Agnieszka Mierczynska

The influence of substrate stiffness gradients on primary human dermal fibroblasts.

Materials mechanical properties are known to be an important regulator of cellular processes such as proliferation, differentiation and migration, and have seen increasing attention in recent years. At present, there are only few approaches where the mechanical properties of thin films can be controllably varied across an entire surface. In this work, we present a technique for controlled generation of gradients of surface elastic moduli involving a weak polyelectrolyte multilayer (PEM) system of approximately 100 nm thickness and time dependent immersion in a solution of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) as a crosslinking agent. Uniform surface chemistry across the gradient and wettability was provided by the addition of a 10 nm thick plasma polymer layer deposited from vapour of either allylamine or acrylic acid. We used the resultant stiffness gradients (0.5-110 MPa in hydrated state) to investigate the adhesion, morphology and proliferation on human dermal fibroblasts (HDFs). We show that substrate mechanical properties strongly influence HDF cell fate. We also found that in the experimental range of surface properties used in this study, the surface stiffness was a stronger driving force to cells fate compared to chemistry and wettability.

Creating gradients of two proteins by differential passive adsorption onto a PEG-density gradient

Many fundamental biological processes, including early embryo development, immune responses and the progression of pathogens, are mediated by gradients of biological molecules. Understanding these vital physiological processes requires the development of biomaterial platforms that can mimic them in-vitro. Such platforms include laboratory generated surface gradients of biological molecules. In this work, we report a method for the generation of surface gradients of two proteins. We used a surface grafting density gradient of polyethylene glycol (PEG) to control protein adsorption. In addition, we used protein size as a tool to control the position and the adsorbed amount of both proteins. To demonstrate our concept, we used fibrinogen as an example of a large protein and lysozyme as an example of a small protein. However, we speculate that the same strategy could be extended to any other pair of large and small proteins. We used X-ray photoelectron spectroscopy and sessile drop contact angle measurements to determine the chemical composition and wettability of the gradients. Protein adsorption was studied by surface plasmon resonance imaging.

pH-tunable gradients of wettability and surface potential

Smart materials that can sense and respond to changes in the environment are of interest in numerous and diverse applications. In this paper, we report gradient surfaces where wettability and surface potential respond to changes in the pH. The gradients are produced by controlling the concentration of amine and carboxyl acid groups across the surface. The response of surface wettability to pH changes was studied by water contact angle measurements. The potential across the surface was determined by atomic force microscopy-based surface force measurements. These studies showed that at low pH the surface potential changes from “no charge” at the acid end to a positive charge at the amine end. At high pH the surface potential changed from negative at the acid end to “no charge” at the amine side. At an intermediate pH the charge across the surface changes from negative at the acid end to positive at the amine end. Potential applications include separation or guidance of charged entities such as particles, proteins or bacteria.

Tuning and predicting the wetting of nanoengineered material surface

The wetting of a material can be tuned by changing the roughness on its surface. Recent advances in the field of nanotechnology open exciting opportunities to control macroscopic wetting behaviour. Yet, the benchmark theories used to describe the wettability of macroscopically rough surfaces fail to fully describe the wetting behaviour of systems with topographical features at the nanoscale. To shed light on the events occurring at the nanoscale we have utilised model gradient substrata where surface nanotopography was tailored in a controlled and robust manner. The intrinsic wettability of the coatings was varied from hydrophilic to hydrophobic. The measured water contact angle could not be described by the classical theories. We developed an empirical model that effectively captures the experimental data, and further enables us to predict the wetting of surfaces with nanoscale roughness by considering the physical and chemical properties of the material. The fundamental insights presented here are important for the rational design of advanced materials having tailored surface nanotopography with predictable wettability.

The Effect of ZnAl2O4 on the Performance of Cu/ZnxAlyOx+1.5y Supported Catalysts in Steam Reforming of Methanol

This paper demonstrates the benefit of using spinel (ZnAl2O4) as a support for copper catalysts in hydrogen generation. We have investigated the influence of catalyst pre-treatment, support composition and copper content on the physicochemical and catalytic properties of copper catalysts supported on ZnxAlyOx+1.5y in the methanol steam reforming. The physicochemical properties of the catalysts were examined by X-ray diffraction, temperature-programmed reduction, specific surface area and porosity, X-ray photoelectron spectroscopy, FTIR and chemisorption methods. The reduced copper catalysts showed higher conversion of methanol and higher hydrogen production. We also found that the presence of Cu+ and Cu0 species on the catalyst surface strongly influences the reaction yield and hydrogen production. FTIR measurements performed for copper catalysts confirmed that increasing of aluminium content in the case of catalytic systems caused the growth of adsorbed species on the catalyst surface.

The effect of gold on modern bimetallic Au–Cu/MWCNT catalysts for the oxy-steam reforming of methanol

Copper and gold doped copper catalysts supported on multi-walled carbon nanotubes were prepared by wet impregnation and deposition–precipitation methods, respectively. The catalysts were tested in the oxy-steam reforming of methanol (OSRM) and characterized by XRD, SEM-EDS, TOF-SIMS, thermo-gravimetric analysis and temperature-programmed desorption of ammonia. The reactivity results showed the promotion effect of gold on the activity and selectivity of the copper catalysts in the OSRM. The formed Cu–Au alloy as an active phase was responsible for the activity and selectivity improvement of the bimetallic catalysts in the oxy-steam reforming of methanol. The formation of an Au–Cu alloy was confirmed by the XRD, TOF-SIMS and SEM-EDS techniques. The reducibility and acidity of the tested catalysts are important factors, which influence the activity of the copper and gold–copper catalysts.

Influence of immobilized quaternary ammonium group surface density on antimicrobial efficacy and cytotoxicity

Abstract Bacterial colonization of medical devices causes infections and is a significant problem in healthcare. The use of antibacterial coatings is considered as a potential solution to this problem and has attracted a great deal of attention. Using concentration density gradients of immobilized quaternary ammonium compounds it was demonstrated that a specific threshold of surface concentration is required to induce significant bacterial death. It was determined that this threshold was 4.18% NR4+ bonded nitrogen with a surface potential of + 120.4 mV. Furthermore, it is shown for the first time that adhesion of constituents of the culture medium to the quaternary ammonium modified surface eliminated any cytotoxicity towards eukaryotic cells such as primary human fibroblasts. The implications of this type of surface fouling on the antimicrobial efficacy of surface coatings are also discussed.

The Role of Surface Nanotopography and Chemistry on Primary Neutrophil and Macrophage Cellular Responses

Synthetic materials employed for enhancing, replacing, or restoring biological functionality may be compromised by the host immune responses that they evoke. Surface modification has attracted substantial attention as a tool to modulate the host response to synthetic materials; however, how surface nanotopography combined with chemistry affects immune effector cell responses is still poorly understood. To address this open question, a unique set of model surfaces with controlled surface nanotopography in the range of 16, 38, and 68 nm has been generated. Tailored outermost surface chemistry that was amine, carboxyl, or methyl group rich has been provided. The combinations of these properties yield 12 surface types that are subject to functional assays assessing key immune effector cells, namely, primary neutrophil and macrophage responses in vitro. The data demonstrate that surface nanotopography leads to enhanced matrix metalloproteinase-9 production from primary neutrophils, and a decrease in pro-inflammatory cytokine secretion from primary macrophages. Together, these results are the first to directly compare the immunomodulatory effects of the cooperative interplay between surface nanotopography and chemistry.

Versatile gradients of chemistry, bound ligands and nanoparticles on alumina nanopore arrays

Nanoporous alumina (PA) arrays produced by self-ordering growth, using electrochemical anodization, have been extensively explored for potential applications based upon the unique thermal, mechanical and structural properties, and high surface-to-volume ratio of these materials. However, the potential applications and functionality of these materials may be further extended by molecular-level engineering of the surface of the pore rims. In this paper we present a method for the generation of chemical gradients on the surface of PA arrays based upon plasma co-polymerization of two monomers. We further extend these chemical gradients, which are also gradients of surface charge, to those of bound ligands and number density gradients of nanoparticles. The latter represent a highly exotic new class of materials, comprising aligned PA, capped by gold nanoparticles around the rim of the pores. Gradients of chemistry, ligands and nanoparticles generated by our method retain the porous structure of the substrate, which is important in applications that take advantage of the inherent properties of these materials. This method can be readily extended to other porous materials.

MWCNTs as a catalyst in oxy-steam reforming of methanol

The catalytic activity of multi-walled carbon nanotubes (MWCNTs) in oxy-steam reforming of methanol (ASRM) was investigated for the first time. We demonstrate that CNTs are a potent catalytic material for hydrogen generation in oxy-steam reforming of methanol.