# Charge-Shifting Copolymers of 2‑(N,N‑Dimethylamino)Ethyl Acrylate and 2‑Hydroxyethyl Acrylate via RAFT Polymerization: Balancing the Charge Content and Biological Response

## TL;DR

This paper introduces charge-shifting copolymers that reduce toxicity while maintaining their ability to form complexes, making them suitable for biomedical applications.

## Contribution

The study presents a novel method to balance charge content and biological response using RAFT polymerization of DMAEA and HEA.

## Key findings

- Copolymerization with HEA reduced cytotoxicity while maintaining complexation ability with heparin.
- RAFT polymerization enabled precise control over copolymer characteristics with low dispersities.
- Increasing HEA content led to over 80% cell viability at 30 μg/mL concentration.

## Abstract

Synthetic polycations are key components for engineering
polyelectrolyte
complexes with wide-ranging biomedical potential. However, the high
cytotoxicity of fully charged polycations remains a major limitation
for clinical applications. To address this challenge, we report on
polycations derived from the cationic monomer 2-(N,N-dimethylaminoethyl) acrylate (DMAEA), which gradually loses charge
through hydrolysis, thereby reducing their charge density over time.
The overall charge fraction (from 100% to 20%) was further controlled
through copolymerization with the neutral comonomer 2-hydroxyethyl
acrylate (HEA). The selected conditions of reversible addition–fragmentation
chain transfer (RAFT) copolymerization, specifically protonation of
DMAEA with trifluoroacetic acid to mask its tertiary amino groups,
enabled a precise control over the characteristics of the copolymers
(termed D/H) up to 75% conversions, with close agreement between theoretical
and experimental molecular weights up to 100 000 g/mol, consistently
low dispersities (<1.2), and an excellent match between the theoretical
and actual copolymer compositions. Hydrolysis studies at pH 7.4 showed
that increasing the HEA content in D/H copolymers from 20 to 50 mol
% led to only a 10% increase in the hydrolysis over 3 weeks. Isothermal
titration calorimetry analysis demonstrated that all copolymers retained
their ability to complex with heparin, with binding strength comparable
to that of commonly used polycations. Importantly, the cytotoxicity
of D/H copolymers toward human umbilical vein endothelial cells (HUVECs)
decreased with increasing HEA content, reaching more than 80% cell
viability at a relatively high concentration of 30 μg/mL. These
findings demonstrate that D/H copolymers combine precise structural
control with reduced cytotoxicity, making them promising candidates
for biomedical polyelectrolyte platforms.