Papers by Author: Antoni P. Tomsia

Abstract: The development of novel biodegradable scaffolds for the treatment of bone and cartilage defects is the subject of intense research. A successful scaffold will guide cell-attachment, proliferation and tissue regeneration. The objective of this study is to use freeform fabrication (robocasting) for the preparation of porous hybrid organic/inorganic materials with a well controlled architecture and porosity. Polymer/hydroxyapatite (HA) pastes with ceramic contents ranging between 0 to 70 wt. % are prepared by mixing ceramic powders with a solution of the polymer in methylene chloride. Two different polymers are studied: polylactide (PLA) and polycaprolactone (PCL). During the compression tests, the scaffolds show an elasto-plastic behavior with large plastic yielding and do not fail in a brittle manner. The mechanical response is anisotropic and depends significantly on the ceramic content and the type of polymer.

Abstract: Despite extensive efforts in the development of fabrication methods to prepare porous ceramic scaffolds for osseous tissue regeneration, all porous materials have a fundamental limitation- the inherent lack of strength associated with porosity. Shells (nacre), tooth and bone are frequently used as examples for how nature achieves strong and tough materials made out of weak components. So, the unresolved engineering dilemma is how to create a scaffold that is both porous and strong. The objective of this study was to mimic the architecture of natural materials in order to create a new generation of strong hydroxyapatite-based porous scaffolds. The porous inorganic scaffolds were fabricated by the controlled freezing of water-based hydroxyapatite (HA) slurries. The scaffolds obtained by this process have a lamellar architecture that exhibits similarities with the meso- and micro- structure of the inorganic component of nacre. Compressive strengths of 20 MPa were measured for lamellar scaffolds with densities of 32%, significantly better than for the HA with random porosity. In addition, the lamellar materials exhibit gradual fracture unlike conventional porous HA scaffolds. These biomimetic scaffolds could be the basis for a new generation of porous and composite biomaterials.

Abstract: Microstructural and stress-corrosion cracking characterization of two glass-based coatings on Ti6Al4V with different SiO2 content (61% and 64% of SiO2) have been investigated in this work. These coatings belong to the SiO2-CaO-MgO-Na2O-K2O-P2O5 system and were obtained using a simple enamelling technique. They will be used as the first layer of the bioactive FGM coating. Microstructural characterization performed in the coatings by SEM shows the separation of the sintered glass particles after acid etching. The XRD integration method shows that the percentage of the crystalline phase (2.4CaO•0.6Na2O•P2O5) due to the partial devitrification is between 3-16 % vol. Mechanical characterization was made using Vickers and Hertzian indentation. Both coatings were sensitive to Vickers indentation subcritical crack growth with longer crack lengths for the smaller SiO2 content. This coating was also more sensitive to stress-corrosion “ring” cracking by Hertzian indentation. These two results are related with the larger residual stresses due to the thermal expansion mismatch.