Fabrication of switchable protein resistant and adhesive multilayer membranes

Spectro-kinetic investigations on the release mechanism of lysozyme from layer-by-layer reservoirs

The investigations of protein adsorption and release on interfaces aid in the elucidation of the protein-surface interaction mechanism, which has several applications in the biomedical area. The spectro-kinetic and morphological analysis of the release of lysozyme (Lyz) from chitosan/polystyrene sulphonate (CHI/PSS) multilayer immobilized at pHs 10.6, 8.8 and 5.0 shows that the extent of release strongly depends on the pH of Lyz loading and the ionic strength of the desorbing solution. When compared to pH 8.8, the release for pH 10.6 achieves equilibrium more rapidly. At loading pH 10.6, the release is surface-mediated, at pH 8.8, it is both surface- and bulk-mediated, while at pH 5.0 it is bulk mediated with minimal release. Lyz released for loading pH 10.6 retains its native secondary structure. Kinetic fitting suggests that high loading pH 8.8-10.6 and high release ionic strength (0.5-1.0 M NaCl) lead to burst release of Lyz from CHI/PSS multilayer. Surface morphology changes of multilayer interface upon Lyz loading and release are highlighted by SEM topography and AFM height distribution analysis. The present work indicates that CHI/PSS multilayer system can function as a reservoir for burst as well as controlled release of lysozyme by selecting the loading pH and ionic strength.

The influence of polyanion molecular weight on polyelectrolyte multilayers at surfaces: protein adsorption and protein-polysaccharide complexation/stripping on natural polysaccharide films on solid supports

Two different fucoidan polymers (unfractionated Fucus vesiculosus fucoidan, and fractionated low molecular weight Fucus vesiculosus fucoidan) have been used to create substrates for protein adsorption studies. Polyelectrolyte multilayers were formed using the fucoidans (polyanions) with chitosan as the corresponding polycation. Multilayer formation was studied using zeta potential measurements, quartz crystal microbalance with dissipation monitoring (QCM-D) and attenuated total reflectance (ATR) FTIR spectroscopy. The formation studies reveal that the low molecular weight (LMW) fucoidan produces a less hydrated multilayer, with a significantly increased adsorbed mass, and with fucoidan as the diffusing species during formation. Protein adsorption studies using bovine serum albumin (BSA) were undertaken for solution conditions designed to mimic biological conditions, and to minimise the role of electrical double layer forces in influencing adsorption. Under these conditions, and as revealed by ATR FTIR spectroscopy, BSA is seen to adsorb less substantially to multilayers formed with the LMW fucoidan, and to cause extraction/stripping of the LMW fucoidan from the multilayer. FTIR spectra reveal that the protein adopts a different conformation when adsorbed to the LMW fucoidan multilayer, both relative to the protein in solution and when adsorbed at the surface of the multilayer formed from unfractionated fucoidan.

Sustainable polyelectrolyte multilayer surfaces: possible matrix for salt/dye separation

The development of a sustainable membrane surface based on chitosan/poly(acrylic acid) (CHI/PAA) multilayers suitable for applications in analytical separations is reported here. Bilayers are constructed on polyamide microfiltration membranes at a pH combination of 3/3 (CHI pH/PAA pH) through a layer by layer approach. A 12.5 bilayer yielded a thickness of 400 nm. Low pressure (10 psi) filtrations through a 5.5 bilayered membrane exhibited high flux (7 m(3) m(-2) day(-1)) and selectivity (NaCl/reactive black 5 (RB5) selectivity >8000). The selectivity and flux observed here are the highest reported to date for low pressure filtrations through membranes. The increase in flux with increasing feed salt concentration is correlated with morphological transformations. Salt content above 7500 ppm causes some perturbation of surface layers. The presence of RB5, a model dye in the feed, restores the surface to maintain sustainability. A skin layer as thin as 50 nm imparts a large separation window. An RB5 feed concentration of 500 ppm results in 98.64% rejection with a flux of 25.79 m(3) m(-2) day(-1). The increase in flux with feed dye concentration supports the plasticizing action of RB5. The transport studies with large feed dye concentrations indicate that at a dye concentration of 500 ppm, the linear growing region (pre-exponential, 5.5 bilayer) itself provides a separation window similar to that of 100 ppm. At the same time, 1000 ppm requires a 9.5 bilayer that falls in the nonlinear growing region. Scanning electron microscopy images show the increase in porosity with respect to feed dye. Interesting morphologies that show the sustainable nature of the membrane surfaces along with the transport data of RB5 are presented.

Peptide-surface adsorption free energy comparing solution conditions ranging from low to medium salt concentrations

Multi-technique methods involving surface plasmon resonance spectroscopy and atomic force microscopy provide experimental data for the characterization of peptide adsorption on self-assembled monolayers. A comparative study is carried out in phosphate-buffered saline (PBS) and potassium phosphate-buffered (PPB) water to determine the influence of the salt concentration on the adsorption behavior (see figure; ΔG(0)(ads) : free energy of peptide adsorption, F(des) : force required for peptide desorption).