Versatile synthesis of temperature-sensitive polypeptides by click grafting of oligo(ethylene glycol)† Yilong Cheng, ab Chaoliang He, a Chunsheng Xiao, ab Jianxun Ding, ab Xiuli Zhuang a and Xuesi Chen * a Received 20th June 2011, Accepted 15th July 2011 DOI: 10.1039/c1py00281c A series of novel temperature-sensitive polypeptides were synthesized by ring opening polymerization (ROP) of g-propargyl-L-glutamate N-carboxyanhydride (PLG-NCA) and subsequent click reaction between the pendant alkyne groups and 1-(2-methoxyethoxy)-2-azidoethane (MEO 2 -N 3 ) or 1-(2-(2-methoxyethoxy)ethoxy)-2-azidoethane (MEO 3 -N 3 ). The efficient click grafting and structure of the resultant copolymers were verified by 1 H NMR, 13 C NMR and GPC. All the copolymers hold a- helix conformation, and could self-assemble into amphiphilic nanoparticles in aqueous solution with hydrodynamic radii (R h ) of 32.3–62.8 nm. The graft copolymers exhibited sharp temperature- dependent phase transitions, and the LCST could be adjusted from 22.3 to 74.1  C by varying the molecular weight, the length of the OEG side chain, the polymer concentration and salt concentration. MTT assays revealed that the graft copolymers exhibited no detectable cytotoxicity at all test concentrations up to 1 mg mL 1 . In vitro degradation tests demonstrated that the graft copolymers could be degraded by proteinase K. The drug release behaviors from the PPLG 112 -g-MEO 2 nanoparticles were evaluated at 37  C and 15  C using doxorubicin (DOX) as a model drug. The drug release behavior displayed thermosensitivity, and a sustained release profile was observed at physiological temperature. These results suggested that the novel biodegradable and biocompatible polypeptide derivatives with adjustable temperature sensitivity could be a promising material for biomedical applications. Introduction Stimuli-responsive polymers have received significant attention for their potential applications in the biomedical field in the past few decades. 1–3 The stimuli include temperature, light, electric fields, pH and so on, which are promising for many biomedical applications, including delivery systems of smart drugs and genes, tissue engineering scaffolds and biological separation. 4–12 Among these intelligent polymers, temperature sensitive poly- mers have attracted considerable interest due to their unique advantages in practical applications. 13,14 Typical temperature sensitive polymers include poly(N,N 0 - diethyl acrylamide), 15 poly(dimethylaminoethyl methacrylate), 16 poly(N-acryloylpyrrolidine), 17 poly(2-isopropyl-2-oxazoline), 18 poly(N-isopropylacrylamide) (PNIPAM), 19,20 poly(L-glutamate)- g-oligo(2-(2-(2-methoxyethoxy)ethoxy)ethyl methacrylate) (PGA-g-MEO 2 MA) 21,22 and poly(oligo(ethylene glycol) (meth) acrylate) (POEGMA). 23,24 In aqueous solution, such temperature sensitive polymers undergo a soluble–insoluble phase transition at their lower critical solution temperatures (LCSTs). Recently, an oligo(ethylene glycol) (OEG)-grafted polymethacrylate derivative (POEGMA) was reported, and its LCST can be adjusted by changing the feed ratio of different MEO x MA monomers (MEO x indicates an OEG containing x ethylene glycol repeat units). 25 For instance, the random copolymers of MEO 2 MA and MEO 9 MA exhibited LCST values in between 26 and 90  C. A LCST of 37  C (body temperature) was observed for the copolymer possessing 8% MEO 9 MA units per chain. 26 In our recent work, a type of temperature sensitive polypeptide derivative, PGA-g-MEO 2 MA, was synthesized through the combination of ring opening polymerization (ROP) of g-2- chloroethyl-L-glutamate-N-carboxyanhydride (CELG-NCA) and atom transfer radical polymerization of MEO 2 MA. This type of polymer not only exhibited sharp temperature sensitivity, but also showed good biocompatibility due to the introduction of the polypeptide component. 22 Most currently used temperature sensitive polymers are based on polyacrylate or polyacrylamide derivatives, which are nonbiodegradable and exhibit limited biocompatibility, resulting in limitations in some biomedical applications in vivo. Accord- ingly, in this work, a new class of temperature sensitive copoly- mers based on polypeptides and oligo(ethylene glycol)s was a Key Laboratory of Polymer Ecomaterials, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China. E-mail: xschen@ciac.jl.cn; Fax: +86 431 8526 2112; Tel: +86 431 8526 2112 b Graduate University of Chinese Academy of Sciences, Beijing 100039, P. R. China † Electronic supplementary information (ESI) available. See DOI: 10.1039/c1py00281c This journal is ª The Royal Society of Chemistry 2011 Polym. Chem., 2011, 2, 2627–2634 | 2627 Dynamic Article Links C < Polymer Chemistry Cite this: Polym. Chem., 2011, 2, 2627 www.rsc.org/polymers PAPER Downloaded on 06 December 2012 Published on 22 August 2011 on http://pubs.rsc.org | doi:10.1039/C1PY00281C View Article Online / Journal Homepage / Table of Contents for this issue