publications

2022

1. Adv. Mater.

   Mechanical Janus Structures by Soft‐Hard Material Integration

   Haozhe Zhang, Weizhu Yang, Qingchang Liu, Yuan Gao, Zhufeng Yue, and Baoxing Xu

   2022

   Abs HTML

   Engineering Janus structures that possess anisotropic features in functions have attracted growing attention for a wide range of applications in sensors, catalysis, and biomedicine, and are yet usually designed at the nanoscale with distinct physical or chemical functionalities in their opposite sides. Inspired by the seamless integration of soft and hard materials in biological structures, here we present a mechanical Janus structure composed of soft and hard materials with a dramatic difference of mechanical properties at additively manufacturable macroscale. We establish, in the combination of extensive experimental, theoretical, and computational studies, the design principle of soft-hard materials integrated mechanical Janus structures and address their unique rotation mechanism. We further show the systematic studies of assembling the Janus structure units into superstructures with well-ordered organizations by programing their local rotations, providing a direct route of designing superstructures by leveraging mechanical Janus structures with unique soft-hard material integration. Applications are conducted to demonstrate the features and functionalities of assembled superstructures with local ordered organizations in regulating and filtering acoustic wave propagations, thereby providing exemplification applications of mechanical Janus design in functional structures and devices.

2. ACS nano

   Electrically Suppressed Outflow of Confined Liquid in Hydrophobic Nanopores

   Yuan Gao, Mengtian Yin, Haozhe Zhang, and Baoxing Xu

   2022

   Abs HTML

   Confining liquid in a hydrophobic nanoenvironment has enabled a broad spectrum of applications in biomedical sensors, mechanical actuators, and energy storage and converters, where the outflow of confined liquid is spontaneous and fast due to the intrinsic hydrophobic nature of nanopores with extremely low interfacial friction, challenging design capacity and control tolerance of structures and devices. Here, we present a facile approach of suppressing the outflow of water confined in hydrophobic nanopores with an electric field. Extensive molecular dynamics simulations show that the presence of an electric field could significantly strengthen hydrogen bonds and retard degradations of the associated networks during the outflow. The outflow deformation and strength are extracted to quantitatively characterize the electrical suppression to outflow and agree well with simulations. This study proposes a practical means of impeding the fast liquid outflow in hydrophobic nanopores, potentially useful for devising nanofluidics-based functional structures and devices with controllable performance.

3. Matter

   Electrically Suppressed Outflow of Confined Liquid in Hydrophobic Nanopores

   Yuan Gao, Mingzhe Li, Haozhe Zhang, Yue Zhang, Weiyi Lu, and Baoxing Xu

   2022

   Abs HTML

   A survey of unsupervised learning methods for high-dimensional uncertainty quantification in black-box-type problems

4. Appl. Phys. Lett

   Soft-hard material integration enabled programmable robotic locomotion

   Haozhe Zhang, and Baoxing Xu

   2022

   Abs HTML

   Inspired by the opening and closing mechanism of clams, herein, we present a two-dimensional robot by integrating soft-hard materials with structural design and demonstrate a variety of in-plane locomotion modes from a straight line to a circle. A theoretical model is developed to quantitatively predict the locomotion direction and step distance, and the results show remarkable agreement with finite element analysis. Systematic applications are further conducted to demonstrate programmable locomotion behavior by regulating the mechanical stimuli and arranging the order of soft-hard material integrated units. This work provides a rational route for designing diverse strategies of robotic locomotion with soft-hard material integration.

5. Adv. Mater.

   Ultrahigh Sensitive Au‐Doped Silicon Nanomembrane Based Wearable Sensor Arrays for Continuous Skin Temperature Monitoring with High Precision

   Mingyu Sang, Kyowon Kang, Yue Zhang, Haozhe Zhang, Kiho Kim, Myeongki Cho, Jongwoon Shin, Jung‐Hoon Hong, Taemin Kim, Shin Kyu Lee, Woon‐Hong Yeo, Jung Woo Lee, Taeyoon Lee, Baoxing Xu, and Ki Jun Yu

   2022

   Abs HTML

   Monitoring the body temperature with high accuracy provides a fast, facile, yet powerful route about the human body in a wide range of health information standards. Here, the first ever ultrasensitive and stretchable gold-doped silicon nanomembrane (Au-doped SiNM) epidermal temperature sensor array is introduced. The ultrasensitivity is achieved by shifting freeze-out region to intrinsic region in carrier density and modulation of fermi energy level of p-type SiNM through the development of a novel gold-doping strategy. The Au-doped SiNM is readily transferred onto an ultrathin polymer layer with a well-designed serpentine mesh structure, capable of being utilized as an epidermal temperature sensor array. Measurements in vivo and in vitro show temperature coefficient of resistance as high as −37270.72 ppm °C−1, 22 times higher than existing metal-based temperature sensors with similar structures, and one of the highest thermal sensitivity among the inorganic material based temperature sensors. Applications in the continuous monitoring of body temperature and respiration rate during exercising are demonstrated with a successful capture of information. This work lays a foundation for monitoring body temperature, potentially useful for precision diagnosis (e.g., continuous monitoring body temperature in coronavirus disease 2019 cases) and management of disease relevance to body temperature in healthcare.

2021

1. Chem. Mater.

   Three-Dimensional Printable, Extremely Soft, Stretchable, and Reversible Elastomers from Molecular Architecture-Directed Assembly

   Shifeng Nian, Jinchang Zhu, Haozhe Zhang, Zihao Gong, Guillaume Freychet, Mikhail Zhernenkov, Baoxing Xu, and Li-Heng Cai

   2021

   Abs HTML

   3D printing elastomers enables the fabrication of many technologically important structures and devices such as tissue scaffolds, sensors, actuators, and soft robots. However, conventional 3D printable elastomers are intrinsically stiff; moreover, the process of printing often requires external mechanical support and/or post-treatment. Here, we exploit the self-assembly of a responsive linear-bottlebrush-linear triblock copolymer to create stimuli-reversible, extremely soft, and stretchable elastomers and demonstrate their applicability as inks for in situ direct-write printing 3D structures without the aid of external mechanical support or post-treatment. By developing a procedure for controlled synthesis of such architecturally designed block copolymers, we create elastomers with extensibility up to 600% and Young’s moduli down to ∼102 Pa, 106 times softer than plastics and more than 102 times softer than all existing 3D printable elastomers. Moreover, the elastomers are thermostable and remain to be solid up to 180 °C, yet they are 100% solvent-reprocessable. Their extreme softness, stretchability, thermostability, and solvent-reprocessability bode well for future applications.

2. Nat. Commun.

   All-printed stretchable corneal sensor on soft contact lenses for noninvasive and painless ocular electrodiagnosis

   Kyunghun Kim*, Ho-Joong Kim*, Haozhe Zhang*, Woohyun Park, Dawn Meyer, Min Ku Kim, Bongjoong Kim, Heun Park, Baoxing Xu, Pete Kollbaum, Bryan W Boudouris, and Chi Hwan Lee

   2021

   Abs HTML

   Electroretinogram examinations serve as routine clinical procedures in ophthalmology for the diagnosis and management of many ocular diseases. However, the rigid form factor of current corneal sensors produces a mismatch with the soft, curvilinear, and exceptionally sensitive human cornea, which typically requires the use of topical anesthesia and a speculum for pain management and safety. Here we report a design of an all-printed stretchable corneal sensor built on commercially-available disposable soft contact lenses that can intimately and non-invasively interface with the corneal surface of human eyes. The corneal sensor is integrated with soft contact lenses via an electrochemical anchoring mechanism in a seamless manner that ensures its mechanical and chemical reliability. Thus, the resulting device enables the high-fidelity recording of full-field electroretinogram signals in human eyes without the need of topical anesthesia or a speculum. The device, superior to clinical standards in terms of signal quality and comfortability, is expected to address unmet clinical needs in the field of ocular electrodiagnosis.

2020

1. IJSS

   Rotation mechanics of optical scatters in stretchable metasurfaces

   Haozhe Zhang, Weizhu Yang, and Baoxing Xu

   2020

   Abs HTML

   Stretchable metasurface comprised of an array of optical hard-material scatters on the surface of a soft substrate is emerging as an artificially designed structure to manipulate optical wave propagation through a mechanical means. Upon stretching the soft substrate, along with the increase of the spacing distance between hard scatters, the orientations of the hard scatters will vary due to their strong mechanical mismatch with the soft substrate, but the underlying mechanics mechanism is lacking. In the present study, we establish a theoretical mechanics framework to address the rotation of hard scatters bonded on the surface of a soft substrate subjected to a mechanical stretching load. In this model, we introduce a pseudo-interface between the hard scatters and the soft substrate and decouple the effect of in-plane stretching deformation and out-of-plane deformation in the thickness direction of the soft substrate on the basis of moment equilibrium. Besides, the shear stress field along the thickness direction of three-dimensional soft substrate is formulated from that of a two-dimensional plane model by introducing a thickness factor. The effect of spacing distance, geometric shape, and initial orientation of hard scatters and thickness of the soft substrate on the scatter rotation is elucidated. Extensive finite element analyses (FEA) are performed and the results show good agreement with the theoretical predictions in both scatter rotation and stress distribution. We further construct a stretchable metasurface and demonstrate that the refraction of incident lights can be tuned by controlling the rotation of scatters. The mechanics theory established here provides a foundation to design mechanically controllable metasurfaces by leveraging the rotation of hard-material scatters.