Nanosponge Tunability in Size and Crosslinking Density

Summary

This article describes a process for tuning the size and crosslinking density of covalently crosslinked nanoparticles from linear polyesters containing pendant functionality. By tailoring synthesis parameters (polymer molecular weight, pendant functionality incorporation, and crosslinker equivalents), a desired nanoparticle size and crosslinking density can be achieved for drug delivery applications.

Abstract

We describe a protocol for the synthesis of linear polyesters containing pendant epoxide functionality and their incorporation into a nanosponge with controlled dimensions. This approach begins with synthesis of a functionalized lactone which is key to the pendant functionalization of the resulting polymer. Valerolactone (VL) and allyl-valerolactone (AVL) are then copolymerized using ring-opening polymerization. Post-polymerization modification is then used to install an epoxide moiety on some or all of the pendant allyl groups. Epoxy-amine chemistry is employed to form nanoparticles in a dilute solution of both polymer and small molecule diamine crosslinker based on the desired nanosponge size and crosslinking density. Nanosponge sizes can be characterized by transmission electron microscopy (TEM) imaging to determine the dimension and distribution. This method provides a pathway by which highly tunable polyesters can create tunable nanoparticles, which can be used for small molecule drug encapsulation. Due to the nature of the backbone, these particles are hydrolytically and enzymatically degradable for a controlled release of a wide range of hydrophobic small molecules.

Introduction

Precisely tuning the size and crosslinking density of nanoparticles based on intermolecular crosslinking is of great importance to influence and guide the drug release profile of these nanosystems¹. Designing nanosponge tunability, i.e., preparing particles of different network densities, is reliant upon the pendant functionality of the precursor polymer and the equivalents of the hydrophilic crosslinker incorporated. In this approach, the concentration of the precursor and crosslinker in the solvent is important to form nanoparticles of a discrete size rather than a bulk gel. Utilizing quantitative nuclear magnetic resonance spectrosc....

Protocol

1. Synthesis and Characterization of AVL

1. Place a magnetic stir bar inside a 2 neck 500 mL round bottom flask (Flask 1) and seal with an appropriate sized rubber septum and steel wire. Flame dry the flask to remove moisture by purging with nitrogen gas connected through an inlet needle and open outlet needle in the septum, while using a butane flame torch to gently heat the outside of the flask by moving the flame along the surface.
   1. Continue heating the entire flask by running the flame across the surface until moisture clouding the inside of the flask is not seen. Remove the flame and let the flask cool to room temperature whil....

Results

To evaluate the relationship between the synthesis parameters of the nanosponge and its resultant size, the concentration and pendant functionality of each polymer precursor is important. In Figure 1, a successfulsynthetic scheme of nanosponges is carried out under reflux conditions after incorporating both precursor polymer and diamine crosslinker in DCM for 12 h. The concentration of epoxides in the solution is also critical to forming discrete particles. O.......

Discussion

Obtaining reproducible nanosponge sizes is vital in drug delivery applications. Multiple parameters in polymerization and nanosponge synthesis affect the size and crosslink density of the resulting particle. Three important parameters were identified in our analysis: polymer molecular weight, epoxide pendant functionality, and crosslinker equivalents. In order to produce a range of molecular weights and epoxide functionalities for nanosponge synthesis, the stoichiometry of the VL-co-AVL copolymer must be altered.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
2,2'-(Ethylenedioxy)bis(ethylamine)	Sigma-Aldrich	385506-100ML
3-methyl-1-butanol	Sigma-Aldrich	309435-100ML	anhydrous, ≥99%
Acetone	Sigma-Aldrich	179124-4L
Allyl bromide	Sigma-Aldrich	A29585-5G	≥99%
Ammonium chloride	Fisher Scientific	A661-500	saturated solution in DI water
Cell culture water	Sigma-Aldrich	W3500-500ML	Filtered through 0.45 μm syringe filter
Dichloromethane (DCM)	Sigma-Aldrich	270997-100ML	anhydrous, ≥99%, contains 40 - 150 ppm amylene as stabilizer
Ethyl Acetate	Fisher Scientific	E145SK-4
EZFlow 0.2 μm Syringe Filter	Foxx Life Sciences	386-2116-OEM	Hydrophillic PTFE, 13 mm
EZFlow 0.45 μm Syringe Filter	Foxx Life Sciences	386-3126-OEM	Hydrophillic PTFE, 25 mm
Fisherbrand Disposable Borosilicate Glass Test Tubes with Plain End	Fisher Scientific	14-961-31
Fisherbrand Microcentrifuge Tubes	Fisher Scientific	14-666-318	1.5 mL
Hamilton Microliter Syringe, 100 μL	Hamilton Company	80600	Model 710 N SYR, Cemented NDL, 22s ga, 2 in, point style 2
Hexamethylphosphoramide	Sigma-Aldrich	H11602-100G	≥99%, contains ≤1,000 ppm propylene oxide as stabilizer
Hexanes	Fisher Scientific	H292-4
Magnesium sulfate anhydrous	Fisher Scientific	M65-500
Meta-chloroperoxybenzoic acid	Sigma-Aldrich	273031-100G	Purified to ≥99% by buffer wash
Methanol (MeOH)	Sigma-Aldrich	322415-100ML	anhydrous, ≥99%
N-butyllithium solution	Sigma-Aldrich	230707-100ML	2.5 M in hexanes
N,N-diisopropylethylamine	Sigma-Aldrich	550043-500ML	≥99%
Parafilm M	Sigma-Aldrich	P7793-1EA
PELCO Pro Reverse (Self-Closing) Tweezers	Ted Pella, Inc.	5375-NM
Phosphotungstic acid hydrate	Alfa Aesar	40116
Q55 Sonicator	Qsonica	Q55-110	55 Watts, 20 kHz
SiliaMetS Cysteine	Silicycle	R80530B-10g
SnakeSkin Dialysis Clips	Thermo Scientific	68011
SnakeSkin Dialysis Tubing, 10K MWCO	Thermo Scientific	68100
Sodium bicarbonate	Fisher Scientific	5233-500	saturated solution in DI water
TEM grid	Ted Pella, Inc.	01822-F	Ultrathin Carbon Type-A, 400 mesh, Copper, approx. grid hole size: 42 µm
Tetrahydrofuran (THF)	Sigma-Aldrich	401757-1L	Anhydrous, ≥99.9%, inhibitor-free
Tin(II) trifluoromethanesulfonate	Sigma-Aldrich	388122-1G
Vortex-Genie 2	Scientific Industries	SI-0236
Whatman Filter Paper, Grade 1	Fisher Scientific	09-805H	Circles, 185 mm
δ-valerolactone	Sigma-Aldrich	389579-100ML	Purified by vacuum distillation