Human perivascular stem cells (PSCs) can be isolated in sufficient numbers from multiple tissues for purposes of skeletal tissue engineering [1][2][3] . PSCs are a FACS-sorted population of 'pericytes' (CD146+CD34-CD45-) and 'adventitial cells' (CD146-CD34+CD45-), each of which we have previously reported to have properties of mesenchymal stem cells. PSCs, like MSCs, are able to undergo osteogenic differentiation, as well as secrete pro-osteogenic cytokines 1,2 . In the present protocol, we demonstrate the osteogenicity of PSCs in several animal models including a muscle pouch implantation in SCID (severe combined immunodeficient) mice, a SCID mouse calvarial defect and a femoral segmental defect (FSD) in athymic rats. The thigh muscle pouch model is used to assess ectopic bone formation. Calvarial defects are centered on the parietal bone and are standardly 4 mm in diameter (critically sized) 8 . FSDs are bicortical and are stabilized with a polyethylene bar and K-wires 4 . The FSD described is also a critical size defect, which does not significantly heal on its own 4 . In contrast, if stem cells or growth factors are added to the defect site, significant bone regeneration can be appreciated. The overall goal of PSC xenografting is to demonstrate the osteogenic capability of this cell type in both ectopic and orthotopic bone regeneration models.
Video LinkThe video component of this article can be found at https://www.jove.com/video/2952/ Protocol
Perivascular Stem Cell IsolationThis is described in details in the adjacent article "Purification of Perivascular Stem Cells from Human White Adipose tissue", by M. Corselli et al.
Scaffold Creation1. Scaffolds are custom-made per previously published protocol from poly(lactic-co-glycolic acid) (PLGA, Burmingham Polymer) with hydroxyapatite coating [4][5][6] . Apatite-coated PLGA scaffolds are fabricated from 85/15 PLGA by solvent casting and a particulate leaching process. Scaffolds are created in a spherical shape (2-mm diameter) for muscle pouch implantation, a discoid shape (4 mm in diameter) for calvarial implantation, or cylindrical (4 mm in diameter, 6 mm in length) for femoral segmental defects. 2. Briefly, PLGA/chloroform solutions mixed with sucrose (polymer/sucrose ratio 5/95, w/w) are cast into a 200-300-μm diameter Teflon mold to create the custom-made construct. After freeze-drying overnight, scaffolds are removed from the Teflon mold and immersed in ddH 2 O to dissolve the sucrose. Scaffolds are disinfected by immersion in 70% ethanol for 30 min, followed by three rinses of ddH 2 O. 3. For apatite coating, a simulated body fluid (SBF) solution is prepared by sequentially dissolving CaCl 2 , MgCl2•6H 2 O, NaHCO 3 , and K 2 HPO 4 •3H 2 O in ddH 2 O. Solution pH is lowered to 6 by adding 1M hydrochloric acid to increase the solubility. Na 2 SO 4 , KCl, and NaCl are added and the final pH is adjusted to 6.5 (SBF 1). 4. Mg2+ and HCO 3 -free SBF (SBF 2) is prepared by adding CaCl 2 and K 2 HPO 4 •3H 2 O in ddH 2 O and pH is lowered to 6. KCl and NaC...