Dentin primer based on a highly functionalized gelatin-methacryloyl hydrogel

Abstract

Gelatin-methacryloyl hydrogels (GelMA) have demonstrated their utility as scaffolds in a variety of tissue engineering applications.

Objectives: In this study, a highly functionalized GelMA hydrogel was synthesized and assessed for degree of functionalization. As the proposed GelMA hydrogel was coupled to a visible-light photoinitiator, we hypothesized it might serve as base to formulate a model dentin primer for application in restorative dentistry.

Methods: GelMA was mixed with photoinitiator lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), photopolymerized for 0-40 s using a dental light-curing device and tested for extrudability, degree of photo-crosslinking (DPxlink), water sorption/solubility/swelling (WS/SL/SW) and apparent modulus of elasticity (AE). Model dentin primer was prepared by mixing GelMA+LAP with a primer of a commercial three-step etch-and-rinse adhesive. After application of GelMA-based primer to acid-etched dentin, samples were bonded with correspondent adhesive agent, photopolymerized and had their immediate bond strength compared to control samples primed and bonded with the same commercial material.

Results: Extrudability of hydrogel was confirmed using a microsyringe to write the acronym "CDMI". DPxlink of GelMA+LAP changed significantly as a function of photopolymerization time (20 s < 30 s ≤ 40 s). WS, SL and SW were significantly reduced in hydrogels polymerized for 30 and 40 s. AE of hydrogels varied significantly as a function of photopolymerization time (20 s < 30 s ≤ 40 s; 20 s ‡ 40 s). Bond strength of dentin primed with GelMA-based primer was lower (∼29.3 MPa) but not significantly of that of control (∼34.6 MPa).

Conclusions: Optimization of a GelMA-based dentin primers can lead to the development of promising biomimetic adhesives for dentin rehabilitation.

Keywords: Dentin; Extracellular matrix; Gelatin; Hydrogels; Methacrylamides; Model bonding agents.

Fig. 1 –

Degree of functionalization (DF) and interaction of gelatin with MA to form foam-like GelMA. (a) appearance of highly functionalized GelMA; (b) molar content of free non-reacted ε-amino groups for pure non-functionalized gelatin (cyan) and highly functionalized GelMA (magenta) and DF (insert) as measured by TNBS assay; (c) FTIR spectral analysis of pure non-functionalized gelatin (cyan) and highly functionalized GelMA (magenta); (d) shifts in height and/or absorbance under typical peaks for pure gelatin type A versus GelMA.

Fig. 2 –

Extrudability and degree of photocrosslinking of GelMA+LAP. (a) appearance of highly functionalized GelMA dissolved in PBS containing the photoinitiator LAP; (b) extruded GelMA+LAP photopolymerized with a dental light-curing unit for 20 s; (c) FTIR spectra of GelMA+LAP non-cured (orange) and photopolymerized for 20 s (magenta), 30 s (green) or 40 s (blue); (d) shifts in Number (X, cm⁻¹), Area, Height and/or Arbitrary units of absorbance (Y) for typical peaks and additional peaks in GelMA+LAP spectra as function of photopolymerization time.

Fig. 3 –

Effect of WS, SL and SW on GelMA+LAP hydrogel constructs photopolymerized for different periods of time (n = 8/experimental group). (a) GelMA+LAP specimens’ preparation and appearance after dry and water storage; (b) GelMA+LAP WS. Bars represent mean and standard deviation and different letters indicate statistical differences among groups (p < 0.05). Regression analysis showed negative correlation between WS and photopolymerization time; (c) GelMA+LAP SL. Bars represent mean and standard deviation and different letters indicate statistical differences among groups (p < 0.05). Regression analysis showed negative correlation between SL and photopolymerization time; (d) GelMA+LAP SW. Bars represent mean and standard deviation and different letters indicate statistical differences among groups (p < 0.05). Regression analysis showed negative correlation between SW and photopolymerization time.

Fig. 4 –

Apparent modulus of elasticity (AE, in KPa) of GelMA+LAP constructs photopolymerized by different blue light exposure times (n = 8/experimental group). (a) Custom-made mold use for specimens’ preparation, visual difference between specimens’ appearance as function of polymerization time and a GelMA-LAP specimen polymerized for 40 s positioned on 3-point bending apparatus for AE assessment (b) AE of specimens photopolymerized for 20, 30 or 40 s. Bars represent mean and standard deviation. Different letters indicate significant differences among groups (p < 0.05); (c) Regression analysis of mean AE of GelMA+LAP polymerized for 20, 30 or 40 s plotted against photopolymerization time showing direct correlation about these functions.

Fig. 5 –

Bond strength (MPa) of model GelMA primer in comparison to a commercial material (n = 5 teeth/experimental condition). (a) experimental groups and primers’ composition; (b) μTBS values are mean and SD. No statistical difference in μTBS was detected between control (Scotchbond MP) and experimental group (GelMA+Scotchbond MP) (p > 0.05); (c) Failure mode of resin-dentin bonded specimens in relation to the number of tested specimens per group. Cd= failure located within mineralized dentin. Cc= failure located within restorative composite; A/M= failure located at the resin-dentin interface.