Microphysiological systems: analysis of the current status, challenges and commercial future

The field of microphysiological systems (or organs-on-a-chip) experienced, in the past decade, a surge in publications and efforts towards commercialization. Such systems hold the promise to advance drug discovery, diagnostics, and many other areas. In this review we summarize and analyze the current status of the field, describe the commercial advances and discuss standing challenges and the commercial outlook of the field

Blood Vessel Model using Tissue Modules with on-demand Stimuli

Artificial vascularization of tissue has been a major barrier in the upscaling of tissue engineering. Achieving angiogenesis from a pre-existing vessel in a controlled manner is a possible solution to prevascularize tissue. Microfluidic approaches do not allow yet the creation of a complex hierarchical tissue construct that can be manipulated and removed from the creation template.Thus the challenge is to simulate angiogenesis in a 1:1 scale. We aim to assemble a blood vessel module that will include: on-demand flow, through a tubular structure comprised of endothelial cells, fibroblasts and smooth muscle cells suspended in a hydrogel environment functionalized with growth factors

Engineering vascularised tissues in vitro

Tissue engineering aims at replacing or regenerating tissues lost due to diseases or traumas (Langer and Vacanti, 1993). However, mimicking in vitro the physiological complexity of vascularized tissue is a major obstacle, which possibly contributes to impaired healing in vivo. In higher organisms, native features including the vascular network, the lymphatic networks and interstitial flow promote both mass transport and organ development. Attempts to mimic those features in engineered tissues will lead to more clinically relevant cell-based therapies. Aside from current strategies promoting angiogenesis from the host, an alternative concept termed prevascularization is emerging. It aims at creating a biological vasculature inside an engineered tissue prior to implantation. This vasculature can rapidly anastamose with the host and enhances tissue survival and differentiation. Interestingly, growing evidence supports a role of the vasculature in regulating pattern formation and tissue differentiation. Thus, prevascularized tissues also benefit from an intrinsic contribution of their vascular system to their development. From those early attempts are emerging a body of principles and strategies to grow and maintain, in vitro, those self-assembled biological vascular networks. This could lead to the generation of engineered tissues of more physiologically relevant complexity and improved regenerative potential

The role of mechanical environment in regulating vascular network formation

Introduction: The integration of engineered tissues after implantation is limited due to the lack of a vascular network. When vascular networks are included, they generally are not organized, or lose their initial organization fast1. Due to the ability of cells to sense their environment by mechanotransduction, signaling, maturation, organization and cell survival is regulated. The objective of this study is to analyze the combinatory effect of substrate stiffness and fluid flow on vascular organization and maturation to find the basic parameters for pre-vascularization of engineered tissue. Methods A microfluidic PDMS framed system was used, which makes it possible to investigate different hydrogel compositions in parallel. Pre-glycation by D-(-)-Ribose allowed for the use of one type of hydrogel in the same concentration but with different modulated mechanical properties. During the polymerization process of the hydrogels, needles were integrated into the gels to create hollow channels by their removing afterwards. The down and top side of the system were sealed with thin cover glasses to ensure the visibility of the inner system. The fluid-flow channels were coated with 0.1% Gelatin to improve the cell attachment and seeded with Smooth muscle cells. Afterwards Human Umbilical Vein Endothelial Cells (HUVECs) were seeded on top of the smooth muscle cells to mimic the physiological blood vessel structure. An additional channel was filled with VEGF (50 ng/mL), which is known as one of the main angiogenic factors which diffuse into the hydrogel over time2. Different fluid-flow profiles were applied to the cell seeded channels. The newly formed capillary network was analyzed by ImageJ. Results: The pre-glycation by incubation of different concentrations of D-(-)-Ribose resulted in an increase of stiffness of the same type of hydrogel by additionally crosslinking of the different hydrogels components. The use of different modulated hydrogels allowed for the simultaneous analysis of the effect of fluid flow on the vascular sprouting into the hydrogels triggered by the diffused VEGF. Different mechanical properties in combination with different fluid flow patterns affected the ability of HUVEC to migrate and organize into the hydrogels and show differences in the sprouting morphology. Outlook: To mimic the physiological state, different Endothelial cell types (e.g. HUVECs, HMECs, HIAEC) will be integrated into the fluid flow channels. This will allow us to see if different endothelial cell origins leads to a different sprouting behavior or if the already described endothelial plasticity leads to similar results