Human umbilical cord mesenchymal stem cells (hUCMSCs) are inexhaustible and can be harvested at a low cost without an invasive procedure. However, there has been no report on comparing hUCMSCs with human bone marrow MSCs (hBMSCs) for bone regeneration in vivo. The aim of this study was to investigate hUCMSC and hBMSC seeding on macroporous calcium phosphate cement (CPC), and to compare their bone regeneration in critical-sized cranial defects in rats. Cell attachment, osteogenic differentiation and mineral synthesis on RGD-modified macroporous CPC were investigated in vitro. Scaffolds with cells were implanted in 8-mm defects of athymic rats. Bone regeneration was investigated via micro-CT and histological analysis at 4, 12, and 24 weeks. Three groups were tested: CPC with hUCMSCs, CPC with hBMSCs, and CPC control without cells. Percentage of live cells and cell density on CPC in vitro were similarly good for hUCMSCs and hBMSCs. Both cells had high osteogenic expressions of alkaline phosphatase, osteocalcin, collagen I, and Runx2. Bone mineral density and trabecular thickness in hUCMSC and hBMSC groups in vivo were greater than those of CPC control group. New bone amount for hUCMSC-CPC and hBMSC-CPC constructs was increased by 57% and 88%, respectively, while blood vessel density was increased by 15% and 20%, than CPC control group at 24 weeks. hUCMSC-CPC and hBMSC-CPC groups generally had statistically similar bone mineral density, new bone amount and vessel density. In conclusion, hUCMSCs seeded on CPC were shown to match the bone regeneration efficacy of hBMSCs in vivo for the first time. Both hUCMSC-CPC and hBMSC-CPC constructs generated much more new bone and blood vessels than CPC without cells. Macroporous RGD-grafted CPC with stem cell seeding is promising for craniofacial and orthopedic repairs.

Human induced pluripotent stem cells (hiPSCs) are an exciting cell source with great potential for tissue engineering. Human bone marrow mesenchymal stem cells (hBMSCs) have been used in clinics but are limited by several disadvantages, hence alternative sources of MSCs such as umbilical cord MSCs (hUCMSCs) are being investigated. However, there has been no report comparing hiPSCs, hUCMSCs and hBMSCs for bone regeneration. The objectives of this pilot study were to investigate hiPSCs, hUCMSCs and hBMSCs for bone tissue engineering, and compare their bone regeneration via seeding on biofunctionalized macroporous calcium phosphate cement (CPC) in rat cranial defects. For all three types of cells, approximately 90% of the cells remained alive on CPC scaffolds. Osteogenic genes were up-regulated, and mineral synthesis by cells increased with time in vitro for all three types of cells. The new bone area fractions at 12 weeks (mean ± sd; n = 6) were (30.4 ± 5.8)%, (27.4 ± 9.7)% and (22.6 ± 4.7)% in hiPSC-MSC-CPC, hUCMSC-CPC and hBMSC-CPC respectively, compared to (11.0 ± 6.3)% for control (p < 0.05). No significant differences were detected among the three types of stem cells (p > 0.1). New blood vessel density was higher in cell-seeded groups than control (p < 0.05). De novo bone formation and participation by implanted cells was confirmed via immunohistochemical staining. In conclusion, (1) hiPSCs, hUCMSCs and hBMSCs greatly enhanced bone regeneration, more than doubling the new bone amount of cell-free CPC control; (2) hiPSC-MSCs and hUCMSCs represented viable alternatives to hBMSCs; (3) biofunctionalized macroporous CPC-stem cell constructs had a robust capacity for bone regeneration.

Human induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) are a promising choice of patient-specific stem cells with superior capability of cell expansion. There has been no report on bone morphogenic protein 2 (BMP2) gene modification of iPSC-MSCs for bone tissue engineering. The objectives of this study were to: (1) genetically modify iPSC-MSCs for BMP2 delivery; and (2) to seed BMP2 gene-modified iPSC-MSCs on calcium phosphate cement (CPC) immobilized with RGD for bone tissue engineering. iPSC-MSCs were infected with green fluorescence protein (GFP-iPSC-MSCs), or BMP2 lentivirus (BMP2-iPSC-MSCs). High levels of GFP expression were detected and more than 68% of GFP-iPSC-MSCs were GFP positive. BMP2-iPSC-MSCs expressed higher BMP2 levels than iPSC-MSCs in quantitative RT-PCR and ELISA assays (p < 0.05). BMP2-iPSC-MSCs did not compromise growth kinetics and cell cycle stages compared to iPSC-MSCs. After 14 d in osteogenic medium, ALP activity of BMP2-iPSC-MSCs was 1.8 times that of iPSC-MSCs (p < 0.05), indicating that BMP2 gene transduction of iPSC-MSCs enhanced osteogenic differentiation. BMP2-iPSC-MSCs were seeded on CPC scaffold biofunctionalized with RGD (RGD-CPC). BMP2-iPSC-MSCs attached well on RGD-CPC. At 14 d, COL1A1 expression of BMP2-iPSC-MSCs was 1.9 times that of iPSC-MSCs. OC expression of BMP2-iPSC-MSCs was 2.3 times that of iPSC-MSCs. Bone matrix mineralization by BMP2-iPSC-MSCs was was 1.8 times that of iPSC-MSCs at 21 d. In conclusion, iPSC-MSCs seeded on CPC were suitable for bone tissue engineering. BMP2 gene-modified iPSC-MSCs on RGD-CPC underwent osteogenic differentiation, and the overexpression of BMP2 in iPSC-MSCs enhanced differentiation and bone mineral production on RGD-CPC. BMP2-iPSC-MSC seeding on RGD-CPC scaffold is promising to enhance bone regeneration efficacy.