The term "affinity" is translated as 親和性 in chemistry, but I could not find a good example which relates this term and "release rate". However, the term "release" should be 放出 according to the following link treating a similar drug distribution system.

http://www.sigmaaldrich.com/japan/materialscience/polymer-sc...

「放出制御システムは、当該物質（薬物）の放出をコントロールする方法によって分類されます。」

「薬物は理想的に高分子中に均一に分布しており、薬物を覆う高分子が分解するにつれて薬物が放出されます」


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Note added at 13 hrs (2012-12-12 16:48:38 GMT)
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Or, probably should use some explanatory wording such as 「親和性に基づいて決定される放出率」 since "affinity release rate" does not seem like to have been generalized even as an English term.