Thermal stability and sintering of C x Si y HA ceramics for bone tissue engineering application

One of the most important components of the bone tissue engineering is the scaffold on which the new tissue can grow. It has to provide the mechanical stability of the construct and a template for the three-dimensional new extracellular matrix organization. As the stiffness of scaffold as well as regenerated tissue has to match the stiffness of the native bone, scaffolds for bone engineering often contain calcium phosphates bioceramic. Among them, hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) is commonly used as bone substitute due to its chemical and crystallographic similarities with bone mineral part, in spite of its non-adequate resorption rate. The apatitic lattice of HA is very tolerant with substitutions. Unfortunately, HA shows limited ability to stimulate the development of new bone tissue (bone apposition) and has a very low rate of biodegradation (slow osseointegration). One way to modulate bioactivity of synthetic HA is to incorporate ionic groups in its structure. Thus, carbonate improves resorption of HA closed to natural bone; and the soluble silicon (e.g. silicate ions) stimulates bone cells activity. This work is focused on the elaboration of macroporous bioceramics of a co-substituted hydroxyapatite with a controlled amount of carbonate (x) and silicate groups (y) (C x Si y HA) for bone tissue engineering application. The work consisted first in the synthesis of C x Si y HA powders, followed by the scaffolds shaping by means of a replication process of PMMA skeleton. Finally, the green were debinded sintered and accurately characterized. C x Si y HA powders, of assumed composition Ca 10-x+y (PO 4 ) 6-y-x (SiO 4 ) y (CO 3 ) x (OH) 2-x+y with x>y and x+y 2 atmosphere. The physico-chemical properties of scaffolds were evaluated by infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Their morphology and topography were examined through Scanning Electron Microscopy (SEM) and X-ray microtomography. Finally, solubility constants were determined according to standard procedures.