Enthesis tissue engineering: biological requirements meet at the interface

Tendon-to-bone interface (enthesis) exhibits a complex multiscale architectural and compositional organization maintained by a heterogeneous cellular environment. Orthopedic surgeons have been facing several challenges when treating tendon pullout or tear from the bony insertion due to unsatisfactory surgical outcomes and high retear rates. The limited understanding of enthesis hinders the development of new treatment options toward enhancing regeneration. Mimicking the natural tissue structure and composition is still a major challenge to be overcome. In this review, we critically assess current tendon-to-bone interface tissue engineering strategies through the use of biological, biochemical, or biophysical cues, which must be ultimately combined into sophisticated gradient systems. Cellular strategies are described, focusing on cell sources and cocultures to emulate a physiological heterotypic niche, as well as hypoxic environments, alongside with growth factor delivery and the use of platelet-rich hemoderivatives. Biomaterial design considerations are revisited, highlighting recent progresses in tendon-to-bone scaffolds. Mechanical loading is addressed to uncover prospective engineering advances. Finally, research challenges and translational aspects are considered. In summary, we highlight the importance of deeply investigating enthesis biology toward establishing foundational expertise and integrate cues from the native niche into novel biomaterial engineering, aiming at moving today's research advances into tomorrow's regenerative therapies.Authors thank the support from the European Union Framework Programme for Research and Innovation HORIZON2020 [TEAMING Grant agreement No 739572 - The Discoveries CTR]; FCT–Fundação para a Ciência e a Tecnologia for the PhD grant of IC [PD/BD/128088/2016]; the Project NORTE-01-0145-FEDER-000021:“Accelerating tissue engineering and personalized medicine discoveries by the integration of key enabling nanotechnologies, marine-derived biomaterials and stem cells”, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF) and the ERC Consolidator grant of ME [ERC-2017-CoG-772817]

An In Vitro System to Study Sertoli Cell Blood-Testis Barrier Dynamics

The use of an in vitro system based on primary cultures of Sertoli cells isolated from rat testes has greatly facilitated the study of the blood-testis barrier in recent years. Herein, we summarize the detailed procedures on the isolation of undifferentiated Sertoli cells from 20-day-old rat testes, the culture of these cells as a monolayer on Matrigel-coated bicameral units, the characterization of these cultured cells, and the use of the Sertoli cell epithelium for monitoring the integrity of the Sertoli cell blood-testis barrier. This information is based on the routine use of this system in our laboratory to study the Sertoli cell blood-testis barrier in the past two decades, which should be helpful for investigators in the field