Silastic fibrinogen adsorption

Figure 3. Fibrinogen adsorption onto ungrafted poly(HEMA). The poly-(HEMA) sheets [and grafted poly(HEMA)/Silastic were equilibrated at 37°C in 1 mg/ml fibrinogen solution in O.OIM HEPES, 0J47M NaCl, 0.02% azide, pH 7.4 for the time depicted and then rinsed 60 sec with buffer at room temperature by the dilution displacement technique (see Methods).

The time course of fibrinogen adsorption onto the two types of poly-(HEMA) is depicted in Figure 3 which also includes representative points for poly (HEMA) grafted onto Silastic. The slow rise to the final adsorption level seen for both types of poly (HEMA) is very similar to the kinetics observed for grafted poly (HEMA), as is the actual amount of adsorption. The slight disparity between the poly (HEMA) types is probably related to the more open and thus rougher surface of the heterogeneous poly (HEMA). 

Figure 6. Fibrinogen adsorption isotherms on Silastic, poly(NVP)/Silastic, and poly(H EM A)/Silastic. Untreated Silastic and Silastic grafted with poly-(NVP) (2.7 mg/cm ) or poly(HEMA) (5.8 mg/cm ) were equilibrated at 37°C for 20 hrs in fibrinogen solution of the depicted concentration in O.OJM HEPES, 0.147M NaCl, 0.02% azide, pH 7.4 and then rinsed by dilution displacement and extensive soaking with buffer at room temperature.

Fibrinogen adsorption from citrated blood plasma onto Silastic, poly-(HEMA)/Silastic and poly (NVP)/Silastic have been measured twice with two separate plasma preparations made from the blood of separate... 

Figure 7. Plasma fibrinogen adsorption onto poly( HEM A)/Silastic. Poly-(HEMA)-grafted Silastic (ca. 5 mg/cm ) films were equilibrated in a plasma solution (containing H-fibrinogen) at 37°C for the time depicted and then rinsed briefly by the dilution displacement technique with 0.01 M HEPES, 0.147M NaCl, pH 7.4, and then counted.

In any case, it is clear that the main findings in the two plasma experiments are the same fibrinogen adsorption onto Silastic from plasma is less than onto poly (HEMA)/Silastic, which is the reverse of the situation for adsorption from buffer, as Table V shows. These results thus lead to the conclusion that other plasma constituents are very effective competitors for fibrinogen adsorption onto Silastic while adsorption of fibrinogen onto poly (HEMA)/Silastic from plasma and buffer is quantitatively and qualitatively much more similar. 

Fibrinogen adsorption onto the most highly grafted poly(HEMA)/Silastic films (5.8 mg/cm ) was the same as onto films having only about one-fifth the graft, but films with grafts much below this point (1 mg/cm ) showed increased adsorption characteristic of the underlying Silastic. 

The saturation level of fibrinogen adsorption from buffer varied by about a factor of four in the order poly(HEMA)/Silastic < Silastic = poly(NVP)/Silastic. The NVP graft was intermingled with Silastic so adsorption to pure NVP was not obtained. 

Fibrinogen adsorption from citrated blood plasma was in the order Silastic < poly(HEMA)/Silastic < poly(NVP)/Silastic. The different order from buffer adsorption may be due to lipoprotein adsorption from plasma to Silastic. 

In the case of fibrinogen, the slow time course of adsorption onto poly(HEMA)/Silastic and Silastic make attempts at obtaining true equilibrium adsorption isotherms difficult because the fibrinogen solutions will undergo slow fiber formation unless protected from bacterial degradation. Also, storage of such solutions is a problem since fibrinogen... 

Table V shows that the amount of adsorption onto Silastic from plasma is significantly depressed below its saturation value measured in buflFer presumably because of competition from other components of the plasma. The diflFerence in adsorption from the two plasma pools may result from the increased fibrinogen concentration in one pool which would allow more eflFective competition for adsorption onto Silastic and result in enhanced adsorption. Since the adsorption of fibrinogen onto poly (HEMA)/Silastic from plasma is not so greatly depressed relative to adsorption from buflFer (see Table V), an increase in plasma fibrinogen concentration might not have so large an eflFect on adsorption onto poly-(HEMA)/Silastic as it apparently does on adsorption onto Silastic itself.

The reduced adsorption of fibrinogen from plasma onto Silastic and poly (HEMA)/Silastic compared with that from pure buffered saline solutions could be caused by competition from other proteins for the adsorption sites. Albumin and y-globulin are both present in plasma in relatively high concentrations (about 45 and 10 mg/ml, respectively, compared with ca. 3 mg/ml for fibrinogen), so either might compete effectively with fibrinogen for adsorption. To test this, mixtures of I-fibrinogen... 

Because fibrinogen remains at the gel top in the electrophoresis system used here, we cannot assess its importance because staining artifacts frequently occur at the gel top. However, adsorption of 125I-fibrinogen to polyacrylamide-Silastic shunt surfaces from baboon blood in vivo is much greater than adsorption to Silastic shunt surfaces (46). 

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