Design of an organ-on-a-chip model of soft-hard tissue interfaces

The musculoskeletal system includes soft and hard tissues. Soft-hard tissue interfaces, such as tendon-bone or gum-tooth interfaces, are essential in maintaining the biomechanical function of associated tissues. However, this function can be disrupted, in pathological scenarios and during ageing. Interfacial tissue engineering constitutes an attractive approach to repairing damaged interfaces (Brown & Puetzer, 2022). Their regeneration is challenging due to the composite structure and close connection between function, organization, structure, and mechanical properties. In vitro systems that can recapitulate in vivo scenarios and contexts of these biological interfaces are required to identify and test novel strategies to promote repair or prevent damage (J. Z. Paxton et al., 2012). Three-dimensional (3D) printing and organ-on-achip technologies offer robust and affordable solutions for developing novel 3D models to mimic human physiology and investigate disease progression. This study aims to combine these technologies to investigate soft-hard tissue interfaces. An organ-on-a-chip model of soft-hard tissue interfaces was 3D printed and mechanically actuated with a microfluidic pump. In this model, hydroxyapatite microposts were generated, to mimic hard tissues and to apply a tensile force to a microtissue formed by stromal cells contracting a fibrin hydrogel around the microposts. The resulting 3D printed organ-on-a-chip was characterized (electron microscopy, microscopy). Following this, the maturation of the interface was investigated using immunostaining and confocal microscopy. The actuation of the tissue within the organ-on-a-chip model developed promoted the maturation of a soft-hard tissue interface. The mechanical challenge induced alignment of the cells and matrix deposition at the interface. This model can be further used for in-depth investigation of structure-function relationships and biological processes that lead to these interfaces’ development, regeneration and homeostasis in pathological and physiological scenarios and response to a mechanical challenge. This study provides new insight into how hydroxyapatite and dynamic mechanical loads drive enthesis development. The organ-on-achip model developed is a promising in vitro platform to better understand the cues that regulate enthesis maturation in vivo