Gas-foaming Macroporous CPC Scaffold Encapsulating Human Umbilical-Cord Mesenchymal Stem Cells

Tissue engineering approaches are promising to meet the increasing need for bone regeneration. Calcium phosphate cement (CPC) can be injected and self-set to form a scaffold with excellent osteoconductivity. Objectives: To develop macroporous CPC-chitosan-fiber constructs containing alginate-fibrin microbeads encapsulating human umbilical-cord mesenchymal stem cells (hUCMSCs), and investigate hUCMSC release from the degrading microbeads and proliferation inside porous CPC. Methods: The hUCMSC-encapsulating alginate-fibrin microbeads were completely wrapped inside CPC paste, with gas-foaming porogen (0%, 5%, 10%, 15%, 20%, 25%, and 30% mass fractions) creating macropores in CPC to provide access for culture media. The viability and proliferation of hUCMSCs, microbead degradation, and porosity and mechanical properties of gas-foaming CPC were measured. Results: Increasing porogen content in CPC significantly increased cell viability, from 49% of live cells in CPC without porogen, to 86% of live cells in CPC with 15% porogen (P<0.05). The alginate-fibrin microbeads started to degrade and release cells inside CPC at 7 d. The released cells proliferated inside macroporous CPC. The live cell number inside CPC with 15% porogen significantly increased from 272±24 cells/cm² (n=5) at 1d to 337±27 cells/mm² at 21d (P<0.05). The pore volume fraction of CPC increased from 46.8% to 78.4% via gas-foaming method, with macropore sizes of about 100-400µm. The strength of the CPC-chitosan-fiber scaffold with 15% porogen was 3.8±0.5 MPa, which approximated the reported 3.5 MPa for cancellous bone. Conclusions: A novel gas-foaming macroporous CPC construct containing degradable alginate-fibrin microbeads was developed which encapsulated hUCMSCs. The cells had good viability inside the porous CPC construct. The degradable microbeads in CPC quickly released the cells which proliferated over time inside the porous CPC. The self-setting and strong CPC with alginate-fibrin microbeads for stem cell delivery is promising for bone tissue engineering applications.