Biodegradable scaffold with built-in vasculature for organ-on-a-chip engineering and direct surgical anastomosis

1,2Boyang Zhang, 1,2Miles Montgomery, 2M. Dean Chamberlain, 7Shinichiro Ogawa, 1,2Anastasia Korolj, 1,2Aric

Pahnke, 2Laura A. Wells, 5Stéphane Massé, 3Jihye Kim, 2Lewis Reis, 4Abdulah Momen, 2,4,6Sara S. Nunes,

1,3Aaron R. Wheeler, 5Kumaraswamy Nanthakumar, 7Gordon Keller, 1,2Michael V. Sefton, and 1,2,4,6,*Milica

Radisic

1Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada.

2Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada.

3Department of Chemistry, University of Toronto, Toronto, Ontario, Canada. 4Toronto General Research Institute, University Health Network, Toronto, Ontario, Canada. 5The Toby Hull Cardiac Fibrillation Management

Laboratory, Toronto General Hospital, Toronto, Ontario, Canada.6The Heart and Stroke/Richard Lewar Centre of

Excellence, Toronto, Ontario, Canada. 7McEwen Center for Regenerative Medicine, Toronto, Ontario, Canada

Recapitulating vascular interfaces of different organs in 3-D is critical in both organ-on-a-chip and tissue engineering applications. Vascular networks can be engineered with subtractive fabrication by embedding a sacrificial carbohydrate-glass lattice, Pluronic F127, or dry alginate fibers in hydrogels. However, the soft hydrogel provides only a temporary structural support for the fragile hollow network and does not permit extensive tissue remodeling, which inevitably alters the hydrogel structure and collapses the embedded network. Synthetic biodegradable polymers could provide sufficient structural support to the engineered vessels, but their low permeability prevents biomolecule exchange and cell migration between the vessels and the parenchymal space.

To accommodate these two opposing material criteria we created AngioChip, constructed using a biodegradable elastomer, poly(octamethylene maleate (anhydride) citrate) (POMaC). POMaC was selected since it is UV- polymerizable, allowing rapid assembly under mild conditions, biodegrades by hydrolysis, and is more elastic than FDA approved polyesters. The stable biodegradable scaffold includes a built-in branching micro-channel network that contained two unique features realized by our new 3-D stamping technique. First, the synthetic
built-in vascular walls were thin and flexible, yet strong enough to mechanically support a perfusable vasculature
in a contracting tissue and enable direct surgical anastomosis. Second, to allow efficient molecular exchange and cell migration, nano-pores and micro-holes were incorporated into the vascular walls. By establishing a stable, permeable, vessel network within AngioChips, we were liberated from material constraints, which allowed us to use any soft natural extracellular matrix (e.g. collagen, Matrigel) embedded with cells in the parenchymal space permitting the extensive tissue remodelling.
Cardiac tissues were created from human embryonic stem cell (hESC), human mesenchymal stem cells (MSCs) as a side population and HUVECs for inner lumen coating. To provide an evidence of tissue-level organization, confocal images and histological cross-sections show compact layers of cells throughout the entire tissue volume, including the scaffold interior. Fully human liver-AngioChips were engineered using hESC derived hepatocytes. High-density culture resulted in the formation of junctions between hepatocytes, and a positive staining for albumin and bile canaliculi. Vascularized hepatic tissues and cardiac tissues, engineered using AngioChips, were shown to process clinically relevant drugs delivered through their internal
vasculature. Incorporation of nano-pores and micro-holes in the vessel walls enhanced vessel permeability, permitted inter-cellular crosstalk, extravasation of monocytes and sprouting of endothelial cells upon stimulation. AngioChip cardiac tissues were also implanted via direct surgical anastomoses to the femoral vessels of rat hindlimbs, establishing immediate blood perfusion.