Poly(ether imide) membranes: studies on the effect of surface modification and protein pre-adsorption on endothelial cell adhesion, growth and function.

Poly(ether imide) (PEI) membranes of which the surface was modified with carboxylic groups were tested in comparison to pure PEI and poly(ethylene terephtalate) (PET) for their ability to support attachment, growth and function of human umbilical vein endothelial cells (HUVEC) with respect to endothelization of the above materials. Flat sheet PEI membranes were modified by covalent binding of iminodiacetic acid (IDA) for different periods of time (1 to 30 min) to obtain surfaces with various content of carboxylic groups. In addition, fibronectin (FN) and fibrinogen (FNG) pre-adsorption on the various membranes were studied for their effect on HUVEC behaviour. The results show a decreased protein adsorption and HUVEC adhesion, growth and function in terms of prostacyclin production with an increase in carboxylic groups. Pre-adsorption of the membranes with FN or FNG promoted activity of HUVEC, which became superior to cells on PET. FN-coated membranes were found to be a better substrate for HUVEC adhesion and prostacyclin production, while on FNG-coated membranes cells grew better. Overall it can be concluded that PEI is a promising materials for endothelial cells immobilization as it is needed for improving the haemocompatibility of cardiovascular devices.

Hemocompatibility of poly(ether imide) membranes functionalized with carboxylic groups.

Materials for blood-contacting applications have to meet high requirements in terms to prevent thrombotic complications after the medical treatment. Surface induced thrombosis, e.g., after application of cardiovascular devices, is linked clearly to the activation of coagulation system and platelet adhesion and activation. The flat sheet poly(ether imide) membrane (PEI) was modified by binding of iminodiacetic acid (IDA) for different periods of time to obtain surfaces with carboxylic (-COOH) groups, namely PEI-1 (modified for 1 min) and PEI-2 (modified for 30 min). The successful binding of the ligands was monitored by thionin acetate assay. The physico-chemical characteristics of the materials were analyzed by SEM, AFM, water contact angle, and Zeta potential measurements. Hemocompatibility of the polymer materials was studied by analyzing the activation of coagulation system (plasma kallikrein-like activity) and platelet adhesion/activation by using immunofluorescence technique. The blood response to PEI membranes was compared to that of a commercial poly(ethylene terephthalate) (PET) membrane. Our results showed that the increase of the negative charges on the modified PEI membrane surfaces (number of -COOH groups) caused a higher contact activation of the coagulation system and a higher rate of platelet adhesion and activation compared to non-modified PEI. However, overall the hemocompatibility of all PEI membranes was higher than that of PET.

Wettability of substrata controls cell-substrate and cell-cell adhesions.

The maintenance of endothelial cell (EC) monolayer architecture requires stable adhesions not only between neighboring cells but also between cells and the extracellular matrix. While the influence of biomaterials surface wettability on cell-substratum adhesion is rather well studied, its impact on cell-cell cohesion has not been extensively investigated. In the present study a model system consisting of hydrophilic and hydrophobic glass pre-coated with fibronectin and fibrinogen was used to study the influence of surface wettability on both types of cell adhesions. It was demonstrated that the substrate wettability controls the adhesion and cytoskeletal organization of endothelial cells, which has an impact on the subsequent ability of cells to establish stable cell-cell cohesions. These effects were related to the accessibility of specific domains of the adsorbed proteins. While the hydrophobic substratum promoted cell-cell cohesion, on hydrophilic substrata cell-substrate adhesion was dominant. In addition, evidence for an influence of surface wettability on the cross talk between integrins and cadherins was found.

A calorimetric study of pH-dependent thermal unfolding of leghemoglobin a from soybean.

The purpose of the present work is to study the pH-dependent thermal denaturation of soybean leghemoglobin fraction a in a cyanide complex (Lba.CN) and to compare the results with those of myoglobin (Mb), apomyoglobin (apoMb) and cyanometmyoglobin (Mb.CN) as well. Comparing measured calorimetrically change of enthalpy (DeltaHcal) and calculated Van't Hoff change of enthalpy (DeltaHvh) we have found that heat denaturation of Lba.CN can be described by the two-state transition model. The average value of the change of heat capacity (DeltaCpd) of Lba.CN is between such values for apoMb and Mb.CN suggesting for some stabilisation role of the cyanide ion (CN-) on the protein molecule. The maximum change of Gibbs free energy (DeltaGmax) of Lba.CN is between 7.0 and 11.2 kcal/mol depending on pH. The heat-denaturation of the protein occurs on heating the protein solution above 25 degrees C while the cold-denaturation occurs on cooling the protein below 25 degrees C.