Modulating Shape of Polyester Based Polymersomes using Osmotic Pressure

Summary

Polymersomes are self-assembled polymeric vesicles that are formed in spherical shapes to minimize Gibb's Free Energy. In the case of drug delivery, more elongated structures are beneficial. This protocol establishes methods to create more rod-like polymersomes, with elongated aspect ratios, using salt to induce osmotic pressure and reduce internal vesicle volumes.

Abstract

Polymersomes are membrane-bound, bilayer vesicles created from amphiphilic block copolymers that can encapsulate both hydrophobic and hydrophilic payloads for drug delivery applications. Despite their promise, polymersomes are limited in application due to their spherical shape, which is not readily taken up by cells, as demonstrated by solid nanoparticle scientists. This article describes a salt-based method for increasing the aspect ratios of spherical poly(ethylene glycol) (PEG)- based polymersomes. This method can elongate polymersomes and ultimately control their final shape by adding sodium chloride in post-formation dialysis. Salt concentration can be varied, as described in this method, based on the hydrophobicity of the block copolymer being used as the base for the polymersome and the target shape. Elongated nanoparticles have the potential to better target the endothelium in larger diameter blood vessels, like veins, where margination is observed. This protocol can expand therapeutic nanoparticle applications by utilizing elongation techniques in tandem with the dual-loading, long-circulating benefits of polymersomes.

Introduction

Shape modulation is a relatively new and efficient way to improve nanoparticle-mediated drug delivery. Not only does the change in morphology increase the surface area of particles, which in turn allows for a greater carrying capacity, but it also has implications across the board to improve stability, circulation time, bioavailability, molecular targeting, and controlled release¹. Polymersomes, the nanoparticle of focus in this method, tend to thermodynamically self-assemble into a spherical shape, which has proven to be impractical in cellular uptake and is more easily detected in the immune system as a foreign body. Being able to elongate th....

Protocol

1. Spherical polymersome formation using a solvent injection method

1. Dissolution of polyesters in organic solvent
   NOTE: Only one polyester should be dissolved in its respective organic solvent at a time to form polymersomes.
   1. Dissolve polyesters PEG-PLA or PEG-b-poly(lactic-co-glycolic acid) (PEG-PLGA) in dimethyl sulfoxide (DMSO) at a concentration of 1.5% weight. Specifically, dissolve 0.015 g of selected polyester in 1 mL of DMSO (15 mg/mL). Full dissolution of the polymer may require periods of up to 15 min of vortexing.
2. While the polyester is dissolving in organic solvent, set up the solvent injection apparatus....

Discussion

Self-assembled systems are notoriously uncontrollable. Their final properties, including size, shape, and structure, are driven by the chosen amphiphile's hydrophobic properties and the solvent environment selected. Amphiphilic block copolymers tend towards spherical shapes, which minimizes Gibb's free energy and leads to the thermodynamic equilibrium²³, thus forming polymersomes. Because of their equilibrium nature, polymersomes are significantly more challenging to elongate or alter in s.......

Materials

Name	Company	Catalog Number	Comments
15*45 vials screw thread w/cap attached	Fisherbrand	9609104000
Dimethyl Sulfoxide	Fisher Chemical	D128-1
Dimethyl Sulfoxide	BDH	BDH1115-1LP
Isoremp stirrers, hotplates, and stirring hotplates	Fisher scientific	CIC00008110V19
LEGATO 130 SYRINGE PUMP	kd Scientific	788130
PEG(1000)-b-PLA(5000), Diblock Polymer	Polysciences Inc	24381-1	note the molecular weights when replicating
Poly(ethylene glycol) (2000) Methyl ether-block-poly(lactide-co-glycolide) (4500)	Sigma aldrich	764825-1G	note the molecular weights when replicating
Single-Use Syringe/BD PrecisionGlide Needle combination, sterile, BD medical	BD medical	BD305620	Tuberculin
Sodium Chloride	BDH	BDH9286
Zetasizer Nano ZS	Malvern