape memory polymers with tunable thermomechanical properties based on hard segment content was synthesized using a solvent-free method. Polymer surface chemistry, thermomechanical and shape memory properties, and biostability were assessed. We also investigated the effects of processing methods on thermomechanical and shape memory properties. All polymers showed high glass transition temperatures (>50 °C), which indicates that their temporary shape could be preserved after implantation. Polymers also demonstrate high shape fixity (73-80%) and shape recovery (93-95%). Minimal mass loss (<5%) was observed in accelerated oxidative (20% H2O2) and hydrolytic (0.1 M NaOH) media. Additionally, minimal shape recovery (∼0%) occurred in programmed samples with higher hard segment content that were stored in degradation media. After 40 days of storage in media, programmed samples recovered their primary shapes upon heating to temperatures above their transition temperature. Annealing to above the polymer melting point and solvent casting of polymers improved shape memory and thermal properties. To enable their potential use as biomaterial scaffolds, fiber formation of synthesized polyurethanes was compared with those of samples synthesized using a previously reported solvent-based method. The new method provided polymers that can form fibrous scaffolds with improved mechanical and shape memory properties, which is attributed to the higher molecular weight and crystalline content of polymers synthesized using the new, solvent-free approach. These biostable segmented polyurethanes could be coupled with a range of components that respond to specific stimuli, such as enzymes, magnetic field, pH, or light, to enable a specific shape change response, which could be coupled with drug and/or bioactive material delivery in future work.

Self-Defensive Antimicrobial Shape Memory Polyurethanes with Honey-Based Compounds.

Infection treatment plays a crucial role in aiding the body in wound healing. To that end, we developed a library of antimicrobial polymers based on segmented shape memory polyurethanes with nondrug-based antimicrobials (i.e., honey-based phenolic acids (PAs)) using both chemical and physical incorporation approaches. The antimicrobial shape memory polymers (SMPs) have high transition temperatures (>55 °C) to enable maintenance of temporary, programmed shapes in physiological conditions unless a specific external stimulus is present. Polymers showed tunable mechanical and shape memory properties by changing the ratio, chemistry, and incorporation method of PAs. Cytocompatible (∼100% cell viability) synthesized polymers inhibited growth rates of Staphylococcus aureus (∼100% with physically incorporated PAs and >80% with chemically incorporated PAs) and Escherichia coli (∼100% for samples with cinnamic acid (physical and chemical)). Crystal violet assays showed that all formulations inhibit biofilm formation in surrounding solutions, and chemically incorporated samples showed surface antibiofilm properties with S. aureus. Molecular dynamics simulations confirm that PAs have higher levels of interactions with S. aureus cell membranes than E. coli. Long-term antimicrobial properties were measured after storage of the sample in aqueous conditions; the polymers retained their antimicrobial properties against E. coli after up to 20 days. As a proof of concept, magnetic particles were incorporated into the polymer to trigger user-defined shape recovery by applying an external magnetic field. Shape recovery disrupted preformed S. aureus biofilms on polymer surfaces. This antimicrobial biomaterial platform could enable user- or environmentally controlled shape change and/or antimicrobial release to enhance infection treatment efforts.

Shape2SAS: a web application to simulate small-angle scattering data and pair distance distributions from user-defined shapes.

Shape2SAS is a web application that allows researchers and students to build intuition about and understanding of small-angle scattering. It is available at https://somo.chem.utk.edu/shape2sas. The user defines a model of arbitrary shape by combining geometrical subunits, and Shape2SAS then calculates and displays the scattering intensity and the pair distance distribution, as well as a visualization of the user-defined shape. Simulated data with realistic noise are also generated. Here, it is demonstrated how Shape2SAS can calculate and display the different scattering patterns for various geometrical shapes, such as spheres and cylinders. It is also shown how the effect of structure factors can be visualized. Finally, it is indicated how multi-contrast particles can readily be generated, and how the calculated scattering may be used to validate and visualize analytical models generated in analysis software for fitting small-angle scattering data.

Shape defect analysis from volumetric data - Application to lattice struts in additive manufacturing

Additive manufacturing (AM) revolutionises the way parts are produced as it offers a variety of design freedom. Lattice structures are an illustration of this AM freedom, allowing for the production of complex geometries that are being investigated in many applications. However, lattice structures present different typology of defects such as surface quality, porosity or dimensional inaccuracies. The most adapted measurement technology to reveal AM internal defects falls into X-ray computed tomography (XCT). Although there have been significant efforts in modelling lattice structure defects from XCT, a direct and accurate link between volumetric data of the part being measured and the CAD model is still required. This direct link would have the noteworthy advantage of not involving XCT surface determination tool, which choice may be discussed. In this paper, shape defects from metal laser powder bed fusion (PBF) strut-based lattice structures are studied. Different struts are printed as representative of BCCz lattice cells. Struts are successively measured by XCT and focus variation (FV). A virtual volume correlation (V2C) method is presented where shape defect contained in XCT volumetric data is successively approached by modal decomposition relying on a generated defect basis. The modal decomposition approach is firstly validated by comparing its efficiency towards least square cylinder approximation. Then, correlation intrinsic parameters are found, by conducting 2-dimensional sensitivity studies to identify optimal V2C parameters. V2C is further applied to the entire XCT measurements for each considered strut. Comparisons between correlated envelopes and registered FV and XCT measurements are performed to numerically estimate RMS errors. Results show that RMS errors between correlated envelopes and registered measurements are in the same order as the XCT resolution. Conclusions can then be drawn regarding the ability of V2C to estimate lattice strut shape defect relying on an user-defined shape defect basis.

A new higher-order RBF-FD scheme with optimal variable shape parameter for partial differential equation

Radial basis functions (RBFs) with multiquadric (MQ) kernel have been commonly used to solve partial differential equation (PDE). The MQ kernel contains a user-defined shape parameter (ε), and the solution accuracy is strongly dependent on the value of this ε. In this study, the MQ-based RBF finite difference (RBF-FD) method is derived in a polynomial form. The optimal value of ε is computed such that the leading error term of the RBF-FD scheme is eliminated to improve the solution accuracy and to accelerate the rate of convergence. The optimal ε is computed by using finite difference (FD) and combined compact differencing (CCD) schemes. From the analyses, the optimal ε is found to vary throughout the domain. Therefore, by using the localized shape parameter, the computed PDE solution accuracy is higher as compared to the RBF-FD scheme which employs a constant value of ε. In general, the solution obtained by using the ε computed from CCD scheme is more accurate, but at a higher computational cost. Nevertheless, the cost-effectiveness study shows that when the number of iterative prediction of ε is limited to two, the present RBF-FD with ε by CCD scheme is as effective as the one using FD scheme.

Application of RBF-DQ Method to Time-Dependent Analysis of Unsaturated Seepage

Richards’ equation is a nonlinear partial differential equation governing unsteady seepage flow through unsaturated porous media. This paper investigates applicability of radial basis function-based differential quadrature (RBF-DQ), as a meshless method, to simulate one-dimensional flow processes in the unsaturated zone under different initial and boundary conditions. Fourth-order Runge–Kutta scheme has been adopted for time integration. Results of solving three numerical examples using RBF-DQ are compared with those of analytical, numerical, and experimental solutions presented in the literature. The comparison indicates that RBF-DQ can provide more accurate results comparing with traditional FDM or FEM without the need to discretize the computational domain. Moreover, the merit of mesh-free characteristic in RBF-DQ makes it suitable not only for solving nonlinear problems but also for dealing with multidimensional problems since meshless methods are not restricted to dimensional limitations. A key parameter in utilizing multiquadratic approximation in RBF-DQ method is the user-defined shape parameter C, which may significantly affect solution accuracy. Thus, a sensitivity analysis has been conducted to study possible effects of shape parameter on achieved results.

Arbitrary Waveform Generation Based on Dispersion-Free Wavelength-to-Time Mapping Technique

We proposed and experimentally demonstrated an approach of dispersion-free arbitrary waveform generation based on a wavelength-swept laser, for the first time to the best of our knowledge. The system has been proven to generate a variety of waveforms, such as Gaussian pulses, rectangular pulses, and a chirped pulse with a large time-bandwidth product of 273.6. Thanks to the linear relationship of frequency to the time of the wavelength-swept laser, time-domain optical signal exhibits the user-defined shape of the optical spectrum without any dispersive element. Furthermore, the proposed method features simple structure, full reconfiguration, and, especially, the high potential for integration.

Self-assembly of genetically encoded DNA-protein hybrid nanoscale shapes.

We describe an approach to bottom-up fabrication that allows integration of the functional diversity of proteins into designed three-dimensional structural frameworks. A set of custom staple proteins based on transcription activator-like effector proteins folds a double-stranded DNA template into a user-defined shape. Each staple protein is designed to recognize and closely link two distinct double-helical DNA sequences at separate positions on the template. We present design rules for constructing megadalton-scale DNA-protein hybrid shapes; introduce various structural motifs, such as custom curvature, corners, and vertices; and describe principles for creating multilayer DNA-protein objects with enhanced rigidity. We demonstrate self-assembly of our hybrid nanostructures in one-pot mixtures that include the genetic information for the designed proteins, the template DNA, RNA polymerase, ribosomes, and cofactors for transcription and translation.

Genetically Encoded DNA-Protein Hybrid Origami

Here we describe an approach to bottom-up fabrication with nanometer-precision that allows integrating the functional diversity of proteins in designed three-dimensional structural frameworks. We reimagined the successful DNA origami design principle using a set of custom staple proteins to fold a double-stranded DNA template into a user-defined shape. Each staple protein recognizes two distinct double-helical DNA sequences and can carry additional functionalities. The staple proteins we present here are based on the transcription activator-like (TAL) effector proteins. Due to their repetitive structure these proteins offer a unique programmability that enables us to construct numerous staple proteins targeting any desired DNA sequence. Our approach is general, meaning that many different objects may be created using the same set of rules, and it is modular, because components can be modified or exchanged individually. We present rules for constructing megadalton-scale DNA-protein hybrid nanostructures; introduce important structural motifs, such as curvature, corners, and vertices; describe principles for creating multi-layer DNA-protein objects with enhanced rigidity; and demonstrate the possibility to combine our DNA-protein hybrid origami with conventional DNA nanotechnology. Since all components can be encoded genetically, our structures should be amenable to biotechnological mass-production. Moreover, since the target objects can self-assemble at room temperature in near-physiological buffer, our hybrid origami may also provide an attractive method to realize positioning and scaffolding tasks in vivo. We expect our method to find application both in scaffolding protein functionalities and in manipulating the spatial arrangement of genomic DNA.

User-defined feature comparison for vector field ensembles

Most of the existing approaches to visualize vector field ensembles are to reveal the uncertainty of individual variables, for example, statistics, variability, etc. However, a user-defined derived feature like vortex or air mass is also quite significant, since they make more sense to domain scientists. In this paper, we present a new framework to extract user-defined derived features from different simulation runs. Specially, we use a detail-to-overview searching scheme to help extract vortex with a user-defined shape. We further compute the geometry information including the size, the geo-spatial location of the extracted vortexes. We also design some linked views to compare them between different runs. At last, the temporal information such as the occurrence time of the feature is further estimated and compared. Results show that our method is capable of extracting the features across different runs and comparing them spatially and temporally.

Evaluation of automated contour detection to produce regional delay maps from high temporal resolution cine images in patients undergoing CRT

Background Recently, high temporal resolution short-axis cine images have been used to create left ventricular (LV) regional mechanical delay (RMD) maps in patients undergoing cardiac resynchronization therapy (CRT). Generating the endocardial segmentation required for RMD analysis is both time-consuming and subjective. A semi-automated segmentation method for time-continuous contour detection that uses multi-dimensional dynamic programming to enforce user-defined shape constraints without the need for extensive training sets has been previously developed (Uzumcu 2006). Our goal was to compare RMD maps generated from semiautomated and manual segmentation in patients enrolled for CRT.

Rigid DNA Beams for High‐Resolution Single‐Molecule Mechanics

Rigid DNA Beams for High‐Resolution Single‐Molecule Mechanics

Programmable microfluidic patterning of protein gradients on hydrogels

Computer-controlled hydrodynamic flow focusing was utilized to generate tethered protein gradients of any user-defined shape on the surface of soft synthetic hydrogels.

New developments in the radial basis functions analysis of composite shells

In this paper, we use the third order shear deformation theory of Reddy [Reddy JN. Mechanics of laminated composite plates and shells. CRC Press; 2004] with a meshless numerical method to analyze the static deformation of composite plates and shells. Numerical results are compared with Navier solutions in various examples. The meshless collocation method based on radial basis functions requires a user-defined shape parameter than can compromise the quality of the solution when poorly chosen. To improve the choice of this shape parameter, we apply an optimization technique based on the leave-one-out cross validation analysis to obtain the shape parameter in a given interval. The results obtained were significantly better than those produced with a user-defined shape parameter.

All-Fiber Ultrawideband Pulse Generation Based on Spectral Shaping and Dispersion-Induced Frequency-to-Time Conversion

An approach to generating and distributing ultrawideband (UWB) pulses based on optical spectral shaping and frequency-to-time conversion using all-fiber components is proposed and demonstrated. In the system, the spectrum of an ultrashort pulse from a mode-locked fiber laser is spectrally shaped by an all-fiber spectrum shaper, to produce a monocycle- or a doublet-shaped power spectrum. Thanks to the frequency-to-time conversion in a dispersive fiber, time-domain optical pulses exhibiting the user-defined shape of the optical power spectrum are obtained. Experiments based on the proposed approach are carried out. UWB monocycle or doublet pulses are generated

Error-based segmentation of cloud data for direct rapid prototyping

This paper proposes an error-based segmentation approach for direct rapid prototyping (RP) of random cloud data. The objective is to fully integrate reverse engineering and RP for rapid product development. By constructing an intermediate point-based curve model (IPCM), a layer-based RP model is directly generated from the cloud data and served as the input to the RP machine for fabrication. In this process, neither a surface model nor an STL file is generated. This is accomplished via three steps. First, the cloud data is adaptively subdivided into a set of regions according to a given subdivision error, and the data in each region is compressed by keeping the feature points (FPs) within the user-defined shape tolerance using a digital image based reduction method. Second, based on the FPs of each region, an IPCM is constructed, and RP layer contours are then directly extracted from the models. Finally, the RP layer contours are faired with a discrete curvature based fairing method and subsequently closed to generate the final layer-based RP model. This RP model can be directly submitted to the RP machine for prototype manufacturing. Two case studies are presented to illustrate the efficacy of the approach.

Design of unstable laser resonators with user-defined mode shape

By introducing surface-structured mirrors into stable laser resonators, the generation of user-defined mode profiles and properties has become possible. On a wave-optical basis, we show that there is a general connection between the property of the modes to be phase-conjugated during reflection at the mirrors and their diffraction losses at apertures. This connection makes the design method known for stable resonators with predefined modes unsuitable for the design of such resonators of unstable geometry. An alternative method for the calculation of unstable resonators with user-defined output beam shape is presented and demonstrated by an example design.

A Method for Generating Simulated Plasmodes and Artificial Test Clusters with User-Defined Shape, Size, and Orientation

We present a simple method for generating simulated plasmodes and artificial test clusters with user-defined shape, size, and orientation. Our method differs from other cluster generation techniques in that it focuses on the validity of the cluster indicators. For J clusters, indicator validity is defined as the squared correlation ratio between the cluster indicator (i.e., the observed variable) and J-1 dummy variables. The within-cluster correlation structure and the univariate distributions of the cluster indicators are specified with procedures outlined by Fleishman (1978) and Vale and Maurelli (1983). Simulation results illustrate the utility of the method for cluster analysis evaluation research.

Focusing and targeting of magnetic brain stimulation using multiple coils.

Neurones can be excited by an externally applied time-varying electromagnetic field. Focused magnetic brain stimulation is attained using multiple small coils instead of one large coil, the resultant induced electric field being a superposition of the fields from each coil. In multichannel magnetic brain stimulation, partial cancellation of fields from individual coils provides a significant improvement in the focusing of the stimulating field, and independent coil channels allow targeting of the stimuli on a given spot without moving the coils. The problem of shaping the stimulating field in multichannel stimulation is analysed, and a method is derived that yields the driving currents required to induce a field with a user-defined shape. The formulation makes use of lead fields and minimum-norm estimation from magneto-encephalography. Using these methods, some properties of multichannel coil arrays are examined. Computer-assisted multichannel stimulation of the cortex will enable several new studies, including quick determination of the cortical regions, the stimulation of which disrupts cortical processing required by a task.

Experimental study of stresses

This paper proposes an error-based segmentation approach for direct rapid prototyping (RP) of random cloud data. The objective is to fully integrate reverse engineering and RP for rapid product development. By constructing an intermediate point-based curve model (IPCM), a layer-based RP model is directly generated from the cloud data and served as the input to the RP machine for fabrication. In this process, neither a surface model nor an STL file is generated. This is accomplished via three steps. First, the cloud data is adaptively subdivided into a set of regions according to a given subdivision error, and the data in each region is compressed by keeping the feature points (FPs) within the user-defined shape tolerance using a digital image based reduction method. Second, based on the FPs of each region, an IPCM is constructed, and RP layer contours are then directly extracted from the models. Finally, the RP layer contours are faired with a discrete curvature based fairing method and subsequently closed to generate the final layer-based RP model. This RP model can be directly submitted to the RP machine for prototype manufacturing. Two case studies are presented to illustrate the efficacy of the approach.