In response to the letter by Dr. Amir Arav I would like to mention the following. The application of the principle of directional solidification to cryopreservation of living cells was, as far as I am aware, not the invention of Dr. Arav. It was first published and patented by Rubinsky (Berkeley, CA, US) in 1985. Furthermore, in the early nineties there were at least two papers by the group of the Helmholz Institute at Aachen, Germany and MIT, Massachussets, US showing further application and development of that concept. There were papers from other groups as well in that time. In my paper for the 2003 Proceedings of the Boar Semen Preservation (BSP) conference I have referred to the papers by Rubinsky and Ikeda (1985) (Cryobiology) and Beckmann et al. (1990) (also Cryobiology). In the mid-90s, we came up with a design of a conveyor belt like freezing device that encompassed the principle of directional solidification. Originally we actually designed the conveyor belt system for logistical reasons and only later found out that it could also have advantages for cell survival. The novel elements that we have introduced in our device warranted that patents have been granted in the US and the EU. I was aware of the fact that Arav had a patent application also on an apparatus that encompasses the principle of directional solidification. As said above, in my 2003 BSP conference presentation I referred to the original papers on directional solidification by Rubinsky and Ikeda (1985) and Beckmann et al. (1990). I thought to have served well in this respect. Obviously, in my 2003 BSP conference address I could not refer to papers by Arav that were published in 2004 and 2005. But I could have referred to his two papers published in 2002. In these papers Arav and co-workers failed to show a split sample comparison of the post-thaw survival obtained with directional solidification versus conventional straw freezing. However, one of these 2002 papers does mention the application of the technique to boar semen, and in retrospect I regret that I did not refer to that paper in my Boar Semen Preservation conference contribution. It is therefore good that Dr. Arav now brought these papers to our attention
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