A poly(ethylene glycol) (PEG)-based matrix for studies of affinity interactions is developed and demonstrated. The PEG matrix, less than 0.1 μm thick, is graft copolymerized onto a cycloolefin polymer from a mixture of PEG methacrylates using a free radical reaction initiated by UV light at 254 nm. The grafting process is monitored in real time, and characteristics such as thickness, homogeneity, relative composition, photostability, and performance in terms of protein resistance in complex biofluids and sensor qualities are investigated with null ellipsometry, infrared spectroscopy, and surface plasmon resonance. The matrix is subsequently modified to contain carboxyl groups, thereby making it possible to immobilize ligands in a controlled and functional manner. Human serum albumin and fibrinogen are immobilized and successfully detected by antibody recognition using surface plasmon resonance. The results are encouraging and suggest that the PEG matrix is suitable for biochip and biosensor applications in demanding biofluids.

This work describes the fabrication, characterization, and protein adsorption behavior of charged polymer gradients. The thin gradient films were fabricated by a two-step technique using UV-initiated free-radical polymerization in a reactor with a moving shutter. A homogeneous layer of cationic poly(2-aminoethyl methacrylate hydrochloride) was first formed, followed by a layer of oppositely charged poly(2-carboxyethyl acrylate) with a continuously increasing thickness. Adsorption from protein solutions as well as human blood plasma was investigated by imaging surface plasmon resonance and infrared microscopy. The results showed excessive protein adsorption in the areas where one of the polymers dominated the composition, while there was a clear minimum at an intermediate position of the gradient. The charge of the surface was estimated by direct force measurements and found to correlate well with the protein adsorption, showing the lowest net charge in the same area as the protein adsorption minimum. We therefore hypothesize that a combination of the charged polymers, in the right proportions, can result in a protein-resistant surface due to balanced charges.

In this work we have evaluated the haemocompatibility of different surface modifications, intended for biomaterials and biosensor applications. Polystyrene slides were coated with thin hydrogel films by self-initiated photografting of four different monomers. The hydrogel surface modifications were thoroughly characterized and tested for their protein resistance and ability to facilitate platelet adhesion and activation of the coagulation system. There was very little protein adsorption from human plasma on the hydrogels formed from poly(ethylene glycol) methacrylate (PEGMA) and 2-hydroxyethyl methacrylate (HEMA). Platelet adhesion tests performed under both static and flow conditions showed that these coatings also demonstrated very high resistance towards platelet adhesion. A small amount of platelets were found to adhere to hydrogels formed from ethylene glycol methyl ether methacrylate (EGMEMA) and 2-carboxyethyl methacrylate (CEA). The polystyrene substrates themselves facilitated large amounts of platelet adhesion under both static and flow conditions. Utilizing a novel setup for imaging of coagulation, it was shown that none of the hydrogel surfaces activated the coagulation system to any great extent. We suggest that this simple fabrication method can be used to produce hydrogel coatings with unusually high blood compatibility, suitable for demanding biomaterials applications.

This work describes the preparation and properties of hydrogel surface chemistries enabling controlled and well-defined cell adhesion. The hydrogels may be prepared directly on plastic substrates, such as polystyrene slides or dishes, using a quick and experimentally simple photopolymerization process, compatible with photolithographic and microfluidic patterning methods. The intended application for these materials is as substrates for diagnostic cell adhesion assays, particularly for the analysis of human platelet function. The adsorption of fibrinogen and other platelet promoting molecules is shown to be completely inhibited by the hydrogel, provided that the film thickness is sufficient (>5 nm). This allows the hydrogel to be used as a matrix for presenting selected bioactive ligands without risking interference from nonspecifically adsorbed platelet adhesion factors, even in undiluted whole blood and blood plasma. This concept is demonstrated by preparing patterns of proteins on hydrogel surfaces, resulting in highly controlled platelet adhesion. Further insights into the protein immobilization and platelet adhesion processes are provided by studies using imaging surface plasmon resonance. The hydrogel surfaces used in this work appear to provide an ideal platform for cell adhesion studies of platelets, and potentially also for other cell types.

Hydrogels are used to enhance biocompatibility and reduce inflammation in biomedical applications, and as area-enlarging matrices in bioanalytical devices. For either of these applications, the structure of the hydrogel is important for the function, and thus structural understanding of hydrogels in their wet state is highly relevant for the use and development of these materials. Also, processing of these materials is frequently made in ambient air, and it is of interest to relate the properties of dry, or humid air-swollen hydrogels, to their wet properties.

We use neutron reflectometry to follow the swelling of hydrogels in air of controlled humidity. Comparing hydrogels prepared on silica and gold substrates { both of relevance to bioanalytical applications { we observe that the swelling is different, reflecting a structural difference between these polymers, but that the water content of the polymer films near saturation is near 33% in both cases. Upon immersion in water, the swelling is estimated to approximately 2 x the dry thickness of the polymer, though a consistent quantitative determination of the polymer profile could not be made. Finally, we observe that the hydrogels are unaffected by either positively and negatively charged proteins.

The surface interactions of exploring cyprids of the barnacle Semibalanus balanoides were studied in situ using imaging surface plasmon resonance. It was demonstrated how the deposition of a proteinaceous adhesive could be followed in real time as the cyprids explored and temporarily attached to a surface. Furthermore, the amount of protein left on the surface when the cyprids moved on could be quantified. Clear differences were demonstrated between an oligo(ethyleneglycol) coated surface and a bare gold substrate. It is anticipated that this technique will be a valuable tool in the development of novel surface chemistries that can prevent biofouling.

Imaging surface plasmon resonance (iSPR) was employed to investigate the interfacial adhesion phenomena that occur during the exploration of immersed surfaces by barnacle cyprids (Semibalanus balanoides). It was hypothesised that since the footprint material used by cyprids for temporary adhesion has previously been related to a large cuticular glycoprotein (SIPC), the passive deposition of cyprid footprints and the binding of SIPC to surfaces might correlate. Increased surface exploration (and footprint deposition) has also been related to increased likelihood of settlement in barnacle cyprids. If a correlation between footprint deposition and SIPC binding were to exist, therefore, there would be potential for the development of a high‐throughput assay to determine the efficacy of putative antifouling chemistries against cyprids prior to, or instead of, lengthy bio‐assays. Footprints were deposited in large numbers on carboxyl‐terminated self‐assembled monolayers (SAMs) and in very small numbers on ethylene glycol‐containing SAMs and hydrogel coatings. SIPC binding also followed the same trend. An exception to the correlation was an amineterminated SAM that accumulated few cyprid footprints, but bound SIPC strongly. It is concluded that there is great potential for the iSPR technique to be used in the evaluation of putatively non‐fouling surfaces as well as improving our understanding of the nature of the cyprid footprint material and its interactions with surfaces of different chemistry. However, the use of SIPC binding as a predictor of footprint accumulation/likelihood of settlement of cyprids to surfaces would be premature at this stage without first understanding the exceptions highlighted in this study.