Mechanical behavior of chemically treated ostrich pericardium subjected to uniaxial tensile testing: influence of the suture

Changes in the mechanical properties of chemically treated bovine pericardium after a short uniaxial cyclic test

The mechanical behavior of calf pericardium, a biomaterial utilized in the manufacture of cardiac bioprostheses, in response to a short tensile cyclic test has been evaluated. The trial involved 120 samples cut longitudinally or transversely, subjected to 10 cycles until a stress of between 1 and 3 MPa was reached. Tests of hardness and tear propagation were performed, and the results were compared with a control series. The energy loss was also computed, and it was approximately 10-fold greater in the first cycle than the loss in the subsequent nine cycles. Despite this singularity, they correlated very precisely. The effect of the direction in which the tissue is cut on energy loss was not significant nor the difference between hardness prior to and after testing. The results of the tear propagation tests gave no statistical differences prior to and after testing. From the obtained results, it seems that the test carried out does not affect significantly the mechanical properties of calf pericardium.

Fatigue behaviour of young ostrich pericardium

Young ostrich pericardia (biomaterial under study for manufacturing cardiac valve leaflets), has been subjected to biaxial tension fatigue until breakage. Supraphysiological values of pressure (1 to 6 atm) have been employed to accelerate damage and, therefore, to reduce testing time but at physiological frequency in order to avoid viscoelastic behaviour changes. The lifetime fatigue curves have been obtained and large scatter has been observed in the results but this can be strongly reduced with adequate material selection. The thickness-based selection of samples has proved to be ineffective both in reducing scatter or improving strength, but the energy-based selection aided with statistical decision techniques has been shown to be very successful. The energy loss (energy under the hysteresis loop of each load and unload cycle) appears to be a very accurate predictor of the expected fatigue lifetime of the tissue.

Ostrich leather quality: a review

This review summarises the research that has been published on factors that influence the various aspects of ostrich leather quality, a vital aspect to the economic viability of the commercial ostrich industry. The review is divided into three main sections: discussing intrinsic, pre-slaughter and post-slaughter factors that influence leather quality. Only one literature source that investigated the morphology of ostrich skin could be found. The high vascularity near the surface of the skin was indicated in making the skin susceptible to bruising, which influences skin quality, while the strength and flexibility of ostrich leather was attributed to the three-dimensional cross-weave arrangement of collagen fibres. Various studies reported a high degree of variation in quality within and between ostrich skins. The potential of genetic selection for improved skin quality was also considered, and it was demonstrated that most ostrich leather traits exhibited significant genetic variation. Findings on pre-slaughter factors, such as the effects of age, weight, nutrition and management practices, are also summarised. Few research reports on post-slaughter factors that influence leather quality were found. A few studies looked at the effect of storage on ostrich skin quality, but literature on the effect of processing techniques are lacking. Research priorities identified include the development of methods to assess skin quality on-farm and finding objective methods of evaluating ostrich leather quality.

Mechanical resistance of a new biomaterial, ostrich pericardium, and a new method of joining tissues combining suturing and a biological adhesive

We studied the mechanical behavior in response to tensile stress of samples of ostrich pericardium bonded with a cyanoacrylate glue or sewn with a rectangular, overlapping suture that was subsequently sealed with the same bioadhesive. Seventy-two trials were performed in three series of 24 samples each: series AG, glued with an overlap of 1 cm2; series ASG, sewn with a rectangular, overlapping suture and sealed; and series AC, control samples that were left intact. The mean stress at rupture in series AG (glued) was 0.1 MPa, much lower than the working stress of a human valve leaflet, which is approximately 0.25 MPa. In the control series, this stress was 26.28 MPa. At rupture in series ASG (sutured/glued), the suture material was being subjected to a stress of 64.91 MPa, thus confirming the existence of an interaction between the suture and the shear stress exerted by the suture on the samples of pericardium. In series ASG, the mean value for the resistance to rupture when measured in machine kg was 8.83 kg, lower than but similar to that recorded in the control series AC (10.26 kg). The percentages of reversible deformation, or elongation, once the samples were torn were similar in series AC (19.15%) and ASG (21.93%). This phenomenon can only be explained by the damage to the collagen fibers in the area around the rupture, while other more distant regions work at a lower load within the elastic limit. We conclude that cyanocrylate adhesives alone are not suitable as bonding materials in cardiac bioprostheses. The results with the rectangular, overlapping suture, when subsequently sealed with an adhesive, can be considered good because, although this approach does not impede shear stress, it does maintain an excellent degree of resistance to rupture of the samples thus joined. We stress the need to take into account the concentration of the load in the design of bioprostheses.