Blending with Poly(l-lactic acid) Improves the Printability of Poly(l-lactide-co-caprolactone) and Enhances the Potential Application in Cartilage Tissue Engineering.

Poly(l-lactide-co-caprolactone) (PLCL, 50:50) has been used in cartilage tissue engineering because of its high elasticity. However, its mechanical properties, including its rigidity and viscoelasticity, must be improved for compatibility with native cartilage. In this study, a set of PLCL/poly(l-lactic acid) (PLLA) blends was prepared by blending with different mass ratios of PLLA that range from 10 to 50%, using thermoplastic techniques. After testing the properties of these PLCL/PLLA blends, they were used to fabricate scaffolds by the 3D printing technology. The structures and viscoelastic behavior of the PLCL/PLLA scaffolds were determined, and then, the potential application of the scaffolds in cartilage tissue engineering was evaluated by chondrocytes culture. All blends demonstrate good thermal stability for the 3D printing technology. All blends show good toughness, while the rigidity of PLCL is increased through PLLA blending, and Young's modulus of blends with 10-20% PLLA is similar to that of native cartilage. Furthermore, blending with PLLA improves the processability of PLCL for 3D printing, and the compression modulus and viscoelasticity of 3D-printed PLCL/PLLA scaffolds are different from that of PLCL. Additionally, the stress relaxation time (t 1/2) of the PLCL/PLLA scaffolds, which is important for chondrogenesis, is dramatically shortened compared with the pure PLCL scaffold at the same 3D-printing filling rate. Consistently, the PLCL90PLLA10 scaffold at a 70% filling rate with much shorter t 1/2 is more conducive to the proliferation and chondrogenesis of in vitro seeded chondrocytes accompanied by upregulated expression of SOX9 than the PLCL scaffold. Taken together, these results demonstrate that blending with PLLA improves the printability of PLCL and enhances its potential application, particularly PLCL/PLLA scaffolds with a low ratio of PLLA, in cartilage tissue engineering.

A Collagen Fiber Membrane Aided Chondroprotective-Based Strategy for Enhancing Integration of Regenerative Neo-Cartilage.

The lack of neo-cartilage integration with host tissues is a great challenge for the clinical translation of new technologies for the repair of articular cartilage (AC) defect. Recently, we developed a promising double-layered collagen-based system for targeted delivery of fibroblast growth factor 2 (FGF2) to the subchondral bone for AC repair. The system effectively promoted the regeneration of both cartilage and subchondral bone. However, neo-cartilage integration was unsatisfactory, which might be due to the presence of a zone of cell death (ZCD) in the cartilage induced by injury. Here, we hypothesized that maintaining cell viability in the region surrounding the defect and decreasing the size of ZCD by using chondroprotective agents such as insulin-like growth factor-1 (IGF-1), might be an effective strategy to improve neo-cartilage integration. A targeted delivery system for IGF-1 to cartilage based on the FGF2 delivery system was formulated to weaken the impact on the effects of FGF2. The two growth factors were incorporated into the different layers of the membrane without interdiffusion. Due to the different densities of collagen fibers in the different layers, the in vitro and in vivo assays demonstrated that both proteins were released via unidirectional diffusion without mixing or lateral diffusion. Particularly, the released IGF-1 increased the viability of chondrocytes, decreased the ZCD size, and enhanced the integration of regenerative neo-cartilage with host tissues, without any undesirable effects on the FGF2mediated regeneration of cartilage and subchondral bone. Taken together, our findings demonstrate that the collagen fiber membrane-aided chondroprotective-based strategy is an effective way to improve neo-cartilage integration.

Targeted delivery of FGF2 to subchondral bone enhanced the repair of articular cartilage defect.

It is reported that growth factor (GF) is able to enhance the repair of articular cartilage (AC) defect, however underlying mechanisms of which are not fully elucidated yet. Moreover, the strategy for delivering GF needs to be optimized. The crosstalk between AC and subchondral bone (SB) play important role in the homeostasis and integrity of AC, therefore SB targeted delivery of GF represents one promising way to facilitate the repair of AC defect. In this study, we firstly investigated the effects and mechanism of FGF2 on surrounding SB and cartilage of detect defects in rabbits by using a homogenous collagen-based membranes. It was found that FGF2 had a modulating effect on the defect-surrounding SB via upregulation of bone morphogenetic protein (BMP)-2, BMP4 and SOX9 at the early stage. Low dose FGF2 improved the repair upon directly injected to SB. Inhibition of BMP signaling pathway compromised the beneficial effects of FGF2, which indicated the pivotal roles of BMP in the process. To facilitate SB targeted FGF2 delivery, a double-layered inhomogeneous collagen membrane was prepared and it induced increase of BMP2 and BMP4 in the synovial fluid, and subsequent successful repair of AC defect. Taken together, this targeted delivery of FGF2 to SB provides a promising strategy for AC repair owing to the relatively clear mechanism, less amount of it, and short duration of delivery. STATEMENT OF SIGNIFICANCE: Articular cartilage (AC) and subchondral bone (SB) form an integral functional unit. The homeostasis and integrity of AC depend on its crosstalk with the SB. However, the function of the SB in AC defect repair is not completely understood. The application of growth factors to promote the repair articular cartilage defect is a promising strategy, but still under the optimization. Our study demonstrate that SB plays important roles in the repair of AC defect. Particularly, SB is the effective target of fibroblast growth factor 2 (FGF2), and targeted delivery of FGF2 can modulate SB and thus significantly enhances the repair of AC defect. Therefore, targeted delivery of growth factor to SB is a novel promising strategy to improve the repair of AC defect.