Mannitol-Containing Macroporous Calcium-Phosphate Cement Encapsulating Human Umbilical Cord Stem Cells

Stem cell-based tissue engineering offers immense promise for bone regeneration. Human umbilical cord mesenchymal stem cells (hUCMSCs) may be an inexhaustible and low-cost alternative to bone marrow MSCs, which require an invasive procedure to harvest. Objective: Develop self-setting, mannitol-containing calcium phosphate cements (CPC) encapsulating hUCMSCs for bone tissue engineering. Methods: hUCMSCs were encapsulated in alginate beads and mixed into 3 different CPC pastes: (1) CPC alone; (2) CPC-mannitol, where water-soluble mannitol was added to create macropores; (3) CPC-mannitol reinforced with degradable poly(lactide-co-glycolide) fibers. Mechanical properties were measured using a 3-point bending test. Cell viability was assayed via live/dead staining. Osteodifferentiation was measured by RT-PCR (alkaline phosphatase (ALP) and osteocalcin (OC) gene expression), ALP activity and mineral staining. Results: Porosity increased from 49% for hUCMSC-encapsulating CPC to 64% after adding mannitol and fibers (p<0.05). Flexural strength (mean±s.d.;n=5) increased from (0.3±0.04)MPa to (1.97±0.67)MPa via fibers. Live cells were above 80% for all constructs. At 14 d, mannitol-containing constructs had significantly greater ALP gene expression (28.33±1.79) and OC gene expression (7.64±0.81) compared to constructs without mannitol, where ALP and OC gene expression were (21.03±2.03) and (5.4±0.93), respectively (mean±s.d.;n=5; p<0.05). ALP activity of hUCMSCs inside CPC with mannitol and fiber was significantly higher than that without mannitol (p<0.05). At 14 days, mineralization by the encapsulated hUCMSCs was 8-fold higher than that at 1 day. Conclusions: A novel porous CPC-hUCMSC construct was developed for bone tissue engineering. Its advantages include cell delivery inside a load-bearing CPC that has injectable and in situ-setting capabilities. hUCMSCs inside CPC had high viability and successfully osteodifferentiated. The self-setting and strong hUCMSC-encapsulating CPC scaffold is promising for bone tissue engineering in orthopedic and craniofacial applications. Supported by NIH/NIDCR R01 DE14190 (HX) and Maryland Stem Cell Research Fund (HX).