Manufacturing a Bone Marrow-On-A-Chip Using Maskless Photolithography

Why Animal Experiments Are Still Indispensable in Bone Research: A Statement by the European Calcified Tissue Society

Major achievements in bone research have always relied on animal models and in vitro systems derived from patient and animal material. However, the use of animals in research has drawn intense ethical debate and the complete abolition of animal experimentation is demanded by fractions of the population. This phenomenon is enhanced by the reproducibility crisis in science and the advance of in vitro and in silico techniques. 3D culture, organ-on-a-chip, and computer models have improved enormously over the last few years. Nevertheless, the overall complexity of bone tissue cross-talk and the systemic and local regulation of bone physiology can often only be addressed in entire vertebrates. Powerful genetic methods such as conditional mutagenesis, lineage tracing, and modeling of the diseases enhanced the understanding of the entire skeletal system. In this review endorsed by the European Calcified Tissue Society (ECTS), a working group of investigators from Europe and the US provides an overview of the strengths and limitations of experimental animal models, including rodents, fish, and large animals, as well the potential and shortcomings of in vitro and in silico technologies in skeletal research. We propose that the proper combination of the right animal model for a specific hypothesis and state-of-the-art in vitro and/or in silico technology is essential to solving remaining important questions in bone research. This is crucial for executing most efficiently the 3R principles to reduce, refine, and replace animal experimentation, for enhancing our knowledge of skeletal biology, and for the treatment of bone diseases that affect a large part of society. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Organoids and microphysiological systems: Promising models for accelerating AAV gene therapy studies

The FDA has predicted that at least 10-20 gene therapy products will be approved by 2025. The surge in the development of such therapies can be attributed to the advent of safe and effective gene delivery vectors such as adeno-associated virus (AAV). The enormous potential of AAV has been demonstrated by its use in over 100 clinical trials and the FDA’s approval of two AAV-based gene therapy products. Despite its demonstrated success in some clinical settings, AAV-based gene therapy is still plagued by issues related to host immunity, and recent studies have suggested that AAV vectors may actually integrate into the host cell genome, raising concerns over the potential for genotoxicity. To better understand these issues and develop means to overcome them, preclinical model systems that accurately recapitulate human physiology are needed. The objective of this review is to provide a brief overview of AAV gene therapy and its current hurdles, to discuss how 3D organoids, microphysiological systems, and body-on-a-chip platforms could serve as powerful models that could be adopted in the preclinical stage, and to provide some examples of the successful application of these models to answer critical questions regarding AAV biology and toxicity that could not have been answered using current animal models. Finally, technical considerations while adopting these models to study AAV gene therapy are also discussed.

Strategies for vascularized skin models in vitro

As the largest organ of the human body, the skin has a complex multi-layered structure. The composition of the skin includes cells, extracellular matrix (ECM), vascular networks, and other appendages. Because of the shortage of donor sites, skin substitutes are of great significance in the field of skin tissue repair. Moreover, skin models for disease research, drug screening, and cosmetic testing fall far short of the demand. Skin tissue engineering has made remarkable progress in developing skin models over the years. However, there are still several problems to be resolved. One of the crucial aspects is the lack of vascular systems for nutrient transport and waste disposal. Here, we will focus on the discussion and analysis of advanced manufacturing strategies for prevascularized skin, such as a scaffold-based method, cell coating technology, cell sheet engineering, skin-on-a-chip, and three-dimensional (3D) bioprinting. These key challenges, which restrict the prevascularized skin and provide perspectives on future directions will also be highlighted.

Bone Marrow Niches of Hematopoietic Stem and Progenitor Cells

The mammalian hematopoietic system is remarkably efficient in meeting an organism’s vital needs, yet is highly sensitive and exquisitely regulated. Much of the organismal control over hematopoiesis comes from the regulation of hematopoietic stem cells (HSCs) by specific microenvironments called niches in bone marrow (BM), where HSCs reside. The experimental studies of the last two decades using the most sophisticated and advanced techniques have provided important data on the identity of the niche cells controlling HSCs functions and some mechanisms underlying niche-HSC interactions. In this review we discuss various aspects of organization and functioning of the HSC cell niche in bone marrow. In particular, we review the anatomy of BM niches, various cell types composing the niche, niches for more differentiated cells, metabolism of HSCs in relation to the niche, niche aging, leukemic transformation of the niche, and the current state of HSC niche modeling in vitro.

Rapid Prototyping of Organ-on-a-Chip Devices Using Maskless Photolithography

Organ-on-a-chip (OoC) and microfluidic devices are conventionally produced using microfabrication procedures that require cleanrooms, silicon wafers, and photomasks. The prototyping stage often requires multiple iterations of design steps. A simplified prototyping process could therefore offer major advantages. Here, we describe a rapid and cleanroom-free microfabrication method using maskless photolithography. The approach utilizes a commercial digital micromirror device (DMD)-based setup using 375 nm UV light for backside exposure of an epoxy-based negative photoresist (SU-8) on glass coverslips. We show that microstructures of various geometries and dimensions, microgrooves, and microchannels of different heights can be fabricated. New SU-8 molds and soft lithography-based polydimethylsiloxane (PDMS) chips can thus be produced within hours. We further show that backside UV exposure and grayscale photolithography allow structures of different heights or structures with height gradients to be developed using a single-step fabrication process. Using this approach: (1) digital photomasks can be designed, projected, and quickly adjusted if needed; and (2) SU-8 molds can be fabricated without cleanroom availability, which in turn (3) reduces microfabrication time and costs and (4) expedites prototyping of new OoC devices.

Hematopoietic progenitors polarize in contact with bone marrow stromal cells in response to SDF1

The fate of hematopoietic stem and progenitor cells (HSPCs) is regulated by their interaction with stromal cells in the bone marrow. However, the cellular mechanisms regulating HSPC interaction with these cells and their potential impact on HSPC polarity are still poorly understood. Here we evaluated the impact of cell–cell contacts with osteoblasts or endothelial cells on the polarity of HSPC. We found that an HSPC can form a discrete contact site that leads to the extensive polarization of its cytoskeleton architecture. Notably, the centrosome was located in proximity to the contact site. The capacity of HSPCs to polarize in contact with stromal cells of the bone marrow appeared to be specific, as it was not observed in primary lymphoid or myeloid cells or in HSPCs in contact with skin fibroblasts. The receptors ICAM, VCAM, and SDF1 were identified in the polarizing contact. Only SDF1 was independently capable of inducing the polarization of the centrosome–microtubule network.