Thermal Properties and In Vitro Dissolution of Bioactive Borosilicate Glasses
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: Bioaktiivisten borosilikaattilasien termiset ominaisuudet ja liukeneminen
Tissue engineering and biodegradable implants were developed to avoid problems caused by long-term use of non-metabolizing implants. Tissue engineering aspires to produce new tissues by using the patient’s own cells. Commonly, a porous three-dimensional (3D) scaffold is used as a supporting structure until enough new tissue has grown. Typical bioactive silicate glasses have many good qualities, such as their ability to bond to bone by forming a hydroxycarbonate apatite (HCA) layer, but due to their tendency to crystallize during sintering and excessively long dissolution time, more suit-able scaffold materials need to be developed. Borosilicate glasses based on commercial silicate glass S53P4 have emerged as a new and promising scaffold material due to their higher bioactivity and dissolution rate and better resistance to crystallization. In this thesis, three borosilicate glasses based on S53P4 were studied and compared with the S53P4 glass. The glasses’ thermal proper-ties, bioactivity and dissolution were studied with differential thermal analysis (DTA), dissolution tests, inductively coupled plasma optical emission spectrometry (ICP-OES) and Fourier transform infrared spectroscopy (FTIR) to evaluate which composition has the most promising properties to be used as a tissue engineering scaffold material. Of these, DTA was used to determine the glasses’ ability to be processed at high tempera-tures by determining their thermal processing window (∆T). Dissolution tests were con-ducted by immersing glass particle in simulated body fluid (SBF) and 2-amino-2-(hydroxymethyl)propane-1,3-diol (TRIS) solution for 6–168 h, and then measuring the pH of the solutions after each time point. From the obtained pH curves, dissolution rate and HCA layer formation were observed. Ion release of the glass particles was further studied with ICP-OES and structural changes in the glasses’ surface and precipitation of the HCA layer with increasing immersion time were studied with FTIR. Based on the results, borosilicate glasses dissolve quicker than S53P4 and they form a thicker and more crystallized HCA layer. B50 was the only borosilicate glass to have a wider ∆T than S53P4. Out of the three borosilicate glasses, B50 has the most promising properties concerning its use in tissue engineering as it has the widest ∆T, it dissolves the quickest and it forms the thickest and most crystallized HCA layer on its surface.