Michael R. Brunstedt

Protein adsorption and macrophage activation on polydimethylsiloxane and silicone rubber

Static and dynamic human blood adsorption studies on polydimethylsiloxane, PDMS, and silicone rubber show that these materials are similar, but not identical, in their protein adsorption behavior. Fibrinogen, immunoglobulin G, and albumin were the predominant proteins identified on the material surfaces with fibronectin, Hageman factor (factor XII), and factor VIII/vWF adsorbing at intermediate levels. While the protein adsorption characteristics for the two materials were similar, higher levels of the respective proteins were identified on silicone rubber compared to PDMS. Monocytes/macrophages incubated on PDMS, silicone rubber and low density polyethylene, LDPE, with or without protein adsorption produced variable levels of IL-1 beta, IL-6 and TNF-alpha dependent on the polymer and adsorbed protein. PDMS showed lower levels of the cytokines when compared to the polystyrene control and polyethylene. Protein preadsorption on the PDMS, polystyrene, and LDPE surfaces showed lower levels of cytokines when compared to the respective quantities produced with no protein adsorption suggesting a passivating effect by the protein adsorption phenomenon on monocyte/macrophage activation. Preadsorption of IgG, fibrinogen or fibronectin decreased the quantitative expression of IL-1 beta but increased the functional activity in the thymocyte proliferation assay indicating the presence of monocyte/macrophage activation products which either downregulated the activity of IL-1 beta or upregulated thymocyte proliferation in an independent fashion.

Amphiphilic networks. V: Polar/nonpolar surface characteristics, protein adsorption from human plasma and cell adhesion

The surface energetics, specifically the balance of polar/nonpolar forces on the interfaces of various amphiphilic networks comprising hydroxyethyl methacrylate (HEMA) or N,N-dimethylacrylamide (DMAAm) hydrophilic chains linked by polyisobutylene (PIB) hydrophobic chains (for brevity H and A networks) in contact with water have been studied by dynamic contact angle measurements. Both networks show large contactangle hysteresis due to surface heterogenity and surface rearrangements. The balance of the polar/nonpolar forces of the dry networks, as quantitated by the Ip/WAd ratio is much below unity; upon equilibrating in water the Ip/WAd ratio increases but remains below unity. Protein adsorption from human plasma and human monocyte adhesion to A and H amphiphilic networks possessing polar/nonpolar ratios lower than unity have been investigated. Both networks adsorb less fibrinogen, albumin and Hageman factor (factor XII) than glass, polyethylene (PE), and polydimethylsiloxane (PDMS). The extent of adsorption of factor VIII on A, H and glass are very similar. Adsorption of IgG on A was appreciable, however, on H it was less than on any of the other surfaces studied. Monocyte adhesion was significantly inhibited on both networks and glass, relative to a positive adhesive surface such as tissue culture polystyrene (TCPS). Evidently both the A and the H networks exhibit reduced protein adsorption and cell adhesion which indicates biocompatibility of these networks at blood contacting surfaces. The ratio of the polar/nonpolar forces expresed by the Ip/WAd ratio may be useful to predict low protein adsorption and cell adhesion on polymer surfaces.

In vivo leucocyte interactions on Pellethane® surfaces

In vivo leucocyte interactions of three Pellethane materials of varying hardness were qualitatively and quantitatively characterized using a cage implant system over a 21 d implantation period. Scanning electron microscopy (SEM) and cytochemical staining were utilized to observe the cellular events occurring at the leucocyte-biomaterial interface. Many of the quantitative assays performed, the intracellular alkaline phosphatase activity of exudate leucocytes, the intracellular acid phosphatase activity of adherent leucocytes, the density of adherent leucocytes and the foreign body giant cell network formation tendencies of adherent leucocytes, suggest increased cellular activation with increased Pellethane hardness. Qualitative SEM evaluation of Pellethane surfaces revealed a variety of cellular activities. These included macrophage adherence, cytoplasmic spreading and macrophage-macrophage membrane fusions to form foreign body giant cells. The foreign body giant cells exhibited nuclear reorganization and, when compared with adherent macrophages, they displayed an enhanced ability to fuse to neighbouring leucocytes, increased spreading of membrane processes over the polymer surface, the presence of large cytoplasmic vacuoles, and a lengthened duration of enzymatic activity. Contact angle analysis showed the Pellethane surfaces to be hydrophobic and of low hysteresis. The critical surface tension and the dispersive component of the total surface tension were found to increase with Pellethane hardness.