Analysing protein competition on self-assembled mono-layers studied with quartz crystal microbalance.

The mechanisms by which proteins adsorb to surfaces of biomaterials have long been of interest. The present work started with the premise that small/hard and large/soft proteins will yield different sets of normalized frequency shift and dissipation signals when studied with a quartz crystal microbalance. The aim was to evaluate the usefulness of these raw data to study protein competition using protein incubations in sequence and from mixtures of albumin (BSA) and gamma-globulin (BGG) at various ratios. Increasing the concentration of BSA decreases the adsorption of subsequently incubated BGG. For BSA/BGG mixtures the dissipation is similar for all logarithmic molar ratios BGG/BSA below 1 but soon decreases when the molar ratio of BSA/BGG (and opposite for the normalized frequency shift) is above 1, indicating preferential binding of BGG. Modelling indicated that differences in the film shear modulus and viscosity depend more on the properties of the self-assembling mono-layers (SAMs) than on the proteins. Films high in BSA tentatively differ in film shear modulus and viscosity from that of films high in BGG but only on the hydrophobic surfaces. The results were encouraging as the raw data were deemed to be able to point at protein adsorption competition.

Proteins and their peptide motifs in acellular apatite mineralization of scaffolds for tissue engineering.

Many proteins in the inorganic/organic matrix of bone induce or modulate or inhibit mineralization of apatite in vivo. Many attempts have been made to mimic and understand this mechanism as part of bone formation, and ectopic mineralization and control thereof. Many attempts have also been made to use such proteins or protein fragments to harness their potential for improved mineralization. Such proteins and peptide motifs have also been the inspiration for attempts of making mimics of their structures and motifs using chemical or biological synthesis. The aim of this review is to highlight how proteins and (poly)peptides themselves impact mineralization in the human body, and how those could be used and have been used for improving apatite mineralization, for example, on or in materials that by themselves do not induce apatite mineralization but otherwise have interesting properties for use as bone tissue engineering scaffolds.

Plasma surface modification of chitosan membranes: characterization and preliminary cell response studies.

Surface modification of biomaterials is a way to tailor cell responses whilst retaining the bulk properties. In this work, chitosan membranes were prepared by solvent casting and treated with nitrogen or argon plasma at 20 W for 10-40 min. AFM indicated an increase in the surface roughness as a result of the ongoing etching process. XPS and contact angle measurements showed different surface elemental compositions and higher surface free energy. The MTS test and direct contact assays with an L929 fibroblast cell line indicated that the plasma treatment improved the cell adhesion and proliferation. Overall, the results demonstrated that such plasma treatments could significantly improve the biocompatibility of chitosan membranes and thus improve their potential in wound dressings and tissue engineering applications.

Surface plasmon resonance detection of blood coagulation and platelet adhesion under venous and arterial shear conditions.

A surface plasmon resonance (SPR) based flow chamber device was designed for real time detection of blood coagulation and platelet adhesion in platelet rich plasma (PRP) and whole blood. The system allowed the detection of surface interactions throughout the 6mm length of the flow chamber. After deposition of thromboplastin onto a section of the sensor surface near the inlet of the flow chamber, coagulation was detected downstream of this position corresponding to a SPR signal of 7 to 8 mRIU (7 to 8 ng/mm2). A nonmodified control surface induced coagulation 3.5 times slower. Platelet adhesion to gold and fibrinogen coated surfaces in the magnitude of 1.25 and 1.66 mRIU was also shown with platelets in buffer, respectively. SPR responses obtained with PRP and whole blood on surfaces that were methylated or coated with von Willebrand factor (vWF), fibrinogen, or collagen, coincided well with platelet adhesion as observed with fluorescence microscopy in parallel experiments. The present SPR detection equipped flow chamber system is a promising tool for studies on coagulation events and blood cell adhesion under physiological flow conditions, and allows monitoring of short-range surface processes in whole blood.

Fluorescence probe techniques to monitor protein adsorption-induced conformation changes on biodegradable polymers.

The study of protein adsorption and any associated conformational changes on interaction with biomaterials is of great importance in the area of implants and tissue constructs. This study aimed to evaluate some fluorescent techniques to probe protein conformation on a selection of biodegradable polymers currently under investigation for biomedical applications. Because of the fluorescence emanating from the polymers, the use of monitoring intrinsic protein fluorescence was precluded. A highly solvatochromic fluorescent dye, Nile red, and a well-known protein label, fluorescein isothiocyanate, were employed to study the adsorption of serum albumin to polycaprolactone and to some extent also to two starch-containing polymer blends (SPCL and SEVA-C). A variety of fluorescence techniques, steady state, time resolved, and imaging were employed. Nile red was found to leach from the protein, while fluorescein isothiocyanate proved useful in elucidating a conformational change in the protein and the observation of protein aggregates adsorbed to the polymer surface. These effects were seen by making use of the phenomenon of energy migration between the fluorescent tags to monitor interprobe distance and the use of fluorescence lifetime imaging to ascertain the surface packing of the protein on polymer.

Effect of the labelling ratio on the photophysics of fluorescein isothiocyanate (FITC) conjugated to bovine serum albumin.

The non-linearity of the fluorescence emission on increasing the probe to protein ratio has long been regarded as problematic and has lead to the development of dyes to overcome this effect. One of the causes of this non-linear response can be ascribed to the overlap of the label's own absorption and emission spectra. At higher labelling ratios, this affords the possibility of a reasonably efficient energy migration pathway, thus reducing the observed quantum yield of the dye. In this work we study the photophysics of fluorescein isothiocyanate (FITC) when conjugated to bovine serum albumin (BSA) at different labelling ratios (in the range FITC : BSA 1 : 17-15 : 1) using both steady state and time-resolved fluorescence techniques where on going from under labelled to over labelled samples a decrease in the initial (and steady state) anisotropy is observed, accompanied by an increase in the complexity of the decay kinetics and a decrease in the average lifetime. The band structure, elucidated by synchronous scan fluorescence spectroscopy, is also found to change on increased labelling. These results can be applied to the study of protein conformation and were confirmed by the analysis of denaturing BSA using urea.

Blood protein adsorption onto chitosan.

Chitosan was recently indicated to enhance osteogenesis, improve wound healing but to activate the coagulation and the complement systems. In the present study approximately 10 nm thick chitosan film were prepared on aminopropyltriethoxysilane (APTES) coated silicon. The surfaces were incubated in serum or plasma and subsequently in antibodies towards key complement and contact activation of coagulation proteins. The deposited amounts were compared with those on hydrophilic and hydrophobic silicon, APTES and IgG coated reference samples. Although large amounts of serum deposited to chitosan only a weak transient activation of the complement system and no activation of the intrinsic pathway was observed. Upon acetylation the chitosan layer became a strong activator of the alternative pathway of the complement. After incubation in human plasma anti-fibrinogen deposited onto chitosan but not onto the acetylated chitosan, a finding that may explain previous observations of procoagulant activity by chitosan.

The determination of thickness and surface mass density of mesothick immunoprecipitate layers by null ellipsometry and protein 125iodine labeling.

The aim of the present study was to ellipsometrically determine the thickness and surface mass density in air for up to 110-nm-thick organic layers made of alternatingly deposited layers of HSA and polyclonal anti-HSA on hydrophobic silicon. The ellipsometrically determined thickness was compared to that obtained by AFM and the deposited surface mass density calibrated with (125)I-labeled proteins. The results indicate a good agreement in protein layer thickness between AFM and ellipsometry when the protein film refractive index N(film)=1.5-0i, although then the calculated surface mass density from the ellipsometry data became grossly overestimated by the Cuypers one-component formula. A good agreement in the surface mass density was obtained when the M/A ratio in this formula was lowered from 4.14 to 2.35. This approach indicates a convenient means of determining the refractive indices and surface mass densities of mesothick organic layers proteins on solid supports.