Porous Silicon-Based Cell Microarrays: Optimizing Human Endothelial Cell-Material Surface Interactions and Bioactive Release

Porous silicon (pSi) substrates are a promising platform for cell expansion, since pore size and chemistry can be tuned to control cell behavior. In addition, a variety of bioactives can be loaded into the pores and subsequently released to act on cells adherent to the substrate. Here, we construct a cell microarray on a plasma polymer coated pSi substrate that enables the simultaneous culture of human endothelial cells on printed immobilized protein factors, while a second soluble growth factor is released from the same substrate. This allows three elements of candidate pSi scaffold materialstopography, surface functionalization, and controlled factor releaseto be assessed simultaneously in high throughput. We show that protein conjugation within printed microarray spots is more uniform on the pSi substrate than on flat glass or silicon surfaces. Active growth factors are released from the pSi surface over a period of several days. Using an endothelial progenitor cell line, we investigate changes in cell behavior in response to the microenvironment. This platform facilitates the design of advanced functional biomaterials, including scaffolds, and carriers for regenerative medicine and cell therapy

Affinity Binding of EMR2 Expressing Cells by Surface-Grafted Chondroitin Sulfate B

The propensity of glycosaminoglycans to mediate cell–cell and cell–matrix interactions opens the door to capture cells, including circulating blood cells, onto biomaterial substrates. Chondroitin sulfate (CS)-B is of particular interest, since it interacts with the receptor (EGF)-like module-containing mucin-like hormone receptor-like 2 precursor (EMR2) displayed on the surface of leukocytes and endothelial progenitor cells. Herein, CS-B and its isomer CS-A were covalently immobilized onto heptylamine plasma polymer films via three different binding chemistries to develop platform technology for the capture of EMR2 expressing cells onto solid carriers. Surface characterization verified the successful immobilization of both glycosaminoglycans. The EMR2 expressing human myeloid cell line U937 preferentially bound onto CS-B-modified substrates, and U937 cells preincubated with CS-B in solution exhibited reduced affinity for the substrate. The direct capture of hematopoietic and blood-circulating endothelial cell types via a glycosaminoglycan-binding surface receptor opens an unexplored route for the development of biomaterials targeted at these cell types

MALDI-tof/tof-MS of N-glysocylated naEFC membrane proteins using hydrazide-bead capture.

<p>The consensus motif for N-linked glycosylation is highlighted in bold.</p

Gene expression analysis of naEFCs versus HUVEC.

<p>In (A), a heat map illustrating the hierarchical clustering of Log2 relative gene expression in 3 separate HUVEC and naEFC samples. In (B), scatter data showing the average gene expression data in naEFCs and HUVEC. The dots represent the gene expression of UCB CD133+ 4 day cultured naEFCs versus HUVEC. The diagonal lines indicate the cut off value of 1.5 fold activation and genes coloured on the basis of expression level (yellow, evenly expressed genes; blue, naEFC upregulated genes; red, naEFC downregulated genes). In (C), ICAM-3 mRNA levels in naEFCs and HUVEC as determined by qPCR with relative gene expression normalised to CycA. Data are expressed as relative fold change (mean ± sem) normalised to HUVEC, n = 3,*<i>p</i><0.05 versus HUVEC. In (D–F), flow cytometric analysis of ICAM-3 on (D) naEFCs, (E) HUVEC and (F) freshly isolated peripheral blood CD133⁺CD117⁺ gated cells. Light dotted line represents the unstained control and the dark line represents cells stained for ICAM-3. One representative experiment is shown n≥3.</p

Hematopoietic properties of naEFCs.

<p>naEFCs were seeded in MethoCult and growth factors GM-CSF, IL-3, SCF and EPO for 14 days prior to colony counting and staining with May Grunwald/Giemsa to assess cellular morphology. naEFCs formed blast-forming unit-erythroid (BFU-E), colony-forming units (CFU)-GEMM, -GM, -G and -M colonies in methylcellulose. Colony formation was photographed and quantified after 14 days and compared between naEFCs and freshly isolated CD133⁺ and CD133⁻ cells (mean ± sem, n = 3).</p

Fold change values of well-established markers in the naEFCs when compared with HUVEC.

↑<p>denotes significantly higher mRNA expression;</p>↓<p>denotes significantly lower mRNA expression.</p

naEFCs express mature EC markers and form perfused tubes in vivo.

<p>In (A), CFSE-labelled naEFCs mixed with Matrigel prior to injection into the flank of NOD/SCID mice, after 7 days the plugs were removed, processed and sections counterstained for nuclei with DAPI prior to imaging by confocal microscopy. The upper left image shows the cross section of a CFSE-naEFC generated tube-like structure (green) within which the nuclei of cells can be seen (blue) at 60× mag (arrows). The upper right image is the control plug in which no naEFCs were added. Images represent one experiment of n≥3. Similar sections were stained for CD144 and images captured by confocal microscopy with CFSE-naEFCs (green) exhibiting CD144 (red) as a cross section of a tube (lower left image) and CD144 staining in the junctions of the CFSE-naEFCs (lower right panel). Images are a representative of n≥3. In (B), similar experiments were executed and at day 7 post-implant the mice were injected i.v. with TRITC-lectin prior to exsanguinations, plugs removed, processed and sections counterstained for nuclei with DAPI prior to imaging by confocal microscopy. The representative image shows the cross section of a CFSE-naEFC generated tube-like structure (green, upper left image), TRITIC-lectin (red, upper right image), DAPI counterstain (blue, lower left image) and the merged image (lower right). In (C), CFSE-naEFCs were digested from explanted Matrigel plugs using dispase and phenotyped for hematopoietic progenitor cell and endothelial cell markers by flow cytometry (right panel); cells from contra-lateral control Matrigel plugs were similarly examined for antigen expression (left panel). In the histograms, the light dotted lines represent unstained cells and the dark lines represent stained cells of a representative of repeated experiments.</p

ICAM-3 mediates rolling and adhesion of naEFCs.

<p>In (A), still images of Video S1 illustrate the interaction of naEFCs with untreated (left panel), TNFα treated (5 ng/ml for 5 hours, middle and right panels) where naEFCs were pre-treated with an isotype control antibody (middle panel) or an antibody to ICAM-3 (right panel) prior to perfusion over HUVEC at 2 dynes/cm². In (B and C), data of rolling and adherent naEFCs is represented as the mean ± sem per field of view (fov) for n = 3;*<i>p</i><0.05 versus untreated; #<i>p</i><0.05 versus iso ctl. In (D and E), data of rolling and adherent whole blood treated with an isotype control or antibody to ICAM-3 is represented as the mean ± sem per field of view (fov) for n = 4–5;*<i>p</i><0.05 versus untreated; #<i>p</i><0.05 versus iso ctl.</p

Surface expression profiling of freshly isolated CD133⁺ cells, naEFCs and HUVEC.

<p>In (A), freshly isolated CD133⁺ cells were phenotyped for hematopoietic progenitor cell and endothelial cell markers by flow cytometry. In the histograms, the light dotted lines represent unstained cells and the dark lines represent stained cells of one representative experiment from n≥3. In (B), CD133⁺ enriched cells at 4 days of culture (naEFCs) and HUVEC were more extensively assessed for surface antigen phenotype. The histograms show one representative experiment from n≥3 with the light and dark lines as above. In (C), the pan-leukocyte marker CD45 and the myeloid markers CD11b and CD14 were examined with the light dotted lines representing unstained cells and the dark lines representing stained cells of one representative experiment from n≥3.</p