Hydrogel-encapsulated 3D microwell array for neuronal differentiation

Cryopreserving 3D cell culture models of Alzheimer's disease in hydrogel microbeads

Long-term preservation of fully differentiated human neurons poses a longstanding challenge in neuroscience research. Numerous cellular disease models have been established using cultured human neuronal cells, including our three-dimensional (3D) human neural cell culture model of Alzheimer's disease (AD). However, the absence of a reliable method for preserving fully differentiated human neural cell cultures for a long time has hindered the sharing and standardization of these models. To address this critical limitation, we focused on cryopreservation, which is the gold standard for long-term preservation, and combined this with three key technological advancements. First, we employed parallelized microfluidic devices for the efficient generation of 3D cell cultures within uniform hydrogel microbeads (~ 220 μm), which facilitate the rapid exchange of media ingredients and cryoprotectants. Second, we implemented a cytophobic microwell system to safeguard neuron-encapsulated microbeads from fusion and aggregation. Third, we developed a novel inducible AD cell model optimized for cryopreservation and AD drug testing. We have successfully maintained encapsulated control and AD neural progenitor cells in microwells during differentiation for 12 days. Notably, fully differentiated human neural cells can be cryopreserved within Matrigel microbeads while retaining intact and mature neuronal processes, exhibiting no signs of damage to neurites following freeze/thaw cycles. Furthermore, we have demonstrated the successful cryopreservation, thawing, and induction of pathogenic Amyloid-β 42 (Aβ42) generation in fully differentiated AD neural progenitor cells. Our study offers a solution for one of the major challenges in neuroscience research, utilizing porous hydrogel microbead structures to facilitate rapid delivery of cryoprotectants and protect complex neuronal structures without undergoing damaging cell dissociation steps. The inducible "3D human microbead model of AD" enhances the speed, efficacy, and reproducibility of AD drug screening.

Hybrid-integrated devices for mimicking malignant brain tumors ("tumor-on-a-chip") for in vitro development of targeted drug delivery and personalized therapy approaches

Acute and requiring attention problem of oncotheranostics is a necessity for the urgent development of operative and precise diagnostics methods, followed by efficient therapy, to significantly reduce disability and mortality of citizens. A perspective way to achieve efficient personalized treatment is to use methods for operative evaluation of the individual drug load, properties of specific tumors and the effectiveness of selected therapy, and other actual features of pathology. Among the vast diversity of tumor types-brain tumors are the most invasive and malignant in humans with poor survival after diagnosis. Among brain tumors glioblastoma shows exceptionally high mortality. More studies are urgently needed to understand the risk factors and improve therapy approaches. One of the actively developing approaches is the tumor-on-a-chip (ToC) concept. This review examines the achievements of recent years in the field of ToC system developments. The basics of microfluidic chips technologies are considered in the context of their applications in solving oncological problems. Then the basic principles of tumors cultivation are considered to evaluate the main challengers in implementation of microfluidic devices, for growing cell cultures and possibilities of their treatment and observation. The main achievements in the culture types diversity approaches and their advantages are being analyzed. The modeling of angiogenesis and blood-brain barrier (BBB) on a chip, being a principally important elements of the life system, were considered in detail. The most interesting examples and achievements in the field of tumor-on-a-chip developments have been presented.

Review: 3D cell models for organ-on-a-chip applications

Two-dimensional (2D) cultures do not fully reflect the human organs' physiology and the real effectiveness of the used therapy. Therefore, three-dimensional (3D) models are increasingly used in bioanalytical science. Organ-on-a-chip systems are used to obtain cellular in vitro models, better reflecting the human body's in vivo characteristics and allowing us to obtain more reliable results than standard preclinical models. Such 3D models can be used to understand the behavior of tissues/organs in response to selected biophysical and biochemical factors, pathological conditions (the mechanisms of their formation), drug screening, or inter-organ interactions. This review characterizes 3D models obtained in microfluidic systems. These include spheroids/aggregates, hydrogel cultures, multilayers, organoids, or cultures on biomaterials. Next, the methods of formation of different 3D cultures in Organ-on-a-chip systems are presented, and examples of such Organ-on-a-chip systems are discussed. Finally, current applications of 3D cell-on-a-chip systems and future perspectives are covered.

Electroresponsive Hydrogels for Therapeutic Applications in the Brain

Electroresponsive hydrogels possess a conducting material component and respond to electric stimulation through reversible absorption and expulsion of water. The high level of hydration, soft elastomeric compliance, biocompatibility, and enhanced electrochemical properties render these hydrogels suitable for implantation in the brain to enhance the transmission of neural electric signals and ion transport. This review provides an overview of critical electroresponsive hydrogel properties for augmenting electric stimulation in the brain. A background on electric stimulation in the brain through electroresponsive hydrogels is provided. Common conducting materials and general techniques to integrate them into hydrogels are briefly discussed. This review focuses on and summarizes advances in electric stimulation of electroconductive hydrogels for therapeutic applications in the brain, such as for controlling delivery of drugs, directing neural stem cell differentiation and neurogenesis, improving neural biosensor capabilities, and enhancing neural electrode-tissue interfaces. The key challenges in each of these applications are discussed and recommendations for future research are also provided.

Inflammatory Modulation of Polyethylene Glycol-AuNP for Regulation of the Neural Differentiation Capacity of Mesenchymal Stem Cells

A nanocomposite composed of polyethylene glycol (PEG) incorporated with various concentrations (~17.4, ~43.5, ~174 ppm) of gold nanoparticles (Au) was created to investigate its biocompatibility and biological performance in vitro and in vivo. First, surface topography and chemical composition was determined through UV-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), free radical scavenging ability, and water contact angle measurement. Additionally, the diameters of the PEG-Au nanocomposites were also evaluated through dynamic light scattering (DLS) assay. According to the results, PEG containing 43.5 ppm of Au demonstrated superior biocompatibility and biological properties for mesenchymal stem cells (MSCs), as well as superior osteogenic differentiation, adipocyte differentiation, and, particularly, neuronal differentiation. Indeed, PEG-Au 43.5 ppm induced better cell adhesion, proliferation and migration in MSCs. The higher expression of the SDF-1α/CXCR4 axis may be associated with MMPs activation and may have also promoted the differentiation capacity of MSCs. Moreover, it also prevented MSCs from apoptosis and inhibited macrophage and platelet activation, as well as reactive oxygen species (ROS) generation. Furthermore, the anti-inflammatory, biocompatibility, and endothelialization capacity of PEG-Au was measured in a rat model. After implanting the nanocomposites into rats subcutaneously for 4 weeks, PEG-Au 43.5 ppm was able to enhance the anti-immune response through inhibiting CD86 expression (M1 polarization), while also reducing leukocyte infiltration (CD45). Moreover, PEG-Au 43.5 ppm facilitated CD31 expression and anti-fibrosis ability. Above all, the PEG-Au nanocomposite was evidenced to strengthen the differentiation of MSCs into various cells, including fat, vessel, and bone tissue and, particularly, nerve cells. This research has elucidated that PEG combined with the appropriate amount of Au nanoparticles could become a potential biomaterial able to cooperate with MSCs for tissue regeneration engineering.

Fabrication approaches for high-throughput and biomimetic disease modeling

There is often a tradeoff between in vitro disease modeling platforms that capture pathophysiologic complexity and those that are amenable to high-throughput fabrication and analysis. However, this divide is closing through the application of a handful of fabrication approaches-parallel fabrication, automation, and flow-driven assembly-to design sophisticated cellular and biomaterial systems. The purpose of this review is to highlight methods for the fabrication of high-throughput biomaterial-based platforms and showcase examples that demonstrate their utility over a range of throughput and complexity. We conclude with a discussion of future considerations for the continued development of higher-throughput in vitro platforms that capture the appropriate level of biological complexity for the desired application. STATEMENT OF SIGNIFICANCE: There is a pressing need for new biomedical tools to study and understand disease. These platforms should mimic the complex properties of the body while also permitting investigation of many combinations of cells, extracellular cues, and/or therapeutics in high-throughput. This review summarizes emerging strategies to fabricate biomimetic disease models that bridge the gap between complex tissue-mimicking microenvironments and high-throughput screens for personalized medicine.

Gelatin Methacrylate (GelMA)-Based Hydrogels for Cell Transplantation: an Effective Strategy for Tissue Engineering

Gelatin methacrylate (GelMA)-based hydrogels are gaining a great deal of attention as potentially implantable materials in tissue engineering applications because of their biofunctionality and mechanical tenability. Since different natural tissues respond differently to mechanical stresses, an ideal implanted material would closely match the mechanical properties of the target tissue. In this regard, applications employing GelMA hydrogels are currently limited by the low mechanical strength and biocompatibility of GelMA. Therefore, this review focuses on modifications made to GelMA hydrogels to make them more suitable for tissue engineering applications. A large number of reports detail rational synthetic processes for GelMA or describe the incorporation of various biomaterials into GelMA hydrogels to tune their various properties, e.g., physical strength, chemical properties, conductivity, and porosity, and to promote cell loading and accelerate tissue repair. A novel strategy for repairing tissue injuries, based on the transplantation of cell-loaded GelMA scaffolds, is examined and its advantages and challenges are summarized. GelMA-cell combinations play a critical and pioneering role in this process and could potentially accelerate the development of clinically relevant applications.

Recent advances in photo-crosslinkable hydrogels for biomedical applications

Photo-crosslinkable hydrogels have recently attracted significant scientific interest. Their properties can be manipulated in a spatiotemporal manner through exposure to light to achieve the desirable functionality for various biomedical applications. This review article discusses the recent advances of the most common photo-crosslinkable hydrogels, including poly(ethylene glycol) diacrylate, gelatin methacryloyl and methacrylated hyaluronic acid, for various biomedical applications. We first highlight the advantages of photopolymerization and discuss diverse photosensitive systems used for the synthesis of photo-crosslinkable hydrogels. We then introduce their synthesis methods and review their latest state of development in biomedical applications, including tissue engineering and regenerative medicine, drug delivery, cancer therapies and biosensing. Lastly, the existing challenges and future perspectives of engineering photo-crosslinkable hydrogels for biomedical applications are briefly discussed.

Generation of uniform-sized multicellular tumor spheroids using hydrogel microwells for advanced drug screening

Even though in vitro co-culture tumor spheroid model plays an important role in screening drug candidates, its wide applications are currently limited due to the lack of reliable and high throughput methods for generating well-defined and 3D complex co-culture structures. Herein, we report the development of a hydrogel microwell array to generate uniform-sized multicellular tumor spheroids. Our developed multicellular tumor spheroids are structurally well-defined, robust and can be easily transferred into the widely used 2D culture substrates while maintaining our designed multicellular 3D-sphere structures. Moreover, to develop effective anti-cancer therapeutics we integrated our recently developed gold-graphene hybrid nanomaterial (Au@GO)-based photothermal cancer therapy into a series of multicellular tumor spheroid co-culture system. The multicellular tumor spheroids were harvested onto a two-dimensional (2D) substrate, under preservation of their three-dimensional (3D) structure, to evaluate the photothermal therapy effectiveness of graphene oxide (GO)-wrapped gold nanoparticles (Au@GO). From the model of co-culture spheroids of HeLa/Ovarian cancer and HeLa/human umbilical vein endothelial cell (HUVEC), we observed that Au@GO nanoparticles displayed selectivity towards the fast-dividing HeLa cells, which could not be observed to this extent in 2D cultures. Overall, our developed uniform-sized 3D multicellular tumor spheroid could be a powerful tool for anticancer drug screening applications.

Poisson statistics-mediated particle/cell counting in microwell arrays

Precise determination of particle or cell numbers is of importance for a wide array of applications in environmental studies, medical and biological applications, or manufacturing and monitoring applications in industrial production processes. A number of techniques ranging from manual counting to sophisticated equipment (e.g., flow cytometry) are available for this task. However, these methods are either labour intensive, prone to error, or require expensive equipment. Here, we present a fast, simple method for determining the number density of cells or microparticles using a microwell array. We analyze the light transmission of the microwells and categorize the microwells into two groups. As particles/cells contained in a microwell locally reduce the light transmission, these wells displayed a lower average transmission compared to unoccupied microwells. The number density of particles/cells can be calculated by Poisson statistics from the ratio of occupied to unoccupied microwells. Following this approach, the number densities of two different types of microparticles, as well as HeLa and E. Coli cells, ranging over four orders of magnitude were determined. Through the microwell array defined by microfabrication, a simple image recognition algorithm can be used with the formation of aggregates or irregular shaped samples providing no additional difficulty to the microwell recognition. Additionally, this method can be carried out using only simple equipment and data analysis automated by a computer program.

Prediction analysis and quality assessment of microwell array images

Microwell arrays are widely used for the analysis of fluorescent-labelled biomaterials. For rapid detection and automated analysis of microwell arrays, the computational image analysis is required. Support Vector Machines (SVM) can be used for this task. Here, we present a SVM-based approach for the analysis of microwell arrays consisting of three distinct steps: labeling, training for feature selection, and classification into three classes. The three classes are filled, partially filled, and unfilled microwells. Next, the partially filled wells are analyzed by SVM and their tendency towards filled or unfilled tested through applying a Gaussian filter. Through this, all microwells can be categorized as either filled or unfilled by our algorithm. Therefore, this SVM-based computational image analysis allows for an accurate and simple classification of microwell arrays.

Microdevice Platform for In Vitro Nervous System and Its Disease Model

The development of precise microdevices can be applied to the reconstruction of in vitro human microenvironmental systems with biomimetic physiological conditions that have highly tunable spatial and temporal features. Organ-on-a-chip can emulate human physiological functions, particularly at the organ level, as well as its specific roles in the body. Due to the complexity of the structure of the central nervous system and its intercellular interaction, there remains an urgent need for the development of human brain or nervous system models. Thus, various microdevice models have been proposed to mimic actual human brain physiology, which can be categorized as nervous system-on-a-chip. Nervous system-on-a-chip platforms can prove to be promising technologies, through the application of their biomimetic features to the etiology of neurodegenerative diseases. This article reviews the microdevices for nervous system-on-a-chip platform incorporated with neurobiology and microtechnology, including microfluidic designs that are biomimetic to the entire nervous system. The emulation of both neurodegenerative disorders and neural stem cell behavior patterns in micro-platforms is also provided, which can be used as a basis to construct nervous system-on-a-chip.