T16 - Controlling Nanoparticle Size and Surface Properties Through Chain Transfer Agent-Mediated Polymer Design for Drug Delivery

Friday, October 10, 2025

10:00 AM - 11:00 AM PDT

Location: Exhibit Hall F, G & H

Presenting Author(s)

Autumn Hengen, BS

PhD Student
Georgia Institute of Technology
Atlanta, Georgia, United States

Co-Author(s)

AG

Arha Gandhi

Undergraduate Student
Georgia Institute of Technology, United States
LG

Lesley Gutierrez

Undergraduate Student
Georgia Institute of Technology, United States
Simone Douglas-Green, PhD

Assistant Professor
Georgia Institute of Technology & Emory University
Atlanta, Georgia, United States
MA

Marian Ackun-Farmmer

Principal Investigator
Georgia Institute of Technology, United States

Primary Investigator(s)

MA

Marian Ackun-Farmmer

Principal Investigator
Georgia Institute of Technology, United States

Introduction: : Polymer-based micelle nanoparticles (NPs) have emerged as promising drug delivery systems for enhancing drug circulation time, bioavailability, and selective cellular uptake due to their favorable core-shell architectures and tunable physicochemical properties (i.e., size, surface charge)1. Fine-tuning micelle NP properties requires sophisticated synthesis strategies such as reversible addition-fragmentation chain transfer (RAFT) polymerization. RAFT is a well-established polymerization technique that utilizes highly efficient chain transfer agents (CTAs) to precisely control molecular weight and maintain low polydispersity of the synthesized polymers2. Previous studies using one-step RAFT polymerizations to synthesize poly(styrene-alt-maleic anhydride)-poly(styrene) (PSMA-b-PS) amphiphilic diblock copolymers (Fig. 1A) using excess styrene (STY) yielded monodisperse, sub-100 nm, thermodynamically stable NPs capable of loading a variety of drugs3. Further studies have shown that these same micelle NPs can be modified with targeting peptides for drug delivery4. In this current study, we aimed to investigate how varying the maleic anhydride [(MA)]:[CTA] molar ratios (Fig. 1Ai), without altering the hydrophobic-to-hydrophilic block ratios, affects micelle formation and enables tuning of NP physicochemical properties. We hypothesized that changing the molar ratio of [MA]:[CTA], while maintaining the molar ratio of [STY]:[MA], would yield polymers with differing chain lengths owing to the changes in CTA content (Fig. 1Aii). To test this hypothesis, we measured the size, surface charge, and thermodynamic stability of formed NPs and assessed protein corona formation by remeasuring their size and zeta potential after human plasma incubation.

Materials and

Methods: : PSMA-b-PS diblock copolymers were synthesized via one-step RAFT polymerizations using styrene in molar excess of maleic anhydride ([STY]:[MA] = 12:1] in the presence of the CTA, 4-cyano-4-dodecylsulfanyltrithiocarbonyl sulfanyl pentanoic acid (DCT) and the initiator azobisisobutyronitrile (AIBN) in dioxane3, 4. To adjust the target degree of polymerization (Dp), the molar ratio of [MA]:[DCT] was tuned as follows: 1:0.03, 1:0.02, 1:0.008, 1:0.004, and 1:0.0002. Diblock copolymers were then dissolved in dimethylformamide (DMF) at 5 mg/mL, and an equal amount of ddH2O was added using a serological pipette to form micelle NPs. After an hour of stirring, NPs were dialyzed in water overnight to remove the DMF. The NP hydrodynamic radius and zeta potential were measured in 1X PBS and ddH2O, respectively, using dynamic light scattering (DLS), and critical micelle concentrations (CMC) were calculated using PRODAN3. In parallel studies, NPs were incubated in human plasma at 37 °C for 1 hour, and centrifugation was used to remove loosely bound proteins before DLS measurements in 1X PBS.

Results, Conclusions, and Discussions:: Results and

Discussion: Adjusting the molar ratio of [MA]:[DCT] to achieve target Dps of 30, 60, 120, 240, and 480 led to a plateau in NP radius of 51± 1 nm (Fig. 1B). Notably, these changes did not impact the overall zeta potential of the NPs (Fig. 1C). CMC measurements showed that at the target Dp of 240, the CMC was the lowest, indicating increased thermodynamic stability and more favorable micelle formation. Interestingly, the NPs with the target Dps of 30 and 60 exhibited the highest CMC values, indicating less favorable chain interactions (Fig. 1D). Upon incubating the NPs in PBS at 37 °C, the size of the NPs increased compared to the 4 °C NPs, likely due to swelling experienced following temperature changes during incubation (Fig. 1E). After plasma incubation, NPs doubled in size while there was a decrease in negative surface charge compared to their initial counterparts (Fig. 2). These changes in plasma suggest the presence of proteins forming a hard corona and shielding charges on the NP surface, a phenomenon that has been observed in other studies5. Altogether, this data showed that altering the target Dp of PSMA-b-PS diblock copolymers impacts the physicochemical properties of formed micelle NPs, indicating that CTA should be carefully considered as a contributing factor in the rational design of these NPs.

Conclusions: The studies presented here highlight the role that the CTA plays in micelle formation and the physicochemical properties of these micelles. Current studies are validating the molecular weights of the synthesized polymers, and future studies will determine the reaction kinetics resulting from changing the [MA]:[DCT] molar ratios. These findings will inform future work to develop similar polymers for targeting specific cell types.

Acknowledgements and/or References (Optional): : Acknowledgements: This research was supported by startup funding awarded from Georgia Institute of Technology, Department of Biomedical Engineering, to SDG and MAF.

References:
1. Ghezzi M, Pescina S, Padula C, Santi P, Del Favero E, Cantu L, Nicoli S. Polymeric micelles in drug delivery: An insight of the techniques for their characterization and assessment in biorelevant conditions. J Control Release. 2021;332:312-36. Epub 20210227. doi: 10.1016/j.jconrel.2021.02.031. PubMed PMID: 33652113.
2. Perrier S. 50th Anniversary Perspective: RAFT Polymerization—A User Guide. Macromolecules. September 27, 2017;50(19). doi: 10.1021/acs.macromol.7b00767.
3. Baranello MP, Bauer L, Benoit DS. Poly(styrene-alt-maleic anhydride)-based diblock copolymer micelles exhibit versatile hydrophobic drug loading, drug-dependent release, and internalization by multidrug resistant ovarian cancer cells. Biomacromolecules. 2014;15(7):2629-41. Epub 20140702. doi: 10.1021/bm500468d. PubMed PMID: 24955779.
4. Ackun-Farmmer MA, Soto CA, Lesch ML, Byun D, Yang L, Calvi LM, Benoit DSW, Frisch BJ. Reduction of leukemic burden via bone-targeted nanoparticle delivery of an inhibitor of C-chemokine (C-C motif) ligand 3 (CCL3) signaling. FASEB J. 2021;35(4):e21402. doi: 10.1096/fj.202000938RR. PubMed PMID: 33724567; PMCID: PMC8594422.
5. Rampado R, Crotti S, Caliceti P, Pucciarelli S, Agostini M. Recent Advances in Understanding the Protein Corona of Nanoparticles and in the Formulation of "Stealthy" Nanomaterials. Front Bioeng Biotechnol. 2020;8:166. Epub 20200403. doi: 10.3389/fbioe.2020.00166. PubMed PMID: 32309278; PMCID: PMC7145938.