Thermal Properties of Mineralized and Non Mineralized Type I Collagen in Bone

摘要

The research about the structural stability of bone, as a composite material, compromises a complete understanding of the interaction between the mineral and organic phases. The thermal stability of human bone and type 1 collagen extracted from human bone by different methods was studied in order to understand the interactions between the mineral and organic phases when is affected by a degradation/combustion process. The experimental techniques employed were calorimetry and infrared spectroscopy (FTIR) techniques. The extracted type I collagens result to have a bigger thermal stability with a Tmax at 500 and 530 Celsius degrees compared with the collagen present in bone with Tmax at 350 Celsius degrees. The enthalpy value for the complete degradation/combustion process were similar for all the samples, being 8.4 +- 0.11 kJ/g for recent bones diminishing with the antiquity, while for extracted collagens were 8.9 +- 0.07 and 7.9 +-1.01 kJ/g. These findings demonstrate that the stability loss of type 1 collagen is due to its interactions with the mineral phase, namely carbonate hydroxyapatite. This cause a change in the molecular properties of the collagen during mineralization, specifically in its cross-links and other chemical interactions, which have a global effect over the fibers elasticity, but gaining tensile strength in bone as a whole tissue. We are applying this characterization to analyze the diagenetic process of bones with archaeological interest in order to identify how the environmental factors affect the molecular structure of type I collagen. In bone samples that proceed from an specific region with the same environmental conditions, the enthalpy value per unit mass was found to diminish exponentially with respect to the bone antiquity.