Maryam Rahmati 1, Ali Samadikuchaksaraei 2,3,4, Masoud Mozafari 1,5, 2nd Iranian Congress on Progress in Tissue Engineering and Regenerative Medicine How to modify gelation time and temperature of chitosan based hydrogels Maryam Rahmati 1, Ali Samadikuchaksaraei 2,3,4, Masoud Mozafari 1,5,   1 Bioengineering Research Group, Nanotechnology and Advanced Materials Department, Materials and Energy Research Center (MERC), P.O. Box 14155-4777, Tehran, Iran 2 Cellular and Molecular Research Center, Iran University of Medical Sciences, Tehran, Iran 3 Department of Tissue Engineering & Regenerative Medicine, Iran University of Medical Sciences, Tehran, Iran 4 Department of Medical Biotechnology, Faculty of Allied Medicine, Iran University of Medical Sciences, Tehran, Iran 5 Helmerich Advanced Technology Research Center, School of Materials Science and Engineering, Oklahoma State University, OK 74106, USA Abstract After that, the final solutions were mixed for 15 min to achieve a homogeneous liquid solution. three different combinations including 2wt% of chitosan and 12wt% of β-GP as a control sample, 2wt% of chitosan and 12wt% of β-GP containing urea or isobutanol were prepared. pH, Rheological, and Chemical bonding Characterizations were measured. urea or isobutanol, which can be potentially used for different biomedical applicationsThe aim of this study is to evaluate the possibility of tuning gelation time and temperature of thermo responsive chitosan-β-glycerolphosphate (GP) hydrogels, which undertake sol–gel alteration around body temperature. We investigated the interactions between urea or isobutanol and chitosan-based hydrogels. Urea can hinder hydrophobicity and on contrary, isobutanol can rise hydrophobicity of chitosan-based hydrogels. Thus we profoundly scrutinize the effect of adding urea and isobutanol on chitosan 2%(w/v) /12% (w/v) β-GP solutions to getting a better understanding of the interactive effects of urea or isobutanol on the rheological behavior, mechanism of increasing pH of chitosan solutions, and chemical bonding of them. Results pH measurement The pH values of all samples were in the range between 7.2 and 7.4. The pH value of chitosan (2%wt)-β-GP (12%wt) and chitosan (2%wt)-β-GP (12%wt) containing isobutanol were at 7.2. while chitosan(2%wt)-β-GP(12%wt) containing urea was 7.4. Gelation time for the sample containing isobutanol was 1400s, however for control sample was 1550s, and for the sample containing urea was more than 1800s. Gelation temperature for the sample containing isobutanol was 36˚C, however for control sample was 37˚C, and for the sample containing urea was more than 42˚C. (see Fif 1-3). Introduction Recently, Injectable hydrogels have remarkably involved considerable attention in biomedical applications, because of their rapid gelation after injection into the favorite organ. In present study we more profoundly scrutinize the effect of adding urea and isobutanol on chitosan 2%(w/v) /12% (w/v) β-GP solutions to getting a better understanding of the interactive effects of urea or isobutanol on the rheological behavior, mechanism of increasing pH of chitosan solutions, and chemical bonding of them. Thus, we prepared three type of samples that comprising chitosan 2% (w/v)/12% (w/v) β-GP containing urea or isobutanol. In addition, Conclusion This work provided facts on the interactive effects of urea and isobutanol on thermosensitive chitosan/β-GP hydrogels. It has been presented that, the gelation time and temperature in the sample containing urea was higher than control sample because it disorders the hydrogen bonding and delays the hydrophobic interactions. But for the sample containing isobutanol was lower than control sample through the strengthening of Chitosan–Chitosan hydrophobic interactions. Because the gelation mechanism is critical to the possible improvement and of thermosensitive chitosan/β-GP hydrogel, we believe the useful data existing in this paper supports more optimization of this biocompatible thermosensitive hydrogel for different biomedical applications. Materials and Methods Preparation of chitosan-β-GP hydrogels In a typical manner, 3.6 g chitosan powder was dissolved in 180 mL 0.1M acetic acid solution with stirring and mixing around 24h at 25˚C for complete dissolution. Then, a given amount of 12wt% β-GP and urea or isobutanol were dissolved in deionized water, and after that sterilized with a 0.22 μm syringe filter. The chitosan solutions and 12 wt% β-GP and urea or isobutanol solutions were chilled to 4˚C for 20 min before being mixed together. Then, the 12 wt% β-GP solutions containing urea or isobutanol were added dropwise to the chitosan solution under continuous stirring in an ice bath. References [1]. Tang, Y.-F., et al., Rheological characterisation of a novel thermosensitive chitosan/poly (vinyl alcohol) blend hydrogel. Carbohydrate Polymers, 2007. 67(4): p. 491-499. [2]. Yan, J., et al., Biocompatibility evaluation of chitosan-based injectable hydrogels for the culturing mice mesenchymal stem cells in vitro. Journal of biomaterials applications, 2010. 24(7): p. 625-637. [3]. Chenite, A., et al., Novel injectable neutral solutions of chitosan form biodegradable gels in situ. Biomaterials, 2000. 21(21): p. 2155-2161. [4]. Derwent, J.J.K. and W.F. Mieler, Thermoresponsive hydrogels as a new ocular drug delivery platform to the posterior segment of the eye. Transactions of the American Ophthalmological Society, 2008. 106: p. 206.