Development and characterization of Cold-Sprayed non-doped and silver doped carbonated biomimetic nanocrystalline apatites: application to TA6V medical implants

摘要

Introduction: Plasma-sprayed hydroxyapatite (HA) coatings are considered as industrial standards in the field of the orthopaedic implants. However, according to literature, a decomposition of HA due to the high temperature of the process could limit the long term service life of implants. And although they are supposed to mimic bone calcium phosphates, HA coatings have a different chemical composition and different crystallographic features. Moreover, nosocomial infections can appear few days or months after surgery. In this study, we propose some solutions to reduce those two limitations listed before. An industrial and relatively low thermal spray process was investigated in order to obtain bone like apatite coatings onto TA6V samples: the Cold Spray (CS). In this process, the particles are not melted, thereby, the initial characteristics of the particles can be maintained. Materials and Methods: A carbonated biomimetic nanocrystalline apatite powder (BNAc) and a silver doped carbonated biomimetic nanocrystalline apatite powder (AgBNAc) were produced through a biomimetic-like approach. In order to retain the physico-chemical properties of these materials, the Cold Spray technique was implemented. After optimization of the process parameters, coatings were obtained and were characterized by several methods such as SEM, XRD, Raman, FTIR to be compared with the starting powders. Mechanical and biological tests were also realized on the coatings. Results and Discussion: BNAc and AgBNAc coatings were obtained by Cold Spray, for the first time. They revealed an excellent physico-chemical agreement to the starting powders and the mineral bone, in contrast to HA: the observations made by FTIR reveal some slight modifications on the composition of the apatitic domains of the nanocrystals (Figure 1). figure 1: FTIR spectrum for HA powder (HA), Bone, BNAc powder, BNAc coating, AgBNAc powder and AgBNAc coating A preliminary biological test was performed on the BNAc and AgBNAc coatings. After 9 days of incubation with stem cells, coatings were observed by SEM. The cells appear to be spread on the rough surface of the coatings, proving the biocompatibility of the coatings. Stem Cell growth was observed across all samples, in particular in the presence of BNAc and AgBNAc promoted the uptake of calcium in the cells as displayed in stem cells undergoing osteodifferentiation. This is result is confirmed by Alizarin stain light microscopy, in which the cells appear stained orange with in increasing level of deposited calcium (Figure 2). figure 2; Alizarin strain observations BNAc coating, AgBNAc coating and HA coating Mechanical tests were also realized: the adhesion strength of the apatitic cold sprayed coatings was measured and revealed a good adhesion confirming the interest of the Cold Spray process for medical applications (Figure 3). figure 3: Microtensile test BNAc coating, AgBNAc coating and HA coating. Conclusions: Cold Spray process can produce biomimetic coatings which have the potential to improve the integration of implants and are expected to reduce the nosocomial infections when using silver doped materials.