| Abstract(Please copy/paste the abstract send to the congress) : |
THE NOVEL BIOACTIVE GLASS COATINGS FOR BONE TISSUE ENGNEERING: AN IN VITRO STUDY
Introduction:
Metallic prostheses are widely used to treat joint and skeletal injuries and disease. However, metal alloy implants can sometimes fail due to complications of fibrous encapsulation and poor stress transfer between the bone and the implant. Bioactive glass (BG) coatings may promote the formation of a strong bond with living bone tissue thus decreasing the likelihood of fibrous encapsulation and have the added benefit that their dissolution ions stimulate cell activity [1,2]. Strontium (Sr) ranelate, a drug used to treat and prevent osteoporosis, works via the action of Sr ions which stimulate the formation of new bone and prevent osteoclast-mediated resorption [3]. We have previously shown that Sr-substituted BGs promote osteoblast activity in vitro [4] and explored the effect of altering phosphate content on the material structure of soda-lime-phosphosilicate glasses [5]. The effect of increasing phosphate content in Sr-substituted BG on cultured osteoblasts, however, remains unexplored. Here, we created Sr-substituted BG coatings with a range of phosphate contents and thermal expansion coefficients that matched that of Ti alloy, producing materials that combine the bone remodelling benefits of Sr and BG with phosphate to mediate pH changes which can affect cell viability. In the study presented here we report the characterisation of these multicomponent BG coatings in terms of their bioactivity and interaction with cells.
Materials and Methods:
Bioactive glasses in the system SiO2-MgO-Na2O-K2O-ZnO-P2O5-CaO in which 10% of the Ca was replaced by Sr and the P2O5 content was increased from 1.07 to 6.42 mol% were produced by a melt quench route. Sufficient cations were added to ensure charge neutrality in the PO43- complex formed. Simulated body fluid (SBF) was prepared according to Kokubo [6]. Glass particles (<38 micrometer) were immersed for up to 28 days and agitated at 60 rpm at 37°C. At indicated time points samples were filtered and dried for X-Ray Diffraction (XRD) analysis.
Culture media containing ions from glasses were created by incubating 1.5g/L of glass powder (<38 micrometer) in RPMI 1640 on a roller for 4 hours at 37°C and then passed through a 0.2 micrometer filter. This media was then supplemented with 10% (v/v) foetal bovine serum (FBS), 2mM L-glutamine and 1% (v/v) penicillin/streptomycin. The human osteosarcoma cell line, Saos-2, was seeded at 30,000 cells/cm2 in conditioned medium and cultured for up to 28 days. On days 1, 14, 21 and 28 cell metabolic activity was measured using the tetrazole MTT as an indicator of cell proliferation. Glasses were coated on the surface of
Ti6AL4V coupons with an enameling technique. 10,000 Saos-2/cm2 were seeded on BG coatings and viability was assessed after 1, 7 and 14 days with a LIVE/DEAD stain. Some glass coatings cultures were also fixed, gold coated and viewed on a Leo 1525 Gemini SEM.
Results and Discussion:
BG with high P2O5 content forms more apatite after immersion in SBF for 4 weeks than BG with low P2O5 content, as examined by XRD. MTT activity in Saos-2 cells treated with dissolution ions from BG increased in all samples with time in culture. MTT activity was also significantly greater (p<0.01) in cells treated with dissolution ions from 4.28 and 6.24 mol% P2O5 BGs as compared to controls at day 28. LIVE/DEAD staining indicated that all coating materials were not cytotoxic. SEM imaging demonstrated that the BG coating encouraged cell attachment and that cells spread well over the surface.
Conclusion:
With increasing P2O5 content in the series of Sr-substituted BG, Bragg peaks in XRD traces associated with apatite crystallisation increase suggesting the glass becomes more bioactive. Apatite formation on the coating surface is an essential factor for bone bonding as the more apatite that forms on the glass coating the more bone bonding will be expected. Adding P2O5 to the glass composition in a controlled range prevents extreme pH rises, which can affect cell viability and proliferation.
References:
[1] Hench LL et al. J. Inorg Mater 2002;17:897–909
[2] Jell, G, Stevens MM, J Mater Sci Mater Med, 2006. 17(11): 997
[3] Hamdy NA, Rheumatology, 2009; 48(4): 9
[4] Gentleman E, Fredholm YC, Jell G, Lotfibakhshaiesh N, O'Donnell MD, Hill RG, Stevens MM. , Biomaterials, 2010; 31(14): 3949
[5] O’Donnell MD et al., J Mater Sci Mater Med, 2009. 20:1611
[6] Kokubo T et al., Biomaterials, 2006; 27:2907–15 |