Potential of using ceramic materials as biomaterial is studied

Hydroxyapatite (HA) is one of the ceramic materials most commonly used to substitute bone tissue in orthopedic and dental implants. Its chemical composition is similar to the inorganic constituent of bone tissue and it possesses mechanical properties similar to those of mineral bone as well. Nevertheless, a prosthesis made of pure hydroxyapatite is limited to supporting light loads due to its inherent fragility, so its mechanical properties must be modified if we wish the implant to be able to handle heavier weights.

A method that is frequently used to achieve this consists in obtaining a composite of hydroxyapatite and biocompatible oxides (for example, TiO₂, Al₂O₃, ZrO₂ or Y₂O₃), which allows us to obtain a harder composite with greater strength under compression and resistance to breakage than pure hydroxyapatite. However, we must also take into account that it is important, in the design and optimization of the new biomaterials, to establish an equal balance between their mechanical and biological properties. In order to verify that a new material can be applied as a biomaterial, a complete structural and mechanical characterization will be necessary; an analysis of its biocompatibility by means of, first, in vitro tests and, later, in vivo tests will also be absolutely essential.

All of these matters are dealt with as part of the study "Physical and biological characterization of composite materials made of hydroxyapatite reinforced with Y₂O₃ nanoparticles produced by slip casting." This technique consists in preparing an aqueous suspension of the material that is to be strengthened, in this case hydroxyapatite powder and yttrium powder, and then filling a plaster mold that is the desired shape and letting the water filter through the plaster so that the solid part of the solution remains. "The resulting piece is known as 'green material' and it is typically subjected to a sinterization process, a heat treatment that allows the material to be strengthened," explains Prof. Mª Angustias Auger, of the UC3M Physics Department.

A team project

The process of preparing material by means of the slip casting technique has been carried out at the Instituto de Cerámica y Vidrio (Ceramic and Glass Institute) of the Consejo Superior de Investigaciones Científicas (CSIC -- Spanish Council for Scientific Research) and the biocompatibility tests using in vitro cultures in cells previously used for blood and amniotic liquid diagnosis are being performed in the Genetics Unit of the Gregorio Marañón General Hospital of Madrid. The characterization of the material for the different phases of development of the project will be carried out at the Laboratorio de Materiales Nanoestructurados y Multifuncionales (Nanostructured and Multifunctional Materials Laboratory) of UC3M. "It is very important to characterize the hydroxyapatite material before subjecting it to the cell culture process," explains Prof. Auger. "To do this, we measure its density, porosity and mechanical properties, such as its micro hardness, the elastic module or its resistance to compression, as well as its crystallized structure, its microstructure, the size and distribution of pores, etc.," she continues. Once the cell culture is done, the material will be analyzed using optic microscopes and electronic microscopes to verify and, if appropriate, quantify the proliferation of cells.

This research is being financed thanks to funds obtained in the 2009 competition for grants to carry out projects that promote the creation and consolidation of research groups at Carlos III University of Madrid. The Nanostructured and Multifunctional Materials Group at UC3M participates in this project as part of the ESTRUMAT program, which is financed by the Department of Education of the Autonomous Community of Madrid for the development of R and D activities carried out by groups in the Region. This work also presents an interesting opportunity for collaboration through an agreement which was recently signed by UC3M and the Department of Health of the Autonomous Community of Madrid, allowing undergraduate and graduate students in Biomedical Engineering to participate in internships and develop lines of research at Gregorio Marañón Hospital in Madrid and Getafe Hospital.