Research
Materials Fundamental:
Understanding how 3-dimensional (3D) polymer micro-structures are assembled from inter-crosslinkable building-blocks
3D polymer microstructures have broad applications, ranging from soft electronics to biomedical implants. Top-down and bottom-up fabrications are the most common strategies for making these microstructures, and have been implemented by photolithography and molecules self-assembly. However, these methods often lead to low yield, small scales and long fabrication time, which led to limited industrial applications. To overcome these limitations, we recently created a Building-blocks Strategy to facilitate 3D polymer microstructures formation.
By using cost-effective methods such as wet-spinning and emulsification, spherical, rod-like and ribbon-shaped building-blocks were produced at large quantity with micron-sized features and crosslinkable chemicals, and were assembled covalently into complex 3D microstructures, including interconnected porosity and microchannels. Currently we are investigating the following topics: (a) how do shapes, stiffness and chemical properties influence the self-alignments and cross-linking among building blocks; (b) what else platforms can be used to better customize the building-blocks; and (c) to what applications can we best apply the building-block strategy.
By using cost-effective methods such as wet-spinning and emulsification, spherical, rod-like and ribbon-shaped building-blocks were produced at large quantity with micron-sized features and crosslinkable chemicals, and were assembled covalently into complex 3D microstructures, including interconnected porosity and microchannels. Currently we are investigating the following topics: (a) how do shapes, stiffness and chemical properties influence the self-alignments and cross-linking among building blocks; (b) what else platforms can be used to better customize the building-blocks; and (c) to what applications can we best apply the building-block strategy.
Microfabrication Technique:
Patterning multi-polymers microstructure in 3D
Using millions of micromirrors as a dynamic photomask, DMD projection-printing creates micro-structures by shedding a sequence of photo-patterns onto a photopolymerizable precursor, forming layers of thin cross-sections that stack into a structure in 3D. Microfabrication as such requires motions in only one axis (along the direction of light), and allows much faster fabrication speed in comparison with the conventional stereo-lithography, which demands XYZ scanning motions. In addition, we incorporated a liquid-manipulating system to switch precursors, and thus enabled the patterning of multiple polymers.
This work achieved the following results: (a) forming a broad variety of microstructures; (b) patterning multiple materials with distinct mechanical and chemical properties; and (c) incorporating sacrificial structures in 3D, which enables the control of Z-resolution.
This work achieved the following results: (a) forming a broad variety of microstructures; (b) patterning multiple materials with distinct mechanical and chemical properties; and (c) incorporating sacrificial structures in 3D, which enables the control of Z-resolution.
Applications:
Polymer microstructures for actuators and tissue engineering scaffolds
Photocrosslinkable Microribbons (Building-block Strategy): Gelatin was spun into photocrosslinkable microribbons, and used as the building-blocks for tissue-engineering scaffolds. In comparison with other biomaterials, the microribbon-based scaffold provides unique advantages: (a) supporting direct cell-encapsulation and uniform cell distribution; (b) providing interconnected pore-spaces to facilitate nutrient diffusion, cell proliferation and the cell production of extracellular matrix components; and (c) providing independently tunable niche properties, i.e. stiffness, macroporosity and biochemical ligands, which facilitates the optimization of cell-niche interactions. This work was done with Prof. Fan Yang at Stanford University.
Light-powered Motor (DMD-Projection Printing): Using the DMD system, a light-powered micromotor was created to run by photon energy. The motor has four curved blades and an axially asymmetric geometry. Upon lateral irradiation, the asymmetry of the blades induces an asymmetric photon heating to the surrounding gas molecules, generating a gas convection that forces the micromotor to spin. The micromotor was applied to actuate a scanning mirror for a laser beam:
Light-powered Motor (DMD-Projection Printing): Using the DMD system, a light-powered micromotor was created to run by photon energy. The motor has four curved blades and an axially asymmetric geometry. Upon lateral irradiation, the asymmetry of the blades induces an asymmetric photon heating to the surrounding gas molecules, generating a gas convection that forces the micromotor to spin. The micromotor was applied to actuate a scanning mirror for a laser beam:
We investigated the working principle behind the operation of the light-power motor using a Direct Simulation Monte Carlo (DSMC) model. The simulation results were consistent to the experimental data, and indicated that the mean free path of the surrounding gas takes an important role. This work was done with Prof. Shaochen Chen at The University of California, San Diego.