Joe Fujiou Lo

Polarization-sensitive imaging enhances contrast and reveals structural features in biological tissues that are often missed by intensity-based methods, but its adoption is limited by bulky optics. We present a compact silicon-rich nitride (SRN) metalens array for high-resolution, polarization-resolved imaging of plant tissue at the chlorophyll absorption peak (660\,nm). The array integrates orthogonally sensitive metalenses to simultaneously capture X- and Y-linearly polarized transmission images, enabling real-time, label-free assessment of plant microstructure and stress responses. Polarization fusion and difference mapping reveal structural anisotropy and pigment variation in both healthy and stressed leaves. The SRN metalens, designed via an inverse approach using birefringent meta-atoms and fabricated through CMOS-compatible processes, achieves a large numerical aperture, high transmission, and spectral alignment with biological absorbers. This work demonstrates the feasibility of compact, integrated polarization-resolved imaging, offering a scalable alternative to conventional systems. The approach holds potential for biomedical and agricultural applications, where detecting subtle polarization-dependent changes could enable early diagnosis and tissue characterization

Obesity‐associated beta cell dysfunction is a crucial factor in the pathogenesis of Type 2 Diabetes (T2D), driven by a dysfunctional crosstalk between adipose tissues and pancreatic beta cells. Traditional culture systems cannot capture this crosstalk in a dynamic and controlled manner. A flow‐enabled microfluidic is developed with an embedded micro‐Tesla (µTesla) pump to assess the adipocyte‐beta cell crosstalk. This recirculating system allows them to study the transport of soluble‐factor‐based between cultured 3T3 L1 adipocytes and INS1 beta cells. It is found that flow‐enabled incubation with elevated glucose and insulin increased the levels of adipocyte‐derived secretions of IL‐6, TNF‐α, and adiponectin in the media. In turn, adipocyte‐derived IL‐6 enhanced beta‐cell insulin secretions in the same media, establishing a feed‐forward loop. This mechanism can contribute to the hyperinsulinemia and pro‐inflammatory conditions characteristic of obesity‐related T2D. The findings highlight the advantages of flow‐enabled microfluidics in modeling adipocyte‐beta cell crosstalk in obesity, providing novel insights into obesity‐associated beta cell dysfunction.

Migration and scratch assays are helpful tools to investigate wound healing and tissue regeneration processes, especially under disease conditions such as diabetes. However, traditional migration (injury-free) assays and scratch (with injury) assays are limited in their control over cellular environments and provide only simplified read-outs of their results. On the other hand, microfluidic-based cell assays offer a distinct advantage in their integration and scalability for multiple modalities and concentrations in a single device. Additionally, in situ stimulation and detection helps to avoid variabilities between individual bioassays. To realize an enhanced, smarter migration assay, we leveraged our multilayered oxygen gradient (1%–16%) to study HaCaT migrations in diabetic conditions with spatial and metabolic read-outs. An analysis of spatial migration over time revealed a new dynamic between hypoxia (at 4.2%–9.1% O2) and hyperglycemia. Furthermore, in situ adenosine triphosphate (ATP) and reactive oxygen species (ROS) responses suggest that this dynamic represents a switch between stationary versus motile modes of metabolism. Thus, low glucose and hypoxia have synergistic effects promoting the migration of cells. These findings illustrate the benefits of spatial microfluidics for modeling complex diseases such as hypoxia and diabetes, where multimodal measurements provide a more deterministic view of the underlying processes.

Migration and scratch assays are helpful tools to investigate wound healing and tissue regeneration processes, especially under disease conditions such as diabetes. However, traditional migration (injury-free) assays and scratch (with injury) assays are limited in their control over cellular environments and provide only simplified read-outs of their results. On the other hand, microfluidic-based cell assays offer a distinct advantage in their integration and scalability for multiple modalities and concentrations in a single device. Additionally, in situ stimulation and detection helps to avoid variabilities between individual bioassays. To realize an enhanced, smarter migration assay, we leveraged our multilayered oxygen gradient (1-16%) to study HaCaT migrations in diabetic conditions with spatial and metabolic read-outs. An analysis of the spatial migration over time observed a new dynamic between hypoxia (at 4.16-9.14% O2) and hyperglycemia. Furthermore, in situ adenosine triphosphate (ATP) and reactive oxygen species (ROS) responses suggest that this dynamic represents a switch between stationary versus motile modes of metabolism. Thus, elevated glucose and hypoxia are synergistic triggers of this switch under disease conditions. These findings illustrate the benefits of spatial microfluidics for modeling complex diseases such as hypoxia and diabetes, where multimodal measurements provide a more deterministic view of the underlying processes.

Hydrogel droplets are biodegradable and biocompatible materials with promising applications in tissue engineering, cell encapsulation, and clinical treatments. They represent a well-controlled microstructure to bridge the spatial divide between two-dimensional cell cultures and three-dimensional tissues, toward the recreation of entire organs. The applications of hydrogel droplets in regenerative medicine require a thorough understanding of microfluidic techniques, the biocompatibility of hydrogel materials, and droplet production and manipulation mechanisms. Although hydrogel droplets were well studied, several emerging advances promise to extend current applications to tissue engineering and beyond. Hydrogel droplets can be designed with high surface-to-volume ratios and a variety of matrix microstructures. Microfluidics provides precise control of the flow patterns required for droplet generation, leading to tight distributions of particle size, shape, matrix, and mechanical properties in the resultant microparticles. This review focuses on recent advances in microfluidic hydrogel droplet generation. First, the theoretical principles of microfluidics, materials used in fabrication, and new 3D fabrication techniques were discussed. Then, the hydrogels used in droplet generation and their cell and tissue engineering applications were reviewed. Finally, droplet generation mechanisms were addressed, such as droplet production, droplet manipulation, and surfactants used to prevent coalescence. Lastly, we propose that microfluidic hydrogel droplets can enable novel shear-related tissue engineering and regeneration studies.

One distinct advantage of microfluidic-based cell assays is their scalability for multiple concentrations or gradients. Microfluidic scaling can be extremely powerful when combining multiple parameters and modalities. Moreover, in situ stimulation and detection eliminates variability between individual bioassays. However, conventional microfluidics must combat diffusion, which limits the spatial distance and time for molecules traveling through microchannels. Here, we leveraged a multilayered microfluidic approach to integrate a novel oxygen gradient (0–20%) with an enhanced hydrogel sensor to study pancreatic beta cells. This enabled our microfluidics to achieve spatiotemporal detection that is difficult to achieve with traditional microfluidics. Using this device, we demonstrated the in situ detection of calcium, insulin, and ATP (adenosine triphosphate) in response to glucose and oxygen stimulation. Specifically, insulin was quantified at levels as low as 25 pg/mL using our imaging technique. Furthermore, by analyzing the spatial detection data dynamically over time, we uncovered a new relationship between oxygen and beta cell oscillations. We observed an optimum oxygen level between 10 and 12%, which is neither hypoxic nor normoxic in the conventional cell culture sense. These results provide evidence to support the current islet oscillator model. In future applications, this spatial microfluidic technique can be adapted for discrete protein detection in a robust platform to study numerous oxygen-dependent tissue dysfunctions.

Microfluidics has earned a reputation for providing numerous transformative but disconnected devices and techniques. Active research seeks to address this challenge by integrating microfluidic components, including embedded miniature pumps. However, a significant portion of existing microfluidic integration relies on the time-consuming manual fabrication that introduces device variations. We put forward a framework for solving this disconnect by combining new pumping mechanics and 3D printing to demonstrate several novel, integrated and wirelessly driven microfluidics. First, we characterized the simplicity and performance of printed microfluidics with a minimum feature size of 100 µm. Next, we integrated a microtesla (µTesla) pump to provide non-pulsatile flow with reduced shear stress on beta cells cultured on-chip. Lastly, the integration of radio frequency (RF) device and a hobby-grade brushless motor completed a self-enclosed platform that can be remotely controlled without wires. Our study shows how new physics and 3D printing approaches not only provide better integration but also enable novel cell-based studies to advance microfluidic research.

Continuous measurements of dissolved oxygen (DO) variation is important in water monitoring and biomedical applications, which require low-cost and low-maintenance sensors capable of automated operation. A frequency-domain optofluidic DO sensor with total internal reflection (TIR) design has been developed based on fluorescence quenching of Ruthenium complex (Ru(dpp)3Cl2). To minimize artifacts causing drift in fluorescence measurements such as background autofluorescence, photobleaching, optical alignment variation, a low-cost frequency-domain approach is implemented in an optofluidic platform to measure the phase shift between the excitation and emission light. We show that the frequency domain optofluidic DO sensor provides absolute DO concentrations in repeated measurements. TIR design can enhance fluorescence signal in the integrated device and minimize background autofluorescence in the sample, which can subsequently improve overall sensitivity. Furthermore, photobleaching in the samples would be mitigated as the incident light does not enter the microfluidic channel. Our results demonstrate DO concentration measurement resolution of 0.2 ppm and response times of less than one minute. In accelerated photobleaching conditions, the long-term drift is shown to be less than ±0.4 ppm. These results suggest the potential of this optofluidic DO sensor as an in situ platform for water monitoring and biomedical applications.

In contrast to labor intensive and destructive histological techniques, intrinsic autofluorescence lifetimes of extra cellular matrix proteins can provide label-free imaging of tissue modifications in diseases, including the diabetic ulcers. However, decoupling the complex mixture of tissue fluorophores requires costly and complicated fluorescent lifetime instrumentation. Furthermore, a list of autofluorescent and fluorogenic proteins must be characterized to profile their changes during disease progression. Towards these goals, an imaging system based on frequency domain light-emitting diode (LED) modulation was designed and demonstrated, using off-the-shelf components in a low complexity design. The system was operated by coupling and imaging fluorescence intensities using a pair of objectives. The system’s scanning and signal acquisition performances were optimized with respect to etendues. To study fluorescent proteins in diabetic ulcers, lifetimes from purified and pentosidine modified collagen I, collagen III, and elastin were measured. Pentosidine measurements showed a decrease in autofluorescent lifetimes while elevated collagen III in diabetic ulcers showed increased lifetimes. These lifetimes, plus future protein measurements enabled by our system, can serve as standards for developing a biophotonic model of diabetic ulcers. As a proof-of-concept, a 3 cm × 3 cm diabetic foot ulcer was imaged using the developed system. Phasor analysis was applied to aid the interpretation of lifetime images. As a result, a compact biophotonic imaging system targeting diabetic tissue was achieved, towards making the technique accessible for clinical histology.