BMES 2018: Organ on a chip and cell-ECM interactions

Adeel and I summarized our key takeaways from the BMES in this post. I personally tried to attend organ on a chip talks and posters, which included a micro- or nano-porous membrane or a micro/nano-structured co-culture system. I tried to identify weaknesses and strengths  to highlight our potential opportunities to contribute, and to improve our current approach.   

Directly and Indirectly Co-cultured hiPSC-Derived Pericytes Have Differential Effects on the Barrier Function of Brain Microvascular Endothelial Cells

John Jamieson, Raleigh Linville, Yuan Yuan Ding, Peter Searson, and Sharon Gerecht

Johns Hopkins University, Baltimore, MD

Short Desciption of the model: The authors differentiated RFP-pericytes and GFP-BMECs from hiPSCs and monitored transendothelial electrical resistance (TEER) across BMECs on transwell inserts while pericytes were either directly co-cultured on the membrane or indirectly co-cultured in the basolateral chamber (Fig 1A). The spatial organization of pericytes relative to BMECs in direct co-culture was examined using confocal microscopy. Next, to recapitulate the three-dimensional nature of the pericyte microenvironment, we embedded pericytes in a collagen I gel formed on a transwell insert, seeded BMECs on the surface of the gel, and similarly monitored TEER and pericyte localization. Finally, the authors established a bicellular hiPSC-derived three-dimensional microvessel model by sequentially seeding pericytes and BMECs, and monitored pericyte localization and microvessel permeability.

Significance of the Work:

• Indirectly co-cultured pericytes increased TEER up to two-fold (3800 Ωcm2) in a concentration-dependent manner (Fig 1B)
• Directly co-cultured pericytes localized between BMEC and the substrate regardless of the cell seeding order, and resulted in a concentration dependent decrease in TEER (Fig 1C).
• Pericytes embedded in a collagen I gel beneath the BMEC had no effect on TEER, and were observed migrating away from BMECs.
• hiPSC-derived pericytes are capable of increasing TEER across BMECs, and the effect is platform dependent
• They also developed a bicellular hiPSC-derived microvessel model that could be used to examine vascular dysfunctions in the CNS

Lab website: http://gerechtlab.johnshopkins.edu/

Abstract link: https://drive.google.com/open?id=1Mko5ZVFkAQDriuFjH2-37tR9lYml_mWg

Fabrication of Phenotypically Stable Human Liver Co-Cultures Using 4 Primary Cell Types

Chase Monckton and Salman Khetani

University of Illinois at Chicago, Chicago, IL

Model: Tissue culture polystyrene 24-well plates were subjected to polydimethylsiloxane (PDMS)-based soft lithography to pattern collagen I into circular domains (500μm diameter with 1200μm center to center spacing), an architecture shown to induce the formation of tight junctions in neighboring hepatocytes.

Significance: first-of-its-kind micropatterned co-culture model containing 4 key primary human liver cell types

Abstract link: https://drive.google.com/open?id=1-kqeDkgriQorgEK-itSiLLZyKOJlS_dF

Voice link: https://drive.google.com/open?id=1BDW-ooMNhQSusCg5A8z-J-_FkLDYJCu8

Published paper: https://www.cmghjournal.org/article/S2352-345X(17)30173-X/fulltext

Key takeaways from the conference:

• Although we may use well-established micro/nano-fabrication methods to make our membranes, our work has still a higher level of sophistication.
• Many groups presented their initial attempts using nano/micro-porous membranes
• When it comes down to presenting the work in a “shiny” manner, we may need improvement. 
• Although we are as capable as many groups to work on many micro and nano-patterning/printing applications in mono-culture/co-culture studies, we have not dug deep enough into this area.
  

Cornea Tissue Engineering – Gaining control over collagen orientation

The field of corneal tissue engineering remains relatively untouched at BMES and the tissue engineering community in general. A part of this might be owing to the lack of data on the corneal transport properties, a highly organized yet complex microstructure and the presence of several cell types. The most targeted element of the cornea at BMES was the corneal stroma which was mentioned passively by almost everyone who was working towards the development of organized collagen fibers.

Development of organized collagen fibers has progress from being confined to microfluidic channels at small lengths scales (100-300µm) to the order of several centimeters. At BMES, 2 main methods of orienting collagen were ubiquitously discussed:

1. Taking advantage of molecular crowding in a microfluidic system
2. 3D printing

Microfluidic Methods:

Microfluidic methods have developed to a level of sophistication where we are no longer restricted to a channel with dimensions on the order of 100-300µm. An effort between Axel Guenther from UofT and Elliot Chaikof from Beth Israel Deaconess Medical Center demonstrated a microfluidic system capable of producing collagen sheets of indefinite length, up to 3cm wide and 8µm thick.

The talk consisted of unpublished data and therefore more pictures of results are not available but they did indicate a very high degree of alignment in their results. They also claimed to be the first group to be able to fabricate free standing collagen sheets. Their process seems to be inspired by work from Thomas Scheibel’s goup (Nano Lett., 2016, 16 (9), pp 5917–5922 DOI: 10.1021/acs.nanolett.6b02828)

Most microfluidic alignment is also based on molecular crowding, not purely the effect of shear as shown in Biomaterials. 2012 Oct;33(30):7366-74. doi: 10.1016/j.biomaterials.2012.06.041.

3D printing

3D bioprinting of collagen seems to have picked up greatly after the introduction of the ‘Freefrom reversible embedding of suspended hydrogels (FRESH)’ method introduced by Adam Feinberg’s group in 2015 (Science Advances 23 Oct 2015: Vol. 1, no. 9, e1500758 DOI: 10.1126/sciadv.1500758).

A number of groups presented talks and posters utilizing FRESH 3D printing for their purpose of aligning collagen fibers, examples include Adam Feinberg’s group using FRESH to develop cardiac muscle and other muscle types and Celeste Nelson at Princeton.

Overall, the above methods have demonstrated a high degree of versatility and maybe adept for corneal tissue engineering. A major implication of the knowledge gained from these talks is that we might be able to leverage it for our benefit since our current method is far from perfect and the return in developing a brand new method to align collagen is not the most glamorous. However, the questions that can be answered with aligned collagen in conjunction with membranes are many, including those of the cornea.