Decreased mechanical properties of heart valve tissue constructs cultured in platelet lysate as compared to fetal bovine serum.

In autologous heart valve tissue engineering, there is an ongoing search for alternatives of fetal bovine serum (FBS). Human platelet-lysate (PL) might be a promising substitute. In the present article, we aimed to examine the tissue formation, functionality, and mechanical properties of engineered three-dimensional tissue constructs cultured in PL as a substitute for FBS. Our results show that tissue constructs that were cultured in PL and FBS produce similar amounts of collagen, glycosoaminoglycans, and collagen crosslinks, and that the cellular phenotype remains unchanged. Nevertheless, mechanical testing showed that the ultimate tensile strength in PL constructs was on average approximately three times lower as compared to FBS (0.25 vs. 0.74 MPa, respectively, p<0.01), and also the elastic modulus was almost three times lower (1.33 MPa of PL constructs vs. 3.94 MPa of FBS constructs, p<0.01). Additional tests indicated that this difference might be explained by different collagen fiber architecture possibly due to increased production of matrix-degrading proteases by cells cultured in PL. In summary, our results indicate that PL is not preferred for the culture of strong heart valve tissue constructs.

European Society of Biomechanics S.M. Perren Award 2010: an adaptation mechanism for fibrous tissue to sustained shortening.

The mechanism by which fibrous tissues adapt upon alterations in their mechanical environment remains unresolved. Here, we determine that periosteum in chick embryos resides in an identical mechanical state, irrespective of the developmental stage. This state is characterized by a residual tissue strain that corresponds to the strain in between the pliant and stiffer region of the force-strain curve. We demonstrate that periosteum is able to regain that mechanical equilibrium state in vitro, within three days upon perturbation of that equilibrium state. This adaptation process is not dependent on protein synthesis, because the addition of cycloheximide did not affect the response. However, a functional actin filament network is required, as is illustrated by a lack of adaptation in the presence of cytochalasin D. This led us to hypothesize that cells actively reduce collagen fiber crimp after tissue shortening, i.e. that in time the number of recruited fibers is increased via cell contraction. Support for this mechanism is found by visualization of fiber crimp with multiphoton microscopy before the perturbation and at different time points during the adaptive response.