Biocompatible hydrogels by oxime Click chemistry

Abstract

Oxime Click chemistry was used to form hydrogels that support cell adhesion. Eight-armed aminooxy poly(ethylene glycol) (PEG) was mixed with glutaraldehyde to form oxime-linked hydrogels. The mechanical properties, gelation kinetics, and water swelling ratios were studied and found to be tunable. It was also shown that gels containing the integrin ligand arginine-glycine-aspartic acid (RGD) supported mesenchymal stem cell (MSC) incorporation. High cell viability and proliferation of the encapsulated cells demonstrated biocompatibility of the material.

Figure 1

Mechanical characterization of AO-PEG/glutaraldehyde hydrogels. Storage and elastic modulus can be modified by adjusting PEG polymer percentage and/or the r ratio. (A-B) Altering polymer percentage while keeping the crosslinking ratio constant (r = 1.0) can significantly change the mechanical properties of the hydrogel. (C-D) Likewise, changing the crosslinking ratio while keeping the polymer percentage constant (PEG: 3%) can drastically change the storage/loss modulus.

Figure 2

Hydrogel gelation kinetics can be altered by adjusting the pH of the solution. (A) Making the solution more acidic can increase the rate of gelation whereas a more basic solution slows down the gelation kinetics for 3 wt% AO-PEG (r = 1). Increasing the storage modulus by adjusting the PEG percentage (PEG = 3, 5, 7% from left to right) while keeping the crosslinking ratio constant at r = 1 (open circles) decreases the water content (B) and increases the swell ratios (C). Increasing the storage modulus by changing the r ratio (r = 0.7, 0.8, 1.0 from left to right) while keeping the PEG percentage constant at 3 wt% (closed triangles) decreases the water content (B) and decreases the swelling ratio (C). Data is displayed as the average and standard deviation of three independent experiments.

Figure 3

Live/Dead staining of the encapsulated mouse MSCs shows good viability at (A) day 1, (B) day 4, (C) and day 7. (D) Cells seeded on top of the hydrogel spread after one day, whereas cells encapsulated inside did not spread at (E) day 1, (F) day 4, (G) and day 7. (H) MTT assay shows an increased reduction over time, which indicates that cells are proliferating inside the hydrogel. (I) SEM image of hydrogel structure.

Scheme 1

Synthesis and encapsulation of MSCs within RGD-functionalized oxime-cross-linked PEG hydrogels. Note: Glutaraldehyde is generally a mixture of species and thus the structure shown is idealized.