In situ-forming robust chitosan-poly(ethylene glycol) hydrogels prepared by copper-free azide-alkyne click reaction for tissue engineering.

Vinh X Truong,James Bowen,Stephen M Richardson,Judith A Hoyland,Andrew P Dove,Hamish T J Gilbert,Matthew P Ablett

doi:10.1039/c3bm60159e

Abstract

A water-soluble azide-functionalised chitosan was crosslinked with propiolic acid ester-functional poly(ethylene glycol) using copper-free click chemistry. The resultant hydrogel materials were formed within 5-60 min at 37 °C and resulted in mechanically robust materials with tuneable properties such as swelling, mechanical strength and degradation. Importantly, the hydrogels supported mesenchymal stem cell attachment and proliferation and were also non-toxic to encapsulated cells. As such these studies indicate that the hydrogels have potential to be used as injectable biomaterials for tissue engineering.

Highlights

Following dialysis of the resultant material to remove small molecule side products and impurities, the presence of the azide functional group in the structure of the chitosan product was evidenced by the presence of a peak at 2150 cm−1 in the IR spectrum (Fig. 1A). 1H NMR spectroscopic analysis of the purified product showed new resonances at δ = 1.55, 2.26 and 3.27 ppm (Fig. 1B) which correspond to the protons within the azido-pentanoate side chain, which confirms the incorporation of the azido-pentanoate pendant group in the chitosan product
The degree of deacetylation of the chitosan before and after grafting were estimated from 1H NMR spectra as described elsewhere.[39]. These values were found to be 84% and 64.5% respectively which in turn enabled estimation of the degree of the substitution with azide groups calculated as 19.5%
We have developed a method for preparing in situ-forming chitosan-poly(ethylene glycol) (PEG) hydrogels by copper free alkyne– azide click chemistry

Summary

Introduction

Chitosan is a linear polysaccharide that can be readily obtained from natural sources such as shrimp and other crustacean shells. Paper which mimics the extracellular environment of natural tissues.[28,29] Michael addition reactions are probably the most common bioorthogonal crosslinking chemistries utilised to prepare in situ-forming hydrogels on account of the mild reaction conditions, which require only basic buffer environment, and the availability of the functional precursors.[28,30] More recently, several other click reactions have been introduced to the expanding bioorthogonal click toolkit for hydrogel preparation in biological media They include reaction of an azide with a ring-strained alkyne (SPAAC),[31,32] oxime click reaction with glutaraldehyde,[33] tetrazine–norbonene reaction,[34] and the tetrazole–alkene click reaction.[35]. The tuneable nature of the gelation and gel properties are demonstrated

Materials and methods general considerations

Results and discussion

Conclusions