Polymeric Hydrogels for Intervertebral Disc Replacement/Integration: Playing with the Chemical Composition for Tuning Shear Behavior and Hydrophilicity

Damages to the intervertebral disc (IVD) due to improper loading or degeneration result in back pain, which is a common disease affecting an increasing number of patients. Different strategies for IVD remediation have been developed, from surgical treatment to disc replacement, by using both metallic and non-metallic materials. Hydrogels are very attractive materials due to their ability to simulate the properties of many soft tissues; moreover, their chemical composition can be varied in order to assure performances similar to the natural disc. In particular, for the replacement of the IVD outer ring, namely, the anulus fibrosus, the shear properties are of paramount importance. In this work, we produced hydrogels through the photo-induced crosslinking of different mixtures composed of two hydrophilic monofunctional and difunctional polymers, namely, poly(ethyleneglycol) methyl ether methacrylate (PEGMEMA) and poly(ethyleneglycol) dimethacrylate (PEGDMA), together with a hydrophobic molecule, i.e., tert-butyl acrylate (tBA). By changing the ratio among the precursors, we demonstrated the tunability of both the shear properties and hydrophilicity. The structural properties of hydrogels were studied by solid-state nuclear magnetic resonance (NMR). These experiments provided insights on both the structure and molecular dynamics of polymeric networks and, together with information obtained by differential scanning calorimetry (DSC), allowed for correlating the physical properties of the hydrogels with their chemical composition.

Development of Polyethylene Glycol-based Hydrogels Optimized for In Vitro 3D Culture of HepG2 Hepatocarcinoma Cells

BACKGROUND/AIM

We report an in vitro three-dimensional (3D) culture system optimized for the growth of HepG2 hepatocarcinoma cells.

MATERIALS AND METHODS

The 3D culture system was fabricated based on polyethylene glycol (PEG)-based hydrogels; their mechanical strength was controlled by differences in the arm number and concentration of PEG-vinylsulfone. Moreover, cellular growth was evaluated after culturing HepG2 cells in PEG-based hydrogels with various mechanical strengths.

RESULTS

HepG2 cell culture in the 3D PEG-based hydrogels induced the formation of spherical colonies. Moreover, the highest number of spherical colonies formed from HepG2 cells at the single-cell level, and the formation of spherical colonies with a uniform size was observed in HepG2 cells cultured in 5% (w/v) 8-arm PEG-based hydrogels.

CONCLUSION

5% (w/v) 8-arm PEG-based hydrogels may be developed as a 3D culture system optimized for stimulating the in vitro growth of HepG2 cells.

Influence of Network Structure on the Crystallization Behavior in Chemically Crosslinked Hydrogels

The network structure of hydrogels is a vital factor to determine their physical properties. Two network structures within hydrogels based on eight-arm star-shaped poly(ethylene glycol)(8PEG) have been obtained; the distinction between the two depends on the way in which the macromonomers were crosslinked: either by (i) commonly-used photo-initiated chain-growth polymerization (8PEG⁻UV), or (ii) Michael addition step-growth polymerization (8PEG⁻NH₃). The crystallization of hydrogels is facilitated by a solvent drying process to obtain a thin hydrogel film. Polarized optical microscopy (POM) results reveal that, while in the 8PEG⁻UV hydrogels only nano-scaled crystallites are apparent, the 8PEG⁻NH₃ hydrogels exhibit an assembly of giant crystalline domains with spherulite sizes ranging from 100 to 400 µm. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses further confirm these results. A model has been proposed to elucidate the correlations between the polymer network structures and the crystallization behavior of PEG-based hydrogels.