Ready to use, thermoresponsive and fast setting Calcium Phosphate Cements
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Materials that regenerate bone tissue have been developed during the last decades due to the increment of bone illnesses caused by the aging of word population. Recent works of the Biomaterials, Biomechanics and Tissue Engineering laboratory are focused on this field, especially on calcium phosphate cements used as an injectable pastes for bone grafting applications. The goal of this work was to develop a thermoresponsive injectable calcium phosphate cement (CPC) for bone regeneration using alpha-tricalcium phosphate (α-TCP) as solid phase. The novelty of this work lies in the use of a Poloxamer hydrogel as cement liquid phase. Poloxamers are amphiphilic triblock copolymers accepted by pharmacopoeias for drug delivery applications. Poloxamer hydrogels present the advantage to be rheologically thermoresponsive increasing their viscosity with temperature. This property provided the cement with an excellent injectability close to room temperature and excellent cohesion at physiological conditions. Emphasis was put in the optimisation of the components that have to be mixed and the way to mix them. Thanks to this work, the liquid to powder ratio, the weight percentage of Pluronic F127 on the liquid phase and the temperature of mixing and injecting have been optimised taking into account important parameters linked with its utilisation in a surgeon room as the cohesion of the paste, the setting times or the compressive strength of the cement. In order to control the temperature of the paste a water bath was created. It has been shown that the incorporation of Pluronic F127 in the liquid phase of the cement permitted to increase the viscosity of the paste and in consequence a non-desired phenomenon called “filter-pressing” was avoided. Moreover, cooling down the temperature, a bigger amount of powder could be mixed improving the mechanical resistance of the set cement. Although the high content of solid in the paste, the injection load of the cement could be minimalized by controlling the temperature of the paste. Therefore, the cement paste presented thermoresponsible properties. Finally, another aim during this project was to obtain a ready to use calcium phosphate cement requiring no manipulation from the surgeon before injection in the surgery room. Freezing the paste, cement could be stored at least during 49 days without any begin of reaction. After unfreezing the paste, same properties as for a non-frozen paste were observed, showing the total possibility of storing this kind of paste for a long time.
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