Nanoparticles for intestinal sepsis prevention synthesized via inverse miniemulsion polymerization

Conference Dates

May 20-25, 2018


Previous research has shown that phosphate becomes depleted in the intestinal mucosa following local surgical injury or disease, triggering bacterial virulence and sepsis. Consequently, replenishment of depleted phosphate levels has been shown to prevent bacterial virulence in vitro[3] and sepsis in vivo[1]. Inverse phase miniemulsion polymerization (IPMP) has been extensively used in recent years in the production of nanocapsules for drug delivery of water-soluble therapeutic compounds that can be rendered degradable with time while allowing for sustained release of the encapsulated agent. In previous work we have successfully encapsulated inorganic phosphate salts, such as potassium monophosphate[2], into nanoparticles formed using IPMP. Our in vitro studies, however, have shown that polyphosphate salts, specifically sodium hexametaphosphate (PPi), are more effective at suppressing bacterial virulence[3]. This study focuses on the production and encapsulation of sodium hexametaphosphate into nanoparticles for controlled and extended release.

Previous studies demonstrated[3] that encapsulation of sodium hexametaphosphate presents a series of challenges affecting the reproducibility of the IPMP process. Sodium hexametaphosphate is a strong lipophobe whose presence induces a high degree of order for water molecules. This modification in water structure weakens the surfactant interaction with water molecules, actively affecting the stability of the emulsion. This process, known as “salting-out”, has been shown to shift the hydrophilic-lipophilic balance (HLB) of nonionic surfactants towards a more lipophilic value[4]. While this issue has been addressed in a variety of previous studies, no mathematical correlation currently exists describing the effect of salt concentration on the HLB of a specific surfactant. Since miniemulsions require combinations of different phase-soluble surfactants, this adds to the complexity in predicting the extent and strength of the electrolyte effect on the stability of the emulsion system.

In this study, we adjusted the IPMP process to counter the unstabilizing force created by the presence of sodium hexametaphosphate in the aqueous phase of the system. A precursor solution containing PEG diacrylate (PEGDA) macromer and NVP comonomer were chosen to create the hydrogel matrix, due to its biocompatibility and the ability to control the crosslinking density. The emulsion was formed of water in cyclohexane with the help of two nonionic surfactants, Tween 20 and SPAN 80. The effect of variations in HLB ranging from 4.0 to 9.5 on emulsion droplet size was investigated, for which the optimum overall HLB occurred at 6.5, an increase of two HLB points over the theoretical required value without salt interference[2, 3]. The effects of total surfactant amounts, reaction time, temperature and initiator concentration on nanoparticle yield were also explored. A final emulsion with 3.2% w/v of surfactants, 2 hours of reaction time, 64ºC and an initiator concentration equal to 1% of the initial double concentration resulted in a maximum nanoparticle mass yield of ~39%. Finally, the particles were characterized in terms of crosslink density, showing an efficient encapsulation of the studied salt and a promising path for in-vivo testing. This study helped us develop a reproduceable formulation of an IPMP process that yields stable nanoparticles with suitable therapeutic levels of phosphates.

[1] Hyoju, S.K. et al, “Oral Polyphosphate Suppresses Bacterial Collagenase Production and Prevents Anastomotic Leak Due to Serratia marcescens and Pseudomonas aeruginosa”, Annals of Surgery, Feb, 2017.

[2]Vadlamudi, S. et al., “Inverse miniemulsion polymerization of phosphate-loaded hydrogel nanoparticles for sepsis prevention”, Unpublished master dissertation, Illinois Institute of Technology, Chicago, Illinois (2014)

[3] Yin Y et al, “De Novo Synthesis and Functional Analysis of Polyphosphate-Loaded Poly(Ethylene) Glycol Hydrogel Nanoparticles Targeting Pyocyanin and Pyoverdin Production in Pseudomonas aeruginosa as a Model Intestinal Pathogen”. Annals of Biomedical Engineering. 45(4):1058-1068, 2017.

[4] Shinoda, K., & Takeda, H. “The effect of added salts in water on the hydrophile-lipophile balance of nonionic surfactants: The effect of added salts on the phase inversion temperature of emulsions”. Journal of Colloid And Interface Science, 32(4), 642–646, 1970.

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