IntroductionBioprinting has emerged as a promising technology for cartilage tissue engineering. In cartilage, the mechanical properties are closely associated with the extracellular matrix (ECM) and of paramount importance for tissue functionality. However, to date mechanical analysis of biofabricated cartilaginous constructs is often limited to single parameters, and a detailed analysis of the concomitant development of ECM and mechanical properties is lacking. Therefore, in this study, we investigate the post-fabrication development of the ECM and comprehensively analyze the large-strain viscoelastic properties of cartilaginous constructs made from mesenchymal stromal cells (MSC) in a hyaluronic acid (HA)-based bioink.MethodsMSC are embedded in a HA-based bioink and chondrogenically differentiated post-production for 6 weeks. A time-matched analysis is performed monitoring the ECM development represented by glycosaminoglycans and collagen as well as the changes in mechanical properties, such as hysteresis, classical shear modulus, nonlinearity and stress relaxation, using a multimodal testing approach at six different time points.ResultsDistinctly increasing amounts of ECM components are detected in the cartilaginous constructs over the whole cultivation period. Glycosaminoglycans and collagen content increase by 57- and 52-fold, respectively, from day 1 to day 42. In turn, the ECM development markedly influences the overall multimodal mechanical response over time, leading to distinct changes in nonlinear and stress relaxation behavior and a 265-fold increase in hysteresis and a 174-fold increase in classical shear modulus reaching 50 kPa in total. We find a strong correlation between the amount of glycosaminoglycans and collagen, and the classical shear modulus as well as the hysteresis during cyclic loading. When partially inhibiting collagen production in the constructs, the robustness of the correlation between collagen and classical shear modulus is confirmed.DiscussionOur study underlines the substantial impact of matrix components on the mechanical behavior in biofabricated chondrogenic constructs. The results emphasize the importance of a comprehensive analysis of the mechanical properties. We propose a matrix-based prediction function that can estimate the classical shear modulus of constructs made from HA-based bioinks. Overall, our findings contribute to the understanding of tissue maturation in engineered constructs for cartilage regeneration.

In breast cancer, local invasion of cancer cells into surrounding tissue marks the first step of metastasis. However, to elucidate the impact of cells from the tumor microenvironment on this process, advanced 3D migration models are still urgently needed. To enable migration and invasion studies in a fully 3D bioprinted tumor-stroma model, a migration-permissive bioink composed of methacrylated collagen type I and thiolated hyaluronic acid with low polymer content is developed. In a printed co-culture model comprising metastatic breast cancer cells (MDA-MB-231) and adipose-derived stromal cells (ASCs), real-time single-cell tracking reveals that ASCs in the stromal compartment profoundly promote migration and invasion dynamics of individual tumor cells. This is reflected by increased speed, migration distance, and invasion into the stroma, and is accompanied by collagen remodeling and a shift in tumor cell morphology. A correlation between tumor cell morphology and migration speed is evident, which is modulated by ASCs. A highly motile and invasive subset of tumor cells is significantly enhanced in the presence of ASCs. These insights into the influence of ASCs on the heterogeneity of breast cancer cells in terms of their migratory behavior may inform the development of more specific and effective treatment options for metastatic breast cancer.

Articular cartilage serves an important mechanical function in the human body. For the design of implants for cartilage repair after injury or disease, it is key to thoroughly understand the unique mechanical properties of the native tissue. Here, we use multimodal mechanical testing combined with poro-viscoelastic modeling, finite element simulations, and histology to characterize the region-specific macroscopic large-strain mechanical properties of healthy and osteoarthritic human articular cartilage as well as their relation to the underlying microanatomy. We individually characterize tissue from medial and lateral sides, respectively, of the human femoral condyle and tibial plateau. Our results show that there are no significant differences between the medial and lateral sides, but tissue from the tibial plateau is slightly softer than tissue from the femoral condyle. Osteoarthritis leads to a significantly softened mechanical response, which correlates with corresponding microstructural changes. Through the presented combination of experiments and poro-viscoelastic material parameter identification for healthy and osteoarthritic cartilage, we confirm a reduction in stiffness and an increase in permeability due to the disease. The parameters can be valuable for future finite element simulations of the knee joint The presented results will help guide the design of implants that are able to restore cartilage structure and function, bridging biomechanics and regenerative medicine for osteoarthritis treatment.

Glioblastoma multiforme is the most devastating brain tumor without cure. Although in vitro and in vivo research on glioblastoma multiforme have demonstrated its complexity, including interactions with brain cells and the tumor microenvironment, 3D models resembling those key features and allowing to study therapeutic interventions of this aggressive tumor are scarce. Here, a 3D glioblastoma model is developed that establishes a tumor microenvironment including a hyaluronic acid-based hydrogel cross-linked with laminin, both of which are key components of the brain's extracellular matrix. This hydrogel mimics the mechanical properties of the brain's extracellular matrix at the macroscopic and mesoscopic levels, as evaluated by stiffness, viscosity using rheological and nanoindentation measurements. The ultra-soft hydrogel with a storage modulus of 100 Pa is reinforced by 3D printed microfiber scaffolds which allow the setup of a multicellular 3D model including primary cortical neurons and astrocytes and glioblastoma cells. Tumor microenvironment interactions are characterized through nanoindentation and confocal shadow imaging with the 3D in vitro disease model resembling in vivo properties of glioblastoma tumor entities characterized by functional interactions with the surrounding astrocytes and neurons and the tumor's hijacking capability using neuronal signaling to promote its own proliferation.

Adipose tissue represents an active metabolic and endocrine organ that influences (patho‐)physiological processes in metabolism, immune response, or cancer progression. Given the close relationship between morphology and functionality, adipose models that recapitulate the phenotype of mature adipocytes embedded in a tissue‐specific matrix are essential for studies on adipose tissue biology. In order to mimic the high cell density and 3D architecture of the native tissue, scaffolds made of ultrathin fibers produced with melt electrowriting (MEW) technology are combined with adipose‐derived stromal cell (ASC) spheroids. Fabricated constructs develop an adipose phenotype, demonstrated by storage of triglycerides, expression of adipogenic marker genes, and the development of a tissue‐specific extracellular matrix. Upon oleic acid supplementation, differentiated adipocytes significantly increase lipid storage. Tissue functionality is demonstrated by analysis of secreted adipokines and β‐adrenergic stimulation of lipolysis. Long‐term culture (10 weeks) favors adipocyte maturation to lipid droplet sizes close to those in native tissue, while tissue stability and functionality are unaffected. This hybrid tissue engineering approach, using spheroids as building blocks in tailored MEW scaffolds, provides an adipose model that closely mimics structural and functional characteristics of fat tissue and is therefore an excellent tool for studies on the function and (patho‐)physiology of adipose tissue.

Articular cartilage is crucial for joint function but its avascularity limits intrinsic repair, leading to conditions like osteoarthritis (OA). Chondromodulin-I (Cnmd) has emerged as a key molecule in cartilage biology, with potential implications for OA therapy. Cnmd is primarily expressed in cartilage and plays an important role in chondrocyte proliferation, cartilage homeostasis, and the blocking of angiogenesis. In vivo and in vitro studies on Cnmd, also suggest an involvement in bone repair and in delaying OA progression. Its downregulation correlates with OA severity, indicating its potential as a therapeutic target. Further research is needed to fully understand the mode of action of Cnmd and its beneficial implications for managing OA. This comprehensive review aims to elucidate the molecular characteristics of Cnmd, from its expression pattern, role in cartilage maintenance, callus formation during bone repair and association with OA.

Three-dimensional (3D) cell culture techniques have become a valuable tool to mimic the complex interactions of cells with each other and their surrounding extracellular matrix as they occur in vivo. In this respect, 3D spheroids are widely acknowledged as self-assembled cellular aggregates that can be generated from a variety of cell types without the need for exogenous material while being highly reproducible, easy to handle, and cost-effective. Furthermore, due to their capacity to be developed into microtissues, spheroids represent potential building blocks for various tissue engineering applications, including 3D bioprinting approaches for tissue model development. Adipose-derived stromal/stem cells (ASCs), due to their ease of isolation, multipotent nature, and secretory capacity, represent an attractive cell source employed in numerous tissue engineering studies and other cell-based therapy approaches. In this chapter, we describe two procedures for robust spheroid generation, namely the liquid overlay technique, either using agarose-coated 96-well plates or employing agarose-cast micromolds. Furthermore, we show, in principle, the generation of ASC spheroids with subsequent adipogenic differentiation and the spheroid generation using adipogenically differentiated ASCs, as well as the morphological characterization of generated spheroids.

Breast cancer develops in close proximity to mammary adipose tissue and interactions with the local adipose environment have been shown to drive tumor progression. The specific role, however, of this complex tumor microenvironment in cancer cell migration still needs to be elucidated. Therefore, in this study, a 3D bioprinted breast cancer model was developed that allows for a comprehensive analysis of individual tumor cell migration parameters in dependence of adjacent adipose stroma. In this co-culture model, a breast cancer compartment with MDA-MB-231 breast cancer cells embedded in collagen is surrounded by an adipose tissue compartment consisting of adipose-derived stromal cell (ASC) or adipose spheroids in a printable bioink based on thiolated hyaluronic acid. Printing parameters were optimized for adipose spheroids to ensure viability and integrity of the fragile lipid-laden cells. Preservation of the adipogenic phenotype after printing was demonstrated by quantification of lipid content, expression of adipogenic marker genes, the presence of a coherent adipo-specific extracellular matrix, and cytokine secretion. The migration of tumor cells as a function of paracrine signaling of the surrounding adipose compartment was then analyzed using live-cell imaging. The presence of ASC or adipose spheroids substantially increased key migration parameters of MDA-MB-231 cells, namely motile fraction, persistence, invasion distance, and speed. These findings shed new light on the role of adipose tissue in cancer cell migration. They highlight the potential of our 3D printed breast cancer-stroma model to elucidate mechanisms of stroma-induced cancer cell migration and to serve as a screening platform for novel anti-cancer drugs targeting cancer cell dissemination.

Triple-negative breast cancer (TNBC) is the most invasive type of breast cancer with high risk of brain metastasis. To better understand interactions between breast tumors with the brain extracellular matrix (ECM), a 3D cell culture model is implemented using a thiolated hyaluronic acid (HA-SH) based hydrogel. The latter is used as HA represents a major component of brain ECM. Melt-electrowritten (MEW) scaffolds of box- and triangular-shaped polycaprolactone (PCL) micro-fibers for hydrogel reinforcement are utilized. Two different molecular weight HA-SH materials (230 and 420 kDa) are used with elastic moduli of 148 ± 34 Pa (soft) and 1274 ± 440 Pa (stiff). Both hydrogels demonstrate similar porosities. The different molecular weight of HA-SH, however, significantly changes mechanical properties, e.g., stiffness, nonlinearity, and hysteresis. The breast tumor cell line MDA-MB-231 forms mainly multicellular aggregates in both HA-SH hydrogels but sustains high viability (75%). Supplementation of HA-SH hydrogels with ECM components does not affect gene expression but improves cell viability and impacts cellular distribution and morphology. The presence of other brain cell types further support numerous cell-cell interactions with tumor cells. In summary, the present 3D cell culture model represents a novel tool establishing a disease cell culture model in a systematic way.

In living tissues, cells express their functions following complex signals from their surrounding microenvironment. Capturing both hierarchical architectures at the micro- and macroscale, and anisotropic cell patterning remains a major challenge in bioprinting, and a bottleneck toward creating physiologically-relevant models. Addressing this limitation, a novel technique is introduced, termed Embedded Extrusion-Volumetric Printing (EmVP), converging extrusion-bioprinting and layer-less, ultra-fast volumetric bioprinting, allowing spatially pattern multiple inks/cell types. Light-responsive microgels are developed for the first time as bioresins (µResins) for light-based volumetric bioprinting, providing a microporous environment permissive for cell homing and self-organization. Tuning the mechanical and optical properties of gelatin-based microparticles enables their use as support bath for suspended extrusion printing, in which features containing high cell densities can be easily introduced. µResins can be sculpted within seconds with tomographic light projections into centimeter-scale, granular hydrogel-based, convoluted constructs. Interstitial microvoids enhanced differentiation of multiple stem/progenitor cells (vascular, mesenchymal, neural), otherwise not possible with conventional bulk hydrogels. As proof-of-concept, EmVP is applied to create complex synthetic biology-inspired intercellular communication models, where adipocyte differentiation is regulated by optogenetic-engineered pancreatic cells. Overall, EmVP offers new avenues for producing regenerative grafts with biological functionality, and for developing engineered living systems and (metabolic) disease models.

Volumetric bioprinting (VBP) is a light-based 3D printing platform, which recently prompted a paradigm shift for additive manufacturing (AM) techniques considering its capability to enable the fabrication of complex cell-laden geometries in tens of seconds with high spatiotemporal control and pattern accuracy. A flexible allyl-modified gelatin (gelAGE)-based photoclick resin is developed in this study to fabricate matrices with exceptionally soft polymer networks (0.2-1.0 kPa). The gelAGE-based resin formulations are designed to exploit the fast thiol-ene crosslinking in combination with a four-arm thiolated polyethylene glycol (PEG4SH) in the presence of a photoinitiator. The flexibility of the gelAGE biomaterial platform allows one to tailor its concentration spanning from 2.75% to 6% and to vary the allyl to thiol ratio without hampering the photocrosslinking efficiency. The thiol-ene crosslinking enables the production of viable cell-material constructs with a high throughput in tens of seconds. The suitability of the gelAGE-based resins is demonstrated by adipogenic differentiation of adipose-derived stromal cells (ASC) after VBP and by the printing of more fragile adipocytes as a proof-of-concept. Taken together, this study introduces a soft photoclick resin which paves the way for volumetric printing applications toward soft tissue engineering.

Two-dimensional (2D) cancer models have been the standard for drug development over the past few years, but they frequently do not resemble in vivo properties adequately. 3D models are superior in many aspects and are, therefore, more similar to human pathophysiology. Over the past years, the emerging field of biofabrication has made significant advances, resulting in even more sophisticated 3D models. With this study, a hydrogel is created for biofabrication that is suitable for mimicking the tumor microenvironment in vitro and is further tested as a new vascularized melanoma model in vivo. The alginate/hyaluronic acid/gelatin bioink shows good shape-fidelity, high cell survival rates, and enables successful cultivation of melanoma cells and adipose-derived stem cells as well as cell differentiation in vitro. In vivo, in the arteriovenous loop model, it proves to be a unique method to study melanoma progression, tumor vascularization, and ultimately and reliably metastases in an isolated and controlled environment. These results show that this 3D model is very application-oriented for molecular research and therapy development.

The tumor microenvironment (TME) in breast cancer is determined by the complex crosstalk of cancer cells with adipose tissue-inherent cells such as adipose-derived stromal cells (ASCs) and adipocytes resulting from the local invasion of tumor cells in the mammary fat pad. This leads to heterotypic cellular contacts between these cell types. To adequately mimic the specific cell-to-cell interaction in an in vivo-like 3D environment, we developed a direct co-culture spheroid model using ASCs or differentiated adipocytes in combination with MDA-MB-231 or MCF-7 breast carcinoma cells. Co-spheroids were generated in a well-defined and reproducible manner in a high-throughput process. We compared the expression of the tumor-promoting chemokine CCL5 and its cognate receptors in these co-spheroids to indirect and direct standard 2D co-cultures. A marked up-regulation of CCL5 and in particular the receptor CCR1 with strict dependence on cell-cell contacts and culture dimensionality was evident. Furthermore, the impact of direct contacts between ASCs and tumor cells and the involvement of CCR1 in promoting tumor cell migration were demonstrated. Overall, these results show the importance of direct 3D co-culture models to better represent the complex tumor-stroma interaction in a tissue-like context. The unveiling of tumor-specific markers that are up-regulated upon direct cell-cell contact with neighboring stromal cells, as demonstrated in the 3D co-culture spheroids, may represent a promising strategy to find new targets for the diagnosis and treatment of invasive breast cancer.

Hypertrophic cartilage is an important characteristic of osteoarthritis and can often be found in patients suffering from osteoarthritis. Although the exact pathomechanism remains poorly understood, hypertrophic de-differentiation of chondrocytes also poses a major challenge in the cell-based repair of hyaline cartilage using mesenchymal stromal cells (MSCs). While different members of the transforming growth factor beta (TGF-β) family have been shown to promote chondrogenesis in MSCs, the transition into a hypertrophic phenotype remains a problem. To further examine this topic we compared the effects of the transcription growth and differentiation factor 5 (GDF-5) and the mutant R57A on in vitro chondrogenesis in MSCs. Bone marrow-derived MSCs (BMSCs) were placed in pellet culture and in-cubated in chondrogenic differentiation medium containing R57A, GDF-5 and TGF-ß1 for 21 days. Chondrogenesis was examined histologically, immunohistochemically, through biochemical assays and by RT-qPCR regarding the expression of chondrogenic marker genes. Treatment of BMSCs with R57A led to a dose dependent induction of chondrogenesis in BMSCs. Biochemical assays also showed an elevated glycosaminoglycan (GAG) content and expression of chondrogenic marker genes in corresponding pellets. While treatment with R57A led to superior chondrogenic differentiation compared to treatment with the GDF-5 wild type and similar levels compared to incubation with TGF-ß1, levels of chondrogenic hypertrophy were lower after induction with R57A and the GDF-5 wild type. R57A is a stronger inducer of chondrogenesis in BMSCs than the GDF-5 wild type while leading to lower levels of chondrogenic hypertrophy in comparison with TGF-ß1.

In 3D bioprinting for cartilage regeneration, bioinks that support chondrogenic development are of key importance. Growth factors covalently bound in non-printable hydrogels have been shown to effectively promote chondrogenesis. However, studies that investigate the functionality of tethered growth factors within 3D printable bioinks are still lacking. Therefore, in this study, we established a dual-stage crosslinked hyaluronic acid-based bioink that enabled covalent tethering of transforming growth factor-beta 1 (TGF-β1). Bone marrow-derived mesenchymal stromal cells (MSCs) were cultured over three weeks in vitro, and chondrogenic differentiation of MSCs within bioink constructs with tethered TGF-β1 was markedly enhanced, as compared to constructs with non-covalently incorporated TGF-β1. This was substantiated with regard to early TGF-β1 signaling, chondrogenic gene expression, qualitative and quantitative ECM deposition and distribution, and resulting construct stiffness. Furthermore, it was successfully demonstrated, in a comparative analysis of cast and printed bioinks, that covalently tethered TGF-β1 maintained its functionality after 3D printing. Taken together, the presented ink composition enabled the generation of high-quality cartilaginous tissues without the need for continuous exogenous growth factor supply and, thus, bears great potential for future investigation towards cartilage regeneration. Furthermore, growth factor tethering within bioinks, potentially leading to superior tissue development, may also be explored for other biofabrication applications.

Cortical Neurons In article 2201826 by Carmen Villmann and coworkers, box shaped poly(ɛ-caprolactone) frames made via melt electrowriting are used to reinforce hydrogels (back). The foreground shows the immunocytochemical image of a cortical neuron cocultured with astrocytes in HA-SH (neuron-MAP2 green; synaptophysin-magenta; DAPI blue).

3D neuronal cultures attempt to better replicate the in vivo environment to study neurological/neurodegenerative diseases compared to 2D models. A challenge to establish 3D neuron culture models is the low elastic modulus (30–500 Pa) of the native brain. Here, an ultra‐soft matrix based on thiolated hyaluronic acid (HA‐SH) reinforced with a microfiber frame is formulated and used. Hyaluronic acid represents an essential component of the brain extracellular matrix (ECM). Box‐shaped frames with a microfiber spacing of 200 µm composed of 10‐layers of poly(ɛ‐caprolactone) (PCL) microfibers (9.7 ± 0.2 µm) made via melt electrowriting (MEW) are used to reinforce the HA‐SH matrix which has an elastic modulus of 95 Pa. The neuronal viability is low in pure HA‐SH matrix, however, when astrocytes are pre‐seeded below this reinforced construct, they significantly support neuronal survival, network formation quantified by neurite length, and neuronal firing shown by Ca 2+ imaging. The astrocyte‐seeded HA‐SH matrix is able to match the neuronal viability to the level of Matrigel, a gold standard matrix for neuronal culture for over two decades. Thus, this 3D MEW frame reinforced HA‐SH composite with neurons and astrocytes constitutes a reliable and reproducible system to further study brain diseases.

Hyaluronic acid (HA)-based hydrogels are very commonly applied as cell carriers for different approaches in regenerative medicine. HA itself is a well-studied biomolecule that originates from the physiological extracellular matrix (ECM) of mammalians and, due to its acidic polysaccharide structure, offers many different possibilities for suitable chemical modifications which are necessary to control, for example, network formation. Most of these chemical modifications are performed using the free acid function of the polymer and, additionally, lead to an undesirable breakdown of the biopolymer's backbone. An alternative modification of the vicinal diol of the glucuronic acid is oxidation with sodium periodate to generate dialdehydes via a ring opening mechanism that can subsequently be further modified or crosslinked via Schiff base chemistry. Since this oxidation causes a structural destruction of the polysaccharide backbone, it was our intention to study a novel synthesis protocol frequently applied to selectively oxidize the C6 hydroxyl group of saccharides. On the basis of this TEMPO/TCC oxidation, we studied an alternative hydrogel platform based on oxidized HA crosslinked using adipic acid dihydrazide as the crosslinker.

Biofabrication, including printing technologies, has emerged as a powerful approach to the design of disease models, such as in cancer research. In breast cancer, adipose tissue has been acknowledged as an important part of the tumor microenvironment favoring tumor progression. Therefore, in this study, a 3D-printed breast cancer model for facilitating investigations into cancer cell-adipocyte interaction was developed. First, we focused on the printability of human adipose-derived stromal cell (ASC) spheroids in an extrusion-based bioprinting setup and the adipogenic differentiation within printed spheroids into adipose microtissues. The printing process was optimized in terms of spheroid viability and homogeneous spheroid distribution in a hyaluronic acid-based bioink. Adipogenic differentiation after printing was demonstrated by lipid accumulation, expression of adipogenic marker genes, and an adipogenic ECM profile. Subsequently, a breast cancer cell (MDA-MB-231) compartment was printed onto the adipose tissue constructs. After nine days of co-culture, we observed a cancer cell-induced reduction of the lipid content and a remodeling of the ECM within the adipose tissues, with increased fibronectin, collagen I and collagen VI expression. Together, our data demonstrate that 3D-printed breast cancer-adipose tissue models can recapitulate important aspects of the complex cell–cell and cell–matrix interplay within the tumor-stroma microenvironment.

Stem Cells and DevelopmentVol. 30, No. 23 Guest EditorialInternational Federation for Adipose Therapeutics and Science and Stem Cells and Development: A Long-Term Relationship That Has Been Growing in Plain SightJeffrey M. Gimble, Torsten Blunk, Ricardo Rodriguez, J. Peter Rubin, and Bruce A. BunnellJeffrey M. GimbleAddress correspondence to: Dr. Jeffrey M. Gimble, Obatala Sciences Inc., 2000 Lakeshore Drive #4020, New Orleans, LA 70148-0001, USA, E-mail Address: jeffrey.gimble@obatalasciences.comObatala Sciences Inc., New Orleans, Louisiana, USA.Department of Medicine; Tulane University School of Medicine, New Orleans, Louisiana, USA.Search for more papers by this author, Torsten BlunkDepartment of Trauma, Hand, Plastic and Reconstructive Surgery, University of Würzburg, Würzburg, Germany.Search for more papers by this author, Ricardo RodriguezCosmeticSurg, Baltimore, Maryland, USA.Search for more papers by this author, J. Peter RubinDepartment of Plastic Surgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA.Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.Search for more papers by this author, and Bruce A. BunnellDepartment of Microbiology, Immunology and Genetics, University of North Texas Health Science Center, Fort Worth, Texas, USA.Search for more papers by this authorPublished Online:3 Dec 2021https://doi.org/10.1089/scd.2021.29008.jmgAboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View article"International Federation for Adipose Therapeutics and Science and Stem Cells and Development: A Long-Term Relationship That Has Been Growing in Plain Sight." Stem Cells and Development, 30(23), pp. 1139–1140FiguresReferencesRelatedDetails Volume 30Issue 23Dec 2021 InformationCopyright 2021, Mary Ann Liebert, Inc., publishersTo cite this article:Jeffrey M. Gimble, Torsten Blunk, Ricardo Rodriguez, J. Peter Rubin, and Bruce A. Bunnell.International Federation for Adipose Therapeutics and Science and Stem Cells and Development: A Long-Term Relationship That Has Been Growing in Plain Sight.Stem Cells and Development.Dec 2021.1139-1140.http://doi.org/10.1089/scd.2021.29008.jmgPublished in Volume: 30 Issue 23: December 3, 2021Online Ahead of Print:November 22, 2021PDF download