In vitro cyclic compressive loads potentiate early osteogenic events in engineered bone tissue

Abstract

Application of dynamic mechanical loads on bone and bone explants has been reported to enhance osteogenesis and mineralization. To date, published studies have incorporated a range of cyclic strains on 3D scaffolds and platforms to demonstrate the effect of mechanical loading on osteogenesis. However, most of the loading parameters used in these studies do not emulate the in vivo loading conditions. In addition, the scaffolds/platforms are not representative of the native osteoinductive environment of bone tissue and hence may not be entirely accurate to study the in vivo mechanical loading. We hypothesized that biomimicry of physiological loading will potentiate accelerated osteogenesis in bone grafts. In this study, we present a compression bioreactor system that applies cyclic compression to cellular grafts in a controlled manner. Polycaprolactone-β Tricalcium Phosphate (PCL-TCP) scaffolds seeded with Mesenchymal Stem Cells (MSC) were cyclically compressed in bioreactor for a period of 4 weeks at 1 Hz and physiological strain value of 0.22% for 4 h per day. Gene expression studies revealed increased expressions of osteogenesis-related genes (Osteonectin and COL1A1) on day 7 of cyclic loading group relative to its static controls. Cyclic compression resulted in a 3.76-fold increase in the activity of Alkaline Phosphatase (ALP) on day 14 when compared to its static group (p < 0.001). In addition, calcium deposition of cyclic loading group was found to attain saturation on day 14 (1.96 fold higher than its static scaffolds). The results suggested that cyclic, physiological compression of stem cell-seeded scaffolds generated highly mineralized bone grafts. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2366-2375, 2017.

Biomimetic fetal rotation bioreactor for engineering bone tissues—Effect of cyclic strains on upregulation of osteogenic gene expression

“…This would act as the baseline for all the modes. Cyclic compression would include compression at 0.22%, 1 Hz for 4 hr/day based on our previous study (Ravichandran et al, ). Biaxial rotation would involve chamber rotation about two axes ( x axis and z axis) at 5 rpm and an angle of rotation at 90°.…”

“…Total DNA content in the cell lysate of each graft was measured using PicoGreen DNA Quantification Kit (Molecular Probes, USA) according to manufacturer's instructions ( n = 3). DNA quantities were used to indicate the total cell numbers in each graft as previously described (Ravichandran et al, ).…”

“…This fluid flow applies amplified strains to the cytoskeleton of bone cell processes leading to bone remodelling by activation of downstream signalling events (You, Cowin, Schaffler, & Weinbaum, ). Consequently, biomimetic bioreactors for bone tissue engineering have focused on emulating the interstitial fluid stresses (Yeatts & Fisher, ) and/or tissue‐level mechanical strains (Baumgartner et al, ; Matziolis et al, ; Michalopoulos et al, ; Ravichandran et al, ; Zong ming et al, ). These fluid shear stresses and mechanical strains stimulate the cell membrane's structural proteins such as integrins to form focal adhesion complexes that in turn will enable transduction of these specific mechanical signals to respective biochemical signals (Uzer, Fuchs, Rubin, & Thompson, ).…”

“…These fluid shear stresses and mechanical strains stimulate the cell membrane's structural proteins such as integrins to form focal adhesion complexes that in turn will enable transduction of these specific mechanical signals to respective biochemical signals (Uzer, Fuchs, Rubin, & Thompson, ). We have earlier shown the potential of physiologically relevant compressive stimuli to induce enhanced and accelerated mineralization (2 weeks) of 3D premature bone grafts in comparison with static cultures over a period of 4 weeks (Ravichandran et al, ). As we move towards the development of a more complex platform of clinical relevance, there is a need to elucidate the combined effects of fluid shear stresses and mechanical forces on stem cells for tissue engineering.…”

Biophysics Rules the Cell Culture but Has Yet to Reach the Clinic: Why Is That?

“…37,38 It is not a coincidence, after all, that exercise is an integral element of any orthopaedic rehabilitation regime. 39,40 Several bioreactor systems of variable complexity have been used as means to control tenocyte, 41 chondrocyte, 42 and osteoblast 43 phenotype in vitro and to direct stem cells toward tenogenic, 44 chondrogenic, 45 and osteogenic 46,47 lineages. Musculoskeletal tissues, like any other tissue, are highly dense ECM assemblies.…”