Mechanical Properties of Poly(propylene fumarate) Reinforced Brushite Cement: Effects of Cement Composition and Powder to Liquid Ratio

Statement of Purpose: Calcium phosphate cements are prepared by mixing calcium phosphate powder with a liquid component to form a paste that hardens over time via a dissolution-precipitation reaction. Thus, in addition to being osteoconductive and resorbable, these biomaterials have the advantageous property of being injectable. This property can be leveraged for castingbased approaches to scaffold fabrication. While brittleness has previously limited the use of calcium phosphate cements as bone tissue engineering scaffolds, it is possible to reinforce these biomaterials by infiltrating them with a polymer and then cross-linking the polymer in situ. Our lab is interested in developing a poly(propylene fumarate) (PPF) reinforced brushite cement scaffold. PPF is an unsaturated polyester that has previously been used in bone tissue engineering. Brushite cement, on the other hand, is of interest because it has shown excellent resorbability and enhanced bone formation in vivo compared to hydroxyapatite cements. One variable that will affect the mechanical properties of the reinforced composite is the cement composition. Brushite cement is typically prepared by mixing monocalcium phosphate monohydrate (MCPM) and βtricalcium phosphate (β-TCP) with water, and the MCPM:β-TCP molar ratio is known to affect the mechanical properties as well as the acidity of the cement. The powder to liquid mass ratio (P/L) used during cement preparation is another important variable, as it controls the cement porosity, and consequently how much polymer can be incorporated into the cement. Thus, the objective of this study was to characterize the effects of these two variables on the mechanical properties of PPF reinforced brushite composites.