Injectable scaffold as minimally invasive technique for cartilage tissue engineering: in vitro and in vivo preliminary study

Cartilage is a tissue with limited repair capacity and also sparse population of cells entrapped within a dense extracellular matrix, therefore, delivery of the cells to site of damaged cartilage can improve its healing potential. Synthetic biomaterials such as poly (d,l-lactide-co-glycolide) (PLGA) have been used as both preformed or injectable scaffolds in tissue engineering in order to carry and keep cells in the site of injury with minimal side effects. The injectable biocompatible polymeric scaffolds can reach to effected area via minimally invasive injection without need to open the joint, less painful approach and also having possibility to fill complicated shape defects. In this study, it was hypothesized that PLGA solved in n-methyl pyrrolidine (NMP) may act as a proper carrier for cell delivery to the site of the damage and also supports their growth. The results of in vitro assays including both live/dead (AO/PI) and MTT showed the majority of the cells were remained alive between 3 up to 21 days, respectively. The amount of resealed GAG from the mesenchymal stem cells (MSCs) which were in contact with both PLGA and alginate constructs (used as control) indicated that for day 7 MSCs in contact with alginate secreted more GAG (3.45 ± 0.453 µg/mL for alginate and 2.36 ± 0.422 µg/mL for PLGA matrices), but at longer times (21 days) cells in contact with PLGA elicited more GAG (6.26 ± 0.968 µg/mL for alginate and 8.47 ± 0.871 µg/mL for the PLGA matrices). Sol–gel systems comprising PLGA, NMP, and cells as well as alginate/cells were subcutaneously injected into four nude mice (each mouse had three injection sites). PLGA/NMP was solidify immediately and formed an interconnecting 3-D porous structure that allowed body fluid to penetrate through them. In vivo evaluation showed that PLGA/NMP scaffolds could support injected cells as a fibrocartilage tissue was formed after 6 months of injection. We found that PLGA/NMP system might be a proper minimally invasive therapeutics option for cartilage repair.