With his help, I was able to learn more about the field of biomaterials and gain experience with various laboratory equipment. I would also like to thank Timothy Keenan and Lana Placek for helping us prepare and run our samples, helping us make the simulated body fluid, and helping us reduce stress. I would like to thank Terry Guild for teaching me how to use the SDT 2960 simultaneous DSC-TGA to perform differential thermal analysis on my glasses as well.
I would also like to thank Gerry Wynick for running some samples on the Scanning Electron Microscope for me as well. Thanks to Emily Allan for working alongside me on our various sample preparation and analyses. Finally, I want to thank my family, friends and everyone else who helped along the way.
Structural analysis was performed using Differential Thermal Analysis (DTA), which produced a thermal profile of each glass. Also included in the study was whether or not the incorporation of Ga affects the formation of a calcium phosphate layer on the glass surfaces after immersion in simulated body fluid (SBF).
Introduction
Previous Studies
Methods
To obtain flat glass plates for SBF studies, powdered mixtures of analytical grade reagents were calcined (1500 °C, 1 h) in platinum crucibles and poured into graphite molds. These glass rods were then polished to produce flat surfaces and cut into equally sized rectangular plates.
Synthesis
X-Ray Diffraction
Sample Preparation
Differential Thermal Analysis (DTA)
Simulated Body Fluid
Figures 6, 8, 10 and 12 are SEM images and you can clearly see the crystal formations on each of the glass samples. SEM image of TGA-2 glass after 14 days of immersion in SBF at 1000x original magnification. TGa-2 decreased from 16.79 mass percent Ga after one day of immersion to 3.74 mass percent Ga after 14 days of immersion in SBF.
Partial dissolution of the surface of the glass particles results in the formation of a gel layer rich in silica gel and then the precipitation of a layer of calcium phosphate10. DTA was performed to determine the glass transition temperatures of each of the glasses. Glass transition temperature (Tg), crystallization temperature (Tc) and melting temperature (Tm) for each of the three glasses, all in °C.
Depending on the coordination states of Ga and other elements of the glass series under investigation, the release rate of ions can also be changed10. Consequently, laser profilometry scans must be different for each sample, based on coordination states due to the molar concentrations of the different elements in each glass. Together, SEM images and quantitative analysis were able to identify elements present on the surfaces of the glasses.
The quantitative analyzes from Tables V and VII show that the Si content for the TGa-1 glass decreased with longer immersion in SBF. The ability to form apatite on the surface allows the prediction of the in vivo bone bioactivity of the bioglass. Laser profilemetry images also proved that all glass surfaces had some surface roughness; however, no linear trend was found in the mean height of the.
Crystals had formed on the surface of each glass even after only one day of immersion in SBF. Precipitation and dissolution of glass surfaces are notable for their effects on bioactivity for this series of bioglasses. Finally, the surfaces of the glasses sample changed structurally due to the incorporation of Ga as well as the immersion time in SBF.
Besides these sample limitations, several other experiments can be performed, including: annealing samples of each glass 20°C above their glass transition temperatures (Tg), Atomic Force Microscopy (AFM), cross-polarization, elemental analysis of the ions released in the simulated body fluid, and solubility testing. One of the first experiments to be performed would be to anneal each glass 20°C above its respective Tg determined using Differential Thermal Analysis (DTA). This experiment would eliminate the polishing process because the surface of the glasses would already be smooth.
Annealing a few degrees above the glass transition temperature would not cause unnecessary stresses due to polishing the glass surface.
Scanning Electron Microscope (SEM), Electron Dispersive X-Ray
Laser Profilometry
Results and Discussion
Figures 6-13 and Tables V-VIII include SEM images, EDS spectra and quantitative analysis for the TGa-1 and TGa-2 glasses after one and 14 days of. The SEM and EDS results for the TGa-1 and TGa-2 glasses show that Ga concentration in each glass decreased with increasing time spent in the SBF. If Ga assumes a network-changing role, it will be released from the glass into the aqueous environment.
Tables V and VII show that the silicon (Si) concentration in the TGa-1 glass decreased from 12.78 to 11.71 wt% as a result of being immersed in SBF for 14 days instead of just one day. This trend was not seen in the TGa-2 glass, but the Si concentration could have increased if the glass samples were allowed to be immersed for a period of more than 14 days. Bioactive elements involved in network-forming roles can play a significant role, where their incorporation can further control the glass degradation rate and the ion exchange process10.
Figures 15-18 are sample surface roughness scans for the TGa-1 and TGa-2 samples after one and seven days of immersion. Quantitative analyzes from Tables VI and VIII highlight the decrease in Si concentration for TGa-2 the longer it was kept in SBF. AFM must be used on samples annealed above the glass transition temperature because the high resolution scans are extremely surface sensitive.
The quantitative analysis in Tables V-VIII can be used to compare the amount of each element in the glass after being immersed in the SBF for the respective number of days.
Powder Analyses
Glass Analyses
TGa-1 decreased from 6.49 mass percent Ga after one day of immersion to 1.06 mass percent Ga after 14 days of immersion. The reduction of Ga in TGa-2 was more noticeable, as this glass had double the Ga mole fraction of the TGa-1 glass. The reduction of Ga in glasses may be due to Ga acting as a lattice modifier10.
Nevertheless, the TGa-1 sample is more likely to be bioactive because the higher rate of silica dissolution further increases bioactivity10. As the concentration of Silica increases, equal molar concentrations of sodium oxide and calcium oxide are also found. Therefore, TGa-1 may be more bioactive due to the decrease in Si content and TGa-2 may be bioactive because it aids apatite formation.
DTA Results
This result is significant because an increase in Si concentration means that Silica concentration would have increased. This shift in Tg suggests increased glass stability that may have occurred due to bridging formation. If Ga takes on a network modifying role, it will be released into an aqueous environment, which may then provide a therapeutic benefit10.
Consequently, DTA results can be used to find the Tg for each glass as well as identify trends in Tg data as a result of glass composition.
Laser Profilometry Results
Conclusions
Overall, this study investigated how the surface of three bioactive glasses changed with the incorporation of more Ga at the expense of Zn. Since the dissolution of the glass depends on the coordination states of the ions and the release rate of these ions, it seems that the sample roughness should follow some trend for each individual sample.
Suggestions for Future Work
Similar to the AFM experiments, cross-polarization experiments should also be taken before and after SBF immersion. Cross polarization can be done on samples annealed at the Tg and above the Tg. Elemental analysis should also be used to determine which ions were released into the SBF after the glasses were immersed.
Adamson, "Antitumor Activity and Toxicity of Group IIIa Inorganic Metal Salts: Aluminum, Gallium, Indium, and Thallium." Patrick, et al., "Synthesis and characterization of bifunctional vanadyl curcumin, gallium, and indium complexes for medicinal applications," Journal of Inorganic Biochemistry. Malavasi, "Gallium-containing phosphorosilicate glasses: synthesis and in vitro bioactivity," Materials Science and Engineering C.
Annealing Above T g
Atomic Force Microscopy (AFM)
Cross Polarization
Elemental Analysis
Literature References
