Enhanced vascular regeneration with chemically/physically treated bovine/human pericardium in rodents.

BACKGROUND: Glutaraldehyde-treated pericardia for cardiovascular applications have poor long-term clinical results. The efficacy of a combined physical/chemical treatment to improve pericardium biocompatibility and vascular regeneration was assessed and compared with detergent treatment and two commercial bovine pericardia: PeriGuard (DGBP) and Edwards pericardium (nDGBP). The physical and chemical process was applied to bovine and human pericardia (DBP-DHP), and the detergent process was applied to bovine (DDBP). MATERIAL AND METHODS: Native (NBP) and treated bovine tissues were assessed for decellularization (HE/DAPI/DNA/α-Gal and MHC-1 staining) and mechanical integrity ex vivo. Twenty Wistar rats received subcutaneous patches of each bovine tissue to assess immunogenic response up to 4 months (flow cytometry). Ten additional rats received four subcutaneous bovine-treated patches (one/condition) to evaluate the inflammatory reaction (CD3/CD68 immunostaining), calcification (von Kossa staining/calcium quantification), and integration assessment (Hematoxylin and eosin staining). Finally, 15 rodents received a patch on the aorta (DBP n = 5, DHP n = 5, and DGBP n = 5), and vascular biocompatibility and arterial wall regeneration were assessed after 4 months (CD3/CD68/CD31/ASMA and Miller staining). RESULTS: DBP reached the higher level of decellularization, no immunogenic response whereas maintaining mechanical properties. DBP induced the lowest level grade of inflammation after 2 months (P < 0.05) concomitantly for better remodeling. No complications occurred with DBP and DHP where vascular regeneration was confirmed. Moreover, they induced a low level of CD3/CD68 infiltrations. CONCLUSIONS: This process significantly reduces immunogenicity and improves biocompatibility of bovine and human pericardia for better vascular regeneration.

Application of compression optical coherence elastography for characterization of human pericardium: A pilot study.

The recent impressive progress in Compression Optical Coherence Elastography (C-OCE) demonstrated diverse biomedical applications, comprising ophthalmology, oncology, etc. High resolution of C-OCE enables spatially resolved characterization of elasticity of rather thin (thickness < 1 mm) samples, which previously was impossible. Besides Young's modulus, C-OCE enables obtaining of nonlinear stress-strain dependences for various tissues. Here, we report the first application of C-OCE to nondestructively characterize biomechanics of human pericardium, for which data of conventional tensile tests are very limited and controversial. C-OCE revealed pronounced differences among differently prepared pericardium samples. Ample understanding of the influence of chemo-mechanical treatment on pericardium biomechanics is very important because of rapidly growing usage of own patients' pericardium for replacement of aortic valve leaflets in cardio-surgery. The figure demonstrates differences in the tangent Young's modulus after glutaraldehyde-induced cross-linking for two pericardium samples. One sample was over-stretched during the preparation, which caused some damage to the tissue.

Influence of inflammation and cardiac hypertrophy on mechanical properties of human pericardium.

Different devices for mechanical circulatory support (MCS) have been developed for the treatment of refractory cardiogenic shock. However, all of them are associated with direct blood contact, the need for anticoagulation and bleeding complications. To overcome these limitations the pericardial sac got into the focus as a promising implantation site for MCS. For this purpose, further knowledge about the mechanical properties of human pericardium is required. In this prospective, monocentric, experimental pilot study 56 samples of human pericardium were extracted postmortem from 13 critically ill patients. After preparation of test specimens uniaxial tensile tests were performed. The primary end points were load at fracture per sample width and strain at fracture. Acute inflammation was assessed by blood levels of C-reactive protein, white blood count and procalcitonin measured at several times during hospital stay. Inflammatory load was estimated by area under the inflammatory curves. Correlation and regression analysis were used to assess the relationship of primary end points to inflammation, comorbidities and postmortem time to preparation. Human pericardium showed a load at fracture per sample width of 1.95 [1.38-2.94] N/mm (median [inter quartile range]) and a strain at fracture of 89.29 [73.84-135.23] %. Markers of acute inflammation and cardiac hypertrophy did not correlate to load or strain at fracture. However, strain at fracture increased with higher body mass index and an increasing number of postmortem days. In contrast, higher patient age was associated with a lower strain at fracture. Inflammation and cardiac hypertrophy did not influence mechanical properties of human pericardium.

The influence of glutaraldehyde on the microscopic structure of human pericardium.

OBJECTIVES: In our study, we investigate the collagen structure of human pericardium microscopically in dependence of glutaraldehyde (GA) concentration and fixation time. METHODS: Pericardial samples were taken from 9 patients aged 40+ years who underwent cardiac surgery, either coronary artery bypass surgery or valve implantation/reconstruction. Specimens were cut in 5 equal pieces and treated with GA at fixed concentrations (0.3125%, 0.625%, or 1.25%) but different exposer times (5 min, 10 min, 20 min, 30 min, and 60 min). Elastica van Gieson (EvG) staining was used for microscopic examination of pericardial collagen structure. RESULTS: The collagen structure studied microscopically depended on both GA incubation time and GA concentration. At low GA concentrations (0.3125%, 0.625%) and short incubation times, individual collagen fibers appeared separately. After one hour incubation period, single collagen fibers could not be distinguished at any GA concentration. For fixed incubation times no differences were seen in the collagen structure when 0.3125% and 0.625% GA were used. However, at a concentration of 1.25% GA fusion of individual collagen fibers was already observed at low incubation times. CONCLUSION: Pericardial collagen structure changes with increasing incubation time and increasing GA concentration by raising fusion of single fibers. For GA concentrations of ≤0.625%, fiber fusion depends plainly on incubation time. That is relevant as this concentration is used in cardiac surgery. At a concentration of 1.25% GA, single collagen fibers could not be separated, even at short incubation times. Fusion of individual collagen fibers and changes in appearance (less undulating) were assumed to be responsible for stiffening of GA-fixed pericardium.

A human pericardium biopolymeric scaffold for autologous heart valve tissue engineering: cellular and extracellular matrix structure and biomechanical properties in comparison with a normal aortic heart valve.

The objective of our study was to compare the cellular and extracellular matrix (ECM) structure and the biomechanical properties of human pericardium (HP) with the normal human aortic heart valve (NAV). HP tissues (from 12 patients) and NAV samples (from 5 patients) were harvested during heart surgery. The main cells in HP were pericardial interstitial cells, which are fibroblast-like cells of mesenchymal origin similar to the valvular interstitial cells in NAV tissue. The ECM of HP had a statistically significantly (p < 0.001) higher collagen I content, a lower collagen III and elastin content, and a similar glycosaminoglycans (GAGs) content, in comparison with the NAV, as measured by ECM integrated density. However, the relative thickness of the main load-bearing structures of the two tissues, the dense part of fibrous HP (49 ± 2%) and the lamina fibrosa of NAV (47 ± 4%), was similar. In both tissues, the secant elastic modulus (Es) was significantly lower in the transversal direction (p < 0.05) than in the longitudinal direction. This proved that both tissues were anisotropic. No statistically significant differences in UTS (ultimate tensile strength) values and in calculated bending stiffness values in the longitudinal or transversal direction were found between HP and NAV. Our study confirms that HP has an advantageous ECM biopolymeric structure and has the biomechanical properties required for a tissue from which an autologous heart valve replacement may be constructed.

Biomechanical behavior of pericardial human tissue: a constitutive formulation.

This work aims to present a constitutive model suitable to interpret the biomechanical response of human pericardial tissues. The model is consistent with the need of describing large strains, anisotropy, almost incompressibility, and time-dependent effects. Attention is given to human pericardial tissue because of the increased interest in its application as a substitute in reconstructive surgery. Specific, even limited, experimental investigation has been performed on human samples taken from surgical grafts in order to verify the capability of the constitutive model in supplying a correct description of tissue mechanical response. Experimental data include uni-axial tensile tests and stress relaxation tests up to 300 s, developed along different directions of the tissue. The grafts tested show different mechanical characteristics for what concern the level of anisotropy of the tissue. The constitutive model proposed shows to adapt to the different configurations of the human pericardium grafts, as emerged by experimental data considered, and it is capable to describe the variability of the mechanical characteristics.