Nanofibrous poly(3-hydroxybutyrate)/poly(3-hydroxyoctanoate) scaffolds provide a functional microenvironment for cartilage repair.

Articular cartilage defects, when repaired ineffectively, often lead to further deterioration of the tissue, secondary osteoarthritis and, ultimately, joint replacement. Unfortunately, current surgical procedures are unable to restore normal cartilage function. Tissue engineering of cartilage provides promising strategies for the regeneration of damaged articular cartilage. As yet, there are still significant challenges that need to be overcome to match the long-term mechanical stability and durability of native cartilage. Using electrospinning of different blends of biodegradable poly(3-hydroxybutyrate)/poly(3-hydroxyoctanoate), we produced polymer scaffolds and optimised their structure, stiffness, degradation rates and biocompatibility. Scaffolds with a poly(3-hydroxybutyrate)/poly(3-hydroxyoctanoate) ratio of 1:0.25 exhibit randomly oriented fibres that closely mimic the collagen fibrillar meshwork of native cartilage and match the stiffness of native articular cartilage. Degradation of the scaffolds into products that could be easily removed from the body was indicated by changes in fibre structure, loss of molecular weight and a decrease in scaffold stiffness after one and four months. Histological and immunohistochemical analysis after three weeks of culture with human articular chondrocytes revealed a hyaline-like cartilage matrix. The ability to fine tune the ultrastructure and mechanical properties using different blends of poly(3-hydroxybutyrate)/poly(3-hydroxyoctanoate) allows to produce a cartilage repair kit for clinical use to reduce the risk of developing secondary osteoarthritis. We further suggest the development of a toolbox with tailor-made scaffolds for the repair of other tissues that require a 'guiding' structure to support the body's self-healing process.

Application of an acoustofluidic perfusion bioreactor for cartilage tissue engineering.

Cartilage grafts generated using conventional static tissue engineering strategies are characterised by low cell viability, suboptimal hyaline cartilage formation and, critically, inferior mechanical competency, which limit their application for resurfacing articular cartilage defects. To address the limitations of conventional static cartilage bioengineering strategies and generate robust, scaffold-free neocartilage grafts of human articular chondrocytes, the present study utilised custom-built microfluidic perfusion bioreactors with integrated ultrasound standing wave traps. The system employed sweeping acoustic drive frequencies over the range of 890 to 910 kHz and continuous perfusion of the chondrogenic culture medium at a low-shear flow rate to promote the generation of three-dimensional agglomerates of human articular chondrocytes, and enhance cartilage formation by cells of the agglomerates via improved mechanical stimulation and mass transfer rates. Histological examination and assessment of micromechanical properties using indentation-type atomic force microscopy confirmed that the neocartilage grafts were analogous to native hyaline cartilage. Furthermore, in the ex vivo organ culture partial thickness cartilage defect model, implantation of the neocartilage grafts into defects for 16 weeks resulted in the formation of hyaline cartilage-like repair tissue that adhered to the host cartilage and contributed to significant improvements to the tissue architecture within the defects, compared to the empty defects. The study has demonstrated the first successful application of the acoustofluidic perfusion bioreactors to bioengineer scaffold-free neocartilage grafts of human articular chondrocytes that have the potential for subsequent use in second generation autologous chondrocyte implantation procedures for the repair of partial thickness cartilage defects.