Comportement rhéologique de biomatériaux pour l’ingénierie ostéoarticulaire et dentaire : matrices extracellulaires synthétiques et suspensions phosphocalciques

Abstract

Injectable biomaterials are a particular field of biomaterials used for noninvasive surgical techniques (e.g. percutaneous surgery). The fundamental characteristic of this type of biomaterials is their rheological properties during implantation. In this context, the subject of this research work was to evaluate the rheological properties of two injectable biomaterials used in osteoarticular and dental tissue engineering: (i) a synthetic extracellular matrix and (ii) an injectable calcium phosphate suspension. The rheological properties of silated hydroxypropylmethylcellulose hydrogel were studied. It is shown that although silanization reduces the hydrodynamic volume in dilute solution, it does not affect significantly the rheological behavior of the concentrated solutions. In dilute solution, intrinsic viscosity of different HPMC-Si solutions before steam sterilization indicated that macromolecular chains occupied larger hydrodynamic volume compared to the sterilized HPMC-Si solutions. For the sterilized HPMC-Si concentrated solutions, the limiting viscosities decreased when the pH increased. This change, remarked in dilute and concentrated domain has been attributed to the formation of both intra- and intermolecular associations during the phase separation process of HPMC-Si during steam sterilization. The formation of HPMC-Si hydrogels from injectable aqueous solution was studied after neutralization. The study of the gelation process revealed the dependence of the final concentration of HPMC-Si hydrogel, pH and temperature on cross-linking kinetics and viscoelastic properties. An injectable calcium phosphate ceramic suspension was studied. This “ready-to-use” injectable bone substitute is consisting of an aqueous HPMC solution as matrix and calcium phosphate particles as fillers. The rheological characterization revealed the macromolecular behavior of the HPMC. The investigations of settling kinetics showed the dependence of the particle size and the HPMC concentration on the settling velocity and sediment compactness before and after sterilization. The rheological properties and injectability of this suspension were also studied. The suspensions showed a strongly increased viscosity as compared to the HPMC solution. The rheological proprieties of suspensions depend on the composition. A simple device has been used to characterize extrusion of the paste using a disposable syringe fitted with a needle. The injectability modeling was realized. A theoretical approach based on the capillary flow of non newtonian fluids was used to predict the necessary pressure for injection, on the basis of rheological properties and extrusion conditions. The theoretical estimation of the extrusion pressure showed a wall slip in the suspensions, so that the injection pressure is less than anticipated. The influence of wall slip leads, however, to a constant proportionality factor between theory and injection experiments.