Human serum albumin (HSA) was labeled in various ways and with different radioactive labels . Characterization with electrophoresis on polyacryl gel and immunoelectrophoresis did not reveal differences between labeled and nonlabeled HSA. The release of the label from labeled proteins in phosphate buffer (pH 7.4) was studied as a function of time. IzSI-labeled proteins were stable and 99mTc-labeled proteins showed different stabilities depending on the labeling method which was used. The adsorption behavior of labeled HSA and HSA onto polystyrene (PS) and silicon rubber (SR) was studied by using two methods. It appeared that all labeled HSA compounds showed a preferential adsorption onto PS (and SR) substrates. The 99mTc-labeled HSA showed a high value of the preferential adsorption factor (4~ >> 1). The value for 125I-labeled HSA was about 1.4. It was also shown that q~ was dependent on the kind of substrate used. The methods developed to determine preferential adsorption of labeled proteins compared to their nonlabeled analogs are also generally applicable for different types of compounds.

Human fibrinogen (HFB) was labeled with different radioactive labels (Technetium -99m and iodine -125) in various ways. Characterization by chromatographic and electrophoretic methods did not show differences between the labeled and the nonlabeled proteins. The effect of the label and the labeling method on the adsorption behaviour of 99mTc and 125I labeled HFB at a polystyrene surface was investigated. In all cases labeled HFB showed preferential adsorption as compared to nonlabeled HFB. The preferential adsorption was expressed in terms of a factor ø (van der Scheer et al. 1978a), which will be 1, when no preferential adsorption occurs. 99mTc - and 125I - HFB showed ø values from 1.48 - 1.88. It is concluded that only meaningful adsorption experiments with labeled proteins can be performed when the possible occurrence of preferential adsorption has been investigated by appropriate methods. The results of prior work on protein adsorption at biomaterials using radiolabeled proteins have to be reconsidered.