Microphysiological models of human skin and brain vasculature for drug testing
June 5-9, 2018
Organs-on-a-chip systems are biomimetic devices containing microfluidic channels and chambers populated by engineered tissues/cells that replicate key functional units of living organs. In these systems, each tissue chamber has to be connected to other tissues typically through endothelialized microchannels to accurately mimic systemic transport of drugs or soluble factors to/from tissues. We aim to establish this capability by i) restoring the physiological phenotype of endothelial cells (ECs) by recapitulating the vascular microenvironment, and ii) reproducing tissue-specific drug permeability properties within tissues of interest (e.g. blood-brain-barrier).
To generate an in vivo-like endothelial phenotype, we first developed a microfluidic system recapitulating both physiological shear stress and oxygen levels on ECs. The physiological relevance of this model was validated in terms of its responses to a broadly studied vasotoxic chemotherapeutic drug, 5-FU, and to a vasoprotective agent, Resveratrol. Next, we developed a microfluidic blood-brain-barrier (BBB) model that is capable of mimicking in vivo BBB characteristics for a prolonged period. We derived brain microvascular endothelial cells from human induced pluripotent stem cells (iPSCs) and co-cultured them with primary astrocytes on the two sides of a porous membrane on a pumpless microfluidic platform. This BBB-on-a-chip model exhibited significant barrier integrity as evident by continuous tight junction formation and in vivo-like values of trans-endothelial electrical resistance (TEER). We further validated the capacity of our microfluidic BBB model to be used for drug permeability studies using large molecules (FITC-dextrans) and model drugs (caffeine, cimetidine, and doxorubicin). Our BBB-on-a-chip model closely mimics physiological BBB barrier functions and can be used for human-relevant screening of drug candidates.
We next focused on the skin vasculature since the current engineered human skin constructs (HSCs) are typically maintained under static conditions, which do not allow for studying drug transport between the skin and circulation. We employed two separate strategies to address this limitation: (i) developing a skin-on-a-chip platform that can create physiologically relevant flow rates; and (ii) incorporating three-dimensional perfusable microvasculature into HSCs to recapitulate the endothelial barrier function. In the first strategy, we designed and developed a skin-on-a-chip platform that has the capability to recirculate the medium at physiological flow rates without the need for a pump or external tube connections. We demonstrated that the platform can be used to maintain HSCs for three weeks with proliferating keratinocytes and intact skin barrier function. In the second strategy, we micropatterned spatially controlled and perfusable vascular networks in HSCs using both primary and iPSC-derived ECs. The 3D-printing technology enabled us to control the geometry of the micropatterned vascular networks. We further verified that vascularized human skin constructs can form a robust epidermis and establish an endothelial barrier function, which allows for the recapitulation of both topical and systemic delivery of drugs. These new vascularization methods now allow us to connect our 3D skin constructs with other microphysiological tissues of interest, such as heart and liver, towards building more comprehensive drug screening platforms.
Hasan Abaci, "Microphysiological models of human skin and brain vasculature for drug testing" in "Nanotechnology in Medicine II: Bridging Translational in vitro and in vivo Interfaces", Millicent Sullivan, PhD, University of Delaware, USA Josué Sznitman, Dr. Sc., Technion-Israel Institute of Technology, Israel Lola Eniola-Adefeso, PhD, University of Michigan, USA Srivatsan Kidambi, PhD, University of Nebraska - Lincoln, USA Eds, ECI Symposium Series, (2018). http://dc.engconfintl.org/nanotech_med_ii/27