Histologic Characterization of Human Ear Ossicles for the Development of Tissue-Engineered Replacements

Hypothesis: Precise knowledge of the expression and distribution of extracellular matrix (ECM) molecules and osteochondrogenic markers helps target the proper in vitro regeneration of novel ossicular chain (OC) replacements via tissue engineering (TE). Background: We performed an extensive histologic analysis of human ear ossicles in healthy adults. A variety of OC prostheses are currently available, but extrusion of synthetic devices still represents an important clinical phenomenon. TE is a novel discipline combining stem cells, bioresorbable biomaterials, and stimulatory factors for the development of new living tissues in vitro, which might offer forefront opportunities to otologic surgery. However, to drive stem cell differentiation correctly, the final tissue target must be accurately known. Methods: Malleus, incus, and stapes were collected from cadaveric temporal bones. TE PORPs were obtained via osteodifferentiation of human mesenchymal stromal cells on polymeric scaffolds. Histochemical and immunohistochemical analyses were performed to detect ECM molecules and osteochondrogenic markers. Results: Malleus and incus showed the same histologic tissue type, with similar levels of expression and distributions for both ECM molecules and osteochondrogenic markers, whereas the stapes showed self-standing histologic patterns. In TE PORPs, mesenchymal ECM synthesis and early stage development of ossification sites could be observed, highlighting good cellular integration with the scaffold biomaterial. Conclusion: Detailed morphologic study of the ossicles provides data related to tissue dynamics involved in their development, defining features of tissue differentiation and maturation. Such findings underpin the future development of biomimetic ossicular replacement, data that can guide tissue-engineered ossiculoplasty.