Olgun Güven, obtained his PhD degree in Physical Chemistry from Hacettepe University, Ankara,Turkey in 1977. He became Associate Professor in 1981 and then Professor in 1988. For more than 40 years he and his group have been involved in R & D works on radiation chemistry and processing of polymers. He is the author and co-author of more than 340 scientific papers published in peer reviewed journals, holding 2 international patents and author and editor of 3 books published abroad, supervised more than 70 graduate theses. Currently his h-index is 40. He has been a lecturer in the graduate schools of Pavia University (Italy), Kazak National University (Kazakhstan), Kasertsat University (Thailand) and in the ERASMUS program of EU. He worked as the technical officer in charge of radiation technology programs in the International Atomic Energy Agency, a UN organization in Vienna, Austria from 1996 to 2003. He also serves as Associate Editor in Rad. Phys.Chem. (Elsevier). In 2011 his worldwide contribution to the promotion of radiation technology was appreciated by giving him IMRP Laureate Award.
Olgun Güven and Murat Barsbay
In tissue engineering for cell sheet harvesting commercially available polystyrene (PS) dishes are used after grafting with a thermo-responsive polymer namely, poly(N-isopropylacrylamide) (PNiPAAm). This polymer exhibits lower critical solution temperature at around 32 oC, showing hydrophobic behavior above this temperature and hydrophilic below, in aqueous media. Very thin layers of PNiPAAm in hydrophobic state at ~ 37 oC allows the growth of cell sheets whereas lowering it to ambient temperature transforms the PNiPAAm chains into hydrophilic state with subsequent release of cell sheets non-invasively. The thickness of PNiPAAm layer is the key factor affecting the hydration/dehydration features hence cell sheet recovery process. For clinical applications rapid detachment of cell sheets is most desirable which is possible by enhanced hydration of PNiPAAm layer in a relatively short time. In this work in order to facilitate hydration of PNiPAAm chains, highly hydrophilic polyacrylamide (PAAm) was first grafted from PS surfaces followed by consecutive grafting of PNiPAAm over this layer. Controlling of nano-scale thickness of graft layers of both polymers on PS surfaces was achieved by “Reversible Addition-Fragmentation chain Transfer” (RAFT) polymerization technique via radiation-induced post-irradiation grafting. Electron beam irradiated PS surfaces were first grafted with PAAm in the presence of a RAFT agent. The reactive chain end moeities of RAFT agent was further utilizied to grow PNiPAAm chains again in a controlled fashion. A detailed ellipsometric study showed that it was possible to develop (PNiPAAm-block-PAAm)-grafted-PS surfaces with 58 nm thick PAAm and depending on the conversion, 23-60 nm thick PNiPAAm layers. Such a precise control of thickness of these layers is expected shorten the overall process of cell sheet harvesting.