Fatigue and fracture of soft collagenous tissues mineralized in vitro

Abstract

Biomineralization occurs in natural organisms, such as bones, teeth, shells and tendons. The formation mechanism and mechanical properties have been extensively studied for mineralized hard tissues, especially for bone and teeth. However, the research on the evolution of mechanical properties for mineralized soft tissues remains challenging due to the long period of mineralization. Here we use polymer-induced liquid-precursor (PILP) method to achieve accelerated in vitro mineralization of bovine pericardium with SrCO3. The modulus, tensile strength, toughness, and suture retention force of mineralized tissues have been characterized. After 30 days of mineralization, both the tensile strength and toughness decrease by two orders of magnitude. We carry out cyclic suture retention test to characterize the fatigue properties of mineralized tissues, and find that the cycle to failure of mineralized tissues is 10-100 times lower than that of unmineralized tissues. The degradation of mechanical properties results from the microstructure change of mineralized tissues, where collagen fibers change from curled to straight configuration. After mineralization, the interfibrous slippage is limited, and the fracture mode changes from fiber pullout to fiber break. Finite element analysis has been carried out to simulate the fracture and suture retention properties, and the simulation can well reproduce experimental results. The study may provide insights for tissue replacement and repairing.