Bioinspired polymer-lipid hybrid nanoplatform with pH-responsive gating for controlled therapeutic delivery.

Stimuli- responsive nanocarriers must retain their therapeutic cargo in the body yet release it efficiently at disease sites. Achieving both properties in a simple, stable, and adjustable system remains challenging. In this study, we developed a pH- responsive polymer- lipid hybrid nanovesicle, PC7ALV, by incorporating poly(2- hexamethyleneiminoethyl methacrylate) (PC7A) into dimyristoylphosphatidylcholine (DMPC) bilayers. We investigated whether PC7A domains within the membrane could enhance stability under physiological pH conditions and promote cargo release under mildly acidic conditions. The novelty of this approach lies in using PC7A as a structural component of the membrane that responds to pH changes, rather than as a conventional self- assembling polymer carrier. Using a combination of techniques, including dynamic light scattering, zeta-potential analysis, electron microscopy, fluorescence colocalization, Förster resonance energy transfer (FRET), and Laurdan membrane-fluidity measurements, we demonstrated that PC7A integrates with the lipid bilayer and forms small polymer-rich regions at pH 7.4. This organization enhances the membrane's order and stability. Upon decreasing the pH to 6.4, PC7A becomes protonated and undergoes disassembly; the association between the polymer and lipid weakens, FRET decreases, vesicle shape changes, and the membrane becomes more permeable and less stable, thereby facilitating cargo release. For the 1:1 lipid-to-PC7A formulation, approximately 16% of FAM-labeled ovalbumin was released at pH 7.4, whereas release increased to approximately 48% at pH 6.4 after 12 h. Increasing the PC7A content accelerated cargo release under acidic conditions while further improving vesicle stability at physiological pH. In MDA-MB-231 cells, PC7ALVs resulted in higher intracellular fluorescence and increased paclitaxel-mediated cytotoxicity under acidic conditions compared with a non-pH-responsive model vesicle. These findings demonstrate that incorporation of PC7A into the membrane enables pH-dependent control over polymer- lipid vesicle organization, vesicle stability, and molecular transport. PC7ALVs provide a proof-of-concept for designing pH-responsive nanocarriers that preserve cargo integrity during circulation while promoting release under acidic conditions. Further research with other models is warranted to understand how this system works and to assess its broader use, stability, and safety.