Osteogenic differentiation of dura mater stem cells cultured in vitro on three-dimensional porous scaffolds of poly(epsilon-caprolactone) fabricated via co-extrusion and gas foaming

A novel scaffold fabrication method utilizing both polymer blend extrusion and gas foaming techniques to control pore size distribution is presented. Seventy-five per cent of all pores produced using polymer blend extrusion alone were less than 50microm. Introducing a gas technique provided better control of pore size distribution, expanding the range from 0-50 to 0-350microm. Varying sintering time, annealing temperature and foaming pressure also helped to reduce the percentage of pore sizes below 50microm. Scaffolds chosen for in vitro cellular studies had a pore size distribution of 0-300microm, average pore size 66+/-17microm, 0.54+/-0.02% porosity and 98% interconnectivity, measured by micro-computed tomography (microCT) analysis. The ability of the scaffolds to support osteogenic differentiation for subsequent cranial defect repair was evaluated by static and dynamic (0.035+/-0.006ms(-1) terminal velocity) cultivation with dura mater stem cells (DSCs). In vitro studies showed minimal increases in proliferation over 28 days in culture in osteogenic media. Alkaline phosphatase expression remained constant throughout the study. Moderate increases in matrix deposition, as assessed by histochemical staining and microCT analysis, occurred at later time points, days 21 and 28. Although constructs cultured dynamically showed greater mineralization than static conditions, these trends were not significant. It remains unclear whether bioreactor culture of DSCs is advantageous for bone tissue engineering applications. However, these studies show that polycaprolactone (PCL) scaffolds alone, without the addition of other co-polymers or ceramics, support long-term attachment and mineralization of DSCs throughout the entire porous scaffold.

Mesenchymal stem cells from rat visceral fat exhibit multipotential differentiation in vitro

Human subcutaneous fat-derived stem cells were recently shown to have the potential to differentiate in vitro into a variety of cell types, including adipocytes, osteoblasts, chondrocytes, and myoblasts (Zuk et al., Tissue Eng. 2001;7:211-228). Subcutaneous adipose tissue may therefore prove to be an easily acquired and abundant source of stem cells. Presently it is unclear whether mammals such as rats (which possess small or nonexistent subcutaneous fat pads) contain mesenchymal stem cells within the visceral fat of the abdominal cavity, or whether the visceral fat of any species contains stem cells. In this study we isolated and expanded a pool of mesenchymal cells from visceral fat of adult Sprague-Dawley rats and induced their differentiation in vitro into adipocytes, osteoblasts, neural cells, and chondrocytes. The differentiated phenotypes were verified by morphology as well as detection and expression of tissue-specific protein and mRNA. We conclude that despite well-documented differences in the metabolic and biochemical properties among anatomically distinct depots of fat, the visceral fat of rats contains adult mesenchymal stem cells with developmental potential similar to those isolated from subcutaneous fat in humans. Therefore, animals such as rats provide both a source of fat-derived stem cells and an immunocompetent, autologous host animal in which to investigate the capacity of the fat-derived cells to differentiate and form tissues in vivo.

Repair of an osseous facial critical-size defect using augmented fibrin sealant

OBJECTIVE

Osseous defects of the head and neck are a common challenge for the otolaryngologist. To develop improved reconstructive options, osteoconductive engineering experiments are being conducted. A nasal critical-size defect (CSD) model has previously been described in which less than 7% bone healing is observed over 6 months. An implant containing fibrin sealant with and without osteoprogenitor cells is evaluated in this model.

STUDY DESIGN

Randomized controlled trial using a rodent model.

METHODS

A nasal CSD was surgically created in 18 male retired breeder Sprague-Dawley rats. Six animals were not implanted with any material, six received fibrin sealant consisting of fibrin (25 mg/mL) and thrombin (1000 U/mL), and six were implanted with fibrin sealant and rat calvarial osteoprogenitor cells (1.8 x 10(6) cells/mL). Thirty days later, the animals were examined at necropsy by planimetry, histological analysis of new bone growth, and radiodensitometric analysis of bone thickness.

RESULTS

A thin layer of bone covered the defect in all of the treated animals. A statistically significant increase in bone density (P < .05) between fibrin sealant plus osteoprogenitor cells and each of the other groups was shown using radiodensitometric analysis. Histological analysis also confirmed this difference.

CONCLUSION

Osteoprogenitor cells contained within fibrin sealant result in a greater augmentation of bone regeneration than controls or fibrin sealant alone.