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Transcatheter Heart Valve Downstream Fluid Dynamics in an Accelerated Evaluation Environment. Ann Biomed Eng 2021; 49:2170-2182. [PMID: 33638029 DOI: 10.1007/s10439-021-02751-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 02/12/2021] [Indexed: 10/22/2022]
Abstract
Transcatheter aortic valve replacements (TAVRs) provide minimally invasive delivery of bioprosthetic heart valves (BHVs) for the treatment of aortic valve disease. While surgical BHVs show efficacy for 8-10 years, long-term TAVR durability remains unknown. Pre-clinical testing evaluates BHV durability in an ISO:5840 compliant accelerated wear tester (AWT), yet, the design and development of AWTs and their accuracy in predicting in vivo performance, is unclear. As a result of limited knowledge on AWT environment and BHV loading, durability assessment of candidate valves remains fundamentally empirical. For the first time, high-speed particle image velocimetry quantified an ISO:5840 compliant downstream AWT velocity field, Reynolds stresses, and turbulence intensity. TAVR enface imaging quantified the orifice area and estimated the flow rate. When valve area and flow rate were at their maximum during peak systole (1.49 cm2 and 16.05 L/min, respectively), central jet velocity, Reynolds normal and shear stress, and turbulence intensity grew to 0.50 m/s, 265.1 Pa, 124.6 Pa, and 37.3%, respectively. During diastole, unique AWT recirculation produced retrograde flow and the directional changes created eddies. These novel AWT findings demonstrated a substantially reduced valve fully loaded period and pressure not matching in vivo or in vitro studies, despite the comparable fluid environment and TAVR motion.
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Bioprosthetic Heart Valve Calcification: Clinicopathologic Correlations, Mechanisms, and Prevention. CONTEMPORARY CARDIOLOGY 2020. [DOI: 10.1007/978-3-030-46725-8_9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Krings M, Kanellopoulou D, Koutsoukos PG, Mavrilas D, Glasmacher B. Development of a New Combined Test Setup for Accelerated Dynamic pH-Controlled in vitro Calcification of Porcine Heart Valves. Int J Artif Organs 2018; 32:794-801. [DOI: 10.1177/039139880903201105] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Fifty years after their first implantation, bioprosthetic heart valves still suffer from tissue rupture and calcification. Since new bioprostheses exhibit a lower risk of calcification, fast and reliable in vitro methods need to be evaluated for testing the application of new anti-calcification techniques. This report describes a modification of the well-known in vitro dynamic calcification test method (Glasmacher et al, Leibniz University Hannover (LUH)), combined with the pH-controlled, constant solution supersaturation (CSS) method (University of Patras (UP)). The CSS method is based on monitoring the pH of the solution and the addition of calcium and phosphate ion solutions through the implementation of two syringe pumps. The pH and the activities of all ions in the solutions are thus kept constant, resulting in higher calcification rates compared to conventional in vitro methods in which solution supersaturation is allowed to decrease without any further control. To verify this hypothesis, five glutaraldehyde preserved porcine aortic valves were tested. Three of the valves were tested according to a free-drift methodology: the valves were immersed in a supersaturated calcification solution, with an initial total calcium times total phosphate product of (CaxP)=10.5 (mmol/L)2 renewed weekly. Two valves were tested by the new pH-controlled loop system, implementing the CSS methodology. All valves were tested for a 4-week period, loaded at 300 cycles per minute, resulting in a total of 12 million cycles at the end of the testing period. The degree of calcification was determined weekly by means of μx-ray, and by conventional, clinical and micro-computer tomography (CT, μCT). The results showed that the valves mineralizing at constant solution supersaturation in vitro yielded higher rates of calcification compared to the valves tested at conditions of decreasing solution supersaturation without any control, indicating the development of a new, accelerated, controllable in vitro calcification method.
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Affiliation(s)
- Martin Krings
- Institute for Multiphase Processes/Center for Biomedical Engineering, Leibniz University Hannover (LUH), Hannover - Germany
| | - Dimitra Kanellopoulou
- FORTH-ICEHT and Dept. of Chemical Engineering, University of Patras, Patras - Greece
| | - Petros G. Koutsoukos
- FORTH-ICEHT and Dept. of Chemical Engineering, University of Patras, Patras - Greece
| | | | - Birgit Glasmacher
- Institute for Multiphase Processes/Center for Biomedical Engineering, Leibniz University Hannover (LUH), Hannover - Germany
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Abstract
The commercial and biobased polyurethane foams (PUF) were produced and characterized in this study. Commercial polyether polyol, crude glycerol, methanol-free crude glycerol, and pure glycerol were used as polyols. Crude glycerol is byproduct of the biodiesel production, and it is a kind of biofuel residue. Polyol blends were prepared by mixing the glycerol types and the commercial polyol with different amounts, 10 wt%, 30 wt%, 50 wt%, and 80 wt%. All types of polyol blends were reacted with polymeric diphenyl methane diisocyanates (PMDI) for the production of rigid foams. Thermal properties of polyurethane foams are examined by thermogravimetric analysis (TGA) and thermal conductivity tests. The structures of polyurethane foams were examined by Fourier Transformed Infrared Spectroscopy (FTIR). Changes in morphology of foams were investigated by Scanning Electron Microscopy (SEM). Mechanical properties of polyurethane foams were determined by compression tests. This study identifies the critical aspects of polyurethane foam formation by the use of various polyols and furthermore offers new uses of crude glycerol and methanol-free crude glycerol which are byproducts of biodiesel industry.
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Abstract
Introduction In this paper we propose a novel method for developing a polymeric heart valve that could potentially offer an optimum solution for a heart valve substitute. The valve design proposed will provide superior hydrodynamic performance and excellent structural integrity. A full description of the design process is given together with an analysis of the hemodynamic performance using a 2-way strongly coupled Fluid Structure Interaction (FSI). Method A polymeric tri-leaflet heart valve is designed based on a patient's sinus of Valsalva (SOV) geometry. The design strategy aims to improve valve hemodynamic performance as well as valve durability by avoiding stress concentrations in the leaflets and reducing the maximum stress level. The valve dynamics and stress levels are also validated by comparing the predicted data to existing experimental and numerical data. Results The stress distribution in the valve structure is fully characterized throughout the simulation and Von Mises stress is found to be up to 5.32 Mpa during diastole. The results show that an effective orifice area (EOA) and a pressure drop of 3.22 cm^2, and 3.52 mmHg, respectively, can be achieved using the proposed design. Conclusions The optimized valve demonstrates high hemodynamic performance with no sign of damaging stress concentration in the entire cardiac cycle.
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Polymeric heart valves for surgical implantation, catheter-based technologies and heart assist devices. Biomaterials 2015; 36:6-25. [DOI: 10.1016/j.biomaterials.2014.09.013] [Citation(s) in RCA: 107] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Accepted: 09/12/2014] [Indexed: 11/18/2022]
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Rose JB, Pacelli S, Haj AJE, Dua HS, Hopkinson A, White LJ, Rose FRAJ. Gelatin-Based Materials in Ocular Tissue Engineering. MATERIALS (BASEL, SWITZERLAND) 2014; 7:3106-3135. [PMID: 28788609 PMCID: PMC5453355 DOI: 10.3390/ma7043106] [Citation(s) in RCA: 191] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Revised: 03/17/2014] [Accepted: 03/24/2014] [Indexed: 12/13/2022]
Abstract
Gelatin has been used for many years in pharmaceutical formulation, cell culture and tissue engineering on account of its excellent biocompatibility, ease of processing and availability at low cost. Over the last decade gelatin has been extensively evaluated for numerous ocular applications serving as cell-sheet carriers, bio-adhesives and bio-artificial grafts. These different applications naturally have diverse physical, chemical and biological requirements and this has prompted research into the modification of gelatin and its derivatives. The crosslinking of gelatin alone or in combination with natural or synthetic biopolymers has produced a variety of scaffolds that could be suitable for ocular applications. This review focuses on methods to crosslink gelatin-based materials and how the resulting materials have been applied in ocular tissue engineering. Critical discussion of recent innovations in tissue engineering and regenerative medicine will highlight future opportunities for gelatin-based materials in ophthalmology.
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Affiliation(s)
- James B Rose
- School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, UK.
| | - Settimio Pacelli
- Department of Drug Chemistry and Technologies, "Sapienza" University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy.
| | - Alicia J El Haj
- Institute for Science and Technology in Medicine, Keele University, Stoke-on-Trent ST4 7QB, UK.
| | - Harminder S Dua
- Academic Ophthalmology, Division of Clinical Neuroscience, University of Nottingham, Nottingham NG7 2RD, UK.
| | - Andrew Hopkinson
- Academic Ophthalmology, Division of Clinical Neuroscience, University of Nottingham, Nottingham NG7 2RD, UK.
| | - Lisa J White
- School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, UK.
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Schoen FJ, Levy RJ. Pathological Calcification of Biomaterials. Biomater Sci 2013. [DOI: 10.1016/b978-0-08-087780-8.00063-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Flexible Leaflet Polymeric Heart Valves. CARDIOVASCULAR AND CARDIAC THERAPEUTIC DEVICES 2013. [DOI: 10.1007/8415_2013_166] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Connolly JM, Bakay MA, Alferiev IS, Gorman RC, Gorman JH, Kruth HS, Ashworth PE, Kutty JK, Schoen FJ, Bianco RW, Levy RJ. Triglycidyl amine crosslinking combined with ethanol inhibits bioprosthetic heart valve calcification. Ann Thorac Surg 2011; 92:858-65. [PMID: 21871270 DOI: 10.1016/j.athoracsur.2011.04.104] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/18/2011] [Revised: 04/22/2011] [Accepted: 04/29/2011] [Indexed: 11/26/2022]
Abstract
BACKGROUND One of the most important factors responsible for the calcific failure of bioprosthetic heart valves is glutaraldehyde crosslinking. Ethanol (EtOH) incubation after glutaraldehyde crosslinking has previously been reported to confer anticalcification efficacy for bioprostheses. The present studies investigated the anticalcification efficacy in vivo of the novel crosslinking agent, triglycidyl amine (TGA), with or without EtOH incubation, in comparison with glutaraldehyde. METHODS The TGA crosslinking (±EtOH) was used to prepare porcine aortic valves for both rat subdermal implants and sheep mitral valve replacements, for comparisons with glutaraldehyde-fixed controls. Thermal denaturation temperature, an index of crosslinking, cholesterol extraction, and hydrodynamic properties were quantified. Explant endpoints included quantitative and morphologic assessment of calcification. RESULTS Thermal denaturation temperatures after TGA were intermediate between unfixed and glutaraldehyde-fixed. EtOH incubation resulted in almost complete extraction of cholesterol from TGA or glutaraldehyde-fixed cusps. Rat subdermal explants (90 days) demonstrated that TGA-EtOH resulted in a significantly greater level of inhibition of calcification than other conditions. Thus, TGA-ethanol stent mounted porcine aortic valve bioprostheses were fabricated for comparisons with glutaraldehyde-pretreated controls. In hydrodynamic studies, TGA-EtOH bioprostheses had lower pressure gradients than glutaraldehyde-fixed. The TGA-ethanol bioprostheses used as mitral valve replacements in juvenile sheep (150 days) demonstrated significantly lower calcium levels in both explanted porcine aortic cusp and aortic wall samples compared with glutaraldehyde-fixed controls. However, TGA-EtOH sheep explants also demonstrated isolated calcific nodules and intracuspal hematomas. CONCLUSIONS The TGA-EtOH pretreatment of porcine aortic valves confers significant calcification resistance in both rat subdermal and sheep circulatory implants, but with associated structural instability.
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Affiliation(s)
- Jeanne M Connolly
- Division of Cardiology, The Children's Hospital of Philadelphia, and University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4318, USA.
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Kuan YH, Dasi LP, Yoganathan A, Leo HL. Recent Advances in Polymeric Heart Valves Research. ACTA ACUST UNITED AC 2011. [DOI: 10.4018/ijbre.2011010101] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Heart valve replacement is fast becoming a routine surgery worldwide, and heart valve prostheses are today considered among the most widely used cardiovascular devices. Mechanical and bioprostheses have been the traditional choices to the replacement surgeries. However, such valves continue to expose patients to risks including thrombosis, infection and limited valve durability. In recent years, advances in polymer science give rise to an important new class of artificial heart valve made predominantly of polyurethane-based materials, which show improved biocompatibility and biostability. These polymeric heart valves have demonstrated excellent hemodynamic performance and good durability with excellent fatigue stress resistance. Advancements in the designs and manufacturing methods also suggested improved in the durability of polymeric heart valves. Animal studies with these valves have also shown good biocompatibility with minimal calcification of the valve leaflets. With these promising progresses, polymeric heart valves could be a viable alternative in the heart valve replacement surgeries in the near future.
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Abstract
Polymeric heart valves could offer an optimum alternative to current prostheses, by joining the advantages of mechanical and bioprosthetic valves. Though a number of materials suitable for this application have recently become available, significant improvements in the valve design are still needed. In this paper, a novel polymeric heart valve design is proposed and its optimization procedure, based on the use of finite elements, is described. The design strategy was aimed at reducing the energy absorbed during the operating cycle, resulting in high hydrodynamic performances and reduced stress levels. The efficacy of the design strategy was assessed by comparing the valve dynamics and stress levels predicted numerically during the cycle with those of an existing and well qualified polymeric valve design. The improved hydrodynamic performance of the proposed design was confirmed experimentally, by in vitro testing in a pulse duplicator.
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Affiliation(s)
- G Burriesci
- Cardiovascular Engineering & Medical Devices Group, Department of Mechanical Engineering, UCL, Torrington Place, WC1E 7JE, London, UK.
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Lee CH. Physiological variables involved in heart valve substitute calcification. Expert Opin Biol Ther 2009; 9:1031-42. [PMID: 19555314 DOI: 10.1517/14712590903085091] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Biochemical, histological and genetic studies using in vitro/in vivo models have demonstrated that pathological calcification of bioprosthetic heart valves (BHV) is regulated by various mechanisms associated with physiological variables. The major objective of this review is to characterize physiological variables involved in BHV calcification. This review examines our understanding of the systemic cellular behavior and physiological regulation processes behind BHV calcification and its clinical applications.
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Affiliation(s)
- Chi H Lee
- University of Missouri-Kansas City, School of Pharmacy, Department of Pharmaceutical Sciences, Kansas City, MO 64110, USA.
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Sacks MS. Biomechanics of engineered heart valve tissues. CONFERENCE PROCEEDINGS : ... ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL CONFERENCE 2008; 2006:853-4. [PMID: 17946864 DOI: 10.1109/iembs.2006.259756] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The vast majority of prosthetic valve designs are either mechanical prosthesis and bioprosthetic heart valves (BHV). Mechanical prostheses are fabricated from synthetic materials, mainly pyrolytic carbon leaflets mounted in a titanium frame. Tissue engineering (TE) offers the potential to create cardiac replacement structures containing living cells, which has the potential for growth and remodeling, overcoming the limitations of current pediatric heart valve devices. The purpose of this paper is to present a review of the structure-strength relationships for native and engineered heart valve tissues.
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Abstract
Calcification plays a major role in the failure of bioprosthetic and other tissue heart valve substitutes. Tissue valve calcification is initiated primarily within residual cells that have been devitalized, usually by glutaraldehyde pretreatment. The mechanism involves reaction of calcium-containing extracellular fluid with membrane-associated phosphorus to yield calcium phosphate mineral deposits. Calcification is accelerated by young recipient age, valve factors such as glutaraldehyde fixation, and increased mechanical stress. Recent studies have suggested that pathologic calcification is regulated by inductive and inhibitory factors, similar to the physiologic mineralization of bone. The most promising preventive strategies have included binding of calcification inhibitors to glutaraldehyde fixed tissue, removal or modification of calcifiable components, modification of glutaraldehyde fixation, and use of tissue cross linking agents other than glutaraldehyde. This review summarizes current concepts in the pathophysiology of tissue valve calcification, including emerging concepts of endogenous regulation, progress toward prevention of calcification, and issues related to calcification of the aortic wall of stentless bioprosthetic valves.
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Affiliation(s)
- Frederick J Schoen
- Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, the Harvard-MIT Division of Health Sciences and Technology, Boston, Massachusetts 02115, USA.
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Pathak CP, Adams AK, Simpson T, Phillips RE, Moore MA. Treatment of bioprosthetic heart valve tissue with long chain alcohol solution to lower calcification potential. J Biomed Mater Res A 2004; 69:140-4. [PMID: 14999761 DOI: 10.1002/jbm.a.20129] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The use of glutaraldehyde-treated biological tissue in heart valve substitutes is an important option in the treatment of heart valve disease. These devices have limited durability, in part, because of tissue calcification and subsequent tearing of the valve leaflets. Components thought to induce calcification include lipids, cell remnants, and residual glutaraldehyde. We hypothesized that treatment of glutaraldehyde-treated bioprosthetic heart valve material using a short and long chain alcohol (LCA) combination, composed of 5% 1,2-octanediol in an ethanolic buffered solution, would reduce phospholipid content and subsequently lower the propensity of these tissues to calcify in vivo. Phospholipid content of glutaraldehyde-treated porcine valve leaflets and bovine pericardium was found to be 10.1 +/- 4.3 (n = 7) and 3.9 +/- 0.48 (n = 2) microg/mg dry tissue, respectively, which was reduced to 0.041 +/- 0.06 (n = 7) and 0.21 +/- 0.05 (n = 4) microg/mg dry tissue, respectively, after LCA treatment. Calcification potential of the treated tissues was assessed using a rat subcutaneous implant model. After 60 days of implantation, calcium levels were found to be 171 +/- 32 (n = 11) and 83 +/- 70 (n = 12) mg/g dry weight for glutaraldehyde-treated porcine leaflets and bovine pericardium, respectively, whereas prior LCA treatment resulted in reduced calcium levels of 1.1 +/- 0.6 (n = 12) and 0.82 +/- 0.1 (n = 12) mg/g dry weight, respectively. These data, taken together, support the notion that treatment of glutaraldehyde-treated tissue with a short and long chain alcohol combination will reduce both extractable phospholipids and the propensity for in vivo calcification.
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Simmons CA, Nikolovski J, Thornton AJ, Matlis S, Mooney DJ. Mechanical stimulation and mitogen-activated protein kinase signaling independently regulate osteogenic differentiation and mineralization by calcifying vascular cells. J Biomech 2004; 37:1531-41. [PMID: 15336928 DOI: 10.1016/j.jbiomech.2004.01.006] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/09/2004] [Indexed: 11/16/2022]
Abstract
Ectopic calcification of vascular tissue is associated with several cardiovascular pathologies and likely involves active regulation by vascular smooth muscle cells and osteoblast-like vascular cells. This process often occurs in sites with altered mechanical environments, suggesting a role for mechanical stimuli in calcification. In this study, we investigated the effect of mechanical stimulation on the proliferation, osteogenic differentiation, calcification, and mitogen-activated protein kinase (MAPK) signaling in calcifying vascular cells (CVCs), a subpopulation of aortic smooth muscle cells putatively involved in vascular calcification. Application of equibiaxial cyclic strain (7%, 0.25 Hz) to CVCs had no effect on cell proliferation, but accelerated alkaline phosphatase expression and significantly increased mineralization by 3.1-fold over unstrained cells. Fluid motion in the absence of strain also enhanced mineralization, but to a lesser degree. Because MAPK pathways mediate mechanically regulated osteoblast differentiation, we tested whether similar signaling was involved in mineralization by CVCs. In static cultures, pharmacological inhibition of the extracellular signal-regulated kinase (ERK1/2), p38 MAPK, and c-Jun N-terminal kinase pathways significantly attenuated mineral production by as much as -94%, compared with uninhibited CVCs. Strikingly, although mechanical stimulation activated each of the MAPK pathways, inhibition of these pathways had no effect on the mechanically induced enhancement of alkaline phosphatase activity or mineralization. These novel data indicate that mechanical signals regulate calcification by CVCs, and although MAPK signaling is critical to CVC osteogenic differentiation and mineralization, it is not involved directly in transduction of mechanical signals to regulate these processes under the conditions utilized in this study.
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Affiliation(s)
- Craig A Simmons
- Department of Biomedical Engineering, University of Michigan, 1011 N University Avenue, Ann Arbor, MI 48109-1078, USA
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Sacks MS, Schoen FJ. Collagen fiber disruption occurs independent of calcification in clinically explanted bioprosthetic heart valves. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 2002; 62:359-71. [PMID: 12209921 DOI: 10.1002/jbm.10293] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The durability of bioprosthetic heart valves (BHV) is severely limited by tissue deterioration, manifested as calcification and mechanical damage to the extracellular matrix. Extensive research on mineralization mechanisms has led to prevention strategies, but little work has been done on understanding the mechanisms of noncalcific matrix damage. The present study tested the hypothesis that calcification-independent damage to the valvular structural matrix mediated by mechanical factors occurs in clinical implants and could contribute to porcine aortic BHV structural failure. We correlated quantitative assessment of collagen fiber orientation and structural integrity by small angle light scattering (SALS) with morphologic analysis in 14 porcine aortic valve bioprostheses removed from patients for structural deterioration following 5-20 years of function. Calcification of the explants varied from 0 (none) to 1+ (minimal) to 4+ (extensive), as assessed radiographically. SALS tests were performed over entire excised cusps using a 0.254-mm spaced grid, and the resultant structural information used to generate maps of the local collagen fiber damage that were compared with sites of calcific deposits. All 42 cusps showed clear evidence of substantial noncalcific structural damage. In 29 cusps that were calcified, structural damage was consistently spatially distinct from the calcification deposits, generally in a distribution similar to that noted in porcine BHV subjected to in vitro durability testing. Our results suggest a mechanism of noncalcific degradation dependent on cuspal mechanics that could contribute to porcine aortic BHV failure.
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Affiliation(s)
- Michael S Sacks
- Tissue Mechanics Laboratory, Department of Bioengineering, Room 749 Benedum Hall, 3500 Ohara St., University of Pittsburgh, Pittsburgh, Pennsyvlania 15261, USA. msacks+@pitt.edu
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Moore MA, Adams AK. Calcification resistance, biostability, and low immunogenic potential of porcine heart valves modified by dye-mediated photooxidation. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 2001; 56:24-30. [PMID: 11309787 DOI: 10.1002/1097-4636(200107)56:1<24::aid-jbm1064>3.0.co;2-q] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The calcification potential, biostability, and immunogenic response of materials intended for long-term in vivo use, such as in heart-valve bioprostheses, are essential components of device performance. Here we explore these properties in photooxidized porcine heart valves. To study immunological sensitization, we injected tissue extracts intradermally into guinea pigs. Test and control animals received a challenge patch of the appropriate extract and were scored for dermal reactions. Neither cottonseed oil nor sodium chloride extracts of photooxidized heart-valve tissues caused any dermal inflammatory response. After implantation in the rat subcutaneous model for 90 days, the calcium content of 48-h-treated photooxidized cusp tissue [0.04 +/- 0.00 mg/g wet weight (gww)] was comparable to that of unimplanted control tissues (usually <1 mg/gww) and much lower than that of glutaraldehyde-treated controls (71 +/- 15 mg/gww). The porcine aortic wall calcium content (49 +/- 31 mg/gww) was comparable to that of glutaraldehyde-treated controls (59 +/- 8 mg/gww). Histologically, a time-dependent decrease in inflammation and vascularization with increasing photooxidation time was noted in the rat model along with an increase in the stability and organization of collagen bundles. In summary, porcine valve tissues treated by dye-mediated photooxidation were resistant to calcification, were biostable, and demonstrated a low immunogenic response, indicating potential for use in heart-valve bioprostheses.
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Affiliation(s)
- M A Moore
- Sulzer Carbomedics, 1300 East Anderson Lane, Austin, TX 78752-1793, USA.
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van Wachem PB, Brouwer LA, Zeeman R, Dijkstra PJ, Feijen J, Hendriks M, Cahalan PT, van Luyn MJ. Tissue reactions to epoxy-crosslinked porcine heart valves post-treated with detergents or a dicarboxylic acid. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 2001; 55:415-23. [PMID: 11255196 DOI: 10.1002/1097-4636(20010605)55:3<415::aid-jbm1031>3.0.co;2-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Calcification limits the long-term durability of xenograft glutaraldehyde (GA)-crosslinked heart valves. Previously, a study in rats showed that epoxy-crosslinked heart valves reduced lymphocyte reactions to the same extent as the GA-crosslinked control and induced a similar foreign-body response and calcification reaction. The present study was aimed at reducing the occurrence of calcification of epoxy-crosslinked tissue. Two modifications were carried out and their influence on cellular reactions and the extent of calcification after 8 weeks' implantation in weanling rats was evaluated. First, epoxy-crosslinked valves were post-treated with two detergents to remove cellular elements, phospholipids and small soluble proteins, known to act as nucleation sites for calcification. The second approach was to study the effect of the impaired balance between negatively and positively charged amino acids by an additional crosslinking step with a dicarboxylic acid. The detergent treatment resulted in a washed-out appearance of especially the cusp tissue. With the dicarboxylic acid, both the cusps and the walls had a limited washed-out appearance. The wall also demonstrated some detachment of the subendothelium. After implantation, both detergent and dicarboxylic acid post-treatment histologically resulted in reduced calcification at the edges of cusps and walls. However, total amounts of calcification, measured by atomic emission spectroscopy, were not significantly reduced. Data concerning the presence of lymphocytes varied slightly, but were in the same range as the GA-crosslinked control, i.e., clearly reduced compared with a noncrosslinked control. It is concluded that both the double detergent and the dicarboxylic acid post-treatment of epoxy-crosslinked heart valve tissue do not represent a sound alternative in the fabrication of heart valve bioprostheses.
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Affiliation(s)
- P B van Wachem
- University of Groningen, Medical Biology, Tissue Engineering, University Hospital, Entrance 25, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
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van Wachem PB, Brouwer LA, Zeeman R, Dijkstra PJ, Feijen J, Hendriks M, Cahalan PT, van Luyn MJ. In vivo behavior of epoxy-crosslinked porcine heart valve cusps and walls. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 2000; 53:18-27. [PMID: 10634948 DOI: 10.1002/(sici)1097-4636(2000)53:1<18::aid-jbm3>3.0.co;2-j] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Calcification limits the long-term durability of xenograft glutaraldehyde-crosslinked heart valves. In this study, epoxy-crosslinked porcine aortic valve tissue was evaluated after subcutaneous implantation in weanling rats. Non-crosslinked valves and valves crosslinked with glutaraldehyde or carbodiimide functioned as control. Epoxy-crosslinked valves had somewhat lower shrinkage temperatures than the crosslinked controls, and within the series also some macroscopic and microscopic differences were obvious. After 8 weeks implantation, cusps from non-crosslinked valves were not retrieved. The matching walls were more degraded than the epoxy- and control-crosslinked walls. This was observed from the higher cellular ingrowth with fibroblasts, macrophages, and giant cells. Furthermore, non-crosslinked walls showed highest numbers of lymphocytes, which were most obvious in the capsules. Epoxy- and control-crosslinked cusps and walls induced lower reactions. Calcification, measured by von Kossa-staining and by Ca-analysis, was always observed. Crosslinked cusps calcified more than walls. Of all wall samples, the non-crosslinked walls showed the highest calcification. It is concluded that epoxy-crosslinked valve tissue induced a foreign body and calcification reaction similar to the two crosslinked controls. Therefore, epoxy-crosslinking does not represent a solution for the calcification problem of heart valve bioprostheses.
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Affiliation(s)
- P B van Wachem
- University of Groningen, Faculty for Medical Sciences, Medical Biology; Cell Biology and Biomaterials, Bloemsingel 10-B2, 9712 KZ Groningen, The Netherlands
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23
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Schoen FJ, Levy RJ. Founder's Award, 25th Annual Meeting of the Society for Biomaterials, perspectives. Providence, RI, April 28-May 2, 1999. Tissue heart valves: current challenges and future research perspectives. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 1999; 47:439-65. [PMID: 10497280 DOI: 10.1002/(sici)1097-4636(19991215)47:4<439::aid-jbm1>3.0.co;2-o] [Citation(s) in RCA: 274] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Substitute heart valves composed of human or animal tissues have been used since the early 1960s, when aortic valves obtained fresh from human cadavers were transplanted to other individuals as allografts. Today, tissue valves are used in 40% or more of valve replacements worldwide, predominantly as stented porcine aortic valves (PAV) and bovine pericardial valves (BPV) preserved by glutaraldehyde (GLUT) (collectively termed bioprostheses). The principal disadvantage of tissue valves is progressive calcific and noncalcific deterioration, limiting durability. Native heart valves (typified by the aortic valve) are cellular and layered, with regional specializations of the extracellular matrix (ECM). These elements facilitate marked repetitive changes in shape and dimension throughout the cardiac cycle, effective stress transfer to the adjacent aortic wall, and ongoing repair of injury incurred during normal function. Although GLUT bioprostheses mimic natural aortic valve structure (a) their cells are nonviable and thereby incapable of normal turnover or remodeling ECM proteins; (b) their cuspal microstructure is locked into a configuration which is at best characteristic of one phase of the cardiac cycle (usually diastole); and (c) their mechanical properties are markedly different from those of natural aortic valve cusps. Consequently, tissue valves suffer a high rate of progressive and age-dependent structural valve deterioration resulting in stenosis or regurgitation (>50% of PAV overall fail within 10-15 years; the failure rate is nearly 100% in 5 years in those <35 years old but only 10% in 10 years in those >65). Two distinct processes-intrinsic calcification and noncalcific degradation of the ECM-account for structural valve deterioration. Calcification is a direct consequence of the inability of the nonviable cells of the GLUT-preserved tissue to maintain normally low intracellular calcium. Consequently, nucleation of calcium-phosphate crystals occurs at the phospholipid-rich membranes and their remnants. Collagen and elastin also calcify. Tissue valve mineralization has complex host, implant, and mechanical determinants. Noncalcific degradation in the absence of physiological repair mechanisms of the valvular structural matrix is increasingly being appreciated as a critical yet independent mechanism of valve deterioration. These degradation mechanisms are largely rationalized on the basis of the changes to natural valves when they are fabricated into a tissue valve (mentioned above), and the subsequent interactions with the physiologic environment that are induced following implantation. The "Holy Grail" is a nonobstructive, nonthrombogenic tissue valve which will last the lifetime of the patient (and potentially grow in maturing recipients). There is considerable activity in basic research, industrial development, and clinical investigation to improve tissue valves. Particularly exciting in concept, yet early in practice is tissue engineering, a technique in which an anatomically appropriate construct containing cells seeded on a resorbable scaffold is fabricated in vitro, then implanted. Remodeling in vivo, stimulated and guided by appropriate biological signals incorporated into the construct, is intended to recapitulate normal functional architecture.
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Affiliation(s)
- F J Schoen
- Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, 75 Francis Street, Boston, Massachusetts 02115, USA
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Giachelli CM. Ectopic calcification: gathering hard facts about soft tissue mineralization. THE AMERICAN JOURNAL OF PATHOLOGY 1999; 154:671-5. [PMID: 10079244 PMCID: PMC1866412 DOI: 10.1016/s0002-9440(10)65313-8] [Citation(s) in RCA: 164] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 01/15/1999] [Indexed: 01/31/2023]
Affiliation(s)
- C M Giachelli
- Pathology Department, University of Washington, Seattle, Washington 98195, USA.
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Coury AJ, Levy RJ, Ratner BD, Schoen FJ, Williams DF, Williams RL. Degradation of Materials in the Biological Environment. Biomater Sci 1996. [DOI: 10.1016/b978-012582460-6/50009-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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