Understanding the Role of Shape and Composition of Star-Shaped Polymers and their Ability to Both Bind and Prevent Bacteria Attachment on Oral Relevant Surfaces

Abstract

In this study, we have prepared a series of 4- and 6-arm star-shaped polymers with varying molecular weight and hydrophobicity in order to provide insight into the role and relationship that shape and composition have on the binding and protecting of oral relevant surfaces (hydroxyapatite, HAP) from bacteria colonization. Star-shaped acrylic acid polymers were prepared by free-radical polymerization in the presence of chain transfer agents with thiol groups, and their binding to the HAP surfaces and subsequent bacteria repulsion was measured. We observed that binding was dependent on both polymer shape and hydrophobicity (star vs. linear), but their relative efficacy to reduce oral bacteria attachment from surfaces was dependent on their hydrophobicity only. We further measured the macroscopic effects of these materials to modify the mucin-coated HAP surfaces through contact angle experiments; the degree of angle change was dependent on the relative hydrophobicity of the materials suggesting future in vivo efficacy. The results from this study highlight that star-shaped polymers represent a new material platform for the development of dental applications to control bacterial adhesion which can lead to tooth decay, with various compositional and structural aspects of materials being vital to effectively design oral care products.

Keywords: acrylic acid; antibacterial; antifouling; composition; dental; hydrophobicity; hydroxyapatite; oral; polymer; star-shaped.

Figure 1

Star-shaped and linear poly(acrylic acid)s used in this study. The chemical structures of linear poly(acrylic acid) polymers (Lin), 4-arm (4Star) and 6-arm (6Star) star-shaped poly(acrylic acid), and 4-arm star-shaped copolymers with methyl acrylate (4StarMA).

Figure 2

Synthesis of star-shaped polymers. (A) Synthesis of 4-arm star-shaped polymers, (B) Chemical structures of chain transfer agents. MMP: methyl 3-mercaptopropionate, PETMP: pentaerythritol tetrakis(3-mercaptopropionate), DPEHMP: dipentaerythritol hexakis(3-mercaptopropionate). (C) Mayo plots. The broken lines present the results of line fitting. C_tr was determined from the slope of the line. [SH]/[monomer] = (The number of thiol groups in a CTA) × [CTA]/[monomer].

Figure 3

Synthesis of fluorescent dye-labeled polymers and their adsorption on hydroxyapatite powder (HAP). (A) Synthesis of rhodamine-labeled 4-arm star-shaped polymers. The rhodamine monomer (0.1 mol.% to the total number of monomers) was polymerized with t-Bu methacrylate. (B) Adsorption of 4-arm star-shaped polymer F-4Star-192 on HAP surfaces. Fluorescence intensities from supernatants of polymer assay solutions with and without HAP. (C) Adsorption isotherm and linear Langmuir plot. q: the amounts of polymers adsorbed onto the HAP surface. C_eq: the polymer concentration of supernatant at equilibrium.

Figure 4

HAP adsorption of linear and 4-ram star-shaped polymers. (A) q_max and (B) K_d were determined by the Langmuir plot.

Figure 5

Effect of hydrophobic monomer composition on HAP adsorption of 4-arm star-shaped polymers.

Figure 6

Anti-bacterial attachment activity of linear and star-shaped polymers. The activity of polymers was assessed by the percent reduction in bacterial attachment relative to control (untreated HAP surface). The data and error bars represent the average of 12 replicates with 95% confidence limits. The alphabetical letters on the bars present statistical grouping.

Figure 7

Water contact angle of polymer treated HAP surfaces pre-treated with artificial saliva. Example contact angle images of treated HAP surfaces: (A) untreated; (B) 4StarMA34-171; (C) 4StarMA56-215.