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Table 3.2 Particle size analysis of each glass composition.
D10 D50 D90 Mean
Control 6.3 8.4 16.8 10.4
CuG6 6.4 8.5 16.9 10.7
CuG12 6.3 8.2 15.9 10.1
The mean surface area of each glass composition was also determined using Advanced Surface Area and Porosity (ASAP). Table 3.3 presents the BET surface area measurements which were found to be similar for each glass at 0.32 m2/g for the Control, 0.88 m2/g for CuG6 and 0.64 m2/g for CuG12.
Table 3.3 BET surface area (m2/g) for each glass composition.
Surface Area (m2/g) S.D.
Control 0.32 0.0096
CuG6 0.88 0.0093
CuG12 0.64 0.0097
The thermal profiles of each glass composition were analyzed using Differential Thermal Analysis (DTA) to determine any differences in the thermal transition point as a function of CuO concentration. The resulting thermograms are presented in Figure 3.3. The thermal profile of Control presented in Figure 3.3 shows the glass transition temperature (Tg) at 661°C and the first primary crystallization temperature (Tc1) evident at a temperature of 856°C. Addition of 6mol% CuO (CuG6) increased the Tg to 773°C and also increased crystallization temperature to 1047°C. By further increasing the CuO concentration to 12 mol% (CuG12), the Tg of the glass increased to 786°C and also increased Tc1 to 994°C.
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Figure 3.3 DTA thermograms Control, CuG6, and CuG12 powdered glass samples.
The morphology and elemental composition of the glass particles were analyzed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) and the results are presented in Figure 3.4. SEM imaging of the Control, CuG6, and CuG12 glass powders present a distribution of glass particulates consisting of large glass particulates measuring approximately <50µm in diameter with a much higher concentration of smaller agglomerated fine particles <10µm. EDX was used to determine the elemental composition of each composition. Regarding the Control glass, the base glass constituents were detected, Si, Zn, Ca, Sr, P and O. Both Cu containing glasses (CuG6, CuG12) were found to have each element present in the base Control glass in addition to Cu.
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Figure 3.4 Energy-dispersive X-ray (EDX) and Scanning Electron Microscopy (SEM) of Control, CuG6, and CuG12 powdered glass samples.
To further confirm the composition of the glass samples and to investigate the structure of the glass, X-ray Photoelecton Spectroscopy (XPS) was employed. Figure 3.5 present the XPS survey scans of Control and CuG12 glass (CuG6 not presented). The Control glass was found to contain zinc, calcium, strontium, silicon and phosphorus in addition to oxygen. No contamination was found for any of the glass compositions.
Addition of CuO resulted in the presence of Cu2p peaks (Cu 2p1, Cu 2p3) for CuG6, and CuG12 glasses. Additionally, the high-resolution oxygen signal was further analyzed to determine the effect that the addition of CuO has on the structure of the oxygen bonds. It is evident in Figure 3.5 that the binding energy of Control was centred at 531.5eV however
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the addition of CuO shifts the binding energy of CuG6 to 533.9eV and the binding energy of CuG12 to 534.3eV.
Figure 3.5 (a) X-ray photoelectron spectroscopy (XPS) survey scans of Control and CuG12 and (b) high-resolution O1s scans of Control, CuG6, and CuG12.
29Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) was performed on the Control and CuG12 glasses. MAS-NMR was employed to determine the effect that the addition of CuO has on the connectivity of the glass structure, in particular the bonding of Si to O. Figure 3.6 presents the 29Si MAS-NMR spectra for Control glass in addition to the relative fraction of Q species. The 29Si MAS-NMR spectrum of Control presents asymmetrical peak centred at -81 ppm. The corresponding distribution of different Q species are presented in Figure 3.6 a. The relative fraction of Q-species was determined within the spectral region of -40 to-120 ppm where the Q-species are centred at -47 ppm for Q0, -65 ppm for Q1, -79 ppm for Q2, -91 ppm for Q3 and -112 ppm for Q4. The percentage of Q-species present in the Control glass includes approximately 5% Q0, 8%
Q1, 57% Q2, 28% Q3 and 2% Q4. The 29Si MAS-NMR spectrum for CuG12 is presented in Figure 3.7. It is evident from Figure 3.7 that for CuG12 a higher degree of asymmetry exists around the region of -110 ppm compared to the Control glass. The 29Si MAS-NMR spectrum of CuG12 composed of Q-species are centred at -55 ppm for Q0, -76 ppm for Q1,
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-85 ppm for Q2, -95 ppm for Q3 and -112 ppm for Q4. The relative fraction of Q-speciation for CuG12 presented in Figure 3.7 presents 2% Q0, 24% Q1, 25% Q2, 36% Q3 and 13% Q4.
Figure 3.6 (a) 29Si MAS-NMR spectrum of Control glass, and (b) corresponding Q-species.
Figure 3.7 (a) 29Si MAS-NMR spectrum of CuG12 glass, and (b) corresponding Q- species.
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Ion release profiles were determined for each component of the glass including Si, Zn, Ca, and Sr, however, no ion release was detected for Cu or P. Each glass powder was incubated in de-ionized water for 1, 10, 100 and 1000 hours, and the ion release profiles of liquid glass extracts presented in Figure 3.8. Regarding Si release, presented in Figure 3.8a, the level of Si release from the Control was found to increase from 18-31mg/L after incubating over 1-1000 hours. CuG6 was also found to increase with respect to time and experienced similar release levels from 20-30mg/L. CuG12 presented slightly lower final Si levels after 1000 hours, which ranged from 20-25mg/L. Zn release was relatively low for each of the glasses and was below 3mg/L for each glass tested at each time period. Ion release profiles for Ca and Sr are presented in Figure 3.8c-d. with respect to Ca release, similar profiles were evident for Control, CuG6 and CuG12, where Control ranged from 13-16mg/L, CuG6 ranged from 13-15mg/L and CuG12 also ranged from 13-15mg/L with each glass exhibiting an increase with respect to incubation time. Sr release is presented in Figure 3.8c. Sr release was also found to increase with respect to incubation time for each glass composition. Control Sr release ranged from 2-8 mg/L, CuG6 ranged from 1-7 mg/L and CuG12 ranged from 2-10mg/L, with the maximum Sr release being evident after 1000 hours incubation.
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Figure 3.8 Ion release profiles of Control, CuG6, and CuG12, investigating (a) silica, (b) zinc, (c) calcium, and (d) strontium release after 1, 10, 100 and 1000 hours incubation in deionized water.
In addition to analyzing ion release profiles, the pH of the incubated liquid extracts was recorded over the same incubation periods and the results are presented in Figure 3.9.
The Control glass presented a pH of 9.6 after 1-hour incubation and remained consistent to 100 hours, but then reduced to 8.3. CuG6 presented a similar profile where the pH remained consisted at 9.2-9.4 over 1-100 hours, and then reduced to 7.7. CuG12 exhibited a trend where the pH ranged from 9.2-9.4 over 1-100 hours and subsequently reduced to 7.7.
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Figure 3.9 pH of extracts from samples release after 1, 10, 100 and 1000 hours incubation in deionized water
GPCs were formulated with 40, 50 and 60wt% PAA concentrations for the rheological and mechanical property evaluation. GPCs were labelled with their corresponding glass compositions as ConC, Cu6C, and Cu12C, attributed to glass compositions of Control, CuG6, and CuG12, respectively. The working (Tw) and setting (Ts) times of the GPCs were conducted according to ISO9917 and the results are presented in Figure 3.10 and also in Table 3.4.
Table 3.4 Working (Tw) and Setting (Ts) times of ConC, Cu6C and Cu12C formulated with 40, 50 and 60wt% PAA.
Working Times (min,sec) Setting Times (min,sec) ConC Cu6C Cu12C ConC Cu6C Cu12C 40wt% PAA 1m, 58s 1m, 38s 1m, 10s 10m, 16s 7m, 45s 6m, 04s 50wt% PAA 1m, 40s 1m, 11s 1m, 00s 16m, 15s 14m, 10s 8m, 35s 60wt% PAA 1m, 07s 1m, 01s 0m 54s 18m, 05s 24m, 45s 11m, 07s
From Figure 3.10 it is evident that the Tw of the GPCs were found to decrease as the PAA concentration increased. The Tw of ConC reduced from 1m, 58s to 1m, 07s as the PAA concentration increased from 40-60wt% PAA. The Cu6C experienced a similar trend
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where Tw reduced from 1m, 38s to 1m, 01s and Cu12C also reduced from 1m, 10s – 0m, 54s as the PAA concentration increased from 40-60wt%. The Ts of the GPCs are presented in Figure 3.10 and Table 3.4. Conversely, the Ts were found to increase as the PAA concentration increase from 40-60wt%. Regarding the ConC, the Ts increased from 10m,16s to 18m, 05s. The Cu-GPCs experienced shorter Ts, however a similar trend is evident. The Ts of Cu6C increased from 7m, 45s to 24m, 45s and Cu12C increased from 6m, 04s to 11m, 07s.
Figure 3.10 (a) Working times and (b) setting times of ConC, Cu6C and Cu12C mixed with 40, 50 and 60 wt% PAA.
Mechanical testing was conducted on each cement formulation, specifically compressive and shear bond strength testing. Compressive testing was conducted after 7 days immersion in deionized water considering 40wt%, 50wt% and 60wt% PAA and the results are presented in Figure 3.11. It is evident from Figure 3.11 that the concentration of PAA did not have a significant effect on the compressive strength of the GPCs. The highest compressive strength was attributed to the ConC with 50% PAA with a strength of 35 MPa, and the lowest strength was found to be Cu12C with 40wt% PAA at 18 MPa. Additionally, a shear bond strength test was conducted to determine the GPCs ability to adhere to hydroxyapatite (Hap). The shear bond strength was measured after 24-hours incubation in water and the results are presented in Figure 3.12. Cements were formulated with 40wt%
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PAA and attained bond strengths of 0.85 MPa, 1.32 MPa and 0.79 MPa for ConC, Cu6C and Cu12C respectively.
Figure 3.11 Compressive strength of GPC series using 40wt%, 50wt% and 60wt%
PAA after 7 days soaking in de-ionized water.
Figure 3.12 Shear bond strength of ConC, Cu6C and Cu12C in addition to SEM imaging of fracture surfaces.
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Antibacterial testing was conducted employing a range of bacteria including E. coli, S. epidermidis, S. aureus (UMAS-1) and Vancomycin Resistant S. aureus (VRSA). Agar diffusion testing was conducted using GPCs formulated with 40wt% PAA and the results are presented in Figure 3.13 and Figure 3.14. From Figure 3.13a, it can be observed that the Cu-GPC presented higher inhibition zones in E. coli than the ConC. The ConC presented an inhibition zone of 1.7mm which Cu6C and Cu12C presented inhibition zones of 3.2mm and 3.8mm, respectively. Testing in S. epidermidis is presented in Figure 3.13b which presented the highest inhibition zones of any bacteria tested. The ConC did not present any inhibition, however, Cu6C and Cu12C GPCs presented inhibition zones of 9.6mm and 7.5mm respectively. The GPCs were also tested in VRSA and the results are presented in Figure 3.13c. No inhibition was observed with the ConC while Cu6C and Cu12C presented inhibition zones of <1mm and 2.1mm respectively. Testing in S. aureus (UMAS-1) is presented in Figure 3.13d. No inhibition was observed for the ConC and inhibition zones were inconsistent for Cu6C and Cu12C (3.9mm).
Figure 3.13 Antibacterial testing of ConC, Cu6C and Cu12C in a.) E. coli, b.) S.
epidermidis, c.) Vancomycin Resistant S. aureus and d.) S. aureus (UMAS-1).
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Figure 3.14 Antibacterial testing plates presented in rows a.) E. coli, b.) S.
epidermidis, Vancomycin Resistant S. aureus and d.) S. aureus (UAMS-1) and columns with samples i.) ConC, ii.) Cu6C and iii.) Cu12C.
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