Antimicrobial Peptide-Polymer Conjugates for Dentistry

Abstract

Bacterial adhesion and growth at the composite/adhesive/tooth interface remain the primary cause of dental composite restoration failure. Early colonizers, including Streptococcus mutans, play a critical role in the formation of dental caries by creating an environment that reduces the adhesive's integrity. Subsequently, other bacterial species, biofilm formation, and lactic acid from S. mutans demineralize the adjoining tooth. Because of their broad spectrum of antibacterial activity and low risk for antibiotic resistance, antimicrobial peptides (AMPs) have received significant attention to prevent bacterial biofilms. Harnessing the potential of AMPs is still very limited in dentistry-a few studies have explored peptide-enabled antimicrobial adhesive copolymer systems using mainly nonspecific adsorption. In the current investigation, to avoid limitations from nonspecific adsorption and to prevent potential peptide leakage out of the resin, we conjugated an AMP with a commonly used monomer for dental adhesive formulation. To tailor the flexibility between the peptide and the resin material, we designed two different spacer domains. The spacer-integrated antimicrobial peptides were conjugated to methacrylate (MA), and the resulting MA-AMP monomers were next copolymerized into dental adhesives as AMP-polymer conjugates. The resulting bioactivity of the polymethacrylate-based AMP conjugated matrix activity was investigated. The antimicrobial peptide conjugated to the resin matrix demonstrated significant antimicrobial activity against S. mutans. Secondary structure analyses of conjugated peptides were applied to understand the activity differential. When mechanical properties of the adhesive system were investigated with respect to AMP and cross-linking concentration, resulting AMP-polymer conjugates maintained higher compressive moduli compared to hydrogel analogues including polyHEMA. Overall, our result provides a robust approach to develop a fine-tuned bioenabled peptide adhesive system with improved mechanical properties and antimicrobial activity. The results of this study represent a critical step toward the development of peptide-conjugated dentin adhesives for treatment of secondary caries and the enhanced durability of dental composite restorations.

Keywords: Streptococcus mutans; antimicrobial peptide; bioactivity; bioconjugation; dental adhesive; mechanical property.

Figure 1.

Schematic illustration (a) and graphical representation (b) of antibacterial activity of AMPs, AMP-monomers, and non-AMP-monomer (MA-non-AMP).

Figure 2.

Schematic illustration (a) and graphical representation (b) of the viability of S. mutans cultures after overnight incubation with polymerized discs containing non-AMP-monomer and AMP-monomers. S. mutans: a positive control without a disc. Peptide control: MA-non-AMP with GGG as a spacer. MA-C0 is the methacrylate control polymer replacing methacrylate peptide conjugates with methacrylate monomer.

Figure 3.

Residue-based flexibility and structural features for AMPs modeled by the PyRosetta peptide-folding script and labeled with DSSP. The top panel shows GH12, the antimicrobial peptide domain by itself. The middle panel shows AMPM3, the GH12 variant with a KGGG spacer. The bottom panel shows AMPM5, the GH12 variant with KSSSGGG spacer. The first row of the grid in each panel is the residue letter and residue number as the bend row. The color coding for the residue letter is by amino acid type: glycine = yellow, polar = green, charged residue = blue, and nonpolar = black. The row key starts with the first row below the residue letters, which is the bend row. The bend row is defined by the dihedral angle of the planes formed by α carbons of neighboring residues. The row key arrow pointing to the right-hand side of the page is in the direction of the cross-product of the position vectors for these two α carbons. The second arrow is the direction of the cross product of the α carbon position vectors for residues (i + 1) and (i + 2). A bend exists at a residue if this angle is greater than 70°. Across the panels, the grayscale of the center portion refers to the mean frequency of the feature, and the grayscale of the border refers to the coefficient of variation of across the ensembles, with black corresponding to 100%. The LH-RH panel describes the sign of the dihedral angle (left-hand indicates an angle less than 180°, while the RH indicates one greater.) The grayscale portion of the pie indicates the proportion of right-hand dihedral angles. A turn, in the row below, exists at a residue if backbone carbonyl hydrogen bonds to an adjacent backbone amide. Helices are one type of hydrogen bond pattern. Helical projections are provided by residue position to determine which residue share the same helical face. The colored portion describes the projection, while the grayscale portion shows the mean frequency.

Figure 4.

Schematic illustration (a) and the graphical presentation (b) of the viability of S. mutans cultures after overnight incubation with polymerized discs containing different cross-linker concentration. S. mutans: a positive control without a disc. Peptide control: MA-non-AMP with GGG as a spacer.

Figure 5.

Representative stress–strain curves from compression test and bar figure of the Young’s moduli of the controls and AMP-polymer conjugates cylindrical samples.