film thickness is less than about 350A. Theoretical analyses (3) have shown that such a direct logarithmic dependence can arise from either of two mechanisms: (i) when the growth rate is controlled by tunne l ing of electrons through the film, or ( i i ) w h e n the growth rate is controlled by passage of gas through pores or other defects in the film to the metal surface. T unne l - ing is impor tant only for films th inner than a few hundred angstroms. The film thicknesses in this re- search were much larger, so that this mechanism can be discarded. The second mechanism, that of passage
KINETICS OF THE FLUORINATION OF IRON 221
of gas through pores in the film, is the most l ikely process. The pores through which the gas moves may be the intersection of three grains, the intersection of two slip-planes, screw, and edge dislocations, or simply fractures in the film. When the compressional stress in one pore exerts a pressure on neighboring pores, some of these will be blocked as the film grows. This is the case of mutua l ly blocking pores and leads to the direct logarithmic growth law as found in this research. At low temperatures, the logarithmic law is found to be obeyed for the oxidation of i ron and copper, where the expansion which occurs when metal is t ransformed to oxide tends to close up neighboring pores. In this research, the fluoride occupies a volume 4.9 times that of the metal from which it is formed, so that mutual blockage by compression can be expected. It is con- cluded that above a film thickness of about 350A the fluoride film on the iron grows by passage of fluorine through pores in the film, and that these pores tend to block one another as the film thickness increases.
Manuscript received June 20, 1966; revised manu- script received Nov. 22, 1966.
Any discussion of this paper wil l appear in a Dis- cussion Section to be published in the December 1967 JOURNAL.
REFERENCES
1. E. Skinner, Chem. Eng., 65, 137 (1958). 2. P. E. Brown, J. M. Crabtree, and J. F. Duncan, J.
Inorg. Nuclear Chem., 1, 202 (1955). 3. U. R. Evans, "The Corrosion and Oxidation of
Metals: Scientific Principles and Practical Appli- cations," St. Mart in 's Press, Inc. (1960).
4. P. M. O'Donnell and A. E. Spakowski, Reaction of Copper and Fluor ine from 800 ~ to 1200~ NASA TN D-768, 1961.
5. P. M. O'Donnell and A. E. Spakowski, This Jour- nal, 111, 633 (1964).
6. Yu. A. Luk 'yanychev, N. S. Nikolaev, I. I. Astak- hov, and V. I. Luk 'yanycheva, Dokl. Akad. Nauk. SSSR, 147, 1130 (1962).
7. R. L. Jarry, J. Fischer, and W. H. Gunther , This Journal, 110, 346 (1963).
8. A. K. Kuriakose and J. L. Margrave, J. Phys. Chem., 68, 290 (1964).
9. E. A. Gulbransen, Trans. Electrochem. Soc., 81, 327 (1942).
10. N. B. Pil l ing and R. E. Bedworth, J. Inst. Metals, 29, 529 (1923).
Electrochemical Aspects of the Interaction Between Materials and Blood
Dennis B. Matthews and Avery Catlin
Department of Materials Science, School of Engineering and Applied Science,
University of Virginia, Charlottesville, Virginia
ABSTRACT
Electrolysis of human plasma, collected under various conditions, and of bovine fibrinogen (a protein normal ly present in blood) was carried out in order to verify conclusions made by earlier investigators. Electrolysis of re- calcified plasma, ACD-plasma (plasma to which an acid solution of dextrose and sodium citrate has been added), c i t ra ted-plasma (plasma to which so- d ium citrate has been added), and heparinized plasma (plasma containing heparin ant icoagulant) in glass, plastic, and silvered tubes did not support the conclusion that electrolysis produced inhibitors of, or catalysts for, the enzymatic blood coagulation reaction. The results were interpreted in terms of the effect of pH on the rate of coagulation.
Blood, w i thd rawn from a h u m a n and placed in con- tact wi th various materials, clots at a rate dependent on the mater ia l with which it is in contact. The rate of clotting is a max imum for such materials as glass, kaolin, celite (diatomaceous silica), and bar ium car-
bonate; it is a m i n i m u m for such materials as the normal vascular endothel ium (the inside l ining of blood vessels), paraffin, plastics including cellophane, and siliconized glass. For use as vascular prostheses such as artificial arteries, heart valves, and hearts, a
222 J. Electrochem. Soc.: E L E C T R O C H E M I C A L SCIENCE M a r c h 1967
mater ia l must, besides other requirements , not init iate blood coagulation.
The intrinsic enzyme mechanism of blood coagula- tion, init iated by contact wi th a foreign surface, is fair ly well documented, and the mechanism current ly accepted by a large number of the workers in this area is shown below.
Surface contact $
XII -~ XIIa $
XI --> XIa $
IX --> IXa $
VIII -> VIIIa $
X-~ Xa $
V-> Va $
II --> IIa (Thrombin) $
I (Fibr inogen --> Ia (.Fibrin)
This enzyme cascade (1, 2) sequence or bioamplifier (3, 4) system is be l ieved to be init iated by adsorption of factor XII (Hageman factor) . The adsorbed factor XII is in an active state, designated as XIIa and ca- pable of act ivat ing factor XI to give XIa which in turn activates factor IX, and so on, unti l the enzyme IIa ( thrombin) attacks factor I (fibrinogen), convert ing it to fibrin which polymerizes, both end- to -end po lymer - ization and crosslinking occurring, forming a net which enmeshes blood cells and serum.
There exists at present in the l i te ra ture sufficient evidence to be able to conclude that electr ical and pos- sibly electrochemical factors play a role in the in ter - action be tween mater ia ls and blood, both "in vitro" and "in vivo" (21, 25).
This paper is concerned wi th the analysis of ex- ist ing data in the l ight of some new results repor ted herein.
Despite the fact that the dependence of blood coagu- lation on electrolysis was observed as early as 1824, the first significant and systematic w o r k on this sub- ject was not carr ied out unt i l 1953. In 1953, Sawyer , Pate, and Weldon (5, 7) observed that the potent ial difference across the canine a r te ry wal l changed sign upon in jury being --3 to --15 mv (inside negat ive wi th respec~ to the outside) before in ju ry and 4 1 to -~10 mv after injury. The current flowing across the ar tery wal l was also observed to change its sign and magni tude upon injury. The reversa l of sign of the potential difference and the appearance of an " in ju ry cur ren t" was accompanied by the format ion of a thrombus, or blood clot, wi thin the in jured artery. A similar result was repor ted by Sawyer and Pate (6, 7) for the canine aorta.
Electrolysis of heparinized or ci trated canine blood between pla t inum electrodes in a glass tube at 0.2-10 ma for 30 min resulted in the format ion of a precipi tate at the anode (8). The precipi tate contained platelets, red blood cells (erythrocytes) , and whi te blood cells ( leukocytes) . In the case of hepar in ized blood, fibrin strands were also reported to be part of the p re - cipitate. No precipi tate was formed at the cathode. It was demonstra ted by Sawyer and Pate (8) that this precipi tate was not caused by gross changes in pH. As the anode and cathode were si tuated in the same vessel separated only by 1 cm of solution it is not surpris ing that no gross changes of pH were ob- served.
The results of Sawyer and Pate (8) have been re - peated by Lamb et al. (14) who used p la t inum wires 5 mm apart in the electrolysis of heparinized whole blood and plasma. The nature and amount of deposit fo rmed on the anode was noted for var ious po%entials
between the anode and cathode and for various quan- tities of charge passed.
Passage of cur ren t across a blood vessel wal l or across the blood vessel in vivo was also found to pro- duce a deposit, or thrombus, on the vessel wal l nearest the anode. On the basis of these exper iments it was postulated by Sawyer, Deutch, and Pate (9) in 1955 that reversal of the normal potent ial difference across the canine blood vessel wal l results in an electro- phoretic migrat ion of platelets, other cel lular elements, and negat ively charged proteins to the in jured vas- cular wall thus precipi tat ing a thrombus (blood clot). In later years, however , Sawyer (15) has concluded th~at electrolysis interferes wi th the intrinsic enzyme mechanism of blood coagulation.
In 1956 the invest igat ions proceeded one step fur ther when it was found by Sawyer and Deutch (10) that thrombosis (blood clot format ion) was delayed at the cathode during electrolysis. Currents greater than 30 ~a, when passed be tween a p la t inum cathode, placed around crushed canine arteries and veins, and an anode located at a distant position in the dog, were able to delay thrombosis compared to a control exper i - ment where no current was passed.
These results were confirmed in 1959 by Schwartz (11) who observed in vivo thrombosis at the anode dur ing electrolysis and who found that cathodic polarization was able to delay thrombin- induced thrombosis. Severa l other workers (12, 13, 16, 17) have since been able to produce in vivo thrombi by anodic polarization.
The exper iments of Sawyer and Pate (8) were repeated by Sawyer, Dennis, and Wesolowski (15) with pla t inum electrodes in separate glass tubes con- nected by a salt bridge. Currents of 0.1-1.0 ~a were found to produce a deposit on the anode in heparinized or ci trated blood. A solution of fibrinogen in sodium chloride was also electrolyzed, and a deposit was eb- served at the anode. This deposit was thought to be fibrin produced f rom fibrinogen by electrolysis. It was conjectured that electrolysis can cause blood coagu- l a t i o n ' b y bypassing all but the final steps in the in- trinsic enzyme clott ing mechanism.
In all the above in vitro exper iments the blood was heparinized or citrated. The intrinsic blood coagulation mechanism was thus checked; in part icular , the acti- vat ion of factor IX is inhibited under these conditions.
In 1964 Naumovski and Dejanov (21) reported some results on the effect of electrolysis on in vitro clotting. Currents of 1.6 ma were passed through citrated plasma for 1 hr. At the cathode the plasma was found to have a markedly prolonged recalcification time, more than 80 times the average spread. The plasma pH was 9.6-9.8. Di lut ing the cathode plasma by imadazole buffer (pH 7.4) did not change the ant icoagulant ef- fect. Plasma at the anode changed negligibly, and the pH was 6.6-6.8.
On the other hand, Lavel le (21) concluded that di- rect electric current does not appear to initiate, or ac- celerate, the enzymatic coagulation system in circu- lating nat ive blood. Lavel le 's work, however , suffered f rom the disadvantage that the anode and cathode were not in separate chambers. Any mater ia l oxidized at the anode may well have been reduced at the cathode. In 1964 Sawyer, Brattain, and Boddy (18) observed that erythrocytes and leukocy~es in Krebs solution (an electrolyte of ionic composition similar to that of blood) at pH 7.4 migrate and adhere to a p la t inum electrode at potentials greater than or equal to ~0.33v (against NHE) . Decrease of this potent ial led to desorption of the blood cells.
A similar behavior was observed with pla te le t sus- pensions (19) except that the adsorption of platelets was irreversible, the platelets visibly dis integrat ing at the electrode. Fibr inogen in buffer solution, however , was not found to deposit under these conditions (20).
The above results obtained by Sawyer and his co- workers and by others have led Sawyer to bel ieve (21) that electrolysis is capable of in te r fe r ing with the in-
Vol. 114, No. 3
trinsic enzyme mechanism of blood coagulation, the rate of blood coagulation being catalyzed at an anode and an inhibitor being produced at the cathode.
It was the aim of the present work to substantiate if possible the above v iewpoint by repeat ing the in vitro exper iments of Sawyer and co-workers under conditions where the intrinsic enzyme mechanism of coagulation is operative.
Exper imenta l
Blood was collected in 450 ml quanti t ies f rom heal thy male donors. The blood was wi thd rawn under vacuum into a double plastic pack containing acid c i t ra te-dext rose (ACD) anticoagulant. In some exper i - ments sodium citrate or hepar in ant icoagulant was used in the place of ACD. The blood was centr i fuged at ei ther 1000g (platelet poor plasma, p.p.p.) or 300g (platelet rich plasma, p.r.p.) for 30 rain to remove red cells and white cells. The plasma was squeezed off f rom the packed cells into the second plastic pack. Aliquots of about 4 ml were gravi ty fed f rom the pack into siliconized glass or polystyrene tubes, sealed and stored at ei ther 4 ~ or --20~ Immedia te ly pr ior to an exper iment a plasma aliquot was thermosta t ted in a water bath at 37~ In the case of plasma stored at --20~ this procedure disrupts the platelets, pro- ducing lysed plasma.
To init iate clotting, 0.20 ml of 0.25M CaCI~ was added to 2 ml of plasma. The rate of coagulation was followed with a photometr ic system (23). Light f rom a voltage regulated 0.25 amp 6-volt lamp was passed through the sample, contained in a block of a luminum thermosta ted at 37 ~ _ 0.5~ and the t ransmit ted l ight was moni tored with a CdS photocell. The resistance of the photocell was measured with a Wheatstone bridge, and the change of resistance wi th t ime was cont inu- ously recorded with a potent iometr ic recorder. The measur ing system is shown in Fig. 1. The type of re- cording obtained is idealized in Fig. 2. The times to and tl mark the onset and completion of fibrin poly- merization, respectively. The shape of the curve ob- tained depended on the exper imenta l conditions. In the case of a simple sigmoidal curve the t ime t~/~ was used as a measure of the rate of coagulation. For more
e I' OLTAOE C L ~ESU LATOR ~ H
r
I I I
L " LAMP S- SAMPLE ~ IWHEAT- I _ P- PHOTOCELL I - l STONE ~RECORDER T - T H E R M O S T A T ~ I B.RIDGE
Fig. 1. Apparatus for photometric determination of the rote of blood coagulation.
k - FIBRIN ---q POLYMERISATION
t O t t / 2 t I I I t
TIME (MINS)
Fig. 2. Idealized representation of the photometric clotting c u r v e .
INTERACTION BETWEEN MATERIALS & BLOOD 223
Table I. Effect of electrolysis an the rate of coagulation of human plasma at 37~
S t o r a g e C u r r e n t , P l a t e l e t Anti- t e m D e r -
P o l a r i t y m a c o n t e n t c o a g u l a n t a t u r e , ~ t~, r a i n
C o n t r o l 0 P o o r N a c i t r a t e - - 20 3.2 ~ 0.2 C a t h o d e 0.5 P o o r N a c i t r a t e - - 2 0 3.5 -4- 0.3 A n o d e 0.5 P o o r N a c i t r a t e - - 2 0 3.1 ~ 0.2
C o n t r o l 0 P o o r A C D - 2 0 2.2 _.+ 0.1 C a t h o d e 2.0 P o o r A C D - 2 0 2.7 ~+ 0,1 A n o d e 2.0 P o o r A C D - -20 2.4 ~ 0.1
C o n t r o l 0 P o o r A C D 4 6.9 ~ 0.7 C a t h o d e 2.0 P o o r A C D 4 6.4 ~ 0.1 A n o d e 2.0 P o o r A C D 4 6.5
C o n t r o l 0 R i c h A C D 4 3.9 ~ 0.4 C a t h o d e 2.a R i c h A C D 4 3.4 ~ 0.4 A n o d e 2 .a R i c h A C D 4 4.2 ~_. 0.2
C o n t r o l 0 R i c h A C D 4 5.6 _-+ 0.3 C a t h o d e 1.0 R i c h A C D 4 4.8 ~ 0.1 A n o d e ] .0 R i c h A C D 4 6.3 ~_- 0.3
C o n t r o l 0 P o o r Na c i t r a t e 4 4.9 ~ 0.3 C a t h o d e 1.0 P o o r Na c i t r a t e 4 4,2 ~ 0.7 A n o d e 1.0 P o o r Na c i t r a t e 4 5.1 ~ 0.2
complex curves, e.g., double sigmoidal, l inear ~ sig- moidal, the t imes to and tl were tabulated.
Electrodes used were, except where otherwise in- dicated, p la t inum wire spirals approximate ly 1 cm 2 in area. The cathode and anode were placed in sep- arate tubes connected by a saturated KCl-ge la t in salt bridge. The salt bridge was conztructed ei ther of sili- conized glass tubing or of polyethylene tubing. The p la t inum electrodes were cleaned in 1:1 mix ture of concentrated HCl-concentra ted H2SO4, rinsed wi th disti l led water, and heated to red heat in a flame.
Bovine fibrinogen obtained from Warner -Chi lco t t was dissolved by standing at 37~ with distil led water.
All pipettes and other glassware used in handl ing plasma were siliconized wi th Clay-Adams Siliclad. Test tubes were discarded after use, fresh tubes being used in each test.
Polys tyrene tubes were silver coated according to a we l l -known procedure (22) and dried at 60~ for 5 hr or more.
Results The effect of electrolysis, af ter recalcification, of
var ious types of plasma, collected and stored under various conditions, is summarized in Table I and Fig. 3. The tests were carr ied out in glass tubes at 37~ In these exper iments the plasma was in contact wi th both glass and an electrode.
In order to e l iminate uncertaint ies brought about by contact wi th glass, a polystyrene tube coated in ternal ly with electr ical ly conducting silver was used both as container and cathode. The effect of cathodic elec- trolysis was tested in these tubes by electrolyzing ci trated plasma for a given time, ta, and then t rans- ferr ing the plasma to a polystyrene tube containing CaC12. The exper iments were carried out at 37~ wi th
f 7
-=4
ANTI -COAGULANT: ACD
PLATELET POOR CONTENT STORAGE TIEMP: -20~
A-ANODIC ELECTROLYSIS I O'CO ROL NO E~TR~LYS,G I C-CATHODIC ELECTROLYSIS l
-STANDARD DEVIATION ] OF RESULTS
Fig. 3. Effect of electrolysis human plasma in glass at 37~
ACD ACD ~'C IT NOCIT POOR RICH POOR POOR
40C 4~C -2OoC 4oC
on the rate of coagulatian of
224 J. Electrochem. Soc.: ELECTROCHEMICAL S C I E N C E M a r c h 1967
Table II. Effect of electrolysis at a silver cathode on the rate of coagulation of platelet poor lysed plasma at 37~
ta, r a i n C u r r e n t , m a t l / , . , , r a i n
Table IV. Effect of prolonged electrolysis on the rate of clotting of heparinlzed platelet-poor fresh plasma at 37~
E l e c t r o l y s i s c a r r i e d o u t f o r 30 m i n a t 3.2 m a in p o l y s t y r e n e t u b e s w i t h P t e l e c t r o d e s . V o l u m e of p l a s m a = 10 cc. P l a s m a c o n t a c t e d w i t h g lass f o r 10 r a in . H e p a r i n n e u t r a l i z e d w i t h p r o t a m i n e s u l f a t e .
* P l a s m a w a s d e a e r a t e d w i t h n i t r o g e n .
platelet poor plasma (lysed) collected in ACD. Results are given in Table II.
The exper iment of Sawyer, Dennis, and Wesolowski (15) on the electrolysis of fibrinogen was repeated. Purified bovine fibrinogen (2.0 ml) was electrolyzed wi th p la t inum electrodes in separate glass tubes con- nected by a salt bridge. At 1 ma a deposit formed on the anode within 25 sec. The deposit consisted of a white precipitate mixed with bubbles of 02 causing the precipi tate to adhere to the anode. No reason was seen for bel ieving the deposit to be fibrin ra ther than fi- brinogen. Addition of sodium citrate to fibrinogen was found to inhibit the format ion of a deposit. Only after 15 min of electrolysis at 1 ma did a ve ry fine precipi- tate form, and this tended to remain in suspension. Electrolysis of ci trated plasma itself, which contained the same concentrat ion of fibrinogen as in the above experiments , resulted in the format ion of a very fine precipi tate only after 15 min of electrolysis at 1 ma. The possibility of fibrinogen being precipi tated by a decrease in pH of the solution in the anode compar t - ment was checked both by calculation and actual measurement of the pH change. In the absence of buffer the pH changed from 6.00 to 3.61 after 1 min of electrolysis at 1 ma, while in the presence of sodium citrate the pH change was f rom 8.16 to 7.58.
The exper iments of Naumovski and Dejanov on the electrolysis of ci trated plasma were repeated using platelet poor plasma. Electrolysis was carr ied out at 1.6 ma wi th 10 ml of plasma in polystyrene tubes using Pt electrodes. Af ter 60 min electrolysis the plasma was thermosta t ted at 37~ and 2 ml recalcified in glass tubes at 37~ Results obtained are shown in Table III. Both cooled and lysed plasma were tested.
The above exper iments were repeated with hepar in- ized platelet poor plasma. Electrolysis was conducted in polystyrene tubes at 3.2 ma for 30 min using 10 ml of fresh plasma. After electrolysis 2 ml of the sample was contacted for 10 min in glass tubes at 37~ 0.20 ml of protamine sulfate was then added to neutral ize the heparin. This exper iment was repeated with a 1:1 sample of fresh plasma and veronal buffer (pH = 7.5),
Table III. Effect of prolonged electrolysis on the rate of clotting of cltrated platelet-poor plasma at 37~
E l e c t r o l y s i s c a r r i e d ou t fo r 60 m i n a t 1.6 m a in p o l y s t y r e n e t u b e s w i t h P t e l e c t r o d e s . Vol . of p l a s m a = 10 cc. P l a s m a r e c a l c i f i e d in g l a s s t ubes .
A. F r e s h p l a s m a
E l e c t r o d e p H to, r a i n
A n o d e 6.59 16.7 ~ 2.3 C a t h o d e 7.29 7.7 • 0.2
B. L y s e d p l a s m a
E l e c t r o d e p H to, r a i n
A n o d e 6.47 9.0 ~- 0.5 C a t h o d e 7.35 3.7 "4- 0.5 No c u r r e n t 7.01 4.7 -~ 0.2
P o l a r i t y p H tl/~, r a i n
A. U n b u f f e r e d
C o n t r o l , no c u r r e n t 7.66 5.5 ----- 0.4 C a t h o d e 8.20 8.9 • 0.2 A n o d e 7.25 6.2 • 0.1
B. B u f f e r e d Con t ro l , no c u r r e n t 7.52 6.3 • 0.4 C a t h o d e 7.90 5.6 -~ 0.3 A n o d e 7.18 6.7
in order to inhibit the pH changes brought about by electrolysis. The results of the exper iments wi th heparinized plasma are given in Table IV.
Discussion Table I shows that for plasma collected in ei ther
ACD or sodium citrate there is l i t t le effect of electrol- ysis ei ther on to or h. This result is independent of whe ther the plasma was platelet rich or platelet poor and whether or not the platelets were lysed by freez- ing and thawing. The variat ions in clotting t ime as a function of platelet concentra, tion and platelet condi- tion are not meaningfu l since each set of results refers to a different batch of plasma. Variations in plasma obtained f rom different donors or f rom the same donor on different days are such as to allow comparison only between results obtained within a given batch of plasma. Such exper iments yield the result that the clott ing t ime to is less for platelet rich than for pla te- let poor plasma. With platelet r ich plasma clot re - t ract ion was very pronounced and prevented deter- mina tkm of tl. Pla te le t lysis led to a decrease in clot- t ing t imes to and h, but the decrease in to was almost independent of the original platelet concentrat ion in- dicating the release of an enzyme f rom the platelets. The decrease in tl was dependent on the original platelet concentration, but when the platelet f ragments were removed by centr i fugat ion at 2500g then lysis caused no change, in h - - to.
A small increase in the ra te of clotting was pro- duced by cathodic electrolysis, but this effect is much smaller and of opposite sign to that previously re- ported for plasma and whole blood containing antico- agulant. Moreover, in the presence of ant icoagulant (ACD), Table II shows that electrolysis in si lvered tubes did not inhibit the format ion of contact factor (factor XIa) nor did it produce an inhibitor to clot- ting, rather, a small increase in coagulat ibi l i ty was ob- served.
Electrolysis of f~brinogen in unbuffered solutions was shown to produce a rapid and large decrease of pH in the anode compar tment with the resulta~nt pre- cipitation of fibrinogen.
Prolonged electrolysis of plasma in polysCyrene tubes wi th Pt electrodes did not produce an inhibi tor in the plasma. The recalcification t ime was not great ly increased by cathodic electrolysis contrary to the ob- servation of Naumovski and Dejanov, rather , the clott ing t ime for ACD-p lasma was sl ightly decreased by cathodic electrolysis. Anodic electrolysis caused an increase in clott ing t ime compared to unelectrolyzed ACD-plasma. These results may be a t t r ibuted to the pH changes produced in the plasma by electrolysis. It is wel l known (24) that the clott ing t ime for blood is a m in im um at pH = 7.5 and increases rapidly wi th ei ther increase or decrease of pH. Inspection of Table III for lysed plasma shows that cathode plasma with pH 7.35 has the smallest clott ing time. Unelectrolyzed plasma of pH 7.01 (due to presence of ACD) has a sl ightly larger clott ing t ime and anode plasma with pH 6.47 has a much larger clott ing time. Similar effects were noted on electrolysis of heparinized plasma.
Vol. 114, No. 3 I N T E R A C T I O N B E T W E E N M A T E R I A L S & B L O O D 225
The present results on the electrolysis of h u m a n plasma and bovine fibrinogen indicate no interference with the intrinsic enzyme mechanism of blood co- agulation, and it is concluded that the results of Sawyer and others on the electrolysis of blood were caused by an electrophoresis mechan~ism, negatively charged erythrocytes, leukocytes and platelets migra t - ing in the field between the anode and the cathode.
The results do not exclude the possibility of elec- trochemically influencing the intrinsic enzyme mech- anism of blood coagulation. One might reasonably hope to influence the adsorption of Hageman factor (factor XII) on a given mater ia l by altering the charge on the material. However, the conditions under which specific proteins are adsorbed and desorbed are by no means obvious and informat ion is required on factors which influence protein adsorption at the solid- l iquid interface. Such informat ion would be of great value not only to the study of blood-mater ials in te r - action but to the general area of compatabil i ty of prosthetic materials and the human body.
Acknowledgments This work was supported by the National Inst i tute
of Dental Research, Grant DE-2111-02. The authors acknowledge the cooperation of the Universi ty of Vir- ginia Medical Center and, in particular, the continued interest and assistance of Doctors Oscar A. Thorup, Jr., Phil l ip M. Allen, and Mary Lou Abram.
Manuscript received Aug. 16, 1966.
Any discussion of this paper will appear in a Dis- cussion Section to be published in the December 1967 Jo URI',iAL.
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Surface Tensions of Co-Ce and Pu-Co-Ce Alloys as Determined from Frozen Menisci
John C. Biery University oS Catibornia, Los A~amos Scientific Laboratory, Los Alamos, New Mexico
ABSTRACT
The surface tensions of three Pu-Co-Ce and three Co-Ce alloys at their freezing point were determined from their frozen menisci. A new calculational procedure was used in which calculated menisci were compared with the experimental menisci. The meniscus shapes were calculated by numerica l ly integrat ing the Laplace-Young equation. The best surface tension for a given meniscus was found by comparing the computed and exper imenta l menisci at 25 points across the meniscus and by varying the surface tension and con- tact angle at the outside of the meniscus section unt i l various restraints were satisfied. The meniscus comparing techniques satisfactorily detected and dis- carded distorted menisci. Of the 28 menisci studied, 15 were found to be ac- ceptable.
Molten p lu tonium alloys with cobalt and cerium were tested as possible fast nuclear reactor fuels. These studies indicated that unusual phenomena occur at and above the l iquid/gas interface of the mol ten fuel when it is contained in t an ta lum capsules. Since some of these phenomena may be associated with the energy in the interface, the surface tensions of these alloys should be known to unders tand the systems better. The usual methods of de termining surface ten- sion such as capil lary rise, pendant drop, sessile drop, and bubble pressure require expensive and t ime-con- suming experiments when p lu tonium is involved. Therefore, a technique was developed to generate sur- face tensions from photographs of menisci since in
many cases wel l - formed menisci are observed in sec- tioned capsules containing the Pu-Co-Ce alloys. The ini t ial mathematical and numer ica l techniques for making these determinat ions from menisci and the test of the method with mercury and water are reported elsewhere (1). Here, the results from analyzing frozen menisci of Co-Ce, Pu-Co-Ce, and Ni -Ce /NaK are pre- sented.
The previously published geometrical and computa- t ional methods (1) were tested exper imenta l ly with l iquid menisci. An impor tant objective of this paper is to test the applicabil i ty of the methods as applied to frozen menisci. The tests of the methods were made by (i) processing m a n y capsules and comparing the
