This paper presents a method for chemical and biomolecule patterning on planar (2D) surfaces using atmospheric
pressure microplasmas. Spatially controlled surface modification is important for the development of emerging
technologies such as microfluidic lab-on-a-chip devices, biosensors and other diagnostics tools. A non-fouling layer of
poly(N-isopropylacrylamide) aldehyde (pNIPAM-ald) polymer, grafted onto heptylamine plasma polymer (HApp)
modified silicon substrates, was used to achieve this goal. The non-fouling behaviour of the pNIPAM-ald coating was
investigated at a temperature below its lower critical solution temperature (LCST) using human serum albumin (HSA).
XPS and ToF-SIMS were used to characterise the plasma polymer coating and its subsequent modification with
pNIPAM-ald before and after HSA adsorption. A 7 x 7 microcavity plasma array device (each cavity had a 250 Νm
diameter and was separated by 500 μm) was used for microplasma patterning. In a non-contact mode, helium
microplasma treatment of the pNIPAM-ald coating was carried out for 60 s. The polymer coating was removed from
regions directly exposed to microplasma cavities, as shown by ToF-SIMS. Microplasma treated regions were able to
support the adsorption of fluorescently-labelled streptavidin whereas the rest of the coating was still non-fouling. This
approach therefore resulted in spatially separated areas of immobilised protein.
Control over biomolecule interactions at interfaces is becoming an increasingly important goal for a range of scientific
fields and is being intensively studied in areas of biotechnological, biomedical and materials science. Improvement in the
control over materials and biomolecules is particularly important to applications such as arrays, biosensors, tissue
engineering, drug delivery and 'lab on a chip' devices. Further development of these devices is expected to be achieved
with thin coatings of stimuli responsive materials that can have their chemical properties 'switched' or tuned to stimulate
a certain biological response such as adsorption/desorption of proteins. Switchable coatings show great potential for the
realisation of spatial and temporal immobilisation of cells and biomolecules such as DNA and proteins.
This study focuses on protein adsorption onto coatings of the thermosensitive polymer poly(N-isopropylacrylamide)
(pNIPAM) which can exhibit low and high protein adsorption properties based on its temperature dependent
conformation. At temperatures above its lower critical solution temperature (LCST) pNIPAM polymer chains are
collapsed and protein adsorbing whilst below the LCST they are hydrated and protein repellent.
Coatings of pNIPAM on silicon wafers were prepared by free radical polymerisation in the presence of surface bound
polymerisable groups. Surface analysis and protein adsorption was carried out using X-ray photoelectron spectroscopy,
time of flight secondary ion mass spectrometry and contact angle measurements.
This study is expected to aid the development of stimuli-responsive coatings for biochips and biodevices.
Two-dimensional control over the location of proteins on surfaces is desired for a number of applications including diagnostic tests and tissue engineered medical devices. Many of these applications require patterns of specific proteins that allow subsequent two-dimensionally controlled cell attachment. The ideal technique would allow the deposition of specific protein patterns in areas where cell attachment is required, with complete prevention of unspecific protein adsorption in areas where cells are not supposed to attach. In our study, collagen I was used as an example for an extracellular matrix protein known to support the attachment of bovine corneal epithelial cells. An allylamine plasma polymer was deposited on a silicon wafer substrate, followed by grafting of poly(ethylene oxide). Two-dimensional control over the surface chemistry was achieved using a 248 nm excimer laser. Results obtained by XPS and AFM show that the combination of extremely low-fouling surfaces with excimer laser ablation can be used effectively for the production of spatially controlled protein patterns with a resolution of less than 1 micrometers . Furthermore, it was shown that bovine corneal epithelial cell attachment followed exactly the created protein patterns. The presented method is an effective tool for a number of in vitro and in vivo applications.
For many applications, it is essential to be able to control the interface between devices and the biological environment by nanoscale control of the composition of the surface chemistry and the surface topography. Application of molecular thickness coatings of biologically active macromolecules provides predictable interfacial control over interactions with biological media. The covalent surface immobilization of polysaccharides, proteins, and synthetic oligopeptides can be achieved via ultrathin interfacial bonding layers deposited by gas plasma methods, and the multistep coating schemes are verified by XPS analyses. Interactions between biomolecular coatings and biological fluids are studied by MALDI mass spectrometry and ELISA assays. Using a colloid-modified AFM tip, quantitative measurement of interfacial forces is achieved. Comparison with theoretical predictions allows elucidation of the key interfacial forces that operate between surfaces and approaching macromolecules. In this way, it is possible to unravel the fundamental information required for the guided design and optimization of biologically active nanoscale coatings that confer predictable properties to synthetic carriers. We have established for instance the key properties that make specific polysaccharide coatings resistant to the adsorption of proteins, which is applicable to biomaterials, biosensors, and biochips research.
The two-dimensional control of cell adhesion is desired for a number of cell- and tissue culture applications. Thus, a suitable method for the two-dimensional control over surface chemistry, which leads to the display of cell-adhesive and non-adhesive signals is required. In our study, allylamine plasma polymer (ALAPP) deposition has been used to provide a cell-adhesive substrate, while additional grafting of poly(ethylene oxide) (PEO) on ALAPP surfaces has been used to prevent cell adhesion. Two-dimensional control over the surface chemistry was achieved using excimer laser ablation. Ablation experiments were carried out using a 248 nm excimer laser with energy densities of 17 - 1181 mJ/cm2 and 1 - 16 pulses per area. Results obtained by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) show controlled thickness ablation of the plasma polymer and the additional PEO graft polymer. Cell culture experiments using bovine corneal epithelial cells show that two-dimensional control of cell adhesion can be achieved by using appropriate masks in the laser beam.
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