Elemental and Structural Characterization of Heterotopic Ossification during Achilles Tendon Healing Provides New Insights on the Formation Process

• Published in: ACS biomaterials science & engineering Vol. 10; no. 8; pp. 4938 - 4946
• Main Authors: Sharma, Kunal, Silva Barreto, Isabella, Dejea, Hector, Hammerman, Malin, Appel, Christian, Geraki, Kalotina, Eliasson, Pernilla, Pierantoni, Maria, Isaksson, Hanna
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 12.08.2024
• Subjects: Basic Medicine; Bio-interactions and Biocompatibility; Cell and Molecular Biology; Cell- och molekylärbiologi; Medical and Health Sciences; Medicin och hälsovetenskap; Medicinska och farmaceutiska grundvetenskaper; small animal model; small-angle X-ray scattering; tissue characterization; wide-angle X-ray scattering; X-ray fluorescence; tissue characterization; X-ray fluorescence; small animal model; small-angle X-ray scattering; wide-angle X-ray scattering
• ISSN: 2373-9878; 2373-9878
• DOI: 10.1021/acsbiomaterials.4c00935

Heterotopic ossification (HO) in tendons can lead to increased pain and poor tendon function. Although it is believed to share some characteristics with bone, the structural and elemental compositions of HO deposits have not been fully elucidated. This study utilizes a multimodal and multiscale approach for structural and elemental characterization of HO deposits in healing rat Achilles tendons at 3, 6, 12, 16, and 20 weeks post transection. The microscale tomography and scanning electron microscopy results indicate increased mineral density and Ca/P ratio in the maturing HO deposits (12 and 20 weeks), when compared to the early time points (3 weeks). Visually, the mature HO deposits present microstructures similar to calcaneal bone. Through synchrotron-based X-ray scattering and fluorescence, the hydroxyapatite (HA) crystallites are shorter along the c-axis and become larger in the ab-plane with increasing healing time, while the HA crystal thickness remains within the reference values for bone. At the mineralization boundary, the overlap between high levels of calcium and prominent crystallite formation was outlined by the presence of zinc and iron. In the mature HO deposits, the calcium content was highest, and zinc was more present internally, which could be indicative of HO deposit remodeling. This study emphasizes the structural and elemental similarities between the calcaneal bone and HO deposits.