Biomedical subjects

A Cordón

Publications and source records attributed to A Cordón.

18 recordsLinked to original sources

PubMed2006

Hysteresis of a biomaterial: influence of sutures and biological adhesives.

We studied the changes in energy consumption of samples of calf pericardium, when joined or not joined by sutures and adhesives, by means of hysteretic cycles. Sixty-four samples were subsequently subjected to tensile stress until rupture. An overlapping suture sewn in the form of a rectangle presented an acceptable mean resistance to rupture of over 10 MPa, although lower than the mean values in an unsutured control series where the mean resistance surpassed 15 MPa. The contribution of an acrylic adhesive to the resistance to rupture was negligible. The sutured samples that were reinforced with adhesives and had not been subjected to hysteretic cycles prior to rupture showed an anisotropic behavior. This behavior appeared to be lost in all the samples that underwent hysteretic cycles. We found an inflection point in the stress/strain curve following the stepwise increase in the load, with a value greater than and proximate to the final load applied. This inflection should be analyzed by means of microscopy. Finally, the mathematical relationship between the energy consumed and the stress applied, the strain or deformation produced and the number of cycles of hysteresis to which the samples were subjected was established as the ultimate objective of this study. The bonding systems provoked a greater consumption of energy, with the greatest consumption corresponding to the first cycle in all the series assayed. An equation relating the energy consumption in a sample to the number of hysteretic cycles to which it was subjected was obtained. Its asymptote on the x-axis indicates the energy consumption for a theoretical number of cycles, making it possible to estimate the durability of the sample.

Animals↗

PubMed2002

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

The mechanical behavior of sutured ostrich pericardium was studied by uniaxial tensile testing. One hundred forty-four tissue specimens were assessed: 96 sutured samples (48 in which a centrally located suture was placed at an angle of 90 degrees with respect to the longitudinal axis, whereas in the remaining 48, a centrally located suture was placed at a 45 degrees angle to the longitudinal axis, in sets of 12 samples each, sewn with sutures made of Gore-Tex, nylon, Prolene, or silk), and 48 unsutured controls. Each group of 24 samples sewn at one angle or the other with the different suture materials was assayed together with a corresponding control group of 12 unsutured samples. The mean tensile strengths in the unsutured controls ranged between 30.16 MPa and 43.42 MPa, whereas those of the sutured sets ranged from 14.68 MPa to 21.91 MPa. The latter presented a statistically significant loss of resistance (p < 0.01) when compared with the unsutured tissue samples. The angle of the suture with respect to the longitudinal axis influenced the degree of shear stress produced by the suture, as well as the behavior of the different suture materials used. The set of samples sewn with Prolene appeared to be that most sensitive to changes in the angle of the suture, whereas tissue sewn at a 45 degrees angle with Gore-Tex presented lower shear stress values in comparison with samples in which the other three materials were used. A method of tissue selection based on morphological and mechanical criteria was used to ensure the homogeneity of the results in such a way that the coefficients of determination (R2) for the stress/strain curve fitting equation ranged between 0.888 and 0.995. This excellent fit made it possible, applying regression analysis, to predict the mechanical behavior of a specimen by determining that of a contiguous tissue sample. Thus, it should be possible, at least theoretically, to characterize the behavior of a specific region or zone of the biomaterial. In conclusion, ostrich pericardium exhibits strong resistance to rupture, even when sutured. The selection method used ensures the homogeneity of the samples and, thus, of the results. The angle of the suture with respect to the longitudinal axis, where the load is centered, determines the shear stress produced by the suture and the mechanical behavior of each suture material.

Animals↗

PubMed2002

The telescoping suture--Part 1: Does this technique improve the mechanical behavior of a biomaterial?: Calf pericardium.

The authors study the mechanical behavior of calf pericardium employed in the construction of cardiac valve leaflets when subjected to telescoping suture, followed by tensile stress until rupture. One hundred twenty pericardial tissue samples were employed, 60 cut from root-to-apex and another 60 cut in transverse direction. Each of these two groups consisted of 12 control samples that were left unsutured and four sets of 12 samples each that were rejoined by telescoping suture using silk, Prolene, nylon or Gore-Tex., and subjected to tensile stress. At the rupture of the sutured tissues, the tensile stress of the suture materials ranged between 57.54 MPa for the series sewn lengthwise with Gore-tex and 114.08 MPa for the series sewn crosswise with silk. At these levels of stress, the deformation of the suture thread was much less marked than that of the calf pericardium, and internal stresses were produced that were difficult for the biomaterial to absorb. There was a loss of real load in all the sutured series when the observed resistance to rupture, expressed in kilograms, was compared with the estimated value. This loss of resistance did not invalidate the telescoping suture technique since the resistance to rupture was still much greater than that associated with suturing the two edges of the cut pericardium together. This report confirms the deleterious role of the shear force generated in the pericardium by the suture.

Animals↗

PubMed2002

The telescoping suture--Part II: A novel method to improve the mechanical behavior of a new biomaterial: ostrich pericardium.

Ostrich pericardium, sutured using a telescoping or overlapping technique, was studied to determine its mechanical behavior. From each of 12 pericardial sacs, four contiguous strips were cut longitudinally, from root to apex, and another four contiguous strips were cut in transverse direction. One of the strips in each set of four was used as an unsutured control and the remaining three were sutured by overlapping 0.5 cm of the tissue and sewing with Gore-tex, Prolene or Pronova. These 96 samples were then subjected to tensile testing along their major axes until rupture. The tensile stresses recorded in the suture materials at the moment tears appeared in the pericardium ranged between 55.99 MPa and 70.23 MPa for Gore-tex in samples cut in the two directions. Shear stress became ostensible at 56 MPa, with clearly evident tears. However, microfracture of the collagen fibers must be produced at much lower stress levels. The comparison of the resistance in kilograms (machine-imposed), without taking into account the sections in which the load was applied, demonstrated only a slight loss of load when the telescoping suture was employed in ostrich pericardium samples. Ostrich pericardium may continue to be an alternative biological material for the construction of heart valve leaflets.

Animals↗

PubMed2001

Ostrich pericardium, a biomaterial for the construction of valve leaflets for cardiac bioprostheses: mechanical behaviour, selection and interaction with suture materials.

The mechanical behavior of ostrich pericardium was studied for the purpose of assessing its utility in the construction of bioprosthetic cardiac valve leaflets. The tissue was tested biaxially using a hydraulic simulator that subjected it to increasing stress until rupture. One hundred eighty trials were performed, 36 with unsutured pericardium and four series of 36 trials each with pericardium sutured with silk, Prolene, nylon or Gore-Tex. The samples were tested in pairs from three different pericardial regions. One sample from each pair (the predictive specimen) was assessed according to morphological and mechanical criteria, while the other (the predicted or selectable specimen) was subjected only to morphological analysis. The findings show that ostrich pericardium treated with glutaraldehyde according to standard methods has an excellent resistance to rupture in biaxial testing, withstanding stresses of up to 100 MPa, and never lower than 30 MPa. Its resistance to rupture is lowered by suturing, a loss that is less pronounced when silk sutures are used. The results with Gore-Tex are very homogeneous and the elastic behavior of the pericardium/suture unit appears to be similar to that of unsutured tissue, suggesting that the interaction between the two biomaterials is minor. Similar results were observed in the series sutured with Prolene and nylon. The use of paired samples makes it possible to closely estimate the mechanical behavior of the tissue in a given zone by determining that of its mate. The statistical study shows that this estimation is not conditioned by the suture employed, thus validating this approach and providing more precise criteria for tissue selection.

Animals↗

PubMed2001

Chemical treatment and tissue selection: factors that influence the mechanical behaviour of porcine pericardium.

Calcification and mechanical failure are the major causes of the loss of cardiac bioprostheses. The chemical treatments used to stabilize the tissue employed are considered to play a fundamental role in the development of these two phenomena, although the problem is multifactorial and the underlying causes are yet to be fully identified. Currently, there is an ongoing search for chemical treatments capable of reducing or eliminating the process of calcification while preserving the mechanoelastic characteristics of the tissue. One of the approaches to this effort is the elimination of the phospholipid component from the biological tissue employed in prosthesis construction. There is evidence that this component may be responsible for the precipitation of calcium salts. The present study compares two delipidating chemical treatments involving chloroform/methanol and sodium dodecyl sulfate (SDS) with the use of glutaraldehyde (GA) alone. For this purpose, porcine pericardial tissue was subjected to tensile strength testing employing a hydraulic simulator. A total of 234 samples were studied 90 treated with GA, 72 treated with chloroform/methanol and 72 treated with SDS. The mean breaking strength was significantly higher in the samples treated with GA (between 43.29 and 63.01 MPa) when compared with those of tissue treated with chloroform/methanol (29.92-42.30 MPa) or with SDS (13.49-19.06 MPa). In a second phase of the study, selection criteria based on morphological and mechanical factors were applied to the pericardial membranes employing a system of paired samples. The mathematical analysis of the findings in one fragment will aid in determining the mechanical behavior of its adjacent twin sample. In conclusion, the anticalcification chemical treatments tested in the experimental model conferred a lesser mechanical resistance than that obtained with GA. On the other hand, the utilization of paired samples was found to be useful in the prediction of the mechanical behavior of porcine pericardial tissue. Nevertheless, in order for our method of selection to be considered the most adequate approach, it will be necessary to validate these findings in dynamic studies involving a real, functional model.

Animals↗

PubMed2001

A new method for selecting calf pericardium for use in cardiac bioprostheses on the basis of morphological and mechanical criteria.

The durability of existing calf pericardium bioprostheses is limited by phenomena such as mechanical stress and calcification, the factors most frequently implicated in valve failure. Varying the preferred direction of the collagen fibers influences the mechanical behavior of the pericardial membrane. Given this possible variation, a strict control of the selection of the biomaterial employed in the construction of valve leaflets is essential, but a reliable method of selection has yet to be established. This study describes the development of a new system of in vitro selection involving a hydraulic simulator that reproduces the mechanical behavior of pericardial membranes subjected to the stress of continuous flow. By combining morphological criteria such as thickness and homogeneity with those of mechanical behavior, and by selecting paired samples from different parts of the pericardium, we obtained excellent mathematical fits. Linear regression analysis provided the mode of predicting the tensile strength in a given sample when this value had been determined in its twin. The upper zones of calf pericardium, corresponding to either right or left ventricle but at a distance from ligamentous structures, showed the best mean results at rupture (60 MPa) and permitted the most reliable prediction. The expected stress for an elongation of 30% was 1.12 MPa, as was previously observed, with a 95% confidence interval of between 1.11 and 1.14 MPa. These trials, together with the careful selection of the pairs, should help to establish definitive selection criteria.

Journal Article↗

PubMed2001

Influence of the selection of the suture material on the mechanical behavior of a biomaterial to be employed in the construction of implants. Part 2: Porcine pericardium.

Using a hydraulic stress simulator, the mechanical behavior of the porcine pericardium used in the construction of cardiac valve leaflets was characterized following the same procedure employed with calf pericardium in Part 1 of this study. One hundred fifty pairs of tissue samples were subjected to tensile testing to rupture. One of the two samples from each of 120 pairs (four series of 30 pairs each) was saturated with commercially available threads made of nylon, silk, Prolene or Gore-Tex, while the other sample in each of these pairs was left unsewn. The remaining 30 pairs were employed as controls in which neither of the two samples was subjected to suturing. The sutured tissue samples showed a significant decrease in tensile strength at rupture (range: 11.61 to 21.22 MPa) when compared with unsutured samples (range: 50.80 to 89.45 MPa; p < 0.01). When these results were compared with their equivalent in calf pericardium, no significant differences were observed (the mean values at rupture in calf pericardium ranged between 211.61 MPa and 26.04 MPa). Again, the application of morphological and mechanical selection criteria to ensure the homogeneity of the samples provided excellent fit with respect to the stress/strain curves. The interaction of the different suture materials with the pericardial tissue was also assessed by comparing the mechanical behavior of the sutured samples with that of the control samples. At the working stress of a cardiac valve leaflet, 0.250 MPa, samples sewn with Gore-Tex were found to show the least difference in behavior with respect to the controls, indicating that this material presented the lowest degree of interaction with the pericardium. In conclusion, the suture clearly has deleterious effects on the resistance of both calf and porcine pericardium, which showed no statistically significant differences in terms of resistance to rupture when their respective sutured or unsutured samples were compared, except in the case of porcine pericardium sewn with silk, which presented lower resistance to rupture in all the zones studied. These findings suggest that the hypothesis that porcine pericardium is less resistant is erroneous. The Gore-Tex suture also presented a lower degree of interaction with the porcine pericardium, with values similar to the working stress of a cardiac valve leaflet. This methodology and the results should be evaluated in dynamic studies, such as fatigue testing, that not only confirm the resistance of the material but establish the durability of the samples being assayed.

Animals↗

PubMed2001

Influence of the selection of the suture material on the mechanical behavior of a biomaterial to be employed in the construction of implants. Part 1: Calf pericardium.

A hydraulic stress simulator was employed to study the mechanical behavior of the calf pericardium used in the construction of cardiac valve leaflets. One hundred eighty pairs of tissue samples were subjected to tensile testing to rupture. One of the two samples from each of 144 pairs (four series of 36 pairs each) was sutured with commercially available threads made of nylon, silk, Prolene or Gore-Tex, while the other sample in each of these pairs was left unsewn. The remaining 36 pairs were employed as controls in which neither of the two samples was subjected to suturing. The sutured tissue samples showed a significant decrease in tensile strength at rupture (range: 11.81 to 26.04 MPa) when compared with unsutured samples (range: 39.38 to 87.96 MPa; p < 0.01). The application of morphological and mechanical selection criteria to maximize the homogeneity of the samples provided excellent fit with respect to the stress/strain curves. This method made it possible to carry out a predictive study of the mechanical behavior of a sutured sample, based on that observed in the corresponding unsutured fragment. The interaction of the different suture materials with the pericardial tissue was also assessed by comparing the mechanical behavior of the sutured samples with that of the control samples. At stresses of less than 0.8 MPa, samples sewn with Gore-Tex were found to show the least difference with respect to the controls, indicating that this material presented the lowest degree of interaction with the pericardium. In conclusion, the degree of the loss of resistance to tearing of the sutured samples is of no value in the selection of the optimal suture material. The selection process applied makes it possible to predict the mechanical behavior in response to suturing of a given unsewn tissue specimen by determining that of its sutured mate. The similarity between the findings in samples sewn with Gore-Tex and in the unsutured controls indicates a lesser degree of interaction between the suture material and the pericardium employed in the construction of cardiac valve leaflets.

Animals↗

PubMed2000

The influence of chemical treatment and suture on the elastic behavior of calf pericardium utilized in the construction of cardiac bioprostheses.

Poor mechanical properties of biological tissue are known to cause wear, leading to the failure of cardiac bioprostheses made of calf pericardium. Different chemical agents such as sodium dodecyl sulfate (SDS) are presently being tested as possible inhibitors of the calcification process. The objective of this report was to determine the mechanical behavior of calf pericardium treated with SDS for 24 h and the influence of the suture on the mechanical properties of the tissue. Forty-eight samples were tested: 24 subjected to a standard treatment with glutaraldehyde (12 sewn with 4/0 silk suture thread) and 24 incubated with SDS for 24 h (12 sewn with the same suture thread). Each sutured and nonsutured sample was cut into two strips to yield paired samples. All were subjected to tensile stress to breaking point. The mean stress at breaking point in the nonsutured series treated with glutaraldehyde alone was 16.42 and 13.85 MPa, depending on the region of the pericardium, while in the sutured samples subjected to glutaraldehyde the mean stress was 7.50 and 7.63 MPa, respectively, differences which were statistically significant (p=0.03 and p=0.003, respectively) when the means for nonsutured samples from equivalent regions treated with glutaraldehyde were compared. The stress at breaking point was lower in the SDS-treated series, ranging between 2.60 and 3.56 MPa. The mathematical functions that govern the stress/strain or deformation were obtained. In the series of pericardium treated with SDS, deformations of 10% were produced with stresses of under 0.4 MPa, an outcome that is intolerable from the constructive point of view. We established a regression model that enabled us to determine the mechanical behavior of a sutured sample by testing a contiguous piece of tissue, with a high correlation coefficient (r\gt 0.99). We consider this finding to be of interest in the selection of pericardium for use in the construction of leaflets for cardiac bioprostheses.

Journal Article↗

PubMed2000

The influence of chemical treatment and suture on the elastic behavior of calf pericardium utilized in the construction of cardiac bioprostheses.

Poor mechanical properties of biological tissue are known to cause wear, leading to the failure of cardiac bioprostheses made of calf pericardium. Different chemical agents such as sodium dodecyl sulfate (SDS) are presently being tested as possible inhibitors of the calcification process. The objective of this report was to determine the mechanical behavior of calf pericardium treated with SDS for 24 h and the influence of the suture on the mechanical properties of the tissue. Forty-eight samples were tested: 24 subjected to a standard treatment with glutaraldehyde (12 sewn with 4/0 silk suture thread) and 24 incubated with SDS for 24 h (12 sewn with the same suture thread). Each sutured and non-sutured sample was cut into two strips to yield paired samples. All were subjected to tensile stress to breaking point. The mean stress at breaking point in the non-sutured series treated with glutaraldehyde alone was 16.42 and 13.85 MPa depending on the region of the pericardium, while in the sutured samples subjected to glutaraldehyde the mean stress was 7.50 and 7.63 MPa, respectively, differences which were statistically significant (p = 0.03 and p = 0.003, respectively) when the means for non-sutured samples from equivalent regions treated with glutaraldehyde were compared. The stress at breaking point was lower in the SDS-treated series, ranging between 2.60 and 3.56 MPa. The mathematical functions that govern the stress/strain or deformation were obtained. In the series of pericardium treated with SDS, deformations of 10% were produced with stresses of under 0.4 MPa, an outcome that is intolerable from the constructive point of view. We established a regression model that enabled us to determine the mechanical behavior of a sutured sample by testing a contiguous piece of tissue, with a high correlation coefficient (r \gt 0.99). We consider this finding to be of interest in the selection of pericardium for use in the construction of leaflets for cardiac bioprostheses.

Journal Article↗

PubMed2000

Uniaxial and biaxial tensile strength of calf pericardium used in the construction of bioprostheses: biomaterial selection criteria.

Using morphological and mechanical criteria and applying a method involving paired samples that is widely employed in epidemiology, we obtained an excellent prediction of the mechanical behavior of the calf pericardium used in the construction of cardiac bioprostheses. The method of selection employed in this study may be a highly useful tool for guaranteeing the mechanical resistance of calf pericardium, with a very low level of error.

Animals↗

PubMed1998

Selection and interaction of biomaterials used in the construction of cardiac bioprostheses.

The mechanical behavior of calf pericardium employed in the manufacture of cardiac bioprostheses was assessed according to the region from which it was selected. For this purpose, selected samples of the tissue were sewn with different types of commercially available sutures and subjected to tensile testing, the results of which were compared with the findings in selected, but not sutured, tissue used as a control. The results confirm a loss of resistance--that is, a reduction of the capacity of sutured samples of the biomaterial to withstand breakage stress compared with control samples. Taking into account the marked resistance to breakage of the suture thread, this phenomenon can only be explained as a consequence of the deleterious mechanical interaction between the suture and chemically treated pericardium. This interaction is illustrated by the shearing force which is responsible for the loss of resistance in the tested samples. These trials demonstrate that the results can be improved and the deleterious interaction diminished, although not eliminated, when the pericardium is selected from a given region.

Animals↗

PubMed1998

Analysis of shearing stress in the limited durability of bovine pericardium used as a biomaterial.

The objective of the study was to determine the shearing stress exerted by the suture thread under conditions of normal working stress. Thirty-six samples of calf pericardium, similar to that employed in the manufacture of bioprosthetic cardiac valve leaflets, were subjected to tensile testing. Prior to the trial, a continuous suture was sewn in the central zone of each sample, at a 45 degrees angle to the longest axis of the sample, using commercially-available threads (silk, Gore-Tex, Surgilene and nylon). Application of the Mohr circle for combined wear revealed that the shearing stress ranged between 2.68-fold greater (for samples sewn with silk) and 5.48-fold greater (for samples sewn with nylon) than the working tensile stress in the region of the suture. It is concluded that the shearing stress is responsible for the limited durability of sutured samples of calf pericardium prepared to simulate bioprosthetic cardiac valve leaflets.

Journal Article↗

PubMed1996

Comparison of elasticities of components of a cardiac bioprosthesis leaflet.

The mechanoelastic behavior of calf pericardium employed in cardiac bioprostheses was compared with that of three types of thread (Nylon, Prolene, and silk) used to suture this biological tissue. The elastic limit (EL) of each material was determined by means of tensile tests and the mathematical functions that govern the stress/strain curves within the EL have been described. The first derivative of these functions for each point to the curves allowed the immediate calculation of the elastic modulus (EM), which was considered the best parameter for comparing the elasticities of the materials being assessed. It was observed that the deformation of the pericardium produced by the working stress of a pericardial leaflet was approximately 1000 times greater than that produced in the surgical threads. When the elasticities were compared on the basis of the EM, that of pericardium was 749.06, 626.95, and 1253.17 times greater than that of the Nylon, Prolene, and silk suture threads, respectively. These results demonstrate that the interaction between these materials (pericardium and the threads) could be generating detrimental forces that can diminish the durability of the leaflets of the bioprostheses constructed of calf pericardium.

Animals↗

PubMed1996

Elastic behaviour of sutured calf pericardium: influence of the suture threads.

The purpose of this study was to assess the elastic behaviour of calf pericardium used in the construction of cardiac bioprosthesis valve leaflets, sutured with different types of commercially available sutures: silk, Gore-Tex, Surgilene and nylon. Thirty-two samples (four series of eight samples each) were subjected to tensile strength testing to breakage. The breaking stress (MPa) ranged between 4.89 MPa for samples sutured with Gore-Tex and 5.22 MPa for those sewn with nylon. Three samples from each series were subjected to a stepwise stress test, involving increasing levels of stress followed by return to zero, to define the elastic limit (the cut-off point beyond which strain is no longer reversible). Analysis of the results provided the mathematical functions that govern the elastic behaviour (stress/strain) within the elastic range for each type of sutured sample. The series sutured with Surgilene presented the highest mean value (1.649 MPa). Finally, a statistical study was carried out to determine which series showed the greatest probability of having the least interaction between the thread and the pericardium. Allowing an interval of +/- 10%, Gore-Tex showed the best probability in this respect. However, real fatigue testing is necessary to definitively determine which is the best suture to use.

Animals↗

PubMed1994

Resistance and elasticity of the suture threads employed in cardiac bioprostheses.

The mechanoelastic features of five types of sutures were studied. The breaking stress for each was determined by means of tensile tests in which a constant strain rate was applied, and a tensile test with graduated stress and relaxation defined the elastic limit, i.e. the point beyond which deformation becomes irreversible. The study of the stress-strain curve during this elastic period enabled us to obtain the mathematical function that governs these reversible deformations, which shows excellence of fit (R2 > 0.98). The prime derivative at each point of the resulting functions is the elastic modulus, the best parameter for comparing the elasticities of the suture threads. Since breaking stress alone does not suitably define the mechanical quality of a suture, we propose the use of other parameters during the elastic period, such as percentage of elongation at a point 10 times lower than the elastic limit (safety coefficient of 10), and tensile stress and elastic modulus at the said point, which are more reliable in the assessment of the resistance and elasticity of these threads.

Animals↗

PubMed1989

[Fulminant hepatic insufficiency].

We studied the patients admitted to the Intensive Medicine Department of the "Carlos Haya" Regional Hospital of Málaga (Spain) with a diagnosis of fulminant liver failure (IHF) between 1980 and October 1986. There were 7 patients, 6 women and one man: 5 had a picture of fulminant hepatitis, one pregnant female had fatty liver, and the man had fulminant hepatitis due to accidental inhalation of carbon tetrachloride. The average age of the group was 32 years. Six patients (85%) died; their average stay was 4.6 days, ranging from 10 hours to 7 days. The woman who survived spent 17 days in the unit. Postmortem studies were made in 4 patients. In the pregnant patient with fatty liver, 36 weeks gestation, a cesarean was performed and a live female fetus of 2,720 g. weight was extracted. Some pathogenic aspects of the disease are discussed, such as the incidence of superinfection by other viruses (delta virus), the influence of immunological factors on the development of fulminant liver failure, morphological findings, therapeutic results and the need for multicenter studies.

Adolescent↗