Pore characteristics of bone substitute materials assessed by microcomputed tomography

Pore configurations of alloplastic biomaterial scaffolds play a major role for new bone formation in vivo. Current studies on characteristics of pores in bone substitute materials focus on individual particles or single blocks. Thus, three-dimensional (3-D) architecture of particle aggregates, representing the clinical relevant in vivo situation is not adequately taken into account. The aim of this study was the visualization and quantification of pore properties, both of the scaffold structure of single particles as well as of the micro-morphology of complex 3-D aggregated particle-conglomerates.

In model experiments, standardized plexiglass cylinders were stuffed with commercial bone substitute material particles with diverse chemical composition (HA, beta-TCP, HA-SiO(2), HA-beta-TCP, bioactive glass), origin (phycogenic, bovine, synthetic) and granulation (50 mum-2000 mum). Analogue to establish procedures for native (human) bone samples, non-fixed bone substitute materials were scanned by high-resolution microcomputed tomography. In addition to computer animated two-dimensional and 3-D reconstruction of the samples, median pore thickness and pore size distribution were determined. Materials representative for their chemical constitution were documented by SEM imaging.

Investigated specimens significantly were different in micro-morophology and pore properties, ranging from highly porous to rather solid. The most voluminous pores were localized interparticularly. Within one product line, the determined pore properties showed a significant correlation with single particle grain sizes.

The generation and interpretation of micro-CT based 3-D pore models can provide further insight into the expected osteoconduction dynamics and therefore might serve as a basis for further modifications of scaffold size and geometry as well as for further invasive studies on the biological behaviour of the scaffolds.