Towards engineering of the meniscus

Abstract

The menisci fulfill essential biomechanical functions since they have a chondroprotective effect on the underlying cartilage by redistributing the contact force across the tibiofemoral (knee) joint. Unfortunately, meniscal injury is quite common and since not all meniscal injuries are amenable for repair (partial) meniscectomy is often performed. However, meniscectome exposes femoral and tibial condyles to excessive wear and increases the risk of osteoarthritis. Therefore, replacement of an injured meniscus with a tissue engineered construct could be a promising solution to treat meniscus defects. In the first part, important current limitations of synthetic polymer implants were tackled such as (1) the lack of biomimetic properties which enhances cell adhesion, proliferation and accelerates tissue ingrowth, (2) the lack of a 100% interconnective and controllable pore network and (4) the lack of potential to produce patient specific implants with RP technology. A double protein (gelatin and fibronectin) surface modification strategy was developed and was, after optimization on 2D films, transferable to tailor made rapid prototyping produced 3D PCL scaffolds with 100% interconnective pores. Finally, we demonstrated that scaffold architecture plays an important role in the seeding efficiency and subsequent differentiation of cells. Altogether, we gained insights in processing 3D tailor made PCL scaffolds and strategies for the bioactivation of these 3D PCL scaffolds. A synergistic effect of scaffold architecture and surface modification on tissue maturation was observed. In a second part we tackled the problem of dedifferentiation of expanded fibrochondrocytes. We demonstrated the beneficial use of an agarose micro-well chip for meniscal fibrochondrocyte aggregation, this is a novel approach for meniscal fibrochondrocytes. Our results showed that we were able to produce large quantities of uniform micro-aggregates with controllable dimensions. Through a combination of aggregation, TGF-β1 and low oxygen tension we succeeded in the redifferentiation of the micro-aggregates towards the fibrochondrocyte phenotype. This was established by the up-regulation and protein expression of the most important and commonly used markers for meniscus gene expression. Although the initial goal of the thesis was the engineering of a bioactive meniscus or an appropriate meniscal scaffold, we are still far from the creation of a functional meniscal construct and the eventual translation towards the clinic. Indeed, the results of this thesis must be considered as a first step in the creation of a tissue engineered meniscus construct and can be used as a very good starting point to further work towards a functional tissue engineered meniscus construct