Tensile Strength of Human Pericardium Treated with Glutaraldehyde

Three-dimensional modelling of aortic leaflet coaptation and load-bearing surfaces: in silico design of aortic valve neocuspidizations

OBJECTIVES

Three-dimensional (3D) modelling of aortic leaflets remains difficult due to insufficient resolution of medical imaging. We aimed to model the coaptation and load-bearing surfaces of the aortic leaflets and adapt this workflow to aid in the design of aortic valve neocuspidizations.

METHODS

Geometric morphometrics, using landmarks and semilandmarks, was applied to the geometric determinants of the aortic leaflets from computed tomography, followed by an isogeometric analysis using Non-Uniform Rational Basis Splines (NURBS). Ten aortic valve models were generated, measuring determinants of leaflet geometry defined as 3D NURBS curves, and leaflet coaptation and load-bearing surfaces were defined as 3D NURBS surfaces. Neocuspidizations were obtained by either shifting the upper central coaptation landmark towards the sinotubular junction or using parametric neo-landmarks placed on a centreline drawn between the centroid of the aortic root base and centroid of a circle circumscribing the 3 upper commissural landmarks.

RESULTS

The ratio of the leaflet free margin length to the geometric height was 1.83, whereas the ratio of the commissural coaptation height to the central coaptation height was 1.93. The median coaptation surface was 137 mm2 (IQR 58) and the median load-bearing surface was 203 mm2 (60) per leaflet. Neocuspidization multiplied the central coaptation height by 3.7 and the coaptation surfaces by 1.97 and 1.92 using the native coaptation axis and centroid coaptation axis, respectively.

CONCLUSIONS

Geometric morphometrics reliably defined the coaptation and load-bearing surfaces of aortic leaflets, enabling an experimental 3D design for the in silico neocuspidization of aortic valves.

Tissue requirements for the application of aortic valve neocuspidization - appropriate pericardium properties and homogeneity?

OBJECTIVE

Aortic valve neocuspidization (AVNeo) using autologous pericardium is a promising technique. Expected advantages are reduced immune response, appropriate biomechanics and lower treatment expenses. Nevertheless, autologous pericardium can be affected by patient's age and comorbidities. Usually, glutaraldehyde (GA) - fixed bovine pericardium is the basic material for aortic valve prostheses, easy available and carefully pre-examined in a standardized fabrication process. Aim of the study is the verification of autologous pericardial tissue homogeneity by analysing tissue thickness, biomechanics and extracellular matrix (ECM) composition.

METHODS

Segments of human GA-fixed pericardium selected by the surgeon based on visual criteria for cusp pre-cut and remaining after surgical AV replacement were investigated in comparison to bovine standard tissue treated equivalently. Pericardium sampling was performed at up to three positions of each sutured cusp for histological or biomechanical analysis, according to tissue availability.

RESULTS AND CONCLUSIONS

Human pericardia exhibited a higher heterogeneity in collagen content, density of vessel structures and elastic moduli. Thickness, vessel density and collagen and elastin content differed significantly between the species. In contrast, significant interindividual differences were detected in most properties investigated for human pericardial samples but only for tissue thickness in bovine tissues. Higher heterogeneity of human pericardium, differing vessel and collagen content compared to bovine state-of-the-art material might be detrimental for long term AV functionality or deterioration and have to be intensely investigated in patients follow up after autologous cusp replacement.

Ozaki procedure-re-construction of aortic valve leaflets using autologous pericardial tissue: a review

The Ozaki procedure has emerged as a valuable option for treating various aortic valve pathologies. This review article delves into the intricacies of this innovative surgical approach by exploring its adaptation to the complex anatomy and physiology of the aortic root. The diverse etiologies of aortic valve diseases, ranging from congenital anomalies to degenerative changes, make treatment selection a complex challenge. Aortic valve replacement has traditionally been the gold standard, but emerging evidence supports valve repair techniques, emphasizing the importance of preserving native tissue. Nevertheless, issues like lifelong anticoagulation with mechanical valves and patient-prosthetic mismatch remain. The Ozaki procedure offers a compelling alternative by utilizing autologous pericardium or a tissue substitute to construct new aortic valve leaflets. This technique, standardized by Dr. Ozaki in 2007, provides a customizable and adaptable solution. The article highlights the anatomy of the aortic root, emphasizing the critical role of the sinus of Valsalva and interleaflet triangles in maintaining proper valve function. The procedure's unique adaptation to aortic root dynamics allows for reduced mechanical stress during systole and diastole, mimicking the natural valve's behavior. Furthermore, Ozaki leaflets exhibit promising hemodynamics and reduced risks of complications, such as permanent pacemaker implantation and patient-prosthetic mismatch. The use of autologous pericardium in the Ozaki procedure presents advantages, including enhanced tissue strength, minimal immunogenicity, and reduced risk of immune-mediated calcification. These factors contribute to the longevity and resilience of the reconstructed valve. This comprehensive review aims to shed light on the procedure's intricacies, its alignment with aortic root anatomy and physiology, and its potential as a valuable tool in the armamentarium of aortic surgeons.

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.

Biological Characterization of Human Autologous Pericardium Treated with the Ozaki Procedure for Aortic Valve Reconstruction

Background: The Ozaki procedure is an innovative surgical technique aiming at reconstructing aortic valves with human autologous pericardium. Even if this procedure is widely used, a comprehensive biological characterization of the glutaraldehyde (GA)-fixed pericardial tissue is still missing. Methods: Morphological analysis was performed to assess the general organization of pericardium subjected to the Ozaki procedure (post-Ozaki) in comparison to native tissue (pre-Ozaki). The effect of GA treatment on cell viability and nuclear morphology was then investigated in whole biopsies and a cytotoxicity assay was executed to assess the biocompatibility of pericardium. Finally, human umbilical vein endothelial cells were seeded on post-Ozaki samples to evaluate the influence of GA in modulating the endothelialization ability in vitro and the production of pro-inflammatory mediators. Results: The Ozaki procedure alters the arrangement of collagen and elastic fibers in the extracellular matrix and results in a significant reduction in cell viability compared to native tissue. GA treatment, however, is not cytotoxic to murine fibroblasts as compared to a commercially available bovine pericardium membrane. In addition, in in vitro experiments of endothelial cell adhesion, no difference in the inflammatory mediators with respect to the commercial patch was found. Conclusions: The Ozaki procedure, despite alteration of ECM organization and cell devitalization, allows for the establishment of a noncytotoxic environment in which endothelial cell repopulation occurs.

Effects of Short-Duration Ethanol Dehydration on Mechanical Properties of Porcine Pericardium

Purpose: Autologous pericardium is an ideal material for cardiovascular reconstruction including pulmonary artery plasty. Despite the fact that dehydration by ethanol has been used to improve its surgical handling, the effects of the ethanol on mechanical properties of the pericardium have not been previously investigated. The effects of short-duration ethanol dehydration on the mechanical properties of porcine pericardium were evaluated.

Methods: Porcine pericardia (n = 3) were separated into three groups: the raw group with no treatments (RAW), the group immersed in 70% ethanol for 10 min (ET group), and the group immersed in 0.6% glutaraldehyde for 10 min (GA). We measured five parameters of mechanical properties as specified in ISO 7198.

Results: ET treatment improved surgical handling as well as GA treatment. There were no significant differences in burst pressure (P = 0.639), suture retention strength (P = 0.529), ultimate tensile strength (UTS; P = 0.486), or Young’s modulus (P = 0.408). Only the ultimate strain of the GA group was significantly higher among the three groups (RAW: 33.34% ± 2.02%, ET: 37.48% ± 1.84%, GA: 44.74% ± 2.87%; P = 0.046).

Conclusions: Short-duration ethanol dehydration did not compromise its mechanical properties while maintaining its surgical handling improvements.

Modifications of the mechanical properties of in vivo tissue-engineered vascular grafts by chemical treatments for a short duration

In vivo tissue-engineered vascular grafts constructed in the subcutaneous spaces of graft recipients have functioned well clinically. Because the formation of vascular graft tissues depends on several recipient conditions, chemical pretreatments, such as dehydration by ethanol (ET) or crosslinking by glutaraldehyde (GA), have been attempted to improve the initial mechanical durability of the tissues. Here, we compared the effects of short-duration (10 min) chemical treatments on the mechanical properties of tissues. Tubular tissues (internal diameter, 5 mm) constructed in the subcutaneous tissues of beagle dogs (4 weeks, n = 3), were classified into three groups: raw tissue without any treatment (RAW), tissue dehydrated with 70% ET (ET), and tissue crosslinked with 0.6% GA (GA). Five mechanical parameters were measured: burst pressure, suture retention strength, ultimate tensile strength (UTS), ultimate strain (%), and Young’s modulus. The tissues were also autologously re-embedded into the subcutaneous spaces of the same dogs for 4 weeks (n = 2) for the evaluation of histological responses. The burst pressure of the RAW group (1275.9 ± 254.0 mm Hg) was significantly lower than those of ET (2115.1 ± 262.2 mm Hg, p = 0.0298) and GA (2570.5 ± 282.6 mm Hg, p = 0.0017) groups. Suture retention strength, UTS or the ultimate strain did not differ significantly among the groups. Young’s modulus of the ET group was the highest (RAW: 5.41 ± 1.16 MPa, ET: 12.28 ± 2.55 MPa, GA: 7.65 ± 1.18 MPa, p = 0.0185). No significant inflammatory tissue response or evidence of residual chemical toxicity was observed in samples implanted subcutaneously for four weeks. Therefore, short-duration ET and GA treatment might improve surgical handling and the mechanical properties of in vivo tissue-engineered vascular tissues to produce ideal grafts in terms of mechanical properties without interfering with histological responses.

Aortic valve neocuspidization with in-body tissue-engineered autologous membranes: preliminary results in a long-term goat model

OBJECTIVES

Aortic valve neocuspidization has shown satisfactory clinical outcomes; however, autologous pericardium durability is a concern for young patients. This study applied an autologous collagenous membrane (Biosheet®), produced by in-body tissue architecture, to aortic valve neocuspidization and investigated its long-term outcome in a goat model.

METHODS

Moulds were embedded subcutaneously in 6 goats. After 2 months, Biosheets formed in the moulds. We performed aortic valve neocuspidization using a portion of the sheets with a thickness of 0.20-0.35 mm, measured by optical coherence tomography. Animals were subjected to echocardiography and histological evaluation at 6 months (n = 3) and 12 months (n = 3). As a control, the glutaraldehyde-treated autologous pericardium was used in 4 goats that were similarly evaluated at 12 months.

RESULTS

All animals survived the scheduled period. At 6 months, Biosheets maintained valve function and showed a regeneration response: fusion to the annulus, cell infiltration to the leaflets and appearance of elastic fibres at the ventricular side. After 12 months, the regenerative structure had changed little without regression, and there was negligible calcification in the 1/9 leaflets. However, all cases had one leaflet tear, resulting in moderate-to-severe aortic regurgitation. In the pericardium group, three-fourths of the animals experienced moderate-to-severe aortic regurgitation with a high rate of calcification (9/12 leaflets).

CONCLUSIONS

Biosheets may have regeneration potential and anti-calcification properties in contrast to autologous pericardium. However, in order to obtain reliable outcome, further improvements are required to strictly control and optimize its thickness, density and homogeneity.

Impact on Mechanical Properties of 10 versus 20 Minute Treatment of Human Pericardium with Glutaraldehyde in OZAKI Procedure

Purpose: The aim of this study was to analyze the effects of 10-minute (standard term) versus 20-minute treatment with glutaraldehyde (GA) on mechanical stability and physical strength of human pericardium in the setting of the OZAKI procedure.

Methods: Leftover pericardium (6 patients) was bisected directly after the operation, and one-half was further fixed for 10 additional minutes. Uniaxial tensile tests were performed and ultimate tensile strength (UTS), ultimate tensile strain (uts), and collagen elastic modulus were evaluated.

Results: Both treatments resulted in similar values of uniaxial stretching-generated elongations at rupture (10 minutes 25 ± 7 % vs. 20 minutes: 22 ± 5 %; p = 0.05), UTS (5.16 ± 2 MPa vs. 6.54 ± 3 MPa; p = 0.59), and collagen fiber stiffness (elastic modulus: 31.80 ± 15.05 MPa vs. 37.35 ± 15.78 MPa; p = 0.25).

Conclusion: Prolongation of the fixation time of autologous pericardium has no significant effect on its mechanical stability; thus, extending the intraoperative treatment cannot be recommended.

Efficacy of Glutaraldehyde-Treated Leaflets for Mitral Valve Repair to Treat Active Infective Endocarditis: A Case Report

We report the use of glutaraldehyde (GA) in a case of valve repair for mitral valve prolapse associated with active infective endocarditis. GA scrubbed at the site of infection decontaminates and reinforces infected fragile tissue, avoids excessive debridement, and strengthens the edges of valve leaflets to facilitate suturing.

A case of aortic valve leaflet tear and perforations after neocuspidization

Although aortic valve (AV) replacement is a curative procedure for severe aortic stenosis, prosthetic heart valves have many disadvantages and cause serious complications. A new promising surgical procedure—aortic valve neocuspidization (AVNeo)—has recently been developed; it is an original method of AV reconstruction with autologous pericardium. It has been reported to yield excellent medium‐term results with respect to durability and complications. Herein, we encountered a first case of AV leaflet tear and perforations 27 months after AVNeo using autologous pericardium. AV leaflet tear or perforation is well recognized as a long‐term serious complication of pericardial xenografts. Interestingly, however, AVNeo caused early structural valve deterioration in the current case. In the present case, an eccentric aortic regurgitation jet observed on colour flow imaging led us to reach the correct diagnosis. Finally, the patient showed complete recovery with redo AV replacement. This case highlights the importance of understanding the potential pitfalls of this new surgical technique and that of colour Doppler echocardiography in reaching a definite diagnosis.

Supercritical carbon dioxide decellularised pericardium: Mechanical and structural characterisation for applications in cardio-thoracic surgery

INTRODUCTION

Many biomaterials are used in cardio-thoracic surgery with good short-term results. However, calcification, dehiscence, and formation of scar tissue are reported. The aim of this research is to characterise decellularised pericardium after supercritical carbon dioxide (scCO₂) processing as an alternative biological material for uses in cardio-thoracic surgery.

METHODS

Porcine and bovine pericardium were decellularised using scCO₂. Mechanical properties such as tensile strength, elastic modulus, fracture toughness and suture retention strength were determined. Ultrastructure was visualised using Scanning Electron Microscopy. Water uptake and swelling was experimentally determined. Commercially available glutaraldehyde treated bovine pericardium was used as gold standard for comparison.

RESULTS

scCO₂ decellularised porcine (and bovine pericardium) maintained their tensile strength compared to untreated native pericardium (13.3 ± 2.4MPa vs 14.0 ± 4.1MPa, p = 0.73). Tensile strength of glutaraldehyde treated pericardium was significantly higher compared to untreated pericardium (19.4 ± 7.3MPa vs 10.2 ± 2.2MPa, p = 0.02). Suture retention strength of scCO₂ treated pericardium was significantly higher than glutaraldehyde treated pericardium (p = 0.01). We found no anisotropy of scCO₂ or glutaraldehyde treated pericardium based on a trouser tear test. Ultrastructure was uncompromised in scCO₂ treated pericardium, while glutaraldehyde treated pericardium showed deterioration of extracellular matrix.

CONCLUSION

scCO₂ processing preserves initial mechanical and structural properties of porcine and bovine pericardium, while glutaraldehyde processing damages the extracellular matrix of bovine pericardium. Decellularisation of tissue using scCO₂ might give long-term solutions for cardio-thoracic surgery without compromising initial good mechanical properties.

Feasibility of pig and human-derived aortic valve interstitial cells seeding on fixative-free decellularized animal pericardium

Glutaraldehyde-fixed pericardium of animal origin is the elective material for the fabrication of bio-prosthetic valves for surgical replacement of insufficient/stenotic cardiac valves. However, the pericardial tissue employed to this aim undergoes severe calcification due to chronic inflammation resulting from a non-complete immunological compatibility of the animal-derived pericardial tissue resulting from failure to remove animal-derived xeno-antigens. In the mid/long-term, this leads to structural deterioration, mechanical failure, and prosthesis leaflets rupture, with consequent need for re-intervention. In the search for novel procedures to maximize biological compatibility of the pericardial tissue into immunocompetent background, we have recently devised a procedure to decellularize the human pericardium as an alternative to fixation with aldehydes. In the present contribution, we used this procedure to derive sheets of decellularized pig pericardium. The decellularized tissue was first tested for the presence of 1,3 α-galactose (αGal), one of the main xenoantigens involved in prosthetic valve rejection, as well as for mechanical tensile behavior and distensibility, and finally seeded with pig- and human-derived aortic valve interstitial cells. We demonstrate that the decellularization procedure removed the αGAL antigen, maintained the mechanical characteristics of the native pig pericardium, and ensured an efficient surface colonization of the tissue by animal- and human-derived aortic valve interstitial cells. This establishes, for the first time, the feasibility of fixative-free pericardial tissue seeding with valve competent cells for derivation of tissue engineered heart valve leaflets.

Aortic valve reconstruction with autologous pericardium for dialysis patients

OBJECTIVES

This study aimed to report on original aortic valve reconstruction for patients on dialysis.

METHODS

Aortic valve reconstruction has been performed on 404 cases from April 2007 through September 2011. Among them, 54 cases on haemodialysis were retrospectively studied. Forty-seven patients had aortic stenosis, 5 had aortic regurgitation (AR), and 2 had infective endocarditis. Mean age was 70.2 ± 8.5 years. There were 35 males and 19 females. There were 27 primary aortic valve reconstructions, 11 with CABG, 6 with ascending aortic replacement, 5 with mitral valve repair and 4 with maze. First, in the procedure, harvested pericardium was treated with 0.6% glutaraldehyde solution. After resecting the cusps, we measured the distance between commissures with original sizing instrument. Then, the pericardium was trimmed with the original template. Three cusps were sutured to each annulus.

RESULTS

Peak pressure gradient averaged to 66.0 ± 28.2 mmHg preoperatively, and decreased to 23.4 ± 10.7, 13.8 ± 5.5 and 13.3 ± 2.3 mmHg, 1 week, 1 year, and 3 years after the operation, respectively. No calcification was detected with echocardiographic follow-up. Recurrence of AR was not recorded with the mean follow-up of 847 days except for 1 case reoperated on for infective endocarditis 2.5 years after the operation. Three hospital deaths were recorded due to non-cardiac causes. Other patients were in good condition. There was no thromboembolic event.

CONCLUSIONS

Medium-term results are excellent. Since warfarin for dialysis patients becomes problematic, a postoperative warfarin-free status is desirable. Aortic valve reconstruction can provide patients with a better quality of life without warfarin.