Microstructural and Geochemical Characterization of Gallstones: Implication for Biomineralization

Stone formation in the gallbladder is one of the growing health issues reported throughout the world. However, studies on the characteristics of gallstone in the Sri Lankan community are very limited. Detail investigation of gallstone is important for identifying the causative factors and understanding the formation process. The present study aimed to investigate the compositional and microstructural characteristics of gallstone in Sri Lankan patients. Twenty-three patients who were admitted for cholecystectomies were selected for the study. The socio-demographic information was collected from patients using a structured questionnaire. Stones that were removed from surgeries were analyzed by their microstructural and compositional features using Fourier Transformed Infra-Red Spectrometer (FT-IR) and Inductively Coupled Plasma Mass spectroscopy (ICP-MS), Scanning Electron Microscope (SEM), and polarizing microscope. 44% of stones were the mixed type that comprised mainly cholesterol and bilirubinate and followed by pigment type (30%) that mainly contained bilirubinate. The pure cholesterol stones which comprise only cholesterol are the least abundant type of stones. Calcium is the major element found in stones followed by Cu, Mn, Fe, Mg, Zn, and Ni. Higher content of these elements was found in pigment stones compared to the other types. The core and crust regions of stones were enriched with Ca compared to the middle part. Concentric layers that comprise alternating dark and light color bands were observed in the crust, reflecting the compositional variation in bile during the formation of gallstones. The electron microscope images confirmed lightly stacked cholesterol with plate- and needle-like crystals and irregularly arranged clumps of bilirubinate. The Ca-rich core of gallstone confirmed that the Ca-salt precipitation possibly provided a nucleus for the stone formation.