Frauke Stenzel

Development of Hydroxyapatite Ceramics with Tailored Pore Structure

The porosity of a hydroxyapatite ceramic was tailored by transfe rring polymeric pore models into ceramic forms via the slip casting technique. The rheolog ical properties of the hydroxyapatite slurries play an important role in facilitating t he casting operation. The optimised slurry with a solids content of 60 wt% hydroxyapatite had a slight s hear thickening flow behaviour and a low viscosity. Via impregnating of polymeric pore models and dip coating of pol ymeric foams ceramic green bodies were fabricated. After sintering at 1250 °C the polymer was burnt out and a porous ceramic was achieved. This porous ceramic could be reasonably handl ed and had a very high interconnecting porosity of 91 – 96 vol%. The pore size varied between 300 and 800 μm. The density value of the bulk hydroxyapatite ceramic covered the range bet w en 94 and 96 % th.d.. The characteristics of the porous ceramics could be varied between high and undirected porosity on the one hand, and lower porosity with defined pore channels in the three dimensiona l directions on the other hand. Introduction There is an increasing clinical requirement for bone graft mate rial, because there are many possible applications such as revision hip surgery, defect filling after e.g . a tumor surgery, or reconstructive orthopaedic surgery. As hydroxyapatite closely resembles the miner al phase of natural bone and is highly biocompatible, it is among other calcium phosphates widely used a s bone substitute material [1]. Synthetic hydroxyapatite can be reproducibly processed, and additionally, pr ovides no danger of infections. A large number of research activities has been dealing with the fabrication of synthetic hydroxyapatite ceramics [2, 3, 4, 5]. In this work the porosity of a hydroxyapatite ceramic was tailore d, so that the resulting bone substitute material is adapted to the requirements of the implanta tion site. The tailoring of the pore structure was carried out by using commercially available polyme ric foams and polymeric pore models, which were produced via rapid prototyping. These polymeric models w ere coated or impregnated with hydroxyapatite using the slip casting technique. This work is part of the research network ForTePro (Bayerische F orschungsstiftung, Germany), in which scientists of different research areas, particularly medical doctors, develop individually adapted implants for bone and cartilage defects, which will be cultivated with the pat ients own cells. Materials and Methods For producing the slurry the commercially available hydroxyapatite powder from Merck, Germany, was used. The specific surface area was characterised by the BET method (model Gemini 2370, micromeritics, Germany). The mean particle size d 50 was determined with a laser particle size analyser (model Granulomètre 850, Cilas Alcatel, France). The powder as slowly added to distilled water under constant stirring. The dispersant agent was a solution of a natrium salt of an acrylic acid copolymer. Additionally, a surfactant for improved wett ability and a binder were used. Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 977-980 doi:10.4028/www.scientific.net/KEM.254-256.977

Hydroxyapatite Ceramics with Tailored Pore Structure

The porosity of a hydroxyapatite ceramic was tailored by transferring polymeric pore models into ceramic forms via the slip casting technique. The rheological properties of the hydroxyapatite slurries play an important role in facilitating the casting operation. Aqueous hydroxyapatite slurries with a high solids content were fabricated. The optimised slurry with 60 wt% hydroxyapatite had a slight shear thickening flow behaviour and a low viscosity. The resulting porous ceramic could be reasonably handled and had a very high interconnecting porosity of 91 – 96 vol%. The pore size varied between 300 and 800 μm. The density value of the bulk hydroxyapatite ceramic covered the range between 94 and 96 % th.d.. The characteristics of the porous ceramics could be varied between high and undirected porosity and low porosity with defined pore channels in the three dimensional directions. Introduction There is an increasing clinical requirement for bone graft material, because there are many possible applications such as revision hip surgery, defect filling after e.g. a tumor surgery, or reconstructive orthopaedic surgery. As hydroxyapatite closely resembles the mineral phase of natural bone and is highly biocompatible, it is among other calcium phosphates widely used as bone substitute material [1]. Synthetic hydroxyapatite can be reproducibly processed, and additionally, provides no danger of infections. A large number of research activities has been dealing with the fabrication of synthetic hydroxyapatite ceramics [2, 3, 4, 5]. In this work the porosity of a hydroxyapatite ceramic was tailored, so that the resulting bone substitute material is adapted to the requirements of the implantation site. The tailoring of the pore structure was carried out by using commercially available polymeric foams and polymeric pore models, which were produced via rapid prototyping. These polymeric models were coated or impregnated with hydroxyapatite using the slip casting technique. This work is part of the research network ForTePro (Bayerische Forschungsstiftung, Germany), in which scientists of different research areas, particularly medical doctors, develop individually adapted implants for bone and cartilage defects, which will be cultivated with the patient’s own cells. Materials and Methods For producing the slurry the commercially available hydroxyapatite powder from Merck, Germany, was used. The specific surface area was characterised by the BET method (model Gemini 2370, micromeritics, Germany). The mean particle size d50 was determined with a laser particle size analyser (model Granulomètre 850, Cilas Alcatel, France). The powder was slowly added to distilled water under constant stirring. The dispersant agent was a solution of a natrium salt of an acrylic acid copolymer. Additionally, a surfactant for better wettability and a binder were used. The Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2047-2050 doi:10.4028/www.scientific.net/KEM.264-268.2047