143 research outputs found
Optimization and Economic Analysis of Green Public Building Envelope Structure in Chongqing
No full textThis article entitled "Optimization and Economic Analysis of Green Public Building Envelope Structure in Chongqing", Authors, Zhiwei Yang Jihuan Chen Xilin Lei Xinran Lin and Shaoting Zhang, published in Volume 19, pp. 77-85 retracted by the authors due to serious similarity problem
Towards robust and effective shape prior modeling: sparse shape composition
No full textOrgan shape plays an important role in many clinical practices, including diagnosis, surgical planning and treatment evaluation. It is usually derived from medical images using low level appearance cues. However, due to diseases and imaging artifacts, low level appearance cues are often weak or misleading. In this situation, shape priors become critical to infer and refine the shape derived from image appearances. Effective modeling of shape priors is challenging because: 1) shape variations are complex and cannot always be modeled by parametric probability distributions; 2) a shape instance derived from image appearance cues (called an input shape) may have significant errors; and 3) local details of an input shape may be important for clinical purposes but difficult to preserve if they are not statistically significant in the training data. In this paper we propose a novel Sparse Shape Composition model (SSC) to address these three challenges in a unified framework. With our method, a sparse set of shapes is selected from the shape repository and composed together to infer and refine an input shape. This way, the prior information is implicitly incorporated on-the-fly. Our model leverages two sparsity observations of the input shape instance: 1) the input shape can be approximately represented by a sparse linear combination of shapes in the shape repository; 2) parts of the input shape may contain large errors but such errors are sparse. Our model is formulated as a sparse learning problem. Using norm relaxation, it can be solved by an efficient expectation-maximization (EM) framework. Furthermore, this model is extended to effectively handle multi-resolution, local shape priors and hierarchical priors. We also propose a framework to generate high quality training data in 3D. Our framework includes geometry processing methods and shape registration algorithms. The proposed shape prior model is extensively validated on five different medical applications: 2D lung localization in chest X-ray images, 3D liver segmentation in low-dose Computed Tomography (CT) scans, 3D segmentation of multiple rodent brain structures in Magnetic Resonance (MR) microscope, real time tracking of left ventricles in Magnetic Resonance Imaging (MRI), and high resolution CT reconstruction. Compared to state-of-the-art methods, our model exhibits better performance in all these studies.Ph. D.Includes bibliographical referencesIncludes vitaby Shaoting Zhan
Predicting fracture energies and crack-tip fields of soft tough materials
No full textSoft materials including elastomers and gels are pervasive in biological systems and technological applications. Whereas it is known that intrinsic fracture energies of soft materials are relatively low, how the intrinsic fracture energy cooperates with mechanical dissipation in process zone to give high fracture toughness of soft materials is not well understood. In addition, it is still challenging to predict fracture energies and crack-tip strain fields of soft tough materials. Here, we report a scaling theory that accounts for synergistic effects of intrinsic fracture energies and dissipation on the toughening of soft materials. We then develop a coupled cohesive-zone and Mullins-effect model capable of quantitatively predicting fracture energies of soft tough materials and strain fields around crack tips in soft materials under large deformation. The theory and model are quantitatively validated by experiments on fracture of soft tough materials under large deformations. We further provide a general toughening diagram that can guide the design of new soft tough materials.United States. Office of Naval Research (N00014-14-1-0528)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie
Tough and tunable adhesion of hydrogels: experiments and models
No full textAs polymer networks infiltrated with water, hydrogels are major constituents of animal and plant bodies and have diverse engineering applications. While natural hydrogels can robustly adhere to other biological materials, such as bonding of tendons and cartilage on bones and adhesive plaques of mussels, it is challenging to achieve such tough adhesions between synthetic hydrogels and engineering materials. Recent experiments show that chemically anchoring long-chain polymer networks of tough synthetic hydrogels on solid surfaces create adhesions tougher than their natural counterparts, but the underlying mechanism has not been well understood. It is also challenging to tune systematically the adhesion of hydrogels on solids. Here, we provide a quantitative understanding of the mechanism for tough adhesions of hydrogels on solid materials via a combination of experiments, theory, and numerical simulations. Using a coupled cohesive-zone and Mullins-effect model validated by experiments, we reveal the interplays of intrinsic work of adhesion, interfacial strength, and energy dissipation in bulk hydrogels in order to achieve tough adhesions. We further show that hydrogel adhesion can be systematically tuned by tailoring the hydrogel geometry and silanization time of solid substrates, corresponding to the control of energy dissipation zone and intrinsic work of adhesion, respectively. The current work further provides a theoretical foundation for rational design of future biocompatible and underwater adhesives.United States. Office of Naval Research (N00014-14-1-0528)National Science Foundation (U.S.) (CMMI-1253495)National Institutes of Health (U.S.) (UH3TR000505
3D Printing of Highly Stretchable and Tough Hydrogels into Complex, Cellularized Structures
No full textA 3D printable and highly stretchable tough hydrogel is developed by combining poly(ethylene glycol) and sodium alginate, which synergize to form a hydrogel tougher than natural cartilage. Encapsulated cells maintain high viability over a 7 d culture period and are highly deformed together with the hydrogel. By adding biocompatible nanoclay, the tough hydrogel is 3D printed in various shapes without requiring support material.National Institutes of Health (U.S.) (Grant UH3TR000505)National Institutes of Health (U.S.) (Grant R01AR48825)National Institutes of Health (U.S.) (Common Fund for the Microphysiological Systems Initiative)AOSpine FoundationNational Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (DRM-1121107
Hydraulic hydrogel actuators and robots optically and sonically camouflaged in water
No full textSea animals such as leptocephali develop tissues and organs composed of active transparent hydrogels to achieve agile motions and natural camouflage in water. Hydrogel-based actuators that can imitate the capabilities of leptocephali will enable new applications in diverse fields. However, existing hydrogel actuators, mostly osmotic-driven, are intrinsically low-speed and/or low-force; and their camouflage capabilities have not been explored. Here we show that hydraulic actuations of hydrogels with designed structures and properties can give soft actuators and robots that are high-speed, high-force, and optically and sonically camouflaged in water. The hydrogel actuators and robots can maintain their robustness and functionality over multiple cycles of actuations, owing to the anti-fatigue property of the hydrogel under moderate stresses. We further demonstrate that the agile and transparent hydrogel actuators and robots perform extraordinary functions including swimming, kicking rubber-balls and even catching a live fish in water.United States. Office of Naval Research (N00014-14-1-0528)National Science Foundation (U.S.) (CMMI-1253495)United States. Office of Naval Research (N00014-13-1-0631
Fringe instability in constrained soft elastic layers
No full textSoft elastic layers with top and bottom surfaces adhered to rigid bodies are abundant in biological organisms and engineering applications. As the rigid bodies are pulled apart, the stressed layer can exhibit various modes of mechanical instabilities. In cases where the layer's thickness is much smaller than its length and width, the dominant modes that have been studied are the cavitation, interfacial and fingering instabilities. Here we report a new mode of instability which emerges if the thickness of the constrained elastic layer is comparable to or smaller than its width. In this case, the middle portion along the layer's thickness elongates nearly uniformly while the constrained fringe portions of the layer deform nonuniformly. When the applied stretch reaches a critical value, the exposed free surfaces of the fringe portions begin to undulate periodically without debonding from the rigid bodies, giving the fringe instability. We use experiments, theory and numerical simulations to quantitatively explain the fringe instability and derive scaling laws for its critical stress, critical strain and wavelength. We show that in a force controlled setting the elastic fingering instability is associated with a snap-through buckling that does not exist for the fringe instability. The discovery of the fringe instability will not only advance the understanding of mechanical instabilities in soft materials but also have implications for biological and engineered adhesives and joints.United States. Office of Naval Research (Grant N00014-14-1-0528)Massachusetts Institute of Technology. Institute for Soldier NanotechnologiesNational Science Foundation (U.S.) (Grant CMMI- 1253495)Samsung Scholarship FoundationNational Institutes of Health (U.S.) (Grant UH3TR000505)MIT-Technion Fellowshi
A FUNDAMENTAL STUDY ON THE THERMOMECHANICAL BEHAVIOR OF ELASTIC SPHERES CHARGED WITH A TWO-PHASE FLUID
No full textThesis (Ph.D.)--Michigan State University. Mechanical Engineering - Doctor of Philosophy, 2025Several studies have examined the elasticity of expanding spheres containing either pure gas or pure liquid. Several other studies have examined encapsulated, phase change materials for energy storage with the focus on solid-solid and solid-liquid phase change. However, it appears that a study characterizing an expanding and contracting elastic sphere charged with a two-phase fluid has yet to be addressed in the open literature. This dissertation aims to fill this gap in the literature by developing an analytical model, along with a numerical investigation and experimental validation, that characterize a slightly more sophisticated system. The system comprises an elastic sphere partially filled with a liquid along with a mixture of its vapor and air. This model predicts the sphere\u2019s volume variation following variations in the conditions of its environment by merging a non-linear elasticity model of the shell with the 1st law of thermodynamics, ideal gas law, law of mass conservation and the theory of psychrometrics.Although the model is based on the quasistatic thermodynamic assumptions and zero permeability of the sphere rubber shells, experimental observations demonstrate that the model adequately describes the sphere-fluid system under both transient and static operating conditions. Two experimental methods were pursued to produce these operating conditions; The first method visually records the sphere expansion and contraction during the evacuation of air out of a vacuum chamber within which the sphere is suspended. In the second equilibrium method, the sphere is submerged in water, and the pressure of the environment (i.e., a vacuum chamber) is reduced to a low enough value to allow for some evaporation of the encapsulated liquid. The spheres were fabricated using a lab-made rubber press, and an elaborate procedure that yields bubble-free spherical shells and perfectly sealed ethanol-charged spheres. A parametric study was conducted with a basis of six parameters to characterize the spheres; the parameters include the initial diameter of the spherical shell, the final temperature of the fluid, the initial liquid fill level, the fluid used, the elastic shell stiffening factor, and elastomer shear modulus. Prior to conducting an experiment, the shells need to be inflated and deflated ten times to obtain a repeatable elastic response to internal pressure. A laser aligned setup was used to capture the sphere pressure-stretch behavior. It also used a camera fitted with a prime lens to minimize the distortion in the sphere photographs. The same camera was used in the transient experiments. The error between the analytical model and the transient experiments ranged from 17% to 35%. The larger error is due to the sagginess of the larger spheres. The uncertainty in the model output did not exceed 7% when computed using a Monte Carlo simulation. The error between the analytical model and equilibrium experiments ranged from zero to 14.8%. The uncertainty in the equilibrium experimental procedure, however, was not entirely quantifiable due to imperfections in the testing apparatus, which is largely a consequence of using a webcam to measure the sphere diameter, in addition to submerging the spheres in water. The webcam and the water buoyancy effects distorted the sphere dimensions. The reason why water was used was to maintain a constant surrounding temperature. Two other promising methods for maintaining a constant surrounding temperature, without water involvement, were attempted only as proof of concept. The first is black body radiant heating and the second is induction heating. The former only worked in a small plexiglass vacuum chamber lined with aluminum foil. The latter reached the proof-of-concept stage in the custom-built large vacuum chamber. The numerical part of this work was considered sufficient for describing the equilibrium behavior of the spheres, as it strictly adheres to the quasistatic assumption. The transient experiments demonstrated that ignoring the permeability of the elastomer was reasonable provided that the experiment duration remains below 30 minutes.Description based on online resource. Title from PDF t.p. (Michigan State University Fedora Repository, viewed ).Includes bibliographical references
Stretchable Hydrogel Electronics and Devices
No full textStretchable hydrogel electronics and devices are designed by integrating stretchable conductors, functional chips, drug-delivery channels, and reservoirs into stretchable, robust, and biocompatible hydrogel matrices. Novel applications include a smart wound dressing capable of sensing the temperatures of various locations on the skin, delivering different drugs to these locations, and subsequently maintaining sustained releases of drugs
Design stiff, tough and stretchy hydrogels via nanoscale hybrid crosslinking and macroscale fiber reinforcement
No full textHydrogels’ applications are limited by their weak mechanical properties. The toughness, modulus, and strength of conventional hydrogels (single network gels) are, respectively, \u3c10 J m‑2, \u3c100 kPa, and \u3c10 kPa, which fail to provide sufficient mechanical properties in large quantities of applications. Here, we designed highly stretchable, tough, yet stiff hydrogels via nanoscale hybrid crosslinking and macroscale fiber reinforcement. We used 3D printing technology to fabricate 3D patterned fibrous structures. Hydrogel composites were constructed by impregnating the PLA fiber mesh with highly stretchable and tough PAAM-alginate hydrogels. Synthetic gels can reach fracture energies of ~9000 J m‑2. However, modulus of these tough hydrogels is only ~100 kPa. Here, we designed fiber reinforced hydrogels, which can reach fracture energy of about 30 000 J m-2 and modulus of ~6 MPa. The enhancement of toughness is due to multiscale toughening mechanism which spans over multiple length scales ranging from nanometers to millimeters. This design of fiber reinforced hydrogel composites can serve as a model to expand the application of hydrogels in both biomedical and robotic areas
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