Structure-activity relationships of A-and B-type proanthocyanidins in long-term dentin biomodification and biocompatibility

Abstract

Objective: To explore the structure-activity relationships of plant-based proanthocyanidins (PACs) with dental pulp stem cells (DPSCs) and the long-term biomechanical stability of PAC-modified dentin extracellular matrix (ECM).

Methods: Mid-coronal dentin ECM (n = 8) was treated with eight PAC tetramers and trimers with varying A-/B-type linkages. Chemo-mechanical analyses included dynamic mechanical analysis and ATR-FTIR spectroscopy. Viscoelastic components were calculated after PAC biomodification, 18-month incubation, and protein destabilization. Collagen structure was assessed via IR amide absorbance ratios. DPSCs were cultured with PACs at different concentrations (100, 10, and 1 μg/mL) to measure proliferation. ANOVA and post-hoc tests were used for statistical analysis (α=0.05).

Results: PACs increased dentin moduli (p < 0.001), with AB- trimeric and B-type tetrameric PACs inducing the highest E* (∼132-142 MPa). AB, BB trimers, and AAA tetramers remained stable after 18 months, while other PACs decreased significantly yet maintained 6.4- to 9-fold higher E* than control (p < 0.001). Protein destabilization reduced E* and E' in AB-/B-type tetramer groups (p < 0.001) but maintained a 4- to 8-fold increase (p < 0.001). BB and AB trimers exhibited the highest damping capacity, shifting towards a more viscous-like behavior (p < 0.001). Substituting A- for B-type linkages increased damping by 53 %. Biomodified dentin ratios increased after incubation (p < 0.001). Only high PAC concentration reduced DPSCs proliferation (p < 0.001), lower concentrations had no effects (p > 0.067).

Conclusions: PACs increased and subsequently sustained dentin moduli overtime. PAC-treated dentin's chemo-mechanical behavior was driven by interflavanyl linkages type, degree of polymerization, and terminal monomeric unit, where B-type PACs enhanced mechanical and damping due to greater flexibility, while A-type PACs confered long-term stability and resistance to degradation. Biocompatibility depended on PAC concentration, with potential benefits for dental pulp cells.

Clinical relevance: Trimeric and tetrameric proanthocyanidins (PACs) were found to be biocompatible with dental pulp stem cells, and their specific interflavanyl linkages guide the dentin viscoelastic behavior. These findings are relevant for tailoring their development into biomimetic restorative and regenerative biomaterials.

Keywords: Dental pulp stem cells; Dentin; Dynamic mechanical analysis; Extracellular matrix; Proanthocyanidins.