Comparison of haemocompatibility improvement of four polymeric biomaterials by two heparinization techniques.

Two surface heparinization procedures, introduced by Bamford and Al-Lamee (Polymer 22 (1996) 4885; 13 (1994) 2844) and Seifert et al. (J. Mater. Sci.: Mater. Med. 7 (1996) 465), respectively, were applied to four commercially available biomaterials (silicone rubber, polyethylene, polypropylene and polyvinylchloride) in order to compare their efficiency in improving haemocompatibility. The indirect method (Bamford and Al-Lamee) produced a much better heparinization yield-10.5% maximum, compared to the direct one (Seifert et al.), of only 0.20% maximum. Both methods provided a better response of the heparinized biomaterials compared to the uncoated ones in terms of platelet retention and a significantly better response in terms of activation of the coagulation system, suggesting that heparin molecules remained biologically functional in both cases. The results were particularly interesting in the case of polyvinylchloride where the maximum immobilization yield was obtained by the indirect method resulting also to a pronounced haemocompatibility improvement. Scanning electron microscopy studies confirmed adhered platelet morphology whereas atomic force microscopy was used to examine surface morphology of heparinized and reference materials surface.

Effect of surface roughness of the titanium alloy Ti-6Al-4V on human bone marrow cell response and on protein adsorption.

The effect of surface roughness of the titanium alloy Ti-6Al-4V (Ti alloy) on the short- and long-term response of human bone marrow cells in vitro and on protein adsorption was investigated. Three different values in a narrow range of surface roughness were used for the substrata (R(alpha): 0.320, 0.490 and 0.874 microm). Cell attachment, cell proliferation and differentiation (alkaline phosphatase specific activity) were determined past various incubation periods. The protein adsorption of bovine serum albumin and fibronectin, from single protein solutions, on rough and smooth Ti alloy surfaces was examined with two methods, X-ray photoelectron spectroscopy (XPS) and radiolabeling. Cell attachment and proliferation were surface roughness sensitive and increased as the roughness of Ti alloy increased. No statistically significant difference was observed in the expression of ALP activity on all three Ti alloy surfaces and culture plastic. Both methods, XPS and protein radiolabeling, showed that human serum albumin was adsorbed preferentially onto the smooth substratum. XPS technique showed that the rough substratum bound a higher amount of total protein (from culture medium supplied with 10% serum) and fibronectin (10-fold) than did the smooth one. The cell attachment may be explained by the differential adsorption of the two proteins onto smooth and rough Ti alloy surfaces.

Effect of surface roughness of hydroxyapatite on human bone marrow cell adhesion, proliferation, differentiation and detachment strength.

Initial attachment of osteoblast cells and mineralization phenomena are generally enhanced on rough, sandblasted substrata. In the present work the effect of surface roughness of hydroxyapatite (HA) on human bone marrow cell response was investigated. Human bone marrow cells were plated onto HA disc-shaped pellets, prepared from synthetic HA powder. The pellets were sintered and polished with SiC paper 180-, 600- and 1200-grit, resulting in three surface roughness grades. Cell adhesion, proliferation and differentiation (evaluated with the expression of ALP activity) were determined following various incubation periods. Cell detachment strength was determined as the shear stress required to detach a given quantity of the adherent cells from the different substrata, using a rotating disc device that applied a linear range of shear stresses to the cells. The cells attached and grew faster on culture plastic in comparison with HA. No statistically significant differences were observed in the expression of ALP activity on all three HA surfaces and culture plastic. Cell adhesion, proliferation and detachment strength were surface roughness sensitive and increased as the roughness of HA increased. The percentage of the adherent cells decreased in a sigmoidal mode as a function of the applied shear stress. In conclusion, surface roughness of HA generally improved the short- and longer-term response of bone marrow cells in vitro. This behavior could be explained by the selective adsorption of serum proteins.