BLOOD PROTEIN INTERACTIONS WITH TITANIUM SURFACES

Protein adsorption and complement activation were studied on thin evap orated films of titanium (Ti). The surfaces were cleaned in either a r adio frequency (RF) plasma unit, or washed sequentially in trichloroet hylene, acetone, ethanol, and water. Both methods resulted in hydrophi lic surfaces with low carbon contamination on the outermost oxide (app roximate to 11-13 at%) In situ ellipsometry suggested that Ti is an in trinsic coagulation activator in vitro, since significant amounts of f actor XII (F XII) and high molecular weight kininogen (HMWK) were foun d on the surfaces after 1 min incubation in heparin plasma. Ellipsomet ry, performed after serum incubations ranging from 15 s to 30 min show ed that the total amount of serum proteins and the deposition of antib odies to complement factor 3c (C3c) increased with serum incubation ti me. ELISA methods showed increased levels of free iC3b in serum after 10 min incubation of the surfaces, but no detectable amounts of C3 con vertase fractions C4d or Bb. Ellipsometric results indicated, however, an increased deposition of antibodies to C1q and IgG on Ti after shor t serum incubation times. The combined results indicate that Ti-surfac es initially activate complement through the classical pathway. The ac tivation then continues via a positive amplification loop where increa sed amounts of C3 are deposited on the surfaces via the alternative pa thway.