Recent methods of droplet microfluidics and their applications in spheroids and organoids

Harnessing the power of artificial intelligence for human living organoid research

As a powerful paradigm, artificial intelligence (AI) is rapidly impacting every aspect of our day-to-day life and scientific research through interdisciplinary transformations. Living human organoids (LOs) have a great potential for in vitro reshaping many aspects of in vivo true human organs, including organ development, disease occurrence, and drug responses. To date, AI has driven the revolutionary advances of human organoids in life science, precision medicine and pharmaceutical science in an unprecedented way. Herein, we provide a forward-looking review, the frontiers of LOs, covering the engineered construction strategies and multidisciplinary technologies for developing LOs, highlighting the cutting-edge achievements and the prospective applications of AI in LOs, particularly in biological study, disease occurrence, disease diagnosis and prediction and drug screening in preclinical assay. Moreover, we shed light on the new research trends harnessing the power of AI for LO research in the context of multidisciplinary technologies. The aim of this paper is to motivate researchers to explore organ function throughout the human life cycle, narrow the gap between in vitro microphysiological models and the real human body, accurately predict human-related responses to external stimuli (cues and drugs), accelerate the preclinical-to-clinical transformation, and ultimately enhance the health and well-being of patients.

Size and shape control of microgel-encapsulating tumor spheroid via a user-friendly solenoid valve-based sorter and its application on precise drug testing

The precision of previous cancer research based on tumor spheroids, especially the microgel-encapsulating tumor spheroids, was limited by the high heterogeneity in the tumor spheroid size and shape. Here, we reported a user-friendly solenoid valve-based sorter to reduce this heterogeneity. The artificial intelligence algorithm was employed to detect and segmentate the tumor spheroids in real-time for the size and shape calculation. A simple off-chip solenoid valve-based sorting actuation module was proposed to sort out target tumor spheroids with the desired size and shape. Utilizing the developed sorter, we successfully uncovered the drug response variations on cisplatin of lung tumor spheroids in the same population but with different sizes and shapes. Moreover, with this sorter, the precision of drug testing on the spheroid population level was improved to a level comparable to the precise but complex single spheroid analysis. The developed sorter also exhibits significant potential for organoid morphology and sorting for precision medicine research.

Microfluidic Platform for Generating and Releasing Patient-Derived Cancer Organoids with Diverse Shapes: Insight into Shape-Dependent Tumor Growth

Multicellular spheroids and patient-derived organoids find many applications in fundamental research, drug discovery, and regenerative medicine. Advances in the understanding and recapitulation of organ functionality and disease development require the generation of complex organoid models, including organoids with diverse morphologies. Microfluidics-based cell culture platforms enable time-efficient confined organoid generation. However, the ability to form organoids with different shapes with a subsequent transfer from microfluidic devices to unconstrained environments for studies of morphology-dependent organoid growth is yet to be demonstrated. Here, a microfluidic platform is introduced that enables high-fidelity formation and addressable release of breast cancer organoids with diverse shapes. Using this platform, the impact of organoid morphology on their growth in unconstrained biomimetic hydrogel is explored. It is shown that proliferative cancer cells tend to localize in high positive curvature organoid regions, causing their faster growth, while the overall growth pattern of organoids with diverse shapes tends to reduce interfacial tension at the organoid-hydrogel interface. In addition to the formation of organoids with diverse morphologies, this platform can be integrated into multi-tissue micro-physiological systems.

Spontaneous Formation of Solid Shell Polymeric Multicompartments at All-Aqueous Interfaces

Multicompartmental capsules have demonstrated value in fields ranging from drug release, mimetics of artificial cells, to energy conversion and storage. However, the fabrication of devices with different compartments usually requires the use of toxic solvents, and/or the adaptation of technically demanding methods, including precision microfluidics and multistep processes. The spontaneous formation of multi-core capsules resulting from polyelectrolyte complexation at the interface of a prototypic all-aqueous two-phase system is described here. The variation of polyelectrolyte concentration and complexation time are described as simple working parameters capable of driving the formation of compartments at different yields, as well as tailoring their morphology. The mild processing technology enables the encapsulation of animal cells, which are capable of invading capsule walls for specific processing conditions.

Imaging-Based Efficacy Evaluation of Cancer Immunotherapy in Engineered Tumor Platforms and Tumor Organoids

Cancer immunotherapy is used to treat tumors by modulating the immune system. Although the anticancer efficacy of cancer immunotherapy has been evaluated prior to clinical trials, conventional in vivo animal and endpoint models inadequately replicate the intricate process of tumor elimination and reflect human-specific immune systems. Therefore, more sophisticated models that mimic the complex tumor-immune microenvironment must be employed to assess the effectiveness of immunotherapy. Additionally, using real-time imaging technology, a step-by-step evaluation can be applied, allowing for a more precise assessment of treatment efficacy. Here, an overview of the various imaging-based evaluation platforms recently developed for cancer immunotherapeutic applications is presented. Specifically, a fundamental technique is discussed for stably observing immune cell-based tumor cell killing using direct imaging, a microwell that reproduces a confined space for spatial observation, a droplet assay that facilitates cell-cell interactions, and a 3D microphysiological system that reconstructs the vascular environment. Furthermore, it is suggested that future evaluation platforms pursue more human-like immune systems.

Formation of ovarian organoid by co-culture of human endometrial mesenchymal stem cells and mouse oocyte in 3-dimensional culture system

The purpose of this study was to compare the formation of organoid structures by co-culturing of human endometrial mesenchymal stem cells (hEnMSCs) and mouse germinal vesicle (GV) oocytes in hanging drop and sodium alginate hydrogel co-culture methods. Following the preparation of hEnMSCs and partially denuded mouse germinal vesicle oocytes, they were co-cultured in hanging drop and sodium alginate hydrogel systems as two experimental groups. In respected control groups the hEnMSCs were cultured without oocytes. The organoid formation was evaluated under the inverted microscope in all studied groups during the culture period. The hematoxylin and eosin, alcian blue, periodic acid Schiff, and Masson's trichrome methods, were applied for morphological evaluation and extracellular matrix components staining such as glycosaminoglycan, carbohydrate, and collagen fibers. In addition, the germ cell-like characteristics within the organoid structures were investigated via alkaline phosphatase activity immunocytochemistry for DEAD-box polypeptide 4 (DDX4), and the expression of octamer-binding transcription factor 4 (OCT4), DDX4, and synaptonemal complex protein 3 (SYCP3) genes by real-time RT-PCR. The culturing of hEnMSCs in the hanging drop method led to the formation of organoid structures while this structure was not seen in sodium alginate hydrogel culture. The mean diameter of organoid structures was increased during 4 days of culture in both the experimental and control groups in the hanging drop method, reaching 675.50 ± 18.55 µm and 670.25 ± 21.40 µm, respectively (P < 0.05). Morphological staining indicated some large ovoid cells with euchromatin nuclei in the experimental group, whereas, in the control group cells showed dark and dense nuclei. The extracellular matrix components were deposited in organoid structures in both control and experimental groups. The positive alkaline phosphatase activity and immunocytochemistry for DDX4 confirmed the presence of germ cell-like in the experimental group. Real-time RT-PCR showed a significant increase in the expression of DDX4 and SYCP3 genes and a decrease in the level of OCT4 expression in the experimental group compared with its controls. This study successfully generated organoid structures by co-culture of hEnMSCs and oocytes in the hanging drop method and the hEnMSCs could be differentiated into germ cell-like. This organoid structure has potential applications in regenerative medicine and reproductive biology.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-024-00639-w.

3D cellular self-assembly on optical disc-imprinted nanopatterns

Three-dimensional (3D) cellular assemblies, such as cancer spheroids and organoids, are increasingly valued for their physiological relevance, and versatility in biological applications. Nanopatterns that mimic the extracellular matrix provide crucial topological cues, creating a physiologically relevant cellular environment and guiding cellular behaviors. However, the high cost and complex, time-consuming nature of the nanofabrication process have limited the widespread adoption of nanopatterns in diverse biological applications. In this study, we present a straightforward and cost-effective elastomer replica molding method utilizing commercially available optical discs to generate various nanopatterns, such as nanogroove/ridge, nanoposts, and nanopits, varying in spacing and heights. Using the nanopatterned well chips (NW-Chips), we demonstrated the efficient formation of 3D multicellular self-assemblies of three different types of cancer cells. Our findings highlight the accessibility and affordability of optical discs as tools for nanopattern generation, offering promising avenues for modulating cell behaviors and advancing diverse biological applications.

Upscaling Osteoclast Generation by Enhancing Macrophage Aggregation Using Hollow Microgels

Osteoclasts, the bone resorbing cells of hematopoietic origin formed by macrophage fusion, are essential in bone health and disease. However, in vitro research on osteoclasts remains challenging due to heterogeneous cultures that only contain a few multinucleated osteoclasts. Indeed, a strategy to generate homogeneous populations of multinucleated osteoclasts in a scalable manner has remained elusive. Here, the investigation focuses on whether microencapsulation of human macrophages in microfluidically generated hollow, sacrificial tyramine-conjugated dextran (Dex-TA) microgels could facilitate macrophage precursor aggregation and formation of multinucleated osteoclasts. Therefore, human mononuclear cells are isolated from buffy coats and differentiated toward macrophages. Macrophages are encapsulated in microgels using flow focus microfluidics and outside-in enzymatic oxidative phenolic crosslinking, and differentiated toward osteoclasts. Morphology, viability, and osteoclast fusion of microencapsulated cells are assessed. Furthermore, microgels are degraded to allow cell sorting of released cells based on osteoclastic marker expression. The successful encapsulation and osteoclast formation of human macrophages in Dex-TA microgels are reported for the first time using high-throughput droplet microfluidics. Intriguingly, osteoclast formation within these 3D microenvironments occurs at a significantly higher level compared to the conventional 2D culture system. Furthermore, the feasibility of establishing a pure osteoclast culture from cell transfer and release from degradable microgels is demonstrated.

3D Cell Culture Method in Channel-Free Water-in-Oil Droplets

A new channel-free water-in-oil (WO) droplet 3D cell culture method is proposed to address the challenges while maintaining the advantages of the conventional 3D cell culture methods. The proposed WO method can fundamentally solve the constraint of spheroids size, a common challenge in conventional 3D culture, by using droplet size controllability. The 3D cell culture performance of the WO method is verified by comparing it with the conventional 3D cell culture methods. A systematic investigation of the culture conditions of the WO method confirms the working range of cell concentration and droplet size, as well as the scalability of spheroid size. Adjusting droplet size and cell concentration enables rapid spheroid formation with large and high cell concentration droplets or fast spheroid growth with small and low cell concentration droplets, providing control over the spheroid size and growth rate according to the purpose. Furthermore, long-term culture is demonstrated for 1 month with the proposed method, showing the largest spheroid culture and demonstrating the possibility that this method can be used not only for spheroid formation but also for organoid studies. Finally, if a WO-based automated 3D cell culture system is developed, it will be a useful tool for organoid research.

Exploring the Dimensions of Pre-Clinical Research: 3D Cultures as an Investigative Model of Cardiac Fibrosis in Chagas Disease

A three-dimensional (3D) cell culture can more precisely mimic tissues architecture and functionality, being a promising alternative model to study disease pathophysiology and drug screening. Chagas disease (CD) is a neglected parasitosis that affects 7 million people worldwide. Trypanosoma cruzi's (T. cruzi) mechanisms of invasion/persistence continue to be elucidated. Benznidazole (BZ) and Nifurtimox (NF) are trypanocidal drugs with few effects on the clinical manifestations of the chronic disease. Chronic Chagas cardiomyopathy (CCC) is the main manifestation of CD due to its frequency and severity. The development of fibrosis and hypertrophy in cardiac tissue can lead to heart failure and sudden death. Thus, there is an urgent need for novel therapeutic options. Our group has more than fifteen years of expertise using 3D primary cardiac cell cultures, being the first to reproduce fibrosis and hypertrophy induced by T. cruzi infection in vitro. These primary cardiac spheroids exhibit morphological and functional characteristics that are similar to heart tissue, making them an interesting model for studying CD cardiac fibrosis. Here, we aim to demonstrate that our primary cardiac spheroids are great preclinical models which can be used to develop new insights into CD cardiac fibrosis, presenting advances already achieved in the field, including disease modeling and drug screening.

Simple Method for On-Demand Droplet Trapping in a Microfluidic Device Based on the Concept of Hydrodynamic Resistance

We demonstrate an innovative method to catch the desired droplets from a train of droplets and immobilize them in traps located in an integrated microfluidic device. To this end, water-in-oil droplets are generated in a flow-focusing junction and then guided to a channel connected to chambers designated for on-demand droplet trapping. Each chamber is connected to a side channel through a batch of microposts. The side channels are also connected to the flexible poly(vinyl chloride) tubes, which can be closed by attaching binder clips. The hydrodynamic resistance of the routes in the device can be changed by opening and closing the binder clips. In this way, droplets are easily guided into individual traps based on the user's demand. A set of numerical simulations was also conducted to investigate the authenticity of the employed idea and to find the optimal geometry for implementing our strategy. This simple method can be easily employed for on-demand droplet trapping without using on-chip valves or complex off-chip actuators proposed in previous studies.

Evaluation of aconitine cardiotoxicity with a heart-on-a-particle prepared by a microfluidic device

A heart-on-a-particle model based on multicompartmental microgel is proposed to simulate the heart microenvironment and study the cardiotoxicity of drugs. The relevant microgel was fabricated by a biocompatible microfluidic-based approach, where heart function-related HL-1 and HUVEC cells were arranged in separate compartments. Finally, the mechanism of aconitine-induced heart toxicity was elucidated using mass spectrometry and molecular biotechnology.

Acoustofluidic Actuation of Living Cells

Acoutofluidics is an increasingly developing and maturing technical discipline. With the advantages of being label-free, non-contact, bio-friendly, high-resolution, and remote-controllable, it is very suitable for the operation of living cells. After decades of fundamental laboratory research, its technical principles have become increasingly clear, and its manufacturing technology has gradually become popularized. Presently, various imaginative applications continue to emerge and are constantly being improved. Here, we introduce the development of acoustofluidic actuation technology from the perspective of related manipulation applications on living cells. Among them, we focus on the main development directions such as acoustofluidic sorting, acoustofluidic tissue engineering, acoustofluidic microscopy, and acoustofluidic biophysical therapy. This review aims to provide a concise summary of the current state of research and bridge past developments with future directions, offering researchers a comprehensive overview and sparking innovation in the field.

Fabrication of a high performance flexible capacitive porous GO/PDMS pressure sensor based on droplet microfluidic technology

Porous structures are an effective way to improve the performance of flexible capacitive sensors, but the pore size uniformity of porous structures is not easily controlled by current methods, which may affect the inconsistent performance of different batches of sensors. In this paper, a high performance capacitive flexible porous GO/PDMS pressure sensor was prepared based on droplet microfluidic technology. By testing the performance of the sensor, we found that the sensor with a flow rate ratio of 1 : 3 has relatively good performance, with a degree of hysteresis (DH) of 8.64% and a coefficient of variation (CV) of 5.2%. Therefore, we studied the sensor performance based on this process. The result shows that the sensitivity of the flexible capacitive porous GO/PDMS pressure sensor reached 0.627 kPa-1 at low pressure (0-3 kPa), which is significantly higher than that of the pure PDMS thin film sensor (about 0.031 kPa-1) and the porous PDMS pressure sensor (0.263 kPa-1). At the same time, the sensor has a large range with a fast response time of 240 ms and a relaxation time of 300 ms at 30 kPa and an ultra-low detection limit (70 Pa). It can maintain stable operation under continuous force loading/unloading cycles and can respond well to different pressure step changes, so the sensor can be used to detect the movement process of each finger, knee, foot and other joints of the human body. In conclusion, the droplet microfluidic technology can effectively prepare high-performance capacitive flexible porous GO/PDMS pressure sensors.

Development and future of droplet microfluidics

Over the past two decades, advances in droplet-based microfluidics have facilitated new approaches to process and analyze samples with unprecedented levels of precision and throughput. A wide variety of applications has been inspired across multiple disciplines ranging from materials science to biology. Understanding the dynamics of droplets enables optimization of microfluidic operations and design of new techniques tailored to emerging demands. In this review, we discuss the underlying physics behind high-throughput generation and manipulation of droplets. We also summarize the applications in droplet-derived materials and droplet-based lab-on-a-chip biotechnology. In addition, we offer perspectives on future directions to realize wider use of droplet microfluidics in industrial production and biomedical analyses.

Development of Organoids to Study Infectious Host Interactions

Emerging organoid research is paving way for studies in infectious diseases. Described here is a technique for the generation of stem-cell derived organoids for human small intestine and lung together with methods to infect such organoids with a mock pathogen (Cryptosporidium parvum). Such systems are amenable to imaging and processing for molecular biological analyses. It is the intent of this chapter to provide a simple, routine organoid procedure so that in vitro studies with Borrelia such as cell invasion and dissemination can be conducted.

Implementing patient derived organoids in functional precision medicine for patients with advanced colorectal cancer

BACKGROUND

Patient Derived Organoids (PDOs) emerged as the best technology to develop ex vivo tumor avatars. Whether drug testing on PDOs to identify efficient therapies will bring clinical utility by improving patient survival remains unclear. To test this hypothesis in the frame of clinical trials, PDO technology faces three main challenges to be implemented in routine clinical practices: i) generating PDOs with a limited amount of tumor material; ii) testing a wide panel of anti-cancer drugs; and iii) obtaining results within a time frame compatible with patient disease management. We aimed to address these challenges in a prospective study in patients with colorectal cancer (CRC).

METHODS

Fresh surgical or core needle biopsies were obtained from patients with CRC. PDOs were established and challenged with a panel of 25 FDA-approved anti-cancer drugs (chemotherapies and targeted therapies) to establish a scoring method ('chemogram') identifying in vitro responders. The results were analyzed at the scale of the cohort and individual patients when the follow-up data were available.

RESULTS

A total of 25 PDOs were successfully established, harboring 94% concordance with the genomic profile of the tumor they were derived from. The take-on rate for PDOs derived from core needle biopsies was 61.5%. A chemogram was obtained with a 6-week median turnaround time (range, 4-10 weeks). At least one hit (mean 6.16) was identified for 92% of the PDOs. The number of hits was inversely correlated to disease metastatic dissemination and the number of lines of treatment the patient received. The chemograms were compared to clinical data obtained from 8 patients and proved to be predictive of their response with 75% sensitivity and specificity.

CONCLUSIONS

We show that PDO-based drug tests can be achieved in the frame of routine clinical practice. The chemogram could provide clinicians with a decision-making tool to tailor patient treatment. Thus, PDO-based functional precision oncology should now be tested in interventional trials assessing its clinical utility for patients who do not harbor activable genomic alterations or have developed resistance to standard of care treatments.

Microfluidic fabrication of X-ray-visible sodium hyaluronate microspheres for embolization

Catheter embolization is a minimally invasive technique that relies on embolic agents and is now widely used to treat various high-prevalence medical diseases. Embolic agents usually need to be combined with exogenous contrasts to visualize the embolotherapy process. However, the exogenous contrasts are quite simply washed away by blood flow, making it impossible to monitor the embolized location. To solve this problem, a series of sodium hyaluronate (SH) loaded with bismuth sulfide (Bi₂S₃) nanorods (NRs) microspheres (Bi₂S₃@SH) were prepared in this study by using 1,4-butaneglycol diglycidyl ether (BDDE) as a crosslinker through single-step microfluidics. Bi₂S₃@SH-1 microspheres showed the best performance among other prepared microspheres. The fabricated microspheres had uniform size and good dispersibility. Furthermore, the introduction of Bi₂S₃ NRs synthesized by a hydrothermal method as Computed Tomography (CT) contrast agents improved the mechanical properties of Bi₂S₃@SH-1 microspheres and endowed the microspheres with excellent X-ray impermeability. The blood compatibility and cytotoxicity test showed that the Bi₂S₃@SH-1 microspheres had good biocompatibility. In particular, the in vitro simulated embolization experiment results indicate that the Bi₂S₃@SH-1 microspheres had excellent embolization effect, especially for the small-sized blood vessels of 500-300 and 300 μm. The results showed the prepared Bi₂S₃@SH-1 microspheres have good biocompatibility and mechanical properties, as well as certain X-ray visibility and excellent embolization effects. We believe that the design and combination of this material has good guiding significance in the field of embolotherapy.

Leveraging interactions in microfluidic droplets for enhanced biotechnology screens

Microfluidic droplet screens serve as an innovative platform for high-throughput biotechnology, enabling significant advancements in discovery, product optimization, and analysis. This review sheds light on the emerging trends of interaction assays in microfluidic droplets, underscoring the unique suitability of droplets for these applications. Encompassing a diverse range of biological entities such as antibodies, enzymes, DNA, RNA, various microbial and mammalian cell types, drugs, and other molecules, these assays demonstrate their versatility and scope. Recent methodological breakthroughs have escalated these screens to novel scales of bioanalysis and biotechnological product design. Moreover, we highlight pioneering advancements that extend droplet-based screens into new domains: cargo delivery within human bodies, application of synthetic gene circuits in natural environments, 3D printing, and the development of droplet structures responsive to environmental signals. The potential of this field is profound and only set to increase.