Quaternary ammonium salt and polyethylene glycol grafted orthodontic PMMA surfaces – preparation, characterization, and anti-bacterial function
Date Issued
2015
Date
2015
Author(s)
Lee, Chung-Yuan
Abstract
Bacterial infections on biomedical devices have caused dental caries, periodontal disease, and osteomyelitis. Bacteria can easily colonize on the surface of the synthetic material and substance such as acrylic resin that is often used in removable appliances and retainers for orthodontic treatment. The growing bacteria colonies encapsulate themselves in a bacteria-produced matrix (called biofilm) of extracellular polysaccharides, proteins, and lipids, which protects the bacteria from purgation. The biofilm on the orthodontic resin surface causes the users to risk the possibility of oral infections. In this thesis research, a facile method via acid treatment was developed to chemically modify surfaces for inhibition of bacterial colonization on biomedical devices. The modification was performed on an exemplified device of poly (methyl methacrylate) (PMMA) using antibacterial adhesion compounds such as poly (ethylene glycol) (PEG) and quaternary ammonium salt (QAS). PMMA was made via a pressurized process, which is a typical clinical fabrication method. Two synthesis routes were adopted for antibacterial adhesion. The PEG route treated the PMMA surface with PEG and sodium methoxide in methanol to yield the PEG-grafted PMMA (called PEG-g-PMMA). The QAS route treated the PMMA surface with acid first and then with QAS to obtain the QAS-grafted PMMA (called QAS-PMMA). To characterize the treated surface, the PEG-g-PMMA and QAS-PMMA samples were examined by attenuated total reflectance Fourier transform infrared spectroscopy (FTIR), contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), and bacterial tests. Compared with the spectra obtained from pristine PMMA, the decrease in peak intensity at ~289.0 eV and increase in intensity at ~286.4 eV of the XPS C1s spectra obtained from PEG-g-PMMA, the increases in FTIR absorption at ~1096 cm-1 and ~3400 cm-1 due to the C-O-C stretching and O-H stretching vibrations, respectively, and the increased wettability confirmed the success in PEG grafting on the PMMA surface. The large increase in the C/O ratio of XPS survey spectra and the appearance of chloride and quaternary nitrogen signals in the XPS spectra obtained from QAS-g-PMMA confirmed the grafting of QAS on PMMA. The antibacterial function of the pristine or grafted PMMA material was tested via dropping human saliva on the material surface before the surface was brought to get in contact with the bacteria. After removing the bacteria, the materials sample was incubated in a bacteria-free solution and the O.D. value of the solution was measured at the wavelength of 600 nm. PEG-g-PMMA exhibited similar O.D. values with that of pristine PMMA. However, QAS-PMMA exhibited lower O.D. values than that of pristine PMMA. The PEG-g-PMMA gave a measured O.D. value close to that of pristine PMMA, and the QAS-g-PMMA showed a distinctively lower O.D. values. The O.D. value of S. mutans on PEG-g-PMMA was about 1.604 and pristine PMMA was 1.731. Both two high O.D. values expressed that the bacteria could develop on their surfaces. The O.D. value of S. mutans on QAS-g-PMMA was 0.020 which was significantly lower than the other two trials. The O.D. values of E. coli on the three types of PMMA showed the same trend as those of S. mutans. SEM studies of PEG-g-PMMA showed aggregation of PEG on PMMA and PEG-free areas. After antimicrobial tests, SEM images showed more bacteria colonized on PEG-g-PMMA and pristine PMMA than on QAS-g-PMMA. The presence of the PEG-free areas in the synthesized PEG-g-PMMA surface may thus contribute to its poor antimicrobial activity. Compared with the SEM images of PEG-g-PMMA, the images of QAS-g-PMMA showed the QAS grafting molecules to be relatively more evenly distributed in the QAS-g-PMMA surface than the PEG molecules in the PEG-g-PMMA surface. The disruption of bacteria membrane was also observed in the SEM images of QAS-g-PMMA. It indicated that the QAS-g-PMMA surfaces possessed antibacterial ability and would become prospective biomaterial on inhibiting bacteria. The possible antibacterial mechanism of QAS-g-PMMA is discussed. In conclusion, the fabricated method of QAS-g-PMMA we used is relatively low-cost and easy way to fabricate antibacterial material in wet chemistry without plasma instrument. The QAS-g-PMMA was done by only using acid modified PMMA surface and QAS treated to form grafted antibacterial material.
Subjects
QAS
PEG
surface modification
surface analysis
antibacterial ability
SDGs
Type
thesis
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