title: Injectability of a bone filler system based on hydroxyapatite microspheres and a vehicle with in situ gel-forming ability.
abstract: The aim of this study was to test the injectability of a bone filler system based on the combination of ceramic microspheres with a gel-like vehicle, for noninvasive surgery. Porous hydroxyapatite microspheres with a uniform size and an average diameter of 535 +/- 38 mum were prepared, and their compression strength and friability were tested. The sodium-alginate solution with a concentration of 7.25% (w/v) was used as the vehicle. To promote its in situ gelation, calcium carbonate and D-gluconic-delta-lactone were added to the solution. Microspheres were mixed with the vehicle at different percentages (20-40 wt %). Gelation times in the range of 8-20 min, were obtained, depending on the formulation. Mixtures of HAp microspheres with alginate solution at 7.25% originating a gel in 11 min present an adequate handling time to perform an injection. Their injectability was evaluated using an injection device commonly employed in vertebroplasty surgical procedures, coupled to a texturometer in compression mode. Using an extrusion rate of 0.1 mm/s, the force required to extrude any of the mixtures tested was lower than 100 N. For an extrusion rate of 1 mm/s mixtures with 40 wt % of microspheres were very difficult to inject. Mixtures with 35 wt % of microspheres presented the best compromise between injectability and compression strength of the gelled system. MicroCT analysis revealed a homogeneous distribution of the microspheres inside the vehicle, as well as full interconnection of the intra-microspheres spaces. The compression strength for the gelled systems ranged from 80 kPa (gel itself) to 600 kPa (composite with 40 wt % of microspheres).
authors.affiliation: Escola Superior de Tecnologia de Viseu (ESTV), Dep. de Eng. Mecânica e Gestão Industrial, 3504-510 Viseu, Portugal. serafim@ineb.up.pt
authors.forename: Serafim M
authors.initials: SM
authors.lastname: Oliveira
authors.forename: Cristina C
authors.initials: CC
authors.lastname: Barrias
authors.forename: Isabel F
authors.initials: IF
authors.lastname: Almeida
authors.forename: Paulo C
authors.initials: PC
authors.lastname: Costa
authors.forename: Maria R Pena
authors.initials: MR
authors.lastname: Ferreira
authors.forename: Maria F
authors.initials: MF
authors.lastname: Bahia
authors.forename: Mário A
authors.initials: MA
authors.lastname: Barbosa
mesh_terms: D018786:Bone Substitutes / Q000008:administration & dosage / Q000737:chemistry*; D019245:Compressive Strength; D017886:Durapatite; D005782:Gels / Q000138:chemical synthesis*; D008863:Microspheres; D010316:Particle Size
chemical_list: D018786:Bone Substitutes; D005782:Gels; D017886:Durapatite