THE SUBSTANTIVE ECONOMY OF MONEY -KARL POLANYI IN THE TRADITION OF "OLD" INSTITUTIONALISM-A/ The breakout of the "cattalactic triad" B/Money without Market 1

Archaic banking 2/ Coins in Classical Greece §2/ Money as a political means of social integration

A/The case of non-modern economies B/The case of modern money : the paradox of the money of the "Big Market"

Conclusion

Introduction

First Part -The Purpose of a Substantive Economy §1/ Karl Polanyi's Method : a point of view §2 / Substantive Economy and the Question of Value §3 / Institutions and forms of integration : economy as an instituted process A/An institutionnalist conception of institution B/ A few categories of substantive economy 1-Reciprocity and Symmetry

Redistribution and Centricity

-Exchange and Market

Second Part -Money As An Institution §1/ The specificity of Archaic Monetary Institutions

Introduction

The purpose of this contribution is to suggest an interpretation of substantivist thought initiated by Karl Polanyi. An approach such as this is concerned with "historical economics", in the precise sense that substantive concepts do not come from a retrospective projection of modern prejudgements, but rather from an attempt to apprehend universal categories of economic analysis in order to clarify the genuine singularities of different economic systems 1 . In doing this I shall highlight the coherence of institutionalist thought 2 founded by economists such as Mitchell, Commons and Veblen, into which the reflections of Karl Polanyi fit. In this way, Polanyi thinks of money as an institution that submerges the economy into social relationships. As an analytical result, stripping money of its institutional character and trying to reduce it to a commodity, can only create chaos.

In order to give an account of Polanyi's project, I will show, in the first part of my analysis, how Polanyi wants to move away from the idea that economy is created on pure rational logic.As a result, economy owes its very existence to "institutionalised processes" which produce the very inflexibilities necessary for both collective and individual action. Taking this into account, it is impossible to presuppose the unity of "the cattalactic triad" i. e. external trade, money and markets.

From this point on, it is possible, in the second part of this analysis, to specify certain interesting results for the economic history of money. From a transhistorical viewpoint, this institution sets the rules for the quantification and extinction of debts. However, in contrast to modern money, archaic money is characterised by a separation of functions which compel us to talk about "money uses".

Consequently, it is better to speak in terms of accounting and payment practises rather than using the single word of "money". Furthermore, the independence of money in relation to market is a characteristic of numerous archaic societies. Nevertheless, in spite of their differences, both ancient and modern monies politically produce social integration. 1 We are aware that since Polanyi's latest works, there has been series of contributions which have enriched the debate (see for instance, [START_REF] North | L'essor du monde occidental[END_REF], [START_REF] Silver | Karl Polanyi and markets in the ancient near east : the challenge of the evidence[END_REF] and [1985], Mayhew & alii [1985] and Janssen [1975, p. 560] amongst others). This point of view concerns the history of ideas. But we can hope that the history of ideas is also able to put forward arguments in the controversy concerning the analysis of ancient economic facts. See Gentet & Maucourant [1991, b]. We may also notice that the richness of Polanyi's approach is taken into account beyond strict heterodoxical works [START_REF] Orlean | L'origine de la monnaie -la monnaie dans les societes holistes (2)[END_REF].

2 Maucourant [1994, b].

First Part -The Purpose of a Substantive Economy §1/ Karl Polanyi's Method : a point of view Karl Polanyi defines "formal economics" as the pure reign of calculating reason in the context of scarcity of goods when the ends are given. Karl Polanyi is more interested in studying the capacity of power relations and values in order to institute a certain number of economic practices 3 . In this way, Polanyi presupposes that economic activity is not isolated, and that institutional analysis remains a way of carrying out economic reflections. One should note that there is no reason to deny the hypothesis that individual rationality has a large field of effectiveness and, as a result, to imagine the existence of a totality that is radically independent from its component parts. "the premium set on generosity is so great when measured in terms of social prestige as to make any other behavior that of utter selforgetfulness simply not pass". Modern anthropology invalidates fantasies that are connected to "the communist psychology of savages" 6 ; man has always aimed at maximising his social interests 7 : "Aristotle was right : man is not an economic, but a social being. He does not aim at safeguarding his individual interest in the acquisition of material possessions but rather at ensuring social good will, social status, social assets. Man's economy is, as a rule, submerged in his social relations". More generally, the hypothesis which states that institutional constraints structure behaviour does not contradict the idea that self-interest is the driving force behind action, provided that one acknowledges the nature of the ends prescribed by the institution. As a result, individual interests are not autonomous.

Therefore the embeddedness hypothesis in social ties calls for the redefinition of the field of economy. Indeed, one has surrepticiously introduced the impossibility of the "enclosure" of the economic field, a factor which implicitly amounts to a definition of economy as a social subsystem.

Actually, a science of action with a pure rational purpose could, theoretically, urge us to describe all 3 In this respect money as an institution is a device that institutes a "public purpose" into economy. such as Commons stated. According to him, if McLeod is the initiator of institutional economics, it is because of his penetrating analysis of the "commoditisation" of debt, and above all because of the idea that the central bank must eventually go against private banks. If we consider now Mitchell's study of the progress of money economy in England, one must note the importance of the State and power relations in this process (cf. Rutherford in Mitchell [1996] and Mitchell [1996]). Actually, it is not evident that the lowering of transactions costs, which is allowed by the growing use of money, is spontaneous (cf. the case of Africa analysed by Servet [1994, b]).

4 Cf. Neale [1990, p. 147].

5 Polanyi [1957, c, p. 46]. 6 Polanyi [1968, p. 65]. Of course its the same for "the myth of savage devoted to barter" that comes from Smith [Polanyi, 1957, pp. 43-44] in which we find an archeology in [START_REF] Servet | La fable du troc[END_REF].

7 Polanyi [1968, p. 65].

behaviour as economic. Therefore, the question here is of restricting the possible scope of economics while introducing a degree of anthropological complexity. §2 / Substantive Economy and the Question of Value

For Polanyi 8 :

"The truth is that man has been very much the same all through history" 9 .

This concept allows us to advocate a definition of economy which incorporates the institutional varieties that stretch throughout history 10 . Carl Menger supplied Polanyi with a solution to this problem. In the 1923 German edition of his "Principles", Menger sets an "economising direction"a characteristic of civilised societies -against a "technical direction" which only results from physical particularities of production 11 . He does this with the intention of safeguarding his "Principles" which would be challenged by later anthropological discoveries 12 . Thus Polanyi can suggest a definition that is substantive to economy, focusing upon the idea that the livelihood of man is not strictly determined by scarcity, in so far as custom or politics eliminate the choice of agent 13 . Only a specific institutional situation, that of price making markets, can completely reduce the substantive sense of economy to a formal sense of economy. In this case, a general state of scarcity exists as economic agents are able to make a infinite number of choices provided by markets.

Therefore one can say that Polanyi, following Aristotle, rejects the theory of utility-scarcity value. Indeed, Polanyi emancipates himself from the common postulate of an "unquestionning acceptance of the sovereingty of individual wants" 14 considerating the "real" human needs that Aristotle names "natural". Actually, Aristotle understands the social nature of scarcity, which must be distinguished from the obviousness of the "finite state of things" 15 .

According to Aristotle, human choice and desires are not limitless because they had to be submitted to the civil imperative of an honourable life. The essence of life 16 according to Aristotle, 8 Polanyi [1947, p. 99]. 9 Berthoud also highlights that hypothesis that the constancy of human nature entails a hypertrophy of the interest brought to institutions and to the cultural factor.

10 One consequence of this anthropological constancy is that humanity could never construct its society in a lasting fashion using methods that are totally economically individualist or collectivist. Polanyi rightly observes that, in fact, since the oldest Antiquity, one knows always how to escape ideological dichotomies ; liberty vs bureaucracy and economic total planning vs market. On this subject, he cites the example of a mesopotamian trading corporation, of athenian customs of the classic age and of the kingdom of Dahomey in the 18th century [Polanyi, 1977, XLi].

11 Cf. Polanyi [1977, pp. 22-23].

12 One should note Polanyi's profound display of respect with regards to the marginalist school of thought, because, according to us, utalitarian behaviours result from the mental impregnation of market institutions. Mitchell already hold a viewpoint on "money economy" which is not far removed from from Polanyi's thinking [Maucourant, 1993, b]. Elsewhere, the influence of the Austrian school of marginal utility on Polanyi is certain in the socialist economic calculation debate. The future author of the Grande Transformation in 1922 is looking for an alternative to central planning which he considers impossible -as would his brother Mickael later [Polanyi, 1989, pp. 148-149]-and pure market economy that he asseses to be a source of wasting. One can find a presentation of this non-marxist criticism of capitalism in Rosner [1990] and [START_REF]Monnaie et calcul economique socialiste selon Karl Polanyi : le projet d'une economie socialiste federale[END_REF] ; a translation in french Polanyi's text is available in Polanyi [1994]. To our knowledge a translation in English does not exist.

13 Cf. Polanyi [1977, p. 27].

14 Cf. Hodgson [1992, p. 436].

15 Berthoud [1986, p. 67].

16 Polanyi [1977, p. 30].

i. e. theatre, trials, politics and the contemplation of good, prohibits any type of effective economic accumulation. A contrario, the free display of pecuniary activity is contradictory to the "natural" order of the City which is based on three principles, self-sufficiency, community (resting on the value of living together, the phylia) and justice (in the sense that everyone receives that which is due to his "nature")17 . The fact that Aristotle has a substantive conception of economy explains his fear that economy could actually become removed from society. It is this fear that highlights his importance as an economic thinker18 .

It is clear that Polanyi, concerned about justice (in its modern and democratic form), national sovereignty and the permanence of social ties, is just as anxious as Aristotle could have been, when faced with developments of market which contradict the idea that the economy should be the embodiment of a human purpose. Thus, the liberal doctrine, which states that the law can do nothing but institute the means of action, and not the ends, is the antithesis of Polanyi's socialism19 .

In fact, in this type of socialism, democratic debate determines social ends. Polanyi's proximity to

Veblen is just as strong. Both authors agree with the Aristotlian ethic that rejects the continual pursuit of ends that are constantly changing in consumption. Paradoxically the criterion of welfare of utilitarianism is this infinite multiplication of envious comparisons.

However, one should not forget the element that stops us making a direct filiation between

Polanyi, Marx and Aristotle. Indeed, it would be wrong to think that Polanyi supports a radically objectivist conception of value. Perhaps, and here rests our hypothesis, Polanyi even wishes to emancipate himself from the paradigm of value in order to participate in a new paradigm built on the recognition of institutions as creators of economic values.

In the first place, even if the "real needs" of man are changing, a democratic deliberation concerning social needs can choose the preferred kind of technical progress. This is Polanyi's point of view in the 1922 model of federal socialism. In the second place, even if the ends of social activity should not be left, according to Polanyi, to a logic that is purely economic, it does not follow that every type of economic spontaneity should be abolished. He recognises the impossibility of central planning if division of labour is complex.

Consequently, this means that the evaluation of economic cost is not fundamentally a matter of statistical evaluation, but the result of an intersubjective process. The local and concrete activities of collectives of associated workers are the only means of examining the disutility of labour20 .

Elsewhere, central planning, which makes human economy a technique, is a non capitalist form of alienation, as, in taking responsability away from its producers, it denies the fact that ethics should be associated with labour21 : "Humanity will not be free until it knows the cost of its ideals".

Polanyi once again does not base that economy on value but on institutional theory which enables him to return to Commons's question of "reasonable value". Beyond the objectivity of Marx and the subjectivity of Mises, Polanyi lies within institutionalism.

The illusion, which believes that value can exist outside an institutional "vestment" stems from a totally utilitarian idea, common to both marxists and liberals. This illusion states that an economy can exist in an autonomous way. More precisely the transformation that occured in the nineteenth century which aimed at instituting a waterfight "closure" of the economy through the establishment of One Big Market was, in fact, illusory. §3 / Institutions and forms of integration : economy as an instituted process

A/An institutionnalist conception of institution

To place Karl Polanyi's work in institutionalism would signify that his contributions are lost for the contemporary economist : the idea of the existence of economic "laws", that are radically independent to the rest of the social field, are in fact well spread. Nevertheless, it is clear that due to certain recent and comunally accepted developments in economic analysis, a certain number of doubts have arisen, thanks to the "undersocialised" view 22 of economic analysis 23 . Therefore, if one acknowledges that economy is somewhat embedded in social relationships, one must pick out in the economy the inscription of the logic that belongs to the political 24 area and value system that characterise a culture.

According to us, institution is a category which refers to the combination of different fields of society and reveals a human purpose. The laws that govern the nature and possible extent of the transfer of property rights, whether these be exclusive -in the cased of ideal private property -or relative to its functions -in the case of public property in the ancient era -make up an essential part of an institutional analysis.

Money is equally an institution in the sense that it is constituted by the rules which fix the conditions of the issuing, evalutation, circulation and releasing of debts. With this transhistorical perspective there is no exchange, but rather payment, as a social constraint which aims at releasing debts.

The institutionalist tradition demonstrates a consensus on this point. When Polanyi confirms that 25 :

"In primitive societies, credit, through which debt is formalized, is provided originally by the reciprocity practiced within clan and neighborhood",

22 "Oversocialised" economics is unbearable as only a super mind could understand the logic of the whole, which is contradictio in adjecto. Cf. [START_REF] Hayek | Scientism and the Study of Society[END_REF].

23 Granovetter [1994, p. 86] highlights the social networks that create market transactions. This legitimates A. Orlean's assertion about another contribution of Granovetter. The study of a history of a system with the cooperation between economy and sociology would enable to remove from the indetermination relative to the nature of the final equilibrium. Cf. Orlean [1994, p. 31]. 24 Here"political" does not indicate the central authority of social power, assuming that this could actually have some concrete effectiveness ! Power relations can be apprehended at a local level.

25 Polanyi [1977, p. 141].

he assimilates the original category of debt to that of gift. This could lead us to say that there is no such thing as free gift. The institution of gift constitutes the "Invisible Hand of primitive societies 26 . In the same way. Commons observes 27

"Primitive societies often have the institution of "gift" which is their method of creating debt, and they are even known to have set up a money of account.". However, it is right to observe that the institution of social practices is not an arbitrary procedure that arises from a pure will. Institutions express the empirical regularities of social life while taking into account causes which can be economic. Commons is making this precise point when he asserts that the "law" of supply and demand must not be abolished, but rather, utilised 28 . One must not confuse the arbitrary nature of a will that does not institute anything in a lasting way, except chaos, and the device of collective action that fits into history 29 . Actually, institutions are collective mental entities made rigid by history. As a result, institutions, as regularities of collective behaviour which create individual expectations, are the matrix of social order.

In other respects, we have attempted to show that Veblen defined de facto institution in this way, a factor which could unify institutionalist thought. The case of money rightly illustrates this institutionalist conception of institution. Veblen rejects the "conjectural history" 30 :

"As instances of the use of this ceremonal canon of knowledge may be cited the "conjectural history" that plays so large a part in the classical treatment of economic institutions, such as the normalized accounts of the beginnings of barter in the transaction of the putative hunter, fisherman, and boat-builder, or the man with the plane and the two planks, or the two men with the basket of apples and the basket of nuts. Of a similar import is the characterisation of money as "the great wheel of circulation" or as "the medium of exchange". Money is here discussed in terms of the end which, "in the normal case", should work out according to the given writer's ideal of economic life, rather than in term of causal relation".

The problem is not actually knowing exactly what money should be according to the pattern which represents human nature in a way that is just as abstract as utilitarian. Without any doubt, it is not so much exchange which creates money, as the development of money as a way of understanding the world which makes more and more exchanges possible 31 .

B/ A few categories of substantive economy

Starting from macro-social considerations, Karl Polanyi considers the two sided nature of economy : it is partly the process of interaction between man and nature, and partly an "institutionalised process" insofar as the necessary livelihood of man requires the institution of certain rigidities 32 :

26 M. Douglass [1989, p. 111].

27 Commons [1992, p. 474].

28 Commons [1992, p. 802]. 29 Gautier's [1992, pp. 42-52] account concerning Hume , notably on p. 43, is interesting to this respect. 30 Veblen [1898, pp. 382-383]. 31 This view and the deliberate use of this extensive meaning of money was developed by Mitchell [1966Mitchell [ , p. 27 & 1996]].

32 Polanyi [1977, p. 31].

"If the material survival of men were the result of a mere fleeting chain of causation-possessing neither definite location in time or space (that is unity and stability), nor permanent point of reference (that is structure), nor definite mode of action in regard to the whole (that is function), nor ways of being influenced by societal goals (that is policy relevance) -it could never have attained the dignity and importance of human economy". Polanyi therefore defines empirical regularities which are fundamental to all social systems allowing the integration of economy, therefore assuring its permanence. This collective behaviour, called "form of integration" 33 fits into the "supporting structures" of society.

1-Reciprocity and Symmetry

Polanyi defines this form of integration and supporting structure in the following way 34 : "Members of group A could then establish relationships of mutuality with their conterparts in group B, and vice versa ; or three, four, or more groups may be symmetrical with regards to two or more axes, and the members of these groups need not reciprocate with one another but with the corresponding members of third groups toward which they stand in analogous relations. A number of families, living in huts that form a circle, might then assist their right-hand neighbors and be assisted by their left-hand neighbor in a endless chain of reciprocity without any mutuality among them".

-Redistribution and Centricity

"Redistribution designates appropriational movements toward a center and out again" 35 .

Redistribution can experience certain distinctive modalities such as "householding", the Greek "oeconomia" or the roman "familia" 36 . In this way "householding" concerns a social sub-group in which redistribution functions. Here, as Polanyi maintains, we are not concerned with the first form of economic life. Only a certain advancement of agricultural techniques, allows the autonomy of a subgroup 37 .

-Exchange and Market

In contrast to a widespread conception, isolated existences of exchange between individuals does not amount to the existence of a coherent institution, that is to say, the market 38 :

"Acts of exchange on the personal level produce prices only if they occur under a system of price making markets, an institutional set up which is not created by mere random acts of exchange". 33 Polanyi's taxonomy is changing even if his intentions do not change. It is the unity of an idea which is interesting to us here. For the sake of detail, one can note that in 1944 writings "redistribution" is called "principle of behaviour" and in 1977's text "forms of integration" ; the "centricity" is "institutional model" but become "structures". It is clear that these semantic variations do not change anything. We suggest calling "institutional model" a special set of institutions which includes their relations to culture and historical singularities that an economic analysis must, in the first instance, overshadow. In this way the Assyrian institutional model differs from the Egyptian one, even if redistribution is a main feature of these archaic systems.

34 Polanyi [1977, pp. 38-39].

35 Polanyi [1957, b, p. 251].

36 Therefore, the different sub-structures which support redistribution can be sex (the family), setting place (the village) or political power (a feudal centre). 37 The concrete observation moreover shows that, in the case of the most primitive societies, the shortages created by natural disasters are divided up in an equal manner. In order to devise a genuine autonomy for all these subgroups, one must therefore set out more advanced techniques.

38 Polanyi [1957, b, p. 251].

More precisely, for the exchange to be "integrative", that is to say in order that exchange behaviour creates social integration, it is necessary that exchange rates are negociated and not fixed by custom or authority.

Second Part -Money As An Institution

With the publication of the Great Transformation, Polanyi continuously highlights the function of social integration 39 created by money throughout history. Certainly, it does not follow that the appearence and meanings of money are unchanging. The question of social integration seen from the point of view of money will be examined in the period before and after the Big Market. §1/ The specificity of Archaic Monetary Institutions A/ The breakout of the "cattalactic triad"

From the birth of the utopia of the "Big Market", the domination of money as a means of exchange entails concomitant advancements of the "commoditisation" and "monetisation" of society. But this is not always the case as money is linked to requirements prior to the "One Big Market". Money is a means of organising men into a hierarchy and cancelling out debt. The word "debt" here refers to a constraint of a social i. e. here political nature. This is why Polanyi wishes to break up the "cattalactic triad", thinking of an alternative to the "conjectural history" of the market 40 already denounced by Veblen.

" bring about an economic theory which not only unifies production with credit but also history with logic" 41 . Money, as a rule, is independent from the market. In keeping with this institutionalist tradition, it is important to stress that money should not be regarded as a thing but as the institution which governs the issuing, evaluation, circulation and cancelling out of debts. This is why social integration, which money contributes towards fulfilling, is, from its origins, strongly impregnated with power relations. Before examining these methods of politically integrating economy, it is advisable to examine the archaic functions of money.

39 The "integration" here in question can cause political oppressions.

40 Polanyi [1957,b, p. 257].

41 Commons [1992, p. 474].

B/Money without Market

For Polanyi, money should be divided into "special purpose" and "all purpose money". This division corresponds to the contrast between the two states of money, the first appearing before the "One Big Market" and the other appearing after. In this way Polanyi succeeds in breaking up the unity of a phenomenon that the cattactic approach had believed in. It may very well be that, with the case of ancient societies, a type of money object could carry out the accounting function and another object fulfilling the payment function 42 . At times, even the possible field of payment or account is strictly specified.

The fact that money uses are instituted separately, proves the very particular nature of nonmodern money. Money's submission to the singular imperatives of exchange is nothing other than a characteristic of the "One Big Market" institution. Two examples will be raised in order to understand how money does not have a natural vocation to create an integrative exchange. Better still, money contributes 43 to the avoidance of true money-market uses.

1/ Archaic banking

The absence of organised markets and coined money have characterised the institutional pattern of Ancient Mesopotamia 44 . In this case, the requirements of trade and bartering necessitates the use of money as a unit of account and the recording of debts which are the consequence of transactions.

Banking operations are therefore a "functional substitute" necessary in the absence of universally recognised means of exchange. Therefore, the function of the banker is to organise clearing and to witness to the existence of debt in an era when the spoken oath was fundamental 45 : "In the end, there is not much to show that in Mesopotamia banking did actually prove itself an avenue to the changeover from administered trade to market trade".

The archaic bank therefore renders modern forms of money useless. Elsewhere, it is curious to note that even when the Greeks introduce the market and coined money, banking does not develop by conforming to exchange logic. No doubt this is due to the fact that the agora is only a "market element" where the production goods are not exchanged. Anyway banking is reduced because of the custom of paying cash 46 . In fact, the institutional pattern of the bank of ancient Greece seems desperately rudimentary as though the specifically greek invention, the link of trade and money to the market 47 , had not created the natural impetus of banking, despite the notable growth in the market trade.

42 The money in question can be totally abstract. It is this that Polanyi names "ideal unit". However the situation can be ev en more complex. For example, a slave could have served as a unit of account and an external means of payment ; the great local values being expressed in slaves. This signifies that a type of ideal slave was developed. Keynes had, in the same way cited in his Treatise the case of the "average goat" as a unit of account in Africa [Keynes, 1971, pp. 11-12].

43 This fact can be also the result of redistribution requirements. Cf. [START_REF] Gentet | a) La question de la monnaie en Egypte ancienne[END_REF]. 44 Polanyi [1957, c, 15]. 45 Polanyi [1977, p. 142].

46 By the nomismata. Cf. Polanyi [1977, p. 316].

47 Polanyi [1977, p. 253].

A main role of trapetzoi is changing currencies 48 . Elsewhere, the city controls the activity of this banker who is often a slave. Polanyi underlines that the bank is a public affair and not a private one 49 . Even more fundamentally, the bank within this institutional pattern does not create money as each bank loan cannot be made except on the order of the bank depositor. Otherwise, the bank loan can be a capital investment of the bank 50 .

Finally, at no time is public deficit covered by bank loans. One has to wait until the end of the Middle Ages to witness the development of such a phenomenon. This is most certainly due to a mentality which, on principle, excluded deficit, whether it be individual or public, as illustrated by the precepts of Xenophon 51 . If a deficit ever occurred, sumptuary laws were used as an expedient,

as in Rome at a later date 52 . Another possibility for financing was the game on the metallic content of money which made recourse to banking useless.

2/ Coins in Classical Greece

It is usefull to show how political authority is at the heart of the value of coins 53 , which means that money is in essense fiat money. One example, among others quoted by Polanyi, shows to what extent the regularities of market economy are difficult to bring to the fore in ancient Greece. In the same way, a city in Asia Minor, experiencing a shortage of resources and having to pay back large sums of money to mercenaries, found a strategy which alleviated the weight of debt. The rich citizens of the town were forced to lend to the city in precious metals while they received money in iron in return. The iron money was declared to have the same value as the money in silver. Thanks to this procedure, the mercenaries were paid back in cash. One observes that the money supply, internal to the City, did not rise.

Thus the hypothesis which states that a rise of global monetary circulation would be inflationary is quite simply anachronistic, insofar as one implicity assumes the existence of an interconnected market system. This is not not the case and can explain the rigidities of the ancient price system.

Furthermore, it is noticeable that the citizens are still being subjected to tribal prerogatives 54 as the Cities are able to arbitrarily reduce current money to token money and they can easily play on the fineness of monies and regulate prices. §2/ Money as a political means of social integration A/The case of non-modern economies Following Tönnies, Polanyi made a sharp distinction between "community" and "society".

Money, as a pure means of economic exchange is, according to Polanyi, associated to a "tendency to fluidity and instability" 55 . This is the mark of a "society" based on the levelling of conditions, even if it is imaginary. On the contrary, the organic community of premodern times, is characterised by its stability. Thus, a reversal of perspectives is proposed 56 :

"Contrary to all assumptions, the origin of fluctuating prices, not of fixed prices, is the problem for the historian of antiquity".

Polanyi suggests a political hypothesis regarding the nature of non-modern money which takes into account these strong rigidities 57 :

"The variety and often minute articulations of money institution thus help to achieve integration and stabilize status privileges without the use of open force (underlined by us)".

In non-modern societies, money stability, which is at times multi-seculary is the rule while, very openly, the differentiation of money is associated to social status 58 . In this way, in the Mali empire, at around 1352, there exists a "poor man's money" (a fine thread of copper) and a "rich man's money" (a thick thread of copper). The poor could only buy goods of rudimentary consumption, while the rich could buy, not only these goods, but naturally the elite goods (such as slaves and horses). This fact has an important consequence 59 :

"lower class status [...] is maintained by restricting living standards to the coarse food and bare necessities that native money is allowed to purchase ". So, the ostentatious standards of consumption are made rigid by rules that are relative to payment and prevent the eventual richness of the poor person from being converted into prestige and power.

From this moment, one can put forward a hypothesis that is related to a strange ancient rating of money interests. Strangely enough, two different rates of interest were put into practise in the mesopotamian temples. For barley and silver, rates were 20 and 33,3 %. At the same time, the loans agreed on by the temples were particular in that they were made in barley for the peasants and silver for the "citizens". Polanyi notes that if we acknowledge that, in the African manner, one money (here barley) is not able to buy the other (here silver) 60 , it is perhaps not surprising that the rate of 55 Polanyi [1977, p. 118].

56 Polanyi [1977, lii]. 57 Polanyi [1977, p. 120].

58 Polanyi [1977, p. 117];

59 Polanyi [1977, p. 120].

60 Polanyi [1977, p. 118].

interest of the money of low status is higher than that of the money of high status. This phenomenon may be explained by the impossibility of converting the interest of the debt expressed in a quantity of inferior goods into superior goods.

Thus, these customary rates, associated with the differentiation of the money uses, contribute to the establishment of even greater social stratification. Polanyi does not look at this point more closely, however interesting it may be, as he is more concerned sometimes with forms of social integration than forms of oppression. In fact, the crises of Mesopotomian cities from the oldest age, are due to the impossible reimbursement of debt by the dominated levels of society. Now, one can think that the higher levels of interest rates participate in the perpetuation of the state of events, from which come political troubles, moratory institutions etc. In other words, if ancient money greatly solidifies social bonds, while introducing a rigidity that has no need of "bureaucratic control" as asserts Polanyi, it would be right to remember the political breakdowns that characterise such a rigidity. The crises of debt in early antiquity thus allow us to understand more easily Commons's remarks :

"Historically, it is more accurate to say that the bulk of mankind lived in a state of unreleasable debts, and that liberty came by gradually substituing releasable debts" 61 . With modernity, the institution of credit money, which is nothing other than the effective consecration of the principle of free circulation of debt, allows us at least a possible contestation 62 of age-old hierarchies.

Therefore, according to Polanyi, non-modern money was by its nature linked quite directly to a political system. Society's submission to a selfadjusting market would not be possible without the fusion of money uses into one single use, the all purpose money. The modern and contingent idea of all purpose money is the mental product of the commodity-money ideology, which is magnificently illustrated by the reign of the gold-standard. This original metamorphosis, is only one part of the first "transformation" which leads to the selfadjusting market. But the "Big Market" is only an utopia 63 that causes a paradoxical movement of liberation and regulation, that is the "double movement".

B/The case of modern money : the paradox of the money of the "Big Market"

It is necessary to rethink this utopia. Far from Marx and Ricardo, on the subject of the 20's, when nostalgia for the gold-standard governs, Polanyi observes 64 :

"Whether the gold itself has value for the reason that it embodies labor, as the socialists held, or for the reason that it is useful and scarce, as the orthodox doctrine ran, made for once no difference. The war between heaven and hell ignored the money issue, leaving capitalists and 61 Commons [1992, p. 390].

62 This is possible but not necessary. This will be the object of Commons ulterior reflections on monetary policy. The absence or incoherence of these will only abolish the emancipatory possibilities of pure credit money. Cf. [START_REF]Monnaie et calcul economique socialiste selon Karl Polanyi : le projet d'une economie socialiste federale[END_REF].

63 Cf. L. Dumont, "Introduction" in [START_REF] Arensberg | On belief in economic determism[END_REF]Servet [1993].

64 Polanyi [1957, d, p. 25].

socialists miraculously united [...] and Das Kapital implied the commodity theory of money, in its Ricardian form".

Polanyi, refusing to consider money as a commodity, suggests an analysis which conforms to the institutionalist conception of institution. The modern money institution, once more, expresses the impossible "enclosure" of the economy. Despite the role of private institutes in the creation of modern money, Polanyi observes the importance of its "validation by the state" 65 :

"Now the institutional separation of the political and the economical sphere has never been complete, and it was precisely in the matter of currency that it was necessarily incomplete ; the state, whose Mint seemed merely to certify the weight of the coins, was in fact the guarantee of the value of the token money, which it accept ed for the paiement for taxes and otherwise. This money was not (underlined by Polanyi) a means of payment, it was a means of exchange".

According to Polanyi, even all purpose money cannot do without the institutional forms which are the conditions of social integration. The proof of this paradox is that the monetary policy of central banks, render the so-called automatism of the gold-standard meaningless.

The market economy is not possible with a currency that is purely a commodity. The untimely scarcity of this money would be so catastrophic that a token money becomes absolutely necessary 66 . Therefore, Polanyi adopts a non-essentialist view of money. The fact that money practices can be practised simply with symbols does not mean anything in distortion of the "true" monetary system which results from pure commodity 67 . The monetary system of the "One Big

Market" therefore functions on two levels : a) An international level, where money is a full commodity.

b) A national level, where a mediation functions between the space of commodity-money and the space of token or fiat money that is connected to the domestic markets. The central bank is this mediation which makes possible the coexistence of the international gold-standard and of a national credit money.

Thus, the Central Bank is at the exact point of the joining together of two logics : one is purely economic as it rests on the means of exchange, and the other is political, because it embodies the collective identity on which the means of payment is based. The birth of the Federal Reserve System, could be interpreted as the expression of a counter-movement protecting society and participating in the construction of a national identity. Paradoxically, during the era of the goldstandard which lasted the period of 1879 to 1929 68 , "the monetary system was the strongest among the economic forces integrating the nation".

In centralising the supply of credit 69 , the institution of market by money is made possible by the Central Bank. Thus, the Bank can partly protect the national economy against deflationary forces which are created by the functionning of the gold standard 70 . Open market policy organises a fall in 65 Polanyi [1957, d, p. 196]. Guttmann [1994], when analysing the Great Transforaltion, emphasises this fact.

66 Polanyi [1957, d, pp. 192-193].

67 Polanyi [1968, pp. 176-177].

68 Polanyi [1957, d, p. 204].

69 Polanyi [1957, d, p. 194].

70 Thus, according to Polanyi, the creation of money is in part exogene in the gold standard regime.

price while raising the exportable surplus and liquidating marginal firms. From there, an element of rationality in the Big Market reduces the "automatism of gold standard to a mere pretence" 71 .

Thus, at the very moment when one institutes markets with the aim of establishing a pure economic regulation of society, society is protecting itself against the devastating effects of international money-commodity by a monetary interventionnism. This counter-movement of social "protection" which contributes towards the creation of this "double movement", that is so characteristic of liberal societies, shows to what point money is a fictitious commodity, even during the reign of the gold-standard.

Conclusion

Polanyi believes that the money institution is essential 72 to different societies. Whether primitive, archaic, capitalist or socialist 73 they must be thought of as being monetised 74 . In other words,

Polanyi never ceases to maintain that the money and market institutions hold an important place in society, even if market, contrary to money, is a young institution of human history. The only danger lies in the desire to reduce money to a pure commodity and thinking that markets could be selfadjusting.

71 Polanyi [1957, d, p. 195].

72 This is the central to Servet [1993]. Actually, it is possible to extend Polanyi's anthropology : man, as a social being -zoon politicon-necessarily knows money as the institution that solidifies social relationships thanks to "standardising and standardised" devices. However, it is impossible to confirm, as Hodgson does, that Polanyi could have maintained that money existed in the periphery of non-modern economies. Too many of Polanyi's citations regarding money testify the contrary (see again on this subject, [START_REF]Monnaie et calcul economique socialiste selon Karl Polanyi : le projet d'une economie socialiste federale[END_REF]).

73 This is why socialism which makes an abstraction out of the necessity of monetary order has no viability. It is worth noting that, in the case of the decentralised socialist society desired by Polanyi, money is a means of embedding economy into society in a humanist way as a contradictory evaluation of wills are able to express themselves. This necessary to avoid the dangerous dream of a "natural economy" which is technically impossible when neither custom nor tradition produce steady lines of action. Weber [1971, pp. 110-111], may be just before Mises, notices this technical feature of money that Polanyi will never ignores 74 If the continuation of Polanyi's thought on this question of money appears to us to be certain, the same interpretation also appears possible with regards to market. The Great Transformation soundly constitutes the end of market society. But the new reality does not constitute in any way the "absence of markets", these assuring "freedom of consumers, to indicate shifting of demand, to influence producers' income, and to serve as an instrument of accountancy, while ceasing altogether to be an organ of self regulation" [Polanyi, 1957, d, p. 252] and allow accounting. Polanyi never ends in his confirmation that money institution has an important place in society.

  The determinisms resulting from individual interest are not neglected by Polanyi, a factor which once again brings him closer to Commons

4

: according to both authors, political authority intervenes as a result of the reaction of individual interests that are threatened in a convergent manner. Taking the case of tribal society into consideration which is largely founded on gift and counter-gift, Polanyi further remarks that 5 :

Polanyi [1957 a, p. 79].

According to Polanyi, Schumpeter, convinced that the distinctive nature of economic analysis is formalising scarcity mechanisms, cannot accept that.

[START_REF]Monnaie et calcul economique socialiste selon Karl Polanyi : le projet d'une economie socialiste federale[END_REF].

Polanyi [1994, b & c].

Polanyi [1994, a, p. 93].

WEBER M., Economie et Societe, Tome I, Paris : Plon, 1971, pp. 100-110).


D Eberbeck
email: dietmar.eberbeck@ptb.de

M Kettering

C Bergemann

P Zirpel

I Hilger

L Trahms

Quantification of the aggregation of magnetic nanoparticles with different polymeric coatings in cell culture medium

The knowledge of the physico-chemical characteristics of magnetic nanoparticles (MNPs) is essential to enhance the efficacy of MNP-based therapeutic treatments (e.g. magnetic heating, magnetic drug targeting). According to the literature, the MNP uptake by cells may depend on the coating of MNPs, the surrounding medium as well as on the aggregation behaviour of the MNPs. Therefore, in this study, the aggregation behaviour of MNPs in various media was investigated. MNPs with different coatings were suspended in cell culture medium (CCM) containing fetal calf serum (FCS), and the distribution of the hydrodynamic sizes was measured by magnetorelaxometry (MRX). FCS as well as BSA-buffer (phosphate buffered saline with 0.1% bovine serum albumin) may induce MNP aggregation. Its strength depends crucially on the type of coating. The degree of aggregation in CCM depends on its FCS content showing a clear, local maximum at FCS concentrations, where the IgGconcentration (part of FCS) is of the order of the MNP number concentration. Thus, we attribute the observed aggregation behaviour to the mechanism of agglutination of MNPs by serum compartments as for example IgG. No aggregation was induced for MNPs coated with dextran, polyarabic acid, or sodium phosphate, respectively, which were colloidally stable in CCM.

Introduction

Magnetic nanoparticles (MNPs) have been a research topic of great interest over the past 50 years [START_REF] Gupta | Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications[END_REF]. Especially in the last decade, many novel applications of MNPs have been proposed and investigated for biological or medicinal approaches remarkably in the fields of Magnetofection TM (e.g. [START_REF] Mykhaylyk | Recent advances in magnetofection and its potential to deliver siRNAs in vitro Methods[END_REF], magnetic separation procedures (e.g. [START_REF] Clement | Differential interaction of magnetic nanoparticles with tumor cells and peripheral blood cells[END_REF], magnetic resonance imaging (MRI) as contrast agents (e.g. [START_REF] Sosnovik | Magnetic nanoparticles for MR imaging: agents, techniques and cardiovascular applications[END_REF], magnetic drug targeting and delivery (e.g. [START_REF] Alexiou | Delivery of superparamagnetic nanoparticles for local chemotherapy after intraarterial infusion and magnetic drug targeting[END_REF][START_REF] Polyak | Magnetic targeting for site-specific drug delivery: applications and clinical potential Expert[END_REF] as well as in cancer treatments due to hyperthermal (e.g. [START_REF] Ito | Complete regression of mouse mammary carcinoma with a size greater than 15 mm by frequent repeated hyperthermia using magnetite nanoparticles[END_REF][START_REF] Wilhelm | Tumor cell toxicity of intracellular hyperthermia mediated by magnetic nanoparticles[END_REF], Thiesen&Jordan 2008) or thermo ablative therapies (e.g. [START_REF] Hilger | Electromagnetic heating of breast tumors in interventional radiology: in vitro and in vivo studies in human cadavers and mice[END_REF][START_REF] Bruners | Thermoablation of malignant kidney tumors using magnetic nanoparticles: an in vivo feasibility study in a rabbit model[END_REF]).

Among the wide variety of MNPs, iron oxide (magnetit/maghemit) nanoparticles were and still are the most intensively studied MNPs [START_REF] Lin | Development of superparamagnetic iron oxide nanoparticles (SPIONS) for translation to clinical applications[END_REF][START_REF] Peng | Targeted magnetic iron oxide nanoparticles for tumor imaging and therapy[END_REF]. Obviously, this is due to the proven biocompatibility and the approval of superparamagnetic iron oxide nanoparticles (SPIOs) as contrast agents for MRI diagnostics in the clinics. Beside the necessity for biocompatibility studies with MNPs for medical applications, the further behaviour of MNPs in biological environments is relevant to be investigated. For in vivo applications, the knowledge of the aggregation behaviour of MNPs plays an important role, particularly for applications of MNPs into the vascular system for diagnostic or therapeutic purposes. Furthermore, for therapeutic cancer treatment due to magnetic heating, a high intracellular MNP loading is essential for the destruction of tumour cells (Kettering et al. 2007), in addition to a high specific heating power (SHP) (Hergt et al. 2006). To this end, it is essential to know which characteristics of MNPs increase their uptake in cell cultures. Here, the aggregation behaviour, in different surrounding media, in particular in cell cultures, plays an important role, as former studies showed (Tiefenhauer et al. 1996[START_REF] Zhang | Surface modification of superparamagnetic nagnetite nanoparticles and their intracellular uptake[END_REF], Gupta&Gupta 2005, Sahoo&Labhasetwar 2006). Also, the presence of FCS in the cell culture medium (CCM) is known to be of crucial importance [START_REF] Chen | Stability of hydrophilic magnetic nanoparticles under biologically relevant conditions[END_REF], Petri-Fink et al. 2008) as well as the size of the nanoparticles [START_REF] Laconte | Magnetic nanoparticle probes[END_REF]. It was found for example that the efficiency of the uptake of gold nanoparticles or polymeric nanoparticles depends on their size (Sahoo&Labhasetwar 2006, Chitrani et al. 2006, Win&Feng 2005). Here, we will note for example that the parameters coating and MNP size seem to effect independently on the uptake (e.g. Petri-Fink et al. 2008). Furthermore, Dass et al. showed that nanoparticles were ingested by HeLa cells in endosomes both individually (one per endosome) and in form of aggregates (several per endosome), depending on the composition of nanoparticles [START_REF] Dass | Cellular uptake of polymer nanoparticles imaged by electron microscopy based on high-pressure freezing[END_REF].

In this context, the aim of the presented work was to examine the aggregation behaviour of superparamagnetic iron oxide nanoparticle formulations differing in their coatings in relevant media. The knowledge about their aggregation behaviour is important to estimate and understand different internalization amounts into cells with regard to therapeutic approaches like magnetic heating treatments [START_REF] Hilger | Use of magnetic nanoparticle heating in the treatment of breast cancer[END_REF]] or magnetic drug targeting [START_REF] Alexiou | Delivery of superparamagnetic nanoparticles for local chemotherapy after intraarterial infusion and magnetic drug targeting[END_REF]. To this end, the impact of coating and medium on the effective particle size can be evaluated, which is one parameter that determines the uptake process into target cells,. The aggregation behaviour in dependence of the various biocompatible coatings should be investigated in CCM to elucidate the in vitro situation for tests with cultured cell lines and in BSA-buffer (phosphate buffered saline (PBS) with 0.1% bovine serum albumin (BSA)) as a control medium.

Because of their long blood circulation time, MNPs with hydrophilic polymer coatings like dextran or polyethylene glycol (PEG) (Gupta&Gupta 2005) are of particular interest with respect to further in vivo applications. In our own MRX studies, we found that MNPs with hydrophilic electrically charged coatings may aggregate in FCS and human serum, while those with non-charged starch layer do not [START_REF] Eberbeck | Quantificationof aggregates of magnetic nanoparticles in different suspension media by magnetorelaxometry[END_REF][START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF]. In order to keep colloidal stability in salty media, we chose 12 different formulations of superparamagnetic iron oxide nanoparticles with highly hydrophilic polymer coatings. In order to investigate the effect of its electrical charge coatings with neutral (OHgroups), negatively (e.g. COOH-) and positively charged (NH-) groups were chosen. Different negatively charged functional groups were applied in order to disentangle the influences of the charge and the nature of the functional groups.

It was found, that the uptake of MNPs depends on the amount of incubated MNPs (Petri-Fink et al. 2005). In particular, the aggregation of MNPs in FCS containing media depends on the MNP-to-serum concentration ratio, where the mechanism of agglutination of MNPs [START_REF] Eberbeck | Specific binding of magnetic nanoparticle probes to platelets in whole blood detected by magnetorelaxometry[END_REF]) caused by particular FCS-proteins, e.g. antibodies, is discussed [START_REF] Eberbeck | Quantificationof aggregates of magnetic nanoparticles in different suspension media by magnetorelaxometry[END_REF][START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF]. Therefore, within this study, we will address the concentration dependence of the aggregation of MNPs in CCM.

Because of their high performance in Magnetofection TM , we investigated multicore MNPs with hydrodynamic diameters equal or larger than 100 nm . Also the contrast agent Resovist ® was investigated as a reference system, because it is already approved for the clinical application and because its colloidal behaviour was already known from our earlier MRX studies [START_REF] Eberbeck | Quantificationof aggregates of magnetic nanoparticles in different suspension media by magnetorelaxometry[END_REF][START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF]) .

In the present study we again applied MRX which is allows for a very robust measurement of MNPs in non transparent media like blood [START_REF] Eberbeck | Specific binding of magnetic nanoparticle probes to platelets in whole blood detected by magnetorelaxometry[END_REF]. In contrast to the PCS-method (photon correlation spectroscopy), frequently used for the estimation of aggregate size, MRX signals are not affected by other (non magnetic) corpuscular compartments like cells or other particulate impurities which may strongly interfere PCS measurements.

The present study is based on these former studies to deepen the knowledge of the aggregation behaviour of MNPs for further in vitro and in vivo investigations. In this study, we focus on the in vitro aggregation behaviour of MNP in dependence on the biocompatible coating with different functional groups.

Experimental

Materials

Bovine serum albumin buffer (BSA-buffer: phosphate buffered saline (PBS) containing 138 mmol l -1 NaCl, 2.7 mmol l -1 KCl, and 10 mM phosphate with 0.1% bovine serum albumin) was used for the dilution of MNP stock suspensions and for reference samples. The albumin concentration is 0.1% by weight, i.e. 1.5×10 -5 mol l -1 . The medium of our interest is a cell culture medium (CCM) composed of Dulbecco's Modified Eagle Medium with F-12 Nutrient Mixture (D-MEM/F-12, #11320-074, Invitrogen, Karlsruhe, Germany) containing 1% or 10% (v/v) foetal calf serum (FCS, #10270, Invitrogen, Karlsruhe, Germany), corresponding to a total albumin concentration of 0.02% and 0.2% by weight. Furthermore, the FCS-concentration in the CCM was varied within the range 0.022% and 67%. The concentration of -immunoglobulins within the FCS stock solution was β( -immunoglobulin) = 126.5 mg/l. Most of the -immunoglobulins are antibodies being exclusively IgG antibodies in FCS. Thus, the IgG concentration was roughly estimated to be c( -immunoglobulin) = 843 nmol/l c(IgG).

Magnetic nanoparticles (chemicell GmbH, Berlin, Germany) are obtained by converting an acidic iron(II/III) salt solution into iron(II/III)-carbonate by adding equivalent amounts of alkaline carbonate, followed by a successive thermic reaction to iron(II,III) oxide according to a recently described method (Bergemann 1996). After removing of surplus salts, the particles were coated with water soluble polysaccharides or polymers. The 12 investigated MNP formulations mainly differ in its coatings, ranging from electrically nearly neutral dextran and starch over negatively charged carboxymethyl dextran, polygalacturonic acid, polyarabic acid, phosphorylated starch, dextransulphate, heparin, oleic acid to positively charged diethylaminoethyl and polyethylenimine the properties of which are listed in table 1. In contrast to the fluidMAGs, the starch matrix of targetMAG-NC is additionally cross linked and modified with terminal phosphate groups.

For comparison, we also measured the well known commercially available MRI contrast enhancing agent Resovist ® which comprises magnetite cores, where single cores and small clusters (mean hydrodynamic size is 60 nm) are coated with carboxymethyl dextran (table 1; Bayer Health Care, Berlin. Germany). In earlier investigations [START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF]) the effective (cluster!) core size distribution with a mean diameter of about 8.5 nm was deduced from MRX-measurements. The corresponding diameter of the mean core volume is about d V = 10 nm.

MRX-measurements

For the measurement of the magnetic relaxation, a sample of 140 µl volume (within a PE micro vial) was placed in the 10 mm bore of the magnetizing coil. A magnetic field of 1.3 kA/m was applied for 1 s to align the magnetic moments within the sample. After jump-likely switching off the field within about 500 µs, the decay of the magnetic field in z-direction was measured by a low-Tc SQUID at a distance of 10 mm above the sample. The device and the method were described in detail in [START_REF] Matz | A SQUID measurement system for immunoassays[END_REF]. The measurement time window was 450 µs t 0.45 s. The output signal of SQUID sensor contained an unknown offset value B offset . For visual comparison purposes, the offset of each measured relaxation curve B(t) was adjusted so that all relaxation curves coincided at the end of the measurement.

The relaxation curves could be characterized by two main parameters, the relaxation amplitude ∆B=B(0.61 ms)-B(350 ms) and the relaxation time t 1/e which is the time where B(t 1/e )-B(350 ms)=1/e ∆B counted from the reference point of 0.61 ms.

It was previously shown, that from the relaxation curves the distribution of the sizes of hydrodynamic entities -in our case the MNPs including their solvatisation shell as well as clusters of MNPs again with their solvatisation shells -can be extracted. For that purpose, the so called cluster moment superposition model (CMSM) [START_REF] Eberbeck | Quantificationof aggregates of magnetic nanoparticles in different suspension media by magnetorelaxometry[END_REF])

d d T K d d t T H K M d d t d f A H T d M L d f M g t B d d d d ) , , , , ( exp ) , , , , , , ( exp 1 ) , , ( ) , , , ( ) , , ( ) (
C eff C eff eff S C eff mag C C C C C S S C - - - × × = η τ η τ σ µ σ µ (1)
was fitted to the MRX-curves. Here, g is an amplitude factor determined by the measurement geometry, M S is the saturation magnetisation of the cores, f is the distribution of the core diameters d with the median size µ and the size distribution parameter σ, L is the Langevin function depending on d, the magnetising field H, the magnetising time t mag , and the temperature T ; A C is the fraction of MNPs belonging to aggregates, here modelled by spherical clusters with a distribution f C of the cluster (2) we calculated the diameter of the cluster with the mean volume d CV and the mean cluster diameter from the volume weighted cluster diameter distribution function according to

d CwV = d C d C 3 f(d C ) dd C / d C 3 f(d C ) dd C .
This average regarded the sample volume occupied by the clusters as weight.

Results

The aggregation of MNPs was quantified from MRX data measured shortly (about 90 minutes) after preparation. Here, the dispersion parameter of the cluster size distribution, obtained from model fit, has proved to be a suitable parameter for classification of the aggregation. These results were compared with the degree of precipitation, visually observed about 19 hours after preparation, classified in "no", "weak", "medium" and "strong" precipitation (figure 1). On this basis we classified and quantified the aggregation of the different MNPs, suspended in the cell culture medium (CCM) and in BSA-buffer as a reference.

Aggregate size distribution

Fitting the cluster moment superposition model (CMSM) to the relaxation curves, we got the distribution of the hydrodynamic sizes of the relaxing entities, i.e. MNPs and aggregates of them, further on denoted as cluster-or aggregate size distribution. In order to interpret the results for the cluster size distribution, we considered first the data obtained for Resovist ® where the single cores particles had a mean core diameter of around 4 nm coated with a carboxydextran layer with a mean thickness of about 4 nm [START_REF] Lawaczeck | Magnetic iron oxide nanoparticles coated with carboxydextran for parenteral administration and liver contrasting[END_REF]. In BSA buffer, the mean hydrodynamic volume corresponded to a cluster diameter of d CV = 47 nm in good agreement with the data of a previous study [START_REF] Eberbeck | Quantificationof aggregates of magnetic nanoparticles in different suspension media by magnetorelaxometry[END_REF] and with PCS data, d PCS = 61 nm [START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF]) (table 2). In BSA-buffered suspension, we got a moderate width of the cluster size distribution of Resovist ® MNPs indicated by the distribution parameter σ C = 0.54. In contrast, if Resovist ® was suspended in the CCM (containing FCS), σ C was rising to the large value of 1 (table 2). The values of mean aggregate size of d CV = 3 nm and 8 nm were not meaningful, since these values were smaller than the mean diameter of the coreshell particle being about 10 nm + 8 nm = 18 nm. Also for the other MNP samples with strong visual precipitation, high σ C values and a mismatch between mean aggregate sizes estimated by MRX, d CV , and PCS, d PCS , respectively, were observed, except for fluidMAG-PGS suspended in BSA-buffer (see example below). Vice versa, if the apparent cluster size distribution was narrow, indicated by low σ C values (σ C <0.6), then the MNP suspensions were visually long term stable in BSA buffer and d CV and d PCS agreed well (table 2). This preliminary conclusion (working hypothesis) obtained from the measurements on Resovist ® will be further illustrated by the following two examples concerning fluidMAG MNPs:

(i) The shape of the MRX curves of strongly aggregated MNPs (for example fluidMAG-Heparin in CCM with 1% FCS) was very similar to that of immobilised MNPs while those containing smaller (fluidMAG-ARA, d CwV = 290 nm) and even larger but well suspended (targetMAG-NC, d CwV = 597 nm) aggregates distinguished in shape significantly from the curve of immobilised MNPs (figure 2). The CMSM analysis of the MRX curves of immobilised MNPs yields for all MNP formulations large σ C -values, e.g. σ C = 1.74, and very small d CV -values, e.g. d CV = 14.4 nm (fluidMAG-ARA). Hence, we associated large values of σ C with well extended aggregates, where the Brownian relaxation of the MNPs was strongly suppressed. In this case, the assumptions of the CMSM, i.e. the lognormal size distribution of clusters was obviously not valid. Consequently, the values of d CV and d CwV lost the physical meaning.

(ii) In contrast to the other fluidMAGs with strong visual aggregation, where large values of the dispersion parameter σ C > 0.84 were observed, the strong aggregation in fluidMAG-DXS suspended in BSA buffer was accompanied by a relatively small value of σ C = 0.45. Obviously, the aggregate structure of this sample distinguished qualitatively well from that of the other MNP formulations. This seems to correlate with the rather smooth appearance of the precipitate observed in fluidMAG-DXS, compared to that of mentioned other ones, where the appearance of the precipitates had a stronger contrast to the suspension medium.

In conclusion, if σ C is small then f C seems to obey a monomodal size distribution like (2) and ( 1) is applicable. But, if the estimated value for σ C exceeds a value of about 1, there are very large aggregates present, the magnetisation of which behaves like that of immobilised MNPs (within our measurement time window). Therefore, we used the distribution parameter σ C as a tool for the assessment of the type of aggregates. In this latter case, the validity of (2) is questionable and the size distribution parameters µ C and σ C serves only comparative purposes.

Aggregation in BSA-buffer

While all MNP formulations were stable in its original suspension medium (deionised water) some of them aggregated already in BSA buffer. First of all, fluidMAG-DEAE and -PEI aggregated immediately after suspension in BSA buffer, but also in pure PBS i.e. without BSA and in CCM without FCS. Because of this visually observed strong aggregation features, these samples were excluded from further investigations by MRX.

The relaxation behaviour of the different MNPs was measured about 90 minutes after preparation. At this time, no clear visual markers of aggregation in the suspensions were found. Only after 19 hours distinct precipitation was visually observed (figure 1 andtable 2).

According to the tendency of particle aggregation in BSA buffer, we divided the different MNP formulations into 2 main groups: MNPs which are (i) colloidally stable or (ii) unstable in BSA-buffer, respectively. While the samples of group (i) were long term stable in BSA-buffer, i.e. they did not show any visually discernible precipitation after 19 hours, those of group (ii) showed at least weak precipitation (table 2). Within the group (i) there were 2 subgroups: The formulations fluidMAG-DX, -D, -CMX, -PGS showed low σ C values (σ C <0.6) and the mean aggregate sizes estimated by MRX, d CV , and PCS, d PCS , respectively, matched within an accuracy of about 30% (table 2). The σ C -values of the second subgroup (fluidMAG-ARA, fluidMAG-DP and targetMAG-NC) amounted to 0.72 σ C 0.84 and the MRX and PCS sizes differed by about 80% (table 2). The formulations of group (ii) fluidMAG-DXS, fluidMAG-Heparin, and fluidMAG-OS showed high σ C values, σ C 1, except for fluidMAG-DXS, and the aggregate sizes estimated by MRX and PCS, respectively, differed strongly (table 2).

Aggregation in cell culture medium with FCS

The relaxation curves of fluidMAG-DX, fluidMAG-D, fluidMAG-ARA, and targetMAG-NC suspended in CCM containing 1% and 10% FCS, respectively, did not or only slightly distinguish from those of the samples suspended in BSA buffer, indicated by nearly the same values for σ C , d CwV , and d PCS , practically independent on the FCS concentration (table 2). The absence of strong visually observable precipitation after 19 hours (table 2) also indicated the (long term) coloidal stability of these MNP formulations.

All other MNP formulations aggregated strongly in 1% FCS. Interestingly, the precipitation of the MNP formulations fluidMAG-DP, -DXS, and -Heparin was weaker in CCM with 10% FCS than with 1% FCS. In accordance to the above outlined relation, this comparatively weaker aggregation corresponded to σ C -values, all around 0.64, being much smaller than those for the strongly precipitating samples, where σ C was 0.9 (table 2).

In order to study the effect of the FCS concentration on the aggregation more thoroughly, we suspended the ferrofluids fluidMAG-DX, fluidMAG-D, fluidMAG-ARA and targetMAG-NC as well as Resovist ® in FCS and in CCM containing different concentrations of FCS. First, we diluted the MNP suspensions in FCS-free CCM down to an iron concentration of about 4.8 mmol/l. Then, 50 µl MNP suspension were added to 100 µl FCS-CCM-with a FCS volume fraction ranging from 100% to 1%. So we could achieve higher FCS-to-MNP concentration ratios than in that experiments the results of which are presented in table 2. The relaxation curves for the formulations fluidMAG-ARA, fluidMAG-D, fluidMAG-DX and targetMAG-NC did not depend on the FCS concentration (figure 3) supporting the claim that they were colloidal stable in FCS. For fluidMAG-D there was, however, a weak violation of the matching of the relaxation curves at the FCS concentrations of 6.7% and 22% (figure 4). Note, that this behaviour was not caused by the slightly higher viscosity due to the higher FCS content, since this effect was absent in fluidMAG-DX, fluidMAG-ARA and targetMAG-NC (figure 3). In contrast, the curves of Resovist ® samples changed smoothly in shape with respect to the FCS concentration as shown in figure 5. The relaxation curve shape parameters t 1/e and the extracted σ C patterned smooth maxima at a FCS concentration corresponding to an IgG concentration of about 60 nmol/l (figure 3). With given iron concentration and mean particle core volume (being equivalent to a core diameter of 10 nm), for Resovist ® we calculated a MNP concentration of c(MNP) = 80 nmol/l. matching well with the concentration of IgG at the aggregation maximum. This finding agreed well with previous data obtained on basically the same MNP formulation of DDM128 (Meito Sangyo, Japan) [START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF]. The matching of the concentrations of MNPs and IgG at aggregation maximum was interpreted by agglutination of the MNPs by means of the IgG molecules [START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF].

In order to check the long term aggregation stability, we measured the FCS concentration dependency of the extent of aggregation 17 hours after preparation of fluidMAG-D, fluidMAG-DX, fluidMAG-ARA and targetMAG-NC. The relaxation curves for fluidMAG-DX did not show any significant change and those of fluidMAG-ARA and targetMAG-NC indicated a change of hydrodynamic volume, i.e. apparent cluster volume, of about 10%, only. On the other hand, the relaxation curves of fluidMAG-D changed dramatically (figure 5). Here, a FCS (or IgG) concentration dependent aggregation emerged very clearly after 17 hours, where the aggregation showed a local maximum similar to that of the Resovist ® sample after 3 hours (figure 3). Nearly the same result was retrieved for a 10 times lower MNP concentration. Hereby, the position of the aggregation maximum was dependent first and foremost on the MNP-to-FCS concentration ratio. The different shape of this maximum may be associated with reduced aggregation kinetics in the more diluted sample due to the lower concentrations of MNPs and FCS. Assuming a mean core volume corresponding to 12 nm, we got a MNP concentration of about 100 nmol/l and 10 nmol/l for the more diluted sample, respectively, matching well the IgG concentrations at the maximum position (figure 6). Hence, we infer that agglutination took place in fluidMAG-D sample, which was very similar to that in Resovist ® , but with a much longer time constant.

We conclude, that the aggregation of Resovist ® , fluidMAG-D, -DP, -DXS, -Heparin, and -OS in CCM is very likely, at least partially, caused by an agglutination process mediated by IgG or other components (except albumin) of FCS. This interpretation was supported by the finding that the aggregation had its maximum where the concentrations of MNPs and IgG matched (Figures 3 and6, [START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF]) and by the observation that the aggregation was much stronger in CCM with 1% FCS than with 10% FCS (table 2).

Discussion

On the base of the presented results, the analysed MNPs could be described as being (i) colloidally not stable in BSA-buffer and cell culture medium (CCM), (ii) colloidally stable, and (iii) exhibit agglutination behaviour in CCM.

(i) The MNP formulations fluidMAG-DEAE, -PEI and -DXS were colloidally not stable in BSA buffer and CCM. fluidMAG-DEAE and -PEI, having a highly positive zeta potential of about 50 mV in deionised water, showed the strongest aggregation behaviour which was induced by an ion concentration of 140 mmol/l (PBS). Also, fluidMAG-DXS with a negative zeta potential showed a strong aggregation behaviour in BSA buffer. We attributed these aggregations to the known effect of the screening of electrostatic repulsive potential by ions (Sonntag&Strenge 1987) in the suspension medium. It remained the steric repulsion between the MNPs, mediated by the DEAE, PEI and DXS shells, which obviously could not prevent the aggregation in the given case. Thus, in media with high ionic strength the shell thickness was not dense and/or thick enough to compensate the attractive forces generated by van der Waals and magnetic dipolar interaction. For example, it was shown in [START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF] that the total interaction potential of two electrically non-charged magnetite MNPs being in contact, having a core diameter of 15 nm and a thickness of the coating of 4 nm (reasonably parameters for the carboxydextran shell of Resovist ® ), amounted to -650 K at the equilibrium distance, i.e. the interaction potential has a highly attractive effect at room temperature (T = 295 K). Furthermore, a coating consisting of hydrophilic polymer chains contained water. So, note that a high ion concentration may dehydrate the coating partially, presumably leading to its shrinkage which in turn reduces the particle-particle contact distance. Further in vitro studies with cell cultures should show whether these agglutinated particles could be internalized from cells more effectively due to an enlarged internalisation rate or an enhanced magnetically induced pressure of sedimentation. An additional interesting question would be if these particles have a distended cytotoxicity in contrast to particles that do not agglomerate in physiological media. For in vivo purposes, the injection of fluidMAG-DEAE, and -PEI to the vascular system is precarious because of the enhanced risk of vascular obliterations. In contrast, those particles might be suitable for magnetic heating treatments if they are injected directly into target regions and if they have appropriate specific absorption rates to generate enough heat for destroying target cells.

(ii) Long term colloidal stability in both CCM containing FCS and BSA buffer could be detected for fluidMAG-ARA, -DX and targetMAG-NC. Also fluidMAG-D was colloidally stable at room temperature at least for 90 minutes. The high colloidal stability of fluidMAG-DX and -D correlates well with low zeta potentials, this interrelation was already suggested in [START_REF] Eberbeck | Aggregation behaviour of magnetic nanoparticle suspensions investigated by magnetorelaxomery[END_REF]. However, also fluidMAG-ARA and targetMAG-NC are colloidally stable, though they have a significant electrical surface potential due to carboxylic and phosphate functional groups, respectively. Consequently, fluidMAG-ARA, -D and -DX as well as targetMAG-NC seems to be harmless regarding agglomeration and possible vascular obliterations for in vivo purposes. Additional studies with those MNPs in whole blood should be done to confirm these findings.

(iii) On the other hand, the MNP suspensions of Resovist ® , fluidMAG-CMX, -PGS, -DP, -Heparin and -OS exhibited agglutination behaviour only in CCM. They aggregated partially already about 90 minutes after being transferred into CCM. Obviously, this was caused by those CCM components which are not part of BSA buffer, because these formulations were colloidally stable in BSA buffer or showed at least significantly weaker aggregation (fluidMAG-Heparin, -OS). As discussed above for Resovist ® , fluidMAG-D, -DP, (-DXS), -Heparin, and -OS this aggregation was rather caused by an agglutination of MNPs by FCS components like IgG antibodies, indicated by a concentration dependent maximum of aggregation. Note, that there is no obvious link of this aggregation behaviour to a special kind of functional groups, and no correlation to the charge of the MNPs in pure water. Here, we will mention, that the particle charges appear screened in CCM, shown by the reduced absolute value of zeta potential in CCM as well as by inversion of positive charge of DEAE and PEI (table 1). The charge inversion might be the result of attachment of negatively charged molecules, e.g. albumin, to the particle's surface. This picture of stabilisation of MNPs by proteins seems to hold also for the remarkably increased colloidal stability of dimercaptosuccinnic acid-stabilised MNPs in RPMI-1640 medium caused by FCS observed by [START_REF] Chen | Stability of hydrophilic magnetic nanoparticles under biologically relevant conditions[END_REF] In the case of fluidMAG-CMX and -PGS, we did not observe such concentration dependence of aggregation. At least for fluidMAG-CMX this could be understood by the observation of strong aggregation (long relaxation times) already in CCM without FCS. This may be attributed to the much stronger effect to the screening of repulsive potential by higher valence ions (Sonntag&Strenge 1987), present in CCM but not in BSA buffer. Looking at additional in vitro and in vivo investigations those MNPs have to be treated as careful as MNPs that are colloidally not stable in both BSA buffer and CCM (see above). With regard to the different aggregation behaviour in BSA buffer and CCM it is actually not possible to predict their activities in vivo. Therefore, further studies with fluidMAG-CMX, -PGS, -DP, -Heparin and -OS in whole blood as suspension medium have to be performed to assess the aggregation behaviour in vivo.

Conclusion

The method of Magnetorelaxometry (MRX) allows the robust and sensitive quantification of aggregates of magnetic nanoparticles (MNPs) in different media, long before it becomes visible by precipitation. We found that strong visual aggregation correlates well with the aggregate size distribution parameter, derived from MRX data. Among the investigated samples MNPs coated with electrically neutral dextran (fluidMAG-DX) presented the highest colloidal stability followed by fluidMAG-ARA (polyarabic acid coating), targetMAG-NC (sodium phosphate) and fluidMAG-D (starch) which showed also good colloidal stability in cell culture medium (CCM). The other investigated MNP formulations with caboxymethyl dextran, polygalacturonic acid, phosphorylated starch, dextransulfate, heparin, oleic acid diethylaminoethyl and polyethylenimine as coating materials aggregated in CCM. Partially, this aggregation depended on the FCS concentration and was thus attributed to an agglutination of MNPs by serum components presumably IgG antibodies. The corresponding molecular target on the MNP surface remains to be investigated.

It seems likely that the uptake of magnetic nanoparticles depends on their size, thus the aggregation as a result of the interplay between coating of MNPs and the medium may determine the uptake significantly. As a consequence for further in vitro and in vivo investigations and moreover for clinical applications our results illustrate remarkably that the aggregation behaviour of iron oxide magnetic nanoparticles in physiological media depends on their coating and their concentration. Again, the necessity for biocompatibility studies with MNPs in biological environments for biomedical applications was emphasized.

Table 1: List of investigated MNP formulations and its main properties. All cores were composed of magnetite/maghemite. Zeta potential and colloidal behaviour were ascertained for suspensions in salt-free water, BSA buffer (BSA-B) and cell culture medium (CCM) containing 10% FCS.

MNP-Sample

Coating

Zetapot. The iron concentration of all samples was about 5 mmol/l. The measurement was performed 90 min after preparation. For a better visual comparison of the line shapes, the baselines of the relaxation curves were adjusted (see text).

  diameters d C determined by the corresponding median and distribution parameter µ C and σ C , and finally τ eff was the effective relaxation time according to and τ B are the Néel and Brownian relaxation times of the particle moments. From f C ,

Figure 1 :Figure 2 :

 12 Figure1: Examples of MNP suspensions 19 hours after preparation in different media as indicated. "FCS 1%" and "FCS 10%" refers to cell culture medium (CCM) containing 1% and 10% FCS, respectively. According to the quality of the visual appearance of the samples 4 classes of precipitation are defined: (i) no precipitation: the samples are homogeneously coloured; (ii) weak precipitation: A slight precipitate is observable and the supernatant remains homogeneously coloured like the related sample without precipitation (e.g. reference sample in BSA buffer); (iii) medium precipitation: A precipitate is observable and the supernatant is lighter coloured than that of the reference or the staining of the supernatant shows a gradient; (iv) strong precipitation: Almost all MNPs are precipitated, i.e. the supernatant is clear or at least much lighter coloured than the reference sample. Note that the CCM has a red colour determining the colour of supernatant of samples with strong aggregation in CCM.

Figure 3 :

 3 Figure 3: Geometric dispersion parameter σ C of the cluster diameter distribution function obtained by fitting the CMSM to the MRX curves measured for samples with different IgG concentrations being related to the different FCS contents. The iron concentration of all samples was about 1.6 mmol/l. Samples were measured about 3 hours after preparation. The lines serve as guide to the eye only.

Figure 4 :

 4 Figure 4: MRX curves for fluidMAG-D suspended in cell culture medium (CCM) with different FCS concentrations as indicated. For comparison, the MRX curve for immobilised fluidMAG-D was added. The iron concentration was 3.5 mmol/l. The samples were measured 3 hours after preparation.

Figure 5 :

 5 Figure 5: MRX curves for Resovist ® suspended in cell culture medium (CCM) with different FCS concentrations as indicated. For comparison, the MRX curve for immobilised Resovist ® was added. The gray arrow illustrates the development of the MRX curves for decreasing FCS concentration. The iron concentration was 1.7 mmol/l. The samples were measured 3 hours after preparation.

Figure 6 :

 6 Figure 6: Representation of the geometric dispersion parameter σ C of the aggregate size distribution function for fluidMAG-D suspended in FCS for different IgG-to-MNP concentration ratios, measured 1.8 and 17 hours after preparation. The lines serve as guide to the eye.

Table 2 :

 2 Characterisation of MNP aggregates of the different MNP samples suspended in BSA buffer (BSA-B) and cell culture medium (CCM) containing 1% FCS and 10% FCS, as indicated in the table respectively, by visual observation 19 hours after preparation (figure 1), by PCS measurement, and by MRX measurement. The MRX results were represented by the following parameters which describe the distribution of the hydrodynamic sizes of relaxing entities (MNPs, clusters of MNPs assumed to be spherical): the (geometric) dispersion parameter σ C , the diameter of mean (cluster) volume d CV , and the mean diameter of the volume weighted cluster diameter distribution, d >1, see text) corresponding size values which are hard to interpret are expressed by cursive numbers.

	CwV . The samples were measured about

C

Acknowledgement

The research was supported by BMBF Project Nanomagnetomedizin Grant No. FKZ-13N9150.