Mechanical Stimulation of Chondrocyte-agarose Hydrogels

Abstract

Articular cartilage suffers from a limited repair capacity when damaged by mechanical insult or degraded by disease, such as osteoarthritis. To remedy this deficiency, several medical interventions have been developed. One such method is to resurface the damaged area with tissue-engineered cartilage; however, the engineered tissue typically lacks the biochemical properties and durability of native cartilage, questioning its long-term survivability. This limits the application of cartilage tissue engineering to the repair of small focal defects, relying on the surrounding tissue to protect the implanted material. To improve the properties of the developed tissue, mechanical stimulation is a popular method utilized to enhance the synthesis of cartilaginous extracellular matrix as well as the resultant mechanical properties of the engineered tissue. Mechanical stimulation applies forces to the tissue constructs analogous to those experienced in vivo. This is based on the premise that the mechanical environment, in part, regulates the development and maintenance of native tissue(1,2). The most commonly applied form of mechanical stimulation in cartilage tissue engineering is dynamic compression at physiologic strains of approximately 5-20% at a frequency of 1 Hz(1,3). Several studies have investigated the effects of dynamic compression and have shown it to have a positive effect on chondrocyte metabolism and biosynthesis, ultimately affecting the functional properties of the developed tissue(4-8). In this paper, we illustrate the method to mechanically stimulate chondrocyte-agarose hydrogel constructs under dynamic compression and analyze changes in biosynthesis through biochemical and radioisotope assays. This method can also be readily modified to assess any potentially induced changes in cellular response as a result of mechanical stimuli.

Stochastic resonance is a method to improve the biosynthetic response of chondrocytes to mechanical stimulation

“…While combined compression‐vibrational loading induced a decline in DNA content (up to −23%), these changes were lower than the elicited increases in matrix synthesis. This result was not unexpected as decreases in DNA content in response to dynamic compression have been previously reported and vibrational stimuli has also been shown to dampen chondrocyte proliferation …”

“…Several studies have demonstrated that extracellular matrix metabolism and subsequent tissue organization can be controlled through the application of mechanical loading . While dynamic mechanical stimulation has generally been shown to be beneficial for the development of tissue engineered cartilage constructs, the applied stimulation parameters (i.e., strains, durations, frequency of application) tend to vary significantly between studies. This is partly due to empirical optimization needed given the differences in response to mechanical loading as a result of species, age, and culture model .…”

Combined effects of oscillating hydrostatic pressure, perfusion and encapsulation in a novel bioreactor for enhancing extracellular matrix synthesis by bovine chondrocytes

“…By contrast, our system shows striking improvements, double, triple and quintuple the Col of 2.5- and 5.3-fold with perfusion, then 3.3- and 5.5-fold with perfusion plus OHP when comparing to the S− and S+ counterparts. Moreover, our bioreactor is unique in that cell–scaffold constructs can be maintained with or without perfusion or OHP in one seamless system without transfer requirements from Petri dishes to bioreactors for mechanical forces to be applied as is necessary in other systems (Bilgen et al 2013; Kaupp et al 2012). …”

Nanomechanics of Engineered Articular Cartilage: Synergistic Influences of Transforming Growth Factor-<I>β</I>3 and Oscillating Pressure

“…It is a system in which mechanical stimulation can be performed without the requirement of transferring the cell-ECM construct to a separate chamber for OHP. In previous studies such as those done by Kaupp et al 17 and Toyoda et al 60 cells were first encapsulated in scaffold and then cell-seeded scaffolds were transferred to another chamber to be exposed to mechanical stimuli. Transferring step has been bypassed in our newly developed bioreactor system and we believe doing so would reduce the risk of getting contamination.…”

“…16 To provide cells with such physical environments, a disadvantage of common protocols is that cells must first be encapsulated in scaffolds, cultured and then transferred to the bioreactors where mechanical forces are applied. 12,17,18 These types of transformations could increase the risk of bacterial contamination. Furthermore, mass transfer is limited by diffusion from the bulk medium to the construct surface despite the improvements caused by the physical stimulation.…”