Unveiling structure-activity relationships of proanthocyanidins with dentin collagen.

OBJECTIVE To elucidate the structure-activity relationships (SARs) of proanthocyanidins (PACs) with type I collagen using sixteen chemically defined PACs with degree of polymerization (DP) 2-6. METHODS Under a dentin model, the biomimicry of PACs with type I collagen was investigated by dynamic mechanical analysis (DMA) and infrared spectroscopy. The dentin matrix was modified with PACs from Pinus massoniana [monomers (Mon-1 and Mon-2), dimers (Dim-1-Dim-4), trimers (Tri-1-Tri-4), tetramers (Tet-1-Tet-5), and hexamer (Hex-1)]. A strain sweep method in a 3-point bending submersion clamp was used to assess the viscoelastic properties [storage (E'), loss (E"), and complex moduli (E*) and tan δ] of the dentin matrix before and after biomodification. Biochemical analysis of the dentin matrix was assessed with FTIR spectroscopy. Data were statistically analyzed using one-way ANOVA and post-hoc tests (α = 0.05). RESULTS DP had a significant effect on modified dentin moduli (tetramers ≈ trimers > hexamers ≈ dimers > monomers ≈ control, p < 0.001). Trimers and tetramers yielded 6- to 8-fold increase in the mechanical properties of modified dentin and induced conformational changes to the secondary structure of collagen. Modifications to the tertiary structure of collagen was shown in all PAC modified-dentin matrices. SIGNIFICANCE Findings establish three key SARs: (i) increasing DP generally enhances biomimicry potential of PACs in modulating the mechanical and chemical properties of dentin (ii) the secondary structure of dentin collagen is affected by the position of B-type inter-flavanyl linkages (4β → 6 and 4β → 8); and (iii) the terminal monomeric flavan-3-ol unit plays a modulatory role in the viscoelasticity of dentin.