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Schmitt VH, Schmitt C, Hollemann D, Weinheimer O, Mamilos A, Kirkpatrick CJ, Brochhausen C. Tissue expansion of lung bronchi due to tissue processing for histology - A comparative analysis of paraffin versus frozen sections in a pig model. Pathol Res Pract 2019; 215:152396. [PMID: 30954348 DOI: 10.1016/j.prp.2019.03.024] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 03/17/2019] [Accepted: 03/24/2019] [Indexed: 10/27/2022]
Abstract
AIM Tissue shrinking due to fixation and processing is well known. However, the degree of shrinking varies significantly with the tissue type as well as the processing method and is not well studied in various tissues. In daily pathological routine workflow, histological specimens from frozen and paraffin sections are performed from the same tissue. In the present study we compared the thickness of bronchus walls obtained from paraffin and frozen sections. METHODS Pig lungs were frozen in ventilated condition in liquid nitrogen and 36 bronchi were isolated after dissection. Frozen sections of 5 μm thickness were performed and the remaining tissue was fixed and embedded in paraffin after fixation in 4% formalin. Frozen and paraffin sections from the same cutting edge were analysed after haematoxylin and eosin staining by measuring the wall thickness of the bronchi using high power fields of 400-fold magnification. In each bronchus 40 measurements were implemented at different wall positions distributed over the entire wall area. Summed up, in each group 1440 wall measurements were performed in total. Statistical analysis was conducted using the Wilcoxon test and t-test as well as Pearson's correlation coefficient with a significance level at P < 0.05. RESULTS The bronchial wall thickness was significantly (p < 0.001) smaller in frozen sections (median: 0.50 mm; min: 0.37 mm; max: 0.97 mm) compared to paraffin sections (median: 0.58 mm; min: 0.35 mm; max: 1.06 mm). The median difference between paraffin and frozen sections was 0.05 mm (min: -0.11 mm; max: 0.22 mm). The wall thickness ratio of both groups was as follows: frozen/paraffin section = 0.8609, thus yielding a difference between paraffin and frozen of 13.91%. High correlation was found between wall thickness measurements on paraffin and frozen sections (R = 0.87, p < 0.001). CONCLUSIONS The bronchus wall thickness in the frozen section was 14% reduced compared to the paraffin section. In routine pathology as well as in scientific studies these results are of relevance, as airway wall thickness represents a relevant marker for pathological interpretation, especially using CT image techniques.
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Affiliation(s)
- Volker H Schmitt
- Cardiology I, Centre for Cardiology, University Medical Centre, Johannes Gutenberg University of Mainz, Mainz, Germany
| | | | - David Hollemann
- Institute of Clinical and Molecular Pathology, State Hospital Horn, Horn, Austria
| | - Oliver Weinheimer
- Department of Diagnostic and Interventional Radiology, University Hospital Heidelberg, Im Neuenheimer Feld 110, 69120 Heidelberg, Germany; Translational Lung Research Centre Heidelberg (TLRC), German Lung Research Centre (DZL), Im Neuenheimer Feld 430, 69120 Heidelberg, Germany
| | - Andreas Mamilos
- REPAIR-Lab, Institute of Pathology, University of Regensburg, Regensburg, Germany
| | - C James Kirkpatrick
- Institute of Pathology, University Medical Centre, Johannes Gutenberg University of Mainz, Mainz, Germany; University Medical Center, Johann Wolfgang Goethe University of Frankfurt, Frankfurt am Main, Germany
| | - Christoph Brochhausen
- REPAIR-Lab, Institute of Pathology, University of Regensburg, Regensburg, Germany; Central Biobank Regensburg, University and University Hospital Regensburg, Franz-Josef-Strauß Allee 11, 93053 Regensburg, Germany.
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Sacks MS, Zhang W, Wognum S. A novel fibre-ensemble level constitutive model for exogenous cross-linked collagenous tissues. Interface Focus 2016; 6:20150090. [PMID: 26855761 DOI: 10.1098/rsfs.2015.0090] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Exogenous cross-linking of soft collagenous tissues is a common method for biomaterial development and medical therapies. To enable improved applications through computational methods, physically realistic constitutive models are required. Yet, despite decades of research, development and clinical use, no such model exists. In this study, we develop the first rigorous full structural model (i.e. explicitly incorporating various features of the collagen fibre architecture) for exogenously cross-linked soft tissues. This was made possible, in-part, with the use of native to cross-linked matched experimental datasets and an extension to the collagenous structural constitutive model so that the uncross-linked collagen fibre responses could be mapped to the cross-linked configuration. This allowed us to separate the effects of cross-linking from kinematic changes induced in the cross-linking process, which in turn allowed the non-fibrous tissue matrix component and the interaction effects to be identified. It was determined that the matrix could be modelled as an isotropic material using a modified Yeoh model. The most novel findings of this study were that: (i) the effective collagen fibre modulus was unaffected by cross-linking and (ii) fibre-ensemble interactions played a large role in stress development, often dominating the total tissue response (depending on the stress component and loading path considered). An important utility of the present model is its ability to separate the effects of exogenous cross-linking on the fibres from changes due to the matrix. Applications of this approach include the utilization in the design of novel chemical treatments to produce specific mechanical responses and the study of fatigue damage in bioprosthetic heart valve biomaterials.
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Affiliation(s)
- Michael S Sacks
- Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences, Department of Biomedical Engineering , The University of Texas at Austin , 201 East 24th Street, PO Box 5.236, Stop C0200, Austin, TX 78712 , USA
| | - Will Zhang
- Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences, Department of Biomedical Engineering , The University of Texas at Austin , 201 East 24th Street, PO Box 5.236, Stop C0200, Austin, TX 78712 , USA
| | - Silvia Wognum
- Department of Biomedical Engineering , Eindhoven University of Technology , PO Box 513, 5600 MB Eindhoven , The Netherlands
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Rouleau L, Tremblay D, Cartier R, Mongrain R, Leask RL. Regional variations in canine descending aortic tissue mechanical properties change with formalin fixation. Cardiovasc Pathol 2012; 21:390-7. [DOI: 10.1016/j.carpath.2011.12.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2010] [Revised: 10/17/2011] [Accepted: 12/15/2011] [Indexed: 11/16/2022] Open
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Abstract
The purpose of this paper is twofold: first, to review analytical, experimental, and numerical methods for studying the nonlinear, pseudoelastic behavior of membranes of interest in biomechanics, and second, to present illustrative examples from the literature for a variety of biomembranes (e.g., skin, pericardium, pleura, aneurysms, and cells) as well as elastomeric membranes used in balloon catheters and new cell stretching tests. Although a membrane approach affords great simplifications in comparison to the three-dimensional theory of nonlinear elasticity, associated problems are still challenging. Computer-based methods are essential, therefore, for performing the requisite experiments, analyzing data, and solving boundary and initial value problems. Emphasis is on stable equilibria although material instabilities and elastodynamics are discussed.
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Affiliation(s)
- J. D. Humphrey
- Department of Mechanical Engineering, University of Maryland, Baltimore MD 21250
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Schmidt CE, Baier JM. Acellular vascular tissues: natural biomaterials for tissue repair and tissue engineering. Biomaterials 2000; 21:2215-31. [PMID: 11026628 DOI: 10.1016/s0142-9612(00)00148-4] [Citation(s) in RCA: 505] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Various research groups around the world are actively investigating cardiovascular prostheses of biological origin. This review article discusses the need for such bioprosthetics and the potential role for natural tissues in cardiovascular applications such as cardiac valves and vascular grafts. Upon implantation, unmodified natural materials are subject to chemical and enzymatic degradation, seriously decreasing the life of the prosthesis. Therefore, methods such as glutaraldehyde and polyepoxide crosslinking treatments and dye-mediated photooxidation have been developed to stabilize the tissue while attempting to maintain its natural mechanical properties. Also, residual cellular components in a bioprosthetic material have been associated with undesired effects, such as calcification and immunological recognition, and thus have been the motivation for various decellularization processes. The effects of these stabilization and decellularization treatments on mechanical, biological and chemical properties of treated tissues have been investigated, specifically with regard to calcification, immunogenicity, and cytotoxicity concerns. Despite significant advances in the area of cardiovascular prostheses, there has yet to be developed a completely biocompatible, long-lasting implant. However, with the recent advent of tissue engineering, the possibility of applying selective cell seeding to naturally derived bioprosthetics moves us closer to a living tissue replacement.
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Affiliation(s)
- C E Schmidt
- Department of Chemical Engineering, University of Texas at Austin, 78712, USA.
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Chachra D, Gratzer PF, Pereira CA, Lee JM. Effect of applied uniaxial stress on rate and mechanical effects of cross-linking in tissue-derived biomaterials. Biomaterials 1996; 17:1865-75. [PMID: 8889066 DOI: 10.1016/0142-9612(95)00305-3] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Conformational changes in collagen fibrils, and indeed the triple helix, can be produced by application of mechanical stress or strain. We have demonstrated that the rate of cross-linking in glutaraldehyde and epoxide homobifunctional reagents can be modulated by uniaxial stress (strain). Two poly(glycidyl ether) epoxides were used: Denacol EX-810 (a small bifunctional reagent), and Denacol EX-512 (a large polyfunctional reagent). To prevent any possible effect from being masked by saturation of cross-linking sites, bovine pericardium was cross-linked to such an extent that the increase in collagen denaturation temperature, Td, was one-half of the maximal rise achievable with each reagent. Uniaxial tensile stress of 0, 15, 124 or 233 kPa was applied during cross-linking. Cross-linking rate (as observed by increase in Td) increased with increasing stress to a maximum at 124 kPa in glutaraldehyde at pH 7 but decreased in EX-810 at pH 7. In each case, the effect was small but statistically significant. No effect was observed with the larger EX-512. Cross-linking under increasing stress also showed systematic effects on mechanical properties: decreasing extensibility and plastic strain while increasing tensile strength. In each case, the effects of the epoxides were slightly different from those of glutaraldehyde. In preparation for the above experiments, studies of the effect of pH, temperature, and exposure time were carried out for each epoxide and (to a lesser extent) for glutaraldehyde. Again, systematic changes in mechanical properties were observed with increasing Td. Conformational changes in collagen produced by mechanical stress (strain) modulate the rate of cross-linking and the resulting mechanical properties; however, the effects are sensitive to the reagent employed.
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Affiliation(s)
- D Chachra
- Centre for Biomaterials, University of Toronto, Ontario, Canada
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Gratzer PF, Pereira CA, Lee JM. Solvent environment modulates effects of glutaraldehyde crosslinking on tissue-derived biomaterials. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 1996; 31:533-43. [PMID: 8836851 DOI: 10.1002/(sici)1097-4636(199608)31:4<533::aid-jbm14>3.0.co;2-h] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Bioprosthetic materials utilized in the construction of heart valves and vascular grafts possess limited performance and viability in vivo. This is due (in part) to the failure of these materials to mimic the mechanical properties of the host tissue they replace. If bioprosthetic materials could be engineered to meet the mechanical performance required in vivo, the functional lifetime of implants would be increased. In this study, glutaraldehyde/solvent solutions of decreasing dielectric constant (polarity) were utilized to modify the properties of crosslinked collagen in whole bovine pericardial tissue. Solvents included phosphate buffer, methanol, 95% (w/w) ethanol, n-propanol, and n-butanol. Exogenous crosslinking was verified in collagen by thermal denaturation tests and amino acid analyses. Tensile mechanical behavior of collagenous pericardial samples was found to depend upon the dielectric constant (polarity) of the glutaraldehyde/solvent solutions employed; however, treatment in the solvents alone had little, if any, effect. As the dielectric constant of the solvents decreased, three mechanical properties were systematically altered: plastic strain fell from a mean of 8.9 +/- 1.5% (buffer) to 1.6 +/- 0.4% (n-butanol); strain at fracture increased from 32.2 +/- 2.6% (buffer) to 55.6 +/- 4.6% (n-butanol); and percent stress remaining after 1000-s stress relaxation from an 80-g initial load fell from 86.3 +/- 1.1% (buffer) to 76.9 +/- 1.0% (n-butanol). Crosslinking using a glutaraldehyde/n-butanol solution produced materials with tensile mechanical behavior that was very close to that of fresh tissue; however, the flexural properties of the treated tissue were different from those of fresh tissue. This decoupling of the flexural and tensile mechanical behaviors of crosslinked bioprosthetic materials is unique to this form of treatment. The observed phenomena may be the results of conformational changes in collagen facilitated by polar/nonpolar interactions with the solvent that are "locked in" by the action of glutaraldehyde. This technique may aid in the "customized" design of mechanical properties in tissue-derived biomaterials.
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Affiliation(s)
- P F Gratzer
- Centre for Biomaterials, University of Toronto, Ontario, Canada
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Abstract
The use of glutaraldehyde as a fixative in bioprostheses and drug delivery matrices is reviewed. The chemistry of glutaraldehyde cross-linking and its effect on the biological performance of a number of bioprostheses such as tissue heart valves, vascular grafts, pericardial patches, tendon grafts and drug delivery matrices are examined.
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Affiliation(s)
- A Jayakrishnan
- Polymer Chemistry Division, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, India
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Courtman DW, Pereira CA, Kashef V, McComb D, Lee JM, Wilson GJ. Development of a pericardial acellular matrix biomaterial: biochemical and mechanical effects of cell extraction. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 1994; 28:655-66. [PMID: 8071376 DOI: 10.1002/jbm.820280602] [Citation(s) in RCA: 244] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
There is evidence to suggest that the cellular components of homografts and bioprosthetic xenografts may contribute to calcification or immunogenic reactions. A four-step detergent and enzymatic extraction process has been developed to remove cellular components from bovine pericardial tissue. The process results in an acellular matrix material consisting primarily of elastin, insoluble collagen, and tightly bound glycosaminoglycans. Light and electron microscopy confirmed that nearly all cellular constituents are removed without ultrastructural evidence of damage to fibrous components. Collagen denaturation temperatures remained unaltered. Biochemical analysis confirmed the retention of collagen and elastin and some differential extraction of glycosaminoglycans. Low strain rate fracture testing and high strain rate viscoelastic characterization showed that, with the exception of slightly increased stress relaxation, the mechanical properties of the fresh tissue were preserved in the pericardial acellular matrix. Crosslinking of the material in glutaraldehyde or poly(glycidyl ether) produced mechanical changes consistent with the same treatments of fresh tissue. The pericardial acellular matrix is a promising approach to the production of biomaterials for heart valve or cardiovascular patching applications.
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Affiliation(s)
- D W Courtman
- Centre for Biomaterials, University of Toronto, Ontario, Canada
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Zioupos P, Barbenel JC, Fisher J. Anisotropic elasticity and strength of glutaraldehyde fixed bovine pericardium for use in pericardial bioprosthetic valves. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 1994; 28:49-57. [PMID: 8126028 DOI: 10.1002/jbm.820280107] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Uniaxial tensile tests were performed on glutaraldehyde fixed bovine pericardial strips prepared from chemically modified pericardial samples. These samples originated from an area which demonstrated anisotropic mechanical properties in the native material and which is suitable for the construction of leaflets for pericardial bioprostheses. After glutaraldehyde fixation the tissue had retained its anisotropicity in stiffness and strength in two orthogonal directions. In the range of the functional stresses for a heart valve leaflet (< 1 MPa) the unconstrained fixation regime had modified the initial anisotropic elastic behavior into a more isotropic one. The implications of these findings are that leaflets manufactured from bovine pericardium can be made to resemble, to a degree, the well known anisotropy found in two orthogonal directions in natural human heart valve leaflets, or porcine bioprosthetic heart valve leaflets.
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Affiliation(s)
- P Zioupos
- Department of Biology, University of York, UK
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Abstract
The stress and strain states of the valve leaflets during fixation with glutaraldehyde affect their final mechanical parameters. Comparative studies of the stress-strain relationships of aortic valve leaflet strips from fresh, statically and dynamically fixed porcine and human valves were made. Static pressures of 5 mmHg, 16 mmHg, and 95 mmHg result in stress-strain relationships which are in a region between that of fresh porcine and fresh human leaflet strips in the circumferential direction, while they are far from that of fresh porcine tissue (larger strains) in the radial direction. Leaflet strips, fixed under dynamic loading between zero and a predefined maximum load, set at an early post-transition state, give parameters not significantly different from those of human valves.
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Affiliation(s)
- D Mavrilas
- Department of Mechanical Engineering, University of Patras, Greece
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12
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Pereira CA, Lee JM, Haberer SA. Effect of alternative crosslinking methods on the low strain rate viscoelastic properties of bovine pericardial bioprosthetic material. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 1990; 24:345-61. [PMID: 2318899 DOI: 10.1002/jbm.820240307] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Early failures of bovine pericardial heart valves have been due to leaflet perforation/tearing and calcification. Since glutaraldehyde fixation has been shown to produce marked changes in leaflet mechanics and has been linked to the development of calcification, alternative crosslinking techniques have been suggested as means to overcome these obstacles. We have examined the low strain rate viscoelastic behavior of bovine pericardium: (1) fresh; (2) chemically treated with glutaraldehyde, cyanimide, or polyglycidyl ether; or (3) physically treated by freeze-drying or heat-drying. Shrinkage temperature tests were conducted to assess intrahelical crosslinking. Polyglycidyl ether and glutaraldehyde both produced substantial crosslinking, with the shrinkage temperature rising above 80 degrees C. Mechanical changes were nearly equivalent, both showing decreased stress relaxation and increased extensibility consistent with intrahelical crosslinking and shrinkage during fixation. Cyanimide, known to crosslink pure collagen materials, showed no evidence of crosslinking intact tissue. Heat-drying, also effective in pure collagen preparations, produced an increase in UTS and tissue modulus, but otherwise left the tissue unchanged. Freeze-drying had no mechanical effect, and therefore provides an attractive means for the storage of connective tissues for later mechanical testing.
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Affiliation(s)
- C A Pereira
- Centre for Biomaterials, University of Toronto, Ontario, Canada
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Lee JM, Ku M, Haberer SA. The bovine pericardial xenograft: III. Effect of uniaxial and sequential biaxial stress during fixation on the tensile viscoelastic properties of bovine pericardium. JOURNAL OF BIOMEDICAL MATERIALS RESEARCH 1989; 23:491-506. [PMID: 2715162 DOI: 10.1002/jbm.820230504] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Our previous two articles have shown that glutaraldehyde-fixed bovine pericardium is nearly isotropic, whether fixed without constraints, with tethering, or with pressure. In this study, we have used uniaxial stress during fixation to produce bovine pericardial material with marked tensile anisotropy. Rectangular and cruciate pericardial samples have been mechanically examined after one of four treatments: (i) fixation under 88-kPa uniaxial stress, (ii) fixation under 176-kPa uniaxial stress, (iii) 3 h of 176-kPa uniaxial stress in saline followed by 24-h fixation under the same stress, (iv) fixation under 176-kPa uniaxial stress followed by a second fixation under 176-kPa stress in a direction normal to the first. Strips of material were cut at 0 degree, 30 degrees, 60 degrees, and 90 degrees to direction of the initial stress, and tested for response to cyclic loading, stress relaxation, plastic deformation, and fracture properties. Fixation under uniaxial stress produced anistropy similar to that seen in porcine aortic valve leaflets; however, the overall extensibility of the material depended on the applied stress and the aspect ratio of the stressed sample. While loading in saline produced no change, the sequential biaxial stressing produced a reduction in anisotropy, suggesting exposure of additional crosslinking sites. Uniaxial stress during fixation may be a useful method for construction of anisotropic heart valve leaflets.
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Affiliation(s)
- J M Lee
- Centre for Biomaterials, University of Toronto, Ontario, Canada
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