The aim of this study was to compare biological collagen I (ColI) and synthetic poly-(L: -lactide) (PLLA) nanofibers concerning their stability and ability to promote growth and osteogenic differentiation of human mesenchymal stem cells in vitro. Matrices were seeded with human stem cells and cultivated over a period of 28 days under growth and osteoinductive conditions and analyzed during the course. During this time the PLLA nanofibers remained stable while the presence of cells resulted in an attenuation of the ColI nanofiber mesh. Although there was a tendency for better growth and osteoprotegerin production of stem cells when cultured on collagen nanofibers, there was no significant difference compared to PLLA nanofibers or controls. The gene expression of alkaline phosphate, osteocalcin and collagen I diminished in the initial phase of cultivation independent of the polymer used. In the case of PLLA fibers, this gene expression normalized during the course of cultivation, whereas the presence of collagen nanofibers resulted in an increased gene expression of osteocalcin and collagen during the course of the experiment. Taken together the PLLA fibers were easier to produce, more stable and did not compromise growth and differentiation of stem cells over the course of experiment. On the other hand, collagen nanofibers supported the differentiation process to some extent. Nevertheless, the need for fixation as well as the missing stability during cell culture requires further work.

The aim of this study was to enhance synthetic poly(L-lactic acid) (PLLA) nanofibers by blending with collagen I (COLI) in order to improve their ability to promote growth and osteogenic differentiation of stem cells in vitro. Fiber matrices composed of PLLA and COLI in different ratios were characterized with respect to their morphology, as well as their ability to promote growth of human mesenchymal stem cells (hMSC) over a period of 22 days. Furthermore, the course of differentiation was analyzed by gene expression of alkaline phosphatase (ALP), osteocalcin (OC), and COLI. The PLLA-COLI blend nanofibers presented themselves with a relatively smooth surface. They were more hydrophilic as compared to PLLA nanofibers alone and formed a gel-like structure with a stable nanofiber backbone when incubated in aqueous solutions. We examined nanofibers composed of different PLLA and COLI ratios. A composition of 4:1 ratio of PLLA:COLI showed the best results. When hMSC were cultured on the PLLA-COLI nanofiber blend, growth as well as osteoblast differentiation (determined as gene expression of ALP, OC, and COLI) was enhanced when compared to PLLA nanofibers alone. Therefore, the blending of PLLA with COLI might be a suitable tool to enhance PLLA nanofibers with respect to bone tissue engineering.

Growth factors like bone morphogenetic protein 2 (BMP-2) and vascular endothelial growth factor (VEGF) play an important role in bone remodeling and fracture repair. Therefore, with respect to tissue engineering, an artificial graft should have no negative impact on the expression of these factors. In this context, the aim of this study was to analyze the impact of poly(L-lactic acid) (PLLA) nanofibers on VEGF and BMP-2 gene expression during the time course of human mesenchymal stem cell (hMSC) differentiation towards osteoblasts. PLLA matrices were seeded with hMSCs and cultivated over a period of 22 days under growth and osteoinductive conditions, and analyzed during the course of culture, with respect to gene expression of VEGF and BMP-2. Furthermore, BMP-2-enwoven PLLA nanofibers were used in order to elucidate whether initial down-regulation of growth factor expression could be compensated. Although there was a great interpatient variability with respect to the expression of VEGF and BMP-2, PLLA nanofibers tend to result in a down-regulation in BMP-2 expression during the early phase of cultivation. This effect was diminished in the case of VEGF gene expression. The initial down-regulation was overcome when BMP-2 was directly incorporated into the PLLA nanofibers by electrospinning. Furthermore, the incorporation of BMP-2 into the PLLA nanofibers resulted in an increase in VEGF gene expression. Summarized, the results indicate that the PLLA nanofibers have little effect on growth factor production. An enhancement in gene expression of BMP-2 and VEGF can be achieved by an incorporation of BMP-2 into the PLLA nanofibers.KEYWORDS: nanofibers, tissue engineering, human mesenchymal stem cells, PLLA, BMP, VEGF Schofer et al.: Growth Factor Gene Expession in hMSCs TheScientificWorldJOURNAL (2009) 9, 313-319 314 INTRODUCTIONThe reconstruction of large bony defects after injury or tumor resection often requires the use of graft material. Besides autologous bone grafts, artificial scaffolds based on synthetic biomaterials such as metals, ceramics, polymers, and composites have been developed [1,2]. Among them, scaffolds based on nanofibers are becoming more and more important [3,4]. These nanofibers can be produced by a broad spectrum of polymers, including biocompatible and biodegradable polymers, such as poly(glycolic acid) (PGA), poly(L-lactic acid) (PLLA), poly(ε caprolactone) (PCL), polyurethanes, polyphosphazenes, collagen, gelatin, and chitosan, as well as copolymers from the corresponding monomers in various compositions [5,6]. This results in the production of a broad spectrum of nanofiber-based scaffolds with different mechanical and biophysical properties. These fibers allow the differentiation of human mesenchymal stem cells (hMSCs) towards osteoblasts in principal [7,8,9]. Furthermore, they can be supplemented with growth factors like bone morphogenetic protein (BMP) or vascular endothelial growth factor (VEGF) in order to enhance osteoinductivity or angiogenesis.BMP-2 is a well-studied member of ...