(3aw) A Solubility Engineering-Based Nanoformulation Platform for Advanced Delivery and Soft Materials Research

The efficient encapsulation of water-soluble biopharmaceuticals (‘biologics’) into micro- and nano-delivery vehicles is essential for their therapeutic success as antibiotics, vaccines, and gene therapies. For these biologics, encapsulation strategies such as liposomes and water-in-oil-in-water emulsions have struggled to achieve commercial success over the last decade, in part because they suffer from inefficient encapsulation and poor scalability. These molecules comprise the fastest-growing sector of the pharmaceutical market, and a scalable technology to formulate them is necessary for the field to overcome its current translational obstacles.

My future research will use solubility engineering to address the challenge of encapsulating biologics efficiently and at scale.

Engineering the solubility of biologics to increase their hydrophobicity is an attractive approach for encapsulation that benefits from decades of formulation research on molecules with poor water solubility. In my graduate research with Prof. Bob Prud’homme at Princeton University, I have expanded the scope and deepened our understanding of Flash NanoPrecipitation with hydrophobic ion pairing; the former is a continuous single-step nanofabrication platform for encapsulating water-insoluble compounds, and the latter an ionic method of solubility engineering^[6]. Using the combined technique, I have achieved biologic encapsulation efficiencies up to 100% and drug mass loadings (mass_drug/mass_vehicle) up to 40%^[2], which far exceed the field’s typical values of 50% encapsulation efficiency and 2% drug loading. I have demonstrated the technique’s scalability^[7] and effectiveness in encapsulating traditional therapeutics^[7,12], peptides^[13], and proteins^[2], and have promising preliminary results with nucleic acids. I have also shown precise control over drug release rate^[1,2,13], a major goal of encapsulation. My future research group will expand this nanofabrication process into an integrated formulation platform by incorporating additional downstream unit operations such as diafiltration and spray freeze-drying, and will evaluate the platform’s reproducibility for quality control. The end goal will be a continuous process for encapsulating biologics at scale. This work will have applications in and benefit from collaborations with the pharmaceutical, agrochemical, and personal care industries, which I have experience with from projects with Moderna Therapeutics (where I also interned), Genentech, Eli Lilly, the Bill & Malinda Gates Foundation, Nevakar, and Optimeos Life Sciences.

I will also study the soft material fundamentals behind the hydrophobic ion pairing technique to enhance our mechanistic understanding of self-assembly and controlled release in those systems.

During my work in Prof. Ben Boyd’s group at the Monash University Institute of Pharmaceutical Sciences, I discovered that hydrophobic ion paired complexes can assemble into liquid crystal structures in nanoparticle cores^[3]. I showed that the chemical functional groups and quantity of counterion used to form the complexes dictate the liquid crystalline phase behavior, which in turn controls the drug release rate^[1]. The field knew that varying counterion chemistry and quantity affected drug release, but the mechanism behind this phenomenon was not known until this work. My future research group will build on this discovery to rationally design stimulus-responsive and controlled-release formulations by manipulating the internal liquid crystal phases. This work will be bolstered with the use of synchrotron small-angle X-ray scattering (SAXS), for which I have experience writing successful beamtime proposals.

In this vein, I will also continue to study the fundamentals of self-assembly^[5] and polymer physics relevant to the soft matter systems my work will develop. Two recent advancements in these areas are particularly promising: (i) I have fabricated a device that allows synchrotron SAXS measurements of the Flash NanoPrecipitation mixing chamber to study nanoparticle self-assembly in situ; (ii) I have developed a technique for installing a thin layer of a solvent-resistant vitrified cellulosic onto nanoparticle surfaces without losing colloidal stability. These new projects each raise fundamental soft matter questions that my work will pursue in the future.

My research group will consist of these two halves: an industrially-relevant nanofabrication platform and fundamental soft matter projects that support and inform it.

Teaching Interests:

I have a strong love of teaching and have developed my instruction style across more than a thousand hours of classroom lecturing, one-on-one tutoring, TAing, and research mentoring. My experience at Louisiana State University came from serving as TA for a junior-level process design course in bioengineering, tutoring regularly, and TAing for four summers at a program for advanced high school students. At Princeton, I volunteered as TA for an introductory chemical engineering class and have guest lectured in two graduate courses. I also designed and directed four senior thesis projects, one junior-level research project, and an REU. Most recently, I implemented a redesign of Princeton’s undergraduate capstone design course to include a bioengineering-based vaccine project. In addition to TAing the class and acting as project consultant, I designed and gave one-third of the lectures, wrote homework and exam questions, and graded final reports. I am also in the final stages of Princeton’s Teaching Transcript program, which has reinforced the best practices I have learned over the years.

A major goal of my ChE teaching is conveying to the students a physical intuition about the engineering principles at work in the world around them. This helps them develop a toolset for properly analyzing engineering problems, which is necessary before describing and solving them mathematically. I am comfortable teaching any of the core ChE courses but prefer teaching design, mass & energy balances, bioengineering separations, transport, and engineering lab. I plan to offer a technical elective on colloid & surfactant science, into which I will incorporate drug delivery and nanoencapsulation themes from my research. I will also propose a nontechnical elective titled “Rhetoric, Persuasion, and Writing for Engineers.”

Selected Awards:

• Wallace Memorial Fellowship (highest graduate award conferred by Princeton SEAS), 2020
• SAXS/WAXS beamtime grant, Australian Synchrotron, 2020
• Award for Excellence, Princeton SEAS, 2019
• Honorable Mention, Ford Foundation Predoctoral Fellowship, 2019
• 1^st place, Materials Eng. & Science poster, AIChE Annual Meeting 2018
• 3^rd place, 13^th Princeton Innovation Forum, 2018
• National Science Foundation Graduate Research Fellowship, 2016
• Louisiana State University Chancellor’s Alumni Scholar, 2012

Departmental Service:

• Class representative, 2016-present: organized major professional and social events, including the annual departmental Graduate Student Symposium
• Began and host a departmental NSF GRFP application seminar, 2018-present

Publications (July 2020; 5 first author [not including 3 under review]):

[1] K. Ristroph, M. Salim, A. Clulow, et al. Chemistry and geometry of counterions used in hydrophobic ion pairing control mesophase behavior and drug release. Under review (2020)

[2] K. Ristroph, P. Rummaneethorn, B. Johnson-Weaver, et al. Highly-loaded protein nanocarriers prepared by Flash NanoPrecipitation with hydrophobic ion pairing. Under review (2020)

[3] K. Ristroph, M. Salim, B. Wilson, et al. Internal liquid crystal structures in nanocarriers containing drug hydrophobic ion pairs dictate drug release. Under review (2020)

[4] M. McPhillie, Y. Zhou, M. Hickman, J. Gordon, C. Weber, Q. Li, P. Lee, K. Amporndanai, R. Johnson, H. Darby, S. Woods, Z. Li, R. Priestley, K. Ristroph, et al. Potent tetrahydroquinolone eliminates apicomplexan parasites. Front. Cell. Infect. Microbiol. (2020)

[5] D. Kozuch*, K. Ristroph*, R. Prud’homme, P. Debenedetti. Molecular Dynamics Investigation of Hydrophobic Ion Pairing for Nanoprecipitation. ACS Nano (2020)

[6] K. Ristroph and R. Prud’homme. Hydrophobic ion pairing: encapsulating small molecules, peptides, and proteins into nanocarriers. Nanoscale Advances (2019)

[7] K. Ristroph, J. Feng, S. McManus, et al. Spray drying OZ439 nanoparticles to form stable, water-dispersible powders for oral malaria therapy. J. Translational Medicine (2019)

[8] H. Sato, Y. Kaneko, K. Yamada, K. Ristroph, et al. Polymeric nanocarriers with mucus-diffusive and mucus-adhesive properties to control pharmacokinetic behavior of orally-dosed cyclosporine A. J. Pharm Sci. (2019)

[9] M. Salim, G. Ramirez, A. Clulow, Y. Zhang, K. Ristroph, et al. Solid state behaviour and solubilisation of flash nanoprecipitated clofazimine particles during the dispersion and digestion of milk-based formulations. Molecular Pharmaceutics (2019)

[10] J. Feng, Y. Zhang, S. McManus, R. Qian, K. Ristroph, et al. Amorphous nanoparticles by self-assembly: processing for controlled release of hydrophobic molecules. Soft Matter (2019)

[11] C. Markwalter, R. Pagels, B. Wilson, K. Ristroph, R. Prud'homme. Flash NanoPrecipitation for the Encapsulation of Hydrophobic and Hydrophilic Compounds in Polymeric Nanoparticles. JoVE. (2019)

[12] H. Lu*, K. Ristroph*, E. Dobrijevic, et al. Encapsulation of OZ439 into nanoparticles for supersaturated drug release in oral malaria therapy. ACS Infect. Dis., (2018)

[13] H. Lu, P. Rummaneethorn, K. Ristroph, R. Prud’homme, Hydrophobic ion pairing of peptide antibiotics for processing into controlled release nanocarrier formulations. Molecular Pharmaceutics (2018)

[14] H. Lu, E. Pearson, K. Ristroph, et al. Pseudomonas aeruginosa pyocyanin production reduced by quorum-sensing inhibiting nanocarriers. Int. J. Pharm. (2018)

[15] J. Feng, Y. Zhang, S. McManus, K. Ristroph, et al. Rapid recovery of clofazimine-loaded nanoparticles with long-term storage stability as anti-cryptosporidium therapy. ACS Applied Nano Materials (2018)

[16] K. Ristroph, C. Astete, E. Bodoki, C. Sabliov. Zein nanoparticle uptake by hydroponically grown soybean plants. Environ. Sci. Technol. (2017)

[17] Y. Zhang, J. Feng, S. McManus, H. Lu, K. Ristroph, et al. Design and solidification of fast-releasing clofazimine nanoparticles for treatment of cryptosporidiosis. Molecular Pharmaceutics (2017)

* - equal contribution