The same behavior was noticed to the Amide I peak (∼1665 cm−1), which is attributed to C O stretching [18]. Besides, at 1004 cm−1, the intensity of this peak was considerable lower for group A samples. This peak is related to the loss of bulk water from collagen structure [21]. The loss of bulk water on collagen leads

to a great difference in structural state of BP tissue, which modified the tissue leading to a reduction of both the elasticity and rupture tension of the material, as discussed below. The traction test allows the identification of mechanical properties of the BP tissue samples (Table 1). For example, the Young’s modulus decreased 44.76% when AZD6244 cost samples were freeze-dried by the laboratory freeze-dryer. Besides, rupture tension reduced 35.24% for samples from group A. Based on the results we can infer that the modifications suffered by BP, with major effects in the fibrous pericardium, led to a drastic decrease in mechanical properties Akt inhibitor when freeze-drying was performed in the laboratory freeze-dryer. The loss of bulk water left the tissue more susceptible to breakage. Water uptake test was applied in order to evaluate the membrane properties for their possible use as a biomaterial. The ability of a membrane to rehydrate quickly

and preserve water is an important aspect especially in case of application of this tissue as a heart valve substitute, which needs to execute the best performance as a bioprosthesis. The water Tacrolimus (FK506) uptake test (Fig. 4) revealed that swelling degree for group A samples is superior then group B samples. This result indicates that the modifications occurred on BP membranes leave the tissue looser with more space between collagen fibers. TEM analysis is used to successfully obtain structural information of type I collagen [19]. TEM micrographs showed that in fact collagen fibril suffered breakage at some points (black arrows).

This behaviour occurs mainly when freeze-drying was performed by the laboratory freeze-dryer in a ratio of 8:3 when compared to the pilot freeze-dryer (Fig. 5). In summary, it was proven that freeze-drying of bovine pericardium tissue should be performed with controlled parameters to ensure the integrity of collagen fibers, and consequently leading to a better performance in bioprosthesis. Moreover, in this work it has been demonstrated that damages occur in collagen fibers by the loss of structural water of tropocollagen triple helix implicating in a drastic decreasing of BP mechanical properties due to its structural alterations. We can expect that this work has pointed out that freeze-drying of other biological tissues should be carefully studied to determine the appropriate freeze-drying parameters to a better preservation of the biomaterial structure. The authors gratefully acknowledge Simone Jared and Marta M.