Tendon cell and tissue culture: Perspectives and recommendations

Abstract

The wide variety of cell and tissue culture systems used to study and engineer tendons can make it difficult to choose the best approach and “optimal” culture conditions to test a given hypothesis. Therefore, a breakout session was organized at the 2022 ORS Tendon Section Meeting that focused on establishing a set of guidelines for conducting cell and tissue culture studies of tendon. This paper summarizes the outcomes of that discussion and presents recommendations for future studies. In the case of studying tendon cell behavior, cell and tissue culture systems are reductionist models in which the culture conditions should be strictly defined to approximate the in vivo condition as closely as possible. In contrast, for tissue engineering tendon replacements, the culture conditions do not need to replicate native tendon, but the outcome measures for success should be narrowly defined for the specific clinical application. Common recommendations for both applications are that researchers should perform a baseline phenotypic characterization of the cells that are ultimately used for experimentation. For models of tendon cell behavior, culture conditions should be well justified by existing literature and meticulously reported, tissue explant viability should be assessed, and comparisons to in vivo conditions should be made to determine baseline physiological relevance. For tissue engineering applications, the functional/structural/compositional outcome targets should be defined by the specific tendons they seek to replace, with key biologic and material properties prioritized for construct assessment. Lastly, when engineering tendon replacements, researchers should utilize clinically approved cGMP materials to facilitate clinical translation.

Cyclic loading induces anabolic gene expression in ACLs in a load‐dependent and sex‐specific manner

“…First, tissue explant models do not perfectly mimic the in vivo environment. While they do maintain native cell–cell and cell–matrix interactions (in contrast to isolated cell in vitro models), 44 explant culture still alters cell phenotypes and cyclic tensile loading does not perfectly mimic the complicated loading environment of the ACL in vivo 28 . Indeed, we found that the expression of nearly all genes was different in explant culture compared to freshly harvested controls (Supporting Information: Figure ).…”

“…While they do maintain native cell-cell and cell-matrix interactions (in contrast to isolated cell in vitro models), 44 explant culture still alters cell phenotypes and cyclic tensile loading does not perfectly mimic the complicated loading environment of the ACL in vivo. 28 Indeed, we found that the expression of nearly all genes was different in explant culture compared to freshly harvested controls (Supporting Informa- loading. Second, while we selected our loading levels based on in vivo measurements of ACL loading, 31,36 it is possible that the same stress levels cause different amounts of tissue damage for male and female ACLs given that female human ACLs have inferior mechanical properties.…”

“…In contrast to in vitro experiments on isolated cells, explant models retain the native cell-cell and cell-matrix interactions present within the tissue while also enabling precise and reproducible control of the applied external load. 28…”

“…To test these hypotheses, we utilized a novel bioreactor 27 to cyclically load ACL explants from male and female rabbits. In contrast to in vitro experiments on isolated cells, explant models retain the native cell–cell and cell–matrix interactions present within the tissue while also enabling precise and reproducible control of the applied external load 28 …”

Special issue: Guiding the future of tendon research

“…Breakout discussions on several topics were had at the conference and these discussions were summarized in five review/perspective papers in this issue. These topics included tendon cell lineage, 1 tendon cell culture and bioreactors, 2 methods for biomechanical assessment, 3 methods for histological assessment, 4 and preclinical animal models 5 . We have also included 17 original research papers from members of the Tendon Section and colleagues, most of which were based on research that was presented at the conference.…”