Osteochondral tissue engineering for total joint repair : critical steps towards cell-based constructs

Abstract

This thesis identifies critical steps to be taken to develop osteochondral constructs. One of the most significant steps in cell-based tissue engineering (TE) is efficient and effective cell seeding. The application of multipotent mesenchymal stem cells (MSCs) is a major advantage for bone and cartilage generation in osteochondral TE. The major drawback lays, however, in the effective seeding and differentiation of MSCs in the chondral part of osteochondral constructs. Different copolymer compositions (poly(ethylene oxide terephthalate) (PEOT) / poly(butylene terephthalate) (PBT)) could not demonstrate an improved effect on cell attachment, while different seeding strategies were more successful. The incorporation of a single cell suspension into a hydrogel and the aggregation of single cells prior to the seeding have been shown to be most effective in terms of loaded cell number and generated cartilage.\ud To increase the quantity and quality of cartilage, crucial for clinical size defects, we released growth factors such as TGF β1 from PEOT/PBT scaffold. Our results showed a tailored release of bioactive TGF β1 in vitro from 10 to 40 days. A fast and instant release was more effective than the sustained delivery of TGF β1. Furthermore, we induced cell aggregation after 4hrs and chondrogenic differentiation of MSCs after 24hrs. Advantages of this technique include fast and efficient cell incorporation and a cost and time efficient cell differentiation.\ud It is crucial that scaffolds in osteochondral TE provide niches for chondrogenic and osseous differentiation while at the same time withstand mechanical forces. We increased cell entrapment and differentiation by integrating electrospun microfibrillar structures within macrofibers of 3D scaffolds. To assemble osteochondral constructs, we produced osteoinductive calcium phosphate particles and integrated them into hydrophilic PEOT/PBT for the osseous part. Hydrophobic PEOT/PBT was used for the chondral part. Constructs were seeded with MSCs and analysis showed cartilage tissue generation in the chondral part and bone tissue in the osseous part after 4 weeks in vivo.\ud In a clinical trial in humans, the safety, long-term biocompatibility and osteoconductivity of porous PEOT/PBT implants for donor site filling during osteochondral grafting have been demonstrated. In addition, the ease of arthroscopic scaffold insertion, the congruent surface tissue repair of predominantly fibrocartilagenous nature, and the absence of intra-articular\ud adverse events indicates its suitability to prevent postoperative bleeding and donor site morbidity