Topographical control of human macrophages by a regularly microstructured polyvinylidene fluoride surface.

In this study we investigated the influence of surface topography on the inflammatory response of human macrophages. We generated different polyvinylidene fluoride (PVDF) surfaces including (i) a smooth surface of PVDF spherulites as a control, (ii) a randomly nanotextured surface with alumina particles, and (iii) a microstructure using laser ablation. The identical chemistry of all PVDF surfaces was demonstrated by X-ray photoelectron spectroscopy. The topography was evaluated by white light interferometry and X-profile analysis. Macrophages were cultured on the different surfaces including lipopolysaccharide (LPS) treatment as an inflammatory activator. Our results demonstrate that the microstructured surface but not the nanotexured significantly affects the activation of primary human macrophages by inducing a specific cytokine and gene expression pattern. This activation resulted in a subtype of macrophages with pro- but also anti-inflammatory properties. Interestingly, the response on the topography differed from that triggered by LPS, pointing to a different activation state of the cells. Our data clearly show that a particular topography induces an inflammatory response. This suggests that the modification of topography could influence the inflammatory potency of a biomaterial and hence could affect the biocompatibility of implants.

Immobilized DNA aptamers used as potent attractors for porcine endothelial precursor cells.

Because of their insufficient biocompatibility and high thrombogenicity, small diameter artificial vascular prostheses still do not show a satisfactory patency rate. In vitro endothelialization of artificial grafts before implantation has been established experimentally years ago, but, this procedure is extremely time consuming and expensive. This study deals with the coating of graft surfaces with capture molecules (aptamers) for circulating endothelial progenitor cells (EPCs), mimicking a prohoming substrate to fish out EPCs from the bloodstream after implantation and to create an autologous functional endothelium. Using the SELEX technology, aptamers with a high affinity to EPCs were identified, isolated, and grafted onto polymeric discs using a blood compatible star-PEG coating. A porcine in vitro model that demonstrates the specific adhesion of EPCs and their differentiation into vital endothelial-like cells within 10 days in cell culture is presented. We suggest that the rapid adhesion of EPCs to aptamer-coated implants could be useful to promote endothelial wound healing and to prevent increased neointimal hyperplasia. We hypothesize that future in vivo self-endothelialization of blood contacting implants by homing factor mimetic capture molecules for EPCs may bring revolutionary new perspectives towards clinical applications of stem cell and tissue engineering strategies.

Influence of different ECM mimetic peptide sequences embedded in a nonfouling environment on the specific adhesion of human-skin keratinocytes and fibroblasts on deformable substrates.

Mechanical stress is a decisive factor for the differentiation, proliferation, and general behavior of cells. However, the specific signaling of mechanotransduction is not fully understood. One basic problem is the clear distinction between the different extracellular matrix (ECM) constituents that participate in cellular adhesion and their corresponding signaling pathways. Here, a system is proposed that enables mechanical stimulation of human-skin-derived keratinocytes and human dermal fibroblasts that specifically interact with peptide sequences immobilized on a non-interacting but deformable substrate. The peptide sequences mimic fibronectin, laminin, and collagen type IV, three major components of the ECM. To achieve this, PDMS is activated using ammonia plasma and coated with star-shaped isocyanate-terminated poly(ethylene glycol)-based prepolymers, which results in a functional coating that prevents unspecific cell adhesion. Specific cell adhesion is achieved by functionalization of the layers with the peptide sequences in different combinations. Moreover, a method that enables the decoration of deformable substrates with cell-adhesion peptides in extremely defined nanostructures is presented. The distance and clustering of cell adhesion molecules below 100 nm has been demonstrated to be of utmost importance for cell adhesion. Thus we present a new toolbox that allows for the detailed analysis of the adhesion of human-skin-derived cells on structurally and biochemically decorated deformable substrates.