No abstract

Multicellular spheroids generated through cellular self-assembly provide cytoarchitectural complexities of native tissue including three-dimensionality, extensive cell-cell contacts, and appropriate cell-extracellular matrix interactions. They are increasingly suggested as building blocks for larger engineered tissues to achieve shapes, organization, heterogeneity, and other biomimetic complexities. Application of these tissue culture platforms is of particular importance in cardiac research as the myocardium is comprised of distinct but intermingled cell types. Here, we generated scaffold-free 3D cardiac microtissue spheroids comprised of cardiac myocytes (CMs) and/or cardiac fibroblasts (CFs) and used them as building blocks to form larger microtissues with different spatial distributions of CMs and CFs. Characterization of fusing homotypic and heterotypic spheroid pairs revealed an important influence of CFs on fusion kinetics, but most strikingly showed rapid fusion kinetics between heterotypic pairs consisting of one CF and one CM spheroid, indicating that CMs and CFs self-sort in vitro into the intermixed morphology found in the healthy myocardium. We then examined electrophysiological integration of fused homotypic and heterotypic microtissues by mapping action potential propagation. Heterocellular elongated microtissues which recapitulate the disproportionate CF spatial distribution seen in the infarcted myocardium showed that action potentials propagate through CF volumes albeit with significant delay. Complementary computational modeling revealed an important role of CF sodium currents and the spatial distribution of the CM-CF boundary in action potential conduction through CF volumes. Taken together, this study provides useful insights for the development of complex, heterocellular engineered 3D tissue constructs and their engraftment via tissue fusion and has implications for arrhythmogenesis in cardiac disease and repair.

Background: Several reports have shown that altered biomechanics after anterior cruciate ligament reconstruction (ACLR) are associated with the development of posttraumatic osteoarthritis. However, it is not fully understood whether altered biomechanics are associated with meniscal changes after ACLR. Purpose: To investigate changes in gait and landing biomechanics over a 3-year period and their correlation with meniscal matrix alterations present before and after ACLR through use of magnetic resonance T1ρ/T2 mapping, which can allow detection of early meniscal degeneration. Study Design: Cohort study; Level of evidence, 2. Methods: A total of 36 patients with ACLR and 14 healthy controls were included in this study. All patients underwent magnetic resonance imaging and biomechanical analysis during gait of the injured knee and contralateral knee preoperatively and at 6 months, 1 year, 2 years, and 3 years after ACLR, as well as biomechanical analysis during drop-landing from 6 months to 3 years postoperatively. To evaluate biochemical changes of the mensical matrix, T1ρ/T2 relaxation times of the meniscus were calculated. Results: Mean T1ρ/T2 values of ACLR knees were significantly higher than values in the contralateral and control knees in the posterior lateral and medial horns up to 1 year after surgery; however, the differences were not seen at 3 years after surgery. The ACLR knee exhibited significantly lower peak knee flexion moment and angle during gait at 6 months compared with baseline and continued to decrease until 3 years. The ACLR knee exhibited significantly lower peak vertical ground-reaction force and peak knee flexion moment and angle during landing at 6 months. However, the differences were no longer present at 3 years. Biomechanics at 6 months had significant correlations with changes of mean T1ρ/T2 values in the medial posterior horn from 6 months to 3 years after ACLR. Conclusion: Although mean T1ρ/T2 values of meniscus seen before ACLR improved after 3 years, approximately 30% of patients with ACLR did not show decreases from 6 months to 3 years. Patients with abnormal lower limb kinetics of the ACLR knee at 6 months showed less recovery in the medial posterior horn from 6 months to 3 years, suggesting that biomechanical parameters during the early stage of recovery might be potential biomarkers for predicting persistent medial meniscal abnormality after ACLR.