Dual setting [alpha]-tricalcium phosphate cements

An extension of the application of calcium phosphate cements (CPC) to load-bearing defects, e.g. in vertebroplasty, would require less brittle cements with an increased fracture toughness. Here we report the modification of CPC made of alpha-tricalcium phosphate ([alpha]-TCP) with 2-hydroxyethylmethacrylate (HEMA), which is polymerised during setting to obtain a mechanically stable polymer-ceramic composite with interpenetrating organic and inorganic networks. The cement liquid was modified by the addition of 30â[euro]"70Â % HEMA and ammoniumpersulfate/tetramethylethylendiamine as initiator. Modification of [alpha]-TCP cement paste with HEMA decreased the setting time from 14Â min to 3â[euro]"8Â min depending on the initiator concentration. The 4-point bending strength was increased from 9Â MPa to more than 14Â MPa when using 50Â % HEMA, while the bending modulus decreased from 18 GPa to approx. 4 GPa. The addition of â[per thousand]¥50Â % HEMA reduced the brittle fracture behaviour of the cements and resulted in an increase of the work of fracture by more than an order of magnitude. X-ray diffraction analyses revealed that the degree of transformation of [alpha]-TCP to calcium deficient hydroxyapatite was lower for polymer modified cements (82Â % for polymer free cement and 55Â % for 70Â % HEMA) after 24Â h setting, while the polymerisation of HEMA in the cement liquid was quantitative according to FT-IR spectroscopy. This work demonstrated the feasibility of producing fracture resistant dual-setting calcium phosphate cements by adding water soluble polymerisable monomers to the liquid cement phase, which may be suitable for an application in load-bearing bone defects.[PUBLICATION ABSTRACT]