A highly
self-healable polymeric system with enhanced mechanical
properties is prepared by blending conventional polyurethane (PU)
with functional polyimide (PI). PU and PI synthesized in this study
are miscible with each other and the thermal stability of the self-healable
blend (PUPI) is improved by incorporation of PI into PU. Interestingly,
on adding only a small amount of PI to PU, PUPI exhibits higher self-healing
efficiency and faster self-healing kinetics. Furthermore, unlike conventional
self-healing materials, PUPI also has superior surface and bulk mechanical
properties. A model for the mechanism for the improvement of self-healing
and mechanical properties is derived by analyzing FT-IR spectra. The
outstanding self-healing and mechanical properties are attributed
to the unique intermolecular networks resulting from the strong supramolecular
interactions between urethane groups in PU and imide groups in PI.
As a result, the PI chain acts as a polymeric glue inside the PU matrix
of PUPI, which results in significant enhancements in both properties
mentioned previously.
The use of engineered scaffolds or stem cells is investigated widely in the repair of injured musculoskeletal tissue. However, the combined regeneration of hierarchical osteochondral tissue remains a challenge due to delamination between cartilage and subchondral bone or difficulty in spatial control over differentiation of transplanted stem cells. Here, two types of composite spheroids are prepared using adipose‐derived stem cells (hADSCs) and nanofibers coated with either transforming growth factor‐β3 or bone morphogenetic growth factor‐2 for chondrogenesis or osteogenesis, respectively. Each type of spheroid is then cultured within a 3D‐printed microchamber in a spatially arranged manner to recapitulate the bilayer structure of osteochondral tissue. The presence of inductive factors regionally modulates in vitro chondrogenic or osteogenic differentiation of hADSCs within the biphasic construct without dedifferentiation. Furthermore, hADSCs from each spheroid proliferate and sprout and successfully connect the two layers mimicking the osteochondral interface without apertures. In vivo transplantation of the biphasic construct onto a femoral trochlear groove defect in rabbit knee joint results in 21.2 ± 2.8% subchondral bone volume/total volume and a cartilage score of 25.0 ± 3.7. The present approach can be an effective therapeutic platform to engineer complex tissue.
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