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Extracellular deoxyribonucleic acid (eDNA) exists in biological environments such as those around medical implants since prokaryotic or eukaryotic cells can undergo processes such as autolysis, necrosis, and apoptosis. For bacteria, eDNA has been shown to be involved in biofilm formation and gene transfer and acts as a nutrient source. In terms of biofilm formation, eDNA in solution has been shown to be very important in increasing attachment; however, very little is known about the role played by surface immobilized eDNA in initiating bacterial attachment and whether the nature of a DNA layer (physically adsorbed or covalently attached, and molecular weight) influences biofilm formation. In this study, the authors shed light on the role that surface attached DNA plays in the early biofilm formation by using Si wafers (Si) and allylamine plasma polymer (AAMpp) coated Si wafers to adsorb and covalently immobilize salmon sperm DNA of three different molecular weights. Pseudomonas aeruginosa was chosen to study the bacterial interactions with these DNA functionalized surfaces. Characterization of surface chemistry and imaging of attached bacteria were performed via x-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and epi-fluorescence microscopy. XPS results confirmed the successful grafting of DNA on the AAMpp and Si surfaces, and surprisingly the results showed that the surface attached DNA actually reduced initial bacterial attachment, which was contrary to the initial hypothesis. This adds speculation about the specific role played by DNA in the dynamics of how it influences biofilm formation, with the possibility that it could actually be used to make bacterial resistant surfaces.

Ordered surface nanostructures have attracted much attention in different fields including biomedical engineering because of their potential to study the size effect on cellular response and modulation of cell fate. However, the ability to fabricate large-area ordered nanostructures is typically limited due to high costs and low speed of fabrication. Herein, highly ordered nanostructures with large surface areas (>1.5 × 1.5 cm(2)) were fabricated using a combination of facile techniques including colloidal self-assembly, colloidal lithography, and glancing angle deposition (GLAD). An ordered tantalum (Ta) pattern with 60-nm-height was generated using colloidal lithography. A monolayer of colloidal crystal, i.e., hexagonal close packed 720 nm polystyrene particles, was self-assembled and used as a mask. Ta patterns were subsequently generated by evaporation of Ta through the mask. The feature size was further increased by 100 or 200 nm using GLAD, resulting in the fabrication of four different surfaces (FLAT, Ta60, GLAD100, and GLAD200). Cell adhesion, proliferation, and mineralization of MG63 osteoblast-like cells were investigated on these ordered nanostructures over a 1 week period. Our results showed that cell adhesion, spreading, focal adhesion formation, and filopodia formation of the MG63 osteoblast-like cells were inhibited on the GLAD surfaces, especially the initial (24 h) attachment, resulting in a lower cell density on the GLAD surfaces. After 1 week culture, alkaline phosphatase activity and the amount of Ca was higher on the GLAD surfaces compared with Ta60 and FLAT controls, suggesting that the GLAD surfaces facilitate differentiation of osteoblasts. This study demonstrates that ordered Ta nanotopographies synthesized by combining colloidal lithography with GLAD can improve the mineralization of osteoblast-like cells providing a new platform for biomaterials and bone tissue engineering.

Biofilm formation on medical implants and subsequent infections are a global problem. A great deal of effort has focused on developing chemical contrasts based on micro- and nanopatterning for studying and controlling cells and bacteria at surfaces. It has been known that micro- and nanopatterns on surfaces can influence biomolecule adsorption, and subsequent cell and bacterial adhesion. However, less focus has been on precisely controlling patterns to study the initial bacterial attachment mechanisms and subsequently how the patterning influences the role played by biomolecular adsorption on biofilm formation. In this work, the authors have used colloidal self-assembly in a confined area to pattern surfaces with colloidal crystals and used them as masks during allylamine plasma polymer (AAMpp) deposition to generate highly ordered patterns from the micro- to the nanoscale. Polyethylene glycol (PEG)-aldehyde was grafted to the plasma regions via "cloud point" grafting to prevent the attachment of bacteria on the plasma patterned surface regions, thereby controlling the adhesive sites by choice of the colloidal crystal morphology. Pseudomonas aeruginosa was chosen to study the bacterial interactions with these chemically patterned surfaces. Scanning electron microscope, x-ray photoelectron spectroscopy (XPS), atomic force microscopy, and epifluorescence microscopy were used for pattern characterization, surface chemical analysis, and imaging of attached bacteria. The AAMpp influenced bacterial attachment because of the amine groups displaying a positive charge. XPS results confirm the successful grafting of PEG on the AAMpp surfaces. The results showed that PEG patterns can be used as a surface for bacterial patterning including investigating the role of biomolecular patterning on bacterial attachment. These types of patterns are easy to fabricate and could be useful in further applications in biomedical research.

Background: The ability to present signalling molecules within a low fouling 3D environment that mimics the extracellular matrix is an important goal for a range of biomedical applications, both in vitro and in vivo. Cell responses can be triggered by non-specific protein interactions occurring on the surface of a biomaterial, which is an undesirable process when studying specific receptor-ligand interactions. It is therefore useful to present specific ligands of interest to cell surface receptors in a 3D environment that minimizes non-specific interactions with biomolecules, such as proteins., Method: In this study, surface-initiated atom transfer radical polymerization (SI-ATRP) of poly(ethylene glycol)-based monomers was carried out from the surface of electrospun fibers composed of a styrene/vinylbenzyl chloride copolymer. Surface initiated radical addition-fragmentation chain transfer (SI-RAFT) polymerisation was also carried out to generate bottle brush copolymer coatings consisting of poly(acrylic acid) and poly(acrylamide). These were grown from surface trithiocarbonate groups generated from the chloromethyl styrene moieties existing in the original synthesised polymer. XPS was used to characterise the surface composition of the fibers after grafting and after coupling with fluorine functional XPS labels., Results: Bottle brush type coatings were able to be produced by ATRP which consisted of poly(ethylene glycol) methacrylate and a terminal alkyne-functionalised monomer. The ATRP coatings showed reduced non-specific protein adsorption, as a result of effective PEG incorporation and pendant alkynes groups existing as part of the brushes allowed for further conjugation of via azide-alkyne Huisgen 1,3-dipolar cycloaddition. In the case of RAFT, carboxylic acid moieties were effectively coupled to an amine label via amide bond formation. In each case XPS analysis demonstrated that covalent immobilisation had effectively taken place., Conclusion: Overall, the studies presented an effective platform for the preparation of 3D scaffolds which contain effective conjugation sites for attachment of specific bioactive signals of interest, as well as actively reducing non-specific protein interactions.