Biodegradable polycationic polymers that have high transfection efficiency are much needed to replace current non–biodegradable polycationic polymers for non-viral gene delivery. Although these existing polymers are known to be successful in assisting in the delivery of plasmid DNA (pDNA), the non-degradability of the polymers presents a problem with repeated dosage and long-term usage due to their accumulation in the endosomal compartment or cell nucleus.

In our laboratory, novel biodegradable polycationic polymers were synthesized by Michael addition polymerization of an amine monomer, 1-(2-aminoethyl) piperazine (AEPZ) with triacrylate monomer, trimethylolpropane triacrylate (TMPTA) or different types of trimethylolpropane ethoxylate triacrylates (TMPETA) for non-viral gene delivery. Different polymers were synthesized by reacting AEPZ with TMPTA (P1), TMPETA with 1 ethyleneoxy group in each acrylate chain (P2), TMPETA with 7 ethyleneoxy groups in each monomer (P3) and TMPETA with 14 ethyleneoxy groups in each monomer (P4). Previous work in our group has shown that these polymers are non-cytotoxic and the degradation rate of the polymers can be increased by lengthening the hydrophilic spacers in the triacrylate monomer. Furthermore, the buffering capacity of the polymers can be increased with the decrease in hydrophilic spacer length. In this work, the effect of the hydrophilic spacer length of the polycationic polymers on the complexation of the polycationic polymers and pDNA were investigated at different polymer to pDNA (pCMV-GFP, 4.7 kb) weight ratios. The band retardation of the complexes was evaluated by gel electrophoresis with 1 ėg of pDNA. All the polymers were able to complex with the pDNA and neutralize the charges as evident by the retardation of the migration of the pDNA at a weight ratio of 10 or higher except for P4, which was able to retard the migration at a weight ratio of 20 or higher. Compared to the other polymers, the longer spacer length in P4 resulted in a polymer with the lowest number of protonated amines for a given weight of polymer, thus, has less positive charges to interact with the negative charges on the pDNA. The hydrodynamic radius of the different polycationic polymers were evaluated by dynamic light scattering (DLS) at 25°C. The polycationic polymers were able to partially condense the pDNA and resulted in a hydrodynamic radius as low as 160 nm. The hydrodynamic radius of the complexes formed varied with the different polycationic polymers and was seen to decrease as the weight ratio of polymer to pDNA increased and levelled off at a certain weight ratio. In summary, hydrophilic spacers can be incorporated into polymers to produce non-cytotoxic biodegradable polymers with different characteristics which are important in generating vectors for gene delivery.