Advanced mimetic materials for meniscus tissue engineering : targeting segmental vascularization

Meniscus lesions are among the most common orthopaedic injuries which can ultimately lead to degeneration of the knee articular cartilage. The human meniscus has a limited healing potential, partly due to a poor vasculature, and thus meniscus regeneration using tissue engineering strategies has recently been investigated as a promising alternative to total/partial meniscectomy [1]. Advanced scaffolds for tissue engineering of meniscus should be able to mimic and preserve the asymmetric vascular network of this complex tissue, i.e. enable controlling the segmental vascularization during the regeneration process. Novel scaffolds were produced combining a silk polymeric matrix (12 wt%) [2] and the methacrylated gellan gum hydrogel (iGG-MA), which has been shown to be able to prevent the ingrowth of endothelial cells and blood vessels into the hydrogels [3,4]. The angiogenic/ anti-angiogenic potential of acellular and cell-laden silk-12 scaffolds combined with iGG-MA hydrogel was investigated in vivo, using the chick embryo chorioallantoic membrane (CAM) assay. For producing the cell-laden scaffolds, human meniscus cells (HMC¢s) were isolated from morphologically intact human menisci using an enzymatic-based digestion and expanded using standard culture conditions. The HMC’sladen hydrogel/silk scaffolds were produced by encapsulating the HMC’s into a 2 wt% GG-MA hydrogel, followed by impregnation onto the 12 wt% silk scaffold and ionic-crosslinking in a saline solution. A CAM assay was used to investigate the control of segmental vascularization of the acellular and HMC¢s-laden hydrogel/silk scaffolds by the effect of GG-MA hydrogel, until day 14 of embryonic development. The in vivo study allowed investigating the number of macroscopic blood vessels converging to the implants. The evaluation of possible inflammation and endothelial cells ingrowths was performed by histological (haematoxylin and eosin - H&E - staining) and immunohistochemical methods (SNA-lectin staining). When the silk-12 scaffold was combined with the hydrogel, an inhibitory effect was observed as demonstrated by the low number of convergent blood vessels. Results have shown that iGG-MA hydrogel prevented the endothelial cells adhesion and blood vessels infiltration into the HMC’s hydrogel/silk scaffolds, after 4 days of implantation. This study showed that the hydrogel/silk scaffolds enabled controlling the segmental vascularization, thus it can possibly mimic the native vasculature architecture during meniscus regeneration.