Better Vibrations: Eliciting Osteogenesis And Chondrogenesis With A Vibratory Bioreactor
John A. van Aalst, MD, MA, Zach Cashion, PhD, Montserrat Caballero, PhD, Bob Dennis, PhD.
University of North Carolina, Chapel Hill, Chapel Hill, NC, USA.
PURPOSE: Established work in tissue engineering has demonstrated the capacity of tensile strain to induce osteogenesis in mesenchymal stem cells (MSCs) and for compression to induce chondrogenesis. No work has examined the effect of direct vibratory stimulus on MSCs. This work details the design and outcomes of a vibratory bioreactor to induce osteogenesis and chondrogenesis in umbilical cord (UC) MSCs. METHODS: Both human and porcine UC MSCs were harvested by explant technique, grown to subconfluence, and subjected to vibratory stimulus using an in vitro bioreactor programmed to deliver vibrations at 1 hertz (hz) or 100 hz. The schedule for delivery of vibratory signals was 15 minutes every hour for 24 hours. Cells were tracked with adeno-associated fluorescent labeling. At conclusion of the studies, cells were stained with Alizarin red to determine calcium deposition, an indication of osteogenesis; alcian blue for the presence of glycosaminoglycans (GAGS), an indication of chondrogenesis; reverse transcriptase polymerase chain reaction (RT-PCR) was utilized to assess changes in mRNA for Collagen I, and II, and BMP-2. RESULTS: Both human and porcine UC MSCs exposed to vibrations at a frequency of 1 hz stained positively for GAGS (similar to chemical chondrogenesis) and were negative for calcium deposition (Figure 1); RT-PCR demonstrated an increase in the ratio of Collagen II to I mRNA suggesting an elastic chondrogenesis (Figure 2). MSCs stimulated with 100 hz demonstrated calcium staining similar to chemical osteoinduction (Figure 1) and elevation of BMP-2 mRNA, consistent with osteogenesis (Figure 2). CONCLUSIONS: An in vitro bioreactor that delivers vibratory stimulus at low frequencies can induce chondrogenesis in both human and porcine UC MSCs. Higher frequencies generate osteogenesis. These vibratory frequencies may eventually be applicable in clinical scenarios of bone or cartilage defects that require regeneration of these tissue types. The more powerful application may eventually be found in the inhibition of bone formation with low frequency stimulation. Large animal studies are underway to determine translation of these findings into the preclinical arena.
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