Platelet adhesion and cellular interaction with poly(ethylene oxide) immobilized onto silicone rubber membrane surfaces

Anti-biofouling assembly strategies for protein & cell repellent surfaces: a mini-review

The protein/cell interactions with the surface at the blood-biomaterial interface generally control the efficiency of biomedical devices. A wide range of active processes and slow kinetics occur simultaneously with many biomaterials in healthcare applications, leading to multiple biological reactions and reduced clinical functions. In this work, we present a brief review of studies as the interface between proteins and biomaterials. These include mechanisms of resistance to proteins, protein-rejecting polyelectrolyte multilayers, and coatings of hydrophilic, polysaccharide and phospholipid nature. The mechanisms required to attain surfaces that resist adhesion include steric exclusion, water-related effects, and volume effects. Also, approaches in the use of hydrophilic, highly hydrated, and electrically neutral coatings have demonstrated a good ability to decrease cell adhesion. Moreover, amongst the available methods, the approach of layer-by-layer deposition has been known as an interesting process to manipulate protein and cell adhesion behavior.

Tuning the Density of Poly(ethylene glycol) Chains to Control Mammalian Cell and Bacterial Attachment

Surface modification of biomaterials with polymer chains has attracted great attention because of their ability to control biointerfacial interactions such as protein adsorption, cell attachment and bacterial biofilm formation. The aim of this study was to control the immobilisation of biomolecules on silicon wafers using poly(ethylene glycol)(PEG) chains by a "grafting to" technique. In particular, to control the polymer chain graft density in order to capture proteins and preserve their activity in cell culture as well as find the optimal density that would totally prevent bacterial attachment. The PEG graft density was varied by changing the polymer solubility using an increasing salt concentration. The silicon substrates were initially modified with aminopropyl-triethoxysilane (APTES), where the surface density of amine groups was optimised using different concentrations. The results showed under specific conditions, the PEG density was highest with grafting under "cloud point" conditions. The modified surfaces were characterised with X-ray photoelectron spectroscopy (XPS), ellipsometry, atomic force microscopy (AFM) and water contact angle measurements. In addition, all modified surfaces were tested with protein solutions and in cell (mesenchymal stem cells and MG63 osteoblast-like cells) and bacterial (Pseudomonas aeruginosa) attachment assays. Overall, the lowest protein adsorption was observed on the highest polymer graft density, bacterial adhesion was very low on all modified surfaces, and it can be seen that the attachment of mammalian cells gradually increased as the PEG grafting density decreased, reaching the maximum attachment at medium PEG densities. The results demonstrate that, at certain PEG surface coverages, mammalian cell attachment can be tuned with the potential to optimise their behaviour with controlled serum protein adsorption.

Cell adhesion and growth enabled by biomimetic oligopeptide modification of a polydopamine-poly(ethylene oxide) protein repulsive surface

Protein-repulsive surfaces modified with ligands for cell adhesion receptors have been widely developed for controlling the cell adhesion and growth in tissue engineering. However, the question of matrix production and deposition by cells on these surfaces has rarely been addressed. In this study, protein-repulsive polydopamine-poly(ethylene oxide) (PDA-PEO) surfaces were functionalized with an RGD-containing peptide (RGD), with a collagen-derived peptide binding fibronectin (Col), or by a combination of these peptides (RGD + Col, ratio 1:1) in concentrations of 90 fmol/cm(2) and 700 fmol/cm(2) for each peptide type. When seeded with vascular endothelial CPAE cells, the PDA-PEO surfaces proved to be completely non-adhesive for cells. On surfaces with lower peptide concentrations and from days 1 to 3 after seeding, cell adhesion and growth was restored practically only on the RGD-modified surface. However, from days 3 to 7, cell adhesion and growth was improved on surfaces modified with Col and with RGD + Col. At higher peptide concentrations, the cell adhesion and growth was markedly improved on all peptide-modified surfaces in both culture intervals. However, the collagen-derived peptide did not increase the expression of fibronectin in the cells. The deposition of fibronectin on the material surface was generally very low and similar on all peptide-modified surfaces. Nevertheless, the RGD + Col surfaces exhibited the highest cell adhesion stability under a dynamic load, which correlated with the highest expression of talin and vinculin in the cells on these surfaces. A combination of RGD + Col therefore seems to be the most promising for surface modification of biomaterials, e.g. vascular prostheses.

Spatially controlled bacterial adhesion using surface-patterned poly(ethylene glycol) hydrogels

We constructed surface-patterned hydrogels using low-energy focused electron beams to locally crosslink poly(ethylene glycol) (PEG) thin films on silanized glass substrates. Derived from electron-beam lithography, this technique was used to create patterned hydrogels with well-defined spatial positions and degrees of swelling. We found that cells of the bacterium Staphylococcus epidermidis adhered to and grew on the silanized glass substrates. These cells did not, however, adhere to surfaces covered by high-swelling lightly crosslinked PEG hydrogels. This finding is consistent with the cell-repulsiveness generally attributed to PEGylated surfaces. In contrast, S. epidermidis cells did adhere to surfaces covered by low-swelling highly crosslinked hydrogels. By creating precise patterns of repulsive hydrogels combined with adhesive hydrogels or with exposed glass substrate, we were able to spatially control the adhesion of S. epidermidis. Significantly, adhesive areas small enough to trap single bacterial cells could be fabricated. The results suggest that the lateral confinement imposed by cell-repulsive hydrogels hindered the cell proliferation and development into larger bacterial colonies.

Targeted delivery system for juxtacrine signaling growth factor based on rhBMP-2-mediated carrier-protein conjugation

We propose a model of artificial juxtacrine signaling for the controlled release of recombinant human bone morphogenetic protein-2 (rhBMP-2) suitable for guided bone regeneration. A porous three-dimensional scaffold of poly-(lactide-co-glycolide) was fabricated by means of gel molding and particulate leaching. Collagen immobilization onto the scaffold surface was produced by performing photo-induced graft polymerization of acrylic acid, and rhBMP-2 was tethered to the collagenous surface by covalent conjugation. On pharmacokinetic analysis, in vitro enzyme-linked immunosorbent and alkaline phosphatase assays revealed sustained, slow release of rhBMP-2 over 28 days, with a cumulative release of one third of the initial load diffusing out of the scaffold. Conjugation of rhBMP-2 inhibited the free lateral diffusion and internalization of the activated complex of rhBMP-2 and the bone morphogenetic protein receptor. Osteoprogenitor cells were used as bone precursors to determine the expression of biosignaling growth factor in regulating cell proliferation and differentiation. To identify the phenotype of cells seeded on the rhBMP-2-conjugated scaffold, cellular activity was evaluated with scanning electron microscopy and with viability, histological, and immunohistochemical testing. The rhBMP-2-conjugated scaffold prolonged stimulation of intracellular signal proteins in cells. Enhancement of cell growth and differentiation was considered a consequence of juxtacrine signaling transduction. Animal studies of rhBMP-2-containing filling implants showed evidence of resorption and de novo bone formation. The present study revealed the potential of biomimetic constructs with co-immobilized adhesion and growth factors to induce osteoinduction and osteogenesis. Such constructs may be useful as synthetic bone-graft materials in orthopaedic tissue engineering.

Effects of surface-coupled polyethylene oxide on human macrophage adhesion and foreign body giant cell formation in vitro

Surface immobilized polyethylene oxide (PEO) has been shown to efficiently reduce protein adsorption and cellular adhesion, resulting in a biologically passive surface. To explore the in vitro effects of surface immobilized PEO on the human inflammatory cells, macrophages, and foreign body giant cells (FBGCs), we developed a diisocyanate-based method for coupling PEO to amine-modified glass, a surface previously shown to enhance macrophage adhesion and FBGC formation. Contact angle analysis and X-ray photoelectron spectroscopy confirmed the presence of PEO molecules bound to the surface and revealed that PEO molecular weight significantly influenced the efficiency of PEO coupling. We used a 10-day human monocyte culture protocol to demonstrate that the presence of surface coupled PEO molecules does not significantly decrease initial monocyte density or monocyte-derived macrophage density after 3 days. However, PEO-coupled surfaces significantly reduced long-term monocyte-derived macrophage density and virtually eliminated interleukin-4-induced FBGC formation observed at day 10. The cellular response to these PEO-coupled surfaces was related to the molecular weight of the PEO chains, which was varied between 200 Da and 18.5 kDa. These results suggest that an optimized PEO surface treatment may be effective in reducing inflammatory cell adhesion and possible degradation during the inflammatory response to an implanted biomedical device.

Heterobifunctional membranes by plasma induced graft polymerization as an artificial organ for penetration keratoprosthesis

Highly biocompatible polymer membrane was developed for an artificial cornea in this surface modification study. Heterobifunctional silicone rubber membranes (hetero-SR) were prepared by grafting different functional polymers on each side of a silicone rubber membrane (SR). A novel type of bifunctional membrane was developed with the upper-side favoring cell attachment and growth, and the lower-side suppressing cell adhesion. The preparation of heterobifunctional membranes, characterization of polymer membrane surface properties such as ATR-FTIR and ESCA and contact angle, and biological analysis (in vitro and in vivo studies) were investigated in this work. Based on the biological analysis, the heterobifunctional membrane displays promising potential for use as an artificial cornea.