Glycine betaine surfactant-based liposomes: physicochemical characterization and cytocompatibility assessment

The development of non-toxic and environmentally sustainable nanocarriers requires the design of systems with tunable stability, degradability, and surface properties. In this work, we investigated the potential of glycine betaine-derived ester surfactants (CnGB+), with dodecyl (C12) and hexadecyl (C16) alkyl chains, as environmentally friendly edge activators for surfactant-based liposomes (SBLs). The surfactants, synthesized via a solvent-free protocol, were combined with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) to prepare SBLs with varying surfactant molar percentages (10, 30, and 70 mol%). The aim was to evaluate the effects of CnGB+ surfactant chain length and concentration on SBLs' hydrodynamic diameter (DH), zeta potential (zeta), hydrolysis rate, and to assess the SBLs' cytotoxicity. SBLs exhibited smaller and more homogeneous size distributions and enhanced colloidal stability when compared to DOPC liposomes at all the investigated ionic strengths (water, 10 mM NaCl, 100 mM NaCl, PBS buffer). Zeta potential measurements confirmed that increasing surfactant molar percentage enhanced surface charge, with modulated values depending on the dispersing medium. Additionally, NMR kinetic measurements showed a different hydrolysis rate of CnGB+ surfactant depending on whether it was free or embedded within SBLs at physiological pH, suggesting a protective effect of DOPC bilayers against surfactant hydrolysis. Cytotoxicity tests on HaCaT keratinocytes showed that SBLs formulations with elevated surfactant molar percentages, and hence higher surface charge, were more toxic. Among the assayed SBLs, the formulation with lower surfactant molar percentage and shorter alkyl chain (SBL12-10) demonstrated high cytocompatibility, limited hydrolysis, and good colloidal stability. In conclusion, GB-derived surfactants show promise as biocompatible edge activators for stable SBLs, supporting further investigation into drug encapsulation and transdermal delivery performance.