Geometric engineering of organoid culture for enhanced organogenesis in a dish.

Here, we introduce a facile, scalable engineering approach to enable long-term development and maturation of organoids. We have redesigned the configuration of conventional organoid culture to develop a platform that converts single injections of stem cell suspensions to radial arrays of organoids that can be maintained for extended periods without the need for passaging. Using this system, we demonstrate accelerated production of intestinal organoids with significantly enhanced structural and functional maturity, and their continuous development for over 4 weeks. Furthermore, we present a patient-derived organoid model of inflammatory bowel disease (IBD) and its interrogation using single-cell RNA sequencing to demonstrate its ability to reproduce key pathological features of IBD. Finally, we describe the extension of our approach to engineer vascularized, perfusable human enteroids, which can be used to model innate immune responses in IBD. This work provides an immediately deployable platform technology toward engineering more realistic organ-like structures in a dish.

Soft robotic constrictor for in vitro modeling of dynamic tissue compression.

Here we present a microengineered soft-robotic in vitro platform developed by integrating a pneumatically regulated novel elastomeric actuator with primary culture of human cells. This system is capable of generating dynamic bending motion akin to the constriction of tubular organs that can exert controlled compressive forces on cultured living cells. Using this platform, we demonstrate cyclic compression of primary human endothelial cells, fibroblasts, and smooth muscle cells to show physiological changes in their morphology due to applied forces. Moreover, we present mechanically actuatable organotypic models to examine the effects of compressive forces on three-dimensional multicellular constructs designed to emulate complex tissues such as solid tumors and vascular networks. Our work provides a preliminary demonstration of how soft-robotics technology can be leveraged for in vitro modeling of complex physiological tissue microenvironment, and may enable the development of new research tools for mechanobiology and related areas.

Microphysiological Engineering of Self-Assembled and Perfusable Microvascular Beds for the Production of Vascularized Three-Dimensional Human Microtissues.

The vasculature is an essential component of the circulatory system that plays a vital role in the development, homeostasis, and disease of various organs in the human body. The ability to emulate the architecture and transport function of blood vessels in the integrated context of their associated organs represents an important requirement for studying a wide range of physiological processes. Traditional in vitro models of the vasculature, however, largely fail to offer such capabilities. Here we combine microfluidic three-dimensional (3D) cell culture with the principle of vasculogenic self-assembly to engineer perfusable 3D microvascular beds in vitro. Our system is created in a micropatterned hydrogel construct housed in an elastomeric microdevice that enables coculture of primary human vascular endothelial cells and fibroblasts to achieve de novo formation, anastomosis, and controlled perfusion of 3D vascular networks. An open-top chamber design adopted in this hybrid platform also makes it possible to integrate the microengineered 3D vasculature with other cell types to recapitulate organ-specific cellular heterogeneity and structural organization of vascularized human tissues. Using these capabilities, we developed stem cell-derived microphysiological models of vascularized human adipose tissue and the blood-retinal barrier. Our approach was also leveraged to construct a 3D organotypic model of vascularized human lung adenocarcinoma as a high-content drug screening platform to simulate intravascular delivery, tumor-killing effects, and vascular toxicity of a clinical chemotherapeutic agent. Furthermore, we demonstrated the potential of our platform for applications in nanomedicine by creating microengineered models of vascular inflammation to evaluate a nanoengineered drug delivery system based on active targeting liposomal nanocarriers. These results represent a significant improvement in our ability to model the complexity of native human tissues and may provide a basis for developing predictive preclinical models for biopharmaceutical applications.

A bioinspired microfluidic model of liquid plug-induced mechanical airway injury.

Occlusion of distal airways due to mucus plugs is a key pathological feature common to a wide variety of obstructive pulmonary diseases. Breathing-induced movement of airway mucus plugs along the respiratory tract has been shown to generate abnormally large mechanical stresses, acting as an insult that can incite acute injury to the airway epithelium. Here, we describe a unique microengineering strategy to model this pathophysiological process using a bioinspired microfluidic device. Our system combines an air-liquid interface culture of primary human small airway epithelial cells with a microengineered biomimetic platform to replicate the process of mucus exudation induced by airway constriction that leads to the formation of mucus plugs across the airway lumen. Specifically, we constructed a compartmentalized three-dimensional (3D) microfluidic device in which extracellular matrix hydrogel scaffolds reminiscent of airway stroma were compressed to discharge fluid into the airway compartment and form liquid plugs. We demonstrated that this plug formation process and subsequent movement of liquid plugs through the airway channel can be regulated in a precisely controlled manner. Furthermore, we examined the detrimental effect of plug propagation on the airway epithelium to simulate acute epithelial injury during airway closure. Our system allows for a novel biomimetic approach to modeling a complex and dynamic biophysical microenvironment of diseased human airways and may serve as an enabling platform for mechanistic investigation of key disease processes that drive the progression and exacerbation of obstructive pulmonary diseases.

Minimally Intrusive Optical Micro-Strain Sensing in Bulk Elastomer Using Embedded Fabry-Pérot Etalon.

A variety of strain sensors have been developed to measure internal deformations of elastomeric structures. Strain sensors measuring extremely small mechanical strain, however, have not yet been reported due mainly to the inherently intrusive integration of the sensor with the test structure. In this work, we report the development of a minimally intrusive, highly sensitive mechanical strain transducer realized by monolithically embedding a Fabry-Pérot (FP) etalon into a poly(dimethylsiloxane) (PDMS) block test structure. Due to the extreme sensitivity of the FP resonance condition to the thickness of the spacer layer between the two reflectors, the limit of detection in the mechanical deformation can be as low as ~110 nm with a 632.8 nm laser used as the probing light. The compatibility of PDMS with additive fabrication turned out to be the most crucial enabling factor in the realization of the FP etalon-based strain transducer.

Microrobotic tentacles with spiral bending capability based on shape-engineered elastomeric microtubes.

Microscale soft-robots hold great promise as safe handlers of delicate micro-objects but their wider adoption requires micro-actuators with greater efficiency and ease-of-fabrication. Here we present an elastomeric microtube-based pneumatic actuator that can be extended into a microrobotic tentacle. We establish a new, direct peeling-based technique for building long and thin, highly deformable microtubes and a semi-analytical model for their shape-engineering. Using them in combination, we amplify the microtube's pneumatically-driven bending into multi-turn inward spiraling. The resulting micro-tentacle exhibit spiraling with the final radius as small as ~185 µm and grabbing force of ~0.78 mN, rendering itself ideal for non-damaging manipulation of soft, fragile micro-objects. This spiraling tentacle-based grabbing modality, the direct peeling-enabled elastomeric microtube fabrication technique, and the concept of microtube shape-engineering are all unprecedented and will enrich the field of soft-robotics.

Bokeh microscopy-enabled microfluidic channels for facile point-of-care monitoring.

We report the implementation of the bokeh microscopy scheme in microfluidic settings for future applications in point-of-care microchannel monitoring in highly resource-limited environments. We realize the functional integration using a single polymer microlens fabricated over the microchannel. The inherent simplicity of the bokeh microscopy enables image capturing with an off-the-shelf camera. Our pilot devices exhibit 10 ∼ 40 of magnification and 67 ∼ 252 µm of field-of-view extent, confirming their utility for monitoring 50 ∼ 100 µm microchannels carrying 10 ∼ 50 µm objects.

Microsphere-assisted fabrication of high aspect-ratio elastomeric micropillars and waveguides.

High aspect-ratio micropillars are in strong demand for microtechnology, but their realization remains a difficult challenge, especially when attempted with soft materials. Here we present a direct drawing-based technique for fabricating micropillars with poly(dimethylsiloxane). Despite the material's extreme softness, our technique enables routine realization of micropillars exceeding 2,000 µm in height and 100 in aspect-ratio. It also supports in situ integration of microspheres at the tips of the micropillars. As a validation of the new structure's utility, we configure it into airflow sensors, in which the micropillars and microspheres function as flexible upright waveguides and self-aligned reflectors, respectively. High-level bending of the micropillar under an airflow and its optical read-out enables mm s(-1) scale-sensing resolution. This new scheme, which uniquely integrates high aspect-ratio elastomeric micropillars and microspheres self-aligned to them, could widen the scope of soft material-based microdevice technology.

A biomimetic mass-flow transducer utilizing all-optofluidic generation of self-digitized, pulse code-modulated optical pulse trains.

We present a new mass-flow transducer producing responses in the form of optical pulse trains that are encoded with information on the strength and position of the stimulus. We implemented the self-digitization and encoding capabilities all-optofluidically, without involving external electronics, by integrating one optical fiber cantilever with multiple polymer optical waveguides on a microfluidic platform. The transducer can also be configured to respond only to transitional stimuli. These features closely mimic the rate-coding, action potential labeling, and rapid adaptation processes observed in biological mechanoreceptors and allow multiple transducers to transmit signals over a single, shared channel. We fabricated the transducer using polymer-based soft-lithography techniques. Its characterization confirmed the stimulus strength-dependent generation of optical pulses and the feasibility of multiplexing 2(n-1) to 2(n) transducers using n waveguides.

Sucrose-based fabrication of 3D-networked, cylindrical microfluidic channels for rapid prototyping of lab-on-a-chip and vaso-mimetic devices.

We present a new fabrication scheme for 3D-networked, cylindrical microfluidic (MF) channels based on shaping, bonding, and assembly of sucrose fibers. It is a simple, cleanroom-free, and environment-friendly method, ideal for rapid prototyping of lab-on-a-chip devices. Despite its simplicity, it can realize complex 3D MF channel architectures such as cylindrical tapers, internal loops, end-to-side junctions, tapered junctions, and stenosis. The last two will be of special use for realizing vaso-mimetic MF structures. It also enables molding with polymers incompatible with high-temperature processing.

Filter characteristics of a chirped volume holographic grating.

We compare and analyze the filter properties of transmission-type volume holographic gratings, especially the dispersion characteristics for uniform and chirped gratings. It is theoretically and experimentally shown that the dispersion characteristics can be controlled by introducing one-dimensional chirping to the volume grating in a photorefractive crystal. The filter response including output power and dispersion comes from a combined effect of the spatial spectra of the grating structure, input beam, and output-coupling fiber mode. Filter responses can be designed by controlling these parameters for optical communication applications.

Remote multiplexing of holograms with random patterns from multimode fiber bundles.

We propose the remote multiplexing of holograms with random patterns from a multimode fiber bundle used as the reference beams. The random pattern reference beam is characterized by the superposition and concatenation of propagation modes of multimode fiber and free space. For angle, shift, and wavelength remote multiplexing we compare two methods of laser coupling to the fiber bundle, i.e., direct coupling and lens coupling. A theoretical discussion that uses mode orthogonality is provided to describe multiplexing characteristics, and the theory is verified by experimental results. These remote-multiplexing methods can be applied to general multimode waveguide arrays for construction of compact and integrated optical systems in which multiplexing can be controlled remotely.