Ismail, NAB; (2014) Development of novel remineralising antimicrobial brushite cements. Doctoral thesis , UCL (University College London).

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Abstract

Brushite cements have potential as drug carriers and bone filling materials. They can also act as a reservoir for calcium and phosphate ions in remineralisation of hard tissues. Aim and objectives: To optimize brushite cement properties and assess the effect of incorporation of a novel antimicrobial ε-polylysine (PLS) into brushite. Materials and Methods: Powders were mixed with aqueous solutions at a powder to liquid ratio of 3.3:1 or 4:1 to produce cement pastes and start the setting reaction. The powder consisted of 1g of monocalcium phosphate monohydrate (MCPM) and 1.23 g of β -tricalcium phosphate (β-TCP). Two different types of MCPM and different β-TCP particle size range from 4 micron to 34 micron were used. The liquid phase was prepared by dissolving PLS powder in aqueous citric acid 800 mM in incrementally percentages. In control formulations, only citric acid 800 without the PLS was employed. Biaxial flexural strength and modulus were determined using a ball on ring jig. Setting kinetics and chemistry were examined using Fourier transforms infrared spectroscopy (FTIR). Microstructure of brushite cements were examined with scanning electron microscopy (SEM). Results: The largest particle size of â-TCP (34 micron) produced the highest flexural strength of 30 MPa. The handling of brushite cements was better with MCPM 2 (Sigma). This was observed to have much larger flat crystals rather than the more powdered MCPM 1 from Himed. Powder to liquid ratio 4:1 overall increased the strength 5 MPa – 7 MPa compared to powder to liquid ratio 3.3:1. High levels of PLS could be added with only a minor reduction in the strength. Setting time however was delayed and an alternative anhydrous dicalcium phosphate complex formed rather than all brushite which is hydrated dicalcium phosphate. Conclusion: The findings of this research demonstrated that very high levels of PLS could be introduced into brushite cements without serious detrimental effects on mechanical properties. PLS however, did delay the setting time and altered the final chemistry and microstructure of the dicalcium phosphate product.

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