Superhydrophobic chips for cell spheroids high-throughput generation and drug screening

Fundamentals and Applications of Surface Wetting

In an era defined by an insatiable thirst for sustainable energy solutions, responsible water management, and cutting-edge lab-on-a-chip diagnostics, surface wettability plays a pivotal role in these fields. The seamless integration of fundamental research and the following demonstration of applications on these groundbreaking technologies hinges on manipulating fluid through surface wettability, significantly optimizing performance, enhancing efficiency, and advancing overall sustainability. This Review explores the behavior of liquids when they engage with engineered surfaces, delving into the far-reaching implications of these interactions in various applications. Specifically, we explore surface wetting, dissecting it into three distinctive facets. First, we delve into the fundamental principles that underpin surface wetting. Next, we navigate the intricate liquid-surface interactions, unraveling the complex interplay of various fluid dynamics, as well as heat- and mass-transport mechanisms. Finally, we report on the practical realm, where we scrutinize the myriad applications of these principles in everyday processes and real-world scenarios.

Spheroids formation in large drops suspended in superhydrophobic paper cones

The utilization of 3D cell culture for spheroid formation holds significant implications in cancer research, contributing to a fundamental understanding of the disease and aiding drug development. Conventional methods such as the hanging drop technique and other alternatives encounter limitations due to smaller drop volumes, leading to nutrient starvation and restricted culture duration. In this study, we present a straightforward approach to creating superhydrophobic paper cones capable of accommodating large volumes of culture media drops. These paper cones have sterility, autoclavability, and bacterial repellent properties. Leveraging these attributes, we successfully generate large spheroids of ovarian cancer cells and, as a proof of concept, conduct drug screening to assess the impact of carboplatin. Thus, our method enables the preparation of flexible superhydrophobic surfaces for laboratory applications in an expeditious manner, exemplified here through spheroid formation and drug screening demonstrations.

Regulation of cell fate by cell imprinting approach in vitro

Cell culture-based technologies are widely utilized in various domains such as drug evaluation, toxicity assessment, vaccine and biopharmaceutical development, reproductive technology, and regenerative medicine. It has been demonstrated that pre-adsorption of extracellular matrix (ECM) proteins including collagen, laminin and fibronectin provide more degrees of support for cell adhesion. The purpose of cell imprinting is to imitate the natural topography of cell membranes by gels or polymers to create a reliable environment for the regulation of cell function. The results of recent studies show that cell imprinting is a tool to guide the behavior of cultured cells by controlling their adhesive interactions with surfaces. Therefore, in this review we aim to compare different cell cultures with the imprinting method and discuss different cell imprinting applications in regenerative medicine, personalized medicine, disease modeling, and cell therapy.

Fabricating a low-temperature synthesized graphene-cellulose acetate-sodium alginate scaffold for the generation of ovarian cancer spheriod and its drug assessment

3D cell culture can mimic tumor pathophysiology, which reflects cellular morphology and heterogeneity, strongly influencing gene expression, cell behavior, and intracellular signaling. It supports cell-cell and cell-matrix interaction, cell attachment, and proliferation, resulting in rapid and reliable drug screening models. We have generated an ovarian cancer spheroid in interconnected porous scaffolds. The scaffold is fabricated using low-temperature synthesized graphene, cellulose acetate, and sodium alginate. Graphene nanosheets enhance cell proliferation and aggregation, which aids in the formation of cancer spheroids. The spheroids are assessed after day 7 and 14 for the generation of reactive oxygen species (ROS), expression of the hypoxia inducing factor (HIF-1⍺) and vascular endothelial growth factor (VEGF). Production of ROS was observed due to the aggregated tumor mass, and enhanced production of HIF-1⍺ and VEGF results from a lack of oxygen and nutrition. Furthermore, the efficacy of anticancer drug doxorubicin at varying concentrations is assessed on ovarian cancer spheroids by studying the expression of caspase-3/7 at day 7 and 14. The current findings imply that the graphene-cellulose-alginate (GCA) scaffold generates a reliable ovarian cancer spheroid model to test the efficacy of the anticancer drug.

Droplet microarray platforms for high-throughput drug screening

High-throughput screening platforms are fundamental for the rapid and efficient processing of large amounts of experimental data. Parallelization and miniaturization of experiments are important for improving their cost-effectiveness. The development of miniaturized high-throughput screening platforms is essential in the fields of biotechnology, medicine, and pharmacology. Currently, most laboratories use 96- or 384-well microtiter plates for screening; however, they have disadvantages, such as high reagent and cell consumption, low throughput, and inability to avoid cross-contamination, which need to be further optimized. Droplet microarrays, as novel screening platforms, can effectively avoid these shortcomings. Here, the preparation method of the droplet microarray, method of adding compounds in parallel, and means to read the results are briefly described. Next, the latest research on droplet microarray platforms in biomedicine is presented, including their application in high-throughput culture, cell screening, high-throughput nucleic acid screening, drug development, and individualized medicine. Finally, the challenges and future trends in droplet microarray technology are summarized.

Spheroid Engineering in Microfluidic Devices

Two-dimensional (2D) cell culture techniques are commonly employed to investigate biophysical and biochemical cellular responses. However, these culture methods, having monolayer cells, lack cell-cell and cell-extracellular matrix interactions, mimicking the cell microenvironment and multicellular organization. Three-dimensional (3D) cell culture methods enable equal transportation of nutrients, gas, and growth factors among cells and their microenvironment. Therefore, 3D cultures show similar cell proliferation, apoptosis, and differentiation properties to in vivo. A spheroid is defined as self-assembled 3D cell aggregates, and it closely mimics a cell microenvironment in vitro thanks to cell-cell/matrix interactions, which enables its use in several important applications in medical and clinical research. To fabricate a spheroid, conventional methods such as liquid overlay, hanging drop, and so forth are available. However, these labor-intensive methods result in low-throughput fabrication and uncontrollable spheroid sizes. On the other hand, microfluidic methods enable inexpensive and rapid fabrication of spheroids with high precision. Furthermore, fabricated spheroids can also be cultured in microfluidic devices for controllable cell perfusion, simulation of fluid shear effects, and mimicking of the microenvironment-like in vivo conditions. This review focuses on recent microfluidic spheroid fabrication techniques and also organ-on-a-chip applications of spheroids, which are used in different disease modeling and drug development studies.

Superhydrophilic–superhydrophobic patterned surfaces: From simplified fabrication to emerging applications

Superhydrophilic–superhydrophobic patterned surfaces constitute a branch of surface chemistry involving the two extreme states of superhydrophilicity and superhydrophobicity combined on the same surface in precise patterns. Such surfaces have many advantages, including controllable wettability, enrichment ability, accessibility, and the ability to manipulate and pattern water droplets, and they offer new functionalities and possibilities for a wide variety of emerging applications, such as microarrays, biomedical assays, microfluidics, and environmental protection. This review presents the basic theory, simplified fabrication, and emerging applications of superhydrophilic–superhydrophobic patterned surfaces. First, the fundamental theories of wettability that explain the spreading of a droplet on a solid surface are described. Then, the fabrication methods for preparing superhydrophilic–superhydrophobic patterned surfaces are introduced, and the emerging applications of such surfaces that are currently being explored are highlighted. Finally, the remaining challenges of constructing such surfaces and future applications that would benefit from their use are discussed.

Mammalian Cell Spheroids on Mixed Organic–Inorganic Superhydrophobic Coating

Three-dimensional cell culture has become a reliable method for reproducing in vitro cellular growth in more realistic physiological conditions. The surface hydrophobicity strongly influences the promotion of cell aggregate formation. In particular, for spheroid formation, highly water-repellent coatings seem to be required for the significant effects of the process. In this work, surfaces at different wettability have been compared to observe their influence on the growth and promotion of aggregates of representative mammalian cell lines, both tumoral and non-tumoral (3T3, HaCat and MCF-7 cell lines). The effect of increased hydrophobicity from TCPS to agarose hydrogel to mixed organic–inorganic superhydrophobic (SH) coating has been investigated by optical and fluorescence microscopy, and by 3D confocal profilometry, in a time scale of 24 h. The results show the role of less wettable substrates in inducing the formation of spheroid-like cell aggregates at a higher degree of sphericity for the studied cell lines.

Recent Developments in Artificial Super-Wettable Surfaces Based on Bioinspired Polymeric Materials for Biomedical Applications

Inspired by nature, significant research efforts have been made to discover the diverse range of biomaterials for various biomedical applications such as drug development, disease diagnosis, biomedical testing, therapy, etc. Polymers as bioinspired materials with extreme wettable properties, such as superhydrophilic and superhydrophobic surfaces, have received considerable interest in the past due to their multiple applications in anti-fogging, anti-icing, self-cleaning, oil-water separation, biosensing, and effective transportation of water. Apart from the numerous technological applications for extreme wetting and self-cleaning products, recently, super-wettable surfaces based on polymeric materials have also emerged as excellent candidates in studying biological processes. In this review, we systematically illustrate the designing and processing of artificial, super-wettable surfaces by using different polymeric materials for a variety of biomedical applications including tissue engineering, drug/gene delivery, molecular recognition, and diagnosis. Special attention has been paid to applications concerning the identification, control, and analysis of exceedingly small molecular amounts and applications permitting high cell and biomaterial cell screening. Current outlook and future prospects are also provided.

Micro/Nanopatterned Superhydrophobic Surfaces Fabrication for Biomolecules and Biomaterials Manipulation and Analysis

Superhydrophobic surfaces display an extraordinary repulsion to water and water-based solutions. This effect emerges from the interplay of intrinsic hydrophobicity of the surface and its morphology. These surfaces have been established for a long time and have been studied for decades. The increasing interest in recent years has been focused towards applications in many different fields and, in particular, biomedical applications. In this paper, we review the progress achieved in the last years in the fabrication of regularly patterned superhydrophobic surfaces in many different materials and their exploitation for the manipulation and characterization of biomaterial, with particular emphasis on the issues affecting the yields of the fabrication processes and the quality of the manufactured devices.

A superhydrophobic chip integrated with an array of medium reservoirs for long-term hanging drop spheroid culture

Hanging drop (HD) is one of the most popular methods used for forming three-dimensional (3D) cell spheroids. However, conventional hanging drop systems are only applicable for short-term spheroid culture due to their inconvenience in exchanging cell culture media. Here we present a medium-reservoir-integrated superhydrophobic (MRI-SH) chip for long-term HD spheroid cultures. The device consists of two main components: i) a patterned superhydrophobic (SH) surface containing an array of wettable spots which anchor arrays of droplets of cell suspension, and ii) an array of chambers that serve as medium reservoirs, both interconnected via an array of thru-holes. This configuration provides two distinct advantages over conventional HD configurations: i) the high wettability contrast of the SH pattern on the chip leads to the formation and adhesion of nearly spherical hanging droplets on its surface, which minimizes interactions between the liquid and the substrate; ii) the integrated chambers provide large volumes of medium to maintain longer culture durations. Using this device, spheroids of MHCC97H cells were successfully formed, and the cultured spheroids could maintain high viability for up to 30 days and exhibited enhanced spheroid morphology compared to those cultured in the conventional HD systems. STATEMENT OF SIGNIFICANCE: This paper presents a medium-reservoir-integrated superhydrophobic hanging drop (HD) platform for the long-term culture of spheroids with enhanced morphology. By monolithically integrating medium reservoirs and a patterned SH surface into a single device, this HD platform can not only produce high-quality spheroids, but also permit them to sustain high viability for up to 30 days without the need for tedious medium replenishment. We believe that such a platform will be valuable in a wide range of biological or biomedical applications, including tissue engineering, regenerative medicine, and drug discovery.

Using Spheroids as Building Blocks Towards 3D Bioprinting of Tumor Microenvironment

Cancer still ranks as a leading cause of mortality worldwide. Although considerable efforts have been dedicated to anticancer therapeutics, progress is still slow, partially due to the absence of robust prediction models. Multicellular tumor spheroids, as a major three-dimensional (3D) culture model exhibiting features of avascular tumors, gained great popularity in pathophysiological studies and high throughput drug screening. However, limited control over cellular and structural organization is still the key challenge in achieving in vivo like tissue microenvironment. 3D bioprinting has made great strides toward tissue/organ mimicry, due to its outstanding spatial control through combining both cells and materials, scalability, and reproducibility. Prospectively, harnessing the power from both 3D bioprinting and multicellular spheroids would likely generate more faithful tumor models and advance our understanding on the mechanism of tumor progression. In this review, the emerging concept on using spheroids as a building block in 3D bioprinting for tumor modeling is illustrated. We begin by describing the context of the tumor microenvironment, followed by an introduction of various methodologies for tumor spheroid formation, with their specific merits and drawbacks. Thereafter, we present an overview of existing 3D printed tumor models using spheroids as a focus. We provide a compilation of the contemporary literature sources and summarize the overall advancements in technology and possibilities of using spheroids as building blocks in 3D printed tissue modeling, with a particular emphasis on tumor models. Future outlooks about the wonderous advancements of integrated 3D spheroidal printing conclude this review.

Tailoring Materials with Specific Wettability in Biomedical Engineering

As a fundamental feature of solid surfaces, wettability is playing an increasingly important role in our daily life. Benefitting from the inspiration of biological paradigms and the development in manufacturing technology, numerous wettability materials with elaborately designed surface topology and chemical compositions have been fabricated. Based on these advances, wettability materials have found broad technological implications in various fields ranging from academy, industry, agriculture to biomedical engineering. Among them, the practical applications of wettability materials in biomedical-related fields are receiving remarkable researches during the past decades because of the increasing attention to healthcare. In this review, the research progress of materials with specific wettability is discussed. After briefly introducing the underlying mechanisms, the fabrication strategies of artificial materials with specific wettability are described. The emphasis is put on the application progress of wettability biomaterials in biomedical engineering. The prospects for the future trend of wettability materials are also presented.

Acoustic Droplet-Assisted Superhydrophilic-Superhydrophobic Microarray Platform for High-Throughput Screening of Patient-Derived Tumor Spheroids

Cell-based high-throughput screening is a key step in the current disease-based research, drug development, and precision medicine. However, it is challenging to establish a rapid culture and screening platform for rare cells (patient-derived) due to the obvious differences between the traditional 2D cell model and the tumor microenvironment, as well as the lack of a low-consumption screening platform for low numbers of cells. Here, we developed an acoustic drop-assisted superhydrophilic-superhydrophobic microarray platform for the rapid culture and screening of a few cells. By employing hydrophilic and hydrophobic microarrays, we can automatically distribute the cell suspension into uniform droplets, and these cells can spontaneously form compact 3D cell spheroids within 36 h (similar to the microenvironment of tumors in vivo). By using the acoustic droplet ejection device, we can accurately inject a drug solution with a volume of ∼pL to ∼nL into the droplet, and the whole process can be completed within 20 ms (one print). By using three different cell lines (Caco-2, MCF-7, and HeLa) to optimize the platform, the culture and screening of five patients' colon cancer were subsequently realized. Using three conventional chemotherapeutics (5-fluorouracil, cetuximab, and panitumumab) of various concentrations, the best treatment was screened out and compared with the actual treatment effect of the patients, and the results were extremely similar. As a proof-of-concept application, we have proved that our platform can quickly cultivate patient samples and effectively screen the best treatment methods, highlighting its wide application in precision medicine, basic tumor research, and drug development.

Bioinspired wettable-nonwettable micropatterns for emerging applications

Superhydrophilic and superhydrophobic surfaces are prevalent in nature and have received tremendous attention due to their importance in both fundamental research and practical applications. With the high interdisciplinary research and great development of microfabrication techniques, artificial wettable-nonwettable micropatterns inspired by the water-collection behavior of desert beetles have been successfully fabricated. A combination of the two extreme states of superhydrophilicity and superhydrophobicity on the same surface precisely, wettable-nonwettable micropatterns possess unique functionalities, such as controllable superwetting, anisotropic wetting, oriented adhesion, and other properties. In this review, we briefly describe the methods for fabricating wettable-nonwettable patterns, including self-assembly, electrodeposition, inkjet printing, and photolithography. We also highlight some of the emerging applications such as water collection, controllable bioadhesion, cell arrays, microreactors, printing techniques, and biosensors combined with various detection methods. Finally, the current challenges and prospects of this renascent and rapidly developing field are proposed and discussed.

Cutting and Bonding Parafilm® to Fast Prototyping Flexible Hanging Drop Chips for 3D Spheroid Cultures

A fast and low-cost fabrication process of flexible hanging drop chips for 3D spheroid cultures was proposed by cutting and bonding Parafilm®, a cohesive thermoplastic. The Parafilm® Hanging Drop Chip (PHDC) was assembled by two-layer of Parafilm® sheet with different sizes of holes. The hole on the upper layer of the Parafilm® is smaller than the hole on the bottom layer. The impact of hole size and sample volume on hanging drop formation and 3D spheroid formations in the hanging drop were investigated. The results showed that 20 µL solution on PHDC with a 3 mm hole could form stabile drop and facilitate spheroid formation. The initial cell number determinates the size of the formed spheroids. Exchanging liquid from the upper hole of the PHDC enables the co-culture of two types of cells in one spheroid and drug efficacy testing in hanging drops. The relative expression of cell adhesion and hypoxia-related genes from spheroids in hanging drop and conventional culture plate suggested the relevance of 3D spheroids and in vivo tumor tissue. The economical hanging drop chip can be fabricated without wet chemistry or expensive fabrication equipment, strengthening its application potential in conventional biological laboratories.

Proteinaceous Hydrogels for Bioengineering Advanced 3D Tumor Models

The establishment of tumor microenvironment using biomimetic in vitro models that recapitulate key tumor hallmarks including the tumor supporting extracellular matrix (ECM) is in high demand for accelerating the discovery and preclinical validation of more effective anticancer therapeutics. To date, ECM-mimetic hydrogels have been widely explored for 3D in vitro disease modeling owing to their bioactive properties that can be further adapted to the biochemical and biophysical properties of native tumors. Gathering on this momentum, herein the current landscape of intrinsically bioactive protein and peptide hydrogels that have been employed for 3D tumor modeling are discussed. Initially, the importance of recreating such microenvironment and the main considerations for generating ECM-mimetic 3D hydrogel in vitro tumor models are showcased. A comprehensive discussion focusing protein, peptide, or hybrid ECM-mimetic platforms employed for modeling cancer cells/stroma cross-talk and for the preclinical evaluation of candidate anticancer therapies is also provided. Further development of tumor-tunable, proteinaceous or peptide 3D microtesting platforms with microenvironment-specific biophysical and biomolecular cues will contribute to better mimic the in vivo scenario, and improve the predictability of preclinical screening of generalized or personalized therapeutics.

Bio-inspired wettability patterns for biomedical applications

Benefiting from the remarkable wettability heterogeneity, bio-inspired wettability patterns present a progressive and versatile platform for manipulating and patterning liquids, which provides an emerging strategy for operating liquid samples with crucial values in biomedical applications. In this review, we present a general summary of bio-inspired wettability patterns. After a compendious introduction of natural wettability phenomena and their underlying mechanisms, we summarize the general design principles and fabrication methods for preparing artificial wettability materials. Next, we shift to patterned surface wettability with an emphasis on the fabrication approaches. Then, we discuss in detail the various practical applications of wettability patterns in the biomedical field, including cell culture, drug screening and biosensors. Critical thinking about the current challenges and future outlook is also provided. We believe that this review would propel the prosperous development of bio-inspired wettability patterns to flourish in the field of biomedical engineering.

Screening of dual chemo-photothermal cellular nanotherapies in organotypic breast cancer 3D spheroids

Living therapeutics approaches that exploit mesenchymal stem cells (MSCs) as nanomedicine carriers are highly attractive due to MSCs native tropism toward the 3D tumor microenvironment. However, a streamlined pre-clinical evaluation of nano-in-cell anti-cancer therapies remains limited by the lack of in vitro testing platforms for screening MSCs-3D microtumor interactions. Herein we generated dense breast cancer mono and heterotypic 3D micro-spheroids for evaluating MSCs-solid tumors interactions and screen advanced nano-in-MSCs therapies. Breast cancer monotypic and heterotypic models comprising cancer cells and cancer associated fibroblasts (CAFs) were self-assembled under controlled conditions using the liquid overlay technique. The resulting microtumors exhibited high compactness, reproducible morphology and necrotic regions, similarly to native solid tumors. For evaluating tumoritropic therapies in organotypic tumor-stroma 3D models, theranostic polydopamine nanoparticles loaded with indocyanine green-doxorubicin combinations (PDA-ICG-DOX) were synthesized and administered to human bone-marrow derived MSCs (hBM-MSCs). The dual-loaded PDA nano-platforms were efficiently internalized, exhibited highly efficient NIR-light responsivity and assured MSCs viability up to 3 days. The administration of PDA-ICG-DOX nano-in-MSC tumoritropic units to microtumor models was performed in ultra-low adhesion surfaces for simulating in vitro the stem cell-tumor interactions observed in the in vivo scenario. Bioimaging analysis revealed hBM-MSCs adhesion to 3D cancer cells mass and MSCs-chemo-photothermal nanotherapeutics exhibited higher anti-tumor potential when compared to their standalone chemotherapy treated 3D tumor counterparts. Overall, the proposed methodology is suitable for evaluating MSCs-microtumors individualized interactions and enables a rapid high-throughput screening of tumoritropic therapies bioperformance.

Recent advances in the design of implantable insulin secreting heterocellular islet organoids

Islet transplantation has proved one of the most remarkable transmissions from an experimental curiosity into a routine clinical application for the treatment of type I diabetes (T1D). Current efforts for taking this technology one-step further are now focusing on overcoming islet donor shortage, engraftment, prolonged islet availability, post-transplant vascularization, and coming up with new strategies to eliminate lifelong immunosuppression. To this end, insulin secreting 3D cell clusters composed of different types of cells, also referred as heterocellular islet organoids, spheroids, or pseudoislets, have been engineered to overcome the challenges encountered by the current islet transplantation protocols. β-cells or native islets are accompanied by helper cells, also referred to as accessory cells, to generate a cell cluster that is not only able to accurately secrete insulin in response to glucose, but also superior in terms of other key features (e.g. maintaining a vasculature, longer durability in vivo and not necessitating immunosuppression after transplantation). Over the past decade, numerous 3D cell culture techniques have been integrated to create an engineered heterocellular islet organoid that addresses current obstacles. Here, we first discuss the different cell types used to prepare heterocellular organoids for islet transplantation and their contribution to the organoids design. We then introduce various cell culture techniques that are incorporated to prepare a fully functional and insulin secreting organoids with select features. Finally, we discuss the challenges and present a future outlook for improving clinical outcomes of islet transplantation.

Leachable-Free Fabrication of Hydrogel Foams Enabling Homogeneous Viability of Encapsulated Cells in Large-Volume Constructs

The popularity of cell-laden injectable hydrogels has steeply increased due to their compatibility with minimally invasive surgical procedures. However, the diffusion of indispensable molecules for cell survival through bulk hydrogel structures, particularly oxygen, is often limited to micrometric distances, often hampering cell viability or uniform tissue formation in constructs with clinically relevant sizes. The introduction of micropores in hydrogels or the use of oxygen-generating materials has enabled combining advantages of porous 3D scaffolds with the injectability properties of in situ-solidifying hydrogels. Here, cell-laden injectable gelatin methacryloyl (GelMA) foams are fabricated using a single polymer formulation. Air bubbles are introduced into GelMA solutions using a simple-to-implement method based on pulling/pushing the solution through a syringe. Human mesenchymal stem cells derived from the adipose tissue (hASCs) cultured in bulk hydrogels (diameter c.a. 5 mm) show low permanence in the core of the materials and stain for factors associated to hypoxia (hypoxia-inducible factor-1 alpha (HIF-1α)) after 7 days of culture. In opposition, cells cultured in optimized foams do not stain for HIF-1α, show high permanence, homogeneous viability, and consistent phenotype in the whole depth of the biomaterials, while secreting increased amounts of regenerative growth factors to the surrounding medium.

Recent progress in beetle-inspired superhydrophilic-superhydrophobic micropatterned water-collection materials

Biological creatures with unique surface wettability have long served as a source of inspiration for scientists and engineers. More specifically, certain beetle species in the Namib Desert have evolved to collect water from fog on their backs by way of wettability patterns, which attracted an ongoing interest in biomimetic studies. Bioinspired materials exhibiting extreme wetting properties, such as superhydrophilic and superhydrophobic surfaces, have attracted considerable attention because of their potential use in various applications. Combining these two extreme states of superhydrophilicity and superhydrophobicity on the same surface in precise two-dimensional micropatterns opens exciting new functionalities and possibilities for a wide variety of applications. In this review we briefly describe the water-harvesting mechanisms of a genus of Namib Desert beetle, Stenocarpa, consisting of the theory of wetting and transporting. Then we describe the methods for fabricating superhydrophilic-superhydrophobic patterns and highlight some of the newer and emerging applications of these patterned substrates that are currently being explored. Finally, we provide conclusions and outlook concerning the future development of bioinspired surfaces of patterned wettability.

Human Platelet Lysates-Based Hydrogels: A Novel Personalized 3D Platform for Spheroid Invasion Assessment

Fundamental physiologic and pathologic phenomena such as wound healing and cancer metastasis are typically associated with the migration of cells through adjacent extracellular matrix. In recent years, advances in biomimetic materials have supported the progress in 3D cell culture and provided biomedical tools for the development of models to study spheroid invasiveness. Despite this, the exceptional biochemical and biomechanical properties of human-derived materials are poorly explored. Human methacryloyl platelet lysates (PLMA)-based hydrogels are herein proposed as reliable 3D platforms to sustain in vivo-like cell invasion mechanisms. A systematic analysis of spheroid viability, size, and invasiveness is performed in three biomimetic materials: PLMA hydrogels at three different concentrations, poly(ethylene glycol) diacrylate, and Matrigel. Results demonstrate that PLMA hydrogels perfectly support the recapitulation of the tumor invasion behavior of cancer cell lines (MG-63, SaOS-2, and A549) and human bone-marrow mesenchymal stem cell spheroids. The distinct invasiveness ability of each cell type is reflected in the PLMA hydrogels and, furthermore, different mechanical properties produce an altered invasive behavior. The herein presented human PLMA-based hydrogels could represent an opportunity to develop accurate cell invasiveness models and open up new possibilities for humanized and personalized high-throughput screening and validation of anticancer drugs.

All-in-One Hydrogel Realizing Adipose-Derived Stem Cell Spheroid Production and In Vivo Injection via "Gel-Sol" Transition for Angiogenesis in Hind Limb Ischemia

Adipose-derived stem cell (ASC) spheroids exhibit enhanced angiogenic efficacy toward ischemia treatment. Thus, it is necessary to develop an all-in-one platform that enables efficient spheroid production, collection, and injectable implantation in vivo. The present study fabricated a poly(l-glutamic acid) (PLGA)-based porous hydrogel that can not only produce ASC spheroids but also conveniently collect spheroids for in vivo implantation via minimally invasive injection to treat hind limb ischemia. PLGA was cross-linked with cystamine (Cys), which contains disulfide bonds, to form a porous hydrogel that could realize "gel-sol" transition by the reduction effect of glutathione (GSH). For one thing, it was found that the introduction of the disulfide bond in the PLGA hydrogel promoted cellular adhesion via combining fibronectin, preventing the formation of spheroids, while the introduction of polyethylene glycol monomethyl ether (mPEG) could disturb the effect of the disulfide bond on cellular adhesion, supporting spheroid formation inside the porous hydrogel. For another, the porous hydrogel transferred into a syringe could turn into liquid polymer solution within about 40 min for collection of the produced spheroids and in vivo injection. In addition, because of the lubrication of polymer solution, the spheroids were protected during the injection of the spheroids/polymer suspensoid through a 25G syringe needle, avoiding damages from shearing. After the in vivo injection, the enhanced paracrine secretion of ASC spheroids resulted in promoted angiogenesis and muscle regeneration, exhibiting obvious therapeutic effect on limb ischemia in mice after 21 days. At the same time, PLGA-based material exhibited well-performed biocompatibility in vivo.

Micro-/Nanostructured Interface for Liquid Manipulation and Its Applications

Understanding the relationship between liquid manipulation and micro-/nanostructured interfaces has gained much attention due to the wide potential applications in many fields, such as chemical and biomedical assays, environmental protection, industry, and even daily life. Much work has been done to construct various materials with interfacial liquid manipulation abilities, leading to a range of interesting applications. Herein, different fabrication methods from the top-down approach to the bottom-up approach and subsequent surface modifications of micro-/nanostructured interfaces are first introduced. Then, interactions between the surface and liquid, including liquid wetting, liquid transportation, and a number of corresponding models, together with the definition of hydrophilic/hydrophobic, oleophilic/olephobic, the definition and mechanism of superwetting, including superhydrophobicity, superhydrophilicity, and superoleophobicity, are presented. The micro-/nanostructured interface, with major applications in self-cleaning, antifogging, anti-icing, anticorrosion, drag-reduction, oil-water separation, water collection, droplet (micro)array, and surface-directed liquid transport, is summarized, and the mechanisms underlying each application are discussed. Finally, the remaining challenges and future perspectives in this area are included.

One-Step Rapid Fabrication of Cell-Only Living Fibers

Cellular aggregates are used as relevant regenerative building blocks, tissue models, and cell delivery platforms. Biomaterial-free structures are often assembled either as 2D cell sheets or spherical microaggregates, both incompatible with free-form deposition, and dependent on challenging processes for macroscale 3D upscaling. The continuous and elongated nature of fiber-shaped materials enables their deposition in unrestricted multiple directions. Cellular fiber fabrication has often required exogenously provided support proteins and/or the use of biomaterial-based sacrificial templates. Here, the rapid (<24 h) assembly of fiberoids is reported: living centimeter-long scaffold-free fibers of cells produced in the absence of exogenous materials or supplements. Adipose-derived mesenchymal stem cell fiberoids can be easily modulated into complex multidimensional geometries and show tissue-invasive properties while keeping the secretion of trophic factors. Proangiogenic properties studied on a chick chorioallantoic membrane in an ovo model are observed for heterotypic fiberoids containing endothelial cells. These micro-to-macrotissues may find application as morphogenic therapeutic and tissue-mimetic building blocks, with the ability to integrate 3D and 4D full biological materials.

Durable superamphiphobic silica aerogel surfaces for the culture of 3D cellular spheroids

The 3D multicellular spheroids with intact cell-cell junctions have major roles in biological research by virtue of their unique advantage of mimicking the cellular physiological environments. In this work, a durable superamphiphobic silica aerogel surface (SSAS) has been fabricated for the upward culture of 3D multicellular spheroids. Poly(3,4-ethylenedioxythiophene) (PEDOT) was first electrodeposited on a conductive steel mesh as a first template for porous silica coating. Soot particles were then applied as a second template to construct a cauliflower-like silica aerogel nanostructure. After fluorination, a hierarchical structure with re-entrant curvature was finally fabricated as a durable superamphiphobic surface. This superamphiphobic surface also presented excellent antifouling towards biomacromolecules and cells, which has been demonstrated by the successful upward culture of cell spheroids. The upward culture makes the observation of cellular behavior in situ possible, holding great potential for 3D cellular evaluation in vitro.

Droplet on Soft Shuttle: Electrowetting-on-Dielectric Actuation of Small Droplets

Here, we introduce the novel concept of a "soft shuttle" for transportation, manipulation, and diffusion studies of small liquid droplets using electrowetting on the dielectric mechanism. This method enables manipulation of droplets several times smaller than the electrode size and, importantly, minimizes evaporation, contamination, and exposure of the sample to high voltages. We demonstrate various modes of droplet loading, transporting, and unloading. Using advanced imaging processing techniques, we obtained detailed information about the shuttle and droplet centroids. Furthermore, varying water concentration on the soft shuttle allows for modulation of the diffusion kinetics of samples into the shuttle, which also can be controlled with soft shuttle actuation velocity. We believe that this novel approach for the manipulation of droplets will advance the field of droplet-based open microfluidics and can be potentially useful for applications in biotechnology, diagnostics, or analytical chemistry.

Fabrication of size-controllable human mesenchymal stromal cell spheroids from micro-scaled cell sheets

Recently, stromal cell spheroids have been actively studied for use in tissue regeneration. In this study, we report a method for the fabrication of size-controllable stromal cell spheroids in different sizes from micro-scaled cell sheets (μCS) using thermosensitive hydrogels and investigated their effects on stromal cell function. Mesenchymal stromal cells isolated from different tissues such as human turbinate tissue, bone marrow, and adipose tissue were adhered selectively to each micro-pattern (squares with widths of 100 and 400 μm) on the surface of the hydrogel and formed μCS. The diameters of the spheroids were modulated by the size of the patterns (45 ± 5 and 129 ± 4 μm in diameter for the 100 and 400 μm micro-patterns, respectively) and the seeding density (129 ± 4, 149 ± 6, and 163 ± 6 μm for 5.0, 10.0, and 15.0 × 10⁴ cells cm^-2, respectively, on 400 μm micro-pattern). In addition, the spheroids were successfully fabricated regardless of stromal cell origin, and the diameter of the spheroids was also affected by cell spreading area on a cell culture dish. Stemness markers were highly expressed in the spheroids regardless of the spheroid size. Furthermore, an increase in E-cadherin and decrease in N-cadherin gene expression showed the stable formation of spheroids of different sizes. Gene expression levels of hypoxia inducible factors and secretion of vascular endothelial growth factor were increased (13.2 ± 1.4, 325 ± 83.4 and 534.3 ± 121.5 pg ng^-1 DNA in a monolayer, and 100 and 400 μm micro-patterned spheroids, respectively) proportional to the diameters of the spheroids. The size of spheroids were maintained even after injection, cryopreservation and 7 d of suspension culture with high viability (∼90%). In conclusion, this novel technique to fabricate spheroids with controlled size could be widely applied in various applications that require a controlled size in regenerative medicine.

Facile One Step Formation and Screening of Tumor Spheroids Using Droplet-Microarray Platform

Tumor spheroids or microtumors are important 3D in vitro tumor models that closely resemble a tumor's in vivo "microenvironment" compared to 2D cell culture. Microtumors are widely applied in the fields of fundamental cancer research, drug discovery, and precision medicine. In precision medicine tumor spheroids derived from patient tumor cells represent a promising system for drug sensitivity and resistance testing. Established and commonly used platforms for routine screenings of cell spheroids, based on microtiter plates of 96- and 384-well formats, require relatively large numbers of cells and compounds, and often lead to the formation of multiple spheroids per well. In this study, an application of the Droplet Microarray platform, based on hydrophilic-superhydrophobic patterning, in combination with the method of hanging droplet, is demonstrated for the formation of highly miniaturized single-spheroid-microarrays. Formation of spheroids from several commonly used cancer cell lines in 100 nL droplets starting with as few as 150 cells per spheroid within 24-48 h is demonstrated. Established methodology carries a potential to be adopted for routine workflows of high-throughput compound screening in 3D cancer spheroids or microtumors, which is crucial for the fields of fundamental cancer research, drug discovery, and precision medicine.

Integrated cancer tissue engineering models for precision medicine

Tumors are not merely cancerous cells that undergo mindless proliferation. Rather, they are highly organized and interconnected organ systems. Tumor cells reside in complex microenvironments in which they are subjected to a variety of physical and chemical stimuli that influence cell behavior and ultimately the progression and maintenance of the tumor. As cancer bioengineers, it is our responsibility to create physiologic models that enable accurate understanding of the multi-dimensional structure, organization, and complex relationships in diverse tumor microenvironments. Such models can greatly expedite clinical discovery and translation by closely replicating the physiological conditions while maintaining high tunability and control of extrinsic factors. In this review, we discuss the current models that target key aspects of the tumor microenvironment and their role in cancer progression. In order to address sources of experimental variation and model limitations, we also make recommendations for methods to improve overall physiologic reproducibility, experimental repeatability, and rigor within the field. Improvements can be made through an enhanced emphasis on mathematical modeling, standardized in vitro model characterization, transparent reporting of methodologies, and designing experiments with physiological metrics. Taken together these considerations will enhance the relevance of in vitro tumor models, biological understanding, and accelerate treatment exploration ultimately leading to improved clinical outcomes. Moreover, the development of robust, user-friendly models that integrate important stimuli will allow for the in-depth study of tumors as they undergo progression from non-transformed primary cells to metastatic disease and facilitate translation to a wide variety of biological and clinical studies.

Transparent Bioreactors Based on Nanoparticle-Coated Liquid Marbles for in Situ Observation of Suspending Embryonic Body Formation and Differentiation

Transparent liquid marbles coated with hydrophobic silica nanoparticles were used as micro-bioreactors for embryonic stem cell (ESC) culturing. The high transparency of silica liquid marbles enables real-time and in situ monitoring of embryonic body (EB) formation and differentiation. The experimental result shows that ESCs can aggregate with each other close to the bottom of the liquid marble and form EBs, while remaining suspended in the culture media. The differentiation of the suspending EBs into contractile cardiomyocytes has been demonstrated inside the transparent liquid marbles, which enable the in situ microscopic observation. It was also found, through comparison, that ESCs in a bare sessile drop placed on a superhydrophobic substrate tend to anchor onto the substrate and then differentiate following the normal way of cell spreading, i.e., withdrawal from the cell cycle, fusion with nascent myotubes, and final differentiation into cardiomyocytes. In contrast, liquid marble particle shells weaken the adhesion of spherical EBs to the substrate, encouraging them to differentiate in suspension into cardiomyocytes, without anchoring. The results of this study highlight the promising performance of liquid marbles as "one-pot" micro-bioreactors for EB formation and differentiation.

Versatile Fabrication of Size- and Shape-Controllable Nanofibrous Concave Microwells for Cell Spheroid Formation

Although the microfabrication techniques for microwells enabled to guide physiologically relevant three-dimensional cell spheroid formation, there have been substantial interests to more closely mimic nano/microtopographies of in vivo cellular microenvironment. Here, we developed a versatile fabrication process for nanofibrous concave microwells (NCMs) with a controllable size and shape. The key to the fabrication process was the use of an array of hemispherical convex electrolyte solution drops as the grounded collector for electrospinning, which greatly improved the degree of freedom of the size, shape, and curvature of an NCM. A polymer substrate with through-holes was prepared for the electrolyte solution to come out through the hole and to naturally form a convex shape because of surface tension. Subsequent electrolyte-assisted electrospinning process enabled to achieve various arrays of NCMs of triangular, rectangular, and circular shapes with sizes ranging from 1000 μm down to 250 μm. As one example of biomedical applications, the formation of human hepatoma cell line (HepG2) spheroids was demonstrated on the NCMs. The results indicated that the NCM enabled uniform, size-controllable spheroid formation of HepG2 cells, resulting in 1.5 times higher secretion of albumin from HepG2 cells on the NCM on day 14 compared with those on a nanofibrous flat microwell as a control.

Surface-Engineered Paper Hanging Drop Chip for 3D Spheroid Culture and Analysis

Protein corona coated onto the hydrophilic cellulose fiber turns into hydrophobic upon UV irradiation without hindering the porosity of the paper while simultaneously reducing nonspecific adsorption. Taking advantage of the biofouling-resistant, hydrophobic, and fluid transport through property, we demonstrated hanging drop three-dimensional (3D) spheroid culture and in-site analysis, including drug testing, time-dependent detection of secreted protein, and fluorescence staining without disturbing the spheroids. This single hanging drop system can also be extended to a networked hanging drop chip to mimic in vivo microphysiology by combining with wax-patterned microfluidic channels, where well-to-well interaction can be accurately controlled in a passive manner. As a proof of concept, the effects of a concentration gradient of nutrient and variable dosage of anticancer drugs were studied in the 3D spheroids cultured on paper. The experimental results suggested that a complex network device could be fabricated on a large scale on demand at a minimal cost for 3D spheroid culture. Our method demonstrates a future possibility for paper as a low cost, high-throughput 3D spheroid-based "body-on-a-chip" platform material.

Design of spherically structured 3D in vitro tumor models -Advances and prospects

Three-dimensional multicellular tumor models are receiving an ever-growing focus as preclinical drug-screening platforms due to their potential to recapitulate major physiological features of human tumors in vitro. In line with this momentum, the technologies for assembly of 3D microtumors are rapidly evolving towards a comprehensive inclusion of tumor microenvironment elements. Customized spherically structured platforms, including microparticles and microcapsules, provide a robust and scalable technology to imprint unique biomolecular tumor microenvironment hallmarks into 3D in vitro models. Herein, a comprehensive overview of novel advances on the integration of tumor-ECM components and biomechanical cues into 3D in vitro models assembled in spherical shaped platforms is provided. Future improvements regarding spatiotemporal/mechanical adaptability, and degradability, during microtumors in vitro 3D culture are also critically discussed considering the realistic potential of these platforms to mimic the dynamic tumor microenvironment. From a global perspective, the production of 3D multicellular spheroids with tumor ECM components included in spherical models will unlock their potential to be used in high-throughput screening of therapeutic compounds. It is envisioned, in a near future, that a combination of spherically structured 3D microtumor models with other advanced microfluidic technologies will properly recapitulate the flow dynamics of human tumors in vitro.

STATEMENT OF SIGNIFICANCE

The ability to correctly mimic the complexity of the tumor microenvironment in vitro is a key aspect for the development of evermore realistic in vitro models for drug-screening and fundamental cancer biology studies. In this regard, conventional spheroid-based 3D tumor models, combined with spherically structured biomaterials, opens the opportunity to precisely recapitulate complex cell-extracellular matrix interactions and tumor compartmentalization. This review provides an in-depth focus on current developments regarding spherically structured scaffolds engineered into in vitro 3D tumor models, and discusses future advances toward all-encompassing platforms that may provide an improved in vitro/in vivo correlation in a foreseeable future.

Droplet Microarrays: From Surface Patterning to High-Throughput Applications

High-throughput screening of live cells and chemical reactions in isolated droplets is an important and growing method in areas ranging from studies of gene functions and the search for new drug candidates, to performing combinatorial chemical reactions. Compared with microfluidics and well plates, the facile fabrication, high density, and open structure endow droplet microarrays on planar surfaces with great potential in the development of next-generation miniaturized platforms for high-throughput applications. Surfaces with special wettability have served as substrates to generate and/or address droplets microarrays. Here, the formation of droplet microarrays with designed geometry on chemically prepatterned surfaces is briefly described and some of the newer and emerging applications of these microarrays that are currently being explored are highlighted. Next, some of the available technologies used to add (bio-)chemical libraries to each droplet in parallel are introduced. Current challenges and future prospects that would benefit from using such droplet microarrays are also discussed.

Simultaneous detection of multiple HPV DNA via bottom-well microfluidic chip within an infra-red PCR platform

Portable Polymerase Chain Reaction (PCR) devices combined with microfluidic chips or lateral flow stripes have shown great potential in the field of point-of-need testing (PoNT) as they only require a small volume of patient sample and are capable of presenting results in a short time. However, the detection for multiple targets in this field leaves much to be desired. Herein, we introduce a novel PCR platform by integrating a bottom-well microfluidic chip with an infra-red (IR) excited temperature control method and fluorescence co-detection of three PCR products. Microfluidic chips are utilized to partition different samples into individual bottom-wells. The oil phase in the main channel contains multi-walled carbon nanotubes which were used as a heat transfer medium that absorbs energy from the IR-light-emitting diode (LED) and transfers heat to the water phase below. Cyclical rapid heating and cooling necessary for PCR are achieved by alternative power switching of the IR-LED and Universal Serial Bus (USB) mini-fan with a pulse width modulation scheme. This design of the IR-LED PCR platform is economic, compact, and fully portable, making it a promising application in the field of PoNT. The bottom-well microfluidic chip and IR-LED PCR platform were combined to fulfill a three-stage thermal cycling PCR for 40 cycles within 90 min for Human Papilloma Virus (HPV) detection. The PCR fluorescent signal was successfully captured at the end of each cycle. The technique introduced here has broad applications in nucleic acid amplification and PoNT devices.

Superwettable Electrochemical Biosensor toward Detection of Cancer Biomarkers

Bioinspired superwettable micropatterns that combine two extreme states of superhydrophobicity and superhydrophilicity with the ability to enrich and absorb microdroplets are suitable for versatile and robust sensing applications. Here we introduce a superwettable microchip that integrates superhydrophobic-superhydrophilic micropatterns and a nanodendritic electrochemical biosensor toward the detection of prostate cancer biomarkers. On the superwettable microchip, the superhydrophobic area could confine the microdroplets in superhydrophilic microwells; such behavior is extremely helpful for reducing the amount of analytical solution. In contrast, superhydrophilic microwells exhibit a high adhesive force toward microdroplets, and the nanodendritic structures can improve probe-binding capacity and response signals, thus greatly enhancing the sensitivity. Sensitive and selective detection of prostate cancer biomarkers including miRNA-375, miRNA-141, and prostate-specific antigen on a single microchip is also achieved. Such a superwettable microchip with high sensitivity, low sample volume, and upside-down detection capability in a single microdroplet shows great potential to fabricate portable devices toward complex biosensing applications.

Cell-Based Microarrays Using Superhydrophobic Platforms Patterned with Wettable Regions

The use of patterned platforms to print cellular arrays enables the high-throughput study of cell behavior under a multitude of different conditions. This rapid, cost-saving and systematic way of acquiring biologically relevant information has found application in diverse scientific and industrial fields. In an initial stage of development, platforms targeting high-throughput cellular studies were restricted to standard two-dimensional (2D) setups. The design of novel platforms compatible with three-dimensional (3D) cell culture arose after the elucidation of the extreme importance of culturing cells in matrices resembling the native extracellular matrix-cells and cell-cell interactions. This need for biomimetic environments has been established in fields like drug discovery and testing, disease model development, and regenerative medicine. Here, we provide a description of the processing of flat platforms based on wettability contrast, compatible with the high-throughput generation and study of cell response in 3D biomaterials, including cell-laden hydrogels and porous 3D scaffolds. The application of the aforementioned platforms to produce 3D microtissues, which may find application as tissue models for drug screening or as biomimetic building blocks for tissue engineering, is also addressed. In this chapter, a description of the steps for (1) high-throughput platform processing, (2) deposition of cell and biomaterial arrays, and (3) image-based results screening is provided.

Mask-free fabrication of a versatile microwell chip for multidimensional cellular analysis and drug screening

Cells are frequently studied because they are basic structural, functional, and biological units of living organisms. Extracting features from cellular behaviors can facilitate decision making in medical diagnoses and represents an important aspect in the development of biomedical engineering. Previous studies have just focused on either the individual cell or cell clusters separately, which leads to a great lack of information. Microwell technologies could address the challenges of in vitro cellular studies, from individual cell studies to 3D functional assays, by providing more information from smaller sample volumes and enabling the incorporation of low-cost high-throughput assays in the drug discovery process. To this end, the present study describes an easy-to-use method for fabricating a versatile microwell chip that utilizes a digital micro-mirror device printing system, and the chip can be employed in multidimensional cellular analysis, ranging from the single cell to the 3D spheroid level. The microwell manufacturing process, using a digital mask in place of a conventional physical mask, is based on shadowed light and is full of flexibility. Three different dimensions (single cell (1D), cell monolayer (2D) and cell spheroid (3D)) of one cell type can be formed using a microwell array and the analyses of biological characteristics are achieved separately. Single cells and cell clusters can be controlled via customized geometries of microfabricated selectively adhesive poly(ethylene glycol) diacrylate (PEGDA) wells. The effects of shape on cellular growth and hybrid tissue layers were investigated by peeling off the microwells. Furthermore, 3D multicellular spheroids were successfully established in a controllable and high-throughput format. Preclinical drug screening was investigated and distinct differences were observed in the tolerance response to drug testing between the 2D and 3D conditions. The study results further demonstrate that the high-density microwell chip is an easy-to-use multidimensional cellular analysis and rapid drug screening technique, and it could be easily adapted for a wide range of biological research applications.

Open Fluidics: A Cell Culture Flow System Developed Over Wettability Contrast-Based Chips

Biological tissues are recurrently exposed to several dynamic mechanical forces that influence cell behavior. On this work, the focus is on the shear stress forces induced by fluid flow. The study of flow-induced effects on cells leads to important advances in cardiovascular, cancer, stem cell, and bone biology understanding. These studies are performed using cell culture flow (CCF) systems, mainly parallel plate flow chambers (PPFC), and microfluidic systems. Here, it is proposed an original CCF system based on the open fluidics concept. The system is developed using a planar superhydrophobic platform with hydrophilic paths. The paths work as channels to drive cell culture medium flows without using walls for liquid confinement. The liquid streams are controlled just based on the wettability contrast. To validate the concept, the effect of the shear stress stimulus in the osteogenic differentiation of C2C12 myoblast cells is studied. Combining bone morphogenic protein (specifically BMP-2) stimulation with this mechanical stimulus, a synergistic effect is found on osteoblast differentiation. This effect is confirmed by the enhancement of alkaline phosphatase activity, a well-known early marker of osteogenic differentiation. The suggested CCF system combines characteristics and advantages of both the PPFC and microfluidic systems.

Biocompatible hollow polymeric particles produced by a mild solvent- and template free strategy

Macroscopic hollow polymeric particles are attractive materials for various applications such as surgery, food industry, agriculture, etc. However, protocols reporting their synthesis have hitherto made use of organic solvents and/or sacrificial templates, compromising the encapsulation of different bioactive compounds and the process yield. Here, millimeter-size, hollow polymeric particles were synthesized, for the first time, in a solvent- and template free manner onto superhydrophobic surfaces (SHS). The particles were produced upon assembly and double superficial crosslinking of liquid droplets of DNA and methacrylamide chitosan aqueous solutions (CH:MA), leading to liquid-core particles with a hardened hydrogel shell. The particles displayed appealing physical and biological properties. The millimeter-size hydrogel shell, resulting from the double ionic/covalent crosslinking of CH:MA, endowed the hollow particles with softness to the touch and an outstanding structural stability against manipulation by hand and with forceps. Meanwhile, the liquid DNA core guaranteed a biocompatible cell encapsulation followed by a superior release and proliferation of viable cells, as compared to solid CH:MA particles prepared as a blank. Particles with these characteristics show promise for surgical protocols practiced in Tissue Engineering and Regenerative Medicine, where manipulable and biocompatible synthetic implants are often needed to supply living cells and other sensitive bioactive compounds.

Biocompatible hollow polymeric particles produced by a mild solvent- and template free strategy

Macroscopic hollow polymeric particles are attractive materials for various applications such as surgery, food industry, agriculture, etc. However, protocols reporting their synthesis have hitherto made use of organic solvents and/or sacrificial templates, compromising the encapsulation of different bioactive compounds and the process yield. Here, millimeter-size, hollow polymeric particles were synthesized, for the first time, in a solvent- and template free manner onto superhydrophobic surfaces (SHS). The particles were produced upon assembly and double superficial crosslinking of liquid droplets of DNA and methacrylamide chitosan aqueous solutions (CH:MA), leading to liquid-core particles with a hardened hydrogel shell. The particles displayed appealing physical and biological properties. The millimeter-size hydrogel shell, resulting from the double ionic/covalent crosslinking of CH:MA, endowed the hollow particles with softness to the touch and an outstanding structural stability against manipulation by hand and with forceps. Meanwhile, the liquid DNA core guaranteed a biocompatible cell encapsulation followed by a superior release and proliferation of viable cells, as compared to solid CH:MA particles prepared as a blank. Particles with these characteristics show promise for surgical protocols practiced in Tissue Engineering and Regenerative Medicine, where manipulable and biocompatible synthetic implants are often needed to supply living cells and other sensitive bioactive compounds.

Emerging tumor spheroids technologies for 3D in vitro cancer modeling

Cancer is a leading cause of mortality and morbidity worldwide. Around 90% of deaths are caused by metastasis and just 10% by primary tumor. The advancement of treatment approaches is not at the same rhythm of the disease; making cancer a focal target of biomedical research. To enhance the understanding and prompts the therapeutic delivery; concepts of tissue engineering are applied in the development of in vitro models that can bridge between 2D cell culture and animal models, mimicking tissue microenvironment. Tumor spheroid represents highly suitable 3D organoid-like framework elucidating the intra and inter cellular signaling of cancer, like that formed in physiological niche. However, spheroids are of limited value in studying critical biological phenomenon such as tumor-stroma interactions involving extra cellular matrix or immune system. Therefore, a compelling need of tailoring spheroid technologies with physiologically relevant biomaterials or in silico models, is ever emerging. The diagnostic and prognostic role of spheroids rearrangements within biomaterials or microfluidic channel is indicative of patient management; particularly for the decision of targeted therapy. Fragmented information on available in vitro spheroid models and lack of critical analysis on transformation aspects of these strategies; pushes the urge to comprehensively overview the recent technological advancements (e.g. bioprinting, micro-fluidic technologies or use of biomaterials to attain the third dimension) in the shed of translationable cancer research. In present article, relationships between current models and their possible exploitation in clinical success is explored with the highlight of existing challenges in defining therapeutic targets and screening of drug efficacy.