Effect of process parameters on the characteristics of porous calcium phosphate ceramics for bone tissue scaffolds

Porous hydroxyapatite (HA) has already been widely used as a bone substitute due to its similarity with the mineral part of the bone. In this work, cylindrical tablets with micro and macro porosity were produced from stoichiometric and deficient hydroxyapatites by using naphthalene as porosifier agent. The influence of the processing parameters such as Ca/P ratio of start material, calcination temperature, and naphthalene content on the characteristics of porous calcium phosphate tablets was evaluated. Three mineral phases-HA, alpha-TCP (alpha tri-calcium phosphate), and beta-TCP (beta tricalcium phos-phate)-with variable contents were identified by x-ray diffraction (XRD) and Fourier-transformed infrared spectroscopy (FT-IR). Image analysis and density measurements were used to characterize sample porosity. As expected, the total porosity of the calcinated material is not dependent on the stoichiometry of the precursor hydroxyapatite. For calcium-deficient hydroxyapatite, the increase in naphthalene content contributes to stabilize alpha-TCP phase, altering the relative phases content.

[Cellular culture of osteoblasts and fibroblasts on porous calcium-phosphate bone substitutes]

PURPOSE OF THE STUDY

Calcium phosphate ceramics are synthetic bone substitutes able to fill in bone destruction as a support of the bone growth. This work consisted in an in vitro assessment of osteoblasts and fibroblasts cultures on macroporous calcium-phosphate bone substitutes to analyze the interaction between cells and bone substitute.

MATERIALS AND METHODS

The macroporous ceramic was composed of 70% hydroxyapatite and 30% tri-calcium phosphate with known mechanical and physico-chemical properties. Three compounds were processed with different size of macropore and with or without microporosity on their surface. Cells were seeded on discs measuring 10 mm in diameter and 2 mm in thickness. Cellular viability was evaluated by the MTT test for every stage of observation. An histological study to observe the invasion in the depth of discs was performed. Scanning electron microscopy was used to analyze the cellular comportment in contact with the surface of substitutes.

RESULTS

An exponential cellular growth was effective on each substitute with the two cellular types. Cells spread on the surface of the compounds covering macropores and colonized the depth of the discs. A size of macropore of 300 microm or more seemed to support this invasion. 15 microm sized interconnections appeared to be effective to allow cell migration between macropores. The cell proliferation was similar on substitutes with or without microporosity.

CONCLUSION

Biomaterials currently used as bone substitute are more or less osteoconductive but they have no osteoinductive property. A hybrid association of calcium-phosphate ceramic with osteogenic cells should promote the development of a calcium phosphate compound with osteoinductive capacity.

[Tibial valgus osteotomy using a tricalcium phosphate medial wedge: a minimally invasive technique]

PURPOSE OF THE STUDY

We present a minimally invasive technique for tibial valgus osteotomy using a medial wedge composed of tricalcium phosphate.

MATERIAL AND METHODS

The bone substitute is composed of slowly resorbable tricalcium phosphate material shaped to the desired form and having mechanical properties allowing stable osteotomy via a short incision and staple fixation. Intraoperative fluoroscopy enables a reliable and reproducible technique. A lateral fixation staple is required because there is a risk the lateral hinge could break. This technique was used for 58 knees in 55 patients (mean age 47 years). According to the Ahlback classification of femorotibial degeneration, there were 43 grade I knees, 12 grade II, and 3 grade III.

RESULTS

The implant was well tolerated in all cases. Bone healing was achieved in most cases without loss of the osteotomy angle. Complications were: rupture of the lateral hinge in four cases leading to nonunion in one, one low-grade infection. Implant resorption at mid term was significant: among the 22 patients with a follow-up of more than 5 years, the implant was barely visible in 18.

DISCUSSION

This technique provides an easy way to achieve tibial valgus osteotomy without compromising future intervention. The technique can be considered to be minimally invasive because of the size of the incision, the minimal fixation required, and the bone sparing effect of the bone substitute.

The properties of tablets manufactured on an automatically-controlled rotary machine

Four direct-compression bases: Celutab in the hydrous and the anhydrous form, Emcompress Special, and spray-dried lactose, have been compared with a traditional lactose granulation with respect to initial physical properties of the powder, tabletting performance and the characteristics of the tablets produced. The tablets were made on an instrumented rotary machine with feedback weight control operating to minimize time-dependent change within a batch, compression force being continuously monitored. Tensile strength by diametral crushing, porosity, disintegration time and surface indentation hardness were assessed and correlated with changes in compaction force, machine speed and tablet thickness. All materials gave wellformed tablets with no evidence of capping between 90 and 350 MN m−2, and weight variation was small except for Emcompress Special at the highest machine speed, when die filling became erratic.