User-defined morphogen patterning for directing human cell fate stratification

Bioengineering innovations for neural organoids with enhanced fidelity and function

Neural organoids have been utilized to recapitulate different aspects of the developing nervous system. While hailed as promising experimental tools for studying human neural development and neuropathology, current neural organoids do not fully recapitulate the anatomy or microcircuitry-level functionality of the developing brain, spinal cord, or peripheral nervous system. In this review, we discuss emerging bioengineering approaches that control morphogen signals and biophysical microenvironments, which have improved the efficiency, fidelity, and utility of neural organoids. Furthermore, advancements in bioengineered tools have facilitated more sophisticated analyses of neural organoid functions and applications, including improved neural-bioelectronic interfaces and organoid-based information processing. Emerging bioethical issues associated with advanced neural organoids are also discussed. Future opportunities of neural organoid research lie in enhancing their fidelity, maturity, and complexity and expanding their applications in a scalable manner.

A microfluidic platform for anterior-posterior human endoderm patterning via countervailing morphogen gradients in vitro

Understanding how morphogen gradients spatially pattern tissues is a fundamental question in developmental biology but can be difficult to directly address using conventional approaches. Here, we expose hPSC-derived endoderm cells to countervailing gradients of anteriorizing and posteriorizing signals using a widely available microfluidic device. This approach yielded spatially patterned cultures comprising anterior foregut (precursor to the thyroid, esophagus, and lungs) and mid/hindgut (precursor to the intestines) cells, whose identities were confirmed using single-cell RNA sequencing (scRNA-seq). By exposing stem cells to externally applied signaling gradients, this widely accessible microfluidic platform should accelerate the production of spatially patterned tissues, complementing internally self-organizing organoids. Applying artificial morphogen gradients in vitro may also illuminate how developing tissues interpret signaling gradients in systems that are not readily accessible for in vivo studies.

Microgels With Electrostatically Controlled Molecular Affinity to Direct Morphogenesis

Concentration gradients of soluble signaling molecules-morphogens-determine the cellular organization in tissue development. Morphogen-releasing microgels have shown potential to recapitulate this principle in engineered tissue constructs, however, with limited control over the molecular cues in space and time. Inspired by the functionality of sulfated glycosaminoglycans (sGAGs) in morphogen signaling in vivo, a library of sGAG-based microgels is developed and designated as µGel Units to Instruct Development (µGUIDEs). Adjustment of the microgel's sGAG sulfation patterns and concentration enabled the programming of electrostatic affinities that control the release of morphogens. Based on computational analyses of molecular transport processes, µGUIDEs provided unprecedented precision in the spatiotemporal modulation of vascular endothelial growth factor (VEGF) gradients in a microgel-in-gel vasculogenesis model and kidney organoid cultures. The versatile approach offers new options for creating morphogen signaling centers to advance the understanding of tissue and organ development.

Modeling development using hydrogels

The development of multicellular complex organisms relies on coordinated signaling from the microenvironment, including both biochemical and mechanical interactions. To better understand developmental biology, increasingly sophisticated in vitro systems are needed to mimic these complex extracellular features. In this Primer, we explore how engineered hydrogels can serve as in vitro culture platforms to present such signals in a controlled manner and include examples of how they have been used to advance our understanding of developmental biology.

Microfluidic systems for modeling human development

The proper development and patterning of organs rely on concerted signaling events emanating from intracellular and extracellular molecular and biophysical cues. The ability to model and understand how these microenvironmental factors contribute to cell fate decisions and physiological processes is crucial for uncovering the biology and mechanisms of life. Recent advances in microfluidic systems have provided novel tools and strategies for studying aspects of human tissue and organ development in ways that have previously been challenging to explore ex vivo. Here, we discuss how microfluidic systems and organs-on-chips provide new ways to understand how extracellular signals affect cell differentiation, how cells interact with each other, and how different tissues and organs are formed for specialized functions. We also highlight key advancements in the field that are contributing to a broad understanding of human embryogenesis, organogenesis and physiology. We conclude by summarizing the key advantages of using dynamic microfluidic or microphysiological platforms to study intricate developmental processes that cannot be accurately modeled by using traditional tissue culture vessels. We also suggest some exciting prospects and potential future applications of these emerging technologies.

Reaction-diffusion phenomena in antagonistic bipolar diffusion fields

Operating natural or artificial chemical systems requires nonequilibrium conditions under which temporal and spatial control of the process is realizable. Open reaction-diffusion systems provide a general way to create such conditions. A key issue is the proper design of reactors in which the nonequilibrium conditions can be maintained. A hydrogel with flow-through channels is a simple, flexible, and easy-to-make device in which chemical reactions are performed in the diffusion field of localized separated sources of reactants. Two reactants separated in two channels create a bipolar antagonistic diffusion field, where the reaction intermediates firmly separate in space. Numerical simulations and corresponding experiments are performed to present this inhomogeneous diffusion field-induced chemical separation in sequential reactions. A remarkable result of this bipolar spatial control is localized wave phenomena in a nonlinear activatory-inhibitory reaction. These findings may help design functioning artificial nonequilibrium systems with the desired spatial separation of chemicals.

Recent Advancements in Engineering Strategies for Manipulating Neural Stem Cell Behavior

Purpose of Review

Stem cells are exquisitely sensitive to biophysical and biochemical cues within the native microenvironment. This review focuses on emerging strategies to manipulate neural cell behavior using these influences in three-dimensional (3D) culture systems.

Recent Findings

Traditional systems for neural cell differentiation typically produce heterogeneous populations with limited diversity rather than the complex, organized tissue structures observed in vivo. Advancements in developing engineering tools to direct neural cell fates can enable new applications in basic research, disease modeling, and regenerative medicine.

Summary

This review article highlights engineering strategies that facilitate controlled presentation of biophysical and biochemical cues to guide differentiation and impart desired phenotypes on neural cell populations. Specific highlighted examples include engineered biomaterials and microfluidic platforms for spatiotemporal control over the presentation of morphogen gradients.

Engineering Heart Morphogenesis

Recent advances in stem cell biology and tissue engineering have laid the groundwork for building complex tissues in a dish. We propose that these technologies are ready for a new challenge: recapitulating cardiac morphogenesis in vitro. In development, the heart transforms from a simple linear tube to a four-chambered organ through a complex process called looping. Here, we re-examine heart tube looping through the lens of an engineer and argue that the linear heart tube is an advantageous starting point for tissue engineering. We summarize the structures, signaling pathways, and stresses in the looping heart, and evaluate approaches that could be used to build a linear heart tube and guide it through the process of looping.