A novel methacrylate derivative polymer that resists bacterial cell-mediated biodegradation

Abstract

This study tests biodegradation resistance of a custom synthesized novel ethylene glycol ethyl methacrylate (EGEMA) with ester bond linkages that are external to the central polymer backbone when polymerized. Ethylene glycol dimethacrylate (EGDMA) with internal ester bond linkages and EGEMA discs were prepared in a polytetrafluoroethylene (PTFE) mold using 40 μl macromer and photo/co-initiator mixture cured for 40 s at 1000 mW/cm² . The discs were stored in the constant presence of Streptococcus mutans (S. mutans) in Todd Hewitt Yeast + Glucose (THYE+G) media up to 9 weeks (n = 8 for each macromer type) and physical/mechanical properties were assessed. Initial measurements EGEMA versus EGDMA polymer discs showed equivalent degree of conversion (45.69% ± 2.38 vs. 46.79% ± 4.64), diametral tensile stress (DTS; 8.12± 2.92 MPa vs. 6.02 ± 1.48 MPa), and low subsurface optical defects (0.41% ± 0.254% vs. 0.11% ± 0.074%). The initial surface wettability (contact angle) was slightly higher (p ≤ .012) for EGEMA (62.02° ± 3.56) than EGDMA (53.86° ± 5.61°). EGDMA showed higher initial Vicker's hardness than EGEMA (8.03 ± 0.88 HV vs. 5.93 ± 0.69 HV; p ≤ .001). After 9 weeks of S. mutans exposure, EGEMA (ΔDTS-1.30 MPa) showed higher resistance to biodegradation effects with a superior DTS than EGDMA (ΔDTS-6.39 MPa) (p = .0039). Visible and scanning electron microscopy images of EGEMA show less surface cracking and defects than EGDMA. EGDMA had higher loss of material (18.9% vs. 8.5%, p = .0009), relative changes to fracture toughness (92.5% vs. 49.2%, p = .0022) and increased water sorption (6.1% vs. 1.9%, p = .0022) compared to EGEMA discs. The flipped external ester group linkage design is attributed to EGEMA showing higher resistance to bacterial degradation effects than an internal ester group linkage design methacrylate.

Keywords: biodegradation; dental/craniofacial material; mechanical; polymerization; properties.

FIGURE 1

Ethylene glycol dimethacrylate and ethyl methacrylate molecular structure with photo-polymerization reaction schematics

FIGURE 2

Esterase activity of Todd Hewitt yeast-glucose media with and without Streptococcus mutans (S. mutans) cells measured using p-nitrophenol assay (A) and scanning electron microscopy for ethylene glycol dimethacrylate (B,C) and ethyl methacrylate (D,E) discs at week 9, with S. mutans bacterial cells, fixed and discs washed for imaging at 2.5 k magnification

FIGURE 3

The visible light images of ethylene glycol dimethacrylate and ethyl methacrylate polymers, before and after incubating with Streptococcus mutans (S. mutans) cells. S. mutans biofilms are removed with 72 h phosphate buffered saline rinsing prior to images

FIGURE 4

Change in hardness (A) and diametral tensile strength (B) and total energy to fracture (C) before and after incubating in the presence of Streptococcus mutans over the period of 9 weeks. The yielding point calculation (D) using a typical DT-stress versus strain curve (E) for “as prepared” and SM exposed discs. Solid arrows showing fracture point and dotted arrows showing yielding point ($n=6$, * for $p\le .05$ (A), ** for $p\le .01$ (B), *** for $p\le .001$ (C), and **** for $p\le .0001$ (D))

FIGURE 5

Change in wettability in the presence of S. mutans (A), water sorption (B) and the analysis of optical coherence tomography images reported as minor defect % (C) and major defects % (D) ($n=6$, * for $p\le .05$ (A), ** for $p\le .01$ (B), *** for $p\le .001$ (C), and **** for $p\le .0001$ (D))

FIGURE 6

The biodegradation schematic of ethylene glycol dimethacrylate and ethyl methacrylate in the presence of Streptococcus mutans showing ethylene glycol and ethanol as by-products