Effect of photoinitiator concentration on the properties of polyethylene glycol based hydrogels for potential regenerative medicine applications

Photopolymerisation is an attractive in situ formation technique used in tissue engineering because it provides spatial and temporal control for in vivo clinical environments whilst presenting a fast and cost-effective alternative to other crosslinking methods. Photopolymerised hydrogels (three-dimensional networks of hydrophilic polymers that are able to imbibe large amounts of water) can be made resemble the physical characteristics of soft tissue. Hydrogel materials also generally exhibit high permeability and good biocompatibility making these materials attractive for use in cell encapsulation and tissue engineering applications.The main purpose of this study was to analyse the mechanical properties and thermal behaviour of photopolymerised poly(ethylene glycol) dimethacrylate (PEGDMA) hydrogels with varying photoinitiator concentration (0.01-1wt%) and macromolecular monomer molecular weight (400, 600, 1000); the effects of which were apparent. For example the uniaxial tensile testing resulted in tensile strength being reduced as the photoinitiator concentration increased. Additionally asthe molecular weight of the macromolecular monomer increased the tensile strength value reduced. Equally noteworthy variations were observed for the equilibrium swelling with an increase in swelling as the photoinitiator concentration increased. Differential scanning calorimetry showed that there was an increase in glass transition temperature with an increase in the molecular weight of PEGDMA but minimal effect from the photoinitiator concentration. Although high concentrations of photoinitiator resulted in a slight decrease in fibroblastic viability, the overall viability values were above those recommended for biomedical applications providing confirmation that all hydrogels analysed were good candidates for tissue engineering applications. Overall the results demonstrated that by varying the concentration of the photoinitiator concentration and molecular weight of the macromolecular monomer the mechanical strength of the hydrogels could be modulated allowing for use in a wide range of tissue engineering applications.