Low temperature method for the production of calcium phosphate fillers

Abstract

Background: Calcium phosphate manufactured samples, prepared with hydroxyapatite, are used as either spacers or fillers in orthopedic surgery, but these implants have never been used under conditions of mechanical stress. Similar conditions also apply with cements. Many authors have postulated that cements are a useful substitute material when implanted in vivo. The aim of this research is to develop a low cristalline material similar to bone in porosity and cristallinity.

Methods: Commercial hydroxyapatite (HAp) and monetite (M) powders are mixed with water and compacted to produce cylindrical samples. The material is processed at a temperature of 37-120 degrees C in saturated steam to obtain samples that are osteoconductive. The samples are studied by X-ray powder diffraction (XRD), Vickers hardness test (HV), scanning electron microscopy (SEM), and porosity evaluation.

Results: The X-ray diffractions of powders from the samples show patterns typical of HAp and M powders. After thermal treatment, no new crystal phase is formed and no increase of the relative intensity of the peaks is obtained. Vicker hardness data do not show any relationship with treatment temperature. The total porosity decreases by 50-60% according to the specific thermal treatment. Scanning electron microscopy of the surfaces of the samples with either HAp 80%-M 20% (c) or Hap 50%-M 50% (f), show cohesion of the powder grains.

Conclusions: The dissolution-reprecipitation process is more intesive in manufactured samples (c) and (f), according to Vickers hardness data. The process occurs in a steam saturated environment between 37 degrees and 120 degrees C. (c) (f) manufactured samples show pore dimension distributions useful to cellular repopulation in living tissues.

Figure 1

X-ray diffraction patterns of powders; X-ray powder diffraction patterns of: a) commercial hydroxyapatite powder, b) commercial monetite powder, c) compact bovine bone powder.

Figure 2

Electron scanning micrographs of pure powders; Electron scanning micrographs of: a) commercial hydroxyapatite powder, b) commercial monetite powder.

Figure 3

Frequency distribution of particle dimension in powders; Frequency distribution of particle dimensions of: a) commercial hydroxyapatite powder, b) commercial monetite powder.

Figure 4

Calcium concentration and pH values of the several mixtures; a) Final calcium concentration in water of HAp, M and HAp/M mixtures measured within 72 hours from mixing, b) pH values of HAp, M and HAp/M mixtures measured within 72 hours from mixing.

Figure 5

X-ray diffraction pattern of specimen; X-ray powder diffraction patterns of untreated manufactured sample f.

Figure 6

X-ray powder diffraction patterns of specimens; X-ray powder diffraction patterns of samples treated at 120°C and produced with: a) hydroxyapatite (sample a), b) monetite (sample b), c) hydroxyapatite/monetite (sample f).

Figure 7

HV data of specimens; HV data of manufactured samples made with the mixtures described in table 1 at the several treatment temperatures.

Figure 8

Distribution of pore volume in percentage; Relative volume percentage distribution of pores in function of pore radiuses: a) sample f untreated, b) sample f treated at 60°C, c) sample of compact bovine bone.

Figure 9

Electron scanning micrographs of external surface of specimens; a) External surface by scanning electron micrographs of type c (table 1) manufactured sample. b) External surface by scanning electron micrographs of type f (table 1) manufactured sample.

Figure 10

Electron scanning micrographs of fracture surfaces of specimens; a) Fracture surface by scanning electron micrographs of type c (table 1) manufactured sample. b) Fracture surface by scanning electron micrographs of type f (table 1) manufactured sample.