Scientific difficulties are inherent...

Le verrou significes locks and bolts. Wordreference.com gives "deadlock" as a possible translation of verrou. The "lock and bolt" idea can be kept if a word such as "deadlock" is used. Alternatively, "quandary", a synonym for deadlock (according to thesaurus.com), is another possibility and can easily be used alongside "scientific", as can be seen in the article below from startribune.com. This does avoid using "deadlock" if you think the term is too strong, but in this case the idea of locks and bolts is lost.

The example sentance below in the first link, www.psych.... (full address is inserted below), can be seen halfway down page 3. This uses the term "deadlock" with "scientific" and it seems to collocate quite naturally.

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Note added at 1 hr (2010-10-12 13:31:23 GMT)
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"gridlock" is another alternative to "deadlock" but then use of either of these words would depend on the wider context of the phrase which has been given by the Asker. Other synonyms for "deadlock" can also be: checkmate, corner, catch 22, dead end, dilemma, pause, pickle, plight, predicament, standoff, standstill, tie, wall....
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* just to add another idea.

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Note added at 2 heures (2010-10-12 14:09:06 GMT)
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e.g. "The Stumbling Block in Lung Repair of Emphysema: Elastic Fiber Assembly" - Shifren, Adrian, Mecham, Robert P.