Investigation of an effervescent additive as porogenic agent for bone cement macroporosity

Calcium phosphate cements (CPCs) are biocompatible and osteoconductive materials used in dental, craniofacial and orthopaedic applications. One of the most important advantages of these materials is their replacement with bone followed by resorption. Already several attempts have been made to improve the resorption behaviour of calcium phosphate cements by increasing the porosity of the material. In this investigation a mixture of NaHCO(3) and citric acid monohydrate was added to the apatite cement component as an effervescent additive for producing interconnected macropores into the cement matrix. Mercury intrusion porosimetry was employed to determine pore volume and pore size distribution in the calcium phosphate cement (CPC) samples. Results showed that addition of only 10 wt % of the effervescent additive (based on the cement powder) to the CPC components lead to producing about 20 V % macropores (with the size of 10 to 1000 mum) into the cement structure. The setting time was measured in an incubator at 37 degrees C and decreased from 40 min for additive-free CPC to about 14 min for CPC containing effervescent additive. Other properties of the CPCs such as compressive strength, phase composition, microstructure morphology and dissolution behavior were evaluated after immersing them in a simulated body fluid solution. The results showed that the rate of formation of poor crystalline apatite phase have been improved by production of macroporosity into the cement matrix.