Authors: Rasika Phansalkar , Joo-Won Nam , Shao-Nong Chen , Jonathan Bisson , Daniel Kulakowski , James McAlpine , Ariene A. Leme , Cristina M.P. Vidal , Thaiane Aguiar , Ana Bedran-Russo , Guido F. Pauli
Composite-based, tooth colored dental restorations, in spite of their aesthetic appeal, are limited by a short life span. Every subsequent restoration results in the loss of healthy dental tissue. Thus, a bio-mimetic approach has been developed to enhance the mechanical strength of dentin using plant-derived proanthocyanidins (PACs). From a panel of eight active plants, grape seed extract showed the highest dentin biomodification potential, a 15-fold enhancement of dentin stiffness measured in MPa. Fractions with varying degrees of polymerization (DP) were obtained using solvent partitioning and centrifugal partition chromatography (CPC). Oligomeric PACs (OPACs, DP 2 – 7) surfaced as the most promising dentin biomodifiers compared to the constituent monomers and polymers (Dp ≥8). OPACs with DP 3 to 4 showed the most efficacious dentin-PAC interaction as evaluated by bio-mechanical tests. While one arm of the separation focused on the development of a highly active custom-made tri- and tetra-meric OPAC enriched mixture (GSE3+4), OPACs were also purified as single chemical entities. OPACs with predominantly 4β→8/6 B-type interflavan linkages (IFLs) along with one having a unique 2→8 IFL were isolated. Structural characterization employed 1D and 2D NMR at low temperature (255K) to overcome line-broadening due to atropisomerism. The presence of gallate ester moieties is a characteristic feature of grape seed PACs and the biological evaluation also highlighted the enhanced effect of galloylated OPACs on dentin biomodification. Grape seeds are thus, a viable source of novel restorative dental biomaterials and highlight a novel application of plant-based natural products in the biomedical field.