Blackstone BN,Wolever JD and Powell HM
Background: Though mechanical stimulation has been shown to improve mechanical properties of many engineered tissues, little is known about the impact of stimulation on scaffold architecture. In engineered tissues where the scaffold comprises a large portion of the tissue, mechanical signals are transferred from the external environment through the scaffold to the cells. Thus, a greater understanding of the architectural changes a scaffold experiences during mechanical stimulation may provide new knowledge on the communication between the cells and scaffold, during dynamic in vitro tissue development. Methods: Two distinct scaffold architectures were fabricated via lyophilization or electro-spinning of collagen. Pore size of lyophilized scaffolds, fiber diameter and inter-fiber distance of electrospun scaffolds, and ultimate tensile strength, linear stiffness and stress relaxation rates for all scaffolds were determined, prior to mechanical stimulation. Scaffolds were then subjected to 0, 5, 10 or 20% static or cyclic strain. Alignment of lyophilized scaffold pores and electrospun fibers was then quantified after 4 and 7 days of mechanical stimulation. Results: Lyophilized scaffolds displayed significant increases in pore area with magnitude of strain and duration of stimulation, and a pronounced alignment in pore orientation with the direction of strain. In contrast, electrospun
samples showed only modest changes in architecture, in response to applied mechanical strain with small (1-5%) increased in fiber alignment compared to control, and no observed changed in fiber morphology. Conclusion: The current study showed the initial degree of interconnectivity between scaffold elements greatly impacted the scaffold response to mechanical stimulation. Non-woven electro-spun scaffold undergo very little micro structural reorganization during mechanical stimulation, while lyophilized collagen scaffolds undergo significant micro-structural changes. These differences in scaffold response suggest that large stain magnitudes may be required to excite cells within electro spun scaffolds, while modest strain magnitudes may results in significant changes in cellular behavior within lyophilized collagen sponges.
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