Fusion between Cartilage Nodules Differentiated in a Rotating Bioreactor

In order to repair damaged bone an implanted tissue’s size and shape must be configured in a cohesive way with the defect. The inability of the implants to conform to the defect will yield less than favorable results. In tissue engineering, fusion of tissues can produce a larger piece of tissue for implantation, many times larger than what is produced if fusion does not occur. Objective: To study the fusion of cartilage nodules cultured in a bioreactor including any effect on differentiation. Methods:  Limb buds of 12-13 day old mice (C57Bl) were used to make a single cell suspension, which was aggregated on a rotary shaker.  After 24 hours, aggregates were placed in a rotating bioreactor and grown for 3 weeks, then either implanted into defects or fixed for histology. Results: Analysis of histological sections from 3 experiments showed that even the smallest nodules consisted of at least 2 fused portions from different aggregates. Demarcation between nodules is often easily visible as an epithelium intervening between the borders of two aggregates. On occasion, one aggregate appears to have engulfed the other, so that more differentiated tissue is on the inside and less differentiated on the outside. In these uncontrolled fusions, spherical as well as linear and torus forms were evident. Lumens were numerous. Conclusion:   In studies producing bone-forming cartilage for repair of skull defects in mice, cartilage nodules produced in the bioreactor underwent fusion, allowing the growth of a larger piece of tissue for implants. The idea of controlled fusion could lead to creating custom tissue implants specific to a patient’s defect and will be investigated in future studies.