Abstract
Contribution of mechanical loading to tissue growth during both the development and post-natal maturation is of a particular interest, as its understanding would be important to strategies in bone tissue engineering and regenerative medicine. The present study has been performed to investigate how immature bone responds to mechanical loading using an ex vivo culture system. A slice of the tibia, with the thickness of 3mm, was obtained from 0-day-old chick. For the ex vivo culture experiment in conjunction with cyclic compressive loading, we developed a custom-made, bioreactor system where both the load and the deformation applied to the specimen was recorded. Cyclic compression, with an amplitude of 0.3N corresponding to 1 to 2% compressive strain, was applied to immature bone specimen during a 3-day culture period at an overall loading rate 3–4cycles/min, in the presence of β-glycerol phosphate and dexamethasone in culture medium. The stress-strain relationship was obtained at the beginning and the end of the culture experiment. In addition, analyses for alkaline phosphate release, cell viability and tissue calcification were also performed. It was exhibited that elastic moduli of bone slices were significantly elevated at the end of the 3-day culture in the presence of cyclic compression, which was a similar phenomenon to significant elevation of the elastic moduli of bone tissue by the maturation from 0-day old to 3-day old. By contrast, no significant changes in the moduli were observed in the absence of cyclic compression or in deactivated, cell-free samples. The increases in the moduli were coincided with the increase in calcified area in the bone samples. It was confirmed that immature bone can respond to compressive loading in vitro and demonstrate the growth of bone matrix, similar to natural, in vivo maturation. The elevation of the elastic moduli was attributable to the increased calcified area and the realignment of collagen fibers parallel to the loading direction. The ex vivo loading system established here can be further applied to study responses to mechanical loading in osteogenesis as well as callus maturation for better understanding of factors to consider in successful bone regeneration with mechanical factors.
Highlights
It is well established that both tensile and compressive loadings are applied to bone by body movement, which in turn generates hydrostatic pressure and shear stress at a cellular level (Curry, 2002)
The area was increased from the C0 level following the 3-day culture period in cyclic compression culture (CCC), static culture (SC), dCCC and deactivated bone slice (dSC); a significant difference was only observed between dCCC and C0
It was demonstrated that the application of cyclic compressive loading for three days elevated elastic moduli of the bone slices, to the level comparable to that obtained from the tibia of 3-day-old chicks
Summary
It is well established that both tensile and compressive loadings are applied to bone by body movement, which in turn generates hydrostatic pressure and shear stress at a cellular level (Curry, 2002). To overcome difficulties in studying the effects of mechanical loading alone in bone adaptation, experimental models of ex vivo tissue culture in conjunction with an application of controlled mechanical loading have been utilized (for example, (Jones et al, 2003) for studying adult bone tissue remodeling). For understanding immature bone growth, cyclic hydrostatic pressure was applied to isolated whole fetal femur from chick in a culture condition, and bone formation, mineralization and associated change in gene expressions were examined (Henstock et al, 2013). There has been no study to investigate effects of cyclic compressive loading on the growth of immature bones using such ex vivo model
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