Effect of pretreatment with epoxy compounds on the mechanical properties of bovine pericardial bioprosthetic materials

The hybrid crosslinking method improved the stability and anti-calcification properties of the bioprosthetic heart valves

The bioprosthetic heart valves (BHVs) are the best option for the treatment of valvular heart disease. Glutaraldehyde (Glut) is commonly used as the golden standard reagent for the crosslinking of BHVs. However, the obvious defects of Glut, including residual aldehyde toxicity, degradation and calcification, increase the probability of valve failure in vivo and motivated the exploration of alternatives. Thus, the aim of this study is to develop a non-glutaraldehyde hybrid cross-linking method composed of Neomycin Trisulfate, Polyethylene glycol diglycidyl ether and Tannic acid as a substitute for Glut, which was proven to reduce calcification, degradation, inflammation of the biomaterial. Evaluations of the crosslinked bovine pericardial included histological and ultrastructural characterization, biomechanical performance, biocompatibility and structural stability test, and in vivo anti-inflammation and anti-calcification assay by subcutaneous implantation in juvenile Sprague Dawley rats. The results revealed that the hybrid crosslinked bovine pericardial were superior to Glut crosslinked biomaterial in terms of better hydrophilicity, thermodynamics stability, hemocompatibility and cytocompatibility, higher Young’s Modulus, better stability and resistance to enzymatic hydrolysis, and lower inflammation, degradation and calcification levels in subcutaneous implants. Considering all above performances, it indicates that the hybrid cross-linking method is appropriate to replace Glut as the method for BHV preparation, and particularly this hybrid crosslinked biomaterials may be a promising candidate for next-generation BHVs.

Long-Term Stability and Biocompatibility of Pericardial Bioprosthetic Heart Valves

The use of bioprostheses for heart valve therapy has gradually evolved over several decades and both surgical and transcatheter devices are now highly successful. The rapid expansion of the transcatheter concept has clearly placed a significant onus on the need for improved production methods, particularly the pre-treatment of bovine pericardium. Two of the difficulties associated with the biocompatibility of bioprosthetic valves are the possibilities of immune responses and calcification, which have led to either catastrophic failure or slow dystrophic changes. These have been addressed by evolutionary trends in cross-linking and decellularization techniques and, over the last two decades, the improvements have resulted in somewhat greater durability. However, as the need to consider the use of bioprosthetic valves in younger patients has become an important clinical and sociological issue, the requirement for even greater longevity and safety is now paramount. This is especially true with respect to potential therapies for young people who are afflicted by rheumatic heart disease, mostly in low- to middle-income countries, for whom no clinically acceptable and cost-effective treatments currently exist. To extend longevity to this new level, it has been necessary to evaluate the mechanisms of pericardium biocompatibility, with special emphasis on the interplay between cross-linking, decellularization and anti-immunogenicity processes. These mechanisms are reviewed in this paper. On the basis of a better understanding of these mechanisms, a few alternative treatment protocols have been developed in the last few years. The most promising protocol here is based on a carefully designed combination of phases of tissue-protective decellularization with a finely-titrated cross-linking sequence. Such refined protocols offer considerable potential in the progress toward superior longevity of pericardial heart valves and introduce a scientific dimension beyond the largely disappointing 'anti-calcification' treatments of past decades.

Inorganic-polymerization crosslinked tissue-siloxane hybrid as potential biomaterial for bioprosthetic heart valves

Bioprosthetic heart valve (BHV) replacement is increasingly used for treating valve-related diseases worldwide but the current commercially used BHVs treated with glutaraldehyde (Glut) often failed within 12-15 years due to degradation, thrombosis, inferior biocompatibility, and calcification. Herein, 3-glycidyloxypropyl trimethoxysilane (GPTMS) was used to crosslink porcine pericardium (PP) at the concentration (vol/vol) of 0.25%, 1%, 2%, and 4% and their performance for potential application in BHVs was evaluated. The crosslinking mechanism mainly involved the ring-opening of epoxide by amine attack and silanol poly-condensation. The stability of collagen in higher concentration (1%, 2%, and 4%) GPTMS crosslinked PPs (GPTMS-PPs) was clearly increased. GPTMS-PPs showed no cytotoxicity and supported the growth of endothelial cells while Glut-PP did not. GPTMS-PPs were less prothrombotic than Glut-PP. GPTMS-PP crosslinked at 1% concentration showed comparable mechanical properties to Glut-PP while had better anti-tearing performance. The subcutaneous implantation in rat for 30 days showed that GPTMS crosslinking was able to effectively inhibit the calcification of BHV.

Assessment of an Epoxy-Fixed Pericardial Patch with or without Ionically Bound Heparin in a Canine Model

In this study, an epoxy-fixed porcine pericardia I patch with or without ionically bound heparin was evaluated in a canine model as an alternative to the glutaraldehyde-fixed biological patch for clinical applications. To evaluate the effectiveness of this epoxy-fixed patch, a composite membrane composed of: an epoxy-fixed porcine patch with ionically bound heparin; a glutaraldehyde-fixed porcine patch with ionically bound heparin; an ePTFE polymeric patch; a polyester polymeric patch; an epoxy-fixed porcine patch without ionically bound heparin; and a glutaraldehyde-fixed porcine patch without ionically bound heparin was made. This membrane was assessed orthopically in a canine model. The early results (1-4 weeks post implant) revealed that the biological patches with ionically bound heparin had the mildest tissue reactions (inflammatory reaction, fibrosis, and adhesion) among all the test samples. However, by 12 weeks postoperatively, all the test samples had mild to severe tissue reactions. The order of tissue reactions with increasing severity was: the biological patches with ionically bound heparin, the biological patches without ionically bound heparin, and the polymeric patches. The results suggest that heparin may be used to reduce adhesion. Additionally, the epoxy-fixed tissue caused a relatively lower degree of inflammatory reaction than the glutaraldehyde-fixed tissue.

Collagen modified with epoxidized safrole for improving antibacterial activity

An epoxidized safrole, 5-(oxiran-2-ylmethyl)-benzo[d][1,3]dioxole (OYBD), was synthesized and employed to modify collagen for improving its antibacterial activity.

Mapping the calcification of bovine pericardium in rat model by enhanced micro-computed tomography

The calcification initiation and progression of bioprosthetic heart valve were investigated in a rat model by enhanced micro-computed tomography, together with histologic study and scanning electron microscope analysis. The implantation data at early stage showed apparent dendritic patterns in the radiographic images for the glutaraldehyde-treated bovine pericardium and this dendritic pattern was verified to be associated with the vessel distribution in the tissue. Histologic study and scanning electron microscope analysis both indicated that the calcium deposits in the pericardium vessels regions were more grievous than those scattered in the collagen fibers in the first two weeks after implantation. Subsequently, calcification spreaded and the entire sample was severely calcified in 60 days.

Acellular vascular tissues: natural biomaterials for tissue repair and tissue engineering

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.

Crosslinking and modification of dermal sheep collagen using 1, 4-butanediol diglycidyl ether

Crosslinking of dermal sheep collagen (DSC) was accomplished using 1, 4-butanediol diglycidyl ether (BDDGE). At pH values > 8.0, epoxide groups of BDDGE will react with amine groups of collagen. The effects of BDDGE concentration, pH, time, and temperature were studied. Utilization of a 4-wt % BDDGE instead of 1-wt % resulted in a faster reaction. Whereas similar values of shrinkage temperature were obtained, fewer primary amine groups had reacted at a lower BDDGE concentration, which implies that the crosslinking reaction had a higher efficacy. An increase in pH from 8.5 to 10.5 resulted in a faster reaction but reduced crosslink efficacy. Furthermore, an increase in reaction temperature accelerated the reaction without changing the crosslink efficacy. Crosslinking under acidic conditions (pH < 6.0) evoked a reaction between epoxide groups and carboxylic acid groups of collagen. Additional studies showed that no oligomeric crosslinks could be formed. However, hydrolysis of the epoxide groups played a role in the crosslink mechanism especially under acidic reaction conditions. The macroscopic properties of these materials were dependent on the crosslinking method. Whereas a flexible and soft tissue was found if crosslinking was performed at pH < 6.0, a stiff sponge was obtained under alkaline conditions. Reaction of DSC with a monofunctional compound (glycidyl isopropyl ether) led to comparable trends in reaction rate and in similar macroscopical differences in materials as observed with BDDGE.

Characterization of a polyepoxy compound fixed porcine heart valve bioprosthesis

Concerns with the currently available bioprostheses are calcification, long-term durability, and suboptimal hemodynamic performance. It is well known that these concerns are all more or less related to the cross-linking reagent, glutaraldehyde or formaldehyde, used in fixing bioprostheses. To address these concerns, we undertook the development of a porcine bioprosthesis fixed with a polyepoxy compound. In the development of this polyepoxy compound valve, it was found that the porcine leaflets fixed with polyepoxy compound were softer and more pliable than those fixed with glutaraldehyde. In this study, a special microtoming technique was developed to section the biological tissue so that the fixation uniformity in distinct layers of porcine aortic wall could be characterized. The fixation index and the denaturation temperature measurements in distinct layers of aortic walls showed that the cross-linking density was uniform throughout the entire aortic wall for the polyepoxy compound fixed porcine valve. It was also noted that the fixation index of the polyepoxy compound fixed aortic wall (91.5 +/- 0.5, n = 3) was not significantly different from that of its valvular leaflet (90.6 +/- 0.8, n = 3). Similarly, the denaturation temperature of the polyepoxy compound fixed aortic wall (80.4 +/- 0.9 degrees C, n = 5) was statistically comparable to that of its valvular leaflet (79.0 +/- 0.5 degrees C, n = 5). The results of this study indicated that polyepoxy compound can adequately fix the entire porcine aortic wall as well as its valvular leaflets.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of calcification by various treatments in cardiac valves

The importance of glutaraldehyde pretreated bioprosthetic heart valves fabricated from bovine pericardium or porcine aortic valves is well realized in the management of valvular heart diseases. But, calcification limits the durability and is the most frequent cause of failure of these bioprosthetic heart valves. Various research groups in the world are actively involved in describing, understanding, and preventing calcification of bioprosthetic heart valves. Since there is no satisfactory clinical means for preventing or treating this disorder, attempts are made to improve the anticalcification properties of the replacement valves in the preparation stage itself. Research in this area is very active, and many newer approaches are made to mitigate the problem. An attempt has been made in the present article to review various theories put forward to explain the causative factors involved and mechanistic aspects of biocalcification and to present various strategies attempted for the prevention of calcification with the special feature on the work done in the area in our laboratory.

Heparinization on pericardial substitutes can reduce adhesion and epicardial inflammation in the dog

OBJECTIVE

Primary concerns about currently available pericardial substitutes include adhesion and epicardial reaction. The purpose of this study is to evaluate host reaction to pericardial substitutes with and without incorporating slow heparin release.

METHODS

To avoid biologic variation among these pericardial patches, we made a composite of six membranes. The composite membrane consisted of epoxy-fixed patches with (1) or without (2) ionically bound heparin, a glutaraldehyde-fixed patch with (3) or without (4) ionically bound heparin, an expanded polytetrafluoroethylene patch (5), and a polyester polymeric patch (6). Ten recipient dogs weighing from 12 to 19 kg (mean 13.6 kg) were used to assess the composite membranes as pericardial substitutes. The implanted composite membranes were retrieved 1 week (one dog), 2 weeks (one dog), 4 weeks (one dog), 8 weeks (one dog), and 12 weeks (six dogs) after implantation.

RESULTS

Overall, the synthetic patches had a more notable inflammatory reaction than the biologic patches with or without ionically bound heparin. The heparin-bound patches caused significantly less inflammation than their nonheparinized counterparts. The heparinized porcine patches cross-linked with different compounds were found to have less fibrous formation than the nonheparinized patches and the synthetic patches.

CONCLUSIONS

Heparinized pericardial substitutes may cause less adhesion and inflammatory reaction than nonheparinized material.

Degradation potential of biological tissues fixed with various fixatives: an in vitro study

The purpose of this study was to investigate the in vitro degradation potential of porcine pericardia fixed with various aldehyde or epoxy compound (EC) fixatives, using bacterial collagenase and pronase. The fixatives investigated were formaldehyde (FA), glutaraldehyde (GA), monofunctional EC (EX-131), and multifunctional ECs (EX-810, EX-313, and EX-512). Fresh porcine pericardium was used as a control. The test samples were well immersed in a 20-U/mL collagenase solution or a 10-U/mL pronase solution and incubated at 37 degrees C at pH 7.5 for 24 h. The extent of degradation of each test sample was determined by measuring its increment in free amino group content and changes in collagen structure, denaturation temperature, and tensile stress after degradation. In general, the extent of tissue degradation with pronase was more notable than with collagenase. As observed with fresh tissue, the EX-131 EC fixed tissue radically disintegrated after either collagenase or pronase degradation, whereas the other test samples remained intact. The reason for this may reside in the more random molecular packing of the EX-131 EC-fixed tissue, which led to some loss in its helical integrity. This made penetration of enzymes into biological tissue easier. Of the multifunctional EC test groups, tissues fixed with tetrafunctional EC (EX-521) or trifunctional EC (EX-313) had relatively better resistance to degradation than those fixed with bifunctional EC (EX-810). The extent of degradation for the EX-313 or EX-512 EC fixed tissues was similar to that observed for the FA- or GA-fixed tissues. The results of this study indicated that the biological tissue fixed with monofunctional EC (EX-131) cannot resist bacterial collagenase or pronase degradation. However, resistance to degradation of the multifunctional EC (EX-313 or EX-152)-fixed tissues was comparable to that of the aldehyde (FA or GA)-fixed tissues. Therefore, of various EC fixatives, the EC with a greater number of functional groups should be chosen for tissue fixation to increase its resistance to enzymatic degradation.

In vitro study of enzymatic degradation of biological tissues fixed by glutaraldehyde or epoxy compound

The study, using bacterial collagenase, was to investigate the changes in characteristics of a collagen-rich tissue, porcine pericardium, fixed by glutaraldehyde or epoxy compound (ethylene glycol diglycidyl ether) during the course of degradation. Fresh porcine pericardium was used as a control. During degradation, the heat released by the reaction of collagenase with a test sample was monitored by a highly sensitive microcalorimeter. Also, the degree of degradation of each test sample was determined by measuring its increment in free amino group content and changes in denaturation temperature and tensile strength. Microcalorimetric analysis of collagenase degradation of fresh, epoxy-fixed, and glutaraldehyde-fixed tissues revealed that the heat released during degradation correlates well with the degree of tissue degraded. The cleaving of peptide bonds in biological tissue by collagenase degradation may increase its free amino group content and reduce its denaturation temperature and tensile strength. It was noted that the fresh tissue cannot resist bacterial collagenase degradation, while the glutaraldehyde-fixed tissue had a relatively better resistance to degradation than its epoxy-fixed counterpart.

Effect of applied uniaxial stress on rate and mechanical effects of cross-linking in tissue-derived biomaterials

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.

Cross-linking characteristics of biological tissues fixed with monofunctional or multifunctional epoxy compounds

The cross-linking characteristics of biological tissues fixed by various epoxy compounds with different chemical structures (i.e. number of epoxide functional groups and backbone length) were investigated. Generally speaking, the tissues fixed with monofunctional fixatives were more pliable than those fixed with multifunctional fixatives. The fixation indices of the fixed tissues did not seem to be affected by the chemical structures of the fixatives. However, the number of functional groups and backbone length of the fixatives did play an important role in influencing the denaturation temperatures of the fixed tissues. In general, the denaturation temperatures of the multifunctional fixed tissues were higher than those of the monofunctional fixed tissues. Among the monofunctional fixed tissues, it was found that increasing the backbone length of the fixative decreased the denaturation temperature of the fixed tissue. This effect was present until the backbone length of the fixative became large enough.

Glutaraldehyde as a fixative in bioprostheses and drug delivery matrices

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.

Calcification of pericardial tissue pretreated with different amino acids

Since the development of cardiac prostheses, numerous chemical treatments have been assayed to prevent the process of their mineralization. The effect of chemical treatment with amino acids is assessed in a subcutaneous implantation model in rats. Pericardial tissue from young calves was treated with L-lysine, L-glutamine, L-arginine or L-glutamic acid, each at a concentration of 0.5 M, following treatment with 0.625% glutaraldehyde. Then, the tissue was implanted into young rats for periods of 21 and 60 d, after which the calcium accumulated was quantified by atomic absorption spectroscopy. Values similar to or higher than those found in control samples indicated a lack of effectiveness of these treatments. Only in the 21-d implantation samples treated with L-lysine and L-arginine was less calcium accumulated than in the control tissue. After 60 d of implantation, all groups showed high levels of calcium deposition. The values obtained after 60 d of subcutaneous implantation were 87.5 +/- 52.4 mg Ca2+ per g dry weight of tissue for L-lysine, 108.7 +/- 43.5 mg Ca2+ per g dry weight of tissue for L-glutamine, 130.4 +/- 22.4 mg Ca2+ per g dry weight of tissue for L-glutamic acid, 119.3 +/- 27.6 mg Ca2+ per g dry weight of tissue for L-arginine and 100.0 +/- 38.3 mg Ca2+ per g dry weight of tissue for the control group. Treatment with amino acids does not appear to prevent the calcification of cardiac bioprostheses or of collagen-based biomaterials when assayed in a model of subcutaneous implantation.

Studies on epoxy compound fixation

Bioprostheses derived from collagenous tissues have to be fixed and subsequently sterilized before they can be implanted in humans. Clinically, the most commonly used fixative is glutaraldehyde. However, the tendency for glutaraldehyde to markedly alter tissue stiffness and promote tissue calcification are well-recognized drawbacks of this fixative. To address the deficiencies with the glutaraldehyde-fixed tissue, a new fixative, epoxy compound, was used to fix biological prostheses. The study was undertaken to investigate the fixation rates and crosslinking densities of biological tissues fixed with various epoxy compounds. These epoxy compounds are different in their chemical structures. Glutaraldehyde was used as a control. The fixation rates and crosslinking densities of the fixed tissues were determined by measuring their fixation indices and denaturation temperatures, respectively. Generally, the epoxy-fixed tissues were more pliable than the glutaraldehyde-fixed one. Furthermore, the tissues fixed with monofunctional epoxy compound were more pliable than those fixed with multifunctional epoxy compounds. With increasing pH or temperature, the fixation rate of epoxy compound increased. However, the number of epoxide functional groups did not seem to affect the fixation rate of the epoxy compound. The fixation rate of glutaraldehyde was faster than that of epoxy compounds. Additionally, the crosslinking density of the glutaraldehyde-fixed tissue was greater than that of the epoxy-fixed counterparts. Moreover, it was noted that the denaturation temperatures of the tissues fixed with glutaraldehyde or multifunctional epoxy compounds were significantly higher than the fresh ones (p < 0.05), while that fixed with monofunctional epoxy compound stayed roughly the same throughout the entire fixation process (p > 0.05). The results obtained in this study may be used to optimize the fixation process for developing bioprostheses fixed with epoxy compounds.

Biological materials fixed with an epoxy compound: comparison of the effects with or without ionically bound heparin

Biological materials have been used as prosthetic devices such as heart valves, vascular grafts, and pericardial patches. These biological materials have to be fixed with crosslinking reagents and sterilized subsequently before they can be implanted in humans. Recently, a new crosslinking reagent, epoxy compound, has been used to fix bioprostheses. In this fixation technique, heparin may be ionically bound on the tissue surface. It has been shown that the amount of heparin bound to the tissue surface is proportional to the quantity of protamine impregnated in the biological tissues. However, it is not known if the impregnation of protamine will affect the crosslinking density of the biological tissues. This study was designed to compare the crosslinking densities of the epoxy compound fixed biological tissues with or without heparinization. Fresh porcine aortic valves procured from a slaughter house were first impregnated in various concentrations of protamine sulfate (0, 0.5, 1.0, or 1.5%) for about 30 min. The porcine aortic valves were then crosslinked in a 4% epoxy compound solution (Denacol EX-313). The porcine samples were taken out at various elapsed fixation periods: 18, 25, 48, 72, 96, and 120 h. Finally, the crosslinked porcine aortic valves were heparinized in a 0.5% sodium heparin solution for about 1 h. The crosslinking densities of the porcine leaflet and the aortic wall of each sample were determined by measuring their shrinkage temperatures. It was revealed that the impregnation of various concentrations of protamine did not seem to significantly alter the shrinkage temperatures of the porcine leaflet and the aortic wall throughout the entire fixation process (p > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of molecular structure of poly(glycidyl ether) reagents on crosslinking and mechanical properties of bovine pericardial xenograft materials

With the identification of the exacerbating effect of glutaraldehyde on calcification of heart valve materials, there exists a renewed interest in both alternative reagents and the effects of crosslinking on connective tissues. One potentially useful class of reagents are poly(glycidyl ether) compounds. We have examined 5 of these reagents with different molecular sizes and functionalities for their effects on mechanical properties and collagen denaturation (shrinkage) temperature. Samples of bovine pericardium were tested fresh or after 48 h fixation in one of the five compounds for denaturation temperature, stress-strain response, stress relaxation, plastic deformation, and fracture properties. Of the compounds tested, those with intermediate length backbones and 4 or 5 epoxide groups were most effective in producing intrahelical crosslinking and increased denaturation temperature over 48 h. However, in samples examined after 17 months of fixation, all reagents had equivalently increased the denaturation temperature. Examination of mechanical results revealed two distinct mechanisms for mechanical change. Observed shifting of the stress-strain curve to the right (due to shrinkage), increased plastic deformation, and some reduction of stress relaxation are all unrelated to denaturation temperature (and hence to changes in intrahelical crosslinking). An alternate mechanism, perhaps formation of intermolecular crosslinks may be responsible. Intrahelical crosslinking produces only lesser reductions in stress relaxation. Cross-comparison of reagents of differing molecular structure provides a useful tool toward increased understanding of the mechanical consequences of tissue crosslinking.

Inhibition of the calcification of porcine valve tissue by selective lipid removal

Since the development of cardiac prostheses, numerous chemical treatments have been assayed to prevent the process of their mineralization, causing 60% of the failures. The effect of the extraction of lipids from the tissue employed in porcine valves is assessed in a model of subcutaneous implantation in rats. Tissue from aortic and pulmonary porcine valves was treated with chloroform-methanol and 0.625% glutaraldehyde and was implanted into young rats for periods of 21 and 60 d. The calcium accumulated was then quantified by atomic absorption. The effectiveness of this treatment is demonstrated by the detection of much lower calcium values than in the control group. For aortic valve tissue, the values obtained were 40.5 and 188.1 micrograms Ca2+/mg dry weight of tissue for implantation times of 21 and 60 d, respectively, versus 5.48 and 1.4 micrograms Ca2+/mg dry weight of tissue for the same tissue treated with chloroform-methanol. The values obtained with pulmonary valve tissue were very similar: 72.46 and 108.06 micrograms Ca2+/mg dry weight tissue versus 0.67 and 0.80 micrograms Ca2+/mg dry weight tissue for implantation periods of 21 and 60 d, respectively. Thus, phospholipids may be totally or partially responsible for the calcification of the porcine valve tissue employed in the construction of cardiac bioprostheses.