A bioartificial environment for kidney epithelial cells based on a supramolecular polymer basement membrane mimic and an organotypical culture system.

Renal applications in healthcare, such as renal replacement therapies and nephrotoxicity tests, could potentially benefit from bioartificial kidney membranes with fully differentiated and functional human tubular epithelial cells. A replacement of the natural environment of these cells is required to maintain and study cell functionality cell differentiation in vitro. Our approach was based on synthetic supramolecular biomaterials to mimic the natural basement membrane (BM) on which these cells grow and a bioreactor to provide the desired organotypical culture parameters. The BM mimics were constructed from ureidopyrimidinone (UPy)-functionalized polymer and bioactive peptides by electrospinning. The resultant membranes were shown to have a hierarchical fibrous BM-like structure consisting of self-assembled nanofibres within the electrospun microfibres. Human kidney-2 (HK-2) epithelial cells were cultured on the BM mimics under organotypical conditions in a custom-built bioreactor. The bioreactor facilitated in situ monitoring and functionality testing of the cultures. Cell viability and the integrity of the epithelial cell barrier were demonstrated inside the bioreactor by microscopy and transmembrane leakage of fluorescently labelled inulin, respectively. Furthermore, HK-2 cells maintained a polarized cell layer and showed modulation of both gene expression of membrane transporter proteins and metabolic activity of brush border enzymes when subjected to a continuous flow of culture medium inside the new bioreactor for 21 days. These results demonstrated that both the culture and study of renal epithelial cells was facilitated by the bioartificial in vitro environment that is formed by synthetic supramolecular BM mimics in our custom-built bioreactor. Copyright © 2015 John Wiley & Sons, Ltd.

Mechanically Robust Electrospun Hydrogel Scaffolds Crosslinked via Supramolecular Interactions.

One of the major challenges in the processing of hydrogels based on poly(ethylene glycol) (PEG) is to create mechanically robust electrospun hydrogel scaffolds without chemical crosslinking postprocessing. In this study, this is achieved by the introduction of physical crosslinks in the form of supramolecular hydrogen bonding ureido-pyrimidinone (UPy) moieties, resulting in chain-extended UPy-PEG polymers (CE-UPy-PEG) that can be electrospun from organic solvent. The resultant fibrous meshes are swollen in contact with water and form mechanically stable, elastic hydrogels, while the fibrous morphology remains intact. Mixing up to 30 wt% gelatin with these CE-UPy-PEG polymers introduce bioactivity into these scaffolds, without affecting the mechanical properties. Manipulating the electrospinning parameters results in meshes with either small or large fiber diameters, i.e., 0.63 ± 0.36 and 2.14 ± 0.63 µm, respectively. In that order, these meshes provide support for renal epithelial monolayer formation or a niche for the culture of cardiac progenitor cells.

Development of Non-Cell Adhesive Vascular Grafts Using Supramolecular Building Blocks.

Cell-free approaches to in situ tissue engineering require materials that are mechanically stable and are able to control cell-adhesive behavior upon implantation. Here, the development of mechanically stable grafts with non-cell adhesive properties via a mix-and-match approach using ureido-pyrimidinone (UPy)-modified supramolecular polymers is reported. Cell adhesion is prevented in vitro through mixing of end-functionalized or chain-extended UPy-polycaprolactone (UPy-PCL or CE-UPy-PCL, respectively) with end-functionalized UPy-poly(ethylene glycol) (UPy-PEG) at a ratio of 90:10. Further characterization reveals intimate mixing behavior of UPy-PCL with UPy-PEG, but poor mechanical properties, whereas CE-UPy-PCL scaffolds are mechanically stable. As a proof-of-concept for the use of non-cell adhesive supramolecular materials in vivo, electrospun vascular scaffolds are applied in an aortic interposition rat model, showing reduced cell infiltration in the presence of only 10% of UPy-PEG. Together, these results provide the first steps toward advanced supramolecular biomaterials for in situ vascular tissue engineering with control over selective cell capturing.

A modular approach to easily processable supramolecular bilayered scaffolds with tailorable properties.

Engineering of anisotropic tissues demands extracellular matrix (ECM) mimicking scaffolds with an asymmetric distribution of functionalities. We here describe a convenient, modular approach based on supramolecular building blocks to form electrospun bilayered scaffolds with tailorable properties. Polymers and peptides functionalized with hydrogen-bonding ureido-pyrimidinone (UPy) moieties can easily be mixed-and-matched to explore new material combinations with optimal properties. These combinatorial supramolecular biomaterials, processed by electrospinning, enable the formation of modular fibrous scaffolds. We demonstrate how UPy-functionalized polymers based on polycaprolactone and poly(ethylene glycol) enable us to unite both cell-adhesive and non-cell adhesive characters into a single electrospun bilayered scaffold. We furthermore show that the non-cell adhesive layer can be bioactivated and made adhesive for kidney epithelial cells by the incorporation of 4 mol% of UPy-modified Arg-Gly-Asp (RGD) peptide in the electrospinning solution. These findings show that the UPy-based supramolecular biomaterial system offers a versatile toolbox to form modular multilayered scaffolds for tissue engineering and regenerative medicine applications such as the formation of membranes for a living bioartificial kidney.