Variation of cyclic strain parameters regulates development of elastic modulus in fibroblast/substrate constructs

Abstract

Dynamic mechanical culture systems are a widely studied approach for improving the functional mechanical properties of tissue engineering constructs intended for loading-bearing orthopedic applications such as tendon/ligament reconstruction. The design of effective mechanical stimulation regimes requires a fundamental understanding of the effects of cyclic strain parameters on the resulting construct properties. Toward this end, these studies employed a modular cyclic strain bioreactor system and fibroblast-seeded, porous polyurethane substrates to systematically investigate the effect of varying cyclic strain amplitude, rate, frequency, and daily cycle number on construct mechanical properties. Significant differences were observed in response to variation of all four loading parameters tested. In general, the highest values of elastic modulus within each experimental group were observed at low to intermediate values of the experimental variables tested, corresponding to the low to subphysiological range (2.5% strain amplitude, 25%/s strain rate, 0.1-0.5 Hz frequency, and 7,200-28,800 cycles/day). These studies demonstrate that fibroblasts are sensitive and responsive to multiple characteristics of their mechanical environment, and suggest that systematic optimization of dynamic culture conditions may be useful for the acceleration of construct maturation and mechanical function.

The Role of Mechanical Loading in Tendon Development, Maintenance, Injury, and Repair

“…Tissue engineers are incorporating mechanical stimulation to enhance tendon tissue augmentations and replacements [134][135][136][137][138][139][140][141][142][143][144][145][146] . By mechanically preconditioning the tissue-engineered construct cell population prior to in vivo implantation, the cells may be better equipped to enhance the repair since they have been exposed to the appropriate mechanical environment 134,135 .…”

“…Given the importance of physiological loading to maintain tendon homeostasis, investigators have shown that applying load promotes a tendon-like phenotype in both two and threedimensional culture conditions [139][140][141][142][143][144][145][146] . Ralphs et al showed that when tendon cells are cultured on a two-dimensional substrate and subjected to biaxial strain at 1 Hz for eight hours per day for a total of ninety-six hours, cells link together using actin adherens junctions along the principal line of strain to monitor tensile load 142 .…”

Design and Performance of an Optically Accessible, Low-Volume, Mechanobioreactor for Long-Term Study of Living Constructs

“…This has led tissue engineers to include mechanical stimulation in their construct formation protocols. [23][24][25][26][27][28][29][30][31][32][33] However, there is little data that elucidates how mechanical forces change the dynamics of fibroblast populations in cell culture systems. This is because most investigations are performed by examining the culture at fixed time points either during or after the mechanical stimulation protocol is complete.…”

Review of biophysical factors affecting osteogenic differentiation of human adult adipose-derived stem cells

“…Understanding the individual effects of different stimuli is difficult, since a cell is always subject to one influence in the presence of others. For instance, applied strain may modify elastic modulus of cell substrate (McCullen et al 2010b;Joshi and Webb 2008). For best comparison of results from studies in different laboratories, researchers should establish some standard induction schemes that can be logically adapted to suit individual needs (Kroeze et al 2011).…”

“…Additionally, nanoscale topographical features in growth substrates influence stem cell behavior (Teo et al 2010). Finally, elasticity has a plausible effect on osteogenesis of ASC (Hanson et al 2009;Engler et al 2006;McCullen et al 2010b;Joshi and Webb 2008).…”