Author Correction: A complex human gut microbiome cultured in an anaerobic intestine-on-a-chip.

In the version of this Article originally published, the authors mistakenly cited Fig. 5d in the sentence beginning 'Importantly, the microbiome cultured in these primary Intestine Chips...'; the correct citation is Supplementary Table 2. This has now been amended.

A complex human gut microbiome cultured in an anaerobic intestine-on-a-chip.

The diverse bacterial populations that comprise the commensal microbiome of the human intestine play a central role in health and disease. A method that sustains complex microbial communities in direct contact with living human intestinal cells and their overlying mucus layer in vitro would thus enable the investigation of host-microbiome interactions. Here, we show the extended coculture of living human intestinal epithelium with stable communities of aerobic and anaerobic human gut microbiota, using a microfluidic intestine-on-a-chip that permits the control and real-time assessment of physiologically relevant oxygen gradients. When compared to aerobic coculture conditions, the establishment of a transluminal hypoxia gradient in the chip increased intestinal barrier function and sustained a physiologically relevant level of microbial diversity, consisting of over 200 unique operational taxonomic units from 11 different genera and an abundance of obligate anaerobic bacteria, with ratios of Firmicutes and Bacteroidetes similar to those observed in human faeces. The intestine-on-a-chip may serve as a discovery tool for the development of microbiome-related therapeutics, probiotics and nutraceuticals.

Fabrication of Custom Agarose Wells for Cell Seeding and Tissue Ring Self-assembly Using 3D-Printed Molds.

Engineered tissues are being used clinically for tissue repair and replacement, and are being developed as tools for drug screening and human disease modeling. Self-assembled tissues offer advantages over scaffold-based tissue engineering, such as enhanced matrix deposition, strength, and function. However, there are few available methods for fabricating 3D tissues without seeding cells on or within a supporting scaffold. Previously, we developed a system for fabricating self-assembled tissue rings by seeding cells into non-adhesive agarose wells. A polydimethylsiloxane (PDMS) negative was first cast in a machined polycarbonate mold, and then agarose was gelled in the PDMS negative to create ring-shaped cell seeding wells. However, the versatility of this approach was limited by the resolution of the tools available for machining the polycarbonate mold. Here, we demonstrate that 3D-printed plastic can be used as an alternative to machined polycarbonate for fabricating PDMS negatives. The 3D-printed mold and revised mold design is simpler to use, inexpensive to produce, and requires significantly less agarose and PDMS per cell seeding well. We have demonstrated that the resulting agarose wells can be used to create self-assembled tissue rings with customized diameters from a variety of different cell types. Rings can then be used for mechanical, functional, and histological analysis, or for fabricating larger and more complex tubular tissues.

Fabrication and characterization of electrospun polycaprolactone and gelatin composite cuffs for tissue engineered blood vessels.

Sewing cuffs incorporated within tissue-engineered blood vessels (TEBVs) enable graft anastomosis in vivo, and secure TEBVs to bioreactors in vitro. Alternative approaches to cuff design are required to achieve cuff integration with scaffold-free TEBVs during tissue maturation. To create porous materials that promote tissue integration, we used electrospinning to fabricate cuffs from polycaprolactone (PCL), PCL blended with gelatin, and PCL coated with gelatin, and evaluated cuff mechanical properties, porosity, and cellular attachment and infiltration. Gelatin blending significantly decreased cuff ultimate tensile stress and failure strain over PCL alone, but no significant differences were observed in elastic modulus or failure load. Interestingly, gelatin incorporation by blending or coating did not produce significant differences in cellular attachment or pore size. We then created tissue tubes by fusing self-assembled smooth muscle cell rings together with electrospun cuffs on either end. After 7 days, rings and cuffs fused seamlessly, and the resulting tubes were harvested for pull-to-failure tests to measure the strength of cuff-tissue integration. Tubes with gelatin-coated PCL cuffs failed more frequently at the cuff-tissue interface compared to PCL and PCL:gelatin blended groups. This work demonstrates that electrospun cuffs integrated successfully with scaffold-free TEBVs, and that the addition of gelatin did not significantly improve cuff integration over PCL alone for this application. Electrospun cuffs may aid cannulation for dynamic culture and testing of tubular constructs during engineered tissue maturation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 817-826, 2018.