A large number of osteoprogenitor cells may be implanted at the injury site, either alone or combined with a matrix. Autologous bone marrow (BM) is rich in growth factors and osteoprogenitors as MSCs are present in the mononuclear cellular fraction of the bone marrow. Bone marrow MSCs are currently the most appropriate cells for inducing bone repair, as they have a strong osteogenic potential and are easily obtained by culturing iliac crest aspirates. Several MSC-based cell therapy modalities have been developed, i.e., with and without cell culturing, and with or without a matrix. The mononuclear cell fraction of the bone marrow,

which contains the MSCs, can be used directly by percutaneous injection of aspirated BM into the injury site. To increase the number of injected mononuclear cells and consequently of MSCs, it is possible to separate the mononuclear cells by centrifugation and Tanespimycin order concentrate them 3-fold to 6-fold [64] with good results in pseudarthrosis [65]. The healing rate increased in proportion to the injected MSC concentration. Patients whose fractures did

not heal received fewer than 1000 MSCs per mL and fewer than 30,000 MSCs in total, whereas those whose fractures healed received significantly higher MSC concentrations and counts, with a mean of 1500 MSCs per mL and 54,000 MSCs in total, in a volume of 20 mL. Concentrated or unconcentrated mononuclear cells can be mixed in the operating room Axenfeld syndrome with a synthetic or natural osteo-conducting matrix XAV-939 cell line (e.g., allogeneic bone graft or coral) before implantation. Few published studies assessed the combined use of concentrated or unconcentrated BM with a biomaterial [66], [67] and [68]. This method is a valid option for everyday practice, provided that CE-marked (that is, approved for clinical use in Europe) biomaterials are used and concentration (if used) is achieved via an approved procedure. Mononuclear cells may also be cultured in vitro to allow selection and expansion of an adherent fraction corresponding to MSC. This increases the

number of MSC to millions of cells. Expanded MSCs can be extemporaneously mixed with scaffolds during surgery (Fig. 4) so that this composite material is used in the same way as bone grafts. Quarto et al. [69] first reported the use of cultured BM MSCs combined intra-operatively with hydroxyapatite blocks to fill large bone defects (4–7 cm). They successfully treated 3 patients, with defects in the tibia, humerus, and ulna, respectively. A subsequent study confirmed healing of the defects after 6–7 years [70]. The expanded MSCs may also be injected alone percutaneously in the site of fracture or osteotomy with interesting results in two studies [71] and [72]. Tissue engineering combines bone marrow cells or mesenchymal stem cells, synthetic scaffolds and molecular signals (growth or differentiating factors) in order to form hybrid constructs.