Insight into the role of N,N-dimethylaminoethyl methacrylate (DMAEMA) conjugation onto poly(ethylenimine): cell viability and gene transfection studies Alireza Nouri • Rita Castro • Visvaldas Kairys • Jose ´ L. Santos • Joa ˜o Rodrigues • Yulin Li • Helena Toma ´s Received: 10 June 2012 / Accepted: 22 August 2012 / Published online: 4 September 2012 Ó Springer Science+Business Media, LLC 2012 Abstract In the present study, the effect of N,N-dimeth- ylaminoethyl methacrylate (DMAEMA) conjugation onto branched poly(ethylenimine) (PEI) with different grafting degree was examined for gene delivery applications. The DMAEMA-grafted-PEI conjugates were characterized and complexed with plasmid DNA (pDNA) at various con- centrations, and the physicochemical properties, cell via- bility, and in vitro transfection efficiency of the complexes were evaluated in HEK 293T cells. Computational tech- niques were used to analyze the interaction energies and possible binding modes between DNA and conjugates at different grafting degrees. The cytotoxicity analysis and in vitro transfection efficiency of the conjugate/pDNA com- plexes exhibited a beneficial effect of DMAEMA conju- gation when compared to PEI alone. The computational results revealed that the DNA/vector interaction energy decreases with increasing grafting degree, which can be associated to an enhanced release of the pDNA from the carrier once inside cells. The results indicate the significance of DMAEMA conjugation onto PEI as a promising approach for gene delivery applications. 1 Introduction In order to genetically modify a eukaryotic cell, the recombinant DNA has to enter the cell through the cellular membrane, and finally enter the nucleus, where transcrip- tion takes place [1]. Although viral vectors are known to be extremely efficient in gene delivery, nonviral methods exhibit certain advantages over viral ones, such as low cost, stability, simple large-scale production, and low host immunogenicity [2]. Thus, there is a fundamental requirement for the development of novel non-viral vectors to condense plasmid DNA (pDNA) that could efficiently deliver the target gene to cells with minimum toxicity [3]. One of the most promising classes of non-viral vectors for gene therapy is formed by cationic polymers, also known as polycations. Through electrostatic interactions between the positively charged amino groups of polycations and the negatively charged phosphate groups of pDNA, these polymers are able to condense pDNA molecules in small sized nanoparticles and form polymer/pDNA complexes (i.e. polyplexes) with a neutral or positive net charge [4]. Polycations are particularly attractive because of their potential safety, nucleic acid cargo capacity, and design ability [5, 6]. Poly(ethylenimine) (PEI) in its high-molecular weight branched form is amongst the most efficient synthetic polycations used in gene delivery research, containing hydrocarbon chains with primary, secondary, and tertiary amino groups. Its positive charge at neutral and acidic pH makes PEI a pDNA condensing and endosomal disruption agent [7]. However, PEI is not the ideal transfection agent A. Nouri  R. Castro  J. L. Santos  J. Rodrigues  Y. Li (&)  H. Toma ´s (&) CQM—Centro de Quı ´mica da Madeira, MMRG, Universidade da Madeira, Campus da Penteada, 9000-390 Funchal, Portugal e-mail: yulinli@uma.pt H. Toma ´s e-mail: lenat@uma.pt V. Kairys Department of Bioinformatics, Institute of Biotechnology, Vilnius University, Graic ˇiu ¯no 8, 02241 Vilnius, Lithuania Present Address: J. L. Santos Department of Materials Science and Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA 123 J Mater Sci: Mater Med (2012) 23:2967–2980 DOI 10.1007/s10856-012-4753-9