Both passive and active microfluidic chips are used in many biomedical and chemical applications to support fluid mixing, particle manipulations, and signal detection. Passive microfluidic devices are geometry-dependent, and their uses are rather limited. Active microfluidic devices include sensors or detectors that transduce chemical, biological, and physical changes into electrical or optical signals. Also, they are transduction devices that detect biological and chemical changes in biomedical applications, and they are highly versatile microfluidic tools for disease diagnosis and organ modeling. This review provides a comprehensive overview of the significant advances that have been made in the development of microfluidics devices. We will discuss the function of microfluidic devices as micromixers or as sorters of cells and substances (e.g., microfiltration, flow or displacement, and trapping). Microfluidic devices are fabricated using a range of techniques, including molding, etching, three-dimensional printing, and nanofabrication. Their broad utility lies in the detection of diagnostic biomarkers and organ-on-chip approaches that permit disease modeling in cancer, as well as uses in neurological, cardiovascular, hepatic, and pulmonary diseases. Biosensor applications allow for point-of-care testing, using assays based on enzymes, nanozymes, antibodies, or nucleic acids (DNA or RNA). An anticipated development in the field includes the optimization of techniques for the fabrication of microfluidic devices using biocompatible materials. These developments will increase biomedical versatility, reduce diagnostic costs, and accelerate diagnosis time of microfluidics technology.

Multiple myeloma is a hematological cancer type. For its treatment, Bortezomib has been widely used. However, drug resistance to this effective chemotherapeutic has been developed for various reasons. 2D cell cultures and animal models have failed to understand the MM disease and Bortezomib resistance. It is therefore essential to utilize new technologies to reveal a complete molecular profile of the disease. In this review, we in-depth examined the possible molecular mechanisms that cause Bortezomib resistance and specifically addressed MM and Bortezomib resistance. Moreover, we also included the use of nanoparticles, 3D culture methods, microfluidics, and organ-on-chip devices in multiple myeloma. We also discussed whether the emerging technology offers the necessary tools to understand and prevent Bortezomib resistance in multiple myeloma. Despite the ongoing research activities on MM, the related studies cannot provide a complete summary of MM. Nanoparticle and 3D culturing have been frequently used to understand MM disease and Bortezomib resistance. However, the number of microfluidic devices for this application is insufficient. By combining siRNA/miRNA technologies with microfluidic devices, a complete molecular genetic profile of MM disease could be revealed. Microfluidic chips should be used clinically in personal therapy and point-of-care applications. At least with Bortezomib microneedles, it could be ensured that MM patients can go through the treatment process more painlessly. This way, MM can be switched to the curable cancer type list, and Bortezomib can be targeted for its treatment with fewer side effects.

This study investigates hydrodynamic cavitation (HC) inception and development in micro-Venturi channels, focusing on the mechanism that drives spatially irregular cavitation events. The study reveals that cavitation regeneration is primarily governed by the interaction between residual cavitation nuclei and low-pressure vortices. Using ultra-high-speed imaging and advanced bubble dynamics analysis, it was revealed that the residual nuclei trapped in the boundary layer or reverse flow near the sidewall of the microscale reactor are the key to cavitation regeneration. Their interaction with vortices shed from the shear layer, triggering spatially distributed inception events throughout the channel. Bubble velocity analysis showed a size-dependent pattern: smaller residual bubbles migrate upstream (negative velocities) before growing and being advected downstream (positive velocities), directly linking their motion dynamics to cavitation inception. Spectral analysis of the bubble populations demonstrated two frequency components: low-frequency signals in the transient regime, reflecting slow periodic replenishment of residual nuclei and high-frequency fluctuations driven by vortex activity. With increasing upstream pressure, the system shifted to periodic attached cavitation, characterized by regular shedding-driven fluctuations in bubble content. At even higher pressures, fully developed cavitation emerged, marked by intense shear-layer activity, sporadic downstream variations, and shear-induced bubble breakup that sustained mainstream cavitation. The findings of this study illustrate how residual nuclei and their interaction with transient vortices play a pivotal role in microscale cavitation inception, thereby offering critical insights on controlling cavitation in microfluidic systems such as "HC on a chip" reactors, where stochastic nucleation and bubble transport significantly influence performance.

This study introduces the first experimental analysis of shear cavitation in a microscale backward-facing step (BFS) configuration. It explores shear layer cavitation under various flow conditions in a microfluidic device with a depth of 60 μm and a step height of 400 μm. The BFS configuration, with its unique characteristics of upstream turbulence and post-reattachment pressure recovery, provides a controlled environment for studying shear-induced cavitation without the complexities of other microfluidic geometries. Experiments were conducted across four flow patterns: inception, developing, shedding, and intense shedding, by varying upstream pressure and the Reynolds number. The study highlights key differences between microscale and macroscale shear cavitation, such as the dominant role of surface forces on nuclei distribution, vapor formation, and distinct timescales for phenomena like shedding and shockwave propagation. It is hypothesized that vortex strength in the shear layer plays a significant role in cavity shedding during upstream shockwave propagation. Results indicate that increased pressure notably elevates the mean thickness, length, and intensity within the shear layer. Instantaneous data analysis identified two vortex modes (shedding and wake modes) at the reattachment zone, which significantly affect cavitation shedding frequency and downstream penetration. The wake mode, characterized by stronger and lower-frequency vortices, transports cavities deeper into the channel compared to the shedding mode. Additionally, vortex strength, proportional to the Reynolds number, affects condensation caused by shockwaves. The study confirms that nuclei concentration peaks in the latter half of the shear layer during cavitation inception, aligning with the peak void fraction region.

Gas content strongly affects cavitation dynamics; however, most studies rely solely on dissolved gas measurements, overlooking the influence of undissolved bubbles. This study investigates their role by introducing air bubbles (<200 µm) into water samples with identical dissolved gas levels and analyzing cavitation at both inception and developed phases using high-speed imaging and hydrophone measurements. The results show that the presence of pre-existing bubbles alters cavitation dynamics at the inception and developed phases. Under low dissolved gas and in the absence of air bubbles, cavitation can initiate from a single nucleus, and the developed phase exhibits transient vaporous cavitation with the highest acoustic intensity. In contrast, pre-existing bubbles promote the formation of conical-like bubble structures early in the inception phase and affect their dynamics in the developed phase, reducing the acoustic pressure and attenuating the noise spectrum. These effects are reversible upon bubble removal and independent of dissolved gas concentration, demonstrating that dissolved gas alone cannot represent gas-related influences on cavitation. Characterizing not only dissolved but also undissolved gas content is therefore essential for cavitation studies and applications.

This study investigates cavitating flows within a silicon-glass microfluidic venturi reactor using an integrated multi-modal approach that combines cavitation-induced noise analysis and high-speed imaging. Acoustic signal processing, primarily via power spectral density (PSD) and time-resolved frequency analysis (using wavelet transform), was employed to characterize cavitating flows across a wide range of upstream pressures (0.76 to 4.52 MPa). To the best knowledge of the authors, this is the first study on the direct correlation of time-resolved cavitating flow morphology captured via high-speed imaging of arrival, growth, and shedding of cavities with their acoustic signatures in both PSD diagrams and wavelet spectrograms in micro scale. By mapping specific PSD peaks and time-localized wavelet bursts to distinct flow regimes, a unified framework spanning inception through fully developed cavitation was constructed for a micro-venturi reactor. At lower pressures (<0.76 MPa), acoustic emissions in the 2–8 kHz range corresponded to cavitation inception with low cavitation intensity. As the upstream pressure was increased, a shift toward higher frequencies (up to and beyond 18 kHz) and a broadening of the spectral distribution revealed a transition to more intense sheet and cloud cavitation regimes. These acoustic signatures were confirmed by visual observations, which captured the evolution of distinct cavitating flow patterns. The findings highlight the potential of acoustic noise measurements as a real-time diagnostic tool for optimizing microscale hydrodynamic cavitation processes, with high potential for their implementation in applications such as wastewater treatment, energy harvesting, biomedical engineering, and integrated lab-on-a-chip platforms.