Chunguang Xia

First jump of microgel; actuation speed enhancement by elastic instability

Swelling-induced snap-buckling in a 3D micro hydrogel device, inspired by the insect-trapping action of Venus flytrap, makes it possible to generate astonishingly fast actuation. We demonstrate that elastic energy is effectively stored and quickly released from the device by incorporating elastic instability. Utilizing its rapid actuation speed, the device can even jump by itself upon wetting.

3D microfabricated bioreactor with capillaries

We present in this paper the implementation of an innovative three dimensional (3D) microfabrication technology coupled with numerical simulation to enhance the mass transport in 3D cell culture. The core of this microfabrication technology is a high-resolution projection micro stereolithography (PμSL) using a spatial light modulator as a dynamic mask which enables a parallel fabrication of highly complex 3D microstructures. In this work, a set of poly (ethylene glycol) microfabricated bioreactors are demonstrated with PμSL technology. We observed both experimentally and numerically the regulation of metabolism and the growth of yeast cells by controlling the density of micro-capillaries. Further development of these 3D microfabricated bioreactors is expected to provide artificially constructed tissues for clinical applications.

Solvent-driven polymeric micro beam device

The response of current hydrogel devices mainly depends on the diffusion of stimuli. However, diffusion is a slow transport mechanism compared to advection, which therefore limits the response speed of hydrogel devices. To overcome this limitation, we introduce a capillary network and elastic instability mechanism. Particularly, an open surface capillary delivers and distributes solvent, thus triggering the swelling and bending of curved polymeric beams. To demonstrate this concept, we fabricate these polymeric microstructures using projection micro-stereolithography (PµSL). Combined with instability criteria analysis based on static beam theory, this device is designed to exhibit two-way snap-through behavior. Our analysis provides the minimum dimensionless stiffness β for the beam device to snap during solvent actuation. Here, β is a well-defined dimensionless parameter in our analysis that indicates whether the device can provide sufficient axial force to trigger the snap-through of the beam. The actuation displacement can be as high as 45% of the length of the beam. We observe a maximum midpoint speed of 3.1 cm s−1 for a beam 2 mm long—20 times higher than that for a beam without an elastic instability mechanism. This device can be used in artificial muscle and as the key component for fluidic-to-mechanical signal transduction in active micro-fluidic circuits.

Fully three-dimensional microfabrication with a grayscale polymeric self-sacrificial structure

We present in this paper a novel method to fabricate fully three-dimensional (3D) microstructures and moving parts using a partially crosslinked polymer as sacrificial supports. This is realized on a projection microstereolithography (PµSL) which produces both the microstructure and the sacrificial part simultaneously using digital grayscale images. To establish the selectivity of the etchant to the partially crosslinked sacrificial parts, we measured the etching rate as a function of photo-crosslinking light intensity and the light exposure time. This technology may enable more complex scaffolds in tissue engineering and smart hydrogel devices.

BIOMIMETIC MICROACTUATOR POWERED BY POLYMER SWELLING

We propose novel biomimetic polymer microactuators. The actuation mechanism is inspired by nastic movement of the moving plant, Mimosa pudica, which folds its leaves upon external stimulus by regulating turgor pressure of cells in specific location. Photo-cured poly(ethylene glycol) diacrylate (PEGDA) microactuator is fabricated using projection micro-stereolithography (PμSL) capable of complex 3D micro fabrication. The swelling effect of PEG in water and organic solvent is exploited as an actuation mechanism of the device. Stress relaxation in the structure due to solvent absorption is controlled locally by delivering solvent through microfluidic channels embedded in the actuator, thereby generating a net movement in the device. Timescale of the motion derived from analytical swelling model suggests that actuation speed can be effectively increased by scaling down the actuator because the characteristic swelling time depends on the length as L2 , which is verified experimentally.Copyright