The current limitations of calcium phosphate cements (CPCs) used in the field of bone regeneration consist of their brittleness, low injectability, disintegration in body fluids and low biodegradability. Moreover, no method is currently available to measure the setting time of CPCs in correlation with the evolution of the setting reaction. The study proposes that it is possible to improve and tune the properties of CPCs via the addition of a thermosensitive, biodegradable, thixotropic copolymer based on poly(lactic acid), poly(glycolic acid) and poly(ethylene glycol) (PLGA⁻PEG⁻PLGA) which undergoes gelation under physiological conditions. The setting times of alpha-tricalcium phosphate (α-TCP) mixed with aqueous solutions of PLGA⁻PEG⁻PLGA determined by means of time-sweep curves revealed a lag phase during the dissolution of the α-TCP particles. The magnitude of the storage modulus at lag phase depends on the liquid to powder ratio, the copolymer concentration and temperature. A sharp increase in the storage modulus was observed at the time of the precipitation of calcium deficient hydroxyapatite (CDHA) crystals, representing the loss of paste workability. The PLGA⁻PEG⁻PLGA copolymer demonstrates the desired pseudoplastic rheological behaviour with a small decrease in shear stress and the rapid recovery of the viscous state once the shear is removed, thus preventing CPC phase separation and providing good cohesion. Preliminary cytocompatibility tests performed on human mesenchymal stem cells proved the suitability of the novel copolymer/α-TCP for the purposes of mini-invasive surgery.

Biomaterials Biomechanics and Tissue Engineering Group Department of Materials Science and Metallurgical Engineering Universitat Politècnica de Catalunya 08019 Barcelona Spain

CEITEC ⁻ Brno University of Technology Purkynova 656 123 612 00 Brno Czech Republic

Department of Composites and Carbon Materials Institute of Rock Structure and Mechanics The Czech Academy of Sciences 5 Holesovickach 41 182 09 Prague Czech Republic

Department of Mechanics Biomechanics and Mechatronics Faculty of Mechanical Engineering Czech Technical University Prague Technicka 4 166 07 Prague Czech Republic

Lab of Tissue Engineering Institute of Experimental Medicine Czech Academy of Sciences Videnska 1083 14240 Prague Czech Republic

Trauma Surgery Department The University Hospital Brno Jihlavska 340 20 325 00 Brno Czech Republic

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