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1. Scaffold Architecture and Matrix Strain Modulate Mesenchymal Cell and Microvascular Growth and Development in a Time Dependent Manner

   Chiou, Gennifer ; Jui, Elysa ; Rhea, Allison C ; Gorthi, Aparna ; Miar, Solaleh ; Acosta, Francisca M ; Perez, Cynthia ; Suhail, Yasir ; Kz, Kshitiz ; Chen, Yidong ; et al ( August 2020 , Cellular and molecular bioengineering)

   null (Ed.)

   Background Volumetric tissue-engineered constructs are limited in development due to the dependence on well-formed vascular networks. Scaffold pore size and the mechanical properties of the matrix dictates cell attachment, proliferation and successive tissue morphogenesis. We hypothesize scaffold pore architecture also controls stromal-vessel interactions during morphogenesis. Methods The interaction between mesenchymal stem cells (MSCs) seeded on hydroxyapatite scaffolds of 450, 340, and 250 μm pores and microvascular fragments (MVFs) seeded within 20 mg/mL fibrin hydrogels that were cast into the cell-seeded scaffolds, was assessed in vitro over 21 days and compared to the fibrin hydrogels without scaffold but containing both MSCs and MVFs. mRNA sequencing was performed across all groups and a computational mechanics model was developed to validate architecture effects on predicting vascularization driven by stiffer matrix behavior at scaffold surfaces compared to the pore interior. Results Lectin staining of decalcified scaffolds showed continued vessel growth, branching and network formation at 14 days. The fibrin gel provides no resistance to spread-out capillary networks formation, with greater vessel loops within the 450 μm pores and vessels bridging across 250 μm pores. Vessel growth in the scaffolds was observed to be stimulated by hypoxia and successive angiogenic signaling. Fibrin gels showed linear fold increase in VEGF expression and no change in BMP2. Within scaffolds, there was multiple fold increase in VEGF between days 7 and 14 and early multiple fold increases in BMP2 between days 3 and 7, relative to fibrin. There was evidence of yap/taz based hippo signaling and mechanotransduction in the scaffold groups. The vessel growth models determined by computational modeling matched the trends observed experimentally. Conclusion The differing nature of hypoxia signaling between scaffold systems and mechano-transduction sensing matrix mechanics were primarily responsible for differences in osteogenic cell and microvessel growth. The computational model implicated scaffold architecture in dictating branching morphology and strain in the hydrogel within pores in dictating vessel lengths. 

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2. SOUTHERN BIOMEDICAL ENGINEERING CONFERENCE

   Yeoheung Yun ( August 2022 , Vascularized Cortical Organoid Microphysiological System To Model Alzheimer’s Disease)

   Human induced pluripotent stem cell (hiPSC)-derived brain organoids can recapitulate the complex cytoarchitecture of the brain as well as the genetic and epigenetic footprint of human brain development. Although the brain organoids are able to mimic the structures and functions of brain in vitro, the 3D models have difficulty in integrating a complex vascular network that can provide the interaction with organoids. Here we report on a microfluidicbased three-dimensional, vascularized cortical organoid tissue construct consisting of 1) a perfused micro-vessel against an extracellular matrix (ECM), dynamic flow and membrane-free culture of the endothelial layer, 2) a sprouted vascular network using a combination of angiogenic factors, and 3) a vascularized hiPSCderived cortical organoid. We report on an optimization of density/stiffness of ECM to induce angiogenic sprouting and effect of angiogenic factors to trigger robust, rapid, and directional angiogenesis for concentration-driven and repetitive sprout formation. Vascularized network in the microfluidic device was further characterized in terms of morphology, directional alignment under perfusion, lumen formation, and permeability. HiPSCderived cortical organoid was generated, placed, and integrated into a vascularized network in the vascularized microfluidic device. We investigate how vascularized micro-vessels interact with cortical organoid. This paper further demonstrates the potential utility of a membrane-free vascularized cortical organoid in perfusion used to model Alzheimer’s disease and for toxicity screening of nerve agents. 

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3. A modular microfluidic system based on a multilayered configuration to generate large-scale perfusable microvascular networks

   https://doi.org/10.1038/s41378-020-00229-8  

   Yue, Tao ; Zhao, Da ; Phan, Duc T. T. ; Wang, Xiaolin ; Park, Joshua Jonghyun ; Biviji, Zayn ; Hughes, Christopher C. W. ; Lee, Abraham P. ( January 2021 , Microsystems & Nanoengineering)

   The vascular network of the circulatory system plays a vital role in maintaining homeostasis in the human body. In this paper, a novel modular microfluidic system with a vertical two-layered configuration is developed to generate large-scale perfused microvascular networks in vitro. The two-layer polydimethylsiloxane (PDMS) configuration allows the tissue chambers and medium channels not only to be designed and fabricated independently but also to be aligned and bonded accordingly. This method can produce a modular microfluidic system that has high flexibility and scalability to design an integrated platform with multiple perfused vascularized tissues with high densities. The medium channel was designed with a rhombic shape and fabricated to be semiclosed to form a capillary burst valve in the vertical direction, serving as the interface between the medium channels and tissue chambers. Angiogenesis and anastomosis at the vertical interface were successfully achieved by using different combinations of tissue chambers and medium channels. Various large-scale microvascular networks were generated and quantified in terms of vessel length and density. Minimal leakage of the perfused 70-kDa FITC-dextran confirmed the lumenization of the microvascular networks and the formation of tight vertical interconnections between the microvascular networks and medium channels in different structural layers. This platform enables the culturing of interconnected, large-scale perfused vascularized tissue networks with high density and scalability for a wide range of multiorgan-on-a-chip applications, including basic biological studies and drug screening.

    

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4. Engineered tissue vascularization and engraftment depends on host model

   https://doi.org/10.1038/s41598-022-23895-2  

   Brady, Eileen L. ; Prado, Olivia ; Johansson, Fredrik ; Mitchell, Shannon N. ; Martinson, Amy M. ; Karbassi, Elaheh ; Reinecke, Hans ; Murry, Charles E. ; Davis, Jennifer ; Stevens, Kelly R. ( February 2023 , Scientific Reports)

   Developing vascular networks that integrate with the host circulation and support cells engrafted within engineered tissues remains a key challenge in tissue engineering. Most previous work in this field has focused on developing new methods to build human vascular networks within engineered tissues prior to their implant in vivo, with substantively less attention paid to the role of the host in tissue vascularization and engraftment. Here, we assessed the role that different host animal models and anatomic implant locations play in vascularization and cardiomyocyte survival within engineered tissues. We found major differences in the formation of graft-derived blood vessels and survival of cardiomyocytes after implantation of identical tissues in immunodeficient athymic nude miceversusrats. Athymic mice supported robust guided vascularization of human microvessels carrying host blood but relatively sparse cardiac grafts within engineered tissues, regardless of implant site. Conversely, athymic rats produced substantive inflammatory changes that degraded grafts (abdomen) or disrupted vascular patterning (heart). Despite disrupted vascular patterning, athymic rats supported > 3-fold larger human cardiomyocyte grafts compared to athymic mice. This work demonstrates the critical importance of the host for vascularization and engraftment of engineered tissues, which has broad translational implications across regenerative medicine.

    

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5. From Arteries to Capillaries: Approaches to Engineering Human Vasculature

   https://doi.org/10.1002/adfm.201910811  

   Fleischer, Sharon ; Tavakol, Daniel Naveed ; Vunjak‐Novakovic, Gordana ( June 2020 , Advanced Functional Materials)

   From microscaled capillaries to millimeter‐sized vessels, human vasculature spans multiple scales and cell types. The convergence of bioengineering, materials science, and stem cell biology has enabled tissue engineers to recreate the structure and function of different hierarchical levels of the vascular tree. Engineering large‐scale vessels aims to replace damaged arteries, arterioles, and venules and their routine application in the clinic may become a reality in the near future. Strategies to engineer meso‐ and microvasculature are extensively explored to generate models for studying vascular biology, drug transport, and disease progression as well as for vascularizing engineered tissues for regenerative medicine. However, bioengineering tissues for transplantation has failed to result in clinical translation due to the lack of proper integrated vasculature for effective oxygen and nutrient delivery. The development of strategies to generate multiscale vascular networks and their direct anastomosis to host vasculature would greatly benefit this formidable goal. In this review, design considerations and technologies for engineering millimeter‐, meso‐, and microscale vessels are discussed. Examples of recent state‐of‐the‐art strategies to engineer multiscale vasculature are also provided. Finally, key challenges limiting the translation of vascularized tissues are identified and perspectives on future directions for exploration are presented.

    

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